xref: /linux/net/ipv4/tcp_input.c (revision 1a9239bb4253f9076b5b4b2a1a4e8d7defd77a95)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * INET		An implementation of the TCP/IP protocol suite for the LINUX
4  *		operating system.  INET is implemented using the  BSD Socket
5  *		interface as the means of communication with the user level.
6  *
7  *		Implementation of the Transmission Control Protocol(TCP).
8  *
9  * Authors:	Ross Biro
10  *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
11  *		Mark Evans, <evansmp@uhura.aston.ac.uk>
12  *		Corey Minyard <wf-rch!minyard@relay.EU.net>
13  *		Florian La Roche, <flla@stud.uni-sb.de>
14  *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
15  *		Linus Torvalds, <torvalds@cs.helsinki.fi>
16  *		Alan Cox, <gw4pts@gw4pts.ampr.org>
17  *		Matthew Dillon, <dillon@apollo.west.oic.com>
18  *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
19  *		Jorge Cwik, <jorge@laser.satlink.net>
20  */
21 
22 /*
23  * Changes:
24  *		Pedro Roque	:	Fast Retransmit/Recovery.
25  *					Two receive queues.
26  *					Retransmit queue handled by TCP.
27  *					Better retransmit timer handling.
28  *					New congestion avoidance.
29  *					Header prediction.
30  *					Variable renaming.
31  *
32  *		Eric		:	Fast Retransmit.
33  *		Randy Scott	:	MSS option defines.
34  *		Eric Schenk	:	Fixes to slow start algorithm.
35  *		Eric Schenk	:	Yet another double ACK bug.
36  *		Eric Schenk	:	Delayed ACK bug fixes.
37  *		Eric Schenk	:	Floyd style fast retrans war avoidance.
38  *		David S. Miller	:	Don't allow zero congestion window.
39  *		Eric Schenk	:	Fix retransmitter so that it sends
40  *					next packet on ack of previous packet.
41  *		Andi Kleen	:	Moved open_request checking here
42  *					and process RSTs for open_requests.
43  *		Andi Kleen	:	Better prune_queue, and other fixes.
44  *		Andrey Savochkin:	Fix RTT measurements in the presence of
45  *					timestamps.
46  *		Andrey Savochkin:	Check sequence numbers correctly when
47  *					removing SACKs due to in sequence incoming
48  *					data segments.
49  *		Andi Kleen:		Make sure we never ack data there is not
50  *					enough room for. Also make this condition
51  *					a fatal error if it might still happen.
52  *		Andi Kleen:		Add tcp_measure_rcv_mss to make
53  *					connections with MSS<min(MTU,ann. MSS)
54  *					work without delayed acks.
55  *		Andi Kleen:		Process packets with PSH set in the
56  *					fast path.
57  *		J Hadi Salim:		ECN support
58  *	 	Andrei Gurtov,
59  *		Pasi Sarolahti,
60  *		Panu Kuhlberg:		Experimental audit of TCP (re)transmission
61  *					engine. Lots of bugs are found.
62  *		Pasi Sarolahti:		F-RTO for dealing with spurious RTOs
63  */
64 
65 #define pr_fmt(fmt) "TCP: " fmt
66 
67 #include <linux/mm.h>
68 #include <linux/slab.h>
69 #include <linux/module.h>
70 #include <linux/sysctl.h>
71 #include <linux/kernel.h>
72 #include <linux/prefetch.h>
73 #include <net/dst.h>
74 #include <net/tcp.h>
75 #include <net/proto_memory.h>
76 #include <net/inet_common.h>
77 #include <linux/ipsec.h>
78 #include <linux/unaligned.h>
79 #include <linux/errqueue.h>
80 #include <trace/events/tcp.h>
81 #include <linux/jump_label_ratelimit.h>
82 #include <net/busy_poll.h>
83 #include <net/mptcp.h>
84 
85 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
86 
87 #define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
88 #define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
89 #define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
90 #define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
91 #define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
92 #define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
93 #define FLAG_ECE		0x40 /* ECE in this ACK				*/
94 #define FLAG_LOST_RETRANS	0x80 /* This ACK marks some retransmission lost */
95 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
96 #define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/
97 #define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
98 #define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
99 #define FLAG_SET_XMIT_TIMER	0x1000 /* Set TLP or RTO timer */
100 #define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
101 #define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */
102 #define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/
103 #define FLAG_ACK_MAYBE_DELAYED	0x10000 /* Likely a delayed ACK */
104 #define FLAG_DSACK_TLP		0x20000 /* DSACK for tail loss probe */
105 #define FLAG_TS_PROGRESS	0x40000 /* Positive timestamp delta */
106 
107 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
108 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
109 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
110 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
111 
112 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
113 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
114 
115 #define REXMIT_NONE	0 /* no loss recovery to do */
116 #define REXMIT_LOST	1 /* retransmit packets marked lost */
117 #define REXMIT_NEW	2 /* FRTO-style transmit of unsent/new packets */
118 
119 #if IS_ENABLED(CONFIG_TLS_DEVICE)
120 static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
121 
clean_acked_data_enable(struct tcp_sock * tp,void (* cad)(struct sock * sk,u32 ack_seq))122 void clean_acked_data_enable(struct tcp_sock *tp,
123 			     void (*cad)(struct sock *sk, u32 ack_seq))
124 {
125 	tp->tcp_clean_acked = cad;
126 	static_branch_deferred_inc(&clean_acked_data_enabled);
127 }
128 EXPORT_SYMBOL_GPL(clean_acked_data_enable);
129 
clean_acked_data_disable(struct tcp_sock * tp)130 void clean_acked_data_disable(struct tcp_sock *tp)
131 {
132 	static_branch_slow_dec_deferred(&clean_acked_data_enabled);
133 	tp->tcp_clean_acked = NULL;
134 }
135 EXPORT_SYMBOL_GPL(clean_acked_data_disable);
136 
clean_acked_data_flush(void)137 void clean_acked_data_flush(void)
138 {
139 	static_key_deferred_flush(&clean_acked_data_enabled);
140 }
141 EXPORT_SYMBOL_GPL(clean_acked_data_flush);
142 #endif
143 
144 #ifdef CONFIG_CGROUP_BPF
bpf_skops_parse_hdr(struct sock * sk,struct sk_buff * skb)145 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
146 {
147 	bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown &&
148 		BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
149 				       BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG);
150 	bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
151 						    BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG);
152 	struct bpf_sock_ops_kern sock_ops;
153 
154 	if (likely(!unknown_opt && !parse_all_opt))
155 		return;
156 
157 	/* The skb will be handled in the
158 	 * bpf_skops_established() or
159 	 * bpf_skops_write_hdr_opt().
160 	 */
161 	switch (sk->sk_state) {
162 	case TCP_SYN_RECV:
163 	case TCP_SYN_SENT:
164 	case TCP_LISTEN:
165 		return;
166 	}
167 
168 	sock_owned_by_me(sk);
169 
170 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
171 	sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB;
172 	sock_ops.is_fullsock = 1;
173 	sock_ops.is_locked_tcp_sock = 1;
174 	sock_ops.sk = sk;
175 	bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
176 
177 	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
178 }
179 
bpf_skops_established(struct sock * sk,int bpf_op,struct sk_buff * skb)180 static void bpf_skops_established(struct sock *sk, int bpf_op,
181 				  struct sk_buff *skb)
182 {
183 	struct bpf_sock_ops_kern sock_ops;
184 
185 	sock_owned_by_me(sk);
186 
187 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
188 	sock_ops.op = bpf_op;
189 	sock_ops.is_fullsock = 1;
190 	sock_ops.is_locked_tcp_sock = 1;
191 	sock_ops.sk = sk;
192 	/* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */
193 	if (skb)
194 		bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
195 
196 	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
197 }
198 #else
bpf_skops_parse_hdr(struct sock * sk,struct sk_buff * skb)199 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
200 {
201 }
202 
bpf_skops_established(struct sock * sk,int bpf_op,struct sk_buff * skb)203 static void bpf_skops_established(struct sock *sk, int bpf_op,
204 				  struct sk_buff *skb)
205 {
206 }
207 #endif
208 
tcp_gro_dev_warn(const struct sock * sk,const struct sk_buff * skb,unsigned int len)209 static __cold void tcp_gro_dev_warn(const struct sock *sk, const struct sk_buff *skb,
210 				    unsigned int len)
211 {
212 	struct net_device *dev;
213 
214 	rcu_read_lock();
215 	dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
216 	if (!dev || len >= READ_ONCE(dev->mtu))
217 		pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
218 			dev ? dev->name : "Unknown driver");
219 	rcu_read_unlock();
220 }
221 
222 /* Adapt the MSS value used to make delayed ack decision to the
223  * real world.
224  */
tcp_measure_rcv_mss(struct sock * sk,const struct sk_buff * skb)225 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
226 {
227 	struct inet_connection_sock *icsk = inet_csk(sk);
228 	const unsigned int lss = icsk->icsk_ack.last_seg_size;
229 	unsigned int len;
230 
231 	icsk->icsk_ack.last_seg_size = 0;
232 
233 	/* skb->len may jitter because of SACKs, even if peer
234 	 * sends good full-sized frames.
235 	 */
236 	len = skb_shinfo(skb)->gso_size ? : skb->len;
237 	if (len >= icsk->icsk_ack.rcv_mss) {
238 		/* Note: divides are still a bit expensive.
239 		 * For the moment, only adjust scaling_ratio
240 		 * when we update icsk_ack.rcv_mss.
241 		 */
242 		if (unlikely(len != icsk->icsk_ack.rcv_mss)) {
243 			u64 val = (u64)skb->len << TCP_RMEM_TO_WIN_SCALE;
244 			u8 old_ratio = tcp_sk(sk)->scaling_ratio;
245 
246 			do_div(val, skb->truesize);
247 			tcp_sk(sk)->scaling_ratio = val ? val : 1;
248 
249 			if (old_ratio != tcp_sk(sk)->scaling_ratio) {
250 				struct tcp_sock *tp = tcp_sk(sk);
251 
252 				val = tcp_win_from_space(sk, sk->sk_rcvbuf);
253 				tcp_set_window_clamp(sk, val);
254 
255 				if (tp->window_clamp < tp->rcvq_space.space)
256 					tp->rcvq_space.space = tp->window_clamp;
257 			}
258 		}
259 		icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
260 					       tcp_sk(sk)->advmss);
261 		/* Account for possibly-removed options */
262 		DO_ONCE_LITE_IF(len > icsk->icsk_ack.rcv_mss + MAX_TCP_OPTION_SPACE,
263 				tcp_gro_dev_warn, sk, skb, len);
264 		/* If the skb has a len of exactly 1*MSS and has the PSH bit
265 		 * set then it is likely the end of an application write. So
266 		 * more data may not be arriving soon, and yet the data sender
267 		 * may be waiting for an ACK if cwnd-bound or using TX zero
268 		 * copy. So we set ICSK_ACK_PUSHED here so that
269 		 * tcp_cleanup_rbuf() will send an ACK immediately if the app
270 		 * reads all of the data and is not ping-pong. If len > MSS
271 		 * then this logic does not matter (and does not hurt) because
272 		 * tcp_cleanup_rbuf() will always ACK immediately if the app
273 		 * reads data and there is more than an MSS of unACKed data.
274 		 */
275 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_PSH)
276 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
277 	} else {
278 		/* Otherwise, we make more careful check taking into account,
279 		 * that SACKs block is variable.
280 		 *
281 		 * "len" is invariant segment length, including TCP header.
282 		 */
283 		len += skb->data - skb_transport_header(skb);
284 		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
285 		    /* If PSH is not set, packet should be
286 		     * full sized, provided peer TCP is not badly broken.
287 		     * This observation (if it is correct 8)) allows
288 		     * to handle super-low mtu links fairly.
289 		     */
290 		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
291 		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
292 			/* Subtract also invariant (if peer is RFC compliant),
293 			 * tcp header plus fixed timestamp option length.
294 			 * Resulting "len" is MSS free of SACK jitter.
295 			 */
296 			len -= tcp_sk(sk)->tcp_header_len;
297 			icsk->icsk_ack.last_seg_size = len;
298 			if (len == lss) {
299 				icsk->icsk_ack.rcv_mss = len;
300 				return;
301 			}
302 		}
303 		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
304 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
305 		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
306 	}
307 }
308 
tcp_incr_quickack(struct sock * sk,unsigned int max_quickacks)309 static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
310 {
311 	struct inet_connection_sock *icsk = inet_csk(sk);
312 	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
313 
314 	if (quickacks == 0)
315 		quickacks = 2;
316 	quickacks = min(quickacks, max_quickacks);
317 	if (quickacks > icsk->icsk_ack.quick)
318 		icsk->icsk_ack.quick = quickacks;
319 }
320 
tcp_enter_quickack_mode(struct sock * sk,unsigned int max_quickacks)321 static void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
322 {
323 	struct inet_connection_sock *icsk = inet_csk(sk);
324 
325 	tcp_incr_quickack(sk, max_quickacks);
326 	inet_csk_exit_pingpong_mode(sk);
327 	icsk->icsk_ack.ato = TCP_ATO_MIN;
328 }
329 
330 /* Send ACKs quickly, if "quick" count is not exhausted
331  * and the session is not interactive.
332  */
333 
tcp_in_quickack_mode(struct sock * sk)334 static bool tcp_in_quickack_mode(struct sock *sk)
335 {
336 	const struct inet_connection_sock *icsk = inet_csk(sk);
337 
338 	return icsk->icsk_ack.dst_quick_ack ||
339 		(icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
340 }
341 
tcp_ecn_queue_cwr(struct tcp_sock * tp)342 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
343 {
344 	if (tcp_ecn_mode_rfc3168(tp))
345 		tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
346 }
347 
tcp_ecn_accept_cwr(struct sock * sk,const struct sk_buff * skb)348 static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
349 {
350 	if (tcp_hdr(skb)->cwr) {
351 		tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
352 
353 		/* If the sender is telling us it has entered CWR, then its
354 		 * cwnd may be very low (even just 1 packet), so we should ACK
355 		 * immediately.
356 		 */
357 		if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq)
358 			inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
359 	}
360 }
361 
tcp_ecn_withdraw_cwr(struct tcp_sock * tp)362 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
363 {
364 	tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
365 }
366 
tcp_data_ecn_check(struct sock * sk,const struct sk_buff * skb)367 static void tcp_data_ecn_check(struct sock *sk, const struct sk_buff *skb)
368 {
369 	struct tcp_sock *tp = tcp_sk(sk);
370 
371 	if (tcp_ecn_disabled(tp))
372 		return;
373 
374 	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
375 	case INET_ECN_NOT_ECT:
376 		/* Funny extension: if ECT is not set on a segment,
377 		 * and we already seen ECT on a previous segment,
378 		 * it is probably a retransmit.
379 		 */
380 		if (tp->ecn_flags & TCP_ECN_SEEN)
381 			tcp_enter_quickack_mode(sk, 2);
382 		break;
383 	case INET_ECN_CE:
384 		if (tcp_ca_needs_ecn(sk))
385 			tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
386 
387 		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
388 			/* Better not delay acks, sender can have a very low cwnd */
389 			tcp_enter_quickack_mode(sk, 2);
390 			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
391 		}
392 		tp->ecn_flags |= TCP_ECN_SEEN;
393 		break;
394 	default:
395 		if (tcp_ca_needs_ecn(sk))
396 			tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
397 		tp->ecn_flags |= TCP_ECN_SEEN;
398 		break;
399 	}
400 }
401 
tcp_ecn_rcv_synack(struct tcp_sock * tp,const struct tcphdr * th)402 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
403 {
404 	if (tcp_ecn_mode_rfc3168(tp) && (!th->ece || th->cwr))
405 		tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
406 }
407 
tcp_ecn_rcv_syn(struct tcp_sock * tp,const struct tcphdr * th)408 static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
409 {
410 	if (tcp_ecn_mode_rfc3168(tp) && (!th->ece || !th->cwr))
411 		tcp_ecn_mode_set(tp, TCP_ECN_DISABLED);
412 }
413 
tcp_ecn_rcv_ecn_echo(const struct tcp_sock * tp,const struct tcphdr * th)414 static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
415 {
416 	if (th->ece && !th->syn && tcp_ecn_mode_rfc3168(tp))
417 		return true;
418 	return false;
419 }
420 
tcp_count_delivered_ce(struct tcp_sock * tp,u32 ecn_count)421 static void tcp_count_delivered_ce(struct tcp_sock *tp, u32 ecn_count)
422 {
423 	tp->delivered_ce += ecn_count;
424 }
425 
426 /* Updates the delivered and delivered_ce counts */
tcp_count_delivered(struct tcp_sock * tp,u32 delivered,bool ece_ack)427 static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered,
428 				bool ece_ack)
429 {
430 	tp->delivered += delivered;
431 	if (ece_ack)
432 		tcp_count_delivered_ce(tp, delivered);
433 }
434 
435 /* Buffer size and advertised window tuning.
436  *
437  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
438  */
439 
tcp_sndbuf_expand(struct sock * sk)440 static void tcp_sndbuf_expand(struct sock *sk)
441 {
442 	const struct tcp_sock *tp = tcp_sk(sk);
443 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
444 	int sndmem, per_mss;
445 	u32 nr_segs;
446 
447 	/* Worst case is non GSO/TSO : each frame consumes one skb
448 	 * and skb->head is kmalloced using power of two area of memory
449 	 */
450 	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
451 		  MAX_TCP_HEADER +
452 		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
453 
454 	per_mss = roundup_pow_of_two(per_mss) +
455 		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
456 
457 	nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp));
458 	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
459 
460 	/* Fast Recovery (RFC 5681 3.2) :
461 	 * Cubic needs 1.7 factor, rounded to 2 to include
462 	 * extra cushion (application might react slowly to EPOLLOUT)
463 	 */
464 	sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
465 	sndmem *= nr_segs * per_mss;
466 
467 	if (sk->sk_sndbuf < sndmem)
468 		WRITE_ONCE(sk->sk_sndbuf,
469 			   min(sndmem, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_wmem[2])));
470 }
471 
472 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
473  *
474  * All tcp_full_space() is split to two parts: "network" buffer, allocated
475  * forward and advertised in receiver window (tp->rcv_wnd) and
476  * "application buffer", required to isolate scheduling/application
477  * latencies from network.
478  * window_clamp is maximal advertised window. It can be less than
479  * tcp_full_space(), in this case tcp_full_space() - window_clamp
480  * is reserved for "application" buffer. The less window_clamp is
481  * the smoother our behaviour from viewpoint of network, but the lower
482  * throughput and the higher sensitivity of the connection to losses. 8)
483  *
484  * rcv_ssthresh is more strict window_clamp used at "slow start"
485  * phase to predict further behaviour of this connection.
486  * It is used for two goals:
487  * - to enforce header prediction at sender, even when application
488  *   requires some significant "application buffer". It is check #1.
489  * - to prevent pruning of receive queue because of misprediction
490  *   of receiver window. Check #2.
491  *
492  * The scheme does not work when sender sends good segments opening
493  * window and then starts to feed us spaghetti. But it should work
494  * in common situations. Otherwise, we have to rely on queue collapsing.
495  */
496 
497 /* Slow part of check#2. */
__tcp_grow_window(const struct sock * sk,const struct sk_buff * skb,unsigned int skbtruesize)498 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb,
499 			     unsigned int skbtruesize)
500 {
501 	const struct tcp_sock *tp = tcp_sk(sk);
502 	/* Optimize this! */
503 	int truesize = tcp_win_from_space(sk, skbtruesize) >> 1;
504 	int window = tcp_win_from_space(sk, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])) >> 1;
505 
506 	while (tp->rcv_ssthresh <= window) {
507 		if (truesize <= skb->len)
508 			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
509 
510 		truesize >>= 1;
511 		window >>= 1;
512 	}
513 	return 0;
514 }
515 
516 /* Even if skb appears to have a bad len/truesize ratio, TCP coalescing
517  * can play nice with us, as sk_buff and skb->head might be either
518  * freed or shared with up to MAX_SKB_FRAGS segments.
519  * Only give a boost to drivers using page frag(s) to hold the frame(s),
520  * and if no payload was pulled in skb->head before reaching us.
521  */
truesize_adjust(bool adjust,const struct sk_buff * skb)522 static u32 truesize_adjust(bool adjust, const struct sk_buff *skb)
523 {
524 	u32 truesize = skb->truesize;
525 
526 	if (adjust && !skb_headlen(skb)) {
527 		truesize -= SKB_TRUESIZE(skb_end_offset(skb));
528 		/* paranoid check, some drivers might be buggy */
529 		if (unlikely((int)truesize < (int)skb->len))
530 			truesize = skb->truesize;
531 	}
532 	return truesize;
533 }
534 
tcp_grow_window(struct sock * sk,const struct sk_buff * skb,bool adjust)535 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb,
536 			    bool adjust)
537 {
538 	struct tcp_sock *tp = tcp_sk(sk);
539 	int room;
540 
541 	room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
542 
543 	if (room <= 0)
544 		return;
545 
546 	/* Check #1 */
547 	if (!tcp_under_memory_pressure(sk)) {
548 		unsigned int truesize = truesize_adjust(adjust, skb);
549 		int incr;
550 
551 		/* Check #2. Increase window, if skb with such overhead
552 		 * will fit to rcvbuf in future.
553 		 */
554 		if (tcp_win_from_space(sk, truesize) <= skb->len)
555 			incr = 2 * tp->advmss;
556 		else
557 			incr = __tcp_grow_window(sk, skb, truesize);
558 
559 		if (incr) {
560 			incr = max_t(int, incr, 2 * skb->len);
561 			tp->rcv_ssthresh += min(room, incr);
562 			inet_csk(sk)->icsk_ack.quick |= 1;
563 		}
564 	} else {
565 		/* Under pressure:
566 		 * Adjust rcv_ssthresh according to reserved mem
567 		 */
568 		tcp_adjust_rcv_ssthresh(sk);
569 	}
570 }
571 
572 /* 3. Try to fixup all. It is made immediately after connection enters
573  *    established state.
574  */
tcp_init_buffer_space(struct sock * sk)575 static void tcp_init_buffer_space(struct sock *sk)
576 {
577 	int tcp_app_win = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_app_win);
578 	struct tcp_sock *tp = tcp_sk(sk);
579 	int maxwin;
580 
581 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
582 		tcp_sndbuf_expand(sk);
583 
584 	tcp_mstamp_refresh(tp);
585 	tp->rcvq_space.time = tp->tcp_mstamp;
586 	tp->rcvq_space.seq = tp->copied_seq;
587 
588 	maxwin = tcp_full_space(sk);
589 
590 	if (tp->window_clamp >= maxwin) {
591 		WRITE_ONCE(tp->window_clamp, maxwin);
592 
593 		if (tcp_app_win && maxwin > 4 * tp->advmss)
594 			WRITE_ONCE(tp->window_clamp,
595 				   max(maxwin - (maxwin >> tcp_app_win),
596 				       4 * tp->advmss));
597 	}
598 
599 	/* Force reservation of one segment. */
600 	if (tcp_app_win &&
601 	    tp->window_clamp > 2 * tp->advmss &&
602 	    tp->window_clamp + tp->advmss > maxwin)
603 		WRITE_ONCE(tp->window_clamp,
604 			   max(2 * tp->advmss, maxwin - tp->advmss));
605 
606 	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
607 	tp->snd_cwnd_stamp = tcp_jiffies32;
608 	tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,
609 				    (u32)TCP_INIT_CWND * tp->advmss);
610 }
611 
612 /* 4. Recalculate window clamp after socket hit its memory bounds. */
tcp_clamp_window(struct sock * sk)613 static void tcp_clamp_window(struct sock *sk)
614 {
615 	struct tcp_sock *tp = tcp_sk(sk);
616 	struct inet_connection_sock *icsk = inet_csk(sk);
617 	struct net *net = sock_net(sk);
618 	int rmem2;
619 
620 	icsk->icsk_ack.quick = 0;
621 	rmem2 = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);
622 
623 	if (sk->sk_rcvbuf < rmem2 &&
624 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
625 	    !tcp_under_memory_pressure(sk) &&
626 	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
627 		WRITE_ONCE(sk->sk_rcvbuf,
628 			   min(atomic_read(&sk->sk_rmem_alloc), rmem2));
629 	}
630 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
631 		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
632 }
633 
634 /* Initialize RCV_MSS value.
635  * RCV_MSS is an our guess about MSS used by the peer.
636  * We haven't any direct information about the MSS.
637  * It's better to underestimate the RCV_MSS rather than overestimate.
638  * Overestimations make us ACKing less frequently than needed.
639  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
640  */
tcp_initialize_rcv_mss(struct sock * sk)641 void tcp_initialize_rcv_mss(struct sock *sk)
642 {
643 	const struct tcp_sock *tp = tcp_sk(sk);
644 	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
645 
646 	hint = min(hint, tp->rcv_wnd / 2);
647 	hint = min(hint, TCP_MSS_DEFAULT);
648 	hint = max(hint, TCP_MIN_MSS);
649 
650 	inet_csk(sk)->icsk_ack.rcv_mss = hint;
651 }
652 EXPORT_IPV6_MOD(tcp_initialize_rcv_mss);
653 
654 /* Receiver "autotuning" code.
655  *
656  * The algorithm for RTT estimation w/o timestamps is based on
657  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
658  * <https://public.lanl.gov/radiant/pubs.html#DRS>
659  *
660  * More detail on this code can be found at
661  * <http://staff.psc.edu/jheffner/>,
662  * though this reference is out of date.  A new paper
663  * is pending.
664  */
tcp_rcv_rtt_update(struct tcp_sock * tp,u32 sample,int win_dep)665 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
666 {
667 	u32 new_sample = tp->rcv_rtt_est.rtt_us;
668 	long m = sample;
669 
670 	if (new_sample != 0) {
671 		/* If we sample in larger samples in the non-timestamp
672 		 * case, we could grossly overestimate the RTT especially
673 		 * with chatty applications or bulk transfer apps which
674 		 * are stalled on filesystem I/O.
675 		 *
676 		 * Also, since we are only going for a minimum in the
677 		 * non-timestamp case, we do not smooth things out
678 		 * else with timestamps disabled convergence takes too
679 		 * long.
680 		 */
681 		if (!win_dep) {
682 			m -= (new_sample >> 3);
683 			new_sample += m;
684 		} else {
685 			m <<= 3;
686 			if (m < new_sample)
687 				new_sample = m;
688 		}
689 	} else {
690 		/* No previous measure. */
691 		new_sample = m << 3;
692 	}
693 
694 	tp->rcv_rtt_est.rtt_us = new_sample;
695 }
696 
tcp_rcv_rtt_measure(struct tcp_sock * tp)697 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
698 {
699 	u32 delta_us;
700 
701 	if (tp->rcv_rtt_est.time == 0)
702 		goto new_measure;
703 	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
704 		return;
705 	delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
706 	if (!delta_us)
707 		delta_us = 1;
708 	tcp_rcv_rtt_update(tp, delta_us, 1);
709 
710 new_measure:
711 	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
712 	tp->rcv_rtt_est.time = tp->tcp_mstamp;
713 }
714 
tcp_rtt_tsopt_us(const struct tcp_sock * tp)715 static s32 tcp_rtt_tsopt_us(const struct tcp_sock *tp)
716 {
717 	u32 delta, delta_us;
718 
719 	delta = tcp_time_stamp_ts(tp) - tp->rx_opt.rcv_tsecr;
720 	if (tp->tcp_usec_ts)
721 		return delta;
722 
723 	if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
724 		if (!delta)
725 			delta = 1;
726 		delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
727 		return delta_us;
728 	}
729 	return -1;
730 }
731 
tcp_rcv_rtt_measure_ts(struct sock * sk,const struct sk_buff * skb)732 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
733 					  const struct sk_buff *skb)
734 {
735 	struct tcp_sock *tp = tcp_sk(sk);
736 
737 	if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
738 		return;
739 	tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
740 
741 	if (TCP_SKB_CB(skb)->end_seq -
742 	    TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
743 		s32 delta = tcp_rtt_tsopt_us(tp);
744 
745 		if (delta >= 0)
746 			tcp_rcv_rtt_update(tp, delta, 0);
747 	}
748 }
749 
750 /*
751  * This function should be called every time data is copied to user space.
752  * It calculates the appropriate TCP receive buffer space.
753  */
tcp_rcv_space_adjust(struct sock * sk)754 void tcp_rcv_space_adjust(struct sock *sk)
755 {
756 	struct tcp_sock *tp = tcp_sk(sk);
757 	u32 copied;
758 	int time;
759 
760 	trace_tcp_rcv_space_adjust(sk);
761 
762 	tcp_mstamp_refresh(tp);
763 	time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
764 	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
765 		return;
766 
767 	/* Number of bytes copied to user in last RTT */
768 	copied = tp->copied_seq - tp->rcvq_space.seq;
769 	if (copied <= tp->rcvq_space.space)
770 		goto new_measure;
771 
772 	/* A bit of theory :
773 	 * copied = bytes received in previous RTT, our base window
774 	 * To cope with packet losses, we need a 2x factor
775 	 * To cope with slow start, and sender growing its cwin by 100 %
776 	 * every RTT, we need a 4x factor, because the ACK we are sending
777 	 * now is for the next RTT, not the current one :
778 	 * <prev RTT . ><current RTT .. ><next RTT .... >
779 	 */
780 
781 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) &&
782 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
783 		u64 rcvwin, grow;
784 		int rcvbuf;
785 
786 		/* minimal window to cope with packet losses, assuming
787 		 * steady state. Add some cushion because of small variations.
788 		 */
789 		rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
790 
791 		/* Accommodate for sender rate increase (eg. slow start) */
792 		grow = rcvwin * (copied - tp->rcvq_space.space);
793 		do_div(grow, tp->rcvq_space.space);
794 		rcvwin += (grow << 1);
795 
796 		rcvbuf = min_t(u64, tcp_space_from_win(sk, rcvwin),
797 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2]));
798 		if (rcvbuf > sk->sk_rcvbuf) {
799 			WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
800 
801 			/* Make the window clamp follow along.  */
802 			WRITE_ONCE(tp->window_clamp,
803 				   tcp_win_from_space(sk, rcvbuf));
804 		}
805 	}
806 	tp->rcvq_space.space = copied;
807 
808 new_measure:
809 	tp->rcvq_space.seq = tp->copied_seq;
810 	tp->rcvq_space.time = tp->tcp_mstamp;
811 }
812 
tcp_save_lrcv_flowlabel(struct sock * sk,const struct sk_buff * skb)813 static void tcp_save_lrcv_flowlabel(struct sock *sk, const struct sk_buff *skb)
814 {
815 #if IS_ENABLED(CONFIG_IPV6)
816 	struct inet_connection_sock *icsk = inet_csk(sk);
817 
818 	if (skb->protocol == htons(ETH_P_IPV6))
819 		icsk->icsk_ack.lrcv_flowlabel = ntohl(ip6_flowlabel(ipv6_hdr(skb)));
820 #endif
821 }
822 
823 /* There is something which you must keep in mind when you analyze the
824  * behavior of the tp->ato delayed ack timeout interval.  When a
825  * connection starts up, we want to ack as quickly as possible.  The
826  * problem is that "good" TCP's do slow start at the beginning of data
827  * transmission.  The means that until we send the first few ACK's the
828  * sender will sit on his end and only queue most of his data, because
829  * he can only send snd_cwnd unacked packets at any given time.  For
830  * each ACK we send, he increments snd_cwnd and transmits more of his
831  * queue.  -DaveM
832  */
tcp_event_data_recv(struct sock * sk,struct sk_buff * skb)833 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
834 {
835 	struct tcp_sock *tp = tcp_sk(sk);
836 	struct inet_connection_sock *icsk = inet_csk(sk);
837 	u32 now;
838 
839 	inet_csk_schedule_ack(sk);
840 
841 	tcp_measure_rcv_mss(sk, skb);
842 
843 	tcp_rcv_rtt_measure(tp);
844 
845 	now = tcp_jiffies32;
846 
847 	if (!icsk->icsk_ack.ato) {
848 		/* The _first_ data packet received, initialize
849 		 * delayed ACK engine.
850 		 */
851 		tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
852 		icsk->icsk_ack.ato = TCP_ATO_MIN;
853 	} else {
854 		int m = now - icsk->icsk_ack.lrcvtime;
855 
856 		if (m <= TCP_ATO_MIN / 2) {
857 			/* The fastest case is the first. */
858 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
859 		} else if (m < icsk->icsk_ack.ato) {
860 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
861 			if (icsk->icsk_ack.ato > icsk->icsk_rto)
862 				icsk->icsk_ack.ato = icsk->icsk_rto;
863 		} else if (m > icsk->icsk_rto) {
864 			/* Too long gap. Apparently sender failed to
865 			 * restart window, so that we send ACKs quickly.
866 			 */
867 			tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
868 		}
869 	}
870 	icsk->icsk_ack.lrcvtime = now;
871 	tcp_save_lrcv_flowlabel(sk, skb);
872 
873 	tcp_data_ecn_check(sk, skb);
874 
875 	if (skb->len >= 128)
876 		tcp_grow_window(sk, skb, true);
877 }
878 
879 /* Called to compute a smoothed rtt estimate. The data fed to this
880  * routine either comes from timestamps, or from segments that were
881  * known _not_ to have been retransmitted [see Karn/Partridge
882  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
883  * piece by Van Jacobson.
884  * NOTE: the next three routines used to be one big routine.
885  * To save cycles in the RFC 1323 implementation it was better to break
886  * it up into three procedures. -- erics
887  */
tcp_rtt_estimator(struct sock * sk,long mrtt_us)888 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
889 {
890 	struct tcp_sock *tp = tcp_sk(sk);
891 	long m = mrtt_us; /* RTT */
892 	u32 srtt = tp->srtt_us;
893 
894 	/*	The following amusing code comes from Jacobson's
895 	 *	article in SIGCOMM '88.  Note that rtt and mdev
896 	 *	are scaled versions of rtt and mean deviation.
897 	 *	This is designed to be as fast as possible
898 	 *	m stands for "measurement".
899 	 *
900 	 *	On a 1990 paper the rto value is changed to:
901 	 *	RTO = rtt + 4 * mdev
902 	 *
903 	 * Funny. This algorithm seems to be very broken.
904 	 * These formulae increase RTO, when it should be decreased, increase
905 	 * too slowly, when it should be increased quickly, decrease too quickly
906 	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
907 	 * does not matter how to _calculate_ it. Seems, it was trap
908 	 * that VJ failed to avoid. 8)
909 	 */
910 	if (srtt != 0) {
911 		m -= (srtt >> 3);	/* m is now error in rtt est */
912 		srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
913 		if (m < 0) {
914 			m = -m;		/* m is now abs(error) */
915 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
916 			/* This is similar to one of Eifel findings.
917 			 * Eifel blocks mdev updates when rtt decreases.
