xref: /linux/net/ipv4/tcp_input.c (revision 07fdad3a93756b872da7b53647715c48d0f4a2d0)
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 <linux/bitops.h>
74 #include <net/dst.h>
75 #include <net/tcp.h>
76 #include <net/tcp_ecn.h>
77 #include <net/proto_memory.h>
78 #include <net/inet_common.h>
79 #include <linux/ipsec.h>
80 #include <linux/unaligned.h>
81 #include <linux/errqueue.h>
82 #include <trace/events/tcp.h>
83 #include <linux/jump_label_ratelimit.h>
84 #include <net/busy_poll.h>
85 #include <net/mptcp.h>
86 
87 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
88 
89 #define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
90 #define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
91 #define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
92 #define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
93 #define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
94 #define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
95 #define FLAG_ECE		0x40 /* ECE in this ACK				*/
96 #define FLAG_LOST_RETRANS	0x80 /* This ACK marks some retransmission lost */
97 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
98 #define FLAG_ORIG_SACK_ACKED	0x200 /* Never retransmitted data are (s)acked	*/
99 #define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
100 #define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained D-SACK info */
101 #define FLAG_SET_XMIT_TIMER	0x1000 /* Set TLP or RTO timer */
102 #define FLAG_SACK_RENEGING	0x2000 /* snd_una advanced to a sacked seq */
103 #define FLAG_UPDATE_TS_RECENT	0x4000 /* tcp_replace_ts_recent() */
104 #define FLAG_NO_CHALLENGE_ACK	0x8000 /* do not call tcp_send_challenge_ack()	*/
105 #define FLAG_ACK_MAYBE_DELAYED	0x10000 /* Likely a delayed ACK */
106 #define FLAG_DSACK_TLP		0x20000 /* DSACK for tail loss probe */
107 #define FLAG_TS_PROGRESS	0x40000 /* Positive timestamp delta */
108 
109 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
110 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
111 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
112 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
113 
114 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
115 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
116 
117 #define REXMIT_NONE	0 /* no loss recovery to do */
118 #define REXMIT_LOST	1 /* retransmit packets marked lost */
119 #define REXMIT_NEW	2 /* FRTO-style transmit of unsent/new packets */
120 
121 #if IS_ENABLED(CONFIG_TLS_DEVICE)
122 static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ);
123 
124 void clean_acked_data_enable(struct tcp_sock *tp,
125 			     void (*cad)(struct sock *sk, u32 ack_seq))
126 {
127 	tp->tcp_clean_acked = cad;
128 	static_branch_deferred_inc(&clean_acked_data_enabled);
129 }
130 EXPORT_SYMBOL_GPL(clean_acked_data_enable);
131 
132 void clean_acked_data_disable(struct tcp_sock *tp)
133 {
134 	static_branch_slow_dec_deferred(&clean_acked_data_enabled);
135 	tp->tcp_clean_acked = NULL;
136 }
137 EXPORT_SYMBOL_GPL(clean_acked_data_disable);
138 
139 void clean_acked_data_flush(void)
140 {
141 	static_key_deferred_flush(&clean_acked_data_enabled);
142 }
143 EXPORT_SYMBOL_GPL(clean_acked_data_flush);
144 #endif
145 
146 #ifdef CONFIG_CGROUP_BPF
147 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
148 {
149 	bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown &&
150 		BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
151 				       BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG);
152 	bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
153 						    BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG);
154 	struct bpf_sock_ops_kern sock_ops;
155 
156 	if (likely(!unknown_opt && !parse_all_opt))
157 		return;
158 
159 	/* The skb will be handled in the
160 	 * bpf_skops_established() or
161 	 * bpf_skops_write_hdr_opt().
162 	 */
163 	switch (sk->sk_state) {
164 	case TCP_SYN_RECV:
165 	case TCP_SYN_SENT:
166 	case TCP_LISTEN:
167 		return;
168 	}
169 
170 	sock_owned_by_me(sk);
171 
172 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
173 	sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB;
174 	sock_ops.is_fullsock = 1;
175 	sock_ops.is_locked_tcp_sock = 1;
176 	sock_ops.sk = sk;
177 	bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
178 
179 	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
180 }
181 
182 static void bpf_skops_established(struct sock *sk, int bpf_op,
183 				  struct sk_buff *skb)
184 {
185 	struct bpf_sock_ops_kern sock_ops;
186 
187 	sock_owned_by_me(sk);
188 
189 	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
190 	sock_ops.op = bpf_op;
191 	sock_ops.is_fullsock = 1;
192 	sock_ops.is_locked_tcp_sock = 1;
193 	sock_ops.sk = sk;
194 	/* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */
195 	if (skb)
196 		bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb));
197 
198 	BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops);
199 }
200 #else
201 static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb)
202 {
203 }
204 
205 static void bpf_skops_established(struct sock *sk, int bpf_op,
206 				  struct sk_buff *skb)
207 {
208 }
209 #endif
210 
211 static __cold void tcp_gro_dev_warn(const struct sock *sk, const struct sk_buff *skb,
212 				    unsigned int len)
213 {
214 	struct net_device *dev;
215 
216 	rcu_read_lock();
217 	dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
218 	if (!dev || len >= READ_ONCE(dev->mtu))
219 		pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
220 			dev ? dev->name : "Unknown driver");
221 	rcu_read_unlock();
222 }
223 
224 /* Adapt the MSS value used to make delayed ack decision to the
225  * real world.
226  */
227 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
228 {
229 	struct inet_connection_sock *icsk = inet_csk(sk);
230 	const unsigned int lss = icsk->icsk_ack.last_seg_size;
231 	unsigned int len;
232 
233 	icsk->icsk_ack.last_seg_size = 0;
234 
235 	/* skb->len may jitter because of SACKs, even if peer
236 	 * sends good full-sized frames.
237 	 */
238 	len = skb_shinfo(skb)->gso_size ? : skb->len;
239 	if (len >= icsk->icsk_ack.rcv_mss) {
240 		/* Note: divides are still a bit expensive.
241 		 * For the moment, only adjust scaling_ratio
242 		 * when we update icsk_ack.rcv_mss.
243 		 */
244 		if (unlikely(len != icsk->icsk_ack.rcv_mss)) {
245 			u64 val = (u64)skb->len << TCP_RMEM_TO_WIN_SCALE;
246 			u8 old_ratio = tcp_sk(sk)->scaling_ratio;
247 
248 			do_div(val, skb->truesize);
249 			tcp_sk(sk)->scaling_ratio = val ? val : 1;
250 
251 			if (old_ratio != tcp_sk(sk)->scaling_ratio) {
252 				struct tcp_sock *tp = tcp_sk(sk);
253 
254 				val = tcp_win_from_space(sk, sk->sk_rcvbuf);
255 				tcp_set_window_clamp(sk, val);
256 
257 				if (tp->window_clamp < tp->rcvq_space.space)
258 					tp->rcvq_space.space = tp->window_clamp;
259 			}
260 		}
261 		icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
262 					       tcp_sk(sk)->advmss);
263 		/* Account for possibly-removed options */
264 		DO_ONCE_LITE_IF(len > icsk->icsk_ack.rcv_mss + MAX_TCP_OPTION_SPACE,
265 				tcp_gro_dev_warn, sk, skb, len);
266 		/* If the skb has a len of exactly 1*MSS and has the PSH bit
267 		 * set then it is likely the end of an application write. So
268 		 * more data may not be arriving soon, and yet the data sender
269 		 * may be waiting for an ACK if cwnd-bound or using TX zero
270 		 * copy. So we set ICSK_ACK_PUSHED here so that
271 		 * tcp_cleanup_rbuf() will send an ACK immediately if the app
272 		 * reads all of the data and is not ping-pong. If len > MSS
273 		 * then this logic does not matter (and does not hurt) because
274 		 * tcp_cleanup_rbuf() will always ACK immediately if the app
275 		 * reads data and there is more than an MSS of unACKed data.
276 		 */
277 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_PSH)
278 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
279 	} else {
280 		/* Otherwise, we make more careful check taking into account,
281 		 * that SACKs block is variable.
282 		 *
283 		 * "len" is invariant segment length, including TCP header.
284 		 */
285 		len += skb->data - skb_transport_header(skb);
286 		if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
287 		    /* If PSH is not set, packet should be
288 		     * full sized, provided peer TCP is not badly broken.
289 		     * This observation (if it is correct 8)) allows
290 		     * to handle super-low mtu links fairly.
291 		     */
292 		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
293 		     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
294 			/* Subtract also invariant (if peer is RFC compliant),
295 			 * tcp header plus fixed timestamp option length.
296 			 * Resulting "len" is MSS free of SACK jitter.
297 			 */
298 			len -= tcp_sk(sk)->tcp_header_len;
299 			icsk->icsk_ack.last_seg_size = len;
300 			if (len == lss) {
301 				icsk->icsk_ack.rcv_mss = len;
302 				return;
303 			}
304 		}
305 		if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
306 			icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
307 		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
308 	}
309 }
310 
311 static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
312 {
313 	struct inet_connection_sock *icsk = inet_csk(sk);
314 	unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
315 
316 	if (quickacks == 0)
317 		quickacks = 2;
318 	quickacks = min(quickacks, max_quickacks);
319 	if (quickacks > icsk->icsk_ack.quick)
320 		icsk->icsk_ack.quick = quickacks;
321 }
322 
323 static void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
324 {
325 	struct inet_connection_sock *icsk = inet_csk(sk);
326 
327 	tcp_incr_quickack(sk, max_quickacks);
328 	inet_csk_exit_pingpong_mode(sk);
329 	icsk->icsk_ack.ato = TCP_ATO_MIN;
330 }
331 
332 /* Send ACKs quickly, if "quick" count is not exhausted
333  * and the session is not interactive.
334  */
335 
336 static bool tcp_in_quickack_mode(struct sock *sk)
337 {
338 	const struct inet_connection_sock *icsk = inet_csk(sk);
339 
340 	return icsk->icsk_ack.dst_quick_ack ||
341 		(icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk));
342 }
343 
344 static void tcp_data_ecn_check(struct sock *sk, const struct sk_buff *skb)
345 {
346 	struct tcp_sock *tp = tcp_sk(sk);
347 
348 	if (tcp_ecn_disabled(tp))
349 		return;
350 
351 	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
352 	case INET_ECN_NOT_ECT:
353 		/* Funny extension: if ECT is not set on a segment,
354 		 * and we already seen ECT on a previous segment,
355 		 * it is probably a retransmit.
356 		 */
357 		if (tp->ecn_flags & TCP_ECN_SEEN)
358 			tcp_enter_quickack_mode(sk, 2);
359 		break;
360 	case INET_ECN_CE:
361 		if (tcp_ca_needs_ecn(sk))
362 			tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
363 
364 		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR) &&
365 		    tcp_ecn_mode_rfc3168(tp)) {
366 			/* Better not delay acks, sender can have a very low cwnd */
367 			tcp_enter_quickack_mode(sk, 2);
368 			tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
369 		}
370 		/* As for RFC3168 ECN, the TCP_ECN_SEEN flag is set by
371 		 * tcp_data_ecn_check() when the ECN codepoint of
372 		 * received TCP data contains ECT(0), ECT(1), or CE.
373 		 */
374 		if (!tcp_ecn_mode_rfc3168(tp))
375 			break;
376 		tp->ecn_flags |= TCP_ECN_SEEN;
377 		break;
378 	default:
379 		if (tcp_ca_needs_ecn(sk))
380 			tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
381 		if (!tcp_ecn_mode_rfc3168(tp))
382 			break;
383 		tp->ecn_flags |= TCP_ECN_SEEN;
384 		break;
385 	}
386 }
387 
388 /* Returns true if the byte counters can be used */
389 static bool tcp_accecn_process_option(struct tcp_sock *tp,
390 				      const struct sk_buff *skb,
391 				      u32 delivered_bytes, int flag)
392 {
393 	u8 estimate_ecnfield = tp->est_ecnfield;
394 	bool ambiguous_ecn_bytes_incr = false;
395 	bool first_changed = false;
396 	unsigned int optlen;
397 	bool order1, res;
398 	unsigned int i;
399 	u8 *ptr;
400 
401 	if (tcp_accecn_opt_fail_recv(tp))
402 		return false;
403 
404 	if (!(flag & FLAG_SLOWPATH) || !tp->rx_opt.accecn) {
405 		if (!tp->saw_accecn_opt) {
406 			/* Too late to enable after this point due to
407 			 * potential counter wraps
408 			 */
409 			if (tp->bytes_sent >= (1 << 23) - 1) {
410 				u8 saw_opt = TCP_ACCECN_OPT_FAIL_SEEN;
411 
412 				tcp_accecn_saw_opt_fail_recv(tp, saw_opt);
413 			}
414 			return false;
415 		}
416 
417 		if (estimate_ecnfield) {
418 			u8 ecnfield = estimate_ecnfield - 1;
419 
420 			tp->delivered_ecn_bytes[ecnfield] += delivered_bytes;
421 			return true;
422 		}
423 		return false;
424 	}
425 
426 	ptr = skb_transport_header(skb) + tp->rx_opt.accecn;
427 	optlen = ptr[1] - 2;
428 	if (WARN_ON_ONCE(ptr[0] != TCPOPT_ACCECN0 && ptr[0] != TCPOPT_ACCECN1))
429 		return false;
430 	order1 = (ptr[0] == TCPOPT_ACCECN1);
431 	ptr += 2;
432 
433 	if (tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
434 		tp->saw_accecn_opt = tcp_accecn_option_init(skb,
435 							    tp->rx_opt.accecn);
436 		if (tp->saw_accecn_opt == TCP_ACCECN_OPT_FAIL_SEEN)
437 			tcp_accecn_fail_mode_set(tp, TCP_ACCECN_OPT_FAIL_RECV);
438 	}
439 
440 	res = !!estimate_ecnfield;
441 	for (i = 0; i < 3; i++) {
442 		u32 init_offset;
443 		u8 ecnfield;
444 		s32 delta;
445 		u32 *cnt;
446 
447 		if (optlen < TCPOLEN_ACCECN_PERFIELD)
448 			break;
449 
450 		ecnfield = tcp_accecn_optfield_to_ecnfield(i, order1);
451 		init_offset = tcp_accecn_field_init_offset(ecnfield);
452 		cnt = &tp->delivered_ecn_bytes[ecnfield - 1];
453 		delta = tcp_update_ecn_bytes(cnt, ptr, init_offset);
454 		if (delta && delta < 0) {
455 			res = false;
456 			ambiguous_ecn_bytes_incr = true;
457 		}
458 		if (delta && ecnfield != estimate_ecnfield) {
459 			if (!first_changed) {
460 				tp->est_ecnfield = ecnfield;
461 				first_changed = true;
462 			} else {
463 				res = false;
464 				ambiguous_ecn_bytes_incr = true;
465 			}
466 		}
467 
468 		optlen -= TCPOLEN_ACCECN_PERFIELD;
469 		ptr += TCPOLEN_ACCECN_PERFIELD;
470 	}
471 	if (ambiguous_ecn_bytes_incr)
472 		tp->est_ecnfield = 0;
473 
474 	return res;
475 }
476 
477 static void tcp_count_delivered_ce(struct tcp_sock *tp, u32 ecn_count)
478 {
479 	tp->delivered_ce += ecn_count;
480 }
481 
482 /* Updates the delivered and delivered_ce counts */
483 static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered,
484 				bool ece_ack)
485 {
486 	tp->delivered += delivered;
487 	if (tcp_ecn_mode_rfc3168(tp) && ece_ack)
488 		tcp_count_delivered_ce(tp, delivered);
489 }
490 
491 /* Returns the ECN CE delta */
492 static u32 __tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
493 				u32 delivered_pkts, u32 delivered_bytes,
494 				int flag)
495 {
496 	u32 old_ceb = tcp_sk(sk)->delivered_ecn_bytes[INET_ECN_CE - 1];
497 	const struct tcphdr *th = tcp_hdr(skb);
498 	struct tcp_sock *tp = tcp_sk(sk);
499 	u32 delta, safe_delta, d_ceb;
500 	bool opt_deltas_valid;
501 	u32 corrected_ace;
502 
503 	/* Reordered ACK or uncertain due to lack of data to send and ts */
504 	if (!(flag & (FLAG_FORWARD_PROGRESS | FLAG_TS_PROGRESS)))
505 		return 0;
506 
507 	opt_deltas_valid = tcp_accecn_process_option(tp, skb,
508 						     delivered_bytes, flag);
509 
510 	if (!(flag & FLAG_SLOWPATH)) {
511 		/* AccECN counter might overflow on large ACKs */
512 		if (delivered_pkts <= TCP_ACCECN_CEP_ACE_MASK)
513 			return 0;
514 	}
515 
516 	/* ACE field is not available during handshake */
517 	if (flag & FLAG_SYN_ACKED)
518 		return 0;
519 
520 	if (tp->received_ce_pending >= TCP_ACCECN_ACE_MAX_DELTA)
521 		inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
522 
523 	corrected_ace = tcp_accecn_ace(th) - TCP_ACCECN_CEP_INIT_OFFSET;
524 	delta = (corrected_ace - tp->delivered_ce) & TCP_ACCECN_CEP_ACE_MASK;
525 	if (delivered_pkts <= TCP_ACCECN_CEP_ACE_MASK)
526 		return delta;
527 
528 	safe_delta = delivered_pkts -
529 		     ((delivered_pkts - delta) & TCP_ACCECN_CEP_ACE_MASK);
530 
531 	if (opt_deltas_valid) {
532 		d_ceb = tp->delivered_ecn_bytes[INET_ECN_CE - 1] - old_ceb;
533 		if (!d_ceb)
534 			return delta;
535 
536 		if ((delivered_pkts >= (TCP_ACCECN_CEP_ACE_MASK + 1) * 2) &&
537 		    (tcp_is_sack(tp) ||
538 		     ((1 << inet_csk(sk)->icsk_ca_state) &
539 		      (TCPF_CA_Open | TCPF_CA_CWR)))) {
540 			u32 est_d_cep;
541 
542 			if (delivered_bytes <= d_ceb)
543 				return safe_delta;
544 
545 			est_d_cep = DIV_ROUND_UP_ULL((u64)d_ceb *
546 						     delivered_pkts,
547 						     delivered_bytes);
548 			return min(safe_delta,
549 				   delta +
550 				   (est_d_cep & ~TCP_ACCECN_CEP_ACE_MASK));
551 		}
552 
553 		if (d_ceb > delta * tp->mss_cache)
554 			return safe_delta;
555 		if (d_ceb <
556 		    safe_delta * tp->mss_cache >> TCP_ACCECN_SAFETY_SHIFT)
557 			return delta;
558 	}
559 
560 	return safe_delta;
561 }
562 
563 static u32 tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
564 			      u32 delivered_pkts, u32 delivered_bytes,
565 			      int *flag)
566 {
567 	struct tcp_sock *tp = tcp_sk(sk);
568 	u32 delta;
569 
570 	delta = __tcp_accecn_process(sk, skb, delivered_pkts,
571 				     delivered_bytes, *flag);
572 	if (delta > 0) {
573 		tcp_count_delivered_ce(tp, delta);
574 		*flag |= FLAG_ECE;
575 		/* Recalculate header predictor */
576 		if (tp->pred_flags)
577 			tcp_fast_path_on(tp);
578 	}
579 	return delta;
580 }
581 
582 /* Buffer size and advertised window tuning.
583  *
584  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
585  */
586 
587 static void tcp_sndbuf_expand(struct sock *sk)
588 {
589 	const struct tcp_sock *tp = tcp_sk(sk);
590 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
591 	int sndmem, per_mss;
592 	u32 nr_segs;
593 
594 	/* Worst case is non GSO/TSO : each frame consumes one skb
595 	 * and skb->head is kmalloced using power of two area of memory
596 	 */
597 	per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
598 		  MAX_TCP_HEADER +
599 		  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
600 
601 	per_mss = roundup_pow_of_two(per_mss) +
602 		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
603 
604 	nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp));
605 	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
606 
607 	/* Fast Recovery (RFC 5681 3.2) :
608 	 * Cubic needs 1.7 factor, rounded to 2 to include
609 	 * extra cushion (application might react slowly to EPOLLOUT)
610 	 */
611 	sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
612 	sndmem *= nr_segs * per_mss;
613 
614 	if (sk->sk_sndbuf < sndmem)
615 		WRITE_ONCE(sk->sk_sndbuf,
616 			   min(sndmem, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_wmem[2])));
617 }
618 
619 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
620  *
621  * All tcp_full_space() is split to two parts: "network" buffer, allocated
622  * forward and advertised in receiver window (tp->rcv_wnd) and
623  * "application buffer", required to isolate scheduling/application
624  * latencies from network.
625  * window_clamp is maximal advertised window. It can be less than
626  * tcp_full_space(), in this case tcp_full_space() - window_clamp
627  * is reserved for "application" buffer. The less window_clamp is
628  * the smoother our behaviour from viewpoint of network, but the lower
629  * throughput and the higher sensitivity of the connection to losses. 8)
630  *
631  * rcv_ssthresh is more strict window_clamp used at "slow start"
632  * phase to predict further behaviour of this connection.
633  * It is used for two goals:
634  * - to enforce header prediction at sender, even when application
635  *   requires some significant "application buffer". It is check #1.
636  * - to prevent pruning of receive queue because of misprediction
637  *   of receiver window. Check #2.
638  *
639  * The scheme does not work when sender sends good segments opening
640  * window and then starts to feed us spaghetti. But it should work
641  * in common situations. Otherwise, we have to rely on queue collapsing.
642  */
643 
644 /* Slow part of check#2. */
645 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb,
646 			     unsigned int skbtruesize)
647 {
648 	const struct tcp_sock *tp = tcp_sk(sk);
649 	/* Optimize this! */
650 	int truesize = tcp_win_from_space(sk, skbtruesize) >> 1;
651 	int window = tcp_win_from_space(sk, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])) >> 1;
652 
653 	while (tp->rcv_ssthresh <= window) {
654 		if (truesize <= skb->len)
655 			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
656 
657 		truesize >>= 1;
658 		window >>= 1;
659 	}
660 	return 0;
661 }
662 
663 /* Even if skb appears to have a bad len/truesize ratio, TCP coalescing
664  * can play nice with us, as sk_buff and skb->head might be either
665  * freed or shared with up to MAX_SKB_FRAGS segments.
666  * Only give a boost to drivers using page frag(s) to hold the frame(s),
667  * and if no payload was pulled in skb->head before reaching us.
668  */
669 static u32 truesize_adjust(bool adjust, const struct sk_buff *skb)
670 {
671 	u32 truesize = skb->truesize;
672 
673 	if (adjust && !skb_headlen(skb)) {
674 		truesize -= SKB_TRUESIZE(skb_end_offset(skb));
675 		/* paranoid check, some drivers might be buggy */
676 		if (unlikely((int)truesize < (int)skb->len))
677 			truesize = skb->truesize;
678 	}
679 	return truesize;
680 }
681 
682 static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb,
683 			    bool adjust)
684 {
685 	struct tcp_sock *tp = tcp_sk(sk);
686 	int room;
687 
688 	room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh;
689 
690 	if (room <= 0)
691 		return;
692 
693 	/* Check #1 */
694 	if (!tcp_under_memory_pressure(sk)) {
695 		unsigned int truesize = truesize_adjust(adjust, skb);
696 		int incr;
697 
698 		/* Check #2. Increase window, if skb with such overhead
699 		 * will fit to rcvbuf in future.
700 		 */
701 		if (tcp_win_from_space(sk, truesize) <= skb->len)
702 			incr = 2 * tp->advmss;
703 		else
704 			incr = __tcp_grow_window(sk, skb, truesize);
705 
706 		if (incr) {
707 			incr = max_t(int, incr, 2 * skb->len);
708 			tp->rcv_ssthresh += min(room, incr);
709 			inet_csk(sk)->icsk_ack.quick |= 1;
710 		}
711 	} else {
712 		/* Under pressure:
713 		 * Adjust rcv_ssthresh according to reserved mem
714 		 */
715 		tcp_adjust_rcv_ssthresh(sk);
716 	}
717 }
718 
719 /* 3. Try to fixup all. It is made immediately after connection enters
720  *    established state.