918 			 * This solution is a bit different: we use finer gain
919 			 * for mdev in this case (alpha*beta).
920 			 * Like Eifel it also prevents growth of rto,
921 			 * but also it limits too fast rto decreases,
922 			 * happening in pure Eifel.
923 			 */
924 			if (m > 0)
925 				m >>= 3;
926 		} else {
927 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
928 		}
929 		tp->mdev_us += m;		/* mdev = 3/4 mdev + 1/4 new */
930 		if (tp->mdev_us > tp->mdev_max_us) {
931 			tp->mdev_max_us = tp->mdev_us;
932 			if (tp->mdev_max_us > tp->rttvar_us)
933 				tp->rttvar_us = tp->mdev_max_us;
934 		}
935 		if (after(tp->snd_una, tp->rtt_seq)) {
936 			if (tp->mdev_max_us < tp->rttvar_us)
937 				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
938 			tp->rtt_seq = tp->snd_nxt;
939 			tp->mdev_max_us = tcp_rto_min_us(sk);
940 
941 			tcp_bpf_rtt(sk, mrtt_us, srtt);
942 		}
943 	} else {
944 		/* no previous measure. */
945 		srtt = m << 3;		/* take the measured time to be rtt */
946 		tp->mdev_us = m << 1;	/* make sure rto = 3*rtt */
947 		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
948 		tp->mdev_max_us = tp->rttvar_us;
949 		tp->rtt_seq = tp->snd_nxt;
950 
951 		tcp_bpf_rtt(sk, mrtt_us, srtt);
952 	}
953 	tp->srtt_us = max(1U, srtt);
954 }
955 
tcp_update_pacing_rate(struct sock * sk)956 static void tcp_update_pacing_rate(struct sock *sk)
957 {
958 	const struct tcp_sock *tp = tcp_sk(sk);
959 	u64 rate;
960 
961 	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
962 	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
963 
964 	/* current rate is (cwnd * mss) / srtt
965 	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
966 	 * In Congestion Avoidance phase, set it to 120 % the current rate.
967 	 *
968 	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
969 	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
970 	 *	 end of slow start and should slow down.
971 	 */
972 	if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2)
973 		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio);
974 	else
975 		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio);
976 
977 	rate *= max(tcp_snd_cwnd(tp), tp->packets_out);
978 
979 	if (likely(tp->srtt_us))
980 		do_div(rate, tp->srtt_us);
981 
982 	/* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
983 	 * without any lock. We want to make sure compiler wont store
984 	 * intermediate values in this location.
985 	 */
986 	WRITE_ONCE(sk->sk_pacing_rate,
987 		   min_t(u64, rate, READ_ONCE(sk->sk_max_pacing_rate)));
988 }
989 
990 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
991  * routine referred to above.
992  */
tcp_set_rto(struct sock * sk)993 static void tcp_set_rto(struct sock *sk)
994 {
995 	const struct tcp_sock *tp = tcp_sk(sk);
996 	/* Old crap is replaced with new one. 8)
997 	 *
998 	 * More seriously:
999 	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
1000 	 *    It cannot be less due to utterly erratic ACK generation made
1001 	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
1002 	 *    to do with delayed acks, because at cwnd>2 true delack timeout
1003 	 *    is invisible. Actually, Linux-2.4 also generates erratic
1004 	 *    ACKs in some circumstances.
1005 	 */
1006 	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
1007 
1008 	/* 2. Fixups made earlier cannot be right.
1009 	 *    If we do not estimate RTO correctly without them,
1010 	 *    all the algo is pure shit and should be replaced
1011 	 *    with correct one. It is exactly, which we pretend to do.
1012 	 */
1013 
1014 	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
1015 	 * guarantees that rto is higher.
1016 	 */
1017 	tcp_bound_rto(sk);
1018 }
1019 
tcp_init_cwnd(const struct tcp_sock * tp,const struct dst_entry * dst)1020 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
1021 {
1022 	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
1023 
1024 	if (!cwnd)
1025 		cwnd = TCP_INIT_CWND;
1026 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
1027 }
1028 
1029 struct tcp_sacktag_state {
1030 	/* Timestamps for earliest and latest never-retransmitted segment
1031 	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
1032 	 * but congestion control should still get an accurate delay signal.
1033 	 */
1034 	u64	first_sackt;
1035 	u64	last_sackt;
1036 	u32	reord;
1037 	u32	sack_delivered;
1038 	int	flag;
1039 	unsigned int mss_now;
1040 	struct rate_sample *rate;
1041 };
1042 
1043 /* Take a notice that peer is sending D-SACKs. Skip update of data delivery
1044  * and spurious retransmission information if this DSACK is unlikely caused by
1045  * sender's action:
1046  * - DSACKed sequence range is larger than maximum receiver's window.
1047  * - Total no. of DSACKed segments exceed the total no. of retransmitted segs.
1048  */
tcp_dsack_seen(struct tcp_sock * tp,u32 start_seq,u32 end_seq,struct tcp_sacktag_state * state)1049 static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
1050 			  u32 end_seq, struct tcp_sacktag_state *state)
1051 {
1052 	u32 seq_len, dup_segs = 1;
1053 
1054 	if (!before(start_seq, end_seq))
1055 		return 0;
1056 
1057 	seq_len = end_seq - start_seq;
1058 	/* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */
1059 	if (seq_len > tp->max_window)
1060 		return 0;
1061 	if (seq_len > tp->mss_cache)
1062 		dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
1063 	else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq)
1064 		state->flag |= FLAG_DSACK_TLP;
1065 
1066 	tp->dsack_dups += dup_segs;
1067 	/* Skip the DSACK if dup segs weren't retransmitted by sender */
1068 	if (tp->dsack_dups > tp->total_retrans)
1069 		return 0;
1070 
1071 	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
1072 	/* We increase the RACK ordering window in rounds where we receive
1073 	 * DSACKs that may have been due to reordering causing RACK to trigger
1074 	 * a spurious fast recovery. Thus RACK ignores DSACKs that happen
1075 	 * without having seen reordering, or that match TLP probes (TLP
1076 	 * is timer-driven, not triggered by RACK).
1077 	 */
1078 	if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP))
1079 		tp->rack.dsack_seen = 1;
1080 
1081 	state->flag |= FLAG_DSACKING_ACK;
1082 	/* A spurious retransmission is delivered */
1083 	state->sack_delivered += dup_segs;
1084 
1085 	return dup_segs;
1086 }
1087 
1088 /* It's reordering when higher sequence was delivered (i.e. sacked) before
1089  * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
1090  * distance is approximated in full-mss packet distance ("reordering").
1091  */
tcp_check_sack_reordering(struct sock * sk,const u32 low_seq,const int ts)1092 static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
1093 				      const int ts)
1094 {
1095 	struct tcp_sock *tp = tcp_sk(sk);
1096 	const u32 mss = tp->mss_cache;
1097 	u32 fack, metric;
1098 
1099 	fack = tcp_highest_sack_seq(tp);
1100 	if (!before(low_seq, fack))
1101 		return;
1102 
1103 	metric = fack - low_seq;
1104 	if ((metric > tp->reordering * mss) && mss) {
1105 #if FASTRETRANS_DEBUG > 1
1106 		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
1107 			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
1108 			 tp->reordering,
1109 			 0,
1110 			 tp->sacked_out,
1111 			 tp->undo_marker ? tp->undo_retrans : 0);
1112 #endif
1113 		tp->reordering = min_t(u32, (metric + mss - 1) / mss,
1114 				       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
1115 	}
1116 
1117 	/* This exciting event is worth to be remembered. 8) */
1118 	tp->reord_seen++;
1119 	NET_INC_STATS(sock_net(sk),
1120 		      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
1121 }
1122 
1123  /* This must be called before lost_out or retrans_out are updated
1124   * on a new loss, because we want to know if all skbs previously
1125   * known to be lost have already been retransmitted, indicating
1126   * that this newly lost skb is our next skb to retransmit.
1127   */
tcp_verify_retransmit_hint(struct tcp_sock * tp,struct sk_buff * skb)1128 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
1129 {
1130 	if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) ||
1131 	    (tp->retransmit_skb_hint &&
1132 	     before(TCP_SKB_CB(skb)->seq,
1133 		    TCP_SKB_CB(tp->retransmit_skb_hint)->seq)))
1134 		tp->retransmit_skb_hint = skb;
1135 }
1136 
1137 /* Sum the number of packets on the wire we have marked as lost, and
1138  * notify the congestion control module that the given skb was marked lost.
1139  */
tcp_notify_skb_loss_event(struct tcp_sock * tp,const struct sk_buff * skb)1140 static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb)
1141 {
1142 	tp->lost += tcp_skb_pcount(skb);
1143 }
1144 
tcp_mark_skb_lost(struct sock * sk,struct sk_buff * skb)1145 void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
1146 {
1147 	__u8 sacked = TCP_SKB_CB(skb)->sacked;
1148 	struct tcp_sock *tp = tcp_sk(sk);
1149 
1150 	if (sacked & TCPCB_SACKED_ACKED)
1151 		return;
1152 
1153 	tcp_verify_retransmit_hint(tp, skb);
1154 	if (sacked & TCPCB_LOST) {
1155 		if (sacked & TCPCB_SACKED_RETRANS) {
1156 			/* Account for retransmits that are lost again */
1157 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1158 			tp->retrans_out -= tcp_skb_pcount(skb);
1159 			NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,
1160 				      tcp_skb_pcount(skb));
1161 			tcp_notify_skb_loss_event(tp, skb);
1162 		}
1163 	} else {
1164 		tp->lost_out += tcp_skb_pcount(skb);
1165 		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1166 		tcp_notify_skb_loss_event(tp, skb);
1167 	}
1168 }
1169 
1170 /* This procedure tags the retransmission queue when SACKs arrive.
1171  *
1172  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1173  * Packets in queue with these bits set are counted in variables
1174  * sacked_out, retrans_out and lost_out, correspondingly.
1175  *
1176  * Valid combinations are:
1177  * Tag  InFlight	Description
1178  * 0	1		- orig segment is in flight.
1179  * S	0		- nothing flies, orig reached receiver.
1180  * L	0		- nothing flies, orig lost by net.
1181  * R	2		- both orig and retransmit are in flight.
1182  * L|R	1		- orig is lost, retransmit is in flight.
1183  * S|R  1		- orig reached receiver, retrans is still in flight.
1184  * (L|S|R is logically valid, it could occur when L|R is sacked,
1185  *  but it is equivalent to plain S and code short-circuits it to S.
1186  *  L|S is logically invalid, it would mean -1 packet in flight 8))
1187  *
1188  * These 6 states form finite state machine, controlled by the following events:
1189  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1190  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1191  * 3. Loss detection event of two flavors:
1192  *	A. Scoreboard estimator decided the packet is lost.
1193  *	   A'. Reno "three dupacks" marks head of queue lost.
1194  *	B. SACK arrives sacking SND.NXT at the moment, when the
1195  *	   segment was retransmitted.
1196  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1197  *
1198  * It is pleasant to note, that state diagram turns out to be commutative,
1199  * so that we are allowed not to be bothered by order of our actions,
1200  * when multiple events arrive simultaneously. (see the function below).
1201  *
1202  * Reordering detection.
1203  * --------------------
1204  * Reordering metric is maximal distance, which a packet can be displaced
1205  * in packet stream. With SACKs we can estimate it:
1206  *
1207  * 1. SACK fills old hole and the corresponding segment was not
1208  *    ever retransmitted -> reordering. Alas, we cannot use it
1209  *    when segment was retransmitted.
1210  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1211  *    for retransmitted and already SACKed segment -> reordering..
1212  * Both of these heuristics are not used in Loss state, when we cannot
1213  * account for retransmits accurately.
1214  *
1215  * SACK block validation.
1216  * ----------------------
1217  *
1218  * SACK block range validation checks that the received SACK block fits to
1219  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1220  * Note that SND.UNA is not included to the range though being valid because
1221  * it means that the receiver is rather inconsistent with itself reporting
1222  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1223  * perfectly valid, however, in light of RFC2018 which explicitly states
1224  * that "SACK block MUST reflect the newest segment.  Even if the newest
1225  * segment is going to be discarded ...", not that it looks very clever
1226  * in case of head skb. Due to potentional receiver driven attacks, we
1227  * choose to avoid immediate execution of a walk in write queue due to
1228  * reneging and defer head skb's loss recovery to standard loss recovery
1229  * procedure that will eventually trigger (nothing forbids us doing this).
1230  *
1231  * Implements also blockage to start_seq wrap-around. Problem lies in the
1232  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1233  * there's no guarantee that it will be before snd_nxt (n). The problem
1234  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1235  * wrap (s_w):
1236  *
1237  *         <- outs wnd ->                          <- wrapzone ->
1238  *         u     e      n                         u_w   e_w  s n_w
1239  *         |     |      |                          |     |   |  |
1240  * |<------------+------+----- TCP seqno space --------------+---------->|
1241  * ...-- <2^31 ->|                                           |<--------...
1242  * ...---- >2^31 ------>|                                    |<--------...
1243  *
1244  * Current code wouldn't be vulnerable but it's better still to discard such
1245  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1246  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1247  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1248  * equal to the ideal case (infinite seqno space without wrap caused issues).
1249  *
1250  * With D-SACK the lower bound is extended to cover sequence space below
1251  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1252  * again, D-SACK block must not to go across snd_una (for the same reason as
1253  * for the normal SACK blocks, explained above). But there all simplicity
1254  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1255  * fully below undo_marker they do not affect behavior in anyway and can
1256  * therefore be safely ignored. In rare cases (which are more or less
1257  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1258  * fragmentation and packet reordering past skb's retransmission. To consider
1259  * them correctly, the acceptable range must be extended even more though
1260  * the exact amount is rather hard to quantify. However, tp->max_window can
1261  * be used as an exaggerated estimate.
1262  */
tcp_is_sackblock_valid(struct tcp_sock * tp,bool is_dsack,u32 start_seq,u32 end_seq)1263 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1264 				   u32 start_seq, u32 end_seq)
1265 {
1266 	/* Too far in future, or reversed (interpretation is ambiguous) */
1267 	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1268 		return false;
1269 
1270 	/* Nasty start_seq wrap-around check (see comments above) */
1271 	if (!before(start_seq, tp->snd_nxt))
1272 		return false;
1273 
1274 	/* In outstanding window? ...This is valid exit for D-SACKs too.
1275 	 * start_seq == snd_una is non-sensical (see comments above)
1276 	 */
1277 	if (after(start_seq, tp->snd_una))
1278 		return true;
1279 
1280 	if (!is_dsack || !tp->undo_marker)
1281 		return false;
1282 
1283 	/* ...Then it's D-SACK, and must reside below snd_una completely */
1284 	if (after(end_seq, tp->snd_una))
1285 		return false;
1286 
1287 	if (!before(start_seq, tp->undo_marker))
1288 		return true;
1289 
1290 	/* Too old */
1291 	if (!after(end_seq, tp->undo_marker))
1292 		return false;
1293 
1294 	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1295 	 *   start_seq < undo_marker and end_seq >= undo_marker.
1296 	 */
1297 	return !before(start_seq, end_seq - tp->max_window);
1298 }
1299 
tcp_check_dsack(struct sock * sk,const struct sk_buff * ack_skb,struct tcp_sack_block_wire * sp,int num_sacks,u32 prior_snd_una,struct tcp_sacktag_state * state)1300 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1301 			    struct tcp_sack_block_wire *sp, int num_sacks,
1302 			    u32 prior_snd_una, struct tcp_sacktag_state *state)
1303 {
1304 	struct tcp_sock *tp = tcp_sk(sk);
1305 	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1306 	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1307 	u32 dup_segs;
1308 
1309 	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1310 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1311 	} else if (num_sacks > 1) {
1312 		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1313 		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1314 
1315 		if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1))
1316 			return false;
1317 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV);
1318 	} else {
1319 		return false;
1320 	}
1321 
1322 	dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state);
1323 	if (!dup_segs) {	/* Skip dubious DSACK */
1324 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS);
1325 		return false;
1326 	}
1327 
1328 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs);
1329 
1330 	/* D-SACK for already forgotten data... Do dumb counting. */
1331 	if (tp->undo_marker && tp->undo_retrans > 0 &&
1332 	    !after(end_seq_0, prior_snd_una) &&
1333 	    after(end_seq_0, tp->undo_marker))
1334 		tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs);
1335 
1336 	return true;
1337 }
1338 
1339 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1340  * the incoming SACK may not exactly match but we can find smaller MSS
1341  * aligned portion of it that matches. Therefore we might need to fragment
1342  * which may fail and creates some hassle (caller must handle error case
1343  * returns).
1344  *
1345  * FIXME: this could be merged to shift decision code
1346  */
tcp_match_skb_to_sack(struct sock * sk,struct sk_buff * skb,u32 start_seq,u32 end_seq)1347 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1348 				  u32 start_seq, u32 end_seq)
1349 {
1350 	int err;
1351 	bool in_sack;
1352 	unsigned int pkt_len;
1353 	unsigned int mss;
1354 
1355 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1356 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1357 
1358 	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1359 	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1360 		mss = tcp_skb_mss(skb);
1361 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1362 
1363 		if (!in_sack) {
1364 			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1365 			if (pkt_len < mss)
1366 				pkt_len = mss;
1367 		} else {
1368 			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1369 			if (pkt_len < mss)
1370 				return -EINVAL;
1371 		}
1372 
1373 		/* Round if necessary so that SACKs cover only full MSSes
1374 		 * and/or the remaining small portion (if present)
1375 		 */
1376 		if (pkt_len > mss) {
1377 			unsigned int new_len = (pkt_len / mss) * mss;
1378 			if (!in_sack && new_len < pkt_len)
1379 				new_len += mss;
1380 			pkt_len = new_len;
1381 		}
1382 
1383 		if (pkt_len >= skb->len && !in_sack)
1384 			return 0;
1385 
1386 		err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
1387 				   pkt_len, mss, GFP_ATOMIC);
1388 		if (err < 0)
1389 			return err;
1390 	}
1391 
1392 	return in_sack;
1393 }
1394 
1395 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
tcp_sacktag_one(struct sock * sk,struct tcp_sacktag_state * state,u8 sacked,u32 start_seq,u32 end_seq,int dup_sack,int pcount,u64 xmit_time)1396 static u8 tcp_sacktag_one(struct sock *sk,
1397 			  struct tcp_sacktag_state *state, u8 sacked,
1398 			  u32 start_seq, u32 end_seq,
1399 			  int dup_sack, int pcount,
1400 			  u64 xmit_time)
1401 {
1402 	struct tcp_sock *tp = tcp_sk(sk);
1403 
1404 	/* Account D-SACK for retransmitted packet. */
1405 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1406 		if (tp->undo_marker && tp->undo_retrans > 0 &&
1407 		    after(end_seq, tp->undo_marker))
1408 			tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
1409 		if ((sacked & TCPCB_SACKED_ACKED) &&
1410 		    before(start_seq, state->reord))
1411 				state->reord = start_seq;
1412 	}
1413 
1414 	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1415 	if (!after(end_seq, tp->snd_una))
1416 		return sacked;
1417 
1418 	if (!(sacked & TCPCB_SACKED_ACKED)) {
1419 		tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1420 
1421 		if (sacked & TCPCB_SACKED_RETRANS) {
1422 			/* If the segment is not tagged as lost,
1423 			 * we do not clear RETRANS, believing
1424 			 * that retransmission is still in flight.
1425 			 */
1426 			if (sacked & TCPCB_LOST) {
1427 				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1428 				tp->lost_out -= pcount;
1429 				tp->retrans_out -= pcount;
1430 			}
1431 		} else {
1432 			if (!(sacked & TCPCB_RETRANS)) {
1433 				/* New sack for not retransmitted frame,
1434 				 * which was in hole. It is reordering.
1435 				 */
1436 				if (before(start_seq,
1437 					   tcp_highest_sack_seq(tp)) &&
1438 				    before(start_seq, state->reord))
1439 					state->reord = start_seq;
1440 
1441 				if (!after(end_seq, tp->high_seq))
1442 					state->flag |= FLAG_ORIG_SACK_ACKED;
1443 				if (state->first_sackt == 0)
1444 					state->first_sackt = xmit_time;
1445 				state->last_sackt = xmit_time;
1446 			}
1447 
1448 			if (sacked & TCPCB_LOST) {
1449 				sacked &= ~TCPCB_LOST;
1450 				tp->lost_out -= pcount;
1451 			}
1452 		}
1453 
1454 		sacked |= TCPCB_SACKED_ACKED;
1455 		state->flag |= FLAG_DATA_SACKED;
1456 		tp->sacked_out += pcount;
1457 		/* Out-of-order packets delivered */
1458 		state->sack_delivered += pcount;
1459 
1460 		/* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1461 		if (tp->lost_skb_hint &&
1462 		    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
1463 			tp->lost_cnt_hint += pcount;
1464 	}
1465 
1466 	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1467 	 * frames and clear it. undo_retrans is decreased above, L|R frames
1468 	 * are accounted above as well.
1469 	 */
1470 	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1471 		sacked &= ~TCPCB_SACKED_RETRANS;
1472 		tp->retrans_out -= pcount;
1473 	}
1474 
1475 	return sacked;
1476 }
1477 
1478 /* Shift newly-SACKed bytes from this skb to the immediately previous
1479  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1480  */
tcp_shifted_skb(struct sock * sk,struct sk_buff * prev,struct sk_buff * skb,struct tcp_sacktag_state * state,unsigned int pcount,int shifted,int mss,bool dup_sack)1481 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
1482 			    struct sk_buff *skb,
1483 			    struct tcp_sacktag_state *state,
1484 			    unsigned int pcount, int shifted, int mss,
1485 			    bool dup_sack)
1486 {
1487 	struct tcp_sock *tp = tcp_sk(sk);
1488 	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1489 	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1490 
1491 	BUG_ON(!pcount);
1492 
1493 	/* Adjust counters and hints for the newly sacked sequence
1494 	 * range but discard the return value since prev is already
1495 	 * marked. We must tag the range first because the seq
1496 	 * advancement below implicitly advances
1497 	 * tcp_highest_sack_seq() when skb is highest_sack.
1498 	 */
1499 	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1500 			start_seq, end_seq, dup_sack, pcount,
1501 			tcp_skb_timestamp_us(skb));
1502 	tcp_rate_skb_delivered(sk, skb, state->rate);
1503 
1504 	if (skb == tp->lost_skb_hint)
1505 		tp->lost_cnt_hint += pcount;
1506 
1507 	TCP_SKB_CB(prev)->end_seq += shifted;
1508 	TCP_SKB_CB(skb)->seq += shifted;
1509 
1510 	tcp_skb_pcount_add(prev, pcount);
1511 	WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
1512 	tcp_skb_pcount_add(skb, -pcount);
1513 
1514 	/* When we're adding to gso_segs == 1, gso_size will be zero,
1515 	 * in theory this shouldn't be necessary but as long as DSACK
1516 	 * code can come after this skb later on it's better to keep
1517 	 * setting gso_size to something.
1518 	 */
1519 	if (!TCP_SKB_CB(prev)->tcp_gso_size)
1520 		TCP_SKB_CB(prev)->tcp_gso_size = mss;
1521 
1522 	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1523 	if (tcp_skb_pcount(skb) <= 1)
1524 		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1525 
1526 	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1527 	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1528 
1529 	if (skb->len > 0) {
1530 		BUG_ON(!tcp_skb_pcount(skb));
1531 		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1532 		return false;
1533 	}
1534 
1535 	/* Whole SKB was eaten :-) */
1536 
1537 	if (skb == tp->retransmit_skb_hint)
1538 		tp->retransmit_skb_hint = prev;
1539 	if (skb == tp->lost_skb_hint) {
1540 		tp->lost_skb_hint = prev;
1541 		tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1542 	}
1543 
1544 	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1545 	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1546 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1547 		TCP_SKB_CB(prev)->end_seq++;
1548 
1549 	if (skb == tcp_highest_sack(sk))
1550 		tcp_advance_highest_sack(sk, skb);
1551 
1552 	tcp_skb_collapse_tstamp(prev, skb);
1553 	if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1554 		TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1555 
1556 	tcp_rtx_queue_unlink_and_free(skb, sk);
1557 
1558 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1559 
1560 	return true;
1561 }
1562 
1563 /* I wish gso_size would have a bit more sane initialization than
1564  * something-or-zero which complicates things
1565  */
tcp_skb_seglen(const struct sk_buff * skb)1566 static int tcp_skb_seglen(const struct sk_buff *skb)
1567 {
1568 	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1569 }
1570 
1571 /* Shifting pages past head area doesn't work */
skb_can_shift(const struct sk_buff * skb)1572 static int skb_can_shift(const struct sk_buff *skb)
1573 {
1574 	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1575 }
1576 
tcp_skb_shift(struct sk_buff * to,struct sk_buff * from,int pcount,int shiftlen)1577 int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from,
1578 		  int pcount, int shiftlen)
1579 {
1580 	/* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE)
1581 	 * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
1582 	 * to make sure not storing more than 65535 * 8 bytes per skb,
1583 	 * even if current MSS is bigger.
1584 	 */
1585 	if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE))
1586 		return 0;
1587 	if (unlikely(tcp_skb_pcount(to) + pcount > 65535))
1588 		return 0;
1589 	return skb_shift(to, from, shiftlen);
1590 }
1591 
1592 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1593  * skb.
1594  */
tcp_shift_skb_data(struct sock * sk,struct sk_buff * skb,struct tcp_sacktag_state * state,u32 start_seq,u32 end_seq,bool dup_sack)1595 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1596 					  struct tcp_sacktag_state *state,
1597 					  u32 start_seq, u32 end_seq,
1598 					  bool dup_sack)
1599 {
1600 	struct tcp_sock *tp = tcp_sk(sk);
1601 	struct sk_buff *prev;
1602 	int mss;
1603 	int pcount = 0;
1604 	int len;
1605 	int in_sack;
1606 
1607 	/* Normally R but no L won't result in plain S */
1608 	if (!dup_sack &&
1609 	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1610 		goto fallback;
1611 	if (!skb_can_shift(skb))
1612 		goto fallback;
1613 	/* This frame is about to be dropped (was ACKed). */
1614 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1615 		goto fallback;
1616 
1617 	/* Can only happen with delayed DSACK + discard craziness */
1618 	prev = skb_rb_prev(skb);
1619 	if (!prev)
1620 		goto fallback;
1621 
1622 	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1623 		goto fallback;
1624 
1625 	if (!tcp_skb_can_collapse(prev, skb))
1626 		goto fallback;
1627 
1628 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1629 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1630 
1631 	if (in_sack) {
1632 		len = skb->len;
1633 		pcount = tcp_skb_pcount(skb);
1634 		mss = tcp_skb_seglen(skb);
1635 
1636 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1637 		 * drop this restriction as unnecessary
1638 		 */
1639 		if (mss != tcp_skb_seglen(prev))
1640 			goto fallback;
1641 	} else {
1642 		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1643 			goto noop;
1644 		/* CHECKME: This is non-MSS split case only?, this will
1645 		 * cause skipped skbs due to advancing loop btw, original
1646 		 * has that feature too
1647 		 */
1648 		if (tcp_skb_pcount(skb) <= 1)
1649 			goto noop;
1650 
1651 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1652 		if (!in_sack) {
1653 			/* TODO: head merge to next could be attempted here
1654 			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1655 			 * though it might not be worth of the additional hassle
1656 			 *
1657 			 * ...we can probably just fallback to what was done
1658 			 * previously. We could try merging non-SACKed ones
1659 			 * as well but it probably isn't going to buy off
1660 			 * because later SACKs might again split them, and
1661 			 * it would make skb timestamp tracking considerably
1662 			 * harder problem.
1663 			 */
1664 			goto fallback;
1665 		}
1666 
1667 		len = end_seq - TCP_SKB_CB(skb)->seq;
1668 		BUG_ON(len < 0);
1669 		BUG_ON(len > skb->len);
1670 
1671 		/* MSS boundaries should be honoured or else pcount will
1672 		 * severely break even though it makes things bit trickier.
1673 		 * Optimize common case to avoid most of the divides
1674 		 */
1675 		mss = tcp_skb_mss(skb);
1676 
1677 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1678 		 * drop this restriction as unnecessary
1679 		 */
1680 		if (mss != tcp_skb_seglen(prev))
1681 			goto fallback;
1682 
1683 		if (len == mss) {
1684 			pcount = 1;
1685 		} else if (len < mss) {
1686 			goto noop;
1687 		} else {
1688 			pcount = len / mss;
1689 			len = pcount * mss;
1690 		}
1691 	}
1692 
1693 	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1694 	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1695 		goto fallback;
1696 
1697 	if (!tcp_skb_shift(prev, skb, pcount, len))
1698 		goto fallback;
1699 	if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
1700 		goto out;
1701 
1702 	/* Hole filled allows collapsing with the next as well, this is very
1703 	 * useful when hole on every nth skb pattern happens
1704 	 */
1705 	skb = skb_rb_next(prev);
1706 	if (!skb)
1707 		goto out;
1708 
1709 	if (!skb_can_shift(skb) ||
1710 	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1711 	    (mss != tcp_skb_seglen(skb)))
1712 		goto out;
1713 
1714 	if (!tcp_skb_can_collapse(prev, skb))
1715 		goto out;
1716 	len = skb->len;
1717 	pcount = tcp_skb_pcount(skb);
1718 	if (tcp_skb_shift(prev, skb, pcount, len))
1719 		tcp_shifted_skb(sk, prev, skb, state, pcount,
1720 				len, mss, 0);
1721 
1722 out:
1723 	return prev;
1724 
1725 noop:
1726 	return skb;
1727 
1728 fallback:
1729 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1730 	return NULL;
1731 }
1732 
tcp_sacktag_walk(struct sk_buff * skb,struct sock * sk,struct tcp_sack_block * next_dup,struct tcp_sacktag_state * state,u32 start_seq,u32 end_seq,bool dup_sack_in)1733 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1734 					struct tcp_sack_block *next_dup,
1735 					struct tcp_sacktag_state *state,
1736 					u32 start_seq, u32 end_seq,
1737 					bool dup_sack_in)
1738 {
1739 	struct tcp_sock *tp = tcp_sk(sk);
1740 	struct sk_buff *tmp;
1741 
1742 	skb_rbtree_walk_from(skb) {
1743 		int in_sack = 0;
1744 		bool dup_sack = dup_sack_in;
1745 
1746 		/* queue is in-order => we can short-circuit the walk early */
1747 		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1748 			break;
1749 
1750 		if (next_dup  &&
1751 		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1752 			in_sack = tcp_match_skb_to_sack(sk, skb,
1753 							next_dup->start_seq,
1754 							next_dup->end_seq);
1755 			if (in_sack > 0)
1756 				dup_sack = true;
1757 		}
1758 
1759 		/* skb reference here is a bit tricky to get right, since
1760 		 * shifting can eat and free both this skb and the next,
1761 		 * so not even _safe variant of the loop is enough.
1762 		 */
1763 		if (in_sack <= 0) {
1764 			tmp = tcp_shift_skb_data(sk, skb, state,
1765 						 start_seq, end_seq, dup_sack);
1766 			if (tmp) {
1767 				if (tmp != skb) {
1768 					skb = tmp;
1769 					continue;
1770 				}
1771 
1772 				in_sack = 0;
1773 			} else {
1774 				in_sack = tcp_match_skb_to_sack(sk, skb,
1775 								start_seq,
1776 								end_seq);
1777 			}
1778 		}
1779 
1780 		if (unlikely(in_sack < 0))
1781 			break;
1782 
1783 		if (in_sack) {
1784 			TCP_SKB_CB(skb)->sacked =
1785 				tcp_sacktag_one(sk,
1786 						state,
1787 						TCP_SKB_CB(skb)->sacked,
1788 						TCP_SKB_CB(skb)->seq,
1789 						TCP_SKB_CB(skb)->end_seq,
1790 						dup_sack,
1791 						tcp_skb_pcount(skb),
1792 						tcp_skb_timestamp_us(skb));
1793 			tcp_rate_skb_delivered(sk, skb, state->rate);
1794 			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1795 				list_del_init(&skb->tcp_tsorted_anchor);
1796 
1797 			if (!before(TCP_SKB_CB(skb)->seq,
1798 				    tcp_highest_sack_seq(tp)))
1799 				tcp_advance_highest_sack(sk, skb);
1800 		}
1801 	}
1802 	return skb;
1803 }
1804 
tcp_sacktag_bsearch(struct sock * sk,u32 seq)1805 static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
1806 {
1807 	struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
1808 	struct sk_buff *skb;
1809 
1810 	while (*p) {
1811 		parent = *p;
1812 		skb = rb_to_skb(parent);
1813 		if (before(seq, TCP_SKB_CB(skb)->seq)) {
1814 			p = &parent->rb_left;
1815 			continue;
1816 		}
1817 		if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
1818 			p = &parent->rb_right;
1819 			continue;
1820 		}
1821 		return skb;
1822 	}
1823 	return NULL;
1824 }
1825 
tcp_sacktag_skip(struct sk_buff * skb,struct sock * sk,u32 skip_to_seq)1826 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1827 					u32 skip_to_seq)
1828 {
1829 	if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
1830 		return skb;
1831 
1832 	return tcp_sacktag_bsearch(sk, skip_to_seq);
1833 }
1834 
tcp_maybe_skipping_dsack(struct sk_buff * skb,struct sock * sk,struct tcp_sack_block * next_dup,struct tcp_sacktag_state * state,u32 skip_to_seq)1835 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1836 						struct sock *sk,
1837 						struct tcp_sack_block *next_dup,
1838 						struct tcp_sacktag_state *state,
1839 						u32 skip_to_seq)
1840 {
1841 	if (!next_dup)
1842 		return skb;
1843 
1844 	if (before(next_dup->start_seq, skip_to_seq)) {
1845 		skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1846 		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1847 				       next_dup->start_seq, next_dup->end_seq,
1848 				       1);
1849 	}
1850 
1851 	return skb;
1852 }
1853 
tcp_sack_cache_ok(const struct tcp_sock * tp,const struct tcp_sack_block * cache)1854 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1855 {
1856 	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1857 }
1858 
1859 static int
tcp_sacktag_write_queue(struct sock * sk,const struct sk_buff * ack_skb,u32 prior_snd_una,struct tcp_sacktag_state * state)1860 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1861 			u32 prior_snd_una, struct tcp_sacktag_state *state)
1862 {
1863 	struct tcp_sock *tp = tcp_sk(sk);
1864 	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1865 				    TCP_SKB_CB(ack_skb)->sacked);
1866 	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1867 	struct tcp_sack_block sp[TCP_NUM_SACKS];
1868 	struct tcp_sack_block *cache;
1869 	struct sk_buff *skb;
1870 	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1871 	int used_sacks;
1872 	bool found_dup_sack = false;
1873 	int i, j;
1874 	int first_sack_index;
1875 
1876 	state->flag = 0;
1877 	state->reord = tp->snd_nxt;
1878 
1879 	if (!tp->sacked_out)
1880 		tcp_highest_sack_reset(sk);
1881 
1882 	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1883 					 num_sacks, prior_snd_una, state);
1884 
1885 	/* Eliminate too old ACKs, but take into
1886 	 * account more or less fresh ones, they can
1887 	 * contain valid SACK info.
1888 	 */
1889 	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1890 		return 0;
1891 
1892 	if (!tp->packets_out)
1893 		goto out;
1894 
1895 	used_sacks = 0;
1896 	first_sack_index = 0;
1897 	for (i = 0; i < num_sacks; i++) {
1898 		bool dup_sack = !i && found_dup_sack;
1899 
1900 		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1901 		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1902 
1903 		if (!tcp_is_sackblock_valid(tp, dup_sack,
1904 					    sp[used_sacks].start_seq,
1905 					    sp[used_sacks].end_seq)) {
1906 			int mib_idx;
1907 
1908 			if (dup_sack) {
1909 				if (!tp->undo_marker)
1910 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1911 				else
1912 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1913 			} else {
1914 				/* Don't count olds caused by ACK reordering */
1915 				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1916 				    !after(sp[used_sacks].end_seq, tp->snd_una))
1917 					continue;
1918 				mib_idx = LINUX_MIB_TCPSACKDISCARD;
1919 			}
1920 
1921 			NET_INC_STATS(sock_net(sk), mib_idx);
1922 			if (i == 0)
1923 				first_sack_index = -1;
1924 			continue;
1925 		}
1926 
1927 		/* Ignore very old stuff early */
1928 		if (!after(sp[used_sacks].end_seq, prior_snd_una)) {
1929 			if (i == 0)
1930 				first_sack_index = -1;
1931 			continue;
1932 		}
1933 
1934 		used_sacks++;
1935 	}
1936 
1937 	/* order SACK blocks to allow in order walk of the retrans queue */
1938 	for (i = used_sacks - 1; i > 0; i--) {
1939 		for (j = 0; j < i; j++) {
1940 			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1941 				swap(sp[j], sp[j + 1]);
1942 
1943 				/* Track where the first SACK block goes to */
1944 				if (j == first_sack_index)
1945 					first_sack_index = j + 1;
1946 			}
1947 		}
1948 	}
1949 
1950 	state->mss_now = tcp_current_mss(sk);
1951 	skb = NULL;
1952 	i = 0;
1953 
1954 	if (!tp->sacked_out) {
1955 		/* It's already past, so skip checking against it */
1956 		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1957 	} else {
1958 		cache = tp->recv_sack_cache;
1959 		/* Skip empty blocks in at head of the cache */
1960 		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1961 		       !cache->end_seq)
1962 			cache++;
1963 	}
1964 
1965 	while (i < used_sacks) {
1966 		u32 start_seq = sp[i].start_seq;
1967 		u32 end_seq = sp[i].end_seq;
1968 		bool dup_sack = (found_dup_sack && (i == first_sack_index));
1969 		struct tcp_sack_block *next_dup = NULL;
1970 
1971 		if (found_dup_sack && ((i + 1) == first_sack_index))
1972 			next_dup = &sp[i + 1];
1973 
1974 		/* Skip too early cached blocks */
1975 		while (tcp_sack_cache_ok(tp, cache) &&
1976 		       !before(start_seq, cache->end_seq))
1977 			cache++;
1978 
1979 		/* Can skip some work by looking recv_sack_cache? */
1980 		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1981 		    after(end_seq, cache->start_seq)) {
1982 
1983 			/* Head todo? */
1984 			if (before(start_seq, cache->start_seq)) {
1985 				skb = tcp_sacktag_skip(skb, sk, start_seq);
1986 				skb = tcp_sacktag_walk(skb, sk, next_dup,
1987 						       state,
1988 						       start_seq,
1989 						       cache->start_seq,
1990 						       dup_sack);
1991 			}
1992 
1993 			/* Rest of the block already fully processed? */
1994 			if (!after(end_seq, cache->end_seq))
1995 				goto advance_sp;
1996 
1997 			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1998 						       state,
1999 						       cache->end_seq);
2000 
2001 			/* ...tail remains todo... */
2002 			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
2003 				/* ...but better entrypoint exists! */
2004 				skb = tcp_highest_sack(sk);
2005 				if (!skb)
2006 					break;
2007 				cache++;
2008 				goto walk;
2009 			}
2010 
2011 			skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
2012 			/* Check overlap against next cached too (past this one already) */
2013 			cache++;
2014 			continue;
2015 		}
2016 
2017 		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
2018 			skb = tcp_highest_sack(sk);
2019 			if (!skb)
2020 				break;
2021 		}
2022 		skb = tcp_sacktag_skip(skb, sk, start_seq);
2023 
2024 walk:
2025 		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
2026 				       start_seq, end_seq, dup_sack);
2027 
2028 advance_sp:
2029 		i++;
2030 	}
2031 
2032 	/* Clear the head of the cache sack blocks so we can skip it next time */
2033 	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
2034 		tp->recv_sack_cache[i].start_seq = 0;
2035 		tp->recv_sack_cache[i].end_seq = 0;
2036 	}
2037 	for (j = 0; j < used_sacks; j++)
2038 		tp->recv_sack_cache[i++] = sp[j];
2039 
2040 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
2041 		tcp_check_sack_reordering(sk, state->reord, 0);
2042 
2043 	tcp_verify_left_out(tp);
2044 out:
2045 
2046 #if FASTRETRANS_DEBUG > 0
2047 	WARN_ON((int)tp->sacked_out < 0);
2048 	WARN_ON((int)tp->lost_out < 0);
2049 	WARN_ON((int)tp->retrans_out < 0);
2050 	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
2051 #endif
2052 	return state->flag;
2053 }
2054 
2055 /* Limits sacked_out so that sum with lost_out isn't ever larger than
2056  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
2057  */
tcp_limit_reno_sacked(struct tcp_sock * tp)2058 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
2059 {
2060 	u32 holes;
2061 
2062 	holes = max(tp->lost_out, 1U);
2063 	holes = min(holes, tp->packets_out);
2064 
2065 	if ((tp->sacked_out + holes) > tp->packets_out) {
2066 		tp->sacked_out = tp->packets_out - holes;
2067 		return true;
2068 	}
2069 	return false;
2070 }
2071 
2072 /* If we receive more dupacks than we expected counting segments
2073  * in assumption of absent reordering, interpret this as reordering.
2074  * The only another reason could be bug in receiver TCP.
2075  */
tcp_check_reno_reordering(struct sock * sk,const int addend)2076 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
2077 {
2078 	struct tcp_sock *tp = tcp_sk(sk);
2079 
2080 	if (!tcp_limit_reno_sacked(tp))
2081 		return;
2082 
2083 	tp->reordering = min_t(u32, tp->packets_out + addend,
2084 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
2085 	tp->reord_seen++;
2086 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
2087 }
2088 
2089 /* Emulate SACKs for SACKless connection: account for a new dupack. */
2090 
tcp_add_reno_sack(struct sock * sk,int num_dupack,bool ece_ack)2091 static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack)
2092 {
2093 	if (num_dupack) {
2094 		struct tcp_sock *tp = tcp_sk(sk);
2095 		u32 prior_sacked = tp->sacked_out;
2096 		s32 delivered;
2097 
2098 		tp->sacked_out += num_dupack;
2099 		tcp_check_reno_reordering(sk, 0);
2100 		delivered = tp->sacked_out - prior_sacked;
2101 		if (delivered > 0)
2102 			tcp_count_delivered(tp, delivered, ece_ack);
2103 		tcp_verify_left_out(tp);
2104 	}
2105 }
2106 
2107 /* Account for ACK, ACKing some data in Reno Recovery phase. */
2108 
tcp_remove_reno_sacks(struct sock * sk,int acked,bool ece_ack)2109 static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack)
2110 {
2111 	struct tcp_sock *tp = tcp_sk(sk);
2112 
2113 	if (acked > 0) {
2114 		/* One ACK acked hole. The rest eat duplicate ACKs. */
2115 		tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1),
2116 				    ece_ack);
2117 		if (acked - 1 >= tp->sacked_out)
2118 			tp->sacked_out = 0;
2119 		else
2120 			tp->sacked_out -= acked - 1;
2121 	}
2122 	tcp_check_reno_reordering(sk, acked);
2123 	tcp_verify_left_out(tp);
2124 }
2125 
tcp_reset_reno_sack(struct tcp_sock * tp)2126 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2127 {
2128 	tp->sacked_out = 0;
2129 }
2130 
tcp_clear_retrans(struct tcp_sock * tp)2131 void tcp_clear_retrans(struct tcp_sock *tp)
2132 {
2133 	tp->retrans_out = 0;
2134 	tp->lost_out = 0;
2135 	tp->undo_marker = 0;
2136 	tp->undo_retrans = -1;
2137 	tp->sacked_out = 0;
2138 	tp->rto_stamp = 0;
2139 	tp->total_rto = 0;
2140 	tp->total_rto_recoveries = 0;
2141 	tp->total_rto_time = 0;
2142 }
2143 
tcp_init_undo(struct tcp_sock * tp)2144 static inline void tcp_init_undo(struct tcp_sock *tp)
2145 {
2146 	tp->undo_marker = tp->snd_una;
2147 
2148 	/* Retransmission still in flight may cause DSACKs later. */
2149 	/* First, account for regular retransmits in flight: */
2150 	tp->undo_retrans = tp->retrans_out;
2151 	/* Next, account for TLP retransmits in flight: */
2152 	if (tp->tlp_high_seq && tp->tlp_retrans)
2153 		tp->undo_retrans++;
2154 	/* Finally, avoid 0, because undo_retrans==0 means "can undo now": */
2155 	if (!tp->undo_retrans)
2156 		tp->undo_retrans = -1;
2157 }
2158 
tcp_is_rack(const struct sock * sk)2159 static bool tcp_is_rack(const struct sock *sk)
2160 {
2161 	return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) &
2162 		TCP_RACK_LOSS_DETECTION;
2163 }
2164 
2165 /* If we detect SACK reneging, forget all SACK information
2166  * and reset tags completely, otherwise preserve SACKs. If receiver
2167  * dropped its ofo queue, we will know this due to reneging detection.
2168  */
tcp_timeout_mark_lost(struct sock * sk)2169 static void tcp_timeout_mark_lost(struct sock *sk)
2170 {
2171 	struct tcp_sock *tp = tcp_sk(sk);
2172 	struct sk_buff *skb, *head;
2173 	bool is_reneg;			/* is receiver reneging on SACKs? */
2174 
2175 	head = tcp_rtx_queue_head(sk);
2176 	is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
2177 	if (is_reneg) {
2178 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2179 		tp->sacked_out = 0;
2180 		/* Mark SACK reneging until we recover from this loss event. */
2181 		tp->is_sack_reneg = 1;
2182 	} else if (tcp_is_reno(tp)) {
2183 		tcp_reset_reno_sack(tp);
2184 	}
2185 
2186 	skb = head;
2187 	skb_rbtree_walk_from(skb) {
2188 		if (is_reneg)
2189 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2190 		else if (tcp_is_rack(sk) && skb != head &&
2191 			 tcp_rack_skb_timeout(tp, skb, 0) > 0)
2192 			continue; /* Don't mark recently sent ones lost yet */
2193 		tcp_mark_skb_lost(sk, skb);
2194 	}
2195 	tcp_verify_left_out(tp);
2196 	tcp_clear_all_retrans_hints(tp);
2197 }
2198 
2199 /* Enter Loss state. */
tcp_enter_loss(struct sock * sk)2200 void tcp_enter_loss(struct sock *sk)
2201 {
2202 	const struct inet_connection_sock *icsk = inet_csk(sk);
2203 	struct tcp_sock *tp = tcp_sk(sk);
2204 	struct net *net = sock_net(sk);
2205 	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
2206 	u8 reordering;
2207 
2208 	tcp_timeout_mark_lost(sk);
2209 
2210 	/* Reduce ssthresh if it has not yet been made inside this window. */
2211 	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
2212 	    !after(tp->high_seq, tp->snd_una) ||
2213 	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2214 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
2215 		tp->prior_cwnd = tcp_snd_cwnd(tp);
2216 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2217 		tcp_ca_event(sk, CA_EVENT_LOSS);
2218 		tcp_init_undo(tp);
2219 	}
2220 	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1);
2221 	tp->snd_cwnd_cnt   = 0;
2222 	tp->snd_cwnd_stamp = tcp_jiffies32;
2223 
2224 	/* Timeout in disordered state after receiving substantial DUPACKs
2225 	 * suggests that the degree of reordering is over-estimated.
2226 	 */
2227 	reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering);
2228 	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
2229 	    tp->sacked_out >= reordering)
2230 		tp->reordering = min_t(unsigned int, tp->reordering,
2231 				       reordering);
2232 
2233 	tcp_set_ca_state(sk, TCP_CA_Loss);
2234 	tp->high_seq = tp->snd_nxt;
2235 	tp->tlp_high_seq = 0;
2236 	tcp_ecn_queue_cwr(tp);
2237 
2238 	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2239 	 * loss recovery is underway except recurring timeout(s) on
2240 	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2241 	 */
2242 	tp->frto = READ_ONCE(net->ipv4.sysctl_tcp_frto) &&
2243 		   (new_recovery || icsk->icsk_retransmits) &&
2244 		   !inet_csk(sk)->icsk_mtup.probe_size;
2245 }
2246 
2247 /* If ACK arrived pointing to a remembered SACK, it means that our
2248  * remembered SACKs do not reflect real state of receiver i.e.
2249  * receiver _host_ is heavily congested (or buggy).
2250  *
2251  * To avoid big spurious retransmission bursts due to transient SACK
2252  * scoreboard oddities that look like reneging, we give the receiver a
2253  * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2254  * restore sanity to the SACK scoreboard. If the apparent reneging
2255  * persists until this RTO then we'll clear the SACK scoreboard.
2256  */
tcp_check_sack_reneging(struct sock * sk,int * ack_flag)2257 static bool tcp_check_sack_reneging(struct sock *sk, int *ack_flag)
2258 {
2259 	if (*ack_flag & FLAG_SACK_RENEGING &&
2260 	    *ack_flag & FLAG_SND_UNA_ADVANCED) {
2261 		struct tcp_sock *tp = tcp_sk(sk);
2262 		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2263 					  msecs_to_jiffies(10));
2264 
2265 		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, delay, false);
2266 		*ack_flag &= ~FLAG_SET_XMIT_TIMER;
2267 		return true;
2268 	}
2269 	return false;
2270 }
2271 
2272 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2273  * counter when SACK is enabled (without SACK, sacked_out is used for
2274  * that purpose).
2275  *
2276  * With reordering, holes may still be in flight, so RFC3517 recovery
2277  * uses pure sacked_out (total number of SACKed segments) even though
2278  * it violates the RFC that uses duplicate ACKs, often these are equal
2279  * but when e.g. out-of-window ACKs or packet duplication occurs,
2280  * they differ. Since neither occurs due to loss, TCP should really
2281  * ignore them.
2282  */
tcp_dupack_heuristics(const struct tcp_sock * tp)2283 static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2284 {
2285 	return tp->sacked_out + 1;
2286 }
2287 
2288 /* Linux NewReno/SACK/ECN state machine.
2289  * --------------------------------------
2290  *
2291  * "Open"	Normal state, no dubious events, fast path.
2292  * "Disorder"   In all the respects it is "Open",
2293  *		but requires a bit more attention. It is entered when
2294  *		we see some SACKs or dupacks. It is split of "Open"
2295  *		mainly to move some processing from fast path to slow one.
2296  * "CWR"	CWND was reduced due to some Congestion Notification event.
2297  *		It can be ECN, ICMP source quench, local device congestion.
2298  * "Recovery"	CWND was reduced, we are fast-retransmitting.
2299  * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2300  *
2301  * tcp_fastretrans_alert() is entered:
2302  * - each incoming ACK, if state is not "Open"
2303  * - when arrived ACK is unusual, namely:
2304  *	* SACK
2305  *	* Duplicate ACK.
2306  *	* ECN ECE.
2307  *
2308  * Counting packets in flight is pretty simple.
2309  *
2310  *	in_flight = packets_out - left_out + retrans_out
2311  *
2312  *	packets_out is SND.NXT-SND.UNA counted in packets.
2313  *
2314  *	retrans_out is number of retransmitted segments.
2315  *
2316  *	left_out is number of segments left network, but not ACKed yet.
2317  *
2318  *		left_out = sacked_out + lost_out
2319  *
2320  *     sacked_out: Packets, which arrived to receiver out of order
2321  *		   and hence not ACKed. With SACKs this number is simply
2322  *		   amount of SACKed data. Even without SACKs
2323  *		   it is easy to give pretty reliable estimate of this number,
2324  *		   counting duplicate ACKs.
2325  *
2326  *       lost_out: Packets lost by network. TCP has no explicit
2327  *		   "loss notification" feedback from network (for now).
2328  *		   It means that this number can be only _guessed_.
2329  *		   Actually, it is the heuristics to predict lossage that
2330  *		   distinguishes different algorithms.
2331  *
2332  *	F.e. after RTO, when all the queue is considered as lost,
2333  *	lost_out = packets_out and in_flight = retrans_out.
2334  *
2335  *		Essentially, we have now a few algorithms detecting
2336  *		lost packets.
2337  *
2338  *		If the receiver supports SACK:
2339  *
2340  *		RFC6675/3517: It is the conventional algorithm. A packet is
2341  *		considered lost if the number of higher sequence packets
2342  *		SACKed is greater than or equal the DUPACK thoreshold
2343  *		(reordering). This is implemented in tcp_mark_head_lost and
2344  *		tcp_update_scoreboard.
2345  *
2346  *		RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
2347  *		(2017-) that checks timing instead of counting DUPACKs.
2348  *		Essentially a packet is considered lost if it's not S/ACKed
2349  *		after RTT + reordering_window, where both metrics are
2350  *		dynamically measured and adjusted. This is implemented in
2351  *		tcp_rack_mark_lost.
2352  *
2353  *		If the receiver does not support SACK:
2354  *
2355  *		NewReno (RFC6582): in Recovery we assume that one segment
2356  *		is lost (classic Reno). While we are in Recovery and
2357  *		a partial ACK arrives, we assume that one more packet
2358  *		is lost (NewReno). This heuristics are the same in NewReno
2359  *		and SACK.
2360  *
2361  * Really tricky (and requiring careful tuning) part of algorithm
2362  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2363  * The first determines the moment _when_ we should reduce CWND and,
2364  * hence, slow down forward transmission. In fact, it determines the moment
2365  * when we decide that hole is caused by loss, rather than by a reorder.
2366  *
2367  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2368  * holes, caused by lost packets.
2369  *
2370  * And the most logically complicated part of algorithm is undo
2371  * heuristics. We detect false retransmits due to both too early
2372  * fast retransmit (reordering) and underestimated RTO, analyzing
2373  * timestamps and D-SACKs. When we detect that some segments were
2374  * retransmitted by mistake and CWND reduction was wrong, we undo
2375  * window reduction and abort recovery phase. This logic is hidden
2376  * inside several functions named tcp_try_undo_<something>.
2377  */
2378 
2379 /* This function decides, when we should leave Disordered state
2380  * and enter Recovery phase, reducing congestion window.
2381  *
2382  * Main question: may we further continue forward transmission
2383  * with the same cwnd?
2384  */
tcp_time_to_recover(struct sock * sk,int flag)2385 static bool tcp_time_to_recover(struct sock *sk, int flag)
2386 {
2387 	struct tcp_sock *tp = tcp_sk(sk);
2388 
2389 	/* Trick#1: The loss is proven. */
2390 	if (tp->lost_out)
2391 		return true;
2392 
2393 	/* Not-A-Trick#2 : Classic rule... */
2394 	if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
2395 		return true;
2396 
2397 	return false;
2398 }
2399 
2400 /* Detect loss in event "A" above by marking head of queue up as lost.
2401  * For RFC3517 SACK, a segment is considered lost if it
2402  * has at least tp->reordering SACKed seqments above it; "packets" refers to
2403  * the maximum SACKed segments to pass before reaching this limit.
2404  */
tcp_mark_head_lost(struct sock * sk,int packets,int mark_head)2405 static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2406 {
2407 	struct tcp_sock *tp = tcp_sk(sk);
2408 	struct sk_buff *skb;
2409 	int cnt;
2410 	/* Use SACK to deduce losses of new sequences sent during recovery */
2411 	const u32 loss_high = tp->snd_nxt;
2412 
2413 	WARN_ON(packets > tp->packets_out);
2414 	skb = tp->lost_skb_hint;
2415 	if (skb) {
2416 		/* Head already handled? */
2417 		if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
2418 			return;
2419 		cnt = tp->lost_cnt_hint;
2420 	} else {
2421 		skb = tcp_rtx_queue_head(sk);
2422 		cnt = 0;
2423 	}
2424 
2425 	skb_rbtree_walk_from(skb) {
2426 		/* TODO: do this better */
2427 		/* this is not the most efficient way to do this... */
2428 		tp->lost_skb_hint = skb;
2429 		tp->lost_cnt_hint = cnt;
2430 
2431 		if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
2432 			break;
2433 
2434 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2435 			cnt += tcp_skb_pcount(skb);
2436 
2437 		if (cnt > packets)
2438 			break;
2439 
2440 		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST))
2441 			tcp_mark_skb_lost(sk, skb);
2442 
2443 		if (mark_head)
2444 			break;
2445 	}
2446 	tcp_verify_left_out(tp);
2447 }
2448 
2449 /* Account newly detected lost packet(s) */
2450 
tcp_update_scoreboard(struct sock * sk,int fast_rexmit)2451 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2452 {
2453 	struct tcp_sock *tp = tcp_sk(sk);
2454 
2455 	if (tcp_is_sack(tp)) {
2456 		int sacked_upto = tp->sacked_out - tp->reordering;
2457 		if (sacked_upto >= 0)
2458 			tcp_mark_head_lost(sk, sacked_upto, 0);
2459 		else if (fast_rexmit)
2460 			tcp_mark_head_lost(sk, 1, 1);
2461 	}
2462 }
2463 
tcp_tsopt_ecr_before(const struct tcp_sock * tp,u32 when)2464 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2465 {
2466 	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2467 	       before(tp->rx_opt.rcv_tsecr, when);
2468 }
2469 
2470 /* skb is spurious retransmitted if the returned timestamp echo
2471  * reply is prior to the skb transmission time
2472  */
tcp_skb_spurious_retrans(const struct tcp_sock * tp,const struct sk_buff * skb)2473 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2474 				     const struct sk_buff *skb)
2475 {
2476 	return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2477 	       tcp_tsopt_ecr_before(tp, tcp_skb_timestamp_ts(tp->tcp_usec_ts, skb));
2478 }
2479 
2480 /* Nothing was retransmitted or returned timestamp is less
2481  * than timestamp of the first retransmission.
2482  */
tcp_packet_delayed(const struct tcp_sock * tp)2483 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2484 {
2485 	const struct sock *sk = (const struct sock *)tp;
2486 
2487 	if (tp->retrans_stamp &&
2488 	    tcp_tsopt_ecr_before(tp, tp->retrans_stamp))
2489 		return true;  /* got echoed TS before first retransmission */
2490 
2491 	/* Check if nothing was retransmitted (retrans_stamp==0), which may
2492 	 * happen in fast recovery due to TSQ. But we ignore zero retrans_stamp
2493 	 * in TCP_SYN_SENT, since when we set FLAG_SYN_ACKED we also clear
2494 	 * retrans_stamp even if we had retransmitted the SYN.
2495 	 */
2496 	if (!tp->retrans_stamp &&	   /* no record of a retransmit/SYN? */
2497 	    sk->sk_state != TCP_SYN_SENT)  /* not the FLAG_SYN_ACKED case? */
2498 		return true;  /* nothing was retransmitted */
2499 
2500 	return false;
2501 }
2502 
2503 /* Undo procedures. */
2504 
2505 /* We can clear retrans_stamp when there are no retransmissions in the
2506  * window. It would seem that it is trivially available for us in
2507  * tp->retrans_out, however, that kind of assumptions doesn't consider
2508  * what will happen if errors occur when sending retransmission for the
2509  * second time. ...It could the that such segment has only
2510  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2511  * the head skb is enough except for some reneging corner cases that
2512  * are not worth the effort.
2513  *
2514  * Main reason for all this complexity is the fact that connection dying
2515  * time now depends on the validity of the retrans_stamp, in particular,
2516  * that successive retransmissions of a segment must not advance
2517  * retrans_stamp under any conditions.
2518  */
tcp_any_retrans_done(const struct sock * sk)2519 static bool tcp_any_retrans_done(const struct sock *sk)
2520 {
2521 	const struct tcp_sock *tp = tcp_sk(sk);
2522 	struct sk_buff *skb;
2523 
2524 	if (tp->retrans_out)
2525 		return true;
2526 
2527 	skb = tcp_rtx_queue_head(sk);
2528 	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2529 		return true;
2530 
2531 	return false;
2532 }
2533 
2534 /* If loss recovery is finished and there are no retransmits out in the
2535  * network, then we clear retrans_stamp so that upon the next loss recovery
2536  * retransmits_timed_out() and timestamp-undo are using the correct value.
2537  */
tcp_retrans_stamp_cleanup(struct sock * sk)2538 static void tcp_retrans_stamp_cleanup(struct sock *sk)
2539 {
2540 	if (!tcp_any_retrans_done(sk))
2541 		tcp_sk(sk)->retrans_stamp = 0;
2542 }
2543 
DBGUNDO(struct sock * sk,const char * msg)2544 static void DBGUNDO(struct sock *sk, const char *msg)
2545 {
2546 #if FASTRETRANS_DEBUG > 1
2547 	struct tcp_sock *tp = tcp_sk(sk);
2548 	struct inet_sock *inet = inet_sk(sk);
2549 
2550 	if (sk->sk_family == AF_INET) {
2551 		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2552 			 msg,
2553 			 &inet->inet_daddr, ntohs(inet->inet_dport),
2554 			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2555 			 tp->snd_ssthresh, tp->prior_ssthresh,
2556 			 tp->packets_out);
2557 	}
2558 #if IS_ENABLED(CONFIG_IPV6)
2559 	else if (sk->sk_family == AF_INET6) {
2560 		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2561 			 msg,
2562 			 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2563 			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2564 			 tp->snd_ssthresh, tp->prior_ssthresh,
2565 			 tp->packets_out);
2566 	}
2567 #endif
2568 #endif
2569 }
2570 
tcp_undo_cwnd_reduction(struct sock * sk,bool unmark_loss)2571 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2572 {
2573 	struct tcp_sock *tp = tcp_sk(sk);
2574 
2575 	if (unmark_loss) {
2576 		struct sk_buff *skb;
2577 
2578 		skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2579 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2580 		}
2581 		tp->lost_out = 0;
2582 		tcp_clear_all_retrans_hints(tp);
2583 	}
2584 
2585 	if (tp->prior_ssthresh) {
2586 		const struct inet_connection_sock *icsk = inet_csk(sk);
2587 
2588 		tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk));
2589 
2590 		if (tp->prior_ssthresh > tp->snd_ssthresh) {
2591 			tp->snd_ssthresh = tp->prior_ssthresh;
2592 			tcp_ecn_withdraw_cwr(tp);
2593 		}
2594 	}
2595 	tp->snd_cwnd_stamp = tcp_jiffies32;
2596 	tp->undo_marker = 0;
2597 	tp->rack.advanced = 1; /* Force RACK to re-exam losses */
2598 }
2599 
tcp_may_undo(const struct tcp_sock * tp)2600 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2601 {
2602 	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2603 }
2604 
tcp_is_non_sack_preventing_reopen(struct sock * sk)2605 static bool tcp_is_non_sack_preventing_reopen(struct sock *sk)
2606 {
2607 	struct tcp_sock *tp = tcp_sk(sk);
2608 
2609 	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2610 		/* Hold old state until something *above* high_seq
2611 		 * is ACKed. For Reno it is MUST to prevent false
2612 		 * fast retransmits (RFC2582). SACK TCP is safe. */
2613 		if (!tcp_any_retrans_done(sk))
2614 			tp->retrans_stamp = 0;
2615 		return true;
2616 	}
2617 	return false;
2618 }
2619 
2620 /* People celebrate: "We love our President!" */
tcp_try_undo_recovery(struct sock * sk)2621 static bool tcp_try_undo_recovery(struct sock *sk)
2622 {
2623 	struct tcp_sock *tp = tcp_sk(sk);
2624 
2625 	if (tcp_may_undo(tp)) {
2626 		int mib_idx;
2627 
2628 		/* Happy end! We did not retransmit anything
2629 		 * or our original transmission succeeded.
2630 		 */
2631 		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2632 		tcp_undo_cwnd_reduction(sk, false);
2633 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2634 			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2635 		else
2636 			mib_idx = LINUX_MIB_TCPFULLUNDO;
2637 
2638 		NET_INC_STATS(sock_net(sk), mib_idx);
2639 	} else if (tp->rack.reo_wnd_persist) {
2640 		tp->rack.reo_wnd_persist--;
2641 	}
2642 	if (tcp_is_non_sack_preventing_reopen(sk))
2643 		return true;
2644 	tcp_set_ca_state(sk, TCP_CA_Open);
2645 	tp->is_sack_reneg = 0;
2646 	return false;
2647 }
2648 
2649 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
tcp_try_undo_dsack(struct sock * sk)2650 static bool tcp_try_undo_dsack(struct sock *sk)
2651 {
2652 	struct tcp_sock *tp = tcp_sk(sk);
2653 
2654 	if (tp->undo_marker && !tp->undo_retrans) {
2655 		tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
2656 					       tp->rack.reo_wnd_persist + 1);
2657 		DBGUNDO(sk, "D-SACK");
2658 		tcp_undo_cwnd_reduction(sk, false);
2659 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2660 		return true;
2661 	}
2662 	return false;
2663 }
2664 
2665 /* Undo during loss recovery after partial ACK or using F-RTO. */
tcp_try_undo_loss(struct sock * sk,bool frto_undo)2666 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2667 {
2668 	struct tcp_sock *tp = tcp_sk(sk);
2669 
2670 	if (frto_undo || tcp_may_undo(tp)) {
2671 		tcp_undo_cwnd_reduction(sk, true);
2672 
2673 		DBGUNDO(sk, "partial loss");
2674 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2675 		if (frto_undo)
2676 			NET_INC_STATS(sock_net(sk),
2677 					LINUX_MIB_TCPSPURIOUSRTOS);
2678 		inet_csk(sk)->icsk_retransmits = 0;
2679 		if (tcp_is_non_sack_preventing_reopen(sk))
2680 			return true;
2681 		if (frto_undo || tcp_is_sack(tp)) {
2682 			tcp_set_ca_state(sk, TCP_CA_Open);
2683 			tp->is_sack_reneg = 0;
2684 		}
2685 		return true;
2686 	}
2687 	return false;
2688 }
2689 
2690 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2691  * It computes the number of packets to send (sndcnt) based on packets newly
2692  * delivered:
2693  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2694  *	cwnd reductions across a full RTT.
2695  *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2696  *      But when SND_UNA is acked without further losses,
2697  *      slow starts cwnd up to ssthresh to speed up the recovery.
2698  */
tcp_init_cwnd_reduction(struct sock * sk)2699 static void tcp_init_cwnd_reduction(struct sock *sk)
2700 {
2701 	struct tcp_sock *tp = tcp_sk(sk);
2702 
2703 	tp->high_seq = tp->snd_nxt;
2704 	tp->tlp_high_seq = 0;
2705 	tp->snd_cwnd_cnt = 0;
2706 	tp->prior_cwnd = tcp_snd_cwnd(tp);
2707 	tp->prr_delivered = 0;
2708 	tp->prr_out = 0;
2709 	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2710 	tcp_ecn_queue_cwr(tp);
2711 }
2712 
tcp_cwnd_reduction(struct sock * sk,int newly_acked_sacked,int newly_lost,int flag)2713 void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag)
2714 {
2715 	struct tcp_sock *tp = tcp_sk(sk);
2716 	int sndcnt = 0;
2717 	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2718 
2719 	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2720 		return;
2721 
2722 	trace_tcp_cwnd_reduction_tp(sk, newly_acked_sacked, newly_lost, flag);
2723 
2724 	tp->prr_delivered += newly_acked_sacked;
2725 	if (delta < 0) {
2726 		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2727 			       tp->prior_cwnd - 1;
2728 		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2729 	} else {
2730 		sndcnt = max_t(int, tp->prr_delivered - tp->prr_out,
2731 			       newly_acked_sacked);
2732 		if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
2733 			sndcnt++;
2734 		sndcnt = min(delta, sndcnt);
2735 	}
2736 	/* Force a fast retransmit upon entering fast recovery */
2737 	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2738 	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt);
2739 }
2740 
tcp_end_cwnd_reduction(struct sock * sk)2741 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2742 {
2743 	struct tcp_sock *tp = tcp_sk(sk);
2744 
2745 	if (inet_csk(sk)->icsk_ca_ops->cong_control)
2746 		return;
2747 
2748 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2749 	if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
2750 	    (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
2751 		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
2752 		tp->snd_cwnd_stamp = tcp_jiffies32;
2753 	}
2754 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2755 }
2756 
2757 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
tcp_enter_cwr(struct sock * sk)2758 void tcp_enter_cwr(struct sock *sk)
2759 {
2760 	struct tcp_sock *tp = tcp_sk(sk);
2761 
2762 	tp->prior_ssthresh = 0;
2763 	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2764 		tp->undo_marker = 0;
2765 		tcp_init_cwnd_reduction(sk);
2766 		tcp_set_ca_state(sk, TCP_CA_CWR);
2767 	}
2768 }
2769 EXPORT_SYMBOL(tcp_enter_cwr);
2770 
tcp_try_keep_open(struct sock * sk)2771 static void tcp_try_keep_open(struct sock *sk)
2772 {
2773 	struct tcp_sock *tp = tcp_sk(sk);
2774 	int state = TCP_CA_Open;
2775 
2776 	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2777 		state = TCP_CA_Disorder;
2778 
2779 	if (inet_csk(sk)->icsk_ca_state != state) {
2780 		tcp_set_ca_state(sk, state);
2781 		tp->high_seq = tp->snd_nxt;
2782 	}
2783 }
2784 
tcp_try_to_open(struct sock * sk,int flag)2785 static void tcp_try_to_open(struct sock *sk, int flag)
2786 {
2787 	struct tcp_sock *tp = tcp_sk(sk);
2788 
2789 	tcp_verify_left_out(tp);
2790 
2791 	if (!tcp_any_retrans_done(sk))
2792 		tp->retrans_stamp = 0;
2793 
2794 	if (flag & FLAG_ECE)
2795 		tcp_enter_cwr(sk);
2796 
2797 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2798 		tcp_try_keep_open(sk);
2799 	}
2800 }
2801 
tcp_mtup_probe_failed(struct sock * sk)2802 static void tcp_mtup_probe_failed(struct sock *sk)
2803 {
2804 	struct inet_connection_sock *icsk = inet_csk(sk);
2805 
2806 	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2807 	icsk->icsk_mtup.probe_size = 0;
2808 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2809 }
2810 
tcp_mtup_probe_success(struct sock * sk)2811 static void tcp_mtup_probe_success(struct sock *sk)
2812 {
2813 	struct tcp_sock *tp = tcp_sk(sk);
2814 	struct inet_connection_sock *icsk = inet_csk(sk);
2815 	u64 val;
2816 
2817 	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2818 
2819 	val = (u64)tcp_snd_cwnd(tp) * tcp_mss_to_mtu(sk, tp->mss_cache);
2820 	do_div(val, icsk->icsk_mtup.probe_size);
2821 	DEBUG_NET_WARN_ON_ONCE((u32)val != val);
2822 	tcp_snd_cwnd_set(tp, max_t(u32, 1U, val));
2823 
2824 	tp->snd_cwnd_cnt = 0;
2825 	tp->snd_cwnd_stamp = tcp_jiffies32;
2826 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2827 
2828 	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2829 	icsk->icsk_mtup.probe_size = 0;
2830 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2831 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2832 }
2833 
2834 /* Sometimes we deduce that packets have been dropped due to reasons other than
2835  * congestion, like path MTU reductions or failed client TFO attempts. In these
2836  * cases we call this function to retransmit as many packets as cwnd allows,
2837  * without reducing cwnd. Given that retransmits will set retrans_stamp to a
2838  * non-zero value (and may do so in a later calling context due to TSQ), we
2839  * also enter CA_Loss so that we track when all retransmitted packets are ACKed
2840  * and clear retrans_stamp when that happens (to ensure later recurring RTOs
2841  * are using the correct retrans_stamp and don't declare ETIMEDOUT
2842  * prematurely).