721  */
722 static void tcp_init_buffer_space(struct sock *sk)
723 {
724 	int tcp_app_win = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_app_win);
725 	struct tcp_sock *tp = tcp_sk(sk);
726 	int maxwin;
727 
728 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
729 		tcp_sndbuf_expand(sk);
730 
731 	tcp_mstamp_refresh(tp);
732 	tp->rcvq_space.time = tp->tcp_mstamp;
733 	tp->rcvq_space.seq = tp->copied_seq;
734 
735 	maxwin = tcp_full_space(sk);
736 
737 	if (tp->window_clamp >= maxwin) {
738 		WRITE_ONCE(tp->window_clamp, maxwin);
739 
740 		if (tcp_app_win && maxwin > 4 * tp->advmss)
741 			WRITE_ONCE(tp->window_clamp,
742 				   max(maxwin - (maxwin >> tcp_app_win),
743 				       4 * tp->advmss));
744 	}
745 
746 	/* Force reservation of one segment. */
747 	if (tcp_app_win &&
748 	    tp->window_clamp > 2 * tp->advmss &&
749 	    tp->window_clamp + tp->advmss > maxwin)
750 		WRITE_ONCE(tp->window_clamp,
751 			   max(2 * tp->advmss, maxwin - tp->advmss));
752 
753 	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
754 	tp->snd_cwnd_stamp = tcp_jiffies32;
755 	tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd,
756 				    (u32)TCP_INIT_CWND * tp->advmss);
757 }
758 
759 /* 4. Recalculate window clamp after socket hit its memory bounds. */
760 static void tcp_clamp_window(struct sock *sk)
761 {
762 	struct tcp_sock *tp = tcp_sk(sk);
763 	struct inet_connection_sock *icsk = inet_csk(sk);
764 	struct net *net = sock_net(sk);
765 	int rmem2;
766 
767 	icsk->icsk_ack.quick = 0;
768 	rmem2 = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);
769 
770 	if (sk->sk_rcvbuf < rmem2 &&
771 	    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
772 	    !tcp_under_memory_pressure(sk) &&
773 	    sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
774 		WRITE_ONCE(sk->sk_rcvbuf,
775 			   min(atomic_read(&sk->sk_rmem_alloc), rmem2));
776 	}
777 	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
778 		tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
779 }
780 
781 /* Initialize RCV_MSS value.
782  * RCV_MSS is an our guess about MSS used by the peer.
783  * We haven't any direct information about the MSS.
784  * It's better to underestimate the RCV_MSS rather than overestimate.
785  * Overestimations make us ACKing less frequently than needed.
786  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
787  */
788 void tcp_initialize_rcv_mss(struct sock *sk)
789 {
790 	const struct tcp_sock *tp = tcp_sk(sk);
791 	unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
792 
793 	hint = min(hint, tp->rcv_wnd / 2);
794 	hint = min(hint, TCP_MSS_DEFAULT);
795 	hint = max(hint, TCP_MIN_MSS);
796 
797 	inet_csk(sk)->icsk_ack.rcv_mss = hint;
798 }
799 EXPORT_IPV6_MOD(tcp_initialize_rcv_mss);
800 
801 /* Receiver "autotuning" code.
802  *
803  * The algorithm for RTT estimation w/o timestamps is based on
804  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
805  * <https://public.lanl.gov/radiant/pubs.html#DRS>
806  *
807  * More detail on this code can be found at
808  * <http://staff.psc.edu/jheffner/>,
809  * though this reference is out of date.  A new paper
810  * is pending.
811  */
812 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
813 {
814 	u32 new_sample, old_sample = tp->rcv_rtt_est.rtt_us;
815 	long m = sample << 3;
816 
817 	if (old_sample == 0 || m < old_sample) {
818 		new_sample = m;
819 	} else {
820 		/* If we sample in larger samples in the non-timestamp
821 		 * case, we could grossly overestimate the RTT especially
822 		 * with chatty applications or bulk transfer apps which
823 		 * are stalled on filesystem I/O.
824 		 *
825 		 * Also, since we are only going for a minimum in the
826 		 * non-timestamp case, we do not smooth things out
827 		 * else with timestamps disabled convergence takes too
828 		 * long.
829 		 */
830 		if (win_dep)
831 			return;
832 		/* Do not use this sample if receive queue is not empty. */
833 		if (tp->rcv_nxt != tp->copied_seq)
834 			return;
835 		new_sample = old_sample - (old_sample >> 3) + sample;
836 	}
837 
838 	tp->rcv_rtt_est.rtt_us = new_sample;
839 }
840 
841 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
842 {
843 	u32 delta_us;
844 
845 	if (tp->rcv_rtt_est.time == 0)
846 		goto new_measure;
847 	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
848 		return;
849 	delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
850 	if (!delta_us)
851 		delta_us = 1;
852 	tcp_rcv_rtt_update(tp, delta_us, 1);
853 
854 new_measure:
855 	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
856 	tp->rcv_rtt_est.time = tp->tcp_mstamp;
857 }
858 
859 static s32 tcp_rtt_tsopt_us(const struct tcp_sock *tp, u32 min_delta)
860 {
861 	u32 delta, delta_us;
862 
863 	delta = tcp_time_stamp_ts(tp) - tp->rx_opt.rcv_tsecr;
864 	if (tp->tcp_usec_ts)
865 		return delta;
866 
867 	if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) {
868 		if (!delta)
869 			delta = min_delta;
870 		delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
871 		return delta_us;
872 	}
873 	return -1;
874 }
875 
876 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
877 					  const struct sk_buff *skb)
878 {
879 	struct tcp_sock *tp = tcp_sk(sk);
880 
881 	if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
882 		return;
883 	tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
884 
885 	if (TCP_SKB_CB(skb)->end_seq -
886 	    TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
887 		s32 delta = tcp_rtt_tsopt_us(tp, 0);
888 
889 		if (delta > 0)
890 			tcp_rcv_rtt_update(tp, delta, 0);
891 	}
892 }
893 
894 void tcp_rcvbuf_grow(struct sock *sk)
895 {
896 	const struct net *net = sock_net(sk);
897 	struct tcp_sock *tp = tcp_sk(sk);
898 	int rcvwin, rcvbuf, cap;
899 
900 	if (!READ_ONCE(net->ipv4.sysctl_tcp_moderate_rcvbuf) ||
901 	    (sk->sk_userlocks & SOCK_RCVBUF_LOCK))
902 		return;
903 
904 	/* slow start: allow the sender to double its rate. */
905 	rcvwin = tp->rcvq_space.space << 1;
906 
907 	if (!RB_EMPTY_ROOT(&tp->out_of_order_queue))
908 		rcvwin += TCP_SKB_CB(tp->ooo_last_skb)->end_seq - tp->rcv_nxt;
909 
910 	cap = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]);
911 
912 	rcvbuf = min_t(u32, tcp_space_from_win(sk, rcvwin), cap);
913 	if (rcvbuf > sk->sk_rcvbuf) {
914 		WRITE_ONCE(sk->sk_rcvbuf, rcvbuf);
915 		/* Make the window clamp follow along.  */
916 		WRITE_ONCE(tp->window_clamp,
917 			   tcp_win_from_space(sk, rcvbuf));
918 	}
919 }
920 /*
921  * This function should be called every time data is copied to user space.
922  * It calculates the appropriate TCP receive buffer space.
923  */
924 void tcp_rcv_space_adjust(struct sock *sk)
925 {
926 	struct tcp_sock *tp = tcp_sk(sk);
927 	int time, inq, copied;
928 
929 	trace_tcp_rcv_space_adjust(sk);
930 
931 	tcp_mstamp_refresh(tp);
932 	time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
933 	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
934 		return;
935 
936 	/* Number of bytes copied to user in last RTT */
937 	copied = tp->copied_seq - tp->rcvq_space.seq;
938 	/* Number of bytes in receive queue. */
939 	inq = tp->rcv_nxt - tp->copied_seq;
940 	copied -= inq;
941 	if (copied <= tp->rcvq_space.space)
942 		goto new_measure;
943 
944 	trace_tcp_rcvbuf_grow(sk, time);
945 
946 	tp->rcvq_space.space = copied;
947 
948 	tcp_rcvbuf_grow(sk);
949 
950 new_measure:
951 	tp->rcvq_space.seq = tp->copied_seq;
952 	tp->rcvq_space.time = tp->tcp_mstamp;
953 }
954 
955 static void tcp_save_lrcv_flowlabel(struct sock *sk, const struct sk_buff *skb)
956 {
957 #if IS_ENABLED(CONFIG_IPV6)
958 	struct inet_connection_sock *icsk = inet_csk(sk);
959 
960 	if (skb->protocol == htons(ETH_P_IPV6))
961 		icsk->icsk_ack.lrcv_flowlabel = ntohl(ip6_flowlabel(ipv6_hdr(skb)));
962 #endif
963 }
964 
965 /* There is something which you must keep in mind when you analyze the
966  * behavior of the tp->ato delayed ack timeout interval.  When a
967  * connection starts up, we want to ack as quickly as possible.  The
968  * problem is that "good" TCP's do slow start at the beginning of data
969  * transmission.  The means that until we send the first few ACK's the
970  * sender will sit on his end and only queue most of his data, because
971  * he can only send snd_cwnd unacked packets at any given time.  For
972  * each ACK we send, he increments snd_cwnd and transmits more of his
973  * queue.  -DaveM
974  */
975 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
976 {
977 	struct tcp_sock *tp = tcp_sk(sk);
978 	struct inet_connection_sock *icsk = inet_csk(sk);
979 	u32 now;
980 
981 	inet_csk_schedule_ack(sk);
982 
983 	tcp_measure_rcv_mss(sk, skb);
984 
985 	tcp_rcv_rtt_measure(tp);
986 
987 	now = tcp_jiffies32;
988 
989 	if (!icsk->icsk_ack.ato) {
990 		/* The _first_ data packet received, initialize
991 		 * delayed ACK engine.
992 		 */
993 		tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
994 		icsk->icsk_ack.ato = TCP_ATO_MIN;
995 	} else {
996 		int m = now - icsk->icsk_ack.lrcvtime;
997 
998 		if (m <= TCP_ATO_MIN / 2) {
999 			/* The fastest case is the first. */
1000 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
1001 		} else if (m < icsk->icsk_ack.ato) {
1002 			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
1003 			if (icsk->icsk_ack.ato > icsk->icsk_rto)
1004 				icsk->icsk_ack.ato = icsk->icsk_rto;
1005 		} else if (m > icsk->icsk_rto) {
1006 			/* Too long gap. Apparently sender failed to
1007 			 * restart window, so that we send ACKs quickly.
1008 			 */
1009 			tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
1010 		}
1011 	}
1012 	icsk->icsk_ack.lrcvtime = now;
1013 	tcp_save_lrcv_flowlabel(sk, skb);
1014 
1015 	tcp_data_ecn_check(sk, skb);
1016 
1017 	if (skb->len >= 128)
1018 		tcp_grow_window(sk, skb, true);
1019 }
1020 
1021 /* Called to compute a smoothed rtt estimate. The data fed to this
1022  * routine either comes from timestamps, or from segments that were
1023  * known _not_ to have been retransmitted [see Karn/Partridge
1024  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
1025  * piece by Van Jacobson.
1026  * NOTE: the next three routines used to be one big routine.
1027  * To save cycles in the RFC 1323 implementation it was better to break
1028  * it up into three procedures. -- erics
1029  */
1030 static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
1031 {
1032 	struct tcp_sock *tp = tcp_sk(sk);
1033 	long m = mrtt_us; /* RTT */
1034 	u32 srtt = tp->srtt_us;
1035 
1036 	/*	The following amusing code comes from Jacobson's
1037 	 *	article in SIGCOMM '88.  Note that rtt and mdev
1038 	 *	are scaled versions of rtt and mean deviation.
1039 	 *	This is designed to be as fast as possible
1040 	 *	m stands for "measurement".
1041 	 *
1042 	 *	On a 1990 paper the rto value is changed to:
1043 	 *	RTO = rtt + 4 * mdev
1044 	 *
1045 	 * Funny. This algorithm seems to be very broken.
1046 	 * These formulae increase RTO, when it should be decreased, increase
1047 	 * too slowly, when it should be increased quickly, decrease too quickly
1048 	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
1049 	 * does not matter how to _calculate_ it. Seems, it was trap
1050 	 * that VJ failed to avoid. 8)
1051 	 */
1052 	if (srtt != 0) {
1053 		m -= (srtt >> 3);	/* m is now error in rtt est */
1054 		srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
1055 		if (m < 0) {
1056 			m = -m;		/* m is now abs(error) */
1057 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
1058 			/* This is similar to one of Eifel findings.
1059 			 * Eifel blocks mdev updates when rtt decreases.
1060 			 * This solution is a bit different: we use finer gain
1061 			 * for mdev in this case (alpha*beta).
1062 			 * Like Eifel it also prevents growth of rto,
1063 			 * but also it limits too fast rto decreases,
1064 			 * happening in pure Eifel.
1065 			 */
1066 			if (m > 0)
1067 				m >>= 3;
1068 		} else {
1069 			m -= (tp->mdev_us >> 2);   /* similar update on mdev */
1070 		}
1071 		tp->mdev_us += m;		/* mdev = 3/4 mdev + 1/4 new */
1072 		if (tp->mdev_us > tp->mdev_max_us) {
1073 			tp->mdev_max_us = tp->mdev_us;
1074 			if (tp->mdev_max_us > tp->rttvar_us)
1075 				tp->rttvar_us = tp->mdev_max_us;
1076 		}
1077 		if (after(tp->snd_una, tp->rtt_seq)) {
1078 			if (tp->mdev_max_us < tp->rttvar_us)
1079 				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
1080 			tp->rtt_seq = tp->snd_nxt;
1081 			tp->mdev_max_us = tcp_rto_min_us(sk);
1082 
1083 			tcp_bpf_rtt(sk, mrtt_us, srtt);
1084 		}
1085 	} else {
1086 		/* no previous measure. */
1087 		srtt = m << 3;		/* take the measured time to be rtt */
1088 		tp->mdev_us = m << 1;	/* make sure rto = 3*rtt */
1089 		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
1090 		tp->mdev_max_us = tp->rttvar_us;
1091 		tp->rtt_seq = tp->snd_nxt;
1092 
1093 		tcp_bpf_rtt(sk, mrtt_us, srtt);
1094 	}
1095 	tp->srtt_us = max(1U, srtt);
1096 }
1097 
1098 static void tcp_update_pacing_rate(struct sock *sk)
1099 {
1100 	const struct tcp_sock *tp = tcp_sk(sk);
1101 	u64 rate;
1102 
1103 	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
1104 	rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
1105 
1106 	/* current rate is (cwnd * mss) / srtt
1107 	 * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
1108 	 * In Congestion Avoidance phase, set it to 120 % the current rate.
1109 	 *
1110 	 * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
1111 	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
1112 	 *	 end of slow start and should slow down.
1113 	 */
1114 	if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2)
1115 		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio);
1116 	else
1117 		rate *= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio);
1118 
1119 	rate *= max(tcp_snd_cwnd(tp), tp->packets_out);
1120 
1121 	if (likely(tp->srtt_us))
1122 		do_div(rate, tp->srtt_us);
1123 
1124 	/* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
1125 	 * without any lock. We want to make sure compiler wont store
1126 	 * intermediate values in this location.
1127 	 */
1128 	WRITE_ONCE(sk->sk_pacing_rate,
1129 		   min_t(u64, rate, READ_ONCE(sk->sk_max_pacing_rate)));
1130 }
1131 
1132 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
1133  * routine referred to above.
1134  */
1135 static void tcp_set_rto(struct sock *sk)
1136 {
1137 	const struct tcp_sock *tp = tcp_sk(sk);
1138 	/* Old crap is replaced with new one. 8)
1139 	 *
1140 	 * More seriously:
1141 	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
1142 	 *    It cannot be less due to utterly erratic ACK generation made
1143 	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
1144 	 *    to do with delayed acks, because at cwnd>2 true delack timeout
1145 	 *    is invisible. Actually, Linux-2.4 also generates erratic
1146 	 *    ACKs in some circumstances.
1147 	 */
1148 	inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
1149 
1150 	/* 2. Fixups made earlier cannot be right.
1151 	 *    If we do not estimate RTO correctly without them,
1152 	 *    all the algo is pure shit and should be replaced
1153 	 *    with correct one. It is exactly, which we pretend to do.
1154 	 */
1155 
1156 	/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
1157 	 * guarantees that rto is higher.
1158 	 */
1159 	tcp_bound_rto(sk);
1160 }
1161 
1162 __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
1163 {
1164 	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
1165 
1166 	if (!cwnd)
1167 		cwnd = TCP_INIT_CWND;
1168 	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
1169 }
1170 
1171 struct tcp_sacktag_state {
1172 	/* Timestamps for earliest and latest never-retransmitted segment
1173 	 * that was SACKed. RTO needs the earliest RTT to stay conservative,
1174 	 * but congestion control should still get an accurate delay signal.
1175 	 */
1176 	u64	first_sackt;
1177 	u64	last_sackt;
1178 	u32	reord;
1179 	u32	sack_delivered;
1180 	u32	delivered_bytes;
1181 	int	flag;
1182 	unsigned int mss_now;
1183 	struct rate_sample *rate;
1184 };
1185 
1186 /* Take a notice that peer is sending D-SACKs. Skip update of data delivery
1187  * and spurious retransmission information if this DSACK is unlikely caused by
1188  * sender's action:
1189  * - DSACKed sequence range is larger than maximum receiver's window.
1190  * - Total no. of DSACKed segments exceed the total no. of retransmitted segs.
1191  */
1192 static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
1193 			  u32 end_seq, struct tcp_sacktag_state *state)
1194 {
1195 	u32 seq_len, dup_segs = 1;
1196 
1197 	if (!before(start_seq, end_seq))
1198 		return 0;
1199 
1200 	seq_len = end_seq - start_seq;
1201 	/* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */
1202 	if (seq_len > tp->max_window)
1203 		return 0;
1204 	if (seq_len > tp->mss_cache)
1205 		dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache);
1206 	else if (tp->tlp_high_seq && tp->tlp_high_seq == end_seq)
1207 		state->flag |= FLAG_DSACK_TLP;
1208 
1209 	tp->dsack_dups += dup_segs;
1210 	/* Skip the DSACK if dup segs weren't retransmitted by sender */
1211 	if (tp->dsack_dups > tp->total_retrans)
1212 		return 0;
1213 
1214 	tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
1215 	/* We increase the RACK ordering window in rounds where we receive
1216 	 * DSACKs that may have been due to reordering causing RACK to trigger
1217 	 * a spurious fast recovery. Thus RACK ignores DSACKs that happen
1218 	 * without having seen reordering, or that match TLP probes (TLP
1219 	 * is timer-driven, not triggered by RACK).
1220 	 */
1221 	if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP))
1222 		tp->rack.dsack_seen = 1;
1223 
1224 	state->flag |= FLAG_DSACKING_ACK;
1225 	/* A spurious retransmission is delivered */
1226 	state->sack_delivered += dup_segs;
1227 
1228 	return dup_segs;
1229 }
1230 
1231 /* It's reordering when higher sequence was delivered (i.e. sacked) before
1232  * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
1233  * distance is approximated in full-mss packet distance ("reordering").
1234  */
1235 static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
1236 				      const int ts)
1237 {
1238 	struct tcp_sock *tp = tcp_sk(sk);
1239 	const u32 mss = tp->mss_cache;
1240 	u32 fack, metric;
1241 
1242 	fack = tcp_highest_sack_seq(tp);
1243 	if (!before(low_seq, fack))
1244 		return;
1245 
1246 	metric = fack - low_seq;
1247 	if ((metric > tp->reordering * mss) && mss) {
1248 #if FASTRETRANS_DEBUG > 1
1249 		pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
1250 			 tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
1251 			 tp->reordering,
1252 			 0,
1253 			 tp->sacked_out,
1254 			 tp->undo_marker ? tp->undo_retrans : 0);
1255 #endif
1256 		tp->reordering = min_t(u32, (metric + mss - 1) / mss,
1257 				       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
1258 	}
1259 
1260 	/* This exciting event is worth to be remembered. 8) */
1261 	tp->reord_seen++;
1262 	NET_INC_STATS(sock_net(sk),
1263 		      ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
1264 }
1265 
1266  /* This must be called before lost_out or retrans_out are updated
1267   * on a new loss, because we want to know if all skbs previously
1268   * known to be lost have already been retransmitted, indicating
1269   * that this newly lost skb is our next skb to retransmit.
1270   */
1271 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
1272 {
1273 	if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) ||
1274 	    (tp->retransmit_skb_hint &&
1275 	     before(TCP_SKB_CB(skb)->seq,
1276 		    TCP_SKB_CB(tp->retransmit_skb_hint)->seq)))
1277 		tp->retransmit_skb_hint = skb;
1278 }
1279 
1280 /* Sum the number of packets on the wire we have marked as lost, and
1281  * notify the congestion control module that the given skb was marked lost.
1282  */
1283 static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb)
1284 {
1285 	tp->lost += tcp_skb_pcount(skb);
1286 }
1287 
1288 void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
1289 {
1290 	__u8 sacked = TCP_SKB_CB(skb)->sacked;
1291 	struct tcp_sock *tp = tcp_sk(sk);
1292 
1293 	if (sacked & TCPCB_SACKED_ACKED)
1294 		return;
1295 
1296 	tcp_verify_retransmit_hint(tp, skb);
1297 	if (sacked & TCPCB_LOST) {
1298 		if (sacked & TCPCB_SACKED_RETRANS) {
1299 			/* Account for retransmits that are lost again */
1300 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1301 			tp->retrans_out -= tcp_skb_pcount(skb);
1302 			NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,
1303 				      tcp_skb_pcount(skb));
1304 			tcp_notify_skb_loss_event(tp, skb);
1305 		}
1306 	} else {
1307 		tp->lost_out += tcp_skb_pcount(skb);
1308 		TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1309 		tcp_notify_skb_loss_event(tp, skb);
1310 	}
1311 }
1312 
1313 /* This procedure tags the retransmission queue when SACKs arrive.
1314  *
1315  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1316  * Packets in queue with these bits set are counted in variables
1317  * sacked_out, retrans_out and lost_out, correspondingly.
1318  *
1319  * Valid combinations are:
1320  * Tag  InFlight	Description
1321  * 0	1		- orig segment is in flight.
1322  * S	0		- nothing flies, orig reached receiver.
1323  * L	0		- nothing flies, orig lost by net.
1324  * R	2		- both orig and retransmit are in flight.
1325  * L|R	1		- orig is lost, retransmit is in flight.
1326  * S|R  1		- orig reached receiver, retrans is still in flight.
1327  * (L|S|R is logically valid, it could occur when L|R is sacked,
1328  *  but it is equivalent to plain S and code short-circuits it to S.
1329  *  L|S is logically invalid, it would mean -1 packet in flight 8))
1330  *
1331  * These 6 states form finite state machine, controlled by the following events:
1332  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1333  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1334  * 3. Loss detection event of two flavors:
1335  *	A. Scoreboard estimator decided the packet is lost.
1336  *	   A'. Reno "three dupacks" marks head of queue lost.
1337  *	B. SACK arrives sacking SND.NXT at the moment, when the
1338  *	   segment was retransmitted.
1339  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1340  *
1341  * It is pleasant to note, that state diagram turns out to be commutative,
1342  * so that we are allowed not to be bothered by order of our actions,
1343  * when multiple events arrive simultaneously. (see the function below).
1344  *
1345  * Reordering detection.
1346  * --------------------
1347  * Reordering metric is maximal distance, which a packet can be displaced
1348  * in packet stream. With SACKs we can estimate it:
1349  *
1350  * 1. SACK fills old hole and the corresponding segment was not
1351  *    ever retransmitted -> reordering. Alas, we cannot use it
1352  *    when segment was retransmitted.
1353  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1354  *    for retransmitted and already SACKed segment -> reordering..
1355  * Both of these heuristics are not used in Loss state, when we cannot
1356  * account for retransmits accurately.
1357  *
1358  * SACK block validation.
1359  * ----------------------
1360  *
1361  * SACK block range validation checks that the received SACK block fits to
1362  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1363  * Note that SND.UNA is not included to the range though being valid because
1364  * it means that the receiver is rather inconsistent with itself reporting
1365  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1366  * perfectly valid, however, in light of RFC2018 which explicitly states
1367  * that "SACK block MUST reflect the newest segment.  Even if the newest
1368  * segment is going to be discarded ...", not that it looks very clever
1369  * in case of head skb. Due to potentional receiver driven attacks, we
1370  * choose to avoid immediate execution of a walk in write queue due to
1371  * reneging and defer head skb's loss recovery to standard loss recovery
1372  * procedure that will eventually trigger (nothing forbids us doing this).