2843  */
tcp_non_congestion_loss_retransmit(struct sock * sk)2844 static void tcp_non_congestion_loss_retransmit(struct sock *sk)
2845 {
2846 	const struct inet_connection_sock *icsk = inet_csk(sk);
2847 	struct tcp_sock *tp = tcp_sk(sk);
2848 
2849 	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2850 		tp->high_seq = tp->snd_nxt;
2851 		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2852 		tp->prior_ssthresh = 0;
2853 		tp->undo_marker = 0;
2854 		tcp_set_ca_state(sk, TCP_CA_Loss);
2855 	}
2856 	tcp_xmit_retransmit_queue(sk);
2857 }
2858 
2859 /* Do a simple retransmit without using the backoff mechanisms in
2860  * tcp_timer. This is used for path mtu discovery.
2861  * The socket is already locked here.
2862  */
tcp_simple_retransmit(struct sock * sk)2863 void tcp_simple_retransmit(struct sock *sk)
2864 {
2865 	struct tcp_sock *tp = tcp_sk(sk);
2866 	struct sk_buff *skb;
2867 	int mss;
2868 
2869 	/* A fastopen SYN request is stored as two separate packets within
2870 	 * the retransmit queue, this is done by tcp_send_syn_data().
2871 	 * As a result simply checking the MSS of the frames in the queue
2872 	 * will not work for the SYN packet.
2873 	 *
2874 	 * Us being here is an indication of a path MTU issue so we can
2875 	 * assume that the fastopen SYN was lost and just mark all the
2876 	 * frames in the retransmit queue as lost. We will use an MSS of
2877 	 * -1 to mark all frames as lost, otherwise compute the current MSS.
2878 	 */
2879 	if (tp->syn_data && sk->sk_state == TCP_SYN_SENT)
2880 		mss = -1;
2881 	else
2882 		mss = tcp_current_mss(sk);
2883 
2884 	skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2885 		if (tcp_skb_seglen(skb) > mss)
2886 			tcp_mark_skb_lost(sk, skb);
2887 	}
2888 
2889 	tcp_clear_retrans_hints_partial(tp);
2890 
2891 	if (!tp->lost_out)
2892 		return;
2893 
2894 	if (tcp_is_reno(tp))
2895 		tcp_limit_reno_sacked(tp);
2896 
2897 	tcp_verify_left_out(tp);
2898 
2899 	/* Don't muck with the congestion window here.
2900 	 * Reason is that we do not increase amount of _data_
2901 	 * in network, but units changed and effective
2902 	 * cwnd/ssthresh really reduced now.
2903 	 */
2904 	tcp_non_congestion_loss_retransmit(sk);
2905 }
2906 EXPORT_IPV6_MOD(tcp_simple_retransmit);
2907 
tcp_enter_recovery(struct sock * sk,bool ece_ack)2908 void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2909 {
2910 	struct tcp_sock *tp = tcp_sk(sk);
2911 	int mib_idx;
2912 
2913 	/* Start the clock with our fast retransmit, for undo and ETIMEDOUT. */
2914 	tcp_retrans_stamp_cleanup(sk);
2915 
2916 	if (tcp_is_reno(tp))
2917 		mib_idx = LINUX_MIB_TCPRENORECOVERY;
2918 	else
2919 		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2920 
2921 	NET_INC_STATS(sock_net(sk), mib_idx);
2922 
2923 	tp->prior_ssthresh = 0;
2924 	tcp_init_undo(tp);
2925 
2926 	if (!tcp_in_cwnd_reduction(sk)) {
2927 		if (!ece_ack)
2928 			tp->prior_ssthresh = tcp_current_ssthresh(sk);
2929 		tcp_init_cwnd_reduction(sk);
2930 	}
2931 	tcp_set_ca_state(sk, TCP_CA_Recovery);
2932 }
2933 
tcp_update_rto_time(struct tcp_sock * tp)2934 static void tcp_update_rto_time(struct tcp_sock *tp)
2935 {
2936 	if (tp->rto_stamp) {
2937 		tp->total_rto_time += tcp_time_stamp_ms(tp) - tp->rto_stamp;
2938 		tp->rto_stamp = 0;
2939 	}
2940 }
2941 
2942 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2943  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2944  */
tcp_process_loss(struct sock * sk,int flag,int num_dupack,int * rexmit)2945 static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
2946 			     int *rexmit)
2947 {
2948 	struct tcp_sock *tp = tcp_sk(sk);
2949 	bool recovered = !before(tp->snd_una, tp->high_seq);
2950 
2951 	if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) &&
2952 	    tcp_try_undo_loss(sk, false))
2953 		return;
2954 
2955 	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2956 		/* Step 3.b. A timeout is spurious if not all data are
2957 		 * lost, i.e., never-retransmitted data are (s)acked.
2958 		 */
2959 		if ((flag & FLAG_ORIG_SACK_ACKED) &&
2960 		    tcp_try_undo_loss(sk, true))
2961 			return;
2962 
2963 		if (after(tp->snd_nxt, tp->high_seq)) {
2964 			if (flag & FLAG_DATA_SACKED || num_dupack)
2965 				tp->frto = 0; /* Step 3.a. loss was real */
2966 		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
2967 			tp->high_seq = tp->snd_nxt;
2968 			/* Step 2.b. Try send new data (but deferred until cwnd
2969 			 * is updated in tcp_ack()). Otherwise fall back to
2970 			 * the conventional recovery.
2971 			 */
2972 			if (!tcp_write_queue_empty(sk) &&
2973 			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
2974 				*rexmit = REXMIT_NEW;
2975 				return;
2976 			}
2977 			tp->frto = 0;
2978 		}
2979 	}
2980 
2981 	if (recovered) {
2982 		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
2983 		tcp_try_undo_recovery(sk);
2984 		return;
2985 	}
2986 	if (tcp_is_reno(tp)) {
2987 		/* A Reno DUPACK means new data in F-RTO step 2.b above are
2988 		 * delivered. Lower inflight to clock out (re)transmissions.
2989 		 */
2990 		if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
2991 			tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE);
2992 		else if (flag & FLAG_SND_UNA_ADVANCED)
2993 			tcp_reset_reno_sack(tp);
2994 	}
2995 	*rexmit = REXMIT_LOST;
2996 }
2997 
tcp_force_fast_retransmit(struct sock * sk)2998 static bool tcp_force_fast_retransmit(struct sock *sk)
2999 {
3000 	struct tcp_sock *tp = tcp_sk(sk);
3001 
3002 	return after(tcp_highest_sack_seq(tp),
3003 		     tp->snd_una + tp->reordering * tp->mss_cache);
3004 }
3005 
3006 /* Undo during fast recovery after partial ACK. */
tcp_try_undo_partial(struct sock * sk,u32 prior_snd_una,bool * do_lost)3007 static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una,
3008 				 bool *do_lost)
3009 {
3010 	struct tcp_sock *tp = tcp_sk(sk);
3011 
3012 	if (tp->undo_marker && tcp_packet_delayed(tp)) {
3013 		/* Plain luck! Hole if filled with delayed
3014 		 * packet, rather than with a retransmit. Check reordering.
3015 		 */
3016 		tcp_check_sack_reordering(sk, prior_snd_una, 1);
3017 
3018 		/* We are getting evidence that the reordering degree is higher
3019 		 * than we realized. If there are no retransmits out then we
3020 		 * can undo. Otherwise we clock out new packets but do not
3021 		 * mark more packets lost or retransmit more.
3022 		 */
3023 		if (tp->retrans_out)
3024 			return true;
3025 
3026 		if (!tcp_any_retrans_done(sk))
3027 			tp->retrans_stamp = 0;
3028 
3029 		DBGUNDO(sk, "partial recovery");
3030 		tcp_undo_cwnd_reduction(sk, true);
3031 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
3032 		tcp_try_keep_open(sk);
3033 	} else {
3034 		/* Partial ACK arrived. Force fast retransmit. */
3035 		*do_lost = tcp_force_fast_retransmit(sk);
3036 	}
3037 	return false;
3038 }
3039 
tcp_identify_packet_loss(struct sock * sk,int * ack_flag)3040 static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
3041 {
3042 	struct tcp_sock *tp = tcp_sk(sk);
3043 
3044 	if (tcp_rtx_queue_empty(sk))
3045 		return;
3046 
3047 	if (unlikely(tcp_is_reno(tp))) {
3048 		tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
3049 	} else if (tcp_is_rack(sk)) {
3050 		u32 prior_retrans = tp->retrans_out;
3051 
3052 		if (tcp_rack_mark_lost(sk))
3053 			*ack_flag &= ~FLAG_SET_XMIT_TIMER;
3054 		if (prior_retrans > tp->retrans_out)
3055 			*ack_flag |= FLAG_LOST_RETRANS;
3056 	}
3057 }
3058 
3059 /* Process an event, which can update packets-in-flight not trivially.
3060  * Main goal of this function is to calculate new estimate for left_out,
3061  * taking into account both packets sitting in receiver's buffer and
3062  * packets lost by network.
3063  *
3064  * Besides that it updates the congestion state when packet loss or ECN
3065  * is detected. But it does not reduce the cwnd, it is done by the
3066  * congestion control later.
3067  *
3068  * It does _not_ decide what to send, it is made in function
3069  * tcp_xmit_retransmit_queue().
3070  */
tcp_fastretrans_alert(struct sock * sk,const u32 prior_snd_una,int num_dupack,int * ack_flag,int * rexmit)3071 static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
3072 				  int num_dupack, int *ack_flag, int *rexmit)
3073 {
3074 	struct inet_connection_sock *icsk = inet_csk(sk);
3075 	struct tcp_sock *tp = tcp_sk(sk);
3076 	int fast_rexmit = 0, flag = *ack_flag;
3077 	bool ece_ack = flag & FLAG_ECE;
3078 	bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) &&
3079 				      tcp_force_fast_retransmit(sk));
3080 
3081 	if (!tp->packets_out && tp->sacked_out)
3082 		tp->sacked_out = 0;
3083 
3084 	/* Now state machine starts.
3085 	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
3086 	if (ece_ack)
3087 		tp->prior_ssthresh = 0;
3088 
3089 	/* B. In all the states check for reneging SACKs. */
3090 	if (tcp_check_sack_reneging(sk, ack_flag))
3091 		return;
3092 
3093 	/* C. Check consistency of the current state. */
3094 	tcp_verify_left_out(tp);
3095 
3096 	/* D. Check state exit conditions. State can be terminated
3097 	 *    when high_seq is ACKed. */
3098 	if (icsk->icsk_ca_state == TCP_CA_Open) {
3099 		WARN_ON(tp->retrans_out != 0 && !tp->syn_data);
3100 		tp->retrans_stamp = 0;
3101 	} else if (!before(tp->snd_una, tp->high_seq)) {
3102 		switch (icsk->icsk_ca_state) {
3103 		case TCP_CA_CWR:
3104 			/* CWR is to be held something *above* high_seq
3105 			 * is ACKed for CWR bit to reach receiver. */
3106 			if (tp->snd_una != tp->high_seq) {
3107 				tcp_end_cwnd_reduction(sk);
3108 				tcp_set_ca_state(sk, TCP_CA_Open);
3109 			}
3110 			break;
3111 
3112 		case TCP_CA_Recovery:
3113 			if (tcp_is_reno(tp))
3114 				tcp_reset_reno_sack(tp);
3115 			if (tcp_try_undo_recovery(sk))
3116 				return;
3117 			tcp_end_cwnd_reduction(sk);
3118 			break;
3119 		}
3120 	}
3121 
3122 	/* E. Process state. */
3123 	switch (icsk->icsk_ca_state) {
3124 	case TCP_CA_Recovery:
3125 		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3126 			if (tcp_is_reno(tp))
3127 				tcp_add_reno_sack(sk, num_dupack, ece_ack);
3128 		} else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost))
3129 			return;
3130 
3131 		if (tcp_try_undo_dsack(sk))
3132 			tcp_try_to_open(sk, flag);
3133 
3134 		tcp_identify_packet_loss(sk, ack_flag);
3135 		if (icsk->icsk_ca_state != TCP_CA_Recovery) {
3136 			if (!tcp_time_to_recover(sk, flag))
3137 				return;
3138 			/* Undo reverts the recovery state. If loss is evident,
3139 			 * starts a new recovery (e.g. reordering then loss);
3140 			 */
3141 			tcp_enter_recovery(sk, ece_ack);
3142 		}
3143 		break;
3144 	case TCP_CA_Loss:
3145 		tcp_process_loss(sk, flag, num_dupack, rexmit);
3146 		if (icsk->icsk_ca_state != TCP_CA_Loss)
3147 			tcp_update_rto_time(tp);
3148 		tcp_identify_packet_loss(sk, ack_flag);
3149 		if (!(icsk->icsk_ca_state == TCP_CA_Open ||
3150 		      (*ack_flag & FLAG_LOST_RETRANS)))
3151 			return;
3152 		/* Change state if cwnd is undone or retransmits are lost */
3153 		fallthrough;
3154 	default:
3155 		if (tcp_is_reno(tp)) {
3156 			if (flag & FLAG_SND_UNA_ADVANCED)
3157 				tcp_reset_reno_sack(tp);
3158 			tcp_add_reno_sack(sk, num_dupack, ece_ack);
3159 		}
3160 
3161 		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
3162 			tcp_try_undo_dsack(sk);
3163 
3164 		tcp_identify_packet_loss(sk, ack_flag);
3165 		if (!tcp_time_to_recover(sk, flag)) {
3166 			tcp_try_to_open(sk, flag);
3167 			return;
3168 		}
3169 
3170 		/* MTU probe failure: don't reduce cwnd */
3171 		if (icsk->icsk_ca_state < TCP_CA_CWR &&
3172 		    icsk->icsk_mtup.probe_size &&
3173 		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3174 			tcp_mtup_probe_failed(sk);
3175 			/* Restores the reduction we did in tcp_mtup_probe() */
3176 			tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
3177 			tcp_simple_retransmit(sk);
3178 			return;
3179 		}
3180 
3181 		/* Otherwise enter Recovery state */
3182 		tcp_enter_recovery(sk, ece_ack);
3183 		fast_rexmit = 1;
3184 	}
3185 
3186 	if (!tcp_is_rack(sk) && do_lost)
3187 		tcp_update_scoreboard(sk, fast_rexmit);
3188 	*rexmit = REXMIT_LOST;
3189 }
3190 
tcp_update_rtt_min(struct sock * sk,u32 rtt_us,const int flag)3191 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
3192 {
3193 	u32 wlen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen) * HZ;
3194 	struct tcp_sock *tp = tcp_sk(sk);
3195 
3196 	if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
3197 		/* If the remote keeps returning delayed ACKs, eventually
3198 		 * the min filter would pick it up and overestimate the
3199 		 * prop. delay when it expires. Skip suspected delayed ACKs.
3200 		 */
3201 		return;
3202 	}
3203 	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
3204 			   rtt_us ? : jiffies_to_usecs(1));
3205 }
3206 
tcp_ack_update_rtt(struct sock * sk,const int flag,long seq_rtt_us,long sack_rtt_us,long ca_rtt_us,struct rate_sample * rs)3207 static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
3208 			       long seq_rtt_us, long sack_rtt_us,
3209 			       long ca_rtt_us, struct rate_sample *rs)
3210 {
3211 	const struct tcp_sock *tp = tcp_sk(sk);
3212 
3213 	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
3214 	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
3215 	 * Karn's algorithm forbids taking RTT if some retransmitted data
3216 	 * is acked (RFC6298).
3217 	 */
3218 	if (seq_rtt_us < 0)
3219 		seq_rtt_us = sack_rtt_us;
3220 
3221 	/* RTTM Rule: A TSecr value received in a segment is used to
3222 	 * update the averaged RTT measurement only if the segment
3223 	 * acknowledges some new data, i.e., only if it advances the
3224 	 * left edge of the send window.
3225 	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
3226 	 */
3227 	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp &&
3228 	    tp->rx_opt.rcv_tsecr && flag & FLAG_ACKED)
3229 		seq_rtt_us = ca_rtt_us = tcp_rtt_tsopt_us(tp);
3230 
3231 	rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
3232 	if (seq_rtt_us < 0)
3233 		return false;
3234 
3235 	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
3236 	 * always taken together with ACK, SACK, or TS-opts. Any negative
3237 	 * values will be skipped with the seq_rtt_us < 0 check above.
3238 	 */
3239 	tcp_update_rtt_min(sk, ca_rtt_us, flag);
3240 	tcp_rtt_estimator(sk, seq_rtt_us);
3241 	tcp_set_rto(sk);
3242 
3243 	/* RFC6298: only reset backoff on valid RTT measurement. */
3244 	inet_csk(sk)->icsk_backoff = 0;
3245 	return true;
3246 }
3247 
3248 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
tcp_synack_rtt_meas(struct sock * sk,struct request_sock * req)3249 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
3250 {
3251 	struct rate_sample rs;
3252 	long rtt_us = -1L;
3253 
3254 	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
3255 		rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
3256 
3257 	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
3258 }
3259 
3260 
tcp_cong_avoid(struct sock * sk,u32 ack,u32 acked)3261 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
3262 {
3263 	const struct inet_connection_sock *icsk = inet_csk(sk);
3264 
3265 	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
3266 	tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
3267 }
3268 
3269 /* Restart timer after forward progress on connection.
3270  * RFC2988 recommends to restart timer to now+rto.
3271  */
tcp_rearm_rto(struct sock * sk)3272 void tcp_rearm_rto(struct sock *sk)
3273 {
3274 	const struct inet_connection_sock *icsk = inet_csk(sk);
3275 	struct tcp_sock *tp = tcp_sk(sk);
3276 
3277 	/* If the retrans timer is currently being used by Fast Open
3278 	 * for SYN-ACK retrans purpose, stay put.
3279 	 */
3280 	if (rcu_access_pointer(tp->fastopen_rsk))
3281 		return;
3282 
3283 	if (!tp->packets_out) {
3284 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3285 	} else {
3286 		u32 rto = inet_csk(sk)->icsk_rto;
3287 		/* Offset the time elapsed after installing regular RTO */
3288 		if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3289 		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3290 			s64 delta_us = tcp_rto_delta_us(sk);
3291 			/* delta_us may not be positive if the socket is locked
3292 			 * when the retrans timer fires and is rescheduled.
3293 			 */
3294 			rto = usecs_to_jiffies(max_t(int, delta_us, 1));
3295 		}
3296 		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto, true);
3297 	}
3298 }
3299 
3300 /* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
tcp_set_xmit_timer(struct sock * sk)3301 static void tcp_set_xmit_timer(struct sock *sk)
3302 {
3303 	if (!tcp_schedule_loss_probe(sk, true))
3304 		tcp_rearm_rto(sk);
3305 }
3306 
3307 /* If we get here, the whole TSO packet has not been acked. */
tcp_tso_acked(struct sock * sk,struct sk_buff * skb)3308 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3309 {
3310 	struct tcp_sock *tp = tcp_sk(sk);
3311 	u32 packets_acked;
3312 
3313 	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3314 
3315 	packets_acked = tcp_skb_pcount(skb);
3316 	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3317 		return 0;
3318 	packets_acked -= tcp_skb_pcount(skb);
3319 
3320 	if (packets_acked) {
3321 		BUG_ON(tcp_skb_pcount(skb) == 0);
3322 		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3323 	}
3324 
3325 	return packets_acked;
3326 }
3327 
tcp_ack_tstamp(struct sock * sk,struct sk_buff * skb,const struct sk_buff * ack_skb,u32 prior_snd_una)3328 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3329 			   const struct sk_buff *ack_skb, u32 prior_snd_una)
3330 {
3331 	const struct skb_shared_info *shinfo;
3332 
3333 	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3334 	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3335 		return;
3336 
3337 	shinfo = skb_shinfo(skb);
3338 	if (!before(shinfo->tskey, prior_snd_una) &&
3339 	    before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
3340 		tcp_skb_tsorted_save(skb) {
3341 			__skb_tstamp_tx(skb, ack_skb, NULL, sk, SCM_TSTAMP_ACK);
3342 		} tcp_skb_tsorted_restore(skb);
3343 	}
3344 }
3345 
3346 /* Remove acknowledged frames from the retransmission queue. If our packet
3347  * is before the ack sequence we can discard it as it's confirmed to have
3348  * arrived at the other end.
3349  */
tcp_clean_rtx_queue(struct sock * sk,const struct sk_buff * ack_skb,u32 prior_fack,u32 prior_snd_una,struct tcp_sacktag_state * sack,bool ece_ack)3350 static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
3351 			       u32 prior_fack, u32 prior_snd_una,
3352 			       struct tcp_sacktag_state *sack, bool ece_ack)
3353 {
3354 	const struct inet_connection_sock *icsk = inet_csk(sk);
3355 	u64 first_ackt, last_ackt;
3356 	struct tcp_sock *tp = tcp_sk(sk);
3357 	u32 prior_sacked = tp->sacked_out;
3358 	u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
3359 	struct sk_buff *skb, *next;
3360 	bool fully_acked = true;
3361 	long sack_rtt_us = -1L;
3362 	long seq_rtt_us = -1L;
3363 	long ca_rtt_us = -1L;
3364 	u32 pkts_acked = 0;
3365 	bool rtt_update;
3366 	int flag = 0;
3367 
3368 	first_ackt = 0;
3369 
3370 	for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
3371 		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3372 		const u32 start_seq = scb->seq;
3373 		u8 sacked = scb->sacked;
3374 		u32 acked_pcount;
3375 
3376 		/* Determine how many packets and what bytes were acked, tso and else */
3377 		if (after(scb->end_seq, tp->snd_una)) {
3378 			if (tcp_skb_pcount(skb) == 1 ||
3379 			    !after(tp->snd_una, scb->seq))
3380 				break;
3381 
3382 			acked_pcount = tcp_tso_acked(sk, skb);
3383 			if (!acked_pcount)
3384 				break;
3385 			fully_acked = false;
3386 		} else {
3387 			acked_pcount = tcp_skb_pcount(skb);
3388 		}
3389 
3390 		if (unlikely(sacked & TCPCB_RETRANS)) {
3391 			if (sacked & TCPCB_SACKED_RETRANS)
3392 				tp->retrans_out -= acked_pcount;
3393 			flag |= FLAG_RETRANS_DATA_ACKED;
3394 		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
3395 			last_ackt = tcp_skb_timestamp_us(skb);
3396 			WARN_ON_ONCE(last_ackt == 0);
3397 			if (!first_ackt)
3398 				first_ackt = last_ackt;
3399 
3400 			if (before(start_seq, reord))
3401 				reord = start_seq;
3402 			if (!after(scb->end_seq, tp->high_seq))
3403 				flag |= FLAG_ORIG_SACK_ACKED;
3404 		}
3405 
3406 		if (sacked & TCPCB_SACKED_ACKED) {
3407 			tp->sacked_out -= acked_pcount;
3408 		} else if (tcp_is_sack(tp)) {
3409 			tcp_count_delivered(tp, acked_pcount, ece_ack);
3410 			if (!tcp_skb_spurious_retrans(tp, skb))
3411 				tcp_rack_advance(tp, sacked, scb->end_seq,
3412 						 tcp_skb_timestamp_us(skb));
3413 		}
3414 		if (sacked & TCPCB_LOST)
3415 			tp->lost_out -= acked_pcount;
3416 
3417 		tp->packets_out -= acked_pcount;
3418 		pkts_acked += acked_pcount;
3419 		tcp_rate_skb_delivered(sk, skb, sack->rate);
3420 
3421 		/* Initial outgoing SYN's get put onto the write_queue
3422 		 * just like anything else we transmit.  It is not
3423 		 * true data, and if we misinform our callers that
3424 		 * this ACK acks real data, we will erroneously exit
3425 		 * connection startup slow start one packet too
3426 		 * quickly.  This is severely frowned upon behavior.
3427 		 */
3428 		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3429 			flag |= FLAG_DATA_ACKED;
3430 		} else {
3431 			flag |= FLAG_SYN_ACKED;
3432 			tp->retrans_stamp = 0;
3433 		}
3434 
3435 		if (!fully_acked)
3436 			break;
3437 
3438 		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3439 
3440 		next = skb_rb_next(skb);
3441 		if (unlikely(skb == tp->retransmit_skb_hint))
3442 			tp->retransmit_skb_hint = NULL;
3443 		if (unlikely(skb == tp->lost_skb_hint))
3444 			tp->lost_skb_hint = NULL;
3445 		tcp_highest_sack_replace(sk, skb, next);
3446 		tcp_rtx_queue_unlink_and_free(skb, sk);
3447 	}
3448 
3449 	if (!skb)
3450 		tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3451 
3452 	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3453 		tp->snd_up = tp->snd_una;
3454 
3455 	if (skb) {
3456 		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3457 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
3458 			flag |= FLAG_SACK_RENEGING;
3459 	}
3460 
3461 	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3462 		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3463 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3464 
3465 		if (pkts_acked == 1 && fully_acked && !prior_sacked &&
3466 		    (tp->snd_una - prior_snd_una) < tp->mss_cache &&
3467 		    sack->rate->prior_delivered + 1 == tp->delivered &&
3468 		    !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
3469 			/* Conservatively mark a delayed ACK. It's typically
3470 			 * from a lone runt packet over the round trip to
3471 			 * a receiver w/o out-of-order or CE events.
3472 			 */
3473 			flag |= FLAG_ACK_MAYBE_DELAYED;
3474 		}
3475 	}
3476 	if (sack->first_sackt) {
3477 		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3478 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3479 	}
3480 	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3481 					ca_rtt_us, sack->rate);
3482 
3483 	if (flag & FLAG_ACKED) {
3484 		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3485 		if (unlikely(icsk->icsk_mtup.probe_size &&
3486 			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3487 			tcp_mtup_probe_success(sk);
3488 		}
3489 
3490 		if (tcp_is_reno(tp)) {
3491 			tcp_remove_reno_sacks(sk, pkts_acked, ece_ack);
3492 
3493 			/* If any of the cumulatively ACKed segments was
3494 			 * retransmitted, non-SACK case cannot confirm that
3495 			 * progress was due to original transmission due to
3496 			 * lack of TCPCB_SACKED_ACKED bits even if some of
3497 			 * the packets may have been never retransmitted.
3498 			 */
3499 			if (flag & FLAG_RETRANS_DATA_ACKED)
3500 				flag &= ~FLAG_ORIG_SACK_ACKED;
3501 		} else {
3502 			int delta;
3503 
3504 			/* Non-retransmitted hole got filled? That's reordering */
3505 			if (before(reord, prior_fack))
3506 				tcp_check_sack_reordering(sk, reord, 0);
3507 
3508 			delta = prior_sacked - tp->sacked_out;
3509 			tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3510 		}
3511 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
3512 		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
3513 						    tcp_skb_timestamp_us(skb))) {
3514 		/* Do not re-arm RTO if the sack RTT is measured from data sent
3515 		 * after when the head was last (re)transmitted. Otherwise the
3516 		 * timeout may continue to extend in loss recovery.
3517 		 */
3518 		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3519 	}
3520 
3521 	if (icsk->icsk_ca_ops->pkts_acked) {
3522 		struct ack_sample sample = { .pkts_acked = pkts_acked,
3523 					     .rtt_us = sack->rate->rtt_us };
3524 
3525 		sample.in_flight = tp->mss_cache *
3526 			(tp->delivered - sack->rate->prior_delivered);
3527 		icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3528 	}
3529 
3530 #if FASTRETRANS_DEBUG > 0
3531 	WARN_ON((int)tp->sacked_out < 0);
3532 	WARN_ON((int)tp->lost_out < 0);
3533 	WARN_ON((int)tp->retrans_out < 0);
3534 	if (!tp->packets_out && tcp_is_sack(tp)) {
3535 		icsk = inet_csk(sk);
3536 		if (tp->lost_out) {
3537 			pr_debug("Leak l=%u %d\n",
3538 				 tp->lost_out, icsk->icsk_ca_state);
3539 			tp->lost_out = 0;
3540 		}
3541 		if (tp->sacked_out) {
3542 			pr_debug("Leak s=%u %d\n",
3543 				 tp->sacked_out, icsk->icsk_ca_state);
3544 			tp->sacked_out = 0;
3545 		}
3546 		if (tp->retrans_out) {
3547 			pr_debug("Leak r=%u %d\n",
3548 				 tp->retrans_out, icsk->icsk_ca_state);
3549 			tp->retrans_out = 0;
3550 		}
3551 	}
3552 #endif
3553 	return flag;
3554 }
3555 
tcp_ack_probe(struct sock * sk)3556 static void tcp_ack_probe(struct sock *sk)
3557 {
3558 	struct inet_connection_sock *icsk = inet_csk(sk);
3559 	struct sk_buff *head = tcp_send_head(sk);
3560 	const struct tcp_sock *tp = tcp_sk(sk);
3561 
3562 	/* Was it a usable window open? */
3563 	if (!head)
3564 		return;
3565 	if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
3566 		icsk->icsk_backoff = 0;
3567 		icsk->icsk_probes_tstamp = 0;
3568 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3569 		/* Socket must be waked up by subsequent tcp_data_snd_check().
3570 		 * This function is not for random using!
3571 		 */
3572 	} else {
3573 		unsigned long when = tcp_probe0_when(sk, tcp_rto_max(sk));
3574 
3575 		when = tcp_clamp_probe0_to_user_timeout(sk, when);
3576 		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, true);
3577 	}
3578 }
3579 
tcp_ack_is_dubious(const struct sock * sk,const int flag)3580 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3581 {
3582 	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3583 		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3584 }
3585 
3586 /* Decide wheather to run the increase function of congestion control. */
tcp_may_raise_cwnd(const struct sock * sk,const int flag)3587 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3588 {
3589 	/* If reordering is high then always grow cwnd whenever data is
3590 	 * delivered regardless of its ordering. Otherwise stay conservative
3591 	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3592 	 * new SACK or ECE mark may first advance cwnd here and later reduce
3593 	 * cwnd in tcp_fastretrans_alert() based on more states.
3594 	 */
3595 	if (tcp_sk(sk)->reordering >
3596 	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering))
3597 		return flag & FLAG_FORWARD_PROGRESS;
3598 
3599 	return flag & FLAG_DATA_ACKED;
3600 }
3601 
3602 /* The "ultimate" congestion control function that aims to replace the rigid
3603  * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3604  * It's called toward the end of processing an ACK with precise rate
3605  * information. All transmission or retransmission are delayed afterwards.
3606  */
tcp_cong_control(struct sock * sk,u32 ack,u32 acked_sacked,int flag,const struct rate_sample * rs)3607 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3608 			     int flag, const struct rate_sample *rs)
3609 {
3610 	const struct inet_connection_sock *icsk = inet_csk(sk);
3611 
3612 	if (icsk->icsk_ca_ops->cong_control) {
3613 		icsk->icsk_ca_ops->cong_control(sk, ack, flag, rs);
3614 		return;
3615 	}
3616 
3617 	if (tcp_in_cwnd_reduction(sk)) {
3618 		/* Reduce cwnd if state mandates */
3619 		tcp_cwnd_reduction(sk, acked_sacked, rs->losses, flag);
3620 	} else if (tcp_may_raise_cwnd(sk, flag)) {
3621 		/* Advance cwnd if state allows */
3622 		tcp_cong_avoid(sk, ack, acked_sacked);
3623 	}
3624 	tcp_update_pacing_rate(sk);
3625 }
3626 
3627 /* Check that window update is acceptable.
3628  * The function assumes that snd_una<=ack<=snd_next.
3629  */
tcp_may_update_window(const struct tcp_sock * tp,const u32 ack,const u32 ack_seq,const u32 nwin)3630 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3631 					const u32 ack, const u32 ack_seq,
3632 					const u32 nwin)
3633 {
3634 	return	after(ack, tp->snd_una) ||
3635 		after(ack_seq, tp->snd_wl1) ||
3636 		(ack_seq == tp->snd_wl1 && (nwin > tp->snd_wnd || !nwin));
3637 }
3638 
tcp_snd_sne_update(struct tcp_sock * tp,u32 ack)3639 static void tcp_snd_sne_update(struct tcp_sock *tp, u32 ack)
3640 {
3641 #ifdef CONFIG_TCP_AO
3642 	struct tcp_ao_info *ao;
3643 
3644 	if (!static_branch_unlikely(&tcp_ao_needed.key))
3645 		return;
3646 
3647 	ao = rcu_dereference_protected(tp->ao_info,
3648 				       lockdep_sock_is_held((struct sock *)tp));
3649 	if (ao && ack < tp->snd_una) {
3650 		ao->snd_sne++;
3651 		trace_tcp_ao_snd_sne_update((struct sock *)tp, ao->snd_sne);
3652 	}
3653 #endif
3654 }
3655 
3656 /* If we update tp->snd_una, also update tp->bytes_acked */
tcp_snd_una_update(struct tcp_sock * tp,u32 ack)3657 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3658 {
3659 	u32 delta = ack - tp->snd_una;
3660 
3661 	sock_owned_by_me((struct sock *)tp);
3662 	tp->bytes_acked += delta;
3663 	tcp_snd_sne_update(tp, ack);
3664 	tp->snd_una = ack;
3665 }
3666 
tcp_rcv_sne_update(struct tcp_sock * tp,u32 seq)3667 static void tcp_rcv_sne_update(struct tcp_sock *tp, u32 seq)
3668 {
3669 #ifdef CONFIG_TCP_AO
3670 	struct tcp_ao_info *ao;
3671 
3672 	if (!static_branch_unlikely(&tcp_ao_needed.key))
3673 		return;
3674 
3675 	ao = rcu_dereference_protected(tp->ao_info,
3676 				       lockdep_sock_is_held((struct sock *)tp));
3677 	if (ao && seq < tp->rcv_nxt) {
3678 		ao->rcv_sne++;
3679 		trace_tcp_ao_rcv_sne_update((struct sock *)tp, ao->rcv_sne);
3680 	}
3681 #endif
3682 }
3683 
3684 /* If we update tp->rcv_nxt, also update tp->bytes_received */
tcp_rcv_nxt_update(struct tcp_sock * tp,u32 seq)3685 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3686 {
3687 	u32 delta = seq - tp->rcv_nxt;
3688 
3689 	sock_owned_by_me((struct sock *)tp);
3690 	tp->bytes_received += delta;
3691 	tcp_rcv_sne_update(tp, seq);
3692 	WRITE_ONCE(tp->rcv_nxt, seq);
3693 }
3694 
3695 /* Update our send window.
3696  *
3697  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3698  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3699  */
tcp_ack_update_window(struct sock * sk,const struct sk_buff * skb,u32 ack,u32 ack_seq)3700 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3701 				 u32 ack_seq)
3702 {
3703 	struct tcp_sock *tp = tcp_sk(sk);
3704 	int flag = 0;
3705 	u32 nwin = ntohs(tcp_hdr(skb)->window);
3706 
3707 	if (likely(!tcp_hdr(skb)->syn))
3708 		nwin <<= tp->rx_opt.snd_wscale;
3709 
3710 	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3711 		flag |= FLAG_WIN_UPDATE;
3712 		tcp_update_wl(tp, ack_seq);
3713 
3714 		if (tp->snd_wnd != nwin) {
3715 			tp->snd_wnd = nwin;
3716 
3717 			/* Note, it is the only place, where
3718 			 * fast path is recovered for sending TCP.
3719 			 */
3720 			tp->pred_flags = 0;
3721 			tcp_fast_path_check(sk);
3722 
3723 			if (!tcp_write_queue_empty(sk))
3724 				tcp_slow_start_after_idle_check(sk);
3725 
3726 			if (nwin > tp->max_window) {
3727 				tp->max_window = nwin;
3728 				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3729 			}
3730 		}
3731 	}
3732 
3733 	tcp_snd_una_update(tp, ack);
3734 
3735 	return flag;
3736 }
3737 
__tcp_oow_rate_limited(struct net * net,int mib_idx,u32 * last_oow_ack_time)3738 static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3739 				   u32 *last_oow_ack_time)
3740 {
3741 	/* Paired with the WRITE_ONCE() in this function. */
3742 	u32 val = READ_ONCE(*last_oow_ack_time);
3743 
3744 	if (val) {
3745 		s32 elapsed = (s32)(tcp_jiffies32 - val);
3746 
3747 		if (0 <= elapsed &&
3748 		    elapsed < READ_ONCE(net->ipv4.sysctl_tcp_invalid_ratelimit)) {
3749 			NET_INC_STATS(net, mib_idx);
3750 			return true;	/* rate-limited: don't send yet! */
3751 		}
3752 	}
3753 
3754 	/* Paired with the prior READ_ONCE() and with itself,
3755 	 * as we might be lockless.
3756 	 */
3757 	WRITE_ONCE(*last_oow_ack_time, tcp_jiffies32);
3758 
3759 	return false;	/* not rate-limited: go ahead, send dupack now! */
3760 }
3761 
3762 /* Return true if we're currently rate-limiting out-of-window ACKs and
3763  * thus shouldn't send a dupack right now. We rate-limit dupacks in
3764  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3765  * attacks that send repeated SYNs or ACKs for the same connection. To
3766  * do this, we do not send a duplicate SYNACK or ACK if the remote
3767  * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3768  */
tcp_oow_rate_limited(struct net * net,const struct sk_buff * skb,int mib_idx,u32 * last_oow_ack_time)3769 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3770 			  int mib_idx, u32 *last_oow_ack_time)
3771 {
3772 	/* Data packets without SYNs are not likely part of an ACK loop. */
3773 	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3774 	    !tcp_hdr(skb)->syn)
3775 		return false;
3776 
3777 	return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3778 }
3779 
3780 /* RFC 5961 7 [ACK Throttling] */
tcp_send_challenge_ack(struct sock * sk)3781 static void tcp_send_challenge_ack(struct sock *sk)
3782 {
3783 	struct tcp_sock *tp = tcp_sk(sk);
3784 	struct net *net = sock_net(sk);
3785 	u32 count, now, ack_limit;
3786 
3787 	/* First check our per-socket dupack rate limit. */
3788 	if (__tcp_oow_rate_limited(net,
3789 				   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3790 				   &tp->last_oow_ack_time))
3791 		return;
3792 
3793 	ack_limit = READ_ONCE(net->ipv4.sysctl_tcp_challenge_ack_limit);
3794 	if (ack_limit == INT_MAX)
3795 		goto send_ack;
3796 
3797 	/* Then check host-wide RFC 5961 rate limit. */
3798 	now = jiffies / HZ;
3799 	if (now != READ_ONCE(net->ipv4.tcp_challenge_timestamp)) {
3800 		u32 half = (ack_limit + 1) >> 1;
3801 
3802 		WRITE_ONCE(net->ipv4.tcp_challenge_timestamp, now);
3803 		WRITE_ONCE(net->ipv4.tcp_challenge_count,
3804 			   get_random_u32_inclusive(half, ack_limit + half - 1));
3805 	}
3806 	count = READ_ONCE(net->ipv4.tcp_challenge_count);
3807 	if (count > 0) {
3808 		WRITE_ONCE(net->ipv4.tcp_challenge_count, count - 1);
3809 send_ack:
3810 		NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
3811 		tcp_send_ack(sk);
3812 	}
3813 }
3814 
tcp_store_ts_recent(struct tcp_sock * tp)3815 static void tcp_store_ts_recent(struct tcp_sock *tp)
3816 {
3817 	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3818 	tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
3819 }
3820 
__tcp_replace_ts_recent(struct tcp_sock * tp,s32 tstamp_delta)3821 static int __tcp_replace_ts_recent(struct tcp_sock *tp, s32 tstamp_delta)
3822 {
3823 	tcp_store_ts_recent(tp);
3824 	return tstamp_delta > 0 ? FLAG_TS_PROGRESS : 0;
3825 }
3826 
tcp_replace_ts_recent(struct tcp_sock * tp,u32 seq)3827 static int tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3828 {
3829 	s32 delta;
3830 
3831 	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3832 		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3833 		 * extra check below makes sure this can only happen
3834 		 * for pure ACK frames.  -DaveM
3835 		 *
3836 		 * Not only, also it occurs for expired timestamps.
3837 		 */
3838 
3839 		if (tcp_paws_check(&tp->rx_opt, 0)) {
3840 			delta = tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent;
3841 			return __tcp_replace_ts_recent(tp, delta);
3842 		}
3843 	}
3844 
3845 	return 0;
3846 }
3847 
3848 /* This routine deals with acks during a TLP episode and ends an episode by
3849  * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack
3850  */
tcp_process_tlp_ack(struct sock * sk,u32 ack,int flag)3851 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3852 {
3853 	struct tcp_sock *tp = tcp_sk(sk);
3854 
3855 	if (before(ack, tp->tlp_high_seq))
3856 		return;
3857 
3858 	if (!tp->tlp_retrans) {
3859 		/* TLP of new data has been acknowledged */
3860 		tp->tlp_high_seq = 0;
3861 	} else if (flag & FLAG_DSACK_TLP) {
3862 		/* This DSACK means original and TLP probe arrived; no loss */
3863 		tp->tlp_high_seq = 0;
3864 	} else if (after(ack, tp->tlp_high_seq)) {
3865 		/* ACK advances: there was a loss, so reduce cwnd. Reset
3866 		 * tlp_high_seq in tcp_init_cwnd_reduction()
3867 		 */
3868 		tcp_init_cwnd_reduction(sk);
3869 		tcp_set_ca_state(sk, TCP_CA_CWR);
3870 		tcp_end_cwnd_reduction(sk);
3871 		tcp_try_keep_open(sk);
3872 		NET_INC_STATS(sock_net(sk),
3873 				LINUX_MIB_TCPLOSSPROBERECOVERY);
3874 	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3875 			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3876 		/* Pure dupack: original and TLP probe arrived; no loss */
3877 		tp->tlp_high_seq = 0;
3878 	}
3879 }
3880 
tcp_in_ack_event(struct sock * sk,int flag)3881 static void tcp_in_ack_event(struct sock *sk, int flag)
3882 {
3883 	const struct inet_connection_sock *icsk = inet_csk(sk);
3884 
3885 	if (icsk->icsk_ca_ops->in_ack_event) {
3886 		u32 ack_ev_flags = 0;
3887 
3888 		if (flag & FLAG_WIN_UPDATE)
3889 			ack_ev_flags |= CA_ACK_WIN_UPDATE;
3890 		if (flag & FLAG_SLOWPATH) {
3891 			ack_ev_flags |= CA_ACK_SLOWPATH;
3892 			if (flag & FLAG_ECE)
3893 				ack_ev_flags |= CA_ACK_ECE;
3894 		}
3895 
3896 		icsk->icsk_ca_ops->in_ack_event(sk, ack_ev_flags);
3897 	}
3898 }
3899 
3900 /* Congestion control has updated the cwnd already. So if we're in
3901  * loss recovery then now we do any new sends (for FRTO) or
3902  * retransmits (for CA_Loss or CA_recovery) that make sense.
3903  */
tcp_xmit_recovery(struct sock * sk,int rexmit)3904 static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3905 {
3906 	struct tcp_sock *tp = tcp_sk(sk);
3907 
3908 	if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
3909 		return;
3910 
3911 	if (unlikely(rexmit == REXMIT_NEW)) {
3912 		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
3913 					  TCP_NAGLE_OFF);
3914 		if (after(tp->snd_nxt, tp->high_seq))
3915 			return;
3916 		tp->frto = 0;
3917 	}
3918 	tcp_xmit_retransmit_queue(sk);
3919 }
3920 
3921 /* Returns the number of packets newly acked or sacked by the current ACK */
tcp_newly_delivered(struct sock * sk,u32 prior_delivered,int flag)3922 static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
3923 {
3924 	const struct net *net = sock_net(sk);
3925 	struct tcp_sock *tp = tcp_sk(sk);
3926 	u32 delivered;
3927 
3928 	delivered = tp->delivered - prior_delivered;
3929 	NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
3930 	if (flag & FLAG_ECE)
3931 		NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
3932 
3933 	return delivered;
3934 }
3935 
3936 /* This routine deals with incoming acks, but not outgoing ones. */
tcp_ack(struct sock * sk,const struct sk_buff * skb,int flag)3937 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3938 {
3939 	struct inet_connection_sock *icsk = inet_csk(sk);
3940 	struct tcp_sock *tp = tcp_sk(sk);
3941 	struct tcp_sacktag_state sack_state;
3942 	struct rate_sample rs = { .prior_delivered = 0 };
3943 	u32 prior_snd_una = tp->snd_una;
3944 	bool is_sack_reneg = tp->is_sack_reneg;
3945 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3946 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3947 	int num_dupack = 0;
3948 	int prior_packets = tp->packets_out;
3949 	u32 delivered = tp->delivered;
3950 	u32 lost = tp->lost;
3951 	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3952 	u32 prior_fack;
3953 
3954 	sack_state.first_sackt = 0;
3955 	sack_state.rate = &rs;
3956 	sack_state.sack_delivered = 0;
3957 
3958 	/* We very likely will need to access rtx queue. */
3959 	prefetch(sk->tcp_rtx_queue.rb_node);
3960 
3961 	/* If the ack is older than previous acks
3962 	 * then we can probably ignore it.
3963 	 */
3964 	if (before(ack, prior_snd_una)) {
3965 		u32 max_window;
3966 
3967 		/* do not accept ACK for bytes we never sent. */
3968 		max_window = min_t(u64, tp->max_window, tp->bytes_acked);
3969 		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
3970 		if (before(ack, prior_snd_una - max_window)) {
3971 			if (!(flag & FLAG_NO_CHALLENGE_ACK))
3972 				tcp_send_challenge_ack(sk);
3973 			return -SKB_DROP_REASON_TCP_TOO_OLD_ACK;
3974 		}
3975 		goto old_ack;
3976 	}
3977 
3978 	/* If the ack includes data we haven't sent yet, discard
3979 	 * this segment (RFC793 Section 3.9).
3980 	 */
3981 	if (after(ack, tp->snd_nxt))
3982 		return -SKB_DROP_REASON_TCP_ACK_UNSENT_DATA;
3983 
3984 	if (after(ack, prior_snd_una)) {
3985 		flag |= FLAG_SND_UNA_ADVANCED;
3986 		icsk->icsk_retransmits = 0;
3987 
3988 #if IS_ENABLED(CONFIG_TLS_DEVICE)
3989 		if (static_branch_unlikely(&clean_acked_data_enabled.key))
3990 			if (tp->tcp_clean_acked)
3991 				tp->tcp_clean_acked(sk, ack);
3992 #endif
3993 	}
3994 
3995 	prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
3996 	rs.prior_in_flight = tcp_packets_in_flight(tp);
3997 
3998 	/* ts_recent update must be made after we are sure that the packet
3999 	 * is in window.
4000 	 */
4001 	if (flag & FLAG_UPDATE_TS_RECENT)
4002 		flag |= tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4003 
4004 	if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
4005 	    FLAG_SND_UNA_ADVANCED) {
4006 		/* Window is constant, pure forward advance.
4007 		 * No more checks are required.
4008 		 * Note, we use the fact that SND.UNA>=SND.WL2.
4009 		 */
4010 		tcp_update_wl(tp, ack_seq);
4011 		tcp_snd_una_update(tp, ack);
4012 		flag |= FLAG_WIN_UPDATE;
4013 
4014 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
4015 	} else {
4016 		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
4017 			flag |= FLAG_DATA;
4018 		else
4019 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
4020 
4021 		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
4022 
4023 		if (TCP_SKB_CB(skb)->sacked)
4024 			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
4025 							&sack_state);
4026 
4027 		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb)))
4028 			flag |= FLAG_ECE;
4029 
4030 		if (sack_state.sack_delivered)
4031 			tcp_count_delivered(tp, sack_state.sack_delivered,
4032 					    flag & FLAG_ECE);
4033 	}
4034 
4035 	/* This is a deviation from RFC3168 since it states that:
4036 	 * "When the TCP data sender is ready to set the CWR bit after reducing
4037 	 * the congestion window, it SHOULD set the CWR bit only on the first
4038 	 * new data packet that it transmits."
4039 	 * We accept CWR on pure ACKs to be more robust
4040 	 * with widely-deployed TCP implementations that do this.
4041 	 */
4042 	tcp_ecn_accept_cwr(sk, skb);
4043 
4044 	/* We passed data and got it acked, remove any soft error
4045 	 * log. Something worked...
4046 	 */
4047 	WRITE_ONCE(sk->sk_err_soft, 0);
4048 	icsk->icsk_probes_out = 0;
4049 	tp->rcv_tstamp = tcp_jiffies32;
4050 	if (!prior_packets)
4051 		goto no_queue;
4052 
4053 	/* See if we can take anything off of the retransmit queue. */
4054 	flag |= tcp_clean_rtx_queue(sk, skb, prior_fack, prior_snd_una,
4055 				    &sack_state, flag & FLAG_ECE);
4056 
4057 	tcp_rack_update_reo_wnd(sk, &rs);
4058 
4059 	tcp_in_ack_event(sk, flag);
4060 
4061 	if (tp->tlp_high_seq)
4062 		tcp_process_tlp_ack(sk, ack, flag);
4063 
4064 	if (tcp_ack_is_dubious(sk, flag)) {
4065 		if (!(flag & (FLAG_SND_UNA_ADVANCED |
4066 			      FLAG_NOT_DUP | FLAG_DSACKING_ACK))) {
4067 			num_dupack = 1;
4068 			/* Consider if pure acks were aggregated in tcp_add_backlog() */
4069 			if (!(flag & FLAG_DATA))
4070 				num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
4071 		}
4072 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
4073 				      &rexmit);
4074 	}
4075 
4076 	/* If needed, reset TLP/RTO timer when RACK doesn't set. */
4077 	if (flag & FLAG_SET_XMIT_TIMER)
4078 		tcp_set_xmit_timer(sk);
4079 
4080 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
4081 		sk_dst_confirm(sk);
4082 
4083 	delivered = tcp_newly_delivered(sk, delivered, flag);
4084 	lost = tp->lost - lost;			/* freshly marked lost */
4085 	rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
4086 	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
4087 	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
4088 	tcp_xmit_recovery(sk, rexmit);
4089 	return 1;
4090 
4091 no_queue:
4092 	tcp_in_ack_event(sk, flag);
4093 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
4094 	if (flag & FLAG_DSACKING_ACK) {
4095 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
4096 				      &rexmit);
4097 		tcp_newly_delivered(sk, delivered, flag);
4098 	}
4099 	/* If this ack opens up a zero window, clear backoff.  It was
4100 	 * being used to time the probes, and is probably far higher than
4101 	 * it needs to be for normal retransmission.
4102 	 */
4103 	tcp_ack_probe(sk);
4104 
4105 	if (tp->tlp_high_seq)
4106 		tcp_process_tlp_ack(sk, ack, flag);
4107 	return 1;
4108 
4109 old_ack:
4110 	/* If data was SACKed, tag it and see if we should send more data.
4111 	 * If data was DSACKed, see if we can undo a cwnd reduction.
4112 	 */
4113 	if (TCP_SKB_CB(skb)->sacked) {
4114 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
4115 						&sack_state);
4116 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
4117 				      &rexmit);
4118 		tcp_newly_delivered(sk, delivered, flag);
4119 		tcp_xmit_recovery(sk, rexmit);
4120 	}
4121 
4122 	return 0;
4123 }
4124 
tcp_parse_fastopen_option(int len,const unsigned char * cookie,bool syn,struct tcp_fastopen_cookie * foc,bool exp_opt)4125 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
4126 				      bool syn, struct tcp_fastopen_cookie *foc,
4127 				      bool exp_opt)
4128 {
4129 	/* Valid only in SYN or SYN-ACK with an even length.  */
4130 	if (!foc || !syn || len < 0 || (len & 1))
4131 		return;
4132 
4133 	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
4134 	    len <= TCP_FASTOPEN_COOKIE_MAX)
4135 		memcpy(foc->val, cookie, len);
4136 	else if (len != 0)
4137 		len = -1;
4138 	foc->len = len;
4139 	foc->exp = exp_opt;
4140 }
4141 
smc_parse_options(const struct tcphdr * th,struct tcp_options_received * opt_rx,const unsigned char * ptr,int opsize)4142 static bool smc_parse_options(const struct tcphdr *th,
4143 			      struct tcp_options_received *opt_rx,
4144 			      const unsigned char *ptr,
4145 			      int opsize)
4146 {
4147 #if IS_ENABLED(CONFIG_SMC)
4148 	if (static_branch_unlikely(&tcp_have_smc)) {
4149 		if (th->syn && !(opsize & 1) &&
4150 		    opsize >= TCPOLEN_EXP_SMC_BASE &&
4151 		    get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) {
4152 			opt_rx->smc_ok = 1;
4153 			return true;
4154 		}
4155 	}
4156 #endif
4157 	return false;
4158 }
4159 
4160 /* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
4161  * value on success.
4162  */
tcp_parse_mss_option(const struct tcphdr * th,u16 user_mss)4163 u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
4164 {
4165 	const unsigned char *ptr = (const unsigned char *)(th + 1);
4166 	int length = (th->doff * 4) - sizeof(struct tcphdr);
4167 	u16 mss = 0;
4168 
4169 	while (length > 0) {
4170 		int opcode = *ptr++;
4171 		int opsize;
4172 
4173 		switch (opcode) {
4174 		case TCPOPT_EOL:
4175 			return mss;
4176 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4177 			length--;
4178 			continue;
4179 		default:
4180 			if (length < 2)
4181 				return mss;
4182 			opsize = *ptr++;
4183 			if (opsize < 2) /* "silly options" */
4184 				return mss;
4185 			if (opsize > length)
4186 				return mss;	/* fail on partial options */
4187 			if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
4188 				u16 in_mss = get_unaligned_be16(ptr);
4189 
4190 				if (in_mss) {
4191 					if (user_mss && user_mss < in_mss)
4192 						in_mss = user_mss;
4193 					mss = in_mss;
4194 				}
4195 			}
4196 			ptr += opsize - 2;
4197 			length -= opsize;
4198 		}
4199 	}
4200 	return mss;
4201 }
4202 
4203 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
4204  * But, this can also be called on packets in the established flow when
4205  * the fast version below fails.
4206  */
tcp_parse_options(const struct net * net,const struct sk_buff * skb,struct tcp_options_received * opt_rx,int estab,struct tcp_fastopen_cookie * foc)4207 void tcp_parse_options(const struct net *net,
4208 		       const struct sk_buff *skb,
4209 		       struct tcp_options_received *opt_rx, int estab,
4210 		       struct tcp_fastopen_cookie *foc)
4211 {
4212 	const unsigned char *ptr;
4213 	const struct tcphdr *th = tcp_hdr(skb);
4214 	int length = (th->doff * 4) - sizeof(struct tcphdr);
4215 
4216 	ptr = (const unsigned char *)(th + 1);
4217 	opt_rx->saw_tstamp = 0;
4218 	opt_rx->saw_unknown = 0;
4219 
4220 	while (length > 0) {
4221 		int opcode = *ptr++;
4222 		int opsize;
4223 
4224 		switch (opcode) {
4225 		case TCPOPT_EOL:
4226 			return;
4227 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4228 			length--;
4229 			continue;
4230 		default:
4231 			if (length < 2)
4232 				return;
4233 			opsize = *ptr++;
4234 			if (opsize < 2) /* "silly options" */
4235 				return;
4236 			if (opsize > length)
4237 				return;	/* don't parse partial options */
4238 			switch (opcode) {
4239 			case TCPOPT_MSS:
4240 				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
4241 					u16 in_mss = get_unaligned_be16(ptr);
4242 					if (in_mss) {
4243 						if (opt_rx->user_mss &&
4244 						    opt_rx->user_mss < in_mss)
4245 							in_mss = opt_rx->user_mss;
4246 						opt_rx->mss_clamp = in_mss;
4247 					}
4248 				}
4249 				break;
4250 			case TCPOPT_WINDOW:
4251 				if (opsize == TCPOLEN_WINDOW && th->syn &&
4252 				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) {
4253 					__u8 snd_wscale = *(__u8 *)ptr;
4254 					opt_rx->wscale_ok = 1;
4255 					if (snd_wscale > TCP_MAX_WSCALE) {
4256 						net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
4257 								     __func__,
4258 								     snd_wscale,
4259 								     TCP_MAX_WSCALE);
4260 						snd_wscale = TCP_MAX_WSCALE;
4261 					}
4262 					opt_rx->snd_wscale = snd_wscale;
4263 				}
4264 				break;
4265 			case TCPOPT_TIMESTAMP:
4266 				if ((opsize == TCPOLEN_TIMESTAMP) &&
4267 				    ((estab && opt_rx->tstamp_ok) ||
4268 				     (!estab && READ_ONCE(net->ipv4.sysctl_tcp_timestamps)))) {
4269 					opt_rx->saw_tstamp = 1;
4270 					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
4271 					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
4272 				}
4273 				break;
4274 			case TCPOPT_SACK_PERM:
4275 				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
4276 				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_sack)) {
4277 					opt_rx->sack_ok = TCP_SACK_SEEN;
4278 					tcp_sack_reset(opt_rx);
4279 				}
4280 				break;
4281 
4282 			case TCPOPT_SACK:
4283 				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
4284 				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
4285 				   opt_rx->sack_ok) {
4286 					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
4287 				}
4288 				break;
4289 #ifdef CONFIG_TCP_MD5SIG
4290 			case TCPOPT_MD5SIG:
4291 				/* The MD5 Hash has already been
4292 				 * checked (see tcp_v{4,6}_rcv()).
4293 				 */
4294 				break;
4295 #endif
4296 #ifdef CONFIG_TCP_AO
4297 			case TCPOPT_AO:
4298 				/* TCP AO has already been checked
4299 				 * (see tcp_inbound_ao_hash()).
4300 				 */
4301 				break;
4302 #endif
4303 			case TCPOPT_FASTOPEN:
4304 				tcp_parse_fastopen_option(
4305 					opsize - TCPOLEN_FASTOPEN_BASE,
4306 					ptr, th->syn, foc, false);
4307 				break;
4308 
4309 			case TCPOPT_EXP:
4310 				/* Fast Open option shares code 254 using a
4311 				 * 16 bits magic number.
4312 				 */
4313 				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
4314 				    get_unaligned_be16(ptr) ==
4315 				    TCPOPT_FASTOPEN_MAGIC) {
4316 					tcp_parse_fastopen_option(opsize -
4317 						TCPOLEN_EXP_FASTOPEN_BASE,
4318 						ptr + 2, th->syn, foc, true);
4319 					break;
4320 				}
4321 
4322 				if (smc_parse_options(th, opt_rx, ptr, opsize))
4323 					break;
4324 
4325 				opt_rx->saw_unknown = 1;
4326 				break;
4327 
4328 			default:
4329 				opt_rx->saw_unknown = 1;
4330 			}
4331 			ptr += opsize-2;
4332 			length -= opsize;
4333 		}
4334 	}
4335 }
4336 EXPORT_SYMBOL(tcp_parse_options);
4337 
tcp_parse_aligned_timestamp(struct tcp_sock * tp,const struct tcphdr * th)4338 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
4339 {
4340 	const __be32 *ptr = (const __be32 *)(th + 1);
4341 
4342 	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4343 			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
4344 		tp->rx_opt.saw_tstamp = 1;
4345 		++ptr;
4346 		tp->rx_opt.rcv_tsval = ntohl(*ptr);
4347 		++ptr;
4348 		if (*ptr)
4349 			tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
4350 		else
4351 			tp->rx_opt.rcv_tsecr = 0;
4352 		return true;
4353 	}
4354 	return false;
4355 }
4356 
4357 /* Fast parse options. This hopes to only see timestamps.
4358  * If it is wrong it falls back on tcp_parse_options().
4359  */
tcp_fast_parse_options(const struct net * net,const struct sk_buff * skb,const struct tcphdr * th,struct tcp_sock * tp)4360 static bool tcp_fast_parse_options(const struct net *net,
4361 				   const struct sk_buff *skb,
4362 				   const struct tcphdr *th, struct tcp_sock *tp)
4363 {
4364 	/* In the spirit of fast parsing, compare doff directly to constant
4365 	 * values.  Because equality is used, short doff can be ignored here.
4366 	 */
4367 	if (th->doff == (sizeof(*th) / 4)) {
4368 		tp->rx_opt.saw_tstamp = 0;
4369 		return false;
4370 	} else if (tp->rx_opt.tstamp_ok &&
4371 		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
4372 		if (tcp_parse_aligned_timestamp(tp, th))
4373 			return true;
4374 	}
4375 
4376 	tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
4377 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
4378 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
4379 
4380 	return true;
4381 }
4382 
4383 #if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
4384 /*
4385  * Parse Signature options
4386  */
tcp_do_parse_auth_options(const struct tcphdr * th,const u8 ** md5_hash,const u8 ** ao_hash)4387 int tcp_do_parse_auth_options(const struct tcphdr *th,
4388 			      const u8 **md5_hash, const u8 **ao_hash)
4389 {
4390 	int length = (th->doff << 2) - sizeof(*th);
4391 	const u8 *ptr = (const u8 *)(th + 1);
4392 	unsigned int minlen = TCPOLEN_MD5SIG;
4393 
4394 	if (IS_ENABLED(CONFIG_TCP_AO))
4395 		minlen = sizeof(struct tcp_ao_hdr) + 1;
4396 
4397 	*md5_hash = NULL;
4398 	*ao_hash = NULL;
4399 
4400 	/* If not enough data remaining, we can short cut */
4401 	while (length >= minlen) {
4402 		int opcode = *ptr++;
4403 		int opsize;
4404 
4405 		switch (opcode) {
4406 		case TCPOPT_EOL:
4407 			return 0;
4408 		case TCPOPT_NOP:
4409 			length--;
4410 			continue;
4411 		default:
4412 			opsize = *ptr++;
4413 			if (opsize < 2 || opsize > length)
4414 				return -EINVAL;
4415 			if (opcode == TCPOPT_MD5SIG) {
4416 				if (opsize != TCPOLEN_MD5SIG)
4417 					return -EINVAL;
4418 				if (unlikely(*md5_hash || *ao_hash))
4419 					return -EEXIST;
4420 				*md5_hash = ptr;
4421 			} else if (opcode == TCPOPT_AO) {
4422 				if (opsize <= sizeof(struct tcp_ao_hdr))
4423 					return -EINVAL;
4424 				if (unlikely(*md5_hash || *ao_hash))
4425 					return -EEXIST;
4426 				*ao_hash = ptr;
4427 			}
4428 		}
4429 		ptr += opsize - 2;
4430 		length -= opsize;
4431 	}
4432 	return 0;
4433 }
4434 EXPORT_SYMBOL(tcp_do_parse_auth_options);
4435 #endif
4436 
4437 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4438  *
4439  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4440  * it can pass through stack. So, the following predicate verifies that
4441  * this segment is not used for anything but congestion avoidance or
4442  * fast retransmit. Moreover, we even are able to eliminate most of such
4443  * second order effects, if we apply some small "replay" window (~RTO)
4444  * to timestamp space.
4445  *
4446  * All these measures still do not guarantee that we reject wrapped ACKs
4447  * on networks with high bandwidth, when sequence space is recycled fastly,
4448  * but it guarantees that such events will be very rare and do not affect
4449  * connection seriously. This doesn't look nice, but alas, PAWS is really
4450  * buggy extension.
4451  *
4452  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4453  * states that events when retransmit arrives after original data are rare.
4454  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4455  * the biggest problem on large power networks even with minor reordering.
4456  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4457  * up to bandwidth of 18Gigabit/sec. 8) ]
4458  */
4459 
4460 /* Estimates max number of increments of remote peer TSval in
4461  * a replay window (based on our current RTO estimation).
4462  */
tcp_tsval_replay(const struct sock * sk)4463 static u32 tcp_tsval_replay(const struct sock *sk)
4464 {
4465 	/* If we use usec TS resolution,
4466 	 * then expect the remote peer to use the same resolution.
4467 	 */
4468 	if (tcp_sk(sk)->tcp_usec_ts)
4469 		return inet_csk(sk)->icsk_rto * (USEC_PER_SEC / HZ);
4470 
4471 	/* RFC 7323 recommends a TSval clock between 1ms and 1sec.
4472 	 * We know that some OS (including old linux) can use 1200 Hz.
4473 	 */
4474 	return inet_csk(sk)->icsk_rto * 1200 / HZ;
4475 }
4476 
tcp_disordered_ack_check(const struct sock * sk,const struct sk_buff * skb)4477 static enum skb_drop_reason tcp_disordered_ack_check(const struct sock *sk,
4478 						     const struct sk_buff *skb)
4479 {
4480 	const struct tcp_sock *tp = tcp_sk(sk);
4481 	const struct tcphdr *th = tcp_hdr(skb);
4482 	SKB_DR_INIT(reason, TCP_RFC7323_PAWS);
4483 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
4484 	u32 seq = TCP_SKB_CB(skb)->seq;
4485 
4486 	/* 1. Is this not a pure ACK ? */
4487 	if (!th->ack || seq != TCP_SKB_CB(skb)->end_seq)
4488 		return reason;
4489 
4490 	/* 2. Is its sequence not the expected one ? */
4491 	if (seq != tp->rcv_nxt)
4492 		return before(seq, tp->rcv_nxt) ?
4493 			SKB_DROP_REASON_TCP_RFC7323_PAWS_ACK :
4494 			reason;
4495 
4496 	/* 3. Is this not a duplicate ACK ? */
4497 	if (ack != tp->snd_una)
4498 		return reason;
4499 
4500 	/* 4. Is this updating the window ? */
4501 	if (tcp_may_update_window(tp, ack, seq, ntohs(th->window) <<
4502 						tp->rx_opt.snd_wscale))
4503 		return reason;
4504 
4505 	/* 5. Is this not in the replay window ? */
4506 	if ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) >
4507 	    tcp_tsval_replay(sk))
4508 		return reason;
4509 
4510 	return 0;
4511 }
4512 
4513 /* Check segment sequence number for validity.
4514  *
4515  * Segment controls are considered valid, if the segment
4516  * fits to the window after truncation to the window. Acceptability
4517  * of data (and SYN, FIN, of course) is checked separately.
4518  * See tcp_data_queue(), for example.
4519  *
4520  * Also, controls (RST is main one) are accepted using RCV.WUP instead
4521  * of RCV.NXT. Peer still did not advance his SND.UNA when we
4522  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4523  * (borrowed from freebsd)
4524  */
4525 
tcp_sequence(const struct tcp_sock * tp,u32 seq,u32 end_seq)4526 static enum skb_drop_reason tcp_sequence(const struct tcp_sock *tp,
4527 					 u32 seq, u32 end_seq)
4528 {
4529 	if (before(end_seq, tp->rcv_wup))
4530 		return SKB_DROP_REASON_TCP_OLD_SEQUENCE;
4531 
4532 	if (after(seq, tp->rcv_nxt + tcp_receive_window(tp)))
4533 		return SKB_DROP_REASON_TCP_INVALID_SEQUENCE;
4534 
4535 	return SKB_NOT_DROPPED_YET;
4536 }
4537 
4538 
tcp_done_with_error(struct sock * sk,int err)4539 void tcp_done_with_error(struct sock *sk, int err)
4540 {
4541 	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4542 	WRITE_ONCE(sk->sk_err, err);
4543 	smp_wmb();
4544 
4545 	tcp_write_queue_purge(sk);
4546 	tcp_done(sk);
4547 
4548 	if (!sock_flag(sk, SOCK_DEAD))
4549 		sk_error_report(sk);
4550 }
4551 EXPORT_IPV6_MOD(tcp_done_with_error);
4552 
4553 /* When we get a reset we do this. */
tcp_reset(struct sock * sk,struct sk_buff * skb)4554 void tcp_reset(struct sock *sk, struct sk_buff *skb)
4555 {
4556 	int err;
4557 
4558 	trace_tcp_receive_reset(sk);
4559 
4560 	/* mptcp can't tell us to ignore reset pkts,
4561 	 * so just ignore the return value of mptcp_incoming_options().