1373  *
1374  * Implements also blockage to start_seq wrap-around. Problem lies in the
1375  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1376  * there's no guarantee that it will be before snd_nxt (n). The problem
1377  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1378  * wrap (s_w):
1379  *
1380  *         <- outs wnd ->                          <- wrapzone ->
1381  *         u     e      n                         u_w   e_w  s n_w
1382  *         |     |      |                          |     |   |  |
1383  * |<------------+------+----- TCP seqno space --------------+---------->|
1384  * ...-- <2^31 ->|                                           |<--------...
1385  * ...---- >2^31 ------>|                                    |<--------...
1386  *
1387  * Current code wouldn't be vulnerable but it's better still to discard such
1388  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1389  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1390  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1391  * equal to the ideal case (infinite seqno space without wrap caused issues).
1392  *
1393  * With D-SACK the lower bound is extended to cover sequence space below
1394  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1395  * again, D-SACK block must not to go across snd_una (for the same reason as
1396  * for the normal SACK blocks, explained above). But there all simplicity
1397  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1398  * fully below undo_marker they do not affect behavior in anyway and can
1399  * therefore be safely ignored. In rare cases (which are more or less
1400  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1401  * fragmentation and packet reordering past skb's retransmission. To consider
1402  * them correctly, the acceptable range must be extended even more though
1403  * the exact amount is rather hard to quantify. However, tp->max_window can
1404  * be used as an exaggerated estimate.
1405  */
1406 static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
1407 				   u32 start_seq, u32 end_seq)
1408 {
1409 	/* Too far in future, or reversed (interpretation is ambiguous) */
1410 	if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1411 		return false;
1412 
1413 	/* Nasty start_seq wrap-around check (see comments above) */
1414 	if (!before(start_seq, tp->snd_nxt))
1415 		return false;
1416 
1417 	/* In outstanding window? ...This is valid exit for D-SACKs too.
1418 	 * start_seq == snd_una is non-sensical (see comments above)
1419 	 */
1420 	if (after(start_seq, tp->snd_una))
1421 		return true;
1422 
1423 	if (!is_dsack || !tp->undo_marker)
1424 		return false;
1425 
1426 	/* ...Then it's D-SACK, and must reside below snd_una completely */
1427 	if (after(end_seq, tp->snd_una))
1428 		return false;
1429 
1430 	if (!before(start_seq, tp->undo_marker))
1431 		return true;
1432 
1433 	/* Too old */
1434 	if (!after(end_seq, tp->undo_marker))
1435 		return false;
1436 
1437 	/* Undo_marker boundary crossing (overestimates a lot). Known already:
1438 	 *   start_seq < undo_marker and end_seq >= undo_marker.
1439 	 */
1440 	return !before(start_seq, end_seq - tp->max_window);
1441 }
1442 
1443 static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1444 			    struct tcp_sack_block_wire *sp, int num_sacks,
1445 			    u32 prior_snd_una, struct tcp_sacktag_state *state)
1446 {
1447 	struct tcp_sock *tp = tcp_sk(sk);
1448 	u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1449 	u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1450 	u32 dup_segs;
1451 
1452 	if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1453 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1454 	} else if (num_sacks > 1) {
1455 		u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1456 		u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1457 
1458 		if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1))
1459 			return false;
1460 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV);
1461 	} else {
1462 		return false;
1463 	}
1464 
1465 	dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state);
1466 	if (!dup_segs) {	/* Skip dubious DSACK */
1467 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS);
1468 		return false;
1469 	}
1470 
1471 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs);
1472 
1473 	/* D-SACK for already forgotten data... Do dumb counting. */
1474 	if (tp->undo_marker && tp->undo_retrans > 0 &&
1475 	    !after(end_seq_0, prior_snd_una) &&
1476 	    after(end_seq_0, tp->undo_marker))
1477 		tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs);
1478 
1479 	return true;
1480 }
1481 
1482 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1483  * the incoming SACK may not exactly match but we can find smaller MSS
1484  * aligned portion of it that matches. Therefore we might need to fragment
1485  * which may fail and creates some hassle (caller must handle error case
1486  * returns).
1487  *
1488  * FIXME: this could be merged to shift decision code
1489  */
1490 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1491 				  u32 start_seq, u32 end_seq)
1492 {
1493 	int err;
1494 	bool in_sack;
1495 	unsigned int pkt_len;
1496 	unsigned int mss;
1497 
1498 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1499 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1500 
1501 	if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1502 	    after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1503 		mss = tcp_skb_mss(skb);
1504 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1505 
1506 		if (!in_sack) {
1507 			pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1508 			if (pkt_len < mss)
1509 				pkt_len = mss;
1510 		} else {
1511 			pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1512 			if (pkt_len < mss)
1513 				return -EINVAL;
1514 		}
1515 
1516 		/* Round if necessary so that SACKs cover only full MSSes
1517 		 * and/or the remaining small portion (if present)
1518 		 */
1519 		if (pkt_len > mss) {
1520 			unsigned int new_len = (pkt_len / mss) * mss;
1521 			if (!in_sack && new_len < pkt_len)
1522 				new_len += mss;
1523 			pkt_len = new_len;
1524 		}
1525 
1526 		if (pkt_len >= skb->len && !in_sack)
1527 			return 0;
1528 
1529 		err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
1530 				   pkt_len, mss, GFP_ATOMIC);
1531 		if (err < 0)
1532 			return err;
1533 	}
1534 
1535 	return in_sack;
1536 }
1537 
1538 /* Mark the given newly-SACKed range as such, adjusting counters and hints. */
1539 static u8 tcp_sacktag_one(struct sock *sk,
1540 			  struct tcp_sacktag_state *state, u8 sacked,
1541 			  u32 start_seq, u32 end_seq,
1542 			  int dup_sack, int pcount, u32 plen,
1543 			  u64 xmit_time)
1544 {
1545 	struct tcp_sock *tp = tcp_sk(sk);
1546 
1547 	/* Account D-SACK for retransmitted packet. */
1548 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
1549 		if (tp->undo_marker && tp->undo_retrans > 0 &&
1550 		    after(end_seq, tp->undo_marker))
1551 			tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
1552 		if ((sacked & TCPCB_SACKED_ACKED) &&
1553 		    before(start_seq, state->reord))
1554 				state->reord = start_seq;
1555 	}
1556 
1557 	/* Nothing to do; acked frame is about to be dropped (was ACKed). */
1558 	if (!after(end_seq, tp->snd_una))
1559 		return sacked;
1560 
1561 	if (!(sacked & TCPCB_SACKED_ACKED)) {
1562 		tcp_rack_advance(tp, sacked, end_seq, xmit_time);
1563 
1564 		if (sacked & TCPCB_SACKED_RETRANS) {
1565 			/* If the segment is not tagged as lost,
1566 			 * we do not clear RETRANS, believing
1567 			 * that retransmission is still in flight.
1568 			 */
1569 			if (sacked & TCPCB_LOST) {
1570 				sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1571 				tp->lost_out -= pcount;
1572 				tp->retrans_out -= pcount;
1573 			}
1574 		} else {
1575 			if (!(sacked & TCPCB_RETRANS)) {
1576 				/* New sack for not retransmitted frame,
1577 				 * which was in hole. It is reordering.
1578 				 */
1579 				if (before(start_seq,
1580 					   tcp_highest_sack_seq(tp)) &&
1581 				    before(start_seq, state->reord))
1582 					state->reord = start_seq;
1583 
1584 				if (!after(end_seq, tp->high_seq))
1585 					state->flag |= FLAG_ORIG_SACK_ACKED;
1586 				if (state->first_sackt == 0)
1587 					state->first_sackt = xmit_time;
1588 				state->last_sackt = xmit_time;
1589 			}
1590 
1591 			if (sacked & TCPCB_LOST) {
1592 				sacked &= ~TCPCB_LOST;
1593 				tp->lost_out -= pcount;
1594 			}
1595 		}
1596 
1597 		sacked |= TCPCB_SACKED_ACKED;
1598 		state->flag |= FLAG_DATA_SACKED;
1599 		tp->sacked_out += pcount;
1600 		/* Out-of-order packets delivered */
1601 		state->sack_delivered += pcount;
1602 		state->delivered_bytes += plen;
1603 	}
1604 
1605 	/* D-SACK. We can detect redundant retransmission in S|R and plain R
1606 	 * frames and clear it. undo_retrans is decreased above, L|R frames
1607 	 * are accounted above as well.
1608 	 */
1609 	if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1610 		sacked &= ~TCPCB_SACKED_RETRANS;
1611 		tp->retrans_out -= pcount;
1612 	}
1613 
1614 	return sacked;
1615 }
1616 
1617 /* Shift newly-SACKed bytes from this skb to the immediately previous
1618  * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
1619  */
1620 static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
1621 			    struct sk_buff *skb,
1622 			    struct tcp_sacktag_state *state,
1623 			    unsigned int pcount, int shifted, int mss,
1624 			    bool dup_sack)
1625 {
1626 	struct tcp_sock *tp = tcp_sk(sk);
1627 	u32 start_seq = TCP_SKB_CB(skb)->seq;	/* start of newly-SACKed */
1628 	u32 end_seq = start_seq + shifted;	/* end of newly-SACKed */
1629 
1630 	BUG_ON(!pcount);
1631 
1632 	/* Adjust counters and hints for the newly sacked sequence
1633 	 * range but discard the return value since prev is already
1634 	 * marked. We must tag the range first because the seq
1635 	 * advancement below implicitly advances
1636 	 * tcp_highest_sack_seq() when skb is highest_sack.
1637 	 */
1638 	tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
1639 			start_seq, end_seq, dup_sack, pcount, skb->len,
1640 			tcp_skb_timestamp_us(skb));
1641 	tcp_rate_skb_delivered(sk, skb, state->rate);
1642 
1643 	TCP_SKB_CB(prev)->end_seq += shifted;
1644 	TCP_SKB_CB(skb)->seq += shifted;
1645 
1646 	tcp_skb_pcount_add(prev, pcount);
1647 	WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
1648 	tcp_skb_pcount_add(skb, -pcount);
1649 
1650 	/* When we're adding to gso_segs == 1, gso_size will be zero,
1651 	 * in theory this shouldn't be necessary but as long as DSACK
1652 	 * code can come after this skb later on it's better to keep
1653 	 * setting gso_size to something.
1654 	 */
1655 	if (!TCP_SKB_CB(prev)->tcp_gso_size)
1656 		TCP_SKB_CB(prev)->tcp_gso_size = mss;
1657 
1658 	/* CHECKME: To clear or not to clear? Mimics normal skb currently */
1659 	if (tcp_skb_pcount(skb) <= 1)
1660 		TCP_SKB_CB(skb)->tcp_gso_size = 0;
1661 
1662 	/* Difference in this won't matter, both ACKed by the same cumul. ACK */
1663 	TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1664 
1665 	if (skb->len > 0) {
1666 		BUG_ON(!tcp_skb_pcount(skb));
1667 		NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1668 		return false;
1669 	}
1670 
1671 	/* Whole SKB was eaten :-) */
1672 
1673 	if (skb == tp->retransmit_skb_hint)
1674 		tp->retransmit_skb_hint = prev;
1675 
1676 	TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1677 	TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
1678 	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1679 		TCP_SKB_CB(prev)->end_seq++;
1680 
1681 	if (skb == tcp_highest_sack(sk))
1682 		tcp_advance_highest_sack(sk, skb);
1683 
1684 	tcp_skb_collapse_tstamp(prev, skb);
1685 	if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
1686 		TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
1687 
1688 	tcp_rtx_queue_unlink_and_free(skb, sk);
1689 
1690 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
1691 
1692 	return true;
1693 }
1694 
1695 /* I wish gso_size would have a bit more sane initialization than
1696  * something-or-zero which complicates things
1697  */
1698 static int tcp_skb_seglen(const struct sk_buff *skb)
1699 {
1700 	return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1701 }
1702 
1703 /* Shifting pages past head area doesn't work */
1704 static int skb_can_shift(const struct sk_buff *skb)
1705 {
1706 	return !skb_headlen(skb) && skb_is_nonlinear(skb);
1707 }
1708 
1709 int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from,
1710 		  int pcount, int shiftlen)
1711 {
1712 	/* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE)
1713 	 * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need
1714 	 * to make sure not storing more than 65535 * 8 bytes per skb,
1715 	 * even if current MSS is bigger.
1716 	 */
1717 	if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE))
1718 		return 0;
1719 	if (unlikely(tcp_skb_pcount(to) + pcount > 65535))
1720 		return 0;
1721 	return skb_shift(to, from, shiftlen);
1722 }
1723 
1724 /* Try collapsing SACK blocks spanning across multiple skbs to a single
1725  * skb.
1726  */
1727 static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1728 					  struct tcp_sacktag_state *state,
1729 					  u32 start_seq, u32 end_seq,
1730 					  bool dup_sack)
1731 {
1732 	struct tcp_sock *tp = tcp_sk(sk);
1733 	struct sk_buff *prev;
1734 	int mss;
1735 	int pcount = 0;
1736 	int len;
1737 	int in_sack;
1738 
1739 	/* Normally R but no L won't result in plain S */
1740 	if (!dup_sack &&
1741 	    (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1742 		goto fallback;
1743 	if (!skb_can_shift(skb))
1744 		goto fallback;
1745 	/* This frame is about to be dropped (was ACKed). */
1746 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1747 		goto fallback;
1748 
1749 	/* Can only happen with delayed DSACK + discard craziness */
1750 	prev = skb_rb_prev(skb);
1751 	if (!prev)
1752 		goto fallback;
1753 
1754 	if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1755 		goto fallback;
1756 
1757 	if (!tcp_skb_can_collapse(prev, skb))
1758 		goto fallback;
1759 
1760 	in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1761 		  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1762 
1763 	if (in_sack) {
1764 		len = skb->len;
1765 		pcount = tcp_skb_pcount(skb);
1766 		mss = tcp_skb_seglen(skb);
1767 
1768 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1769 		 * drop this restriction as unnecessary
1770 		 */
1771 		if (mss != tcp_skb_seglen(prev))
1772 			goto fallback;
1773 	} else {
1774 		if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1775 			goto noop;
1776 		/* CHECKME: This is non-MSS split case only?, this will
1777 		 * cause skipped skbs due to advancing loop btw, original
1778 		 * has that feature too
1779 		 */
1780 		if (tcp_skb_pcount(skb) <= 1)
1781 			goto noop;
1782 
1783 		in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1784 		if (!in_sack) {
1785 			/* TODO: head merge to next could be attempted here
1786 			 * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1787 			 * though it might not be worth of the additional hassle
1788 			 *
1789 			 * ...we can probably just fallback to what was done
1790 			 * previously. We could try merging non-SACKed ones
1791 			 * as well but it probably isn't going to buy off
1792 			 * because later SACKs might again split them, and
1793 			 * it would make skb timestamp tracking considerably
1794 			 * harder problem.
1795 			 */
1796 			goto fallback;
1797 		}
1798 
1799 		len = end_seq - TCP_SKB_CB(skb)->seq;
1800 		BUG_ON(len < 0);
1801 		BUG_ON(len > skb->len);
1802 
1803 		/* MSS boundaries should be honoured or else pcount will
1804 		 * severely break even though it makes things bit trickier.
1805 		 * Optimize common case to avoid most of the divides
1806 		 */
1807 		mss = tcp_skb_mss(skb);
1808 
1809 		/* TODO: Fix DSACKs to not fragment already SACKed and we can
1810 		 * drop this restriction as unnecessary
1811 		 */
1812 		if (mss != tcp_skb_seglen(prev))
1813 			goto fallback;
1814 
1815 		if (len == mss) {
1816 			pcount = 1;
1817 		} else if (len < mss) {
1818 			goto noop;
1819 		} else {
1820 			pcount = len / mss;
1821 			len = pcount * mss;
1822 		}
1823 	}
1824 
1825 	/* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
1826 	if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
1827 		goto fallback;
1828 
1829 	if (!tcp_skb_shift(prev, skb, pcount, len))
1830 		goto fallback;
1831 	if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
1832 		goto out;
1833 
1834 	/* Hole filled allows collapsing with the next as well, this is very
1835 	 * useful when hole on every nth skb pattern happens
1836 	 */
1837 	skb = skb_rb_next(prev);
1838 	if (!skb)
1839 		goto out;
1840 
1841 	if (!skb_can_shift(skb) ||
1842 	    ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1843 	    (mss != tcp_skb_seglen(skb)))
1844 		goto out;
1845 
1846 	if (!tcp_skb_can_collapse(prev, skb))
1847 		goto out;
1848 	len = skb->len;
1849 	pcount = tcp_skb_pcount(skb);
1850 	if (tcp_skb_shift(prev, skb, pcount, len))
1851 		tcp_shifted_skb(sk, prev, skb, state, pcount,
1852 				len, mss, 0);
1853 
1854 out:
1855 	return prev;
1856 
1857 noop:
1858 	return skb;
1859 
1860 fallback:
1861 	NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1862 	return NULL;
1863 }
1864 
1865 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1866 					struct tcp_sack_block *next_dup,
1867 					struct tcp_sacktag_state *state,
1868 					u32 start_seq, u32 end_seq,
1869 					bool dup_sack_in)
1870 {
1871 	struct tcp_sock *tp = tcp_sk(sk);
1872 	struct sk_buff *tmp;
1873 
1874 	skb_rbtree_walk_from(skb) {
1875 		int in_sack = 0;
1876 		bool dup_sack = dup_sack_in;
1877 
1878 		/* queue is in-order => we can short-circuit the walk early */
1879 		if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1880 			break;
1881 
1882 		if (next_dup  &&
1883 		    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1884 			in_sack = tcp_match_skb_to_sack(sk, skb,
1885 							next_dup->start_seq,
1886 							next_dup->end_seq);
1887 			if (in_sack > 0)
1888 				dup_sack = true;
1889 		}
1890 
1891 		/* skb reference here is a bit tricky to get right, since
1892 		 * shifting can eat and free both this skb and the next,
1893 		 * so not even _safe variant of the loop is enough.
1894 		 */
1895 		if (in_sack <= 0) {
1896 			tmp = tcp_shift_skb_data(sk, skb, state,
1897 						 start_seq, end_seq, dup_sack);
1898 			if (tmp) {
1899 				if (tmp != skb) {
1900 					skb = tmp;
1901 					continue;
1902 				}
1903 
1904 				in_sack = 0;
1905 			} else {
1906 				in_sack = tcp_match_skb_to_sack(sk, skb,
1907 								start_seq,
1908 								end_seq);
1909 			}
1910 		}
1911 
1912 		if (unlikely(in_sack < 0))
1913 			break;
1914 
1915 		if (in_sack) {
1916 			TCP_SKB_CB(skb)->sacked =
1917 				tcp_sacktag_one(sk,
1918 						state,
1919 						TCP_SKB_CB(skb)->sacked,
1920 						TCP_SKB_CB(skb)->seq,
1921 						TCP_SKB_CB(skb)->end_seq,
1922 						dup_sack,
1923 						tcp_skb_pcount(skb),
1924 						skb->len,
1925 						tcp_skb_timestamp_us(skb));
1926 			tcp_rate_skb_delivered(sk, skb, state->rate);
1927 			if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1928 				list_del_init(&skb->tcp_tsorted_anchor);
1929 
1930 			if (!before(TCP_SKB_CB(skb)->seq,
1931 				    tcp_highest_sack_seq(tp)))
1932 				tcp_advance_highest_sack(sk, skb);
1933 		}
1934 	}
1935 	return skb;
1936 }
1937 
1938 static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq)
1939 {
1940 	struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
1941 	struct sk_buff *skb;
1942 
1943 	while (*p) {
1944 		parent = *p;
1945 		skb = rb_to_skb(parent);
1946 		if (before(seq, TCP_SKB_CB(skb)->seq)) {
1947 			p = &parent->rb_left;
1948 			continue;
1949 		}
1950 		if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
1951 			p = &parent->rb_right;
1952 			continue;
1953 		}
1954 		return skb;
1955 	}
1956 	return NULL;
1957 }
1958 
1959 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1960 					u32 skip_to_seq)
1961 {
1962 	if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
1963 		return skb;
1964 
1965 	return tcp_sacktag_bsearch(sk, skip_to_seq);
1966 }
1967 
1968 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1969 						struct sock *sk,
1970 						struct tcp_sack_block *next_dup,
1971 						struct tcp_sacktag_state *state,
1972 						u32 skip_to_seq)
1973 {
1974 	if (!next_dup)
1975 		return skb;
1976 
1977 	if (before(next_dup->start_seq, skip_to_seq)) {
1978 		skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1979 		skb = tcp_sacktag_walk(skb, sk, NULL, state,
1980 				       next_dup->start_seq, next_dup->end_seq,
1981 				       1);
1982 	}
1983 
1984 	return skb;
1985 }
1986 
1987 static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1988 {
1989 	return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1990 }
1991 
1992 static int
1993 tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1994 			u32 prior_snd_una, struct tcp_sacktag_state *state)
1995 {
1996 	struct tcp_sock *tp = tcp_sk(sk);
1997 	const unsigned char *ptr = (skb_transport_header(ack_skb) +
1998 				    TCP_SKB_CB(ack_skb)->sacked);
1999 	struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
2000 	struct tcp_sack_block sp[TCP_NUM_SACKS];
2001 	struct tcp_sack_block *cache;
2002 	struct sk_buff *skb;
2003 	int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
2004 	int used_sacks;
2005 	bool found_dup_sack = false;
2006 	int i, j;
2007 	int first_sack_index;
2008 
2009 	state->flag = 0;
2010 	state->reord = tp->snd_nxt;
2011 
2012 	if (!tp->sacked_out)
2013 		tcp_highest_sack_reset(sk);
2014 
2015 	found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
2016 					 num_sacks, prior_snd_una, state);
2017 
2018 	/* Eliminate too old ACKs, but take into
2019 	 * account more or less fresh ones, they can
2020 	 * contain valid SACK info.