4562 	 */
4563 	if (sk_is_mptcp(sk))
4564 		mptcp_incoming_options(sk, skb);
4565 
4566 	/* We want the right error as BSD sees it (and indeed as we do). */
4567 	switch (sk->sk_state) {
4568 	case TCP_SYN_SENT:
4569 		err = ECONNREFUSED;
4570 		break;
4571 	case TCP_CLOSE_WAIT:
4572 		err = EPIPE;
4573 		break;
4574 	case TCP_CLOSE:
4575 		return;
4576 	default:
4577 		err = ECONNRESET;
4578 	}
4579 	tcp_done_with_error(sk, err);
4580 }
4581 
4582 /*
4583  * 	Process the FIN bit. This now behaves as it is supposed to work
4584  *	and the FIN takes effect when it is validly part of sequence
4585  *	space. Not before when we get holes.
4586  *
4587  *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4588  *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4589  *	TIME-WAIT)
4590  *
4591  *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4592  *	close and we go into CLOSING (and later onto TIME-WAIT)
4593  *
4594  *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4595  */
tcp_fin(struct sock * sk)4596 void tcp_fin(struct sock *sk)
4597 {
4598 	struct tcp_sock *tp = tcp_sk(sk);
4599 
4600 	inet_csk_schedule_ack(sk);
4601 
4602 	WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | RCV_SHUTDOWN);
4603 	sock_set_flag(sk, SOCK_DONE);
4604 
4605 	switch (sk->sk_state) {
4606 	case TCP_SYN_RECV:
4607 	case TCP_ESTABLISHED:
4608 		/* Move to CLOSE_WAIT */
4609 		tcp_set_state(sk, TCP_CLOSE_WAIT);
4610 		inet_csk_enter_pingpong_mode(sk);
4611 		break;
4612 
4613 	case TCP_CLOSE_WAIT:
4614 	case TCP_CLOSING:
4615 		/* Received a retransmission of the FIN, do
4616 		 * nothing.
4617 		 */
4618 		break;
4619 	case TCP_LAST_ACK:
4620 		/* RFC793: Remain in the LAST-ACK state. */
4621 		break;
4622 
4623 	case TCP_FIN_WAIT1:
4624 		/* This case occurs when a simultaneous close
4625 		 * happens, we must ack the received FIN and
4626 		 * enter the CLOSING state.
4627 		 */
4628 		tcp_send_ack(sk);
4629 		tcp_set_state(sk, TCP_CLOSING);
4630 		break;
4631 	case TCP_FIN_WAIT2:
4632 		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4633 		tcp_send_ack(sk);
4634 		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4635 		break;
4636 	default:
4637 		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4638 		 * cases we should never reach this piece of code.
4639 		 */
4640 		pr_err("%s: Impossible, sk->sk_state=%d\n",
4641 		       __func__, sk->sk_state);
4642 		break;
4643 	}
4644 
4645 	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4646 	 * Probably, we should reset in this case. For now drop them.
4647 	 */
4648 	skb_rbtree_purge(&tp->out_of_order_queue);
4649 	if (tcp_is_sack(tp))
4650 		tcp_sack_reset(&tp->rx_opt);
4651 
4652 	if (!sock_flag(sk, SOCK_DEAD)) {
4653 		sk->sk_state_change(sk);
4654 
4655 		/* Do not send POLL_HUP for half duplex close. */
4656 		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4657 		    sk->sk_state == TCP_CLOSE)
4658 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4659 		else
4660 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4661 	}
4662 }
4663 
tcp_sack_extend(struct tcp_sack_block * sp,u32 seq,u32 end_seq)4664 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4665 				  u32 end_seq)
4666 {
4667 	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4668 		if (before(seq, sp->start_seq))
4669 			sp->start_seq = seq;
4670 		if (after(end_seq, sp->end_seq))
4671 			sp->end_seq = end_seq;
4672 		return true;
4673 	}
4674 	return false;
4675 }
4676 
tcp_dsack_set(struct sock * sk,u32 seq,u32 end_seq)4677 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4678 {
4679 	struct tcp_sock *tp = tcp_sk(sk);
4680 
4681 	if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4682 		int mib_idx;
4683 
4684 		if (before(seq, tp->rcv_nxt))
4685 			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4686 		else
4687 			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4688 
4689 		NET_INC_STATS(sock_net(sk), mib_idx);
4690 
4691 		tp->rx_opt.dsack = 1;
4692 		tp->duplicate_sack[0].start_seq = seq;
4693 		tp->duplicate_sack[0].end_seq = end_seq;
4694 	}
4695 }
4696 
tcp_dsack_extend(struct sock * sk,u32 seq,u32 end_seq)4697 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4698 {
4699 	struct tcp_sock *tp = tcp_sk(sk);
4700 
4701 	if (!tp->rx_opt.dsack)
4702 		tcp_dsack_set(sk, seq, end_seq);
4703 	else
4704 		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4705 }
4706 
tcp_rcv_spurious_retrans(struct sock * sk,const struct sk_buff * skb)4707 static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
4708 {
4709 	/* When the ACK path fails or drops most ACKs, the sender would
4710 	 * timeout and spuriously retransmit the same segment repeatedly.
4711 	 * If it seems our ACKs are not reaching the other side,
4712 	 * based on receiving a duplicate data segment with new flowlabel
4713 	 * (suggesting the sender suffered an RTO), and we are not already
4714 	 * repathing due to our own RTO, then rehash the socket to repath our
4715 	 * packets.
4716 	 */
4717 #if IS_ENABLED(CONFIG_IPV6)
4718 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss &&
4719 	    skb->protocol == htons(ETH_P_IPV6) &&
4720 	    (tcp_sk(sk)->inet_conn.icsk_ack.lrcv_flowlabel !=
4721 	     ntohl(ip6_flowlabel(ipv6_hdr(skb)))) &&
4722 	    sk_rethink_txhash(sk))
4723 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
4724 
4725 	/* Save last flowlabel after a spurious retrans. */
4726 	tcp_save_lrcv_flowlabel(sk, skb);
4727 #endif
4728 }
4729 
tcp_send_dupack(struct sock * sk,const struct sk_buff * skb)4730 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4731 {
4732 	struct tcp_sock *tp = tcp_sk(sk);
4733 
4734 	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4735 	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4736 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4737 		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4738 
4739 		if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4740 			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4741 
4742 			tcp_rcv_spurious_retrans(sk, skb);
4743 			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4744 				end_seq = tp->rcv_nxt;
4745 			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4746 		}
4747 	}
4748 
4749 	tcp_send_ack(sk);
4750 }
4751 
4752 /* These routines update the SACK block as out-of-order packets arrive or
4753  * in-order packets close up the sequence space.
4754  */
tcp_sack_maybe_coalesce(struct tcp_sock * tp)4755 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4756 {
4757 	int this_sack;
4758 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4759 	struct tcp_sack_block *swalk = sp + 1;
4760 
4761 	/* See if the recent change to the first SACK eats into
4762 	 * or hits the sequence space of other SACK blocks, if so coalesce.
4763 	 */
4764 	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4765 		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4766 			int i;
4767 
4768 			/* Zap SWALK, by moving every further SACK up by one slot.
4769 			 * Decrease num_sacks.
4770 			 */
4771 			tp->rx_opt.num_sacks--;
4772 			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4773 				sp[i] = sp[i + 1];
4774 			continue;
4775 		}
4776 		this_sack++;
4777 		swalk++;
4778 	}
4779 }
4780 
tcp_sack_compress_send_ack(struct sock * sk)4781 void tcp_sack_compress_send_ack(struct sock *sk)
4782 {
4783 	struct tcp_sock *tp = tcp_sk(sk);
4784 
4785 	if (!tp->compressed_ack)
4786 		return;
4787 
4788 	if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
4789 		__sock_put(sk);
4790 
4791 	/* Since we have to send one ack finally,
4792 	 * substract one from tp->compressed_ack to keep
4793 	 * LINUX_MIB_TCPACKCOMPRESSED accurate.
4794 	 */
4795 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
4796 		      tp->compressed_ack - 1);
4797 
4798 	tp->compressed_ack = 0;
4799 	tcp_send_ack(sk);
4800 }
4801 
4802 /* Reasonable amount of sack blocks included in TCP SACK option
4803  * The max is 4, but this becomes 3 if TCP timestamps are there.
4804  * Given that SACK packets might be lost, be conservative and use 2.
4805  */
4806 #define TCP_SACK_BLOCKS_EXPECTED 2
4807 
tcp_sack_new_ofo_skb(struct sock * sk,u32 seq,u32 end_seq)4808 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4809 {
4810 	struct tcp_sock *tp = tcp_sk(sk);
4811 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4812 	int cur_sacks = tp->rx_opt.num_sacks;
4813 	int this_sack;
4814 
4815 	if (!cur_sacks)
4816 		goto new_sack;
4817 
4818 	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4819 		if (tcp_sack_extend(sp, seq, end_seq)) {
4820 			if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4821 				tcp_sack_compress_send_ack(sk);
4822 			/* Rotate this_sack to the first one. */
4823 			for (; this_sack > 0; this_sack--, sp--)
4824 				swap(*sp, *(sp - 1));
4825 			if (cur_sacks > 1)
4826 				tcp_sack_maybe_coalesce(tp);
4827 			return;
4828 		}
4829 	}
4830 
4831 	if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4832 		tcp_sack_compress_send_ack(sk);
4833 
4834 	/* Could not find an adjacent existing SACK, build a new one,
4835 	 * put it at the front, and shift everyone else down.  We
4836 	 * always know there is at least one SACK present already here.
4837 	 *
4838 	 * If the sack array is full, forget about the last one.
4839 	 */
4840 	if (this_sack >= TCP_NUM_SACKS) {
4841 		this_sack--;
4842 		tp->rx_opt.num_sacks--;
4843 		sp--;
4844 	}
4845 	for (; this_sack > 0; this_sack--, sp--)
4846 		*sp = *(sp - 1);
4847 
4848 new_sack:
4849 	/* Build the new head SACK, and we're done. */
4850 	sp->start_seq = seq;
4851 	sp->end_seq = end_seq;
4852 	tp->rx_opt.num_sacks++;
4853 }
4854 
4855 /* RCV.NXT advances, some SACKs should be eaten. */
4856 
tcp_sack_remove(struct tcp_sock * tp)4857 static void tcp_sack_remove(struct tcp_sock *tp)
4858 {
4859 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4860 	int num_sacks = tp->rx_opt.num_sacks;
4861 	int this_sack;
4862 
4863 	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4864 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4865 		tp->rx_opt.num_sacks = 0;
4866 		return;
4867 	}
4868 
4869 	for (this_sack = 0; this_sack < num_sacks;) {
4870 		/* Check if the start of the sack is covered by RCV.NXT. */
4871 		if (!before(tp->rcv_nxt, sp->start_seq)) {
4872 			int i;
4873 
4874 			/* RCV.NXT must cover all the block! */
4875 			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4876 
4877 			/* Zap this SACK, by moving forward any other SACKS. */
4878 			for (i = this_sack+1; i < num_sacks; i++)
4879 				tp->selective_acks[i-1] = tp->selective_acks[i];
4880 			num_sacks--;
4881 			continue;
4882 		}
4883 		this_sack++;
4884 		sp++;
4885 	}
4886 	tp->rx_opt.num_sacks = num_sacks;
4887 }
4888 
4889 /**
4890  * tcp_try_coalesce - try to merge skb to prior one
4891  * @sk: socket
4892  * @to: prior buffer
4893  * @from: buffer to add in queue
4894  * @fragstolen: pointer to boolean
4895  *
4896  * Before queueing skb @from after @to, try to merge them
4897  * to reduce overall memory use and queue lengths, if cost is small.
4898  * Packets in ofo or receive queues can stay a long time.
4899  * Better try to coalesce them right now to avoid future collapses.
4900  * Returns true if caller should free @from instead of queueing it
4901  */
tcp_try_coalesce(struct sock * sk,struct sk_buff * to,struct sk_buff * from,bool * fragstolen)4902 static bool tcp_try_coalesce(struct sock *sk,
4903 			     struct sk_buff *to,
4904 			     struct sk_buff *from,
4905 			     bool *fragstolen)
4906 {
4907 	int delta;
4908 
4909 	*fragstolen = false;
4910 
4911 	/* Its possible this segment overlaps with prior segment in queue */
4912 	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4913 		return false;
4914 
4915 	if (!tcp_skb_can_collapse_rx(to, from))
4916 		return false;
4917 
4918 	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4919 		return false;
4920 
4921 	atomic_add(delta, &sk->sk_rmem_alloc);
4922 	sk_mem_charge(sk, delta);
4923 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4924 	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4925 	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4926 	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4927 
4928 	if (TCP_SKB_CB(from)->has_rxtstamp) {
4929 		TCP_SKB_CB(to)->has_rxtstamp = true;
4930 		to->tstamp = from->tstamp;
4931 		skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
4932 	}
4933 
4934 	return true;
4935 }
4936 
tcp_ooo_try_coalesce(struct sock * sk,struct sk_buff * to,struct sk_buff * from,bool * fragstolen)4937 static bool tcp_ooo_try_coalesce(struct sock *sk,
4938 			     struct sk_buff *to,
4939 			     struct sk_buff *from,
4940 			     bool *fragstolen)
4941 {
4942 	bool res = tcp_try_coalesce(sk, to, from, fragstolen);
4943 
4944 	/* In case tcp_drop_reason() is called later, update to->gso_segs */
4945 	if (res) {
4946 		u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
4947 			       max_t(u16, 1, skb_shinfo(from)->gso_segs);
4948 
4949 		skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
4950 	}
4951 	return res;
4952 }
4953 
4954 noinline_for_tracing static void
tcp_drop_reason(struct sock * sk,struct sk_buff * skb,enum skb_drop_reason reason)4955 tcp_drop_reason(struct sock *sk, struct sk_buff *skb, enum skb_drop_reason reason)
4956 {
4957 	sk_drops_add(sk, skb);
4958 	sk_skb_reason_drop(sk, skb, reason);
4959 }
4960 
4961 /* This one checks to see if we can put data from the
4962  * out_of_order queue into the receive_queue.
4963  */
tcp_ofo_queue(struct sock * sk)4964 static void tcp_ofo_queue(struct sock *sk)
4965 {
4966 	struct tcp_sock *tp = tcp_sk(sk);
4967 	__u32 dsack_high = tp->rcv_nxt;
4968 	bool fin, fragstolen, eaten;
4969 	struct sk_buff *skb, *tail;
4970 	struct rb_node *p;
4971 
4972 	p = rb_first(&tp->out_of_order_queue);
4973 	while (p) {
4974 		skb = rb_to_skb(p);
4975 		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4976 			break;
4977 
4978 		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4979 			__u32 dsack = dsack_high;
4980 			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4981 				dsack_high = TCP_SKB_CB(skb)->end_seq;
4982 			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4983 		}
4984 		p = rb_next(p);
4985 		rb_erase(&skb->rbnode, &tp->out_of_order_queue);
4986 
4987 		if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
4988 			tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_DROP);
4989 			continue;
4990 		}
4991 
4992 		tail = skb_peek_tail(&sk->sk_receive_queue);
4993 		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
4994 		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
4995 		fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
4996 		if (!eaten)
4997 			tcp_add_receive_queue(sk, skb);
4998 		else
4999 			kfree_skb_partial(skb, fragstolen);
5000 
5001 		if (unlikely(fin)) {
5002 			tcp_fin(sk);
5003 			/* tcp_fin() purges tp->out_of_order_queue,
5004 			 * so we must end this loop right now.
5005 			 */
5006 			break;
5007 		}
5008 	}
5009 }
5010 
5011 static bool tcp_prune_ofo_queue(struct sock *sk, const struct sk_buff *in_skb);
5012 static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb);
5013 
tcp_try_rmem_schedule(struct sock * sk,struct sk_buff * skb,unsigned int size)5014 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
5015 				 unsigned int size)
5016 {
5017 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
5018 	    !sk_rmem_schedule(sk, skb, size)) {
5019 
5020 		if (tcp_prune_queue(sk, skb) < 0)
5021 			return -1;
5022 
5023 		while (!sk_rmem_schedule(sk, skb, size)) {
5024 			if (!tcp_prune_ofo_queue(sk, skb))
5025 				return -1;
5026 		}
5027 	}
5028 	return 0;
5029 }
5030 
tcp_data_queue_ofo(struct sock * sk,struct sk_buff * skb)5031 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
5032 {
5033 	struct tcp_sock *tp = tcp_sk(sk);
5034 	struct rb_node **p, *parent;
5035 	struct sk_buff *skb1;
5036 	u32 seq, end_seq;
5037 	bool fragstolen;
5038 
5039 	tcp_save_lrcv_flowlabel(sk, skb);
5040 	tcp_data_ecn_check(sk, skb);
5041 
5042 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
5043 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
5044 		sk->sk_data_ready(sk);
5045 		tcp_drop_reason(sk, skb, SKB_DROP_REASON_PROTO_MEM);
5046 		return;
5047 	}
5048 
5049 	/* Disable header prediction. */
5050 	tp->pred_flags = 0;
5051 	inet_csk_schedule_ack(sk);
5052 
5053 	tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
5054 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
5055 	seq = TCP_SKB_CB(skb)->seq;
5056 	end_seq = TCP_SKB_CB(skb)->end_seq;
5057 
5058 	p = &tp->out_of_order_queue.rb_node;
5059 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5060 		/* Initial out of order segment, build 1 SACK. */
5061 		if (tcp_is_sack(tp)) {
5062 			tp->rx_opt.num_sacks = 1;
5063 			tp->selective_acks[0].start_seq = seq;
5064 			tp->selective_acks[0].end_seq = end_seq;
5065 		}
5066 		rb_link_node(&skb->rbnode, NULL, p);
5067 		rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
5068 		tp->ooo_last_skb = skb;
5069 		goto end;
5070 	}
5071 
5072 	/* In the typical case, we are adding an skb to the end of the list.
5073 	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
5074 	 */
5075 	if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
5076 				 skb, &fragstolen)) {
5077 coalesce_done:
5078 		/* For non sack flows, do not grow window to force DUPACK
5079 		 * and trigger fast retransmit.
5080 		 */
5081 		if (tcp_is_sack(tp))
5082 			tcp_grow_window(sk, skb, true);
5083 		kfree_skb_partial(skb, fragstolen);
5084 		skb = NULL;
5085 		goto add_sack;
5086 	}
5087 	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
5088 	if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
5089 		parent = &tp->ooo_last_skb->rbnode;
5090 		p = &parent->rb_right;
5091 		goto insert;
5092 	}
5093 
5094 	/* Find place to insert this segment. Handle overlaps on the way. */
5095 	parent = NULL;
5096 	while (*p) {
5097 		parent = *p;
5098 		skb1 = rb_to_skb(parent);
5099 		if (before(seq, TCP_SKB_CB(skb1)->seq)) {
5100 			p = &parent->rb_left;
5101 			continue;
5102 		}
5103 		if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
5104 			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
5105 				/* All the bits are present. Drop. */
5106 				NET_INC_STATS(sock_net(sk),
5107 					      LINUX_MIB_TCPOFOMERGE);
5108 				tcp_drop_reason(sk, skb,
5109 						SKB_DROP_REASON_TCP_OFOMERGE);
5110 				skb = NULL;
5111 				tcp_dsack_set(sk, seq, end_seq);
5112 				goto add_sack;
5113 			}
5114 			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
5115 				/* Partial overlap. */
5116 				tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
5117 			} else {
5118 				/* skb's seq == skb1's seq and skb covers skb1.
5119 				 * Replace skb1 with skb.
5120 				 */
5121 				rb_replace_node(&skb1->rbnode, &skb->rbnode,
5122 						&tp->out_of_order_queue);
5123 				tcp_dsack_extend(sk,
5124 						 TCP_SKB_CB(skb1)->seq,
5125 						 TCP_SKB_CB(skb1)->end_seq);
5126 				NET_INC_STATS(sock_net(sk),
5127 					      LINUX_MIB_TCPOFOMERGE);
5128 				tcp_drop_reason(sk, skb1,
5129 						SKB_DROP_REASON_TCP_OFOMERGE);
5130 				goto merge_right;
5131 			}
5132 		} else if (tcp_ooo_try_coalesce(sk, skb1,
5133 						skb, &fragstolen)) {
5134 			goto coalesce_done;
5135 		}
5136 		p = &parent->rb_right;
5137 	}
5138 insert:
5139 	/* Insert segment into RB tree. */
5140 	rb_link_node(&skb->rbnode, parent, p);
5141 	rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
5142 
5143 merge_right:
5144 	/* Remove other segments covered by skb. */
5145 	while ((skb1 = skb_rb_next(skb)) != NULL) {
5146 		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
5147 			break;
5148 		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
5149 			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
5150 					 end_seq);
5151 			break;
5152 		}
5153 		rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
5154 		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
5155 				 TCP_SKB_CB(skb1)->end_seq);
5156 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
5157 		tcp_drop_reason(sk, skb1, SKB_DROP_REASON_TCP_OFOMERGE);
5158 	}
5159 	/* If there is no skb after us, we are the last_skb ! */
5160 	if (!skb1)
5161 		tp->ooo_last_skb = skb;
5162 
5163 add_sack:
5164 	if (tcp_is_sack(tp))
5165 		tcp_sack_new_ofo_skb(sk, seq, end_seq);
5166 end:
5167 	if (skb) {
5168 		/* For non sack flows, do not grow window to force DUPACK
5169 		 * and trigger fast retransmit.
5170 		 */
5171 		if (tcp_is_sack(tp))
5172 			tcp_grow_window(sk, skb, false);
5173 		skb_condense(skb);
5174 		tcp_skb_set_owner_r(skb, sk);
5175 	}
5176 }
5177 
tcp_queue_rcv(struct sock * sk,struct sk_buff * skb,bool * fragstolen)5178 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
5179 				      bool *fragstolen)
5180 {
5181 	int eaten;
5182 	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
5183 
5184 	eaten = (tail &&
5185 		 tcp_try_coalesce(sk, tail,
5186 				  skb, fragstolen)) ? 1 : 0;
5187 	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
5188 	if (!eaten) {
5189 		tcp_add_receive_queue(sk, skb);
5190 		tcp_skb_set_owner_r(skb, sk);
5191 	}
5192 	return eaten;
5193 }
5194 
tcp_send_rcvq(struct sock * sk,struct msghdr * msg,size_t size)5195 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
5196 {
5197 	struct sk_buff *skb;
5198 	int err = -ENOMEM;
5199 	int data_len = 0;
5200 	bool fragstolen;
5201 
5202 	if (size == 0)
5203 		return 0;
5204 
5205 	if (size > PAGE_SIZE) {
5206 		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
5207 
5208 		data_len = npages << PAGE_SHIFT;
5209 		size = data_len + (size & ~PAGE_MASK);
5210 	}
5211 	skb = alloc_skb_with_frags(size - data_len, data_len,
5212 				   PAGE_ALLOC_COSTLY_ORDER,
5213 				   &err, sk->sk_allocation);
5214 	if (!skb)
5215 		goto err;
5216 
5217 	skb_put(skb, size - data_len);
5218 	skb->data_len = data_len;
5219 	skb->len = size;
5220 
5221 	if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5222 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5223 		goto err_free;
5224 	}
5225 
5226 	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
5227 	if (err)
5228 		goto err_free;
5229 
5230 	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
5231 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
5232 	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
5233 
5234 	if (tcp_queue_rcv(sk, skb, &fragstolen)) {
5235 		WARN_ON_ONCE(fragstolen); /* should not happen */
5236 		__kfree_skb(skb);
5237 	}
5238 	return size;
5239 
5240 err_free:
5241 	kfree_skb(skb);
5242 err:
5243 	return err;
5244 
5245 }
5246 
tcp_data_ready(struct sock * sk)5247 void tcp_data_ready(struct sock *sk)
5248 {
5249 	if (tcp_epollin_ready(sk, sk->sk_rcvlowat) || sock_flag(sk, SOCK_DONE))
5250 		sk->sk_data_ready(sk);
5251 }
5252 
tcp_data_queue(struct sock * sk,struct sk_buff * skb)5253 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
5254 {
5255 	struct tcp_sock *tp = tcp_sk(sk);
5256 	enum skb_drop_reason reason;
5257 	bool fragstolen;
5258 	int eaten;
5259 
5260 	/* If a subflow has been reset, the packet should not continue
5261 	 * to be processed, drop the packet.
5262 	 */
5263 	if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) {
5264 		__kfree_skb(skb);
5265 		return;
5266 	}
5267 
5268 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
5269 		__kfree_skb(skb);
5270 		return;
5271 	}
5272 	tcp_cleanup_skb(skb);
5273 	__skb_pull(skb, tcp_hdr(skb)->doff * 4);
5274 
5275 	reason = SKB_DROP_REASON_NOT_SPECIFIED;
5276 	tp->rx_opt.dsack = 0;
5277 
5278 	/*  Queue data for delivery to the user.
5279 	 *  Packets in sequence go to the receive queue.
5280 	 *  Out of sequence packets to the out_of_order_queue.
5281 	 */
5282 	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
5283 		if (tcp_receive_window(tp) == 0) {
5284 			/* Some stacks are known to send bare FIN packets
5285 			 * in a loop even if we send RWIN 0 in our ACK.
5286 			 * Accepting this FIN does not hurt memory pressure
5287 			 * because the FIN flag will simply be merged to the
5288 			 * receive queue tail skb in most cases.
5289 			 */
5290 			if (!skb->len &&
5291 			    (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
5292 				goto queue_and_out;
5293 
5294 			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5295 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5296 			goto out_of_window;
5297 		}
5298 
5299 		/* Ok. In sequence. In window. */
5300 queue_and_out:
5301 		if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5302 			/* TODO: maybe ratelimit these WIN 0 ACK ? */
5303 			inet_csk(sk)->icsk_ack.pending |=
5304 					(ICSK_ACK_NOMEM | ICSK_ACK_NOW);
5305 			inet_csk_schedule_ack(sk);
5306 			sk->sk_data_ready(sk);
5307 
5308 			if (skb_queue_len(&sk->sk_receive_queue) && skb->len) {
5309 				reason = SKB_DROP_REASON_PROTO_MEM;
5310 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5311 				goto drop;
5312 			}
5313 			sk_forced_mem_schedule(sk, skb->truesize);
5314 		}
5315 
5316 		eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5317 		if (skb->len)
5318 			tcp_event_data_recv(sk, skb);
5319 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
5320 			tcp_fin(sk);
5321 
5322 		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5323 			tcp_ofo_queue(sk);
5324 
5325 			/* RFC5681. 4.2. SHOULD send immediate ACK, when
5326 			 * gap in queue is filled.
5327 			 */
5328 			if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5329 				inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
5330 		}
5331 
5332 		if (tp->rx_opt.num_sacks)
5333 			tcp_sack_remove(tp);
5334 
5335 		tcp_fast_path_check(sk);
5336 
5337 		if (eaten > 0)
5338 			kfree_skb_partial(skb, fragstolen);
5339 		if (!sock_flag(sk, SOCK_DEAD))
5340 			tcp_data_ready(sk);
5341 		return;
5342 	}
5343 
5344 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
5345 		tcp_rcv_spurious_retrans(sk, skb);
5346 		/* A retransmit, 2nd most common case.  Force an immediate ack. */
5347 		reason = SKB_DROP_REASON_TCP_OLD_DATA;
5348 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
5349 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
5350 
5351 out_of_window:
5352 		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
5353 		inet_csk_schedule_ack(sk);
5354 drop:
5355 		tcp_drop_reason(sk, skb, reason);
5356 		return;
5357 	}
5358 
5359 	/* Out of window. F.e. zero window probe. */
5360 	if (!before(TCP_SKB_CB(skb)->seq,
5361 		    tp->rcv_nxt + tcp_receive_window(tp))) {
5362 		reason = SKB_DROP_REASON_TCP_OVERWINDOW;
5363 		goto out_of_window;
5364 	}
5365 
5366 	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5367 		/* Partial packet, seq < rcv_next < end_seq */
5368 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
5369 
5370 		/* If window is closed, drop tail of packet. But after
5371 		 * remembering D-SACK for its head made in previous line.
5372 		 */
5373 		if (!tcp_receive_window(tp)) {
5374 			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5375 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5376 			goto out_of_window;
5377 		}
5378 		goto queue_and_out;
5379 	}
5380 
5381 	tcp_data_queue_ofo(sk, skb);
5382 }
5383 
tcp_skb_next(struct sk_buff * skb,struct sk_buff_head * list)5384 static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
5385 {
5386 	if (list)
5387 		return !skb_queue_is_last(list, skb) ? skb->next : NULL;
5388 
5389 	return skb_rb_next(skb);
5390 }
5391 
tcp_collapse_one(struct sock * sk,struct sk_buff * skb,struct sk_buff_head * list,struct rb_root * root)5392 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
5393 					struct sk_buff_head *list,
5394 					struct rb_root *root)
5395 {
5396 	struct sk_buff *next = tcp_skb_next(skb, list);
5397 
5398 	if (list)
5399 		__skb_unlink(skb, list);
5400 	else
5401 		rb_erase(&skb->rbnode, root);
5402 
5403 	__kfree_skb(skb);
5404 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
5405 
5406 	return next;
5407 }
5408 
5409 /* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
tcp_rbtree_insert(struct rb_root * root,struct sk_buff * skb)5410 void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
5411 {
5412 	struct rb_node **p = &root->rb_node;
5413 	struct rb_node *parent = NULL;
5414 	struct sk_buff *skb1;
5415 
5416 	while (*p) {
5417 		parent = *p;
5418 		skb1 = rb_to_skb(parent);
5419 		if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
5420 			p = &parent->rb_left;
5421 		else
5422 			p = &parent->rb_right;
5423 	}
5424 	rb_link_node(&skb->rbnode, parent, p);
5425 	rb_insert_color(&skb->rbnode, root);
5426 }
5427 
5428 /* Collapse contiguous sequence of skbs head..tail with
5429  * sequence numbers start..end.
5430  *
5431  * If tail is NULL, this means until the end of the queue.
5432  *
5433  * Segments with FIN/SYN are not collapsed (only because this
5434  * simplifies code)
5435  */
5436 static void
tcp_collapse(struct sock * sk,struct sk_buff_head * list,struct rb_root * root,struct sk_buff * head,struct sk_buff * tail,u32 start,u32 end)5437 tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
5438 	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
5439 {
5440 	struct sk_buff *skb = head, *n;
5441 	struct sk_buff_head tmp;
5442 	bool end_of_skbs;
5443 
5444 	/* First, check that queue is collapsible and find
5445 	 * the point where collapsing can be useful.
5446 	 */
5447 restart:
5448 	for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
5449 		n = tcp_skb_next(skb, list);
5450 
5451 		if (!skb_frags_readable(skb))
5452 			goto skip_this;
5453 
5454 		/* No new bits? It is possible on ofo queue. */
5455 		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5456 			skb = tcp_collapse_one(sk, skb, list, root);
5457 			if (!skb)
5458 				break;
5459 			goto restart;
5460 		}
5461 
5462 		/* The first skb to collapse is:
5463 		 * - not SYN/FIN and
5464 		 * - bloated or contains data before "start" or
5465 		 *   overlaps to the next one and mptcp allow collapsing.
5466 		 */
5467 		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
5468 		    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
5469 		     before(TCP_SKB_CB(skb)->seq, start))) {
5470 			end_of_skbs = false;
5471 			break;
5472 		}
5473 
5474 		if (n && n != tail && skb_frags_readable(n) &&
5475 		    tcp_skb_can_collapse_rx(skb, n) &&
5476 		    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
5477 			end_of_skbs = false;
5478 			break;
5479 		}
5480 
5481 skip_this:
5482 		/* Decided to skip this, advance start seq. */
5483 		start = TCP_SKB_CB(skb)->end_seq;
5484 	}
5485 	if (end_of_skbs ||
5486 	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) ||
5487 	    !skb_frags_readable(skb))
5488 		return;
5489 
5490 	__skb_queue_head_init(&tmp);
5491 
5492 	while (before(start, end)) {
5493 		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
5494 		struct sk_buff *nskb;
5495 
5496 		nskb = alloc_skb(copy, GFP_ATOMIC);
5497 		if (!nskb)
5498 			break;
5499 
5500 		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
5501 		skb_copy_decrypted(nskb, skb);
5502 		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
5503 		if (list)
5504 			__skb_queue_before(list, skb, nskb);
5505 		else
5506 			__skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
5507 		tcp_skb_set_owner_r(nskb, sk);
5508 		mptcp_skb_ext_move(nskb, skb);
5509 
5510 		/* Copy data, releasing collapsed skbs. */
5511 		while (copy > 0) {
5512 			int offset = start - TCP_SKB_CB(skb)->seq;
5513 			int size = TCP_SKB_CB(skb)->end_seq - start;
5514 
5515 			BUG_ON(offset < 0);
5516 			if (size > 0) {
5517 				size = min(copy, size);
5518 				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
5519 					BUG();
5520 				TCP_SKB_CB(nskb)->end_seq += size;
5521 				copy -= size;
5522 				start += size;
5523 			}
5524 			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5525 				skb = tcp_collapse_one(sk, skb, list, root);
5526 				if (!skb ||
5527 				    skb == tail ||
5528 				    !tcp_skb_can_collapse_rx(nskb, skb) ||
5529 				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) ||
5530 				    !skb_frags_readable(skb))
5531 					goto end;
5532 			}
5533 		}
5534 	}
5535 end:
5536 	skb_queue_walk_safe(&tmp, skb, n)
5537 		tcp_rbtree_insert(root, skb);
5538 }
5539 
5540 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
5541  * and tcp_collapse() them until all the queue is collapsed.
5542  */
tcp_collapse_ofo_queue(struct sock * sk)5543 static void tcp_collapse_ofo_queue(struct sock *sk)
5544 {
5545 	struct tcp_sock *tp = tcp_sk(sk);
5546 	u32 range_truesize, sum_tiny = 0;
5547 	struct sk_buff *skb, *head;
5548 	u32 start, end;
5549 
5550 	skb = skb_rb_first(&tp->out_of_order_queue);
5551 new_range:
5552 	if (!skb) {
5553 		tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
5554 		return;
5555 	}
5556 	start = TCP_SKB_CB(skb)->seq;
5557 	end = TCP_SKB_CB(skb)->end_seq;
5558 	range_truesize = skb->truesize;
5559 
5560 	for (head = skb;;) {
5561 		skb = skb_rb_next(skb);
5562 
5563 		/* Range is terminated when we see a gap or when
5564 		 * we are at the queue end.