2021 	 */
2022 	if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
2023 		return 0;
2024 
2025 	if (!tp->packets_out)
2026 		goto out;
2027 
2028 	used_sacks = 0;
2029 	first_sack_index = 0;
2030 	for (i = 0; i < num_sacks; i++) {
2031 		bool dup_sack = !i && found_dup_sack;
2032 
2033 		sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
2034 		sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
2035 
2036 		if (!tcp_is_sackblock_valid(tp, dup_sack,
2037 					    sp[used_sacks].start_seq,
2038 					    sp[used_sacks].end_seq)) {
2039 			int mib_idx;
2040 
2041 			if (dup_sack) {
2042 				if (!tp->undo_marker)
2043 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
2044 				else
2045 					mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
2046 			} else {
2047 				/* Don't count olds caused by ACK reordering */
2048 				if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
2049 				    !after(sp[used_sacks].end_seq, tp->snd_una))
2050 					continue;
2051 				mib_idx = LINUX_MIB_TCPSACKDISCARD;
2052 			}
2053 
2054 			NET_INC_STATS(sock_net(sk), mib_idx);
2055 			if (i == 0)
2056 				first_sack_index = -1;
2057 			continue;
2058 		}
2059 
2060 		/* Ignore very old stuff early */
2061 		if (!after(sp[used_sacks].end_seq, prior_snd_una)) {
2062 			if (i == 0)
2063 				first_sack_index = -1;
2064 			continue;
2065 		}
2066 
2067 		used_sacks++;
2068 	}
2069 
2070 	/* order SACK blocks to allow in order walk of the retrans queue */
2071 	for (i = used_sacks - 1; i > 0; i--) {
2072 		for (j = 0; j < i; j++) {
2073 			if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
2074 				swap(sp[j], sp[j + 1]);
2075 
2076 				/* Track where the first SACK block goes to */
2077 				if (j == first_sack_index)
2078 					first_sack_index = j + 1;
2079 			}
2080 		}
2081 	}
2082 
2083 	state->mss_now = tcp_current_mss(sk);
2084 	skb = NULL;
2085 	i = 0;
2086 
2087 	if (!tp->sacked_out) {
2088 		/* It's already past, so skip checking against it */
2089 		cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
2090 	} else {
2091 		cache = tp->recv_sack_cache;
2092 		/* Skip empty blocks in at head of the cache */
2093 		while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
2094 		       !cache->end_seq)
2095 			cache++;
2096 	}
2097 
2098 	while (i < used_sacks) {
2099 		u32 start_seq = sp[i].start_seq;
2100 		u32 end_seq = sp[i].end_seq;
2101 		bool dup_sack = (found_dup_sack && (i == first_sack_index));
2102 		struct tcp_sack_block *next_dup = NULL;
2103 
2104 		if (found_dup_sack && ((i + 1) == first_sack_index))
2105 			next_dup = &sp[i + 1];
2106 
2107 		/* Skip too early cached blocks */
2108 		while (tcp_sack_cache_ok(tp, cache) &&
2109 		       !before(start_seq, cache->end_seq))
2110 			cache++;
2111 
2112 		/* Can skip some work by looking recv_sack_cache? */
2113 		if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
2114 		    after(end_seq, cache->start_seq)) {
2115 
2116 			/* Head todo? */
2117 			if (before(start_seq, cache->start_seq)) {
2118 				skb = tcp_sacktag_skip(skb, sk, start_seq);
2119 				skb = tcp_sacktag_walk(skb, sk, next_dup,
2120 						       state,
2121 						       start_seq,
2122 						       cache->start_seq,
2123 						       dup_sack);
2124 			}
2125 
2126 			/* Rest of the block already fully processed? */
2127 			if (!after(end_seq, cache->end_seq))
2128 				goto advance_sp;
2129 
2130 			skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
2131 						       state,
2132 						       cache->end_seq);
2133 
2134 			/* ...tail remains todo... */
2135 			if (tcp_highest_sack_seq(tp) == cache->end_seq) {
2136 				/* ...but better entrypoint exists! */
2137 				skb = tcp_highest_sack(sk);
2138 				if (!skb)
2139 					break;
2140 				cache++;
2141 				goto walk;
2142 			}
2143 
2144 			skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
2145 			/* Check overlap against next cached too (past this one already) */
2146 			cache++;
2147 			continue;
2148 		}
2149 
2150 		if (!before(start_seq, tcp_highest_sack_seq(tp))) {
2151 			skb = tcp_highest_sack(sk);
2152 			if (!skb)
2153 				break;
2154 		}
2155 		skb = tcp_sacktag_skip(skb, sk, start_seq);
2156 
2157 walk:
2158 		skb = tcp_sacktag_walk(skb, sk, next_dup, state,
2159 				       start_seq, end_seq, dup_sack);
2160 
2161 advance_sp:
2162 		i++;
2163 	}
2164 
2165 	/* Clear the head of the cache sack blocks so we can skip it next time */
2166 	for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
2167 		tp->recv_sack_cache[i].start_seq = 0;
2168 		tp->recv_sack_cache[i].end_seq = 0;
2169 	}
2170 	for (j = 0; j < used_sacks; j++)
2171 		tp->recv_sack_cache[i++] = sp[j];
2172 
2173 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
2174 		tcp_check_sack_reordering(sk, state->reord, 0);
2175 
2176 	tcp_verify_left_out(tp);
2177 out:
2178 
2179 #if FASTRETRANS_DEBUG > 0
2180 	WARN_ON((int)tp->sacked_out < 0);
2181 	WARN_ON((int)tp->lost_out < 0);
2182 	WARN_ON((int)tp->retrans_out < 0);
2183 	WARN_ON((int)tcp_packets_in_flight(tp) < 0);
2184 #endif
2185 	return state->flag;
2186 }
2187 
2188 /* Limits sacked_out so that sum with lost_out isn't ever larger than
2189  * packets_out. Returns false if sacked_out adjustement wasn't necessary.
2190  */
2191 static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
2192 {
2193 	u32 holes;
2194 
2195 	holes = max(tp->lost_out, 1U);
2196 	holes = min(holes, tp->packets_out);
2197 
2198 	if ((tp->sacked_out + holes) > tp->packets_out) {
2199 		tp->sacked_out = tp->packets_out - holes;
2200 		return true;
2201 	}
2202 	return false;
2203 }
2204 
2205 /* If we receive more dupacks than we expected counting segments
2206  * in assumption of absent reordering, interpret this as reordering.
2207  * The only another reason could be bug in receiver TCP.
2208  */
2209 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
2210 {
2211 	struct tcp_sock *tp = tcp_sk(sk);
2212 
2213 	if (!tcp_limit_reno_sacked(tp))
2214 		return;
2215 
2216 	tp->reordering = min_t(u32, tp->packets_out + addend,
2217 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering));
2218 	tp->reord_seen++;
2219 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
2220 }
2221 
2222 /* Emulate SACKs for SACKless connection: account for a new dupack. */
2223 
2224 static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack)
2225 {
2226 	if (num_dupack) {
2227 		struct tcp_sock *tp = tcp_sk(sk);
2228 		u32 prior_sacked = tp->sacked_out;
2229 		s32 delivered;
2230 
2231 		tp->sacked_out += num_dupack;
2232 		tcp_check_reno_reordering(sk, 0);
2233 		delivered = tp->sacked_out - prior_sacked;
2234 		if (delivered > 0)
2235 			tcp_count_delivered(tp, delivered, ece_ack);
2236 		tcp_verify_left_out(tp);
2237 	}
2238 }
2239 
2240 /* Account for ACK, ACKing some data in Reno Recovery phase. */
2241 
2242 static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack)
2243 {
2244 	struct tcp_sock *tp = tcp_sk(sk);
2245 
2246 	if (acked > 0) {
2247 		/* One ACK acked hole. The rest eat duplicate ACKs. */
2248 		tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1),
2249 				    ece_ack);
2250 		if (acked - 1 >= tp->sacked_out)
2251 			tp->sacked_out = 0;
2252 		else
2253 			tp->sacked_out -= acked - 1;
2254 	}
2255 	tcp_check_reno_reordering(sk, acked);
2256 	tcp_verify_left_out(tp);
2257 }
2258 
2259 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2260 {
2261 	tp->sacked_out = 0;
2262 }
2263 
2264 void tcp_clear_retrans(struct tcp_sock *tp)
2265 {
2266 	tp->retrans_out = 0;
2267 	tp->lost_out = 0;
2268 	tp->undo_marker = 0;
2269 	tp->undo_retrans = -1;
2270 	tp->sacked_out = 0;
2271 	tp->rto_stamp = 0;
2272 	tp->total_rto = 0;
2273 	tp->total_rto_recoveries = 0;
2274 	tp->total_rto_time = 0;
2275 }
2276 
2277 static inline void tcp_init_undo(struct tcp_sock *tp)
2278 {
2279 	tp->undo_marker = tp->snd_una;
2280 
2281 	/* Retransmission still in flight may cause DSACKs later. */
2282 	/* First, account for regular retransmits in flight: */
2283 	tp->undo_retrans = tp->retrans_out;
2284 	/* Next, account for TLP retransmits in flight: */
2285 	if (tp->tlp_high_seq && tp->tlp_retrans)
2286 		tp->undo_retrans++;
2287 	/* Finally, avoid 0, because undo_retrans==0 means "can undo now": */
2288 	if (!tp->undo_retrans)
2289 		tp->undo_retrans = -1;
2290 }
2291 
2292 /* If we detect SACK reneging, forget all SACK information
2293  * and reset tags completely, otherwise preserve SACKs. If receiver
2294  * dropped its ofo queue, we will know this due to reneging detection.
2295  */
2296 static void tcp_timeout_mark_lost(struct sock *sk)
2297 {
2298 	struct tcp_sock *tp = tcp_sk(sk);
2299 	struct sk_buff *skb, *head;
2300 	bool is_reneg;			/* is receiver reneging on SACKs? */
2301 
2302 	head = tcp_rtx_queue_head(sk);
2303 	is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
2304 	if (is_reneg) {
2305 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2306 		tp->sacked_out = 0;
2307 		/* Mark SACK reneging until we recover from this loss event. */
2308 		tp->is_sack_reneg = 1;
2309 	} else if (tcp_is_reno(tp)) {
2310 		tcp_reset_reno_sack(tp);
2311 	}
2312 
2313 	skb = head;
2314 	skb_rbtree_walk_from(skb) {
2315 		if (is_reneg)
2316 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2317 		else if (skb != head && tcp_rack_skb_timeout(tp, skb, 0) > 0)
2318 			continue; /* Don't mark recently sent ones lost yet */
2319 		tcp_mark_skb_lost(sk, skb);
2320 	}
2321 	tcp_verify_left_out(tp);
2322 	tcp_clear_all_retrans_hints(tp);
2323 }
2324 
2325 /* Enter Loss state. */
2326 void tcp_enter_loss(struct sock *sk)
2327 {
2328 	const struct inet_connection_sock *icsk = inet_csk(sk);
2329 	struct tcp_sock *tp = tcp_sk(sk);
2330 	struct net *net = sock_net(sk);
2331 	bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
2332 	u8 reordering;
2333 
2334 	tcp_timeout_mark_lost(sk);
2335 
2336 	/* Reduce ssthresh if it has not yet been made inside this window. */
2337 	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
2338 	    !after(tp->high_seq, tp->snd_una) ||
2339 	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2340 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
2341 		tp->prior_cwnd = tcp_snd_cwnd(tp);
2342 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2343 		tcp_ca_event(sk, CA_EVENT_LOSS);
2344 		tcp_init_undo(tp);
2345 	}
2346 	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1);
2347 	tp->snd_cwnd_cnt   = 0;
2348 	tp->snd_cwnd_stamp = tcp_jiffies32;
2349 
2350 	/* Timeout in disordered state after receiving substantial DUPACKs
2351 	 * suggests that the degree of reordering is over-estimated.
2352 	 */
2353 	reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering);
2354 	if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
2355 	    tp->sacked_out >= reordering)
2356 		tp->reordering = min_t(unsigned int, tp->reordering,
2357 				       reordering);
2358 
2359 	tcp_set_ca_state(sk, TCP_CA_Loss);
2360 	tp->high_seq = tp->snd_nxt;
2361 	tp->tlp_high_seq = 0;
2362 	tcp_ecn_queue_cwr(tp);
2363 
2364 	/* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
2365 	 * loss recovery is underway except recurring timeout(s) on
2366 	 * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
2367 	 */
2368 	tp->frto = READ_ONCE(net->ipv4.sysctl_tcp_frto) &&
2369 		   (new_recovery || icsk->icsk_retransmits) &&
2370 		   !inet_csk(sk)->icsk_mtup.probe_size;
2371 }
2372 
2373 /* If ACK arrived pointing to a remembered SACK, it means that our
2374  * remembered SACKs do not reflect real state of receiver i.e.
2375  * receiver _host_ is heavily congested (or buggy).
2376  *
2377  * To avoid big spurious retransmission bursts due to transient SACK
2378  * scoreboard oddities that look like reneging, we give the receiver a
2379  * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
2380  * restore sanity to the SACK scoreboard. If the apparent reneging
2381  * persists until this RTO then we'll clear the SACK scoreboard.
2382  */
2383 static bool tcp_check_sack_reneging(struct sock *sk, int *ack_flag)
2384 {
2385 	if (*ack_flag & FLAG_SACK_RENEGING &&
2386 	    *ack_flag & FLAG_SND_UNA_ADVANCED) {
2387 		struct tcp_sock *tp = tcp_sk(sk);
2388 		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
2389 					  msecs_to_jiffies(10));
2390 
2391 		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, delay, false);
2392 		*ack_flag &= ~FLAG_SET_XMIT_TIMER;
2393 		return true;
2394 	}
2395 	return false;
2396 }
2397 
2398 /* Linux NewReno/SACK/ECN state machine.
2399  * --------------------------------------
2400  *
2401  * "Open"	Normal state, no dubious events, fast path.
2402  * "Disorder"   In all the respects it is "Open",
2403  *		but requires a bit more attention. It is entered when
2404  *		we see some SACKs or dupacks. It is split of "Open"
2405  *		mainly to move some processing from fast path to slow one.
2406  * "CWR"	CWND was reduced due to some Congestion Notification event.
2407  *		It can be ECN, ICMP source quench, local device congestion.
2408  * "Recovery"	CWND was reduced, we are fast-retransmitting.
2409  * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
2410  *
2411  * tcp_fastretrans_alert() is entered:
2412  * - each incoming ACK, if state is not "Open"
2413  * - when arrived ACK is unusual, namely:
2414  *	* SACK
2415  *	* Duplicate ACK.
2416  *	* ECN ECE.
2417  *
2418  * Counting packets in flight is pretty simple.
2419  *
2420  *	in_flight = packets_out - left_out + retrans_out
2421  *
2422  *	packets_out is SND.NXT-SND.UNA counted in packets.
2423  *
2424  *	retrans_out is number of retransmitted segments.
2425  *
2426  *	left_out is number of segments left network, but not ACKed yet.
2427  *
2428  *		left_out = sacked_out + lost_out
2429  *
2430  *     sacked_out: Packets, which arrived to receiver out of order
2431  *		   and hence not ACKed. With SACKs this number is simply
2432  *		   amount of SACKed data. Even without SACKs
2433  *		   it is easy to give pretty reliable estimate of this number,
2434  *		   counting duplicate ACKs.
2435  *
2436  *       lost_out: Packets lost by network. TCP has no explicit
2437  *		   "loss notification" feedback from network (for now).
2438  *		   It means that this number can be only _guessed_.
2439  *		   Actually, it is the heuristics to predict lossage that
2440  *		   distinguishes different algorithms.
2441  *
2442  *	F.e. after RTO, when all the queue is considered as lost,
2443  *	lost_out = packets_out and in_flight = retrans_out.
2444  *
2445  *		Essentially, we have now a few algorithms detecting
2446  *		lost packets.
2447  *
2448  *		If the receiver supports SACK:
2449  *
2450  *		RACK (RFC8985): RACK is a newer loss detection algorithm
2451  *		(2017-) that checks timing instead of counting DUPACKs.
2452  *		Essentially a packet is considered lost if it's not S/ACKed
2453  *		after RTT + reordering_window, where both metrics are
2454  *		dynamically measured and adjusted. This is implemented in
2455  *		tcp_rack_mark_lost.
2456  *
2457  *		If the receiver does not support SACK:
2458  *
2459  *		NewReno (RFC6582): in Recovery we assume that one segment
2460  *		is lost (classic Reno). While we are in Recovery and
2461  *		a partial ACK arrives, we assume that one more packet
2462  *		is lost (NewReno). This heuristics are the same in NewReno
2463  *		and SACK.
2464  *
2465  * The really tricky (and requiring careful tuning) part of the algorithm
2466  * is hidden in the RACK code in tcp_recovery.c and tcp_xmit_retransmit_queue().
2467  * The first determines the moment _when_ we should reduce CWND and,
2468  * hence, slow down forward transmission. In fact, it determines the moment
2469  * when we decide that hole is caused by loss, rather than by a reorder.
2470  *
2471  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2472  * holes, caused by lost packets.
2473  *
2474  * And the most logically complicated part of algorithm is undo
2475  * heuristics. We detect false retransmits due to both too early
2476  * fast retransmit (reordering) and underestimated RTO, analyzing
2477  * timestamps and D-SACKs. When we detect that some segments were
2478  * retransmitted by mistake and CWND reduction was wrong, we undo
2479  * window reduction and abort recovery phase. This logic is hidden
2480  * inside several functions named tcp_try_undo_<something>.
2481  */
2482 
2483 /* This function decides, when we should leave Disordered state
2484  * and enter Recovery phase, reducing congestion window.
2485  *
2486  * Main question: may we further continue forward transmission
2487  * with the same cwnd?
2488  */
2489 static bool tcp_time_to_recover(const struct tcp_sock *tp)
2490 {
2491 	/* Has loss detection marked at least one packet lost? */
2492 	return tp->lost_out != 0;
2493 }
2494 
2495 static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
2496 {
2497 	return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2498 	       before(tp->rx_opt.rcv_tsecr, when);
2499 }
2500 
2501 /* skb is spurious retransmitted if the returned timestamp echo
2502  * reply is prior to the skb transmission time
2503  */
2504 static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
2505 				     const struct sk_buff *skb)
2506 {
2507 	return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
2508 	       tcp_tsopt_ecr_before(tp, tcp_skb_timestamp_ts(tp->tcp_usec_ts, skb));
2509 }
2510 
2511 /* Nothing was retransmitted or returned timestamp is less
2512  * than timestamp of the first retransmission.
2513  */
2514 static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
2515 {
2516 	const struct sock *sk = (const struct sock *)tp;
2517 
2518 	/* Received an echoed timestamp before the first retransmission? */
2519 	if (tp->retrans_stamp)
2520 		return tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
2521 
2522 	/* We set tp->retrans_stamp upon the first retransmission of a loss
2523 	 * recovery episode, so normally if tp->retrans_stamp is 0 then no
2524 	 * retransmission has happened yet (likely due to TSQ, which can cause
2525 	 * fast retransmits to be delayed). So if snd_una advanced while
2526 	 * (tp->retrans_stamp is 0 then apparently a packet was merely delayed,
2527 	 * not lost. But there are exceptions where we retransmit but then
2528 	 * clear tp->retrans_stamp, so we check for those exceptions.
2529 	 */
2530 
2531 	/* (1) For non-SACK connections, tcp_is_non_sack_preventing_reopen()
2532 	 * clears tp->retrans_stamp when snd_una == high_seq.
2533 	 */
2534 	if (!tcp_is_sack(tp) && !before(tp->snd_una, tp->high_seq))
2535 		return false;
2536 
2537 	/* (2) In TCP_SYN_SENT tcp_clean_rtx_queue() clears tp->retrans_stamp
2538 	 * when setting FLAG_SYN_ACKED is set, even if the SYN was
2539 	 * retransmitted.
2540 	 */
2541 	if (sk->sk_state == TCP_SYN_SENT)
2542 		return false;
2543 
2544 	return true;	/* tp->retrans_stamp is zero; no retransmit yet */
2545 }
2546 
2547 /* Undo procedures. */
2548 
2549 /* We can clear retrans_stamp when there are no retransmissions in the
2550  * window. It would seem that it is trivially available for us in
2551  * tp->retrans_out, however, that kind of assumptions doesn't consider
2552  * what will happen if errors occur when sending retransmission for the
2553  * second time. ...It could the that such segment has only
2554  * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2555  * the head skb is enough except for some reneging corner cases that
2556  * are not worth the effort.
2557  *
2558  * Main reason for all this complexity is the fact that connection dying
2559  * time now depends on the validity of the retrans_stamp, in particular,
2560  * that successive retransmissions of a segment must not advance
2561  * retrans_stamp under any conditions.
2562  */
2563 static bool tcp_any_retrans_done(const struct sock *sk)
2564 {
2565 	const struct tcp_sock *tp = tcp_sk(sk);
2566 	struct sk_buff *skb;
2567 
2568 	if (tp->retrans_out)
2569 		return true;
2570 
2571 	skb = tcp_rtx_queue_head(sk);
2572 	if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2573 		return true;
2574 
2575 	return false;
2576 }
2577 
2578 /* If loss recovery is finished and there are no retransmits out in the
2579  * network, then we clear retrans_stamp so that upon the next loss recovery
2580  * retransmits_timed_out() and timestamp-undo are using the correct value.
2581  */
2582 static void tcp_retrans_stamp_cleanup(struct sock *sk)
2583 {
2584 	if (!tcp_any_retrans_done(sk))
2585 		tcp_sk(sk)->retrans_stamp = 0;
2586 }
2587 
2588 static void DBGUNDO(struct sock *sk, const char *msg)
2589 {
2590 #if FASTRETRANS_DEBUG > 1
2591 	struct tcp_sock *tp = tcp_sk(sk);
2592 	struct inet_sock *inet = inet_sk(sk);
2593 
2594 	if (sk->sk_family == AF_INET) {
2595 		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2596 			 msg,
2597 			 &inet->inet_daddr, ntohs(inet->inet_dport),
2598 			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2599 			 tp->snd_ssthresh, tp->prior_ssthresh,
2600 			 tp->packets_out);
2601 	}
2602 #if IS_ENABLED(CONFIG_IPV6)
2603 	else if (sk->sk_family == AF_INET6) {
2604 		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2605 			 msg,
2606 			 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
2607 			 tcp_snd_cwnd(tp), tcp_left_out(tp),
2608 			 tp->snd_ssthresh, tp->prior_ssthresh,
2609 			 tp->packets_out);
2610 	}
2611 #endif
2612 #endif
2613 }
2614 
2615 static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
2616 {
2617 	struct tcp_sock *tp = tcp_sk(sk);
2618 
2619 	if (unmark_loss) {
2620 		struct sk_buff *skb;
2621 
2622 		skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2623 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2624 		}
2625 		tp->lost_out = 0;
2626 		tcp_clear_all_retrans_hints(tp);
2627 	}
2628 
2629 	if (tp->prior_ssthresh) {
2630 		const struct inet_connection_sock *icsk = inet_csk(sk);
2631 
2632 		tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk));
2633 
2634 		if (tp->prior_ssthresh > tp->snd_ssthresh) {
2635 			tp->snd_ssthresh = tp->prior_ssthresh;
2636 			tcp_ecn_withdraw_cwr(tp);
2637 		}
2638 	}
2639 	tp->snd_cwnd_stamp = tcp_jiffies32;
2640 	tp->undo_marker = 0;
2641 	tp->rack.advanced = 1; /* Force RACK to re-exam losses */
2642 }
2643 
2644 static inline bool tcp_may_undo(const struct tcp_sock *tp)
2645 {
2646 	return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2647 }
2648 
2649 static bool tcp_is_non_sack_preventing_reopen(struct sock *sk)
2650 {
2651 	struct tcp_sock *tp = tcp_sk(sk);
2652 
2653 	if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2654 		/* Hold old state until something *above* high_seq
2655 		 * is ACKed. For Reno it is MUST to prevent false
2656 		 * fast retransmits (RFC2582). SACK TCP is safe. */
2657 		if (!tcp_any_retrans_done(sk))
2658 			tp->retrans_stamp = 0;
2659 		return true;
2660 	}
2661 	return false;
2662 }
2663 
2664 /* People celebrate: "We love our President!" */
2665 static bool tcp_try_undo_recovery(struct sock *sk)
2666 {
2667 	struct tcp_sock *tp = tcp_sk(sk);
2668 
2669 	if (tcp_may_undo(tp)) {
2670 		int mib_idx;
2671 
2672 		/* Happy end! We did not retransmit anything
2673 		 * or our original transmission succeeded.
2674 		 */
2675 		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2676 		tcp_undo_cwnd_reduction(sk, false);
2677 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2678 			mib_idx = LINUX_MIB_TCPLOSSUNDO;
2679 		else
2680 			mib_idx = LINUX_MIB_TCPFULLUNDO;
2681 
2682 		NET_INC_STATS(sock_net(sk), mib_idx);
2683 	} else if (tp->rack.reo_wnd_persist) {
2684 		tp->rack.reo_wnd_persist--;
2685 	}
2686 	if (tcp_is_non_sack_preventing_reopen(sk))
2687 		return true;
2688 	tcp_set_ca_state(sk, TCP_CA_Open);
2689 	tp->is_sack_reneg = 0;
2690 	return false;
2691 }
2692 
2693 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2694 static bool tcp_try_undo_dsack(struct sock *sk)
2695 {
2696 	struct tcp_sock *tp = tcp_sk(sk);
2697 
2698 	if (tp->undo_marker && !tp->undo_retrans) {
2699 		tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
2700 					       tp->rack.reo_wnd_persist + 1);
2701 		DBGUNDO(sk, "D-SACK");
2702 		tcp_undo_cwnd_reduction(sk, false);
2703 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2704 		return true;
2705 	}
2706 	return false;
2707 }
2708 
2709 /* Undo during loss recovery after partial ACK or using F-RTO. */
2710 static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
2711 {
2712 	struct tcp_sock *tp = tcp_sk(sk);
2713 
2714 	if (frto_undo || tcp_may_undo(tp)) {
2715 		tcp_undo_cwnd_reduction(sk, true);
2716 
2717 		DBGUNDO(sk, "partial loss");
2718 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2719 		if (frto_undo)
2720 			NET_INC_STATS(sock_net(sk),
2721 					LINUX_MIB_TCPSPURIOUSRTOS);
2722 		WRITE_ONCE(inet_csk(sk)->icsk_retransmits, 0);
2723 		if (tcp_is_non_sack_preventing_reopen(sk))
2724 			return true;
2725 		if (frto_undo || tcp_is_sack(tp)) {
2726 			tcp_set_ca_state(sk, TCP_CA_Open);
2727 			tp->is_sack_reneg = 0;
2728 		}
2729 		return true;
2730 	}
2731 	return false;
2732 }
2733 
2734 /* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
2735  * It computes the number of packets to send (sndcnt) based on packets newly
2736  * delivered:
2737  *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2738  *	cwnd reductions across a full RTT.
2739  *   2) Otherwise PRR uses packet conservation to send as much as delivered.