5565 		 */
5566 		if (!skb ||
5567 		    after(TCP_SKB_CB(skb)->seq, end) ||
5568 		    before(TCP_SKB_CB(skb)->end_seq, start)) {
5569 			/* Do not attempt collapsing tiny skbs */
5570 			if (range_truesize != head->truesize ||
5571 			    end - start >= SKB_WITH_OVERHEAD(PAGE_SIZE)) {
5572 				tcp_collapse(sk, NULL, &tp->out_of_order_queue,
5573 					     head, skb, start, end);
5574 			} else {
5575 				sum_tiny += range_truesize;
5576 				if (sum_tiny > sk->sk_rcvbuf >> 3)
5577 					return;
5578 			}
5579 			goto new_range;
5580 		}
5581 
5582 		range_truesize += skb->truesize;
5583 		if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
5584 			start = TCP_SKB_CB(skb)->seq;
5585 		if (after(TCP_SKB_CB(skb)->end_seq, end))
5586 			end = TCP_SKB_CB(skb)->end_seq;
5587 	}
5588 }
5589 
5590 /*
5591  * Clean the out-of-order queue to make room.
5592  * We drop high sequences packets to :
5593  * 1) Let a chance for holes to be filled.
5594  *    This means we do not drop packets from ooo queue if their sequence
5595  *    is before incoming packet sequence.
5596  * 2) not add too big latencies if thousands of packets sit there.
5597  *    (But if application shrinks SO_RCVBUF, we could still end up
5598  *     freeing whole queue here)
5599  * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
5600  *
5601  * Return true if queue has shrunk.
5602  */
tcp_prune_ofo_queue(struct sock * sk,const struct sk_buff * in_skb)5603 static bool tcp_prune_ofo_queue(struct sock *sk, const struct sk_buff *in_skb)
5604 {
5605 	struct tcp_sock *tp = tcp_sk(sk);
5606 	struct rb_node *node, *prev;
5607 	bool pruned = false;
5608 	int goal;
5609 
5610 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5611 		return false;
5612 
5613 	goal = sk->sk_rcvbuf >> 3;
5614 	node = &tp->ooo_last_skb->rbnode;
5615 
5616 	do {
5617 		struct sk_buff *skb = rb_to_skb(node);
5618 
5619 		/* If incoming skb would land last in ofo queue, stop pruning. */
5620 		if (after(TCP_SKB_CB(in_skb)->seq, TCP_SKB_CB(skb)->seq))
5621 			break;
5622 		pruned = true;
5623 		prev = rb_prev(node);
5624 		rb_erase(node, &tp->out_of_order_queue);
5625 		goal -= skb->truesize;
5626 		tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE);
5627 		tp->ooo_last_skb = rb_to_skb(prev);
5628 		if (!prev || goal <= 0) {
5629 			if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
5630 			    !tcp_under_memory_pressure(sk))
5631 				break;
5632 			goal = sk->sk_rcvbuf >> 3;
5633 		}
5634 		node = prev;
5635 	} while (node);
5636 
5637 	if (pruned) {
5638 		NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
5639 		/* Reset SACK state.  A conforming SACK implementation will
5640 		 * do the same at a timeout based retransmit.  When a connection
5641 		 * is in a sad state like this, we care only about integrity
5642 		 * of the connection not performance.
5643 		 */
5644 		if (tp->rx_opt.sack_ok)
5645 			tcp_sack_reset(&tp->rx_opt);
5646 	}
5647 	return pruned;
5648 }
5649 
5650 /* Reduce allocated memory if we can, trying to get
5651  * the socket within its memory limits again.
5652  *
5653  * Return less than zero if we should start dropping frames
5654  * until the socket owning process reads some of the data
5655  * to stabilize the situation.
5656  */
tcp_prune_queue(struct sock * sk,const struct sk_buff * in_skb)5657 static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb)
5658 {
5659 	struct tcp_sock *tp = tcp_sk(sk);
5660 
5661 	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
5662 
5663 	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
5664 		tcp_clamp_window(sk);
5665 	else if (tcp_under_memory_pressure(sk))
5666 		tcp_adjust_rcv_ssthresh(sk);
5667 
5668 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5669 		return 0;
5670 
5671 	tcp_collapse_ofo_queue(sk);
5672 	if (!skb_queue_empty(&sk->sk_receive_queue))
5673 		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
5674 			     skb_peek(&sk->sk_receive_queue),
5675 			     NULL,
5676 			     tp->copied_seq, tp->rcv_nxt);
5677 
5678 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5679 		return 0;
5680 
5681 	/* Collapsing did not help, destructive actions follow.
5682 	 * This must not ever occur. */
5683 
5684 	tcp_prune_ofo_queue(sk, in_skb);
5685 
5686 	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
5687 		return 0;
5688 
5689 	/* If we are really being abused, tell the caller to silently
5690 	 * drop receive data on the floor.  It will get retransmitted
5691 	 * and hopefully then we'll have sufficient space.
5692 	 */
5693 	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
5694 
5695 	/* Massive buffer overcommit. */
5696 	tp->pred_flags = 0;
5697 	return -1;
5698 }
5699 
tcp_should_expand_sndbuf(struct sock * sk)5700 static bool tcp_should_expand_sndbuf(struct sock *sk)
5701 {
5702 	const struct tcp_sock *tp = tcp_sk(sk);
5703 
5704 	/* If the user specified a specific send buffer setting, do
5705 	 * not modify it.
5706 	 */
5707 	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5708 		return false;
5709 
5710 	/* If we are under global TCP memory pressure, do not expand.  */
5711 	if (tcp_under_memory_pressure(sk)) {
5712 		int unused_mem = sk_unused_reserved_mem(sk);
5713 
5714 		/* Adjust sndbuf according to reserved mem. But make sure
5715 		 * it never goes below SOCK_MIN_SNDBUF.
5716 		 * See sk_stream_moderate_sndbuf() for more details.
5717 		 */
5718 		if (unused_mem > SOCK_MIN_SNDBUF)
5719 			WRITE_ONCE(sk->sk_sndbuf, unused_mem);
5720 
5721 		return false;
5722 	}
5723 
5724 	/* If we are under soft global TCP memory pressure, do not expand.  */
5725 	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5726 		return false;
5727 
5728 	/* If we filled the congestion window, do not expand.  */
5729 	if (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp))
5730 		return false;
5731 
5732 	return true;
5733 }
5734 
tcp_new_space(struct sock * sk)5735 static void tcp_new_space(struct sock *sk)
5736 {
5737 	struct tcp_sock *tp = tcp_sk(sk);
5738 
5739 	if (tcp_should_expand_sndbuf(sk)) {
5740 		tcp_sndbuf_expand(sk);
5741 		tp->snd_cwnd_stamp = tcp_jiffies32;
5742 	}
5743 
5744 	INDIRECT_CALL_1(sk->sk_write_space, sk_stream_write_space, sk);
5745 }
5746 
5747 /* Caller made space either from:
5748  * 1) Freeing skbs in rtx queues (after tp->snd_una has advanced)
5749  * 2) Sent skbs from output queue (and thus advancing tp->snd_nxt)
5750  *
5751  * We might be able to generate EPOLLOUT to the application if:
5752  * 1) Space consumed in output/rtx queues is below sk->sk_sndbuf/2
5753  * 2) notsent amount (tp->write_seq - tp->snd_nxt) became
5754  *    small enough that tcp_stream_memory_free() decides it
5755  *    is time to generate EPOLLOUT.
5756  */
tcp_check_space(struct sock * sk)5757 void tcp_check_space(struct sock *sk)
5758 {
5759 	/* pairs with tcp_poll() */
5760 	smp_mb();
5761 	if (sk->sk_socket &&
5762 	    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5763 		tcp_new_space(sk);
5764 		if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5765 			tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5766 	}
5767 }
5768 
tcp_data_snd_check(struct sock * sk)5769 static inline void tcp_data_snd_check(struct sock *sk)
5770 {
5771 	tcp_push_pending_frames(sk);
5772 	tcp_check_space(sk);
5773 }
5774 
5775 /*
5776  * Check if sending an ack is needed.
5777  */
__tcp_ack_snd_check(struct sock * sk,int ofo_possible)5778 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5779 {
5780 	struct tcp_sock *tp = tcp_sk(sk);
5781 	unsigned long rtt, delay;
5782 
5783 	    /* More than one full frame received... */
5784 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5785 	     /* ... and right edge of window advances far enough.
5786 	      * (tcp_recvmsg() will send ACK otherwise).
5787 	      * If application uses SO_RCVLOWAT, we want send ack now if
5788 	      * we have not received enough bytes to satisfy the condition.
5789 	      */
5790 	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
5791 	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||
5792 	    /* We ACK each frame or... */
5793 	    tcp_in_quickack_mode(sk) ||
5794 	    /* Protocol state mandates a one-time immediate ACK */
5795 	    inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
5796 		/* If we are running from __release_sock() in user context,
5797 		 * Defer the ack until tcp_release_cb().
5798 		 */
5799 		if (sock_owned_by_user_nocheck(sk) &&
5800 		    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_backlog_ack_defer)) {
5801 			set_bit(TCP_ACK_DEFERRED, &sk->sk_tsq_flags);
5802 			return;
5803 		}
5804 send_now:
5805 		tcp_send_ack(sk);
5806 		return;
5807 	}
5808 
5809 	if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5810 		tcp_send_delayed_ack(sk);
5811 		return;
5812 	}
5813 
5814 	if (!tcp_is_sack(tp) ||
5815 	    tp->compressed_ack >= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr))
5816 		goto send_now;
5817 
5818 	if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
5819 		tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
5820 		tp->dup_ack_counter = 0;
5821 	}
5822 	if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) {
5823 		tp->dup_ack_counter++;
5824 		goto send_now;
5825 	}
5826 	tp->compressed_ack++;
5827 	if (hrtimer_is_queued(&tp->compressed_ack_timer))
5828 		return;
5829 
5830 	/* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
5831 
5832 	rtt = tp->rcv_rtt_est.rtt_us;
5833 	if (tp->srtt_us && tp->srtt_us < rtt)
5834 		rtt = tp->srtt_us;
5835 
5836 	delay = min_t(unsigned long,
5837 		      READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns),
5838 		      rtt * (NSEC_PER_USEC >> 3)/20);
5839 	sock_hold(sk);
5840 	hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay),
5841 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns),
5842 			       HRTIMER_MODE_REL_PINNED_SOFT);
5843 }
5844 
tcp_ack_snd_check(struct sock * sk)5845 static inline void tcp_ack_snd_check(struct sock *sk)
5846 {
5847 	if (!inet_csk_ack_scheduled(sk)) {
5848 		/* We sent a data segment already. */
5849 		return;
5850 	}
5851 	__tcp_ack_snd_check(sk, 1);
5852 }
5853 
5854 /*
5855  *	This routine is only called when we have urgent data
5856  *	signaled. Its the 'slow' part of tcp_urg. It could be
5857  *	moved inline now as tcp_urg is only called from one
5858  *	place. We handle URGent data wrong. We have to - as
5859  *	BSD still doesn't use the correction from RFC961.
5860  *	For 1003.1g we should support a new option TCP_STDURG to permit
5861  *	either form (or just set the sysctl tcp_stdurg).
5862  */
5863 
tcp_check_urg(struct sock * sk,const struct tcphdr * th)5864 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5865 {
5866 	struct tcp_sock *tp = tcp_sk(sk);
5867 	u32 ptr = ntohs(th->urg_ptr);
5868 
5869 	if (ptr && !READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_stdurg))
5870 		ptr--;
5871 	ptr += ntohl(th->seq);
5872 
5873 	/* Ignore urgent data that we've already seen and read. */
5874 	if (after(tp->copied_seq, ptr))
5875 		return;
5876 
5877 	/* Do not replay urg ptr.
5878 	 *
5879 	 * NOTE: interesting situation not covered by specs.
5880 	 * Misbehaving sender may send urg ptr, pointing to segment,
5881 	 * which we already have in ofo queue. We are not able to fetch
5882 	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5883 	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5884 	 * situations. But it is worth to think about possibility of some
5885 	 * DoSes using some hypothetical application level deadlock.
5886 	 */
5887 	if (before(ptr, tp->rcv_nxt))
5888 		return;
5889 
5890 	/* Do we already have a newer (or duplicate) urgent pointer? */
5891 	if (tp->urg_data && !after(ptr, tp->urg_seq))
5892 		return;
5893 
5894 	/* Tell the world about our new urgent pointer. */
5895 	sk_send_sigurg(sk);
5896 
5897 	/* We may be adding urgent data when the last byte read was
5898 	 * urgent. To do this requires some care. We cannot just ignore
5899 	 * tp->copied_seq since we would read the last urgent byte again
5900 	 * as data, nor can we alter copied_seq until this data arrives
5901 	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
5902 	 *
5903 	 * NOTE. Double Dutch. Rendering to plain English: author of comment
5904 	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
5905 	 * and expect that both A and B disappear from stream. This is _wrong_.
5906 	 * Though this happens in BSD with high probability, this is occasional.
5907 	 * Any application relying on this is buggy. Note also, that fix "works"
5908 	 * only in this artificial test. Insert some normal data between A and B and we will
5909 	 * decline of BSD again. Verdict: it is better to remove to trap
5910 	 * buggy users.
5911 	 */
5912 	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5913 	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5914 		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5915 		tp->copied_seq++;
5916 		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5917 			__skb_unlink(skb, &sk->sk_receive_queue);
5918 			__kfree_skb(skb);
5919 		}
5920 	}
5921 
5922 	WRITE_ONCE(tp->urg_data, TCP_URG_NOTYET);
5923 	WRITE_ONCE(tp->urg_seq, ptr);
5924 
5925 	/* Disable header prediction. */
5926 	tp->pred_flags = 0;
5927 }
5928 
5929 /* This is the 'fast' part of urgent handling. */
tcp_urg(struct sock * sk,struct sk_buff * skb,const struct tcphdr * th)5930 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5931 {
5932 	struct tcp_sock *tp = tcp_sk(sk);
5933 
5934 	/* Check if we get a new urgent pointer - normally not. */
5935 	if (unlikely(th->urg))
5936 		tcp_check_urg(sk, th);
5937 
5938 	/* Do we wait for any urgent data? - normally not... */
5939 	if (unlikely(tp->urg_data == TCP_URG_NOTYET)) {
5940 		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5941 			  th->syn;
5942 
5943 		/* Is the urgent pointer pointing into this packet? */
5944 		if (ptr < skb->len) {
5945 			u8 tmp;
5946 			if (skb_copy_bits(skb, ptr, &tmp, 1))
5947 				BUG();
5948 			WRITE_ONCE(tp->urg_data, TCP_URG_VALID | tmp);
5949 			if (!sock_flag(sk, SOCK_DEAD))
5950 				sk->sk_data_ready(sk);
5951 		}
5952 	}
5953 }
5954 
5955 /* Accept RST for rcv_nxt - 1 after a FIN.
5956  * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
5957  * FIN is sent followed by a RST packet. The RST is sent with the same
5958  * sequence number as the FIN, and thus according to RFC 5961 a challenge
5959  * ACK should be sent. However, Mac OSX rate limits replies to challenge
5960  * ACKs on the closed socket. In addition middleboxes can drop either the
5961  * challenge ACK or a subsequent RST.
5962  */
tcp_reset_check(const struct sock * sk,const struct sk_buff * skb)5963 static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
5964 {
5965 	const struct tcp_sock *tp = tcp_sk(sk);
5966 
5967 	return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
5968 			(1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
5969 					       TCPF_CLOSING));
5970 }
5971 
5972 /* Does PAWS and seqno based validation of an incoming segment, flags will
5973  * play significant role here.
5974  */
tcp_validate_incoming(struct sock * sk,struct sk_buff * skb,const struct tcphdr * th,int syn_inerr)5975 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
5976 				  const struct tcphdr *th, int syn_inerr)
5977 {
5978 	struct tcp_sock *tp = tcp_sk(sk);
5979 	SKB_DR(reason);
5980 
5981 	/* RFC1323: H1. Apply PAWS check first. */
5982 	if (!tcp_fast_parse_options(sock_net(sk), skb, th, tp) ||
5983 	    !tp->rx_opt.saw_tstamp ||
5984 	    tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW))
5985 		goto step1;
5986 
5987 	reason = tcp_disordered_ack_check(sk, skb);
5988 	if (!reason)
5989 		goto step1;
5990 	/* Reset is accepted even if it did not pass PAWS. */
5991 	if (th->rst)
5992 		goto step1;
5993 	if (unlikely(th->syn))
5994 		goto syn_challenge;
5995 
5996 	/* Old ACK are common, increment PAWS_OLD_ACK
5997 	 * and do not send a dupack.
5998 	 */
5999 	if (reason == SKB_DROP_REASON_TCP_RFC7323_PAWS_ACK) {
6000 		NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWS_OLD_ACK);
6001 		goto discard;
6002 	}
6003 	NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
6004 	if (!tcp_oow_rate_limited(sock_net(sk), skb,
6005 				  LINUX_MIB_TCPACKSKIPPEDPAWS,
6006 				  &tp->last_oow_ack_time))
6007 		tcp_send_dupack(sk, skb);
6008 	goto discard;
6009 
6010 step1:
6011 	/* Step 1: check sequence number */
6012 	reason = tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
6013 	if (reason) {
6014 		/* RFC793, page 37: "In all states except SYN-SENT, all reset
6015 		 * (RST) segments are validated by checking their SEQ-fields."
6016 		 * And page 69: "If an incoming segment is not acceptable,
6017 		 * an acknowledgment should be sent in reply (unless the RST
6018 		 * bit is set, if so drop the segment and return)".
6019 		 */
6020 		if (!th->rst) {
6021 			if (th->syn)
6022 				goto syn_challenge;
6023 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
6024 						  LINUX_MIB_TCPACKSKIPPEDSEQ,
6025 						  &tp->last_oow_ack_time))
6026 				tcp_send_dupack(sk, skb);
6027 		} else if (tcp_reset_check(sk, skb)) {
6028 			goto reset;
6029 		}
6030 		goto discard;
6031 	}
6032 
6033 	/* Step 2: check RST bit */
6034 	if (th->rst) {
6035 		/* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
6036 		 * FIN and SACK too if available):
6037 		 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
6038 		 * the right-most SACK block,
6039 		 * then
6040 		 *     RESET the connection
6041 		 * else
6042 		 *     Send a challenge ACK
6043 		 */
6044 		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
6045 		    tcp_reset_check(sk, skb))
6046 			goto reset;
6047 
6048 		if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
6049 			struct tcp_sack_block *sp = &tp->selective_acks[0];
6050 			int max_sack = sp[0].end_seq;
6051 			int this_sack;
6052 
6053 			for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
6054 			     ++this_sack) {
6055 				max_sack = after(sp[this_sack].end_seq,
6056 						 max_sack) ?
6057 					sp[this_sack].end_seq : max_sack;
6058 			}
6059 
6060 			if (TCP_SKB_CB(skb)->seq == max_sack)
6061 				goto reset;
6062 		}
6063 
6064 		/* Disable TFO if RST is out-of-order
6065 		 * and no data has been received
6066 		 * for current active TFO socket
6067 		 */
6068 		if (tp->syn_fastopen && !tp->data_segs_in &&
6069 		    sk->sk_state == TCP_ESTABLISHED)
6070 			tcp_fastopen_active_disable(sk);
6071 		tcp_send_challenge_ack(sk);
6072 		SKB_DR_SET(reason, TCP_RESET);
6073 		goto discard;
6074 	}
6075 
6076 	/* step 3: check security and precedence [ignored] */
6077 
6078 	/* step 4: Check for a SYN
6079 	 * RFC 5961 4.2 : Send a challenge ack
6080 	 */
6081 	if (th->syn) {
6082 		if (sk->sk_state == TCP_SYN_RECV && sk->sk_socket && th->ack &&
6083 		    TCP_SKB_CB(skb)->seq + 1 == TCP_SKB_CB(skb)->end_seq &&
6084 		    TCP_SKB_CB(skb)->seq + 1 == tp->rcv_nxt &&
6085 		    TCP_SKB_CB(skb)->ack_seq == tp->snd_nxt)
6086 			goto pass;
6087 syn_challenge:
6088 		if (syn_inerr)
6089 			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6090 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
6091 		tcp_send_challenge_ack(sk);
6092 		SKB_DR_SET(reason, TCP_INVALID_SYN);
6093 		goto discard;
6094 	}
6095 
6096 pass:
6097 	bpf_skops_parse_hdr(sk, skb);
6098 
6099 	return true;
6100 
6101 discard:
6102 	tcp_drop_reason(sk, skb, reason);
6103 	return false;
6104 
6105 reset:
6106 	tcp_reset(sk, skb);
6107 	__kfree_skb(skb);
6108 	return false;
6109 }
6110 
6111 /*
6112  *	TCP receive function for the ESTABLISHED state.
6113  *
6114  *	It is split into a fast path and a slow path. The fast path is
6115  * 	disabled when:
6116  *	- A zero window was announced from us - zero window probing
6117  *        is only handled properly in the slow path.
6118  *	- Out of order segments arrived.
6119  *	- Urgent data is expected.
6120  *	- There is no buffer space left
6121  *	- Unexpected TCP flags/window values/header lengths are received
6122  *	  (detected by checking the TCP header against pred_flags)
6123  *	- Data is sent in both directions. Fast path only supports pure senders
6124  *	  or pure receivers (this means either the sequence number or the ack
6125  *	  value must stay constant)
6126  *	- Unexpected TCP option.
6127  *
6128  *	When these conditions are not satisfied it drops into a standard
6129  *	receive procedure patterned after RFC793 to handle all cases.
6130  *	The first three cases are guaranteed by proper pred_flags setting,
6131  *	the rest is checked inline. Fast processing is turned on in
6132  *	tcp_data_queue when everything is OK.
6133  */
tcp_rcv_established(struct sock * sk,struct sk_buff * skb)6134 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
6135 {
6136 	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
6137 	const struct tcphdr *th = (const struct tcphdr *)skb->data;
6138 	struct tcp_sock *tp = tcp_sk(sk);
6139 	unsigned int len = skb->len;
6140 
6141 	/* TCP congestion window tracking */
6142 	trace_tcp_probe(sk, skb);
6143 
6144 	tcp_mstamp_refresh(tp);
6145 	if (unlikely(!rcu_access_pointer(sk->sk_rx_dst)))
6146 		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
6147 	/*
6148 	 *	Header prediction.
6149 	 *	The code loosely follows the one in the famous
6150 	 *	"30 instruction TCP receive" Van Jacobson mail.
6151 	 *
6152 	 *	Van's trick is to deposit buffers into socket queue
6153 	 *	on a device interrupt, to call tcp_recv function
6154 	 *	on the receive process context and checksum and copy
6155 	 *	the buffer to user space. smart...
6156 	 *
6157 	 *	Our current scheme is not silly either but we take the
6158 	 *	extra cost of the net_bh soft interrupt processing...
6159 	 *	We do checksum and copy also but from device to kernel.
6160 	 */
6161 
6162 	tp->rx_opt.saw_tstamp = 0;
6163 
6164 	/*	pred_flags is 0xS?10 << 16 + snd_wnd
6165 	 *	if header_prediction is to be made
6166 	 *	'S' will always be tp->tcp_header_len >> 2
6167 	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
6168 	 *  turn it off	(when there are holes in the receive
6169 	 *	 space for instance)
6170 	 *	PSH flag is ignored.
6171 	 */
6172 
6173 	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
6174 	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
6175 	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
6176 		int tcp_header_len = tp->tcp_header_len;
6177 		s32 delta = 0;
6178 		int flag = 0;
6179 
6180 		/* Timestamp header prediction: tcp_header_len
6181 		 * is automatically equal to th->doff*4 due to pred_flags
6182 		 * match.
6183 		 */
6184 
6185 		/* Check timestamp */
6186 		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
6187 			/* No? Slow path! */
6188 			if (!tcp_parse_aligned_timestamp(tp, th))
6189 				goto slow_path;
6190 
6191 			delta = tp->rx_opt.rcv_tsval -
6192 				tp->rx_opt.ts_recent;
6193 			/* If PAWS failed, check it more carefully in slow path */
6194 			if (delta < 0)
6195 				goto slow_path;
6196 
6197 			/* DO NOT update ts_recent here, if checksum fails
6198 			 * and timestamp was corrupted part, it will result
6199 			 * in a hung connection since we will drop all
6200 			 * future packets due to the PAWS test.
6201 			 */
6202 		}
6203 
6204 		if (len <= tcp_header_len) {
6205 			/* Bulk data transfer: sender */
6206 			if (len == tcp_header_len) {
6207 				/* Predicted packet is in window by definition.
6208 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
6209 				 * Hence, check seq<=rcv_wup reduces to:
6210 				 */
6211 				if (tcp_header_len ==
6212 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
6213 				    tp->rcv_nxt == tp->rcv_wup)
6214 					flag |= __tcp_replace_ts_recent(tp,
6215 									delta);
6216 
6217 				/* We know that such packets are checksummed
6218 				 * on entry.
6219 				 */
6220 				tcp_ack(sk, skb, flag);
6221 				__kfree_skb(skb);
6222 				tcp_data_snd_check(sk);
6223 				/* When receiving pure ack in fast path, update
6224 				 * last ts ecr directly instead of calling
6225 				 * tcp_rcv_rtt_measure_ts()
6226 				 */
6227 				tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
6228 				return;
6229 			} else { /* Header too small */
6230 				reason = SKB_DROP_REASON_PKT_TOO_SMALL;
6231 				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6232 				goto discard;
6233 			}
6234 		} else {
6235 			int eaten = 0;
6236 			bool fragstolen = false;
6237 
6238 			if (tcp_checksum_complete(skb))
6239 				goto csum_error;
6240 
6241 			if ((int)skb->truesize > sk->sk_forward_alloc)
6242 				goto step5;
6243 
6244 			/* Predicted packet is in window by definition.
6245 			 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
6246 			 * Hence, check seq<=rcv_wup reduces to:
6247 			 */
6248 			if (tcp_header_len ==
6249 			    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
6250 			    tp->rcv_nxt == tp->rcv_wup)
6251 				flag |= __tcp_replace_ts_recent(tp,
6252 								delta);
6253 
6254 			tcp_rcv_rtt_measure_ts(sk, skb);
6255 
6256 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
6257 
6258 			/* Bulk data transfer: receiver */
6259 			tcp_cleanup_skb(skb);
6260 			__skb_pull(skb, tcp_header_len);
6261 			eaten = tcp_queue_rcv(sk, skb, &fragstolen);
6262 
6263 			tcp_event_data_recv(sk, skb);
6264 
6265 			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
6266 				/* Well, only one small jumplet in fast path... */
6267 				tcp_ack(sk, skb, flag | FLAG_DATA);
6268 				tcp_data_snd_check(sk);
6269 				if (!inet_csk_ack_scheduled(sk))
6270 					goto no_ack;
6271 			} else {
6272 				tcp_update_wl(tp, TCP_SKB_CB(skb)->seq);
6273 			}
6274 
6275 			__tcp_ack_snd_check(sk, 0);
6276 no_ack:
6277 			if (eaten)
6278 				kfree_skb_partial(skb, fragstolen);
6279 			tcp_data_ready(sk);
6280 			return;
6281 		}
6282 	}
6283 
6284 slow_path:
6285 	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
6286 		goto csum_error;
6287 
6288 	if (!th->ack && !th->rst && !th->syn) {
6289 		reason = SKB_DROP_REASON_TCP_FLAGS;
6290 		goto discard;
6291 	}
6292 
6293 	/*
6294 	 *	Standard slow path.
6295 	 */
6296 
6297 	if (!tcp_validate_incoming(sk, skb, th, 1))
6298 		return;
6299 
6300 step5:
6301 	reason = tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT);
6302 	if ((int)reason < 0) {
6303 		reason = -reason;
6304 		goto discard;
6305 	}
6306 	tcp_rcv_rtt_measure_ts(sk, skb);
6307 
6308 	/* Process urgent data. */
6309 	tcp_urg(sk, skb, th);
6310 
6311 	/* step 7: process the segment text */
6312 	tcp_data_queue(sk, skb);
6313 
6314 	tcp_data_snd_check(sk);
6315 	tcp_ack_snd_check(sk);
6316 	return;
6317 
6318 csum_error:
6319 	reason = SKB_DROP_REASON_TCP_CSUM;
6320 	trace_tcp_bad_csum(skb);
6321 	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
6322 	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6323 
6324 discard:
6325 	tcp_drop_reason(sk, skb, reason);
6326 }
6327 EXPORT_IPV6_MOD(tcp_rcv_established);
6328 
tcp_init_transfer(struct sock * sk,int bpf_op,struct sk_buff * skb)6329 void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
6330 {
6331 	struct inet_connection_sock *icsk = inet_csk(sk);
6332 	struct tcp_sock *tp = tcp_sk(sk);
6333 
6334 	tcp_mtup_init(sk);
6335 	icsk->icsk_af_ops->rebuild_header(sk);
6336 	tcp_init_metrics(sk);
6337 
6338 	/* Initialize the congestion window to start the transfer.
6339 	 * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
6340 	 * retransmitted. In light of RFC6298 more aggressive 1sec
6341 	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
6342 	 * retransmission has occurred.
6343 	 */
6344 	if (tp->total_retrans > 1 && tp->undo_marker)
6345 		tcp_snd_cwnd_set(tp, 1);
6346 	else
6347 		tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, __sk_dst_get(sk)));
6348 	tp->snd_cwnd_stamp = tcp_jiffies32;
6349 
6350 	bpf_skops_established(sk, bpf_op, skb);
6351 	/* Initialize congestion control unless BPF initialized it already: */
6352 	if (!icsk->icsk_ca_initialized)
6353 		tcp_init_congestion_control(sk);
6354 	tcp_init_buffer_space(sk);
6355 }
6356 
tcp_finish_connect(struct sock * sk,struct sk_buff * skb)6357 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
6358 {
6359 	struct tcp_sock *tp = tcp_sk(sk);
6360 	struct inet_connection_sock *icsk = inet_csk(sk);
6361 
6362 	tcp_ao_finish_connect(sk, skb);
6363 	tcp_set_state(sk, TCP_ESTABLISHED);
6364 	icsk->icsk_ack.lrcvtime = tcp_jiffies32;
6365 
6366 	if (skb) {
6367 		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
6368 		security_inet_conn_established(sk, skb);
6369 		sk_mark_napi_id(sk, skb);
6370 	}
6371 
6372 	tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb);
6373 
6374 	/* Prevent spurious tcp_cwnd_restart() on first data
6375 	 * packet.
6376 	 */
6377 	tp->lsndtime = tcp_jiffies32;
6378 
6379 	if (sock_flag(sk, SOCK_KEEPOPEN))
6380 		tcp_reset_keepalive_timer(sk, keepalive_time_when(tp));
6381 
6382 	if (!tp->rx_opt.snd_wscale)
6383 		__tcp_fast_path_on(tp, tp->snd_wnd);
6384 	else
6385 		tp->pred_flags = 0;
6386 }
6387 
tcp_rcv_fastopen_synack(struct sock * sk,struct sk_buff * synack,struct tcp_fastopen_cookie * cookie)6388 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
6389 				    struct tcp_fastopen_cookie *cookie)
6390 {
6391 	struct tcp_sock *tp = tcp_sk(sk);
6392 	struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
6393 	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
6394 	bool syn_drop = false;
6395 
6396 	if (mss == tp->rx_opt.user_mss) {
6397 		struct tcp_options_received opt;
6398 
6399 		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
6400 		tcp_clear_options(&opt);
6401 		opt.user_mss = opt.mss_clamp = 0;
6402 		tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
6403 		mss = opt.mss_clamp;
6404 	}
6405 
6406 	if (!tp->syn_fastopen) {
6407 		/* Ignore an unsolicited cookie */
6408 		cookie->len = -1;
6409 	} else if (tp->total_retrans) {
6410 		/* SYN timed out and the SYN-ACK neither has a cookie nor
6411 		 * acknowledges data. Presumably the remote received only
6412 		 * the retransmitted (regular) SYNs: either the original
6413 		 * SYN-data or the corresponding SYN-ACK was dropped.
6414 		 */
6415 		syn_drop = (cookie->len < 0 && data);
6416 	} else if (cookie->len < 0 && !tp->syn_data) {
6417 		/* We requested a cookie but didn't get it. If we did not use
6418 		 * the (old) exp opt format then try so next time (try_exp=1).
6419 		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
6420 		 */
6421 		try_exp = tp->syn_fastopen_exp ? 2 : 1;
6422 	}
6423 
6424 	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
6425 
6426 	if (data) { /* Retransmit unacked data in SYN */
6427 		if (tp->total_retrans)
6428 			tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED;
6429 		else
6430 			tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
6431 		skb_rbtree_walk_from(data)
6432 			 tcp_mark_skb_lost(sk, data);
6433 		tcp_non_congestion_loss_retransmit(sk);
6434 		NET_INC_STATS(sock_net(sk),
6435 				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
6436 		return true;
6437 	}
6438 	tp->syn_data_acked = tp->syn_data;
6439 	if (tp->syn_data_acked) {
6440 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
6441 		/* SYN-data is counted as two separate packets in tcp_ack() */
6442 		if (tp->delivered > 1)
6443 			--tp->delivered;
6444 	}
6445 
6446 	tcp_fastopen_add_skb(sk, synack);
6447 
6448 	return false;
6449 }
6450 
smc_check_reset_syn(struct tcp_sock * tp)6451 static void smc_check_reset_syn(struct tcp_sock *tp)
6452 {
6453 #if IS_ENABLED(CONFIG_SMC)
6454 	if (static_branch_unlikely(&tcp_have_smc)) {
6455 		if (tp->syn_smc && !tp->rx_opt.smc_ok)
6456 			tp->syn_smc = 0;
6457 	}
6458 #endif
6459 }
6460 
tcp_try_undo_spurious_syn(struct sock * sk)6461 static void tcp_try_undo_spurious_syn(struct sock *sk)
6462 {
6463 	struct tcp_sock *tp = tcp_sk(sk);
6464 	u32 syn_stamp;
6465 
6466 	/* undo_marker is set when SYN or SYNACK times out. The timeout is
6467 	 * spurious if the ACK's timestamp option echo value matches the
6468 	 * original SYN timestamp.