2740  *      But when SND_UNA is acked without further losses,
2741  *      slow starts cwnd up to ssthresh to speed up the recovery.
2742  */
2743 static void tcp_init_cwnd_reduction(struct sock *sk)
2744 {
2745 	struct tcp_sock *tp = tcp_sk(sk);
2746 
2747 	tp->high_seq = tp->snd_nxt;
2748 	tp->tlp_high_seq = 0;
2749 	tp->snd_cwnd_cnt = 0;
2750 	tp->prior_cwnd = tcp_snd_cwnd(tp);
2751 	tp->prr_delivered = 0;
2752 	tp->prr_out = 0;
2753 	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
2754 	tcp_ecn_queue_cwr(tp);
2755 }
2756 
2757 void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int newly_lost, int flag)
2758 {
2759 	struct tcp_sock *tp = tcp_sk(sk);
2760 	int sndcnt = 0;
2761 	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2762 
2763 	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
2764 		return;
2765 
2766 	trace_tcp_cwnd_reduction_tp(sk, newly_acked_sacked, newly_lost, flag);
2767 
2768 	tp->prr_delivered += newly_acked_sacked;
2769 	if (delta < 0) {
2770 		u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2771 			       tp->prior_cwnd - 1;
2772 		sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2773 	} else {
2774 		sndcnt = max_t(int, tp->prr_delivered - tp->prr_out,
2775 			       newly_acked_sacked);
2776 		if (flag & FLAG_SND_UNA_ADVANCED && !newly_lost)
2777 			sndcnt++;
2778 		sndcnt = min(delta, sndcnt);
2779 	}
2780 	/* Force a fast retransmit upon entering fast recovery */
2781 	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
2782 	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt);
2783 }
2784 
2785 static inline void tcp_end_cwnd_reduction(struct sock *sk)
2786 {
2787 	struct tcp_sock *tp = tcp_sk(sk);
2788 
2789 	if (inet_csk(sk)->icsk_ca_ops->cong_control)
2790 		return;
2791 
2792 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
2793 	if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
2794 	    (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
2795 		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
2796 		tp->snd_cwnd_stamp = tcp_jiffies32;
2797 	}
2798 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2799 }
2800 
2801 /* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
2802 void tcp_enter_cwr(struct sock *sk)
2803 {
2804 	struct tcp_sock *tp = tcp_sk(sk);
2805 
2806 	tp->prior_ssthresh = 0;
2807 	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
2808 		tp->undo_marker = 0;
2809 		tcp_init_cwnd_reduction(sk);
2810 		tcp_set_ca_state(sk, TCP_CA_CWR);
2811 	}
2812 }
2813 EXPORT_SYMBOL(tcp_enter_cwr);
2814 
2815 static void tcp_try_keep_open(struct sock *sk)
2816 {
2817 	struct tcp_sock *tp = tcp_sk(sk);
2818 	int state = TCP_CA_Open;
2819 
2820 	if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
2821 		state = TCP_CA_Disorder;
2822 
2823 	if (inet_csk(sk)->icsk_ca_state != state) {
2824 		tcp_set_ca_state(sk, state);
2825 		tp->high_seq = tp->snd_nxt;
2826 	}
2827 }
2828 
2829 static void tcp_try_to_open(struct sock *sk, int flag)
2830 {
2831 	struct tcp_sock *tp = tcp_sk(sk);
2832 
2833 	tcp_verify_left_out(tp);
2834 
2835 	if (!tcp_any_retrans_done(sk))
2836 		tp->retrans_stamp = 0;
2837 
2838 	if (flag & FLAG_ECE)
2839 		tcp_enter_cwr(sk);
2840 
2841 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2842 		tcp_try_keep_open(sk);
2843 	}
2844 }
2845 
2846 static void tcp_mtup_probe_failed(struct sock *sk)
2847 {
2848 	struct inet_connection_sock *icsk = inet_csk(sk);
2849 
2850 	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2851 	icsk->icsk_mtup.probe_size = 0;
2852 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
2853 }
2854 
2855 static void tcp_mtup_probe_success(struct sock *sk)
2856 {
2857 	struct tcp_sock *tp = tcp_sk(sk);
2858 	struct inet_connection_sock *icsk = inet_csk(sk);
2859 	u64 val;
2860 
2861 	tp->prior_ssthresh = tcp_current_ssthresh(sk);
2862 
2863 	val = (u64)tcp_snd_cwnd(tp) * tcp_mss_to_mtu(sk, tp->mss_cache);
2864 	do_div(val, icsk->icsk_mtup.probe_size);
2865 	DEBUG_NET_WARN_ON_ONCE((u32)val != val);
2866 	tcp_snd_cwnd_set(tp, max_t(u32, 1U, val));
2867 
2868 	tp->snd_cwnd_cnt = 0;
2869 	tp->snd_cwnd_stamp = tcp_jiffies32;
2870 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
2871 
2872 	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2873 	icsk->icsk_mtup.probe_size = 0;
2874 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2875 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
2876 }
2877 
2878 /* Sometimes we deduce that packets have been dropped due to reasons other than
2879  * congestion, like path MTU reductions or failed client TFO attempts. In these
2880  * cases we call this function to retransmit as many packets as cwnd allows,
2881  * without reducing cwnd. Given that retransmits will set retrans_stamp to a
2882  * non-zero value (and may do so in a later calling context due to TSQ), we
2883  * also enter CA_Loss so that we track when all retransmitted packets are ACKed
2884  * and clear retrans_stamp when that happens (to ensure later recurring RTOs
2885  * are using the correct retrans_stamp and don't declare ETIMEDOUT
2886  * prematurely).
2887  */
2888 static void tcp_non_congestion_loss_retransmit(struct sock *sk)
2889 {
2890 	const struct inet_connection_sock *icsk = inet_csk(sk);
2891 	struct tcp_sock *tp = tcp_sk(sk);
2892 
2893 	if (icsk->icsk_ca_state != TCP_CA_Loss) {
2894 		tp->high_seq = tp->snd_nxt;
2895 		tp->snd_ssthresh = tcp_current_ssthresh(sk);
2896 		tp->prior_ssthresh = 0;
2897 		tp->undo_marker = 0;
2898 		tcp_set_ca_state(sk, TCP_CA_Loss);
2899 	}
2900 	tcp_xmit_retransmit_queue(sk);
2901 }
2902 
2903 /* Do a simple retransmit without using the backoff mechanisms in
2904  * tcp_timer. This is used for path mtu discovery.
2905  * The socket is already locked here.
2906  */
2907 void tcp_simple_retransmit(struct sock *sk)
2908 {
2909 	struct tcp_sock *tp = tcp_sk(sk);
2910 	struct sk_buff *skb;
2911 	int mss;
2912 
2913 	/* A fastopen SYN request is stored as two separate packets within
2914 	 * the retransmit queue, this is done by tcp_send_syn_data().
2915 	 * As a result simply checking the MSS of the frames in the queue
2916 	 * will not work for the SYN packet.
2917 	 *
2918 	 * Us being here is an indication of a path MTU issue so we can
2919 	 * assume that the fastopen SYN was lost and just mark all the
2920 	 * frames in the retransmit queue as lost. We will use an MSS of
2921 	 * -1 to mark all frames as lost, otherwise compute the current MSS.
2922 	 */
2923 	if (tp->syn_data && sk->sk_state == TCP_SYN_SENT)
2924 		mss = -1;
2925 	else
2926 		mss = tcp_current_mss(sk);
2927 
2928 	skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
2929 		if (tcp_skb_seglen(skb) > mss)
2930 			tcp_mark_skb_lost(sk, skb);
2931 	}
2932 
2933 	if (!tp->lost_out)
2934 		return;
2935 
2936 	if (tcp_is_reno(tp))
2937 		tcp_limit_reno_sacked(tp);
2938 
2939 	tcp_verify_left_out(tp);
2940 
2941 	/* Don't muck with the congestion window here.
2942 	 * Reason is that we do not increase amount of _data_
2943 	 * in network, but units changed and effective
2944 	 * cwnd/ssthresh really reduced now.
2945 	 */
2946 	tcp_non_congestion_loss_retransmit(sk);
2947 }
2948 EXPORT_IPV6_MOD(tcp_simple_retransmit);
2949 
2950 void tcp_enter_recovery(struct sock *sk, bool ece_ack)
2951 {
2952 	struct tcp_sock *tp = tcp_sk(sk);
2953 	int mib_idx;
2954 
2955 	/* Start the clock with our fast retransmit, for undo and ETIMEDOUT. */
2956 	tcp_retrans_stamp_cleanup(sk);
2957 
2958 	if (tcp_is_reno(tp))
2959 		mib_idx = LINUX_MIB_TCPRENORECOVERY;
2960 	else
2961 		mib_idx = LINUX_MIB_TCPSACKRECOVERY;
2962 
2963 	NET_INC_STATS(sock_net(sk), mib_idx);
2964 
2965 	tp->prior_ssthresh = 0;
2966 	tcp_init_undo(tp);
2967 
2968 	if (!tcp_in_cwnd_reduction(sk)) {
2969 		if (!ece_ack)
2970 			tp->prior_ssthresh = tcp_current_ssthresh(sk);
2971 		tcp_init_cwnd_reduction(sk);
2972 	}
2973 	tcp_set_ca_state(sk, TCP_CA_Recovery);
2974 }
2975 
2976 static void tcp_update_rto_time(struct tcp_sock *tp)
2977 {
2978 	if (tp->rto_stamp) {
2979 		tp->total_rto_time += tcp_time_stamp_ms(tp) - tp->rto_stamp;
2980 		tp->rto_stamp = 0;
2981 	}
2982 }
2983 
2984 /* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
2985  * recovered or spurious. Otherwise retransmits more on partial ACKs.
2986  */
2987 static void tcp_process_loss(struct sock *sk, int flag, int num_dupack,
2988 			     int *rexmit)
2989 {
2990 	struct tcp_sock *tp = tcp_sk(sk);
2991 	bool recovered = !before(tp->snd_una, tp->high_seq);
2992 
2993 	if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) &&
2994 	    tcp_try_undo_loss(sk, false))
2995 		return;
2996 
2997 	if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
2998 		/* Step 3.b. A timeout is spurious if not all data are
2999 		 * lost, i.e., never-retransmitted data are (s)acked.
3000 		 */
3001 		if ((flag & FLAG_ORIG_SACK_ACKED) &&
3002 		    tcp_try_undo_loss(sk, true))
3003 			return;
3004 
3005 		if (after(tp->snd_nxt, tp->high_seq)) {
3006 			if (flag & FLAG_DATA_SACKED || num_dupack)
3007 				tp->frto = 0; /* Step 3.a. loss was real */
3008 		} else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
3009 			tp->high_seq = tp->snd_nxt;
3010 			/* Step 2.b. Try send new data (but deferred until cwnd
3011 			 * is updated in tcp_ack()). Otherwise fall back to
3012 			 * the conventional recovery.
3013 			 */
3014 			if (!tcp_write_queue_empty(sk) &&
3015 			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
3016 				*rexmit = REXMIT_NEW;
3017 				return;
3018 			}
3019 			tp->frto = 0;
3020 		}
3021 	}
3022 
3023 	if (recovered) {
3024 		/* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
3025 		tcp_try_undo_recovery(sk);
3026 		return;
3027 	}
3028 	if (tcp_is_reno(tp)) {
3029 		/* A Reno DUPACK means new data in F-RTO step 2.b above are
3030 		 * delivered. Lower inflight to clock out (re)transmissions.
3031 		 */
3032 		if (after(tp->snd_nxt, tp->high_seq) && num_dupack)
3033 			tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE);
3034 		else if (flag & FLAG_SND_UNA_ADVANCED)
3035 			tcp_reset_reno_sack(tp);
3036 	}
3037 	*rexmit = REXMIT_LOST;
3038 }
3039 
3040 /* Undo during fast recovery after partial ACK. */
3041 static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
3042 {
3043 	struct tcp_sock *tp = tcp_sk(sk);
3044 
3045 	if (tp->undo_marker && tcp_packet_delayed(tp)) {
3046 		/* Plain luck! Hole if filled with delayed
3047 		 * packet, rather than with a retransmit. Check reordering.
3048 		 */
3049 		tcp_check_sack_reordering(sk, prior_snd_una, 1);
3050 
3051 		/* We are getting evidence that the reordering degree is higher
3052 		 * than we realized. If there are no retransmits out then we
3053 		 * can undo. Otherwise we clock out new packets but do not
3054 		 * mark more packets lost or retransmit more.
3055 		 */
3056 		if (tp->retrans_out)
3057 			return true;
3058 
3059 		if (!tcp_any_retrans_done(sk))
3060 			tp->retrans_stamp = 0;
3061 
3062 		DBGUNDO(sk, "partial recovery");
3063 		tcp_undo_cwnd_reduction(sk, true);
3064 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
3065 		tcp_try_keep_open(sk);
3066 	}
3067 	return false;
3068 }
3069 
3070 static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
3071 {
3072 	struct tcp_sock *tp = tcp_sk(sk);
3073 
3074 	if (tcp_rtx_queue_empty(sk))
3075 		return;
3076 
3077 	if (unlikely(tcp_is_reno(tp))) {
3078 		tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
3079 	} else {
3080 		u32 prior_retrans = tp->retrans_out;
3081 
3082 		if (tcp_rack_mark_lost(sk))
3083 			*ack_flag &= ~FLAG_SET_XMIT_TIMER;
3084 		if (prior_retrans > tp->retrans_out)
3085 			*ack_flag |= FLAG_LOST_RETRANS;
3086 	}
3087 }
3088 
3089 /* Process an event, which can update packets-in-flight not trivially.
3090  * Main goal of this function is to calculate new estimate for left_out,
3091  * taking into account both packets sitting in receiver's buffer and
3092  * packets lost by network.
3093  *
3094  * Besides that it updates the congestion state when packet loss or ECN
3095  * is detected. But it does not reduce the cwnd, it is done by the
3096  * congestion control later.
3097  *
3098  * It does _not_ decide what to send, it is made in function
3099  * tcp_xmit_retransmit_queue().
3100  */
3101 static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
3102 				  int num_dupack, int *ack_flag, int *rexmit)
3103 {
3104 	struct inet_connection_sock *icsk = inet_csk(sk);
3105 	struct tcp_sock *tp = tcp_sk(sk);
3106 	int flag = *ack_flag;
3107 	bool ece_ack = flag & FLAG_ECE;
3108 
3109 	if (!tp->packets_out && tp->sacked_out)
3110 		tp->sacked_out = 0;
3111 
3112 	/* Now state machine starts.
3113 	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
3114 	if (ece_ack)
3115 		tp->prior_ssthresh = 0;
3116 
3117 	/* B. In all the states check for reneging SACKs. */
3118 	if (tcp_check_sack_reneging(sk, ack_flag))
3119 		return;
3120 
3121 	/* C. Check consistency of the current state. */
3122 	tcp_verify_left_out(tp);
3123 
3124 	/* D. Check state exit conditions. State can be terminated
3125 	 *    when high_seq is ACKed. */
3126 	if (icsk->icsk_ca_state == TCP_CA_Open) {
3127 		WARN_ON(tp->retrans_out != 0 && !tp->syn_data);
3128 		tp->retrans_stamp = 0;
3129 	} else if (!before(tp->snd_una, tp->high_seq)) {
3130 		switch (icsk->icsk_ca_state) {
3131 		case TCP_CA_CWR:
3132 			/* CWR is to be held something *above* high_seq
3133 			 * is ACKed for CWR bit to reach receiver. */
3134 			if (tp->snd_una != tp->high_seq) {
3135 				tcp_end_cwnd_reduction(sk);
3136 				tcp_set_ca_state(sk, TCP_CA_Open);
3137 			}
3138 			break;
3139 
3140 		case TCP_CA_Recovery:
3141 			if (tcp_is_reno(tp))
3142 				tcp_reset_reno_sack(tp);
3143 			if (tcp_try_undo_recovery(sk))
3144 				return;
3145 			tcp_end_cwnd_reduction(sk);
3146 			break;
3147 		}
3148 	}
3149 
3150 	/* E. Process state. */
3151 	switch (icsk->icsk_ca_state) {
3152 	case TCP_CA_Recovery:
3153 		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3154 			if (tcp_is_reno(tp))
3155 				tcp_add_reno_sack(sk, num_dupack, ece_ack);
3156 		} else if (tcp_try_undo_partial(sk, prior_snd_una))
3157 			return;
3158 
3159 		if (tcp_try_undo_dsack(sk))
3160 			tcp_try_to_open(sk, flag);
3161 
3162 		tcp_identify_packet_loss(sk, ack_flag);
3163 		if (icsk->icsk_ca_state != TCP_CA_Recovery) {
3164 			if (!tcp_time_to_recover(tp))
3165 				return;
3166 			/* Undo reverts the recovery state. If loss is evident,
3167 			 * starts a new recovery (e.g. reordering then loss);
3168 			 */
3169 			tcp_enter_recovery(sk, ece_ack);
3170 		}
3171 		break;
3172 	case TCP_CA_Loss:
3173 		tcp_process_loss(sk, flag, num_dupack, rexmit);
3174 		if (icsk->icsk_ca_state != TCP_CA_Loss)
3175 			tcp_update_rto_time(tp);
3176 		tcp_identify_packet_loss(sk, ack_flag);
3177 		if (!(icsk->icsk_ca_state == TCP_CA_Open ||
3178 		      (*ack_flag & FLAG_LOST_RETRANS)))
3179 			return;
3180 		/* Change state if cwnd is undone or retransmits are lost */
3181 		fallthrough;
3182 	default:
3183 		if (tcp_is_reno(tp)) {
3184 			if (flag & FLAG_SND_UNA_ADVANCED)
3185 				tcp_reset_reno_sack(tp);
3186 			tcp_add_reno_sack(sk, num_dupack, ece_ack);
3187 		}
3188 
3189 		if (icsk->icsk_ca_state <= TCP_CA_Disorder)
3190 			tcp_try_undo_dsack(sk);
3191 
3192 		tcp_identify_packet_loss(sk, ack_flag);
3193 		if (!tcp_time_to_recover(tp)) {
3194 			tcp_try_to_open(sk, flag);
3195 			return;
3196 		}
3197 
3198 		/* MTU probe failure: don't reduce cwnd */
3199 		if (icsk->icsk_ca_state < TCP_CA_CWR &&
3200 		    icsk->icsk_mtup.probe_size &&
3201 		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3202 			tcp_mtup_probe_failed(sk);
3203 			/* Restores the reduction we did in tcp_mtup_probe() */
3204 			tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
3205 			tcp_simple_retransmit(sk);
3206 			return;
3207 		}
3208 
3209 		/* Otherwise enter Recovery state */
3210 		tcp_enter_recovery(sk, ece_ack);
3211 	}
3212 
3213 	*rexmit = REXMIT_LOST;
3214 }
3215 
3216 static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
3217 {
3218 	u32 wlen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen) * HZ;
3219 	struct tcp_sock *tp = tcp_sk(sk);
3220 
3221 	if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
3222 		/* If the remote keeps returning delayed ACKs, eventually
3223 		 * the min filter would pick it up and overestimate the
3224 		 * prop. delay when it expires. Skip suspected delayed ACKs.
3225 		 */
3226 		return;
3227 	}
3228 	minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
3229 			   rtt_us ? : jiffies_to_usecs(1));
3230 }
3231 
3232 static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
3233 			       long seq_rtt_us, long sack_rtt_us,
3234 			       long ca_rtt_us, struct rate_sample *rs)
3235 {
3236 	const struct tcp_sock *tp = tcp_sk(sk);
3237 
3238 	/* Prefer RTT measured from ACK's timing to TS-ECR. This is because
3239 	 * broken middle-boxes or peers may corrupt TS-ECR fields. But
3240 	 * Karn's algorithm forbids taking RTT if some retransmitted data
3241 	 * is acked (RFC6298).
3242 	 */
3243 	if (seq_rtt_us < 0)
3244 		seq_rtt_us = sack_rtt_us;
3245 
3246 	/* RTTM Rule: A TSecr value received in a segment is used to
3247 	 * update the averaged RTT measurement only if the segment
3248 	 * acknowledges some new data, i.e., only if it advances the
3249 	 * left edge of the send window.
3250 	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
3251 	 */
3252 	if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp &&
3253 	    tp->rx_opt.rcv_tsecr && flag & FLAG_ACKED)
3254 		seq_rtt_us = ca_rtt_us = tcp_rtt_tsopt_us(tp, 1);
3255 
3256 	rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
3257 	if (seq_rtt_us < 0)
3258 		return false;
3259 
3260 	/* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
3261 	 * always taken together with ACK, SACK, or TS-opts. Any negative
3262 	 * values will be skipped with the seq_rtt_us < 0 check above.
3263 	 */
3264 	tcp_update_rtt_min(sk, ca_rtt_us, flag);
3265 	tcp_rtt_estimator(sk, seq_rtt_us);
3266 	tcp_set_rto(sk);
3267 
3268 	/* RFC6298: only reset backoff on valid RTT measurement. */
3269 	inet_csk(sk)->icsk_backoff = 0;
3270 	return true;
3271 }
3272 
3273 /* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
3274 void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
3275 {
3276 	struct rate_sample rs;
3277 	long rtt_us = -1L;
3278 
3279 	if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
3280 		rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
3281 
3282 	tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
3283 }
3284 
3285 
3286 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
3287 {
3288 	const struct inet_connection_sock *icsk = inet_csk(sk);
3289 
3290 	icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
3291 	tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
3292 }
3293 
3294 /* Restart timer after forward progress on connection.
3295  * RFC2988 recommends to restart timer to now+rto.
3296  */
3297 void tcp_rearm_rto(struct sock *sk)
3298 {
3299 	const struct inet_connection_sock *icsk = inet_csk(sk);
3300 	struct tcp_sock *tp = tcp_sk(sk);
3301 
3302 	/* If the retrans timer is currently being used by Fast Open
3303 	 * for SYN-ACK retrans purpose, stay put.
3304 	 */
3305 	if (rcu_access_pointer(tp->fastopen_rsk))
3306 		return;
3307 
3308 	if (!tp->packets_out) {
3309 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3310 	} else {
3311 		u32 rto = inet_csk(sk)->icsk_rto;
3312 		/* Offset the time elapsed after installing regular RTO */
3313 		if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
3314 		    icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
3315 			s64 delta_us = tcp_rto_delta_us(sk);
3316 			/* delta_us may not be positive if the socket is locked
3317 			 * when the retrans timer fires and is rescheduled.
3318 			 */
3319 			rto = usecs_to_jiffies(max_t(int, delta_us, 1));
3320 		}
3321 		tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto, true);
3322 	}
3323 }
3324 
3325 /* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
3326 static void tcp_set_xmit_timer(struct sock *sk)
3327 {
3328 	if (!tcp_schedule_loss_probe(sk, true))
3329 		tcp_rearm_rto(sk);
3330 }
3331 
3332 /* If we get here, the whole TSO packet has not been acked. */
3333 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3334 {
3335 	struct tcp_sock *tp = tcp_sk(sk);
3336 	u32 packets_acked;
3337 
3338 	BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3339 
3340 	packets_acked = tcp_skb_pcount(skb);
3341 	if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3342 		return 0;
3343 	packets_acked -= tcp_skb_pcount(skb);
3344 
3345 	if (packets_acked) {
3346 		BUG_ON(tcp_skb_pcount(skb) == 0);
3347 		BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3348 	}
3349 
3350 	return packets_acked;
3351 }
3352 
3353 static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
3354 			   const struct sk_buff *ack_skb, u32 prior_snd_una)
3355 {
3356 	const struct skb_shared_info *shinfo;
3357 
3358 	/* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
3359 	if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
3360 		return;
3361 
3362 	shinfo = skb_shinfo(skb);
3363 	if (!before(shinfo->tskey, prior_snd_una) &&
3364 	    before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
3365 		tcp_skb_tsorted_save(skb) {
3366 			__skb_tstamp_tx(skb, ack_skb, NULL, sk, SCM_TSTAMP_ACK);
3367 		} tcp_skb_tsorted_restore(skb);
3368 	}
3369 }
3370 
3371 /* Remove acknowledged frames from the retransmission queue. If our packet
3372  * is before the ack sequence we can discard it as it's confirmed to have
3373  * arrived at the other end.
3374  */
3375 static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
3376 			       u32 prior_fack, u32 prior_snd_una,
3377 			       struct tcp_sacktag_state *sack, bool ece_ack)
3378 {
3379 	const struct inet_connection_sock *icsk = inet_csk(sk);
3380 	u64 first_ackt, last_ackt;
3381 	struct tcp_sock *tp = tcp_sk(sk);
3382 	u32 prior_sacked = tp->sacked_out;
3383 	u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
3384 	struct sk_buff *skb, *next;
3385 	bool fully_acked = true;
3386 	long sack_rtt_us = -1L;
3387 	long seq_rtt_us = -1L;
3388 	long ca_rtt_us = -1L;
3389 	u32 pkts_acked = 0;
3390 	bool rtt_update;
3391 	int flag = 0;
3392 
3393 	first_ackt = 0;
3394 
3395 	for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
3396 		struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3397 		const u32 start_seq = scb->seq;
3398 		u8 sacked = scb->sacked;
3399 		u32 acked_pcount;
3400 
3401 		/* Determine how many packets and what bytes were acked, tso and else */
3402 		if (after(scb->end_seq, tp->snd_una)) {
3403 			if (tcp_skb_pcount(skb) == 1 ||
3404 			    !after(tp->snd_una, scb->seq))
3405 				break;
3406 
3407 			acked_pcount = tcp_tso_acked(sk, skb);
3408 			if (!acked_pcount)
3409 				break;
3410 			fully_acked = false;
3411 		} else {
3412 			acked_pcount = tcp_skb_pcount(skb);
3413 		}
3414 
3415 		if (unlikely(sacked & TCPCB_RETRANS)) {
3416 			if (sacked & TCPCB_SACKED_RETRANS)
3417 				tp->retrans_out -= acked_pcount;
3418 			flag |= FLAG_RETRANS_DATA_ACKED;
3419 		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
3420 			last_ackt = tcp_skb_timestamp_us(skb);
3421 			WARN_ON_ONCE(last_ackt == 0);
3422 			if (!first_ackt)
3423 				first_ackt = last_ackt;
3424 
3425 			if (before(start_seq, reord))
3426 				reord = start_seq;
3427 			if (!after(scb->end_seq, tp->high_seq))
3428 				flag |= FLAG_ORIG_SACK_ACKED;
3429 		}
3430 
3431 		if (sacked & TCPCB_SACKED_ACKED) {
3432 			tp->sacked_out -= acked_pcount;
3433 			/* snd_una delta covers these skbs */
3434 			sack->delivered_bytes -= skb->len;
3435 		} else if (tcp_is_sack(tp)) {
3436 			tcp_count_delivered(tp, acked_pcount, ece_ack);
3437 			if (!tcp_skb_spurious_retrans(tp, skb))
3438 				tcp_rack_advance(tp, sacked, scb->end_seq,
3439 						 tcp_skb_timestamp_us(skb));
3440 		}
3441 		if (sacked & TCPCB_LOST)
3442 			tp->lost_out -= acked_pcount;
3443 
3444 		tp->packets_out -= acked_pcount;
3445 		pkts_acked += acked_pcount;
3446 		tcp_rate_skb_delivered(sk, skb, sack->rate);
3447 
3448 		/* Initial outgoing SYN's get put onto the write_queue
3449 		 * just like anything else we transmit.  It is not
3450 		 * true data, and if we misinform our callers that
3451 		 * this ACK acks real data, we will erroneously exit
3452 		 * connection startup slow start one packet too
3453 		 * quickly.  This is severely frowned upon behavior.
3454 		 */
3455 		if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
3456 			flag |= FLAG_DATA_ACKED;
3457 		} else {
3458 			flag |= FLAG_SYN_ACKED;
3459 			tp->retrans_stamp = 0;
3460 		}
3461 
3462 		if (!fully_acked)
3463 			break;
3464 
3465 		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3466 
3467 		next = skb_rb_next(skb);
3468 		if (unlikely(skb == tp->retransmit_skb_hint))
3469 			tp->retransmit_skb_hint = NULL;
3470 		tcp_highest_sack_replace(sk, skb, next);
3471 		tcp_rtx_queue_unlink_and_free(skb, sk);
3472 	}
3473 
3474 	if (!skb)
3475 		tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
3476 
3477 	if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3478 		tp->snd_up = tp->snd_una;
3479 
3480 	if (skb) {
3481 		tcp_ack_tstamp(sk, skb, ack_skb, prior_snd_una);
3482 		if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
3483 			flag |= FLAG_SACK_RENEGING;
3484 	}
3485 
3486 	if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
3487 		seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
3488 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
3489 
3490 		if (pkts_acked == 1 && fully_acked && !prior_sacked &&
3491 		    (tp->snd_una - prior_snd_una) < tp->mss_cache &&
3492 		    sack->rate->prior_delivered + 1 == tp->delivered &&
3493 		    !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
3494 			/* Conservatively mark a delayed ACK. It's typically
3495 			 * from a lone runt packet over the round trip to
3496 			 * a receiver w/o out-of-order or CE events.
3497 			 */
3498 			flag |= FLAG_ACK_MAYBE_DELAYED;
3499 		}
3500 	}
3501 	if (sack->first_sackt) {
3502 		sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
3503 		ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
3504 	}
3505 	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
3506 					ca_rtt_us, sack->rate);
3507 
3508 	if (flag & FLAG_ACKED) {
3509 		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3510 		if (unlikely(icsk->icsk_mtup.probe_size &&
3511 			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3512 			tcp_mtup_probe_success(sk);
3513 		}
3514 
3515 		if (tcp_is_reno(tp)) {
3516 			tcp_remove_reno_sacks(sk, pkts_acked, ece_ack);
3517 
3518 			/* If any of the cumulatively ACKed segments was
3519 			 * retransmitted, non-SACK case cannot confirm that
3520 			 * progress was due to original transmission due to
3521 			 * lack of TCPCB_SACKED_ACKED bits even if some of
3522 			 * the packets may have been never retransmitted.
3523 			 */
3524 			if (flag & FLAG_RETRANS_DATA_ACKED)
3525 				flag &= ~FLAG_ORIG_SACK_ACKED;
3526 		} else {
3527 			/* Non-retransmitted hole got filled? That's reordering */
3528 			if (before(reord, prior_fack))
3529 				tcp_check_sack_reordering(sk, reord, 0);
3530 		}
3531 
3532 		sack->delivered_bytes = (skb ?
3533 					 TCP_SKB_CB(skb)->seq : tp->snd_una) -
3534 					 prior_snd_una;
3535 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
3536 		   sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
3537 						    tcp_skb_timestamp_us(skb))) {
3538 		/* Do not re-arm RTO if the sack RTT is measured from data sent
3539 		 * after when the head was last (re)transmitted. Otherwise the
3540 		 * timeout may continue to extend in loss recovery.
3541 		 */
3542 		flag |= FLAG_SET_XMIT_TIMER;  /* set TLP or RTO timer */
3543 	}
3544 
3545 	if (icsk->icsk_ca_ops->pkts_acked) {
3546 		struct ack_sample sample = { .pkts_acked = pkts_acked,
3547 					     .rtt_us = sack->rate->rtt_us };
3548 
3549 		sample.in_flight = tp->mss_cache *
3550 			(tp->delivered - sack->rate->prior_delivered);
3551 		icsk->icsk_ca_ops->pkts_acked(sk, &sample);
3552 	}
3553 
3554 #if FASTRETRANS_DEBUG > 0
3555 	WARN_ON((int)tp->sacked_out < 0);
3556 	WARN_ON((int)tp->lost_out < 0);
3557 	WARN_ON((int)tp->retrans_out < 0);
3558 	if (!tp->packets_out && tcp_is_sack(tp)) {
3559 		icsk = inet_csk(sk);
3560 		if (tp->lost_out) {
3561 			pr_debug("Leak l=%u %d\n",
3562 				 tp->lost_out, icsk->icsk_ca_state);
3563 			tp->lost_out = 0;
3564 		}
3565 		if (tp->sacked_out) {
3566 			pr_debug("Leak s=%u %d\n",
3567 				 tp->sacked_out, icsk->icsk_ca_state);
3568 			tp->sacked_out = 0;
3569 		}
3570 		if (tp->retrans_out) {
3571 			pr_debug("Leak r=%u %d\n",
3572 				 tp->retrans_out, icsk->icsk_ca_state);
3573 			tp->retrans_out = 0;
3574 		}
3575 	}
3576 #endif
3577 	return flag;
3578 }
3579 
3580 static void tcp_ack_probe(struct sock *sk)
3581 {
3582 	struct inet_connection_sock *icsk = inet_csk(sk);
3583 	struct sk_buff *head = tcp_send_head(sk);
3584 	const struct tcp_sock *tp = tcp_sk(sk);
3585 
3586 	/* Was it a usable window open? */
3587 	if (!head)
3588 		return;
3589 	if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
3590 		icsk->icsk_backoff = 0;
3591 		icsk->icsk_probes_tstamp = 0;
3592 		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3593 		/* Socket must be waked up by subsequent tcp_data_snd_check().
3594 		 * This function is not for random using!
3595 		 */
3596 	} else {
3597 		unsigned long when = tcp_probe0_when(sk, tcp_rto_max(sk));
3598 
3599 		when = tcp_clamp_probe0_to_user_timeout(sk, when);
3600 		tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, true);
3601 	}
3602 }
3603 
3604 static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
3605 {
3606 	return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3607 		inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3608 }
3609 
3610 /* Decide wheather to run the increase function of congestion control. */
3611 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3612 {
3613 	/* If reordering is high then always grow cwnd whenever data is
3614 	 * delivered regardless of its ordering. Otherwise stay conservative
3615 	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
3616 	 * new SACK or ECE mark may first advance cwnd here and later reduce
3617 	 * cwnd in tcp_fastretrans_alert() based on more states.
3618 	 */
3619 	if (tcp_sk(sk)->reordering >
3620 	    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering))
3621 		return flag & FLAG_FORWARD_PROGRESS;
3622 
3623 	return flag & FLAG_DATA_ACKED;
3624 }
3625 
3626 /* The "ultimate" congestion control function that aims to replace the rigid
3627  * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
3628  * It's called toward the end of processing an ACK with precise rate
3629  * information. All transmission or retransmission are delayed afterwards.
3630  */
3631 static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
3632 			     int flag, const struct rate_sample *rs)
3633 {
3634 	const struct inet_connection_sock *icsk = inet_csk(sk);
3635 
3636 	if (icsk->icsk_ca_ops->cong_control) {
3637 		icsk->icsk_ca_ops->cong_control(sk, ack, flag, rs);
3638 		return;
3639 	}
3640 
3641 	if (tcp_in_cwnd_reduction(sk)) {
3642 		/* Reduce cwnd if state mandates */
3643 		tcp_cwnd_reduction(sk, acked_sacked, rs->losses, flag);
3644 	} else if (tcp_may_raise_cwnd(sk, flag)) {
3645 		/* Advance cwnd if state allows */
3646 		tcp_cong_avoid(sk, ack, acked_sacked);
3647 	}
3648 	tcp_update_pacing_rate(sk);
3649 }
3650 
3651 /* Check that window update is acceptable.
3652  * The function assumes that snd_una<=ack<=snd_next.
3653  */
3654 static inline bool tcp_may_update_window(const struct tcp_sock *tp,
3655 					const u32 ack, const u32 ack_seq,
3656 					const u32 nwin)
3657 {
3658 	return	after(ack, tp->snd_una) ||
3659 		after(ack_seq, tp->snd_wl1) ||
3660 		(ack_seq == tp->snd_wl1 && (nwin > tp->snd_wnd || !nwin));
3661 }
3662 
3663 static void tcp_snd_sne_update(struct tcp_sock *tp, u32 ack)
3664 {
3665 #ifdef CONFIG_TCP_AO
3666 	struct tcp_ao_info *ao;
3667 
3668 	if (!static_branch_unlikely(&tcp_ao_needed.key))
3669 		return;
3670 
3671 	ao = rcu_dereference_protected(tp->ao_info,
3672 				       lockdep_sock_is_held((struct sock *)tp));
3673 	if (ao && ack < tp->snd_una) {
3674 		ao->snd_sne++;
3675 		trace_tcp_ao_snd_sne_update((struct sock *)tp, ao->snd_sne);
3676 	}
3677 #endif
3678 }
3679 
3680 /* If we update tp->snd_una, also update tp->bytes_acked */
3681 static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
3682 {
3683 	u32 delta = ack - tp->snd_una;
3684 
3685 	sock_owned_by_me((struct sock *)tp);
3686 	tp->bytes_acked += delta;
3687 	tcp_snd_sne_update(tp, ack);
3688 	tp->snd_una = ack;
3689 }
3690 
3691 static void tcp_rcv_sne_update(struct tcp_sock *tp, u32 seq)
3692 {
3693 #ifdef CONFIG_TCP_AO
3694 	struct tcp_ao_info *ao;
3695 
3696 	if (!static_branch_unlikely(&tcp_ao_needed.key))
3697 		return;
3698 
3699 	ao = rcu_dereference_protected(tp->ao_info,
3700 				       lockdep_sock_is_held((struct sock *)tp));
3701 	if (ao && seq < tp->rcv_nxt) {
3702 		ao->rcv_sne++;
3703 		trace_tcp_ao_rcv_sne_update((struct sock *)tp, ao->rcv_sne);
3704 	}
3705 #endif
3706 }
3707 
3708 /* If we update tp->rcv_nxt, also update tp->bytes_received */
3709 static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
3710 {
3711 	u32 delta = seq - tp->rcv_nxt;
3712 
3713 	sock_owned_by_me((struct sock *)tp);
3714 	tp->bytes_received += delta;
3715 	tcp_rcv_sne_update(tp, seq);
3716 	WRITE_ONCE(tp->rcv_nxt, seq);
3717 }
3718 
3719 /* Update our send window.
3720  *
3721  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3722  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3723  */
3724 static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3725 				 u32 ack_seq)
3726 {
3727 	struct tcp_sock *tp = tcp_sk(sk);
3728 	int flag = 0;
3729 	u32 nwin = ntohs(tcp_hdr(skb)->window);
3730 
3731 	if (likely(!tcp_hdr(skb)->syn))
3732 		nwin <<= tp->rx_opt.snd_wscale;
3733 
3734 	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3735 		flag |= FLAG_WIN_UPDATE;
3736 		tcp_update_wl(tp, ack_seq);
3737 
3738 		if (tp->snd_wnd != nwin) {
3739 			tp->snd_wnd = nwin;
3740 
3741 			/* Note, it is the only place, where
3742 			 * fast path is recovered for sending TCP.
3743 			 */
3744 			tp->pred_flags = 0;
3745 			tcp_fast_path_check(sk);
3746 
3747 			if (!tcp_write_queue_empty(sk))
3748 				tcp_slow_start_after_idle_check(sk);
3749 
3750 			if (nwin > tp->max_window) {
3751 				tp->max_window = nwin;
3752 				tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3753 			}
3754 		}
3755 	}
3756 
3757 	tcp_snd_una_update(tp, ack);
3758 
3759 	return flag;
3760 }
3761 
3762 static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
3763 				   u32 *last_oow_ack_time)
3764 {
3765 	/* Paired with the WRITE_ONCE() in this function. */
3766 	u32 val = READ_ONCE(*last_oow_ack_time);
3767 
3768 	if (val) {
3769 		s32 elapsed = (s32)(tcp_jiffies32 - val);
3770 
3771 		if (0 <= elapsed &&
3772 		    elapsed < READ_ONCE(net->ipv4.sysctl_tcp_invalid_ratelimit)) {
3773 			NET_INC_STATS(net, mib_idx);
3774 			return true;	/* rate-limited: don't send yet! */
3775 		}
3776 	}
3777 
3778 	/* Paired with the prior READ_ONCE() and with itself,
3779 	 * as we might be lockless.
3780 	 */
3781 	WRITE_ONCE(*last_oow_ack_time, tcp_jiffies32);
3782 
3783 	return false;	/* not rate-limited: go ahead, send dupack now! */
3784 }
3785 
3786 /* Return true if we're currently rate-limiting out-of-window ACKs and
3787  * thus shouldn't send a dupack right now. We rate-limit dupacks in
3788  * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
3789  * attacks that send repeated SYNs or ACKs for the same connection. To
3790  * do this, we do not send a duplicate SYNACK or ACK if the remote
3791  * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
3792  */
3793 bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
3794 			  int mib_idx, u32 *last_oow_ack_time)
3795 {
3796 	/* Data packets without SYNs are not likely part of an ACK loop. */
3797 	if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
3798 	    !tcp_hdr(skb)->syn)
3799 		return false;
3800 
3801 	return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
3802 }
3803 
3804 static void tcp_send_ack_reflect_ect(struct sock *sk, bool accecn_reflector)
3805 {
3806 	struct tcp_sock *tp = tcp_sk(sk);
3807 	u16 flags = 0;
3808 
3809 	if (accecn_reflector)
3810 		flags = tcp_accecn_reflector_flags(tp->syn_ect_rcv);
3811 	__tcp_send_ack(sk, tp->rcv_nxt, flags);
3812 }
3813 
3814 /* RFC 5961 7 [ACK Throttling] */
3815 static void tcp_send_challenge_ack(struct sock *sk, bool accecn_reflector)
3816 {
3817 	struct tcp_sock *tp = tcp_sk(sk);
3818 	struct net *net = sock_net(sk);
3819 	u32 count, now, ack_limit;
3820 
3821 	/* First check our per-socket dupack rate limit. */
3822 	if (__tcp_oow_rate_limited(net,
3823 				   LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
3824 				   &tp->last_oow_ack_time))
3825 		return;
3826 
3827 	ack_limit = READ_ONCE(net->ipv4.sysctl_tcp_challenge_ack_limit);
3828 	if (ack_limit == INT_MAX)
3829 		goto send_ack;
3830 
3831 	/* Then check host-wide RFC 5961 rate limit. */
3832 	now = jiffies / HZ;
3833 	if (now != READ_ONCE(net->ipv4.tcp_challenge_timestamp)) {
3834 		u32 half = (ack_limit + 1) >> 1;
3835 
3836 		WRITE_ONCE(net->ipv4.tcp_challenge_timestamp, now);
3837 		WRITE_ONCE(net->ipv4.tcp_challenge_count,
3838 			   get_random_u32_inclusive(half, ack_limit + half - 1));
3839 	}
3840 	count = READ_ONCE(net->ipv4.tcp_challenge_count);
3841 	if (count > 0) {
3842 		WRITE_ONCE(net->ipv4.tcp_challenge_count, count - 1);
3843 send_ack:
3844 		NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
3845 		tcp_send_ack_reflect_ect(sk, accecn_reflector);
3846 	}
3847 }
3848 
3849 static void tcp_store_ts_recent(struct tcp_sock *tp)
3850 {
3851 	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3852 	tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
3853 }
3854 
3855 static int __tcp_replace_ts_recent(struct tcp_sock *tp, s32 tstamp_delta)
3856 {
3857 	tcp_store_ts_recent(tp);
3858 	return tstamp_delta > 0 ? FLAG_TS_PROGRESS : 0;
3859 }
3860 
3861 static int tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3862 {
3863 	s32 delta;
3864 
3865 	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3866 		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
3867 		 * extra check below makes sure this can only happen
3868 		 * for pure ACK frames.  -DaveM
3869 		 *
3870 		 * Not only, also it occurs for expired timestamps.
3871 		 */
3872 
3873 		if (tcp_paws_check(&tp->rx_opt, 0)) {
3874 			delta = tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent;
3875 			return __tcp_replace_ts_recent(tp, delta);
3876 		}
3877 	}
3878 
3879 	return 0;
3880 }
3881 
3882 /* This routine deals with acks during a TLP episode and ends an episode by
3883  * resetting tlp_high_seq. Ref: TLP algorithm in RFC8985
3884  */
3885 static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
3886 {
3887 	struct tcp_sock *tp = tcp_sk(sk);
3888 
3889 	if (before(ack, tp->tlp_high_seq))
3890 		return;
3891 
3892 	if (!tp->tlp_retrans) {
3893 		/* TLP of new data has been acknowledged */
3894 		tp->tlp_high_seq = 0;
3895 	} else if (flag & FLAG_DSACK_TLP) {
3896 		/* This DSACK means original and TLP probe arrived; no loss */
3897 		tp->tlp_high_seq = 0;
3898 	} else if (after(ack, tp->tlp_high_seq)) {
3899 		/* ACK advances: there was a loss, so reduce cwnd. Reset
3900 		 * tlp_high_seq in tcp_init_cwnd_reduction()
3901 		 */
3902 		tcp_init_cwnd_reduction(sk);
3903 		tcp_set_ca_state(sk, TCP_CA_CWR);
3904 		tcp_end_cwnd_reduction(sk);
3905 		tcp_try_keep_open(sk);
3906 		NET_INC_STATS(sock_net(sk),
3907 				LINUX_MIB_TCPLOSSPROBERECOVERY);
3908 	} else if (!(flag & (FLAG_SND_UNA_ADVANCED |
3909 			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
3910 		/* Pure dupack: original and TLP probe arrived; no loss */
3911 		tp->tlp_high_seq = 0;
3912 	}
3913 }
3914 
3915 static void tcp_in_ack_event(struct sock *sk, int flag)
3916 {
3917 	const struct inet_connection_sock *icsk = inet_csk(sk);
3918 
3919 	if (icsk->icsk_ca_ops->in_ack_event) {
3920 		u32 ack_ev_flags = 0;
3921 
3922 		if (flag & FLAG_WIN_UPDATE)
3923 			ack_ev_flags |= CA_ACK_WIN_UPDATE;
3924 		if (flag & FLAG_SLOWPATH) {
3925 			ack_ev_flags |= CA_ACK_SLOWPATH;
3926 			if (flag & FLAG_ECE)
3927 				ack_ev_flags |= CA_ACK_ECE;
3928 		}
3929 
3930 		icsk->icsk_ca_ops->in_ack_event(sk, ack_ev_flags);
3931 	}
3932 }
3933 
3934 /* Congestion control has updated the cwnd already. So if we're in
3935  * loss recovery then now we do any new sends (for FRTO) or
3936  * retransmits (for CA_Loss or CA_recovery) that make sense.
3937  */
3938 static void tcp_xmit_recovery(struct sock *sk, int rexmit)
3939 {
3940 	struct tcp_sock *tp = tcp_sk(sk);
3941 
3942 	if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT)
3943 		return;
3944 
3945 	if (unlikely(rexmit == REXMIT_NEW)) {
3946 		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
3947 					  TCP_NAGLE_OFF);
3948 		if (after(tp->snd_nxt, tp->high_seq))
3949 			return;
3950 		tp->frto = 0;
3951 	}
3952 	tcp_xmit_retransmit_queue(sk);
3953 }
3954 
3955 /* Returns the number of packets newly acked or sacked by the current ACK */
3956 static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered,
3957 			       u32 ecn_count, int flag)
3958 {
3959 	const struct net *net = sock_net(sk);
3960 	struct tcp_sock *tp = tcp_sk(sk);
3961 	u32 delivered;
3962 
3963 	delivered = tp->delivered - prior_delivered;
3964 	NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
3965 
3966 	if (flag & FLAG_ECE) {
3967 		if (tcp_ecn_mode_rfc3168(tp))
3968 			ecn_count = delivered;
3969 		NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, ecn_count);
3970 	}
3971 
3972 	return delivered;
3973 }
3974 
3975 /* This routine deals with incoming acks, but not outgoing ones. */
3976 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3977 {
3978 	struct inet_connection_sock *icsk = inet_csk(sk);
3979 	struct tcp_sock *tp = tcp_sk(sk);
3980 	struct tcp_sacktag_state sack_state;
3981 	struct rate_sample rs = { .prior_delivered = 0 };
3982 	u32 prior_snd_una = tp->snd_una;
3983 	bool is_sack_reneg = tp->is_sack_reneg;
3984 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
3985 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
3986 	int num_dupack = 0;
3987 	int prior_packets = tp->packets_out;
3988 	u32 delivered = tp->delivered;
3989 	u32 lost = tp->lost;
3990 	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
3991 	u32 ecn_count = 0;	  /* Did we receive ECE/an AccECN ACE update? */
3992 	u32 prior_fack;
3993 
3994 	sack_state.first_sackt = 0;
3995 	sack_state.rate = &rs;
3996 	sack_state.sack_delivered = 0;
3997 	sack_state.delivered_bytes = 0;
3998 
3999 	/* We very likely will need to access rtx queue. */
4000 	prefetch(sk->tcp_rtx_queue.rb_node);
4001 
4002 	/* If the ack is older than previous acks
4003 	 * then we can probably ignore it.