6469 	 */
6470 	syn_stamp = tp->retrans_stamp;
6471 	if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp &&
6472 	    syn_stamp == tp->rx_opt.rcv_tsecr)
6473 		tp->undo_marker = 0;
6474 }
6475 
tcp_rcv_synsent_state_process(struct sock * sk,struct sk_buff * skb,const struct tcphdr * th)6476 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
6477 					 const struct tcphdr *th)
6478 {
6479 	struct inet_connection_sock *icsk = inet_csk(sk);
6480 	struct tcp_sock *tp = tcp_sk(sk);
6481 	struct tcp_fastopen_cookie foc = { .len = -1 };
6482 	int saved_clamp = tp->rx_opt.mss_clamp;
6483 	bool fastopen_fail;
6484 	SKB_DR(reason);
6485 
6486 	tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
6487 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
6488 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
6489 
6490 	if (th->ack) {
6491 		/* rfc793:
6492 		 * "If the state is SYN-SENT then
6493 		 *    first check the ACK bit
6494 		 *      If the ACK bit is set
6495 		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
6496 		 *        a reset (unless the RST bit is set, if so drop
6497 		 *        the segment and return)"
6498 		 */
6499 		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
6500 		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
6501 			/* Previous FIN/ACK or RST/ACK might be ignored. */
6502 			if (icsk->icsk_retransmits == 0)
6503 				tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
6504 						     TCP_TIMEOUT_MIN, false);
6505 			SKB_DR_SET(reason, TCP_INVALID_ACK_SEQUENCE);
6506 			goto reset_and_undo;
6507 		}
6508 
6509 		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
6510 		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
6511 			     tcp_time_stamp_ts(tp))) {
6512 			NET_INC_STATS(sock_net(sk),
6513 					LINUX_MIB_PAWSACTIVEREJECTED);
6514 			SKB_DR_SET(reason, TCP_RFC7323_PAWS);
6515 			goto reset_and_undo;
6516 		}
6517 
6518 		/* Now ACK is acceptable.
6519 		 *
6520 		 * "If the RST bit is set
6521 		 *    If the ACK was acceptable then signal the user "error:
6522 		 *    connection reset", drop the segment, enter CLOSED state,
6523 		 *    delete TCB, and return."
6524 		 */
6525 
6526 		if (th->rst) {
6527 			tcp_reset(sk, skb);
6528 consume:
6529 			__kfree_skb(skb);
6530 			return 0;
6531 		}
6532 
6533 		/* rfc793:
6534 		 *   "fifth, if neither of the SYN or RST bits is set then
6535 		 *    drop the segment and return."
6536 		 *
6537 		 *    See note below!
6538 		 *                                        --ANK(990513)
6539 		 */
6540 		if (!th->syn) {
6541 			SKB_DR_SET(reason, TCP_FLAGS);
6542 			goto discard_and_undo;
6543 		}
6544 		/* rfc793:
6545 		 *   "If the SYN bit is on ...
6546 		 *    are acceptable then ...
6547 		 *    (our SYN has been ACKed), change the connection
6548 		 *    state to ESTABLISHED..."
6549 		 */
6550 
6551 		tcp_ecn_rcv_synack(tp, th);
6552 
6553 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6554 		tcp_try_undo_spurious_syn(sk);
6555 		tcp_ack(sk, skb, FLAG_SLOWPATH);
6556 
6557 		/* Ok.. it's good. Set up sequence numbers and
6558 		 * move to established.
6559 		 */
6560 		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6561 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6562 
6563 		/* RFC1323: The window in SYN & SYN/ACK segments is
6564 		 * never scaled.
6565 		 */
6566 		tp->snd_wnd = ntohs(th->window);
6567 
6568 		if (!tp->rx_opt.wscale_ok) {
6569 			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
6570 			WRITE_ONCE(tp->window_clamp,
6571 				   min(tp->window_clamp, 65535U));
6572 		}
6573 
6574 		if (tp->rx_opt.saw_tstamp) {
6575 			tp->rx_opt.tstamp_ok	   = 1;
6576 			tp->tcp_header_len =
6577 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6578 			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
6579 			tcp_store_ts_recent(tp);
6580 		} else {
6581 			tp->tcp_header_len = sizeof(struct tcphdr);
6582 		}
6583 
6584 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6585 		tcp_initialize_rcv_mss(sk);
6586 
6587 		/* Remember, tcp_poll() does not lock socket!
6588 		 * Change state from SYN-SENT only after copied_seq
6589 		 * is initialized. */
6590 		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6591 
6592 		smc_check_reset_syn(tp);
6593 
6594 		smp_mb();
6595 
6596 		tcp_finish_connect(sk, skb);
6597 
6598 		fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
6599 				tcp_rcv_fastopen_synack(sk, skb, &foc);
6600 
6601 		if (!sock_flag(sk, SOCK_DEAD)) {
6602 			sk->sk_state_change(sk);
6603 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6604 		}
6605 		if (fastopen_fail)
6606 			return -1;
6607 		if (sk->sk_write_pending ||
6608 		    READ_ONCE(icsk->icsk_accept_queue.rskq_defer_accept) ||
6609 		    inet_csk_in_pingpong_mode(sk)) {
6610 			/* Save one ACK. Data will be ready after
6611 			 * several ticks, if write_pending is set.
6612 			 *
6613 			 * It may be deleted, but with this feature tcpdumps
6614 			 * look so _wonderfully_ clever, that I was not able
6615 			 * to stand against the temptation 8)     --ANK
6616 			 */
6617 			inet_csk_schedule_ack(sk);
6618 			tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
6619 			tcp_reset_xmit_timer(sk, ICSK_TIME_DACK,
6620 					     TCP_DELACK_MAX, false);
6621 			goto consume;
6622 		}
6623 		tcp_send_ack(sk);
6624 		return -1;
6625 	}
6626 
6627 	/* No ACK in the segment */
6628 
6629 	if (th->rst) {
6630 		/* rfc793:
6631 		 * "If the RST bit is set
6632 		 *
6633 		 *      Otherwise (no ACK) drop the segment and return."
6634 		 */
6635 		SKB_DR_SET(reason, TCP_RESET);
6636 		goto discard_and_undo;
6637 	}
6638 
6639 	/* PAWS check. */
6640 	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
6641 	    tcp_paws_reject(&tp->rx_opt, 0)) {
6642 		SKB_DR_SET(reason, TCP_RFC7323_PAWS);
6643 		goto discard_and_undo;
6644 	}
6645 	if (th->syn) {
6646 		/* We see SYN without ACK. It is attempt of
6647 		 * simultaneous connect with crossed SYNs.
6648 		 * Particularly, it can be connect to self.
6649 		 */
6650 #ifdef CONFIG_TCP_AO
6651 		struct tcp_ao_info *ao;
6652 
6653 		ao = rcu_dereference_protected(tp->ao_info,
6654 					       lockdep_sock_is_held(sk));
6655 		if (ao) {
6656 			WRITE_ONCE(ao->risn, th->seq);
6657 			ao->rcv_sne = 0;
6658 		}
6659 #endif
6660 		tcp_set_state(sk, TCP_SYN_RECV);
6661 
6662 		if (tp->rx_opt.saw_tstamp) {
6663 			tp->rx_opt.tstamp_ok = 1;
6664 			tcp_store_ts_recent(tp);
6665 			tp->tcp_header_len =
6666 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6667 		} else {
6668 			tp->tcp_header_len = sizeof(struct tcphdr);
6669 		}
6670 
6671 		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6672 		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6673 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6674 
6675 		/* RFC1323: The window in SYN & SYN/ACK segments is
6676 		 * never scaled.
6677 		 */
6678 		tp->snd_wnd    = ntohs(th->window);
6679 		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
6680 		tp->max_window = tp->snd_wnd;
6681 
6682 		tcp_ecn_rcv_syn(tp, th);
6683 
6684 		tcp_mtup_init(sk);
6685 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6686 		tcp_initialize_rcv_mss(sk);
6687 
6688 		tcp_send_synack(sk);
6689 #if 0
6690 		/* Note, we could accept data and URG from this segment.
6691 		 * There are no obstacles to make this (except that we must
6692 		 * either change tcp_recvmsg() to prevent it from returning data
6693 		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
6694 		 *
6695 		 * However, if we ignore data in ACKless segments sometimes,
6696 		 * we have no reasons to accept it sometimes.
6697 		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
6698 		 * is not flawless. So, discard packet for sanity.
6699 		 * Uncomment this return to process the data.
6700 		 */
6701 		return -1;
6702 #else
6703 		goto consume;
6704 #endif
6705 	}
6706 	/* "fifth, if neither of the SYN or RST bits is set then
6707 	 * drop the segment and return."
6708 	 */
6709 
6710 discard_and_undo:
6711 	tcp_clear_options(&tp->rx_opt);
6712 	tp->rx_opt.mss_clamp = saved_clamp;
6713 	tcp_drop_reason(sk, skb, reason);
6714 	return 0;
6715 
6716 reset_and_undo:
6717 	tcp_clear_options(&tp->rx_opt);
6718 	tp->rx_opt.mss_clamp = saved_clamp;
6719 	/* we can reuse/return @reason to its caller to handle the exception */
6720 	return reason;
6721 }
6722 
tcp_rcv_synrecv_state_fastopen(struct sock * sk)6723 static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
6724 {
6725 	struct tcp_sock *tp = tcp_sk(sk);
6726 	struct request_sock *req;
6727 
6728 	/* If we are still handling the SYNACK RTO, see if timestamp ECR allows
6729 	 * undo. If peer SACKs triggered fast recovery, we can't undo here.
6730 	 */
6731 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss && !tp->packets_out)
6732 		tcp_try_undo_recovery(sk);
6733 
6734 	tcp_update_rto_time(tp);
6735 	inet_csk(sk)->icsk_retransmits = 0;
6736 	/* In tcp_fastopen_synack_timer() on the first SYNACK RTO we set
6737 	 * retrans_stamp but don't enter CA_Loss, so in case that happened we
6738 	 * need to zero retrans_stamp here to prevent spurious
6739 	 * retransmits_timed_out(). However, if the ACK of our SYNACK caused us
6740 	 * to enter CA_Recovery then we need to leave retrans_stamp as it was
6741 	 * set entering CA_Recovery, for correct retransmits_timed_out() and
6742 	 * undo behavior.
6743 	 */
6744 	tcp_retrans_stamp_cleanup(sk);
6745 
6746 	/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
6747 	 * we no longer need req so release it.
6748 	 */
6749 	req = rcu_dereference_protected(tp->fastopen_rsk,
6750 					lockdep_sock_is_held(sk));
6751 	reqsk_fastopen_remove(sk, req, false);
6752 
6753 	/* Re-arm the timer because data may have been sent out.
6754 	 * This is similar to the regular data transmission case
6755 	 * when new data has just been ack'ed.
6756 	 *
6757 	 * (TFO) - we could try to be more aggressive and
6758 	 * retransmitting any data sooner based on when they
6759 	 * are sent out.
6760 	 */
6761 	tcp_rearm_rto(sk);
6762 }
6763 
6764 /*
6765  *	This function implements the receiving procedure of RFC 793 for
6766  *	all states except ESTABLISHED and TIME_WAIT.
6767  *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
6768  *	address independent.
6769  */
6770 
6771 enum skb_drop_reason
tcp_rcv_state_process(struct sock * sk,struct sk_buff * skb)6772 tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
6773 {
6774 	struct tcp_sock *tp = tcp_sk(sk);
6775 	struct inet_connection_sock *icsk = inet_csk(sk);
6776 	const struct tcphdr *th = tcp_hdr(skb);
6777 	struct request_sock *req;
6778 	int queued = 0;
6779 	SKB_DR(reason);
6780 
6781 	switch (sk->sk_state) {
6782 	case TCP_CLOSE:
6783 		SKB_DR_SET(reason, TCP_CLOSE);
6784 		goto discard;
6785 
6786 	case TCP_LISTEN:
6787 		if (th->ack)
6788 			return SKB_DROP_REASON_TCP_FLAGS;
6789 
6790 		if (th->rst) {
6791 			SKB_DR_SET(reason, TCP_RESET);
6792 			goto discard;
6793 		}
6794 		if (th->syn) {
6795 			if (th->fin) {
6796 				SKB_DR_SET(reason, TCP_FLAGS);
6797 				goto discard;
6798 			}
6799 			/* It is possible that we process SYN packets from backlog,
6800 			 * so we need to make sure to disable BH and RCU right there.
6801 			 */
6802 			rcu_read_lock();
6803 			local_bh_disable();
6804 			icsk->icsk_af_ops->conn_request(sk, skb);
6805 			local_bh_enable();
6806 			rcu_read_unlock();
6807 
6808 			consume_skb(skb);
6809 			return 0;
6810 		}
6811 		SKB_DR_SET(reason, TCP_FLAGS);
6812 		goto discard;
6813 
6814 	case TCP_SYN_SENT:
6815 		tp->rx_opt.saw_tstamp = 0;
6816 		tcp_mstamp_refresh(tp);
6817 		queued = tcp_rcv_synsent_state_process(sk, skb, th);
6818 		if (queued >= 0)
6819 			return queued;
6820 
6821 		/* Do step6 onward by hand. */
6822 		tcp_urg(sk, skb, th);
6823 		__kfree_skb(skb);
6824 		tcp_data_snd_check(sk);
6825 		return 0;
6826 	}
6827 
6828 	tcp_mstamp_refresh(tp);
6829 	tp->rx_opt.saw_tstamp = 0;
6830 	req = rcu_dereference_protected(tp->fastopen_rsk,
6831 					lockdep_sock_is_held(sk));
6832 	if (req) {
6833 		bool req_stolen;
6834 
6835 		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
6836 		    sk->sk_state != TCP_FIN_WAIT1);
6837 
6838 		SKB_DR_SET(reason, TCP_FASTOPEN);
6839 		if (!tcp_check_req(sk, skb, req, true, &req_stolen, &reason))
6840 			goto discard;
6841 	}
6842 
6843 	if (!th->ack && !th->rst && !th->syn) {
6844 		SKB_DR_SET(reason, TCP_FLAGS);
6845 		goto discard;
6846 	}
6847 	if (!tcp_validate_incoming(sk, skb, th, 0))
6848 		return 0;
6849 
6850 	/* step 5: check the ACK field */
6851 	reason = tcp_ack(sk, skb, FLAG_SLOWPATH |
6852 				  FLAG_UPDATE_TS_RECENT |
6853 				  FLAG_NO_CHALLENGE_ACK);
6854 
6855 	if ((int)reason <= 0) {
6856 		if (sk->sk_state == TCP_SYN_RECV) {
6857 			/* send one RST */
6858 			if (!reason)
6859 				return SKB_DROP_REASON_TCP_OLD_ACK;
6860 			return -reason;
6861 		}
6862 		/* accept old ack during closing */
6863 		if ((int)reason < 0) {
6864 			tcp_send_challenge_ack(sk);
6865 			reason = -reason;
6866 			goto discard;
6867 		}
6868 	}
6869 	SKB_DR_SET(reason, NOT_SPECIFIED);
6870 	switch (sk->sk_state) {
6871 	case TCP_SYN_RECV:
6872 		tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
6873 		if (!tp->srtt_us)
6874 			tcp_synack_rtt_meas(sk, req);
6875 
6876 		if (req) {
6877 			tcp_rcv_synrecv_state_fastopen(sk);
6878 		} else {
6879 			tcp_try_undo_spurious_syn(sk);
6880 			tp->retrans_stamp = 0;
6881 			tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB,
6882 					  skb);
6883 			WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6884 		}
6885 		tcp_ao_established(sk);
6886 		smp_mb();
6887 		tcp_set_state(sk, TCP_ESTABLISHED);
6888 		sk->sk_state_change(sk);
6889 
6890 		/* Note, that this wakeup is only for marginal crossed SYN case.
6891 		 * Passively open sockets are not waked up, because
6892 		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
6893 		 */
6894 		if (sk->sk_socket)
6895 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6896 
6897 		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
6898 		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
6899 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6900 
6901 		if (tp->rx_opt.tstamp_ok)
6902 			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
6903 
6904 		if (!inet_csk(sk)->icsk_ca_ops->cong_control)
6905 			tcp_update_pacing_rate(sk);
6906 
6907 		/* Prevent spurious tcp_cwnd_restart() on first data packet */
6908 		tp->lsndtime = tcp_jiffies32;
6909 
6910 		tcp_initialize_rcv_mss(sk);
6911 		tcp_fast_path_on(tp);
6912 		if (sk->sk_shutdown & SEND_SHUTDOWN)
6913 			tcp_shutdown(sk, SEND_SHUTDOWN);
6914 		break;
6915 
6916 	case TCP_FIN_WAIT1: {
6917 		int tmo;
6918 
6919 		if (req)
6920 			tcp_rcv_synrecv_state_fastopen(sk);
6921 
6922 		if (tp->snd_una != tp->write_seq)
6923 			break;
6924 
6925 		tcp_set_state(sk, TCP_FIN_WAIT2);
6926 		WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | SEND_SHUTDOWN);
6927 
6928 		sk_dst_confirm(sk);
6929 
6930 		if (!sock_flag(sk, SOCK_DEAD)) {
6931 			/* Wake up lingering close() */
6932 			sk->sk_state_change(sk);
6933 			break;
6934 		}
6935 
6936 		if (READ_ONCE(tp->linger2) < 0) {
6937 			tcp_done(sk);
6938 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6939 			return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
6940 		}
6941 		if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
6942 		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
6943 			/* Receive out of order FIN after close() */
6944 			if (tp->syn_fastopen && th->fin)
6945 				tcp_fastopen_active_disable(sk);
6946 			tcp_done(sk);
6947 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
6948 			return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
6949 		}
6950 
6951 		tmo = tcp_fin_time(sk);
6952 		if (tmo > TCP_TIMEWAIT_LEN) {
6953 			tcp_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
6954 		} else if (th->fin || sock_owned_by_user(sk)) {
6955 			/* Bad case. We could lose such FIN otherwise.
6956 			 * It is not a big problem, but it looks confusing
6957 			 * and not so rare event. We still can lose it now,
6958 			 * if it spins in bh_lock_sock(), but it is really
6959 			 * marginal case.
6960 			 */
6961 			tcp_reset_keepalive_timer(sk, tmo);
6962 		} else {
6963 			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
6964 			goto consume;
6965 		}
6966 		break;
6967 	}
6968 
6969 	case TCP_CLOSING:
6970 		if (tp->snd_una == tp->write_seq) {
6971 			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
6972 			goto consume;
6973 		}
6974 		break;
6975 
6976 	case TCP_LAST_ACK:
6977 		if (tp->snd_una == tp->write_seq) {
6978 			tcp_update_metrics(sk);
6979 			tcp_done(sk);
6980 			goto consume;
6981 		}
6982 		break;
6983 	}
6984 
6985 	/* step 6: check the URG bit */
6986 	tcp_urg(sk, skb, th);
6987 
6988 	/* step 7: process the segment text */
6989 	switch (sk->sk_state) {
6990 	case TCP_CLOSE_WAIT:
6991 	case TCP_CLOSING:
6992 	case TCP_LAST_ACK:
6993 		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
6994 			/* If a subflow has been reset, the packet should not
6995 			 * continue to be processed, drop the packet.
6996 			 */
6997 			if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb))
6998 				goto discard;
6999 			break;
7000 		}
7001 		fallthrough;
7002 	case TCP_FIN_WAIT1:
7003 	case TCP_FIN_WAIT2:
7004 		/* RFC 793 says to queue data in these states,
7005 		 * RFC 1122 says we MUST send a reset.
7006 		 * BSD 4.4 also does reset.
7007 		 */
7008 		if (sk->sk_shutdown & RCV_SHUTDOWN) {
7009 			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
7010 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
7011 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
7012 				tcp_reset(sk, skb);
7013 				return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
7014 			}
7015 		}
7016 		fallthrough;
7017 	case TCP_ESTABLISHED:
7018 		tcp_data_queue(sk, skb);
7019 		queued = 1;
7020 		break;
7021 	}
7022 
7023 	/* tcp_data could move socket to TIME-WAIT */
7024 	if (sk->sk_state != TCP_CLOSE) {
7025 		tcp_data_snd_check(sk);
7026 		tcp_ack_snd_check(sk);
7027 	}
7028 
7029 	if (!queued) {
7030 discard:
7031 		tcp_drop_reason(sk, skb, reason);
7032 	}
7033 	return 0;
7034 
7035 consume:
7036 	__kfree_skb(skb);
7037 	return 0;
7038 }
7039 EXPORT_IPV6_MOD(tcp_rcv_state_process);
7040 
pr_drop_req(struct request_sock * req,__u16 port,int family)7041 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
7042 {
7043 	struct inet_request_sock *ireq = inet_rsk(req);
7044 
7045 	if (family == AF_INET)
7046 		net_dbg_ratelimited("drop open request from %pI4/%u\n",
7047 				    &ireq->ir_rmt_addr, port);
7048 #if IS_ENABLED(CONFIG_IPV6)
7049 	else if (family == AF_INET6)
7050 		net_dbg_ratelimited("drop open request from %pI6/%u\n",
7051 				    &ireq->ir_v6_rmt_addr, port);
7052 #endif
7053 }
7054 
7055 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
7056  *
7057  * If we receive a SYN packet with these bits set, it means a
7058  * network is playing bad games with TOS bits. In order to
7059  * avoid possible false congestion notifications, we disable
7060  * TCP ECN negotiation.
7061  *
7062  * Exception: tcp_ca wants ECN. This is required for DCTCP
7063  * congestion control: Linux DCTCP asserts ECT on all packets,
7064  * including SYN, which is most optimal solution; however,
7065  * others, such as FreeBSD do not.
7066  *
7067  * Exception: At least one of the reserved bits of the TCP header (th->res1) is
7068  * set, indicating the use of a future TCP extension (such as AccECN). See
7069  * RFC8311 §4.3 which updates RFC3168 to allow the development of such
7070  * extensions.
7071  */
tcp_ecn_create_request(struct request_sock * req,const struct sk_buff * skb,const struct sock * listen_sk,const struct dst_entry * dst)7072 static void tcp_ecn_create_request(struct request_sock *req,
7073 				   const struct sk_buff *skb,
7074 				   const struct sock *listen_sk,
7075 				   const struct dst_entry *dst)
7076 {
7077 	const struct tcphdr *th = tcp_hdr(skb);
7078 	const struct net *net = sock_net(listen_sk);
7079 	bool th_ecn = th->ece && th->cwr;
7080 	bool ect, ecn_ok;
7081 	u32 ecn_ok_dst;
7082 
7083 	if (!th_ecn)
7084 		return;
7085 
7086 	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
7087 	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
7088 	ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) || ecn_ok_dst;
7089 
7090 	if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
7091 	    (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
7092 	    tcp_bpf_ca_needs_ecn((struct sock *)req))
7093 		inet_rsk(req)->ecn_ok = 1;
7094 }
7095 
tcp_openreq_init(struct request_sock * req,const struct tcp_options_received * rx_opt,struct sk_buff * skb,const struct sock * sk)7096 static void tcp_openreq_init(struct request_sock *req,
7097 			     const struct tcp_options_received *rx_opt,
7098 			     struct sk_buff *skb, const struct sock *sk)
7099 {
7100 	struct inet_request_sock *ireq = inet_rsk(req);
7101 
7102 	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
7103 	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
7104 	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
7105 	tcp_rsk(req)->snt_synack = 0;
7106 	tcp_rsk(req)->snt_tsval_first = 0;
7107 	tcp_rsk(req)->last_oow_ack_time = 0;
7108 	req->mss = rx_opt->mss_clamp;
7109 	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
7110 	ireq->tstamp_ok = rx_opt->tstamp_ok;
7111 	ireq->sack_ok = rx_opt->sack_ok;
7112 	ireq->snd_wscale = rx_opt->snd_wscale;
7113 	ireq->wscale_ok = rx_opt->wscale_ok;
7114 	ireq->acked = 0;
7115 	ireq->ecn_ok = 0;
7116 	ireq->ir_rmt_port = tcp_hdr(skb)->source;
7117 	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
7118 	ireq->ir_mark = inet_request_mark(sk, skb);
7119 #if IS_ENABLED(CONFIG_SMC)
7120 	ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_hs_congested &&
7121 			tcp_sk(sk)->smc_hs_congested(sk));
7122 #endif
7123 }
7124 
7125 /*
7126  * Return true if a syncookie should be sent
7127  */
tcp_syn_flood_action(struct sock * sk,const char * proto)7128 static bool tcp_syn_flood_action(struct sock *sk, const char *proto)
7129 {
7130 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
7131 	const char *msg = "Dropping request";
7132 	struct net *net = sock_net(sk);
7133 	bool want_cookie = false;
7134 	u8 syncookies;
7135 
7136 	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
7137 
7138 #ifdef CONFIG_SYN_COOKIES
7139 	if (syncookies) {
7140 		msg = "Sending cookies";
7141 		want_cookie = true;
7142 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
7143 	} else
7144 #endif
7145 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
7146 
7147 	if (!READ_ONCE(queue->synflood_warned) && syncookies != 2 &&
7148 	    xchg(&queue->synflood_warned, 1) == 0) {
7149 		if (IS_ENABLED(CONFIG_IPV6) && sk->sk_family == AF_INET6) {
7150 			net_info_ratelimited("%s: Possible SYN flooding on port [%pI6c]:%u. %s.\n",
7151 					proto, inet6_rcv_saddr(sk),
7152 					sk->sk_num, msg);
7153 		} else {
7154 			net_info_ratelimited("%s: Possible SYN flooding on port %pI4:%u. %s.\n",
7155 					proto, &sk->sk_rcv_saddr,
7156 					sk->sk_num, msg);
7157 		}
7158 	}
7159 
7160 	return want_cookie;
7161 }
7162 
tcp_reqsk_record_syn(const struct sock * sk,struct request_sock * req,const struct sk_buff * skb)7163 static void tcp_reqsk_record_syn(const struct sock *sk,
7164 				 struct request_sock *req,
7165 				 const struct sk_buff *skb)
7166 {
7167 	if (tcp_sk(sk)->save_syn) {
7168 		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
7169 		struct saved_syn *saved_syn;
7170 		u32 mac_hdrlen;
7171 		void *base;
7172 
7173 		if (tcp_sk(sk)->save_syn == 2) {  /* Save full header. */
7174 			base = skb_mac_header(skb);
7175 			mac_hdrlen = skb_mac_header_len(skb);
7176 			len += mac_hdrlen;
7177 		} else {
7178 			base = skb_network_header(skb);
7179 			mac_hdrlen = 0;
7180 		}
7181 
7182 		saved_syn = kmalloc(struct_size(saved_syn, data, len),
7183 				    GFP_ATOMIC);
7184 		if (saved_syn) {
7185 			saved_syn->mac_hdrlen = mac_hdrlen;
7186 			saved_syn->network_hdrlen = skb_network_header_len(skb);
7187 			saved_syn->tcp_hdrlen = tcp_hdrlen(skb);
7188 			memcpy(saved_syn->data, base, len);
7189 			req->saved_syn = saved_syn;
7190 		}
7191 	}
7192 }
7193 
7194 /* If a SYN cookie is required and supported, returns a clamped MSS value to be
7195  * used for SYN cookie generation.
7196  */
tcp_get_syncookie_mss(struct request_sock_ops * rsk_ops,const struct tcp_request_sock_ops * af_ops,struct sock * sk,struct tcphdr * th)7197 u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
7198 			  const struct tcp_request_sock_ops *af_ops,
7199 			  struct sock *sk, struct tcphdr *th)
7200 {
7201 	struct tcp_sock *tp = tcp_sk(sk);
7202 	u16 mss;
7203 
7204 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
7205 	    !inet_csk_reqsk_queue_is_full(sk))
7206 		return 0;
7207 
7208 	if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
7209 		return 0;
7210 
7211 	if (sk_acceptq_is_full(sk)) {
7212 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
7213 		return 0;
7214 	}
7215 
7216 	mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss);
7217 	if (!mss)
7218 		mss = af_ops->mss_clamp;
7219 
7220 	return mss;
7221 }
7222 EXPORT_IPV6_MOD_GPL(tcp_get_syncookie_mss);
7223 
tcp_conn_request(struct request_sock_ops * rsk_ops,const struct tcp_request_sock_ops * af_ops,struct sock * sk,struct sk_buff * skb)7224 int tcp_conn_request(struct request_sock_ops *rsk_ops,
7225 		     const struct tcp_request_sock_ops *af_ops,
7226 		     struct sock *sk, struct sk_buff *skb)
7227 {
7228 	struct tcp_fastopen_cookie foc = { .len = -1 };
7229 	struct tcp_options_received tmp_opt;
7230 	struct tcp_sock *tp = tcp_sk(sk);
7231 	struct net *net = sock_net(sk);
7232 	struct sock *fastopen_sk = NULL;
7233 	struct request_sock *req;
7234 	bool want_cookie = false;
7235 	struct dst_entry *dst;
7236 	struct flowi fl;
7237 	u8 syncookies;
7238 	u32 isn;
7239 
7240 #ifdef CONFIG_TCP_AO
7241 	const struct tcp_ao_hdr *aoh;
7242 #endif
7243 
7244 	isn = __this_cpu_read(tcp_tw_isn);
7245 	if (isn) {
7246 		/* TW buckets are converted to open requests without
7247 		 * limitations, they conserve resources and peer is
7248 		 * evidently real one.
7249 		 */
7250 		__this_cpu_write(tcp_tw_isn, 0);
7251 	} else {
7252 		syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
7253 
7254 		if (syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) {
7255 			want_cookie = tcp_syn_flood_action(sk,
7256 							   rsk_ops->slab_name);
7257 			if (!want_cookie)
7258 				goto drop;
7259 		}
7260 	}
7261 
7262 	if (sk_acceptq_is_full(sk)) {
7263 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
7264 		goto drop;
7265 	}
7266 
7267 	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
7268 	if (!req)
7269 		goto drop;
7270 
7271 	req->syncookie = want_cookie;
7272 	tcp_rsk(req)->af_specific = af_ops;
7273 	tcp_rsk(req)->ts_off = 0;
7274 	tcp_rsk(req)->req_usec_ts = false;
7275 #if IS_ENABLED(CONFIG_MPTCP)
7276 	tcp_rsk(req)->is_mptcp = 0;
7277 #endif
7278 
7279 	tcp_clear_options(&tmp_opt);
7280 	tmp_opt.mss_clamp = af_ops->mss_clamp;
7281 	tmp_opt.user_mss  = tp->rx_opt.user_mss;
7282 	tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
7283 			  want_cookie ? NULL : &foc);
7284 
7285 	if (want_cookie && !tmp_opt.saw_tstamp)
7286 		tcp_clear_options(&tmp_opt);
7287 
7288 	if (IS_ENABLED(CONFIG_SMC) && want_cookie)
7289 		tmp_opt.smc_ok = 0;
7290 
7291 	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
7292 	tcp_openreq_init(req, &tmp_opt, skb, sk);
7293 	inet_rsk(req)->no_srccheck = inet_test_bit(TRANSPARENT, sk);
7294 
7295 	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
7296 	inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
7297 
7298 	dst = af_ops->route_req(sk, skb, &fl, req, isn);
7299 	if (!dst)
7300 		goto drop_and_free;
7301 
7302 	if (tmp_opt.tstamp_ok) {
7303 		tcp_rsk(req)->req_usec_ts = dst_tcp_usec_ts(dst);
7304 		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
7305 	}
7306 	if (!want_cookie && !isn) {
7307 		int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog);
7308 
7309 		/* Kill the following clause, if you dislike this way. */
7310 		if (!syncookies &&
7311 		    (max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
7312 		     (max_syn_backlog >> 2)) &&
7313 		    !tcp_peer_is_proven(req, dst)) {
7314 			/* Without syncookies last quarter of
7315 			 * backlog is filled with destinations,
7316 			 * proven to be alive.
7317 			 * It means that we continue to communicate
7318 			 * to destinations, already remembered
7319 			 * to the moment of synflood.
7320 			 */
7321 			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
7322 				    rsk_ops->family);
7323 			goto drop_and_release;
7324 		}
7325 
7326 		isn = af_ops->init_seq(skb);
7327 	}
7328 
7329 	tcp_ecn_create_request(req, skb, sk, dst);
7330 
7331 	if (want_cookie) {
7332 		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
7333 		if (!tmp_opt.tstamp_ok)
7334 			inet_rsk(req)->ecn_ok = 0;
7335 	}
7336 
7337 #ifdef CONFIG_TCP_AO
7338 	if (tcp_parse_auth_options(tcp_hdr(skb), NULL, &aoh))
7339 		goto drop_and_release; /* Invalid TCP options */
7340 	if (aoh) {
7341 		tcp_rsk(req)->used_tcp_ao = true;
7342 		tcp_rsk(req)->ao_rcv_next = aoh->keyid;
7343 		tcp_rsk(req)->ao_keyid = aoh->rnext_keyid;
7344 
7345 	} else {
7346 		tcp_rsk(req)->used_tcp_ao = false;
7347 	}
7348 #endif
7349 	tcp_rsk(req)->snt_isn = isn;
7350 	tcp_rsk(req)->txhash = net_tx_rndhash();
7351 	tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
7352 	tcp_openreq_init_rwin(req, sk, dst);
7353 	sk_rx_queue_set(req_to_sk(req), skb);
7354 	if (!want_cookie) {
7355 		tcp_reqsk_record_syn(sk, req, skb);
7356 		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
7357 	}
7358 	if (fastopen_sk) {
7359 		af_ops->send_synack(fastopen_sk, dst, &fl, req,
7360 				    &foc, TCP_SYNACK_FASTOPEN, skb);
7361 		/* Add the child socket directly into the accept queue */
7362 		if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
7363 			reqsk_fastopen_remove(fastopen_sk, req, false);
7364 			bh_unlock_sock(fastopen_sk);
7365 			sock_put(fastopen_sk);
7366 			goto drop_and_free;
7367 		}
7368 		sk->sk_data_ready(sk);
7369 		bh_unlock_sock(fastopen_sk);
7370 		sock_put(fastopen_sk);
7371 	} else {
7372 		tcp_rsk(req)->tfo_listener = false;
7373 		if (!want_cookie) {
7374 			req->timeout = tcp_timeout_init((struct sock *)req);
7375 			if (unlikely(!inet_csk_reqsk_queue_hash_add(sk, req,
7376 								    req->timeout))) {
7377 				reqsk_free(req);
7378 				dst_release(dst);
7379 				return 0;
7380 			}
7381 
7382 		}
7383 		af_ops->send_synack(sk, dst, &fl, req, &foc,
7384 				    !want_cookie ? TCP_SYNACK_NORMAL :
7385 						   TCP_SYNACK_COOKIE,
7386 				    skb);
7387 		if (want_cookie) {
7388 			reqsk_free(req);
7389 			return 0;
7390 		}
7391 	}
7392 	reqsk_put(req);
7393 	return 0;
7394 
7395 drop_and_release:
7396 	dst_release(dst);
7397 drop_and_free:
7398 	__reqsk_free(req);
7399 drop:
7400 	tcp_listendrop(sk);
7401 	return 0;
7402 }
7403 EXPORT_IPV6_MOD(tcp_conn_request);
7404