4004 	 */
4005 	if (before(ack, prior_snd_una)) {
4006 		u32 max_window;
4007 
4008 		/* do not accept ACK for bytes we never sent. */
4009 		max_window = min_t(u64, tp->max_window, tp->bytes_acked);
4010 		/* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
4011 		if (before(ack, prior_snd_una - max_window)) {
4012 			if (!(flag & FLAG_NO_CHALLENGE_ACK))
4013 				tcp_send_challenge_ack(sk, false);
4014 			return -SKB_DROP_REASON_TCP_TOO_OLD_ACK;
4015 		}
4016 		goto old_ack;
4017 	}
4018 
4019 	/* If the ack includes data we haven't sent yet, discard
4020 	 * this segment (RFC793 Section 3.9).
4021 	 */
4022 	if (after(ack, tp->snd_nxt))
4023 		return -SKB_DROP_REASON_TCP_ACK_UNSENT_DATA;
4024 
4025 	if (after(ack, prior_snd_una)) {
4026 		flag |= FLAG_SND_UNA_ADVANCED;
4027 		WRITE_ONCE(icsk->icsk_retransmits, 0);
4028 
4029 #if IS_ENABLED(CONFIG_TLS_DEVICE)
4030 		if (static_branch_unlikely(&clean_acked_data_enabled.key))
4031 			if (tp->tcp_clean_acked)
4032 				tp->tcp_clean_acked(sk, ack);
4033 #endif
4034 	}
4035 
4036 	prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
4037 	rs.prior_in_flight = tcp_packets_in_flight(tp);
4038 
4039 	/* ts_recent update must be made after we are sure that the packet
4040 	 * is in window.
4041 	 */
4042 	if (flag & FLAG_UPDATE_TS_RECENT)
4043 		flag |= tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4044 
4045 	if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) ==
4046 	    FLAG_SND_UNA_ADVANCED) {
4047 		/* Window is constant, pure forward advance.
4048 		 * No more checks are required.
4049 		 * Note, we use the fact that SND.UNA>=SND.WL2.
4050 		 */
4051 		tcp_update_wl(tp, ack_seq);
4052 		tcp_snd_una_update(tp, ack);
4053 		flag |= FLAG_WIN_UPDATE;
4054 
4055 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
4056 	} else {
4057 		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
4058 			flag |= FLAG_DATA;
4059 		else
4060 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
4061 
4062 		flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
4063 
4064 		if (TCP_SKB_CB(skb)->sacked)
4065 			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
4066 							&sack_state);
4067 
4068 		if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb)))
4069 			flag |= FLAG_ECE;
4070 
4071 		if (sack_state.sack_delivered)
4072 			tcp_count_delivered(tp, sack_state.sack_delivered,
4073 					    flag & FLAG_ECE);
4074 	}
4075 
4076 	/* This is a deviation from RFC3168 since it states that:
4077 	 * "When the TCP data sender is ready to set the CWR bit after reducing
4078 	 * the congestion window, it SHOULD set the CWR bit only on the first
4079 	 * new data packet that it transmits."
4080 	 * We accept CWR on pure ACKs to be more robust
4081 	 * with widely-deployed TCP implementations that do this.
4082 	 */
4083 	tcp_ecn_accept_cwr(sk, skb);
4084 
4085 	/* We passed data and got it acked, remove any soft error
4086 	 * log. Something worked...
4087 	 */
4088 	if (READ_ONCE(sk->sk_err_soft))
4089 		WRITE_ONCE(sk->sk_err_soft, 0);
4090 	WRITE_ONCE(icsk->icsk_probes_out, 0);
4091 	tp->rcv_tstamp = tcp_jiffies32;
4092 	if (!prior_packets)
4093 		goto no_queue;
4094 
4095 	/* See if we can take anything off of the retransmit queue. */
4096 	flag |= tcp_clean_rtx_queue(sk, skb, prior_fack, prior_snd_una,
4097 				    &sack_state, flag & FLAG_ECE);
4098 
4099 	tcp_rack_update_reo_wnd(sk, &rs);
4100 
4101 	if (tcp_ecn_mode_accecn(tp))
4102 		ecn_count = tcp_accecn_process(sk, skb,
4103 					       tp->delivered - delivered,
4104 					       sack_state.delivered_bytes,
4105 					       &flag);
4106 
4107 	tcp_in_ack_event(sk, flag);
4108 
4109 	if (tp->tlp_high_seq)
4110 		tcp_process_tlp_ack(sk, ack, flag);
4111 
4112 	if (tcp_ack_is_dubious(sk, flag)) {
4113 		if (!(flag & (FLAG_SND_UNA_ADVANCED |
4114 			      FLAG_NOT_DUP | FLAG_DSACKING_ACK))) {
4115 			num_dupack = 1;
4116 			/* Consider if pure acks were aggregated in tcp_add_backlog() */
4117 			if (!(flag & FLAG_DATA))
4118 				num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs);
4119 		}
4120 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
4121 				      &rexmit);
4122 	}
4123 
4124 	/* If needed, reset TLP/RTO timer when RACK doesn't set. */
4125 	if (flag & FLAG_SET_XMIT_TIMER)
4126 		tcp_set_xmit_timer(sk);
4127 
4128 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
4129 		sk_dst_confirm(sk);
4130 
4131 	delivered = tcp_newly_delivered(sk, delivered, ecn_count, flag);
4132 
4133 	lost = tp->lost - lost;			/* freshly marked lost */
4134 	rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
4135 	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
4136 	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
4137 	tcp_xmit_recovery(sk, rexmit);
4138 	return 1;
4139 
4140 no_queue:
4141 	if (tcp_ecn_mode_accecn(tp))
4142 		ecn_count = tcp_accecn_process(sk, skb,
4143 					       tp->delivered - delivered,
4144 					       sack_state.delivered_bytes,
4145 					       &flag);
4146 	tcp_in_ack_event(sk, flag);
4147 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
4148 	if (flag & FLAG_DSACKING_ACK) {
4149 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
4150 				      &rexmit);
4151 		tcp_newly_delivered(sk, delivered, ecn_count, flag);
4152 	}
4153 	/* If this ack opens up a zero window, clear backoff.  It was
4154 	 * being used to time the probes, and is probably far higher than
4155 	 * it needs to be for normal retransmission.
4156 	 */
4157 	tcp_ack_probe(sk);
4158 
4159 	if (tp->tlp_high_seq)
4160 		tcp_process_tlp_ack(sk, ack, flag);
4161 	return 1;
4162 
4163 old_ack:
4164 	/* If data was SACKed, tag it and see if we should send more data.
4165 	 * If data was DSACKed, see if we can undo a cwnd reduction.
4166 	 */
4167 	if (TCP_SKB_CB(skb)->sacked) {
4168 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
4169 						&sack_state);
4170 		tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag,
4171 				      &rexmit);
4172 		tcp_newly_delivered(sk, delivered, ecn_count, flag);
4173 		tcp_xmit_recovery(sk, rexmit);
4174 	}
4175 
4176 	return 0;
4177 }
4178 
4179 static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
4180 				      bool syn, struct tcp_fastopen_cookie *foc,
4181 				      bool exp_opt)
4182 {
4183 	/* Valid only in SYN or SYN-ACK with an even length.  */
4184 	if (!foc || !syn || len < 0 || (len & 1))
4185 		return;
4186 
4187 	if (len >= TCP_FASTOPEN_COOKIE_MIN &&
4188 	    len <= TCP_FASTOPEN_COOKIE_MAX)
4189 		memcpy(foc->val, cookie, len);
4190 	else if (len != 0)
4191 		len = -1;
4192 	foc->len = len;
4193 	foc->exp = exp_opt;
4194 }
4195 
4196 static bool smc_parse_options(const struct tcphdr *th,
4197 			      struct tcp_options_received *opt_rx,
4198 			      const unsigned char *ptr,
4199 			      int opsize)
4200 {
4201 #if IS_ENABLED(CONFIG_SMC)
4202 	if (static_branch_unlikely(&tcp_have_smc)) {
4203 		if (th->syn && !(opsize & 1) &&
4204 		    opsize >= TCPOLEN_EXP_SMC_BASE &&
4205 		    get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) {
4206 			opt_rx->smc_ok = 1;
4207 			return true;
4208 		}
4209 	}
4210 #endif
4211 	return false;
4212 }
4213 
4214 /* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped
4215  * value on success.
4216  */
4217 u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss)
4218 {
4219 	const unsigned char *ptr = (const unsigned char *)(th + 1);
4220 	int length = (th->doff * 4) - sizeof(struct tcphdr);
4221 	u16 mss = 0;
4222 
4223 	while (length > 0) {
4224 		int opcode = *ptr++;
4225 		int opsize;
4226 
4227 		switch (opcode) {
4228 		case TCPOPT_EOL:
4229 			return mss;
4230 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4231 			length--;
4232 			continue;
4233 		default:
4234 			if (length < 2)
4235 				return mss;
4236 			opsize = *ptr++;
4237 			if (opsize < 2) /* "silly options" */
4238 				return mss;
4239 			if (opsize > length)
4240 				return mss;	/* fail on partial options */
4241 			if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) {
4242 				u16 in_mss = get_unaligned_be16(ptr);
4243 
4244 				if (in_mss) {
4245 					if (user_mss && user_mss < in_mss)
4246 						in_mss = user_mss;
4247 					mss = in_mss;
4248 				}
4249 			}
4250 			ptr += opsize - 2;
4251 			length -= opsize;
4252 		}
4253 	}
4254 	return mss;
4255 }
4256 
4257 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
4258  * But, this can also be called on packets in the established flow when
4259  * the fast version below fails.
4260  */
4261 void tcp_parse_options(const struct net *net,
4262 		       const struct sk_buff *skb,
4263 		       struct tcp_options_received *opt_rx, int estab,
4264 		       struct tcp_fastopen_cookie *foc)
4265 {
4266 	const unsigned char *ptr;
4267 	const struct tcphdr *th = tcp_hdr(skb);
4268 	int length = (th->doff * 4) - sizeof(struct tcphdr);
4269 
4270 	ptr = (const unsigned char *)(th + 1);
4271 	opt_rx->saw_tstamp = 0;
4272 	opt_rx->accecn = 0;
4273 	opt_rx->saw_unknown = 0;
4274 
4275 	while (length > 0) {
4276 		int opcode = *ptr++;
4277 		int opsize;
4278 
4279 		switch (opcode) {
4280 		case TCPOPT_EOL:
4281 			return;
4282 		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
4283 			length--;
4284 			continue;
4285 		default:
4286 			if (length < 2)
4287 				return;
4288 			opsize = *ptr++;
4289 			if (opsize < 2) /* "silly options" */
4290 				return;
4291 			if (opsize > length)
4292 				return;	/* don't parse partial options */
4293 			switch (opcode) {
4294 			case TCPOPT_MSS:
4295 				if (opsize == TCPOLEN_MSS && th->syn && !estab) {
4296 					u16 in_mss = get_unaligned_be16(ptr);
4297 					if (in_mss) {
4298 						if (opt_rx->user_mss &&
4299 						    opt_rx->user_mss < in_mss)
4300 							in_mss = opt_rx->user_mss;
4301 						opt_rx->mss_clamp = in_mss;
4302 					}
4303 				}
4304 				break;
4305 			case TCPOPT_WINDOW:
4306 				if (opsize == TCPOLEN_WINDOW && th->syn &&
4307 				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) {
4308 					__u8 snd_wscale = *(__u8 *)ptr;
4309 					opt_rx->wscale_ok = 1;
4310 					if (snd_wscale > TCP_MAX_WSCALE) {
4311 						net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
4312 								     __func__,
4313 								     snd_wscale,
4314 								     TCP_MAX_WSCALE);
4315 						snd_wscale = TCP_MAX_WSCALE;
4316 					}
4317 					opt_rx->snd_wscale = snd_wscale;
4318 				}
4319 				break;
4320 			case TCPOPT_TIMESTAMP:
4321 				if ((opsize == TCPOLEN_TIMESTAMP) &&
4322 				    ((estab && opt_rx->tstamp_ok) ||
4323 				     (!estab && READ_ONCE(net->ipv4.sysctl_tcp_timestamps)))) {
4324 					opt_rx->saw_tstamp = 1;
4325 					opt_rx->rcv_tsval = get_unaligned_be32(ptr);
4326 					opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
4327 				}
4328 				break;
4329 			case TCPOPT_SACK_PERM:
4330 				if (opsize == TCPOLEN_SACK_PERM && th->syn &&
4331 				    !estab && READ_ONCE(net->ipv4.sysctl_tcp_sack)) {
4332 					opt_rx->sack_ok = TCP_SACK_SEEN;
4333 					tcp_sack_reset(opt_rx);
4334 				}
4335 				break;
4336 
4337 			case TCPOPT_SACK:
4338 				if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
4339 				   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
4340 				   opt_rx->sack_ok) {
4341 					TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
4342 				}
4343 				break;
4344 #ifdef CONFIG_TCP_MD5SIG
4345 			case TCPOPT_MD5SIG:
4346 				/* The MD5 Hash has already been
4347 				 * checked (see tcp_v{4,6}_rcv()).
4348 				 */
4349 				break;
4350 #endif
4351 #ifdef CONFIG_TCP_AO
4352 			case TCPOPT_AO:
4353 				/* TCP AO has already been checked
4354 				 * (see tcp_inbound_ao_hash()).
4355 				 */
4356 				break;
4357 #endif
4358 			case TCPOPT_FASTOPEN:
4359 				tcp_parse_fastopen_option(
4360 					opsize - TCPOLEN_FASTOPEN_BASE,
4361 					ptr, th->syn, foc, false);
4362 				break;
4363 
4364 			case TCPOPT_ACCECN0:
4365 			case TCPOPT_ACCECN1:
4366 				/* Save offset of AccECN option in TCP header */
4367 				opt_rx->accecn = (ptr - 2) - (__u8 *)th;
4368 				break;
4369 
4370 			case TCPOPT_EXP:
4371 				/* Fast Open option shares code 254 using a
4372 				 * 16 bits magic number.
4373 				 */
4374 				if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
4375 				    get_unaligned_be16(ptr) ==
4376 				    TCPOPT_FASTOPEN_MAGIC) {
4377 					tcp_parse_fastopen_option(opsize -
4378 						TCPOLEN_EXP_FASTOPEN_BASE,
4379 						ptr + 2, th->syn, foc, true);
4380 					break;
4381 				}
4382 
4383 				if (smc_parse_options(th, opt_rx, ptr, opsize))
4384 					break;
4385 
4386 				opt_rx->saw_unknown = 1;
4387 				break;
4388 
4389 			default:
4390 				opt_rx->saw_unknown = 1;
4391 			}
4392 			ptr += opsize-2;
4393 			length -= opsize;
4394 		}
4395 	}
4396 }
4397 EXPORT_SYMBOL(tcp_parse_options);
4398 
4399 static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
4400 {
4401 	const __be32 *ptr = (const __be32 *)(th + 1);
4402 
4403 	if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4404 			  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
4405 		tp->rx_opt.saw_tstamp = 1;
4406 		++ptr;
4407 		tp->rx_opt.rcv_tsval = ntohl(*ptr);
4408 		++ptr;
4409 		if (*ptr)
4410 			tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
4411 		else
4412 			tp->rx_opt.rcv_tsecr = 0;
4413 		return true;
4414 	}
4415 	return false;
4416 }
4417 
4418 /* Fast parse options. This hopes to only see timestamps.
4419  * If it is wrong it falls back on tcp_parse_options().
4420  */
4421 static bool tcp_fast_parse_options(const struct net *net,
4422 				   const struct sk_buff *skb,
4423 				   const struct tcphdr *th, struct tcp_sock *tp)
4424 {
4425 	/* In the spirit of fast parsing, compare doff directly to constant
4426 	 * values.  Because equality is used, short doff can be ignored here.
4427 	 */
4428 	if (th->doff == (sizeof(*th) / 4)) {
4429 		tp->rx_opt.saw_tstamp = 0;
4430 		tp->rx_opt.accecn = 0;
4431 		return false;
4432 	} else if (tp->rx_opt.tstamp_ok &&
4433 		   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
4434 		if (tcp_parse_aligned_timestamp(tp, th)) {
4435 			tp->rx_opt.accecn = 0;
4436 			return true;
4437 		}
4438 	}
4439 
4440 	tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
4441 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
4442 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
4443 
4444 	return true;
4445 }
4446 
4447 #if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
4448 /*
4449  * Parse Signature options
4450  */
4451 int tcp_do_parse_auth_options(const struct tcphdr *th,
4452 			      const u8 **md5_hash, const u8 **ao_hash)
4453 {
4454 	int length = (th->doff << 2) - sizeof(*th);
4455 	const u8 *ptr = (const u8 *)(th + 1);
4456 	unsigned int minlen = TCPOLEN_MD5SIG;
4457 
4458 	if (IS_ENABLED(CONFIG_TCP_AO))
4459 		minlen = sizeof(struct tcp_ao_hdr) + 1;
4460 
4461 	*md5_hash = NULL;
4462 	*ao_hash = NULL;
4463 
4464 	/* If not enough data remaining, we can short cut */
4465 	while (length >= minlen) {
4466 		int opcode = *ptr++;
4467 		int opsize;
4468 
4469 		switch (opcode) {
4470 		case TCPOPT_EOL:
4471 			return 0;
4472 		case TCPOPT_NOP:
4473 			length--;
4474 			continue;
4475 		default:
4476 			opsize = *ptr++;
4477 			if (opsize < 2 || opsize > length)
4478 				return -EINVAL;
4479 			if (opcode == TCPOPT_MD5SIG) {
4480 				if (opsize != TCPOLEN_MD5SIG)
4481 					return -EINVAL;
4482 				if (unlikely(*md5_hash || *ao_hash))
4483 					return -EEXIST;
4484 				*md5_hash = ptr;
4485 			} else if (opcode == TCPOPT_AO) {
4486 				if (opsize <= sizeof(struct tcp_ao_hdr))
4487 					return -EINVAL;
4488 				if (unlikely(*md5_hash || *ao_hash))
4489 					return -EEXIST;
4490 				*ao_hash = ptr;
4491 			}
4492 		}
4493 		ptr += opsize - 2;
4494 		length -= opsize;
4495 	}
4496 	return 0;
4497 }
4498 EXPORT_SYMBOL(tcp_do_parse_auth_options);
4499 #endif
4500 
4501 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4502  *
4503  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4504  * it can pass through stack. So, the following predicate verifies that
4505  * this segment is not used for anything but congestion avoidance or
4506  * fast retransmit. Moreover, we even are able to eliminate most of such
4507  * second order effects, if we apply some small "replay" window (~RTO)
4508  * to timestamp space.
4509  *
4510  * All these measures still do not guarantee that we reject wrapped ACKs
4511  * on networks with high bandwidth, when sequence space is recycled fastly,
4512  * but it guarantees that such events will be very rare and do not affect
4513  * connection seriously. This doesn't look nice, but alas, PAWS is really
4514  * buggy extension.
4515  *
4516  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4517  * states that events when retransmit arrives after original data are rare.
4518  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4519  * the biggest problem on large power networks even with minor reordering.
4520  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4521  * up to bandwidth of 18Gigabit/sec. 8) ]
4522  */
4523 
4524 /* Estimates max number of increments of remote peer TSval in
4525  * a replay window (based on our current RTO estimation).
4526  */
4527 static u32 tcp_tsval_replay(const struct sock *sk)
4528 {
4529 	/* If we use usec TS resolution,
4530 	 * then expect the remote peer to use the same resolution.
4531 	 */
4532 	if (tcp_sk(sk)->tcp_usec_ts)
4533 		return inet_csk(sk)->icsk_rto * (USEC_PER_SEC / HZ);
4534 
4535 	/* RFC 7323 recommends a TSval clock between 1ms and 1sec.
4536 	 * We know that some OS (including old linux) can use 1200 Hz.
4537 	 */
4538 	return inet_csk(sk)->icsk_rto * 1200 / HZ;
4539 }
4540 
4541 static enum skb_drop_reason tcp_disordered_ack_check(const struct sock *sk,
4542 						     const struct sk_buff *skb)
4543 {
4544 	const struct tcp_sock *tp = tcp_sk(sk);
4545 	const struct tcphdr *th = tcp_hdr(skb);
4546 	SKB_DR_INIT(reason, TCP_RFC7323_PAWS);
4547 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
4548 	u32 seq = TCP_SKB_CB(skb)->seq;
4549 
4550 	/* 1. Is this not a pure ACK ? */
4551 	if (!th->ack || seq != TCP_SKB_CB(skb)->end_seq)
4552 		return reason;
4553 
4554 	/* 2. Is its sequence not the expected one ? */
4555 	if (seq != tp->rcv_nxt)
4556 		return before(seq, tp->rcv_nxt) ?
4557 			SKB_DROP_REASON_TCP_RFC7323_PAWS_ACK :
4558 			reason;
4559 
4560 	/* 3. Is this not a duplicate ACK ? */
4561 	if (ack != tp->snd_una)
4562 		return reason;
4563 
4564 	/* 4. Is this updating the window ? */
4565 	if (tcp_may_update_window(tp, ack, seq, ntohs(th->window) <<
4566 						tp->rx_opt.snd_wscale))
4567 		return reason;
4568 
4569 	/* 5. Is this not in the replay window ? */
4570 	if ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) >
4571 	    tcp_tsval_replay(sk))
4572 		return reason;
4573 
4574 	return 0;
4575 }
4576 
4577 /* Check segment sequence number for validity.
4578  *
4579  * Segment controls are considered valid, if the segment
4580  * fits to the window after truncation to the window. Acceptability
4581  * of data (and SYN, FIN, of course) is checked separately.
4582  * See tcp_data_queue(), for example.
4583  *
4584  * Also, controls (RST is main one) are accepted using RCV.WUP instead
4585  * of RCV.NXT. Peer still did not advance his SND.UNA when we
4586  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4587  * (borrowed from freebsd)
4588  */
4589 
4590 static enum skb_drop_reason tcp_sequence(const struct sock *sk,
4591 					 u32 seq, u32 end_seq)
4592 {
4593 	const struct tcp_sock *tp = tcp_sk(sk);
4594 
4595 	if (before(end_seq, tp->rcv_wup))
4596 		return SKB_DROP_REASON_TCP_OLD_SEQUENCE;
4597 
4598 	if (after(end_seq, tp->rcv_nxt + tcp_receive_window(tp))) {
4599 		if (after(seq, tp->rcv_nxt + tcp_receive_window(tp)))
4600 			return SKB_DROP_REASON_TCP_INVALID_SEQUENCE;
4601 
4602 		/* Only accept this packet if receive queue is empty. */
4603 		if (skb_queue_len(&sk->sk_receive_queue))
4604 			return SKB_DROP_REASON_TCP_INVALID_END_SEQUENCE;
4605 	}
4606 
4607 	return SKB_NOT_DROPPED_YET;
4608 }
4609 
4610 
4611 void tcp_done_with_error(struct sock *sk, int err)
4612 {
4613 	/* This barrier is coupled with smp_rmb() in tcp_poll() */
4614 	WRITE_ONCE(sk->sk_err, err);
4615 	smp_wmb();
4616 
4617 	tcp_write_queue_purge(sk);
4618 	tcp_done(sk);
4619 
4620 	if (!sock_flag(sk, SOCK_DEAD))
4621 		sk_error_report(sk);
4622 }
4623 EXPORT_IPV6_MOD(tcp_done_with_error);
4624 
4625 /* When we get a reset we do this. */
4626 void tcp_reset(struct sock *sk, struct sk_buff *skb)
4627 {
4628 	int err;
4629 
4630 	trace_tcp_receive_reset(sk);
4631 
4632 	/* mptcp can't tell us to ignore reset pkts,
4633 	 * so just ignore the return value of mptcp_incoming_options().
4634 	 */
4635 	if (sk_is_mptcp(sk))
4636 		mptcp_incoming_options(sk, skb);
4637 
4638 	/* We want the right error as BSD sees it (and indeed as we do). */
4639 	switch (sk->sk_state) {
4640 	case TCP_SYN_SENT:
4641 		err = ECONNREFUSED;
4642 		break;
4643 	case TCP_CLOSE_WAIT:
4644 		err = EPIPE;
4645 		break;
4646 	case TCP_CLOSE:
4647 		return;
4648 	default:
4649 		err = ECONNRESET;
4650 	}
4651 	tcp_done_with_error(sk, err);
4652 }
4653 
4654 /*
4655  * 	Process the FIN bit. This now behaves as it is supposed to work
4656  *	and the FIN takes effect when it is validly part of sequence
4657  *	space. Not before when we get holes.
4658  *
4659  *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4660  *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
4661  *	TIME-WAIT)
4662  *
4663  *	If we are in FINWAIT-1, a received FIN indicates simultaneous
4664  *	close and we go into CLOSING (and later onto TIME-WAIT)
4665  *
4666  *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4667  */
4668 void tcp_fin(struct sock *sk)
4669 {
4670 	struct tcp_sock *tp = tcp_sk(sk);
4671 
4672 	inet_csk_schedule_ack(sk);
4673 
4674 	WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | RCV_SHUTDOWN);
4675 	sock_set_flag(sk, SOCK_DONE);
4676 
4677 	switch (sk->sk_state) {
4678 	case TCP_SYN_RECV:
4679 	case TCP_ESTABLISHED:
4680 		/* Move to CLOSE_WAIT */
4681 		tcp_set_state(sk, TCP_CLOSE_WAIT);
4682 		inet_csk_enter_pingpong_mode(sk);
4683 		break;
4684 
4685 	case TCP_CLOSE_WAIT:
4686 	case TCP_CLOSING:
4687 		/* Received a retransmission of the FIN, do
4688 		 * nothing.
4689 		 */
4690 		break;
4691 	case TCP_LAST_ACK:
4692 		/* RFC793: Remain in the LAST-ACK state. */
4693 		break;
4694 
4695 	case TCP_FIN_WAIT1:
4696 		/* This case occurs when a simultaneous close
4697 		 * happens, we must ack the received FIN and
4698 		 * enter the CLOSING state.
4699 		 */
4700 		tcp_send_ack(sk);
4701 		tcp_set_state(sk, TCP_CLOSING);
4702 		break;
4703 	case TCP_FIN_WAIT2:
4704 		/* Received a FIN -- send ACK and enter TIME_WAIT. */
4705 		tcp_send_ack(sk);
4706 		tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4707 		break;
4708 	default:
4709 		/* Only TCP_LISTEN and TCP_CLOSE are left, in these
4710 		 * cases we should never reach this piece of code.
4711 		 */
4712 		pr_err("%s: Impossible, sk->sk_state=%d\n",
4713 		       __func__, sk->sk_state);
4714 		break;
4715 	}
4716 
4717 	/* It _is_ possible, that we have something out-of-order _after_ FIN.
4718 	 * Probably, we should reset in this case. For now drop them.
4719 	 */
4720 	skb_rbtree_purge(&tp->out_of_order_queue);
4721 	if (tcp_is_sack(tp))
4722 		tcp_sack_reset(&tp->rx_opt);
4723 
4724 	if (!sock_flag(sk, SOCK_DEAD)) {
4725 		sk->sk_state_change(sk);
4726 
4727 		/* Do not send POLL_HUP for half duplex close. */
4728 		if (sk->sk_shutdown == SHUTDOWN_MASK ||
4729 		    sk->sk_state == TCP_CLOSE)
4730 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4731 		else
4732 			sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4733 	}
4734 }
4735 
4736 static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4737 				  u32 end_seq)
4738 {
4739 	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4740 		if (before(seq, sp->start_seq))
4741 			sp->start_seq = seq;
4742 		if (after(end_seq, sp->end_seq))
4743 			sp->end_seq = end_seq;
4744 		return true;
4745 	}
4746 	return false;
4747 }
4748 
4749 static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4750 {
4751 	struct tcp_sock *tp = tcp_sk(sk);
4752 
4753 	if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4754 		int mib_idx;
4755 
4756 		if (before(seq, tp->rcv_nxt))
4757 			mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4758 		else
4759 			mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4760 
4761 		NET_INC_STATS(sock_net(sk), mib_idx);
4762 
4763 		tp->rx_opt.dsack = 1;
4764 		tp->duplicate_sack[0].start_seq = seq;
4765 		tp->duplicate_sack[0].end_seq = end_seq;
4766 	}
4767 }
4768 
4769 static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4770 {
4771 	struct tcp_sock *tp = tcp_sk(sk);
4772 
4773 	if (!tp->rx_opt.dsack)
4774 		tcp_dsack_set(sk, seq, end_seq);
4775 	else
4776 		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4777 }
4778 
4779 static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
4780 {
4781 	/* When the ACK path fails or drops most ACKs, the sender would
4782 	 * timeout and spuriously retransmit the same segment repeatedly.
4783 	 * If it seems our ACKs are not reaching the other side,
4784 	 * based on receiving a duplicate data segment with new flowlabel
4785 	 * (suggesting the sender suffered an RTO), and we are not already
4786 	 * repathing due to our own RTO, then rehash the socket to repath our
4787 	 * packets.
4788 	 */
4789 #if IS_ENABLED(CONFIG_IPV6)
4790 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss &&
4791 	    skb->protocol == htons(ETH_P_IPV6) &&
4792 	    (tcp_sk(sk)->inet_conn.icsk_ack.lrcv_flowlabel !=
4793 	     ntohl(ip6_flowlabel(ipv6_hdr(skb)))) &&
4794 	    sk_rethink_txhash(sk))
4795 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
4796 
4797 	/* Save last flowlabel after a spurious retrans. */
4798 	tcp_save_lrcv_flowlabel(sk, skb);
4799 #endif
4800 }
4801 
4802 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4803 {
4804 	struct tcp_sock *tp = tcp_sk(sk);
4805 
4806 	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4807 	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4808 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4809 		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
4810 
4811 		if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) {
4812 			u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4813 
4814 			tcp_rcv_spurious_retrans(sk, skb);
4815 			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4816 				end_seq = tp->rcv_nxt;
4817 			tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4818 		}
4819 	}
4820 
4821 	tcp_send_ack(sk);
4822 }
4823 
4824 /* These routines update the SACK block as out-of-order packets arrive or
4825  * in-order packets close up the sequence space.
4826  */
4827 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4828 {
4829 	int this_sack;
4830 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4831 	struct tcp_sack_block *swalk = sp + 1;
4832 
4833 	/* See if the recent change to the first SACK eats into
4834 	 * or hits the sequence space of other SACK blocks, if so coalesce.
4835 	 */
4836 	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4837 		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4838 			int i;
4839 
4840 			/* Zap SWALK, by moving every further SACK up by one slot.
4841 			 * Decrease num_sacks.
4842 			 */
4843 			tp->rx_opt.num_sacks--;
4844 			for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4845 				sp[i] = sp[i + 1];
4846 			continue;
4847 		}
4848 		this_sack++;
4849 		swalk++;
4850 	}
4851 }
4852 
4853 void tcp_sack_compress_send_ack(struct sock *sk)
4854 {
4855 	struct tcp_sock *tp = tcp_sk(sk);
4856 
4857 	if (!tp->compressed_ack)
4858 		return;
4859 
4860 	if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
4861 		__sock_put(sk);
4862 
4863 	/* Since we have to send one ack finally,
4864 	 * substract one from tp->compressed_ack to keep
4865 	 * LINUX_MIB_TCPACKCOMPRESSED accurate.
4866 	 */
4867 	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
4868 		      tp->compressed_ack - 1);
4869 
4870 	tp->compressed_ack = 0;
4871 	tcp_send_ack(sk);
4872 }
4873 
4874 /* Reasonable amount of sack blocks included in TCP SACK option
4875  * The max is 4, but this becomes 3 if TCP timestamps are there.
4876  * Given that SACK packets might be lost, be conservative and use 2.
4877  */
4878 #define TCP_SACK_BLOCKS_EXPECTED 2
4879 
4880 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4881 {
4882 	struct tcp_sock *tp = tcp_sk(sk);
4883 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4884 	int cur_sacks = tp->rx_opt.num_sacks;
4885 	int this_sack;
4886 
4887 	if (!cur_sacks)
4888 		goto new_sack;
4889 
4890 	for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4891 		if (tcp_sack_extend(sp, seq, end_seq)) {
4892 			if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4893 				tcp_sack_compress_send_ack(sk);
4894 			/* Rotate this_sack to the first one. */
4895 			for (; this_sack > 0; this_sack--, sp--)
4896 				swap(*sp, *(sp - 1));
4897 			if (cur_sacks > 1)
4898 				tcp_sack_maybe_coalesce(tp);
4899 			return;
4900 		}
4901 	}
4902 
4903 	if (this_sack >= TCP_SACK_BLOCKS_EXPECTED)
4904 		tcp_sack_compress_send_ack(sk);
4905 
4906 	/* Could not find an adjacent existing SACK, build a new one,
4907 	 * put it at the front, and shift everyone else down.  We
4908 	 * always know there is at least one SACK present already here.
4909 	 *
4910 	 * If the sack array is full, forget about the last one.
4911 	 */
4912 	if (this_sack >= TCP_NUM_SACKS) {
4913 		this_sack--;
4914 		tp->rx_opt.num_sacks--;
4915 		sp--;
4916 	}
4917 	for (; this_sack > 0; this_sack--, sp--)
4918 		*sp = *(sp - 1);
4919 
4920 new_sack:
4921 	/* Build the new head SACK, and we're done. */
4922 	sp->start_seq = seq;
4923 	sp->end_seq = end_seq;
4924 	tp->rx_opt.num_sacks++;
4925 }
4926 
4927 /* RCV.NXT advances, some SACKs should be eaten. */
4928 
4929 static void tcp_sack_remove(struct tcp_sock *tp)
4930 {
4931 	struct tcp_sack_block *sp = &tp->selective_acks[0];
4932 	int num_sacks = tp->rx_opt.num_sacks;
4933 	int this_sack;
4934 
4935 	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4936 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
4937 		tp->rx_opt.num_sacks = 0;
4938 		return;
4939 	}
4940 
4941 	for (this_sack = 0; this_sack < num_sacks;) {
4942 		/* Check if the start of the sack is covered by RCV.NXT. */
4943 		if (!before(tp->rcv_nxt, sp->start_seq)) {
4944 			int i;
4945 
4946 			/* RCV.NXT must cover all the block! */
4947 			WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4948 
4949 			/* Zap this SACK, by moving forward any other SACKS. */
4950 			for (i = this_sack+1; i < num_sacks; i++)
4951 				tp->selective_acks[i-1] = tp->selective_acks[i];
4952 			num_sacks--;
4953 			continue;
4954 		}
4955 		this_sack++;
4956 		sp++;
4957 	}
4958 	tp->rx_opt.num_sacks = num_sacks;
4959 }
4960 
4961 /**
4962  * tcp_try_coalesce - try to merge skb to prior one
4963  * @sk: socket
4964  * @to: prior buffer
4965  * @from: buffer to add in queue
4966  * @fragstolen: pointer to boolean
4967  *
4968  * Before queueing skb @from after @to, try to merge them
4969  * to reduce overall memory use and queue lengths, if cost is small.
4970  * Packets in ofo or receive queues can stay a long time.
4971  * Better try to coalesce them right now to avoid future collapses.
4972  * Returns true if caller should free @from instead of queueing it
4973  */
4974 static bool tcp_try_coalesce(struct sock *sk,
4975 			     struct sk_buff *to,
4976 			     struct sk_buff *from,
4977 			     bool *fragstolen)
4978 {
4979 	int delta;
4980 
4981 	*fragstolen = false;
4982 
4983 	/* Its possible this segment overlaps with prior segment in queue */
4984 	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
4985 		return false;
4986 
4987 	if (!tcp_skb_can_collapse_rx(to, from))
4988 		return false;
4989 
4990 	if (!skb_try_coalesce(to, from, fragstolen, &delta))
4991 		return false;
4992 
4993 	atomic_add(delta, &sk->sk_rmem_alloc);
4994 	sk_mem_charge(sk, delta);
4995 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
4996 	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
4997 	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
4998 	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
4999 
5000 	if (TCP_SKB_CB(from)->has_rxtstamp) {
5001 		TCP_SKB_CB(to)->has_rxtstamp = true;
5002 		to->tstamp = from->tstamp;
5003 		skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
5004 	}
5005 
5006 	return true;
5007 }
5008 
5009 static bool tcp_ooo_try_coalesce(struct sock *sk,
5010 			     struct sk_buff *to,
5011 			     struct sk_buff *from,
5012 			     bool *fragstolen)
5013 {
5014 	bool res = tcp_try_coalesce(sk, to, from, fragstolen);
5015 
5016 	/* In case tcp_drop_reason() is called later, update to->gso_segs */
5017 	if (res) {
5018 		u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
5019 			       max_t(u16, 1, skb_shinfo(from)->gso_segs);
5020 
5021 		skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
5022 	}
5023 	return res;
5024 }
5025 
5026 noinline_for_tracing static void
5027 tcp_drop_reason(struct sock *sk, struct sk_buff *skb, enum skb_drop_reason reason)
5028 {
5029 	sk_drops_skbadd(sk, skb);
5030 	sk_skb_reason_drop(sk, skb, reason);
5031 }
5032 
5033 /* This one checks to see if we can put data from the
5034  * out_of_order queue into the receive_queue.
5035  */
5036 static void tcp_ofo_queue(struct sock *sk)
5037 {
5038 	struct tcp_sock *tp = tcp_sk(sk);
5039 	__u32 dsack_high = tp->rcv_nxt;
5040 	bool fin, fragstolen, eaten;
5041 	struct sk_buff *skb, *tail;
5042 	struct rb_node *p;
5043 
5044 	p = rb_first(&tp->out_of_order_queue);
5045 	while (p) {
5046 		skb = rb_to_skb(p);
5047 		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5048 			break;
5049 
5050 		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
5051 			__u32 dsack = dsack_high;
5052 
5053 			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
5054 				dsack = TCP_SKB_CB(skb)->end_seq;
5055 			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
5056 		}
5057 		p = rb_next(p);
5058 		rb_erase(&skb->rbnode, &tp->out_of_order_queue);
5059 
5060 		if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
5061 			tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_DROP);
5062 			continue;
5063 		}
5064 
5065 		tail = skb_peek_tail(&sk->sk_receive_queue);
5066 		eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
5067 		tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
5068 		fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
5069 		if (!eaten)
5070 			tcp_add_receive_queue(sk, skb);
5071 		else
5072 			kfree_skb_partial(skb, fragstolen);
5073 
5074 		if (unlikely(fin)) {
5075 			tcp_fin(sk);
5076 			/* tcp_fin() purges tp->out_of_order_queue,
5077 			 * so we must end this loop right now.
5078 			 */
5079 			break;
5080 		}
5081 	}
5082 }
5083 
5084 static bool tcp_prune_ofo_queue(struct sock *sk, const struct sk_buff *in_skb);
5085 static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb);
5086 
5087 /* Check if this incoming skb can be added to socket receive queues
5088  * while satisfying sk->sk_rcvbuf limit.
5089  *
5090  * In theory we should use skb->truesize, but this can cause problems
5091  * when applications use too small SO_RCVBUF values.
5092  * When LRO / hw gro is used, the socket might have a high tp->scaling_ratio,
5093  * allowing RWIN to be close to available space.
5094  * Whenever the receive queue gets full, we can receive a small packet
5095  * filling RWIN, but with a high skb->truesize, because most NIC use 4K page
5096  * plus sk_buff metadata even when receiving less than 1500 bytes of payload.
5097  *
5098  * Note that we use skb->len to decide to accept or drop this packet,
5099  * but sk->sk_rmem_alloc is the sum of all skb->truesize.
5100  */
5101 static bool tcp_can_ingest(const struct sock *sk, const struct sk_buff *skb)
5102 {
5103 	unsigned int rmem = atomic_read(&sk->sk_rmem_alloc);
5104 
5105 	return rmem + skb->len <= sk->sk_rcvbuf;
5106 }
5107 
5108 static int tcp_try_rmem_schedule(struct sock *sk, const struct sk_buff *skb,
5109 				 unsigned int size)
5110 {
5111 	if (!tcp_can_ingest(sk, skb) ||
5112 	    !sk_rmem_schedule(sk, skb, size)) {
5113 
5114 		if (tcp_prune_queue(sk, skb) < 0)
5115 			return -1;
5116 
5117 		while (!sk_rmem_schedule(sk, skb, size)) {
5118 			if (!tcp_prune_ofo_queue(sk, skb))
5119 				return -1;
5120 		}
5121 	}
5122 	return 0;
5123 }
5124 
5125 static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
5126 {
5127 	struct tcp_sock *tp = tcp_sk(sk);
5128 	struct rb_node **p, *parent;
5129 	struct sk_buff *skb1;
5130 	u32 seq, end_seq;
5131 	bool fragstolen;
5132 
5133 	tcp_save_lrcv_flowlabel(sk, skb);
5134 	tcp_data_ecn_check(sk, skb);
5135 
5136 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
5137 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
5138 		sk->sk_data_ready(sk);
5139 		tcp_drop_reason(sk, skb, SKB_DROP_REASON_PROTO_MEM);
5140 		return;
5141 	}
5142 
5143 	tcp_measure_rcv_mss(sk, skb);
5144 	/* Disable header prediction. */
5145 	tp->pred_flags = 0;
5146 	inet_csk_schedule_ack(sk);
5147 
5148 	tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs);
5149 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
5150 	seq = TCP_SKB_CB(skb)->seq;
5151 	end_seq = TCP_SKB_CB(skb)->end_seq;
5152 
5153 	p = &tp->out_of_order_queue.rb_node;
5154 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5155 		/* Initial out of order segment, build 1 SACK. */
5156 		if (tcp_is_sack(tp)) {
5157 			tp->rx_opt.num_sacks = 1;
5158 			tp->selective_acks[0].start_seq = seq;
5159 			tp->selective_acks[0].end_seq = end_seq;
5160 		}
5161 		rb_link_node(&skb->rbnode, NULL, p);
5162 		rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
5163 		tp->ooo_last_skb = skb;
5164 		goto end;
5165 	}
5166 
5167 	/* In the typical case, we are adding an skb to the end of the list.
5168 	 * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
5169 	 */
5170 	if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
5171 				 skb, &fragstolen)) {
5172 coalesce_done:
5173 		/* For non sack flows, do not grow window to force DUPACK
5174 		 * and trigger fast retransmit.
5175 		 */
5176 		if (tcp_is_sack(tp))
5177 			tcp_grow_window(sk, skb, true);
5178 		kfree_skb_partial(skb, fragstolen);
5179 		skb = NULL;
5180 		goto add_sack;
5181 	}
5182 	/* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
5183 	if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
5184 		parent = &tp->ooo_last_skb->rbnode;
5185 		p = &parent->rb_right;
5186 		goto insert;
5187 	}
5188 
5189 	/* Find place to insert this segment. Handle overlaps on the way. */
5190 	parent = NULL;
5191 	while (*p) {
5192 		parent = *p;
5193 		skb1 = rb_to_skb(parent);
5194 		if (before(seq, TCP_SKB_CB(skb1)->seq)) {
5195 			p = &parent->rb_left;
5196 			continue;
5197 		}
5198 		if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
5199 			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
5200 				/* All the bits are present. Drop. */
5201 				NET_INC_STATS(sock_net(sk),
5202 					      LINUX_MIB_TCPOFOMERGE);
5203 				tcp_drop_reason(sk, skb,
5204 						SKB_DROP_REASON_TCP_OFOMERGE);
5205 				skb = NULL;
5206 				tcp_dsack_set(sk, seq, end_seq);
5207 				goto add_sack;
5208 			}
5209 			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
5210 				/* Partial overlap. */
5211 				tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
5212 			} else {
5213 				/* skb's seq == skb1's seq and skb covers skb1.
5214 				 * Replace skb1 with skb.
5215 				 */
5216 				rb_replace_node(&skb1->rbnode, &skb->rbnode,
5217 						&tp->out_of_order_queue);
5218 				tcp_dsack_extend(sk,
5219 						 TCP_SKB_CB(skb1)->seq,
5220 						 TCP_SKB_CB(skb1)->end_seq);
5221 				NET_INC_STATS(sock_net(sk),
5222 					      LINUX_MIB_TCPOFOMERGE);
5223 				tcp_drop_reason(sk, skb1,
5224 						SKB_DROP_REASON_TCP_OFOMERGE);
5225 				goto merge_right;
5226 			}
5227 		} else if (tcp_ooo_try_coalesce(sk, skb1,
5228 						skb, &fragstolen)) {
5229 			goto coalesce_done;
5230 		}
5231 		p = &parent->rb_right;
5232 	}
5233 insert:
5234 	/* Insert segment into RB tree. */
5235 	rb_link_node(&skb->rbnode, parent, p);
5236 	rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
5237 
5238 merge_right:
5239 	/* Remove other segments covered by skb. */
5240 	while ((skb1 = skb_rb_next(skb)) != NULL) {
5241 		if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
5242 			break;
5243 		if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
5244 			tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
5245 					 end_seq);
5246 			break;
5247 		}
5248 		rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
5249 		tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
5250 				 TCP_SKB_CB(skb1)->end_seq);
5251 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
5252 		tcp_drop_reason(sk, skb1, SKB_DROP_REASON_TCP_OFOMERGE);
5253 	}
5254 	/* If there is no skb after us, we are the last_skb ! */
5255 	if (!skb1)
5256 		tp->ooo_last_skb = skb;
5257 
5258 add_sack:
5259 	if (tcp_is_sack(tp))
5260 		tcp_sack_new_ofo_skb(sk, seq, end_seq);
5261 end:
5262 	if (skb) {
5263 		/* For non sack flows, do not grow window to force DUPACK
5264 		 * and trigger fast retransmit.
5265 		 */
5266 		if (tcp_is_sack(tp))
5267 			tcp_grow_window(sk, skb, false);
5268 		skb_condense(skb);
5269 		skb_set_owner_r(skb, sk);
5270 	}
5271 	/* do not grow rcvbuf for not-yet-accepted or orphaned sockets. */
5272 	if (sk->sk_socket)
5273 		tcp_rcvbuf_grow(sk);
5274 }
5275 
5276 static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
5277 				      bool *fragstolen)
5278 {
5279 	int eaten;
5280 	struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
5281 
5282 	eaten = (tail &&
5283 		 tcp_try_coalesce(sk, tail,
5284 				  skb, fragstolen)) ? 1 : 0;
5285 	tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
5286 	if (!eaten) {
5287 		tcp_add_receive_queue(sk, skb);
5288 		skb_set_owner_r(skb, sk);
5289 	}
5290 	return eaten;
5291 }
5292 
5293 int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
5294 {
5295 	struct sk_buff *skb;
5296 	int err = -ENOMEM;
5297 	int data_len = 0;
5298 	bool fragstolen;
5299 
5300 	if (size == 0)
5301 		return 0;
5302 
5303 	if (size > PAGE_SIZE) {
5304 		int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
5305 
5306 		data_len = npages << PAGE_SHIFT;
5307 		size = data_len + (size & ~PAGE_MASK);
5308 	}
5309 	skb = alloc_skb_with_frags(size - data_len, data_len,
5310 				   PAGE_ALLOC_COSTLY_ORDER,
5311 				   &err, sk->sk_allocation);
5312 	if (!skb)
5313 		goto err;
5314 
5315 	skb_put(skb, size - data_len);
5316 	skb->data_len = data_len;
5317 	skb->len = size;
5318 
5319 	if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5320 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5321 		goto err_free;
5322 	}
5323 
5324 	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
5325 	if (err)
5326 		goto err_free;
5327 
5328 	TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
5329 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
5330 	TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
5331 
5332 	if (tcp_queue_rcv(sk, skb, &fragstolen)) {
5333 		WARN_ON_ONCE(fragstolen); /* should not happen */
5334 		__kfree_skb(skb);
5335 	}
5336 	return size;
5337 
5338 err_free:
5339 	kfree_skb(skb);
5340 err:
5341 	return err;
5342 
5343 }
5344 
5345 void tcp_data_ready(struct sock *sk)
5346 {
5347 	if (tcp_epollin_ready(sk, sk->sk_rcvlowat) || sock_flag(sk, SOCK_DONE))
5348 		sk->sk_data_ready(sk);
5349 }
5350 
5351 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
5352 {
5353 	struct tcp_sock *tp = tcp_sk(sk);
5354 	enum skb_drop_reason reason;
5355 	bool fragstolen;
5356 	int eaten;
5357 
5358 	/* If a subflow has been reset, the packet should not continue
5359 	 * to be processed, drop the packet.
5360 	 */
5361 	if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb)) {
5362 		__kfree_skb(skb);
5363 		return;
5364 	}
5365 
5366 	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
5367 		__kfree_skb(skb);
5368 		return;
5369 	}
5370 	tcp_cleanup_skb(skb);
5371 	__skb_pull(skb, tcp_hdr(skb)->doff * 4);
5372 
5373 	reason = SKB_DROP_REASON_NOT_SPECIFIED;
5374 	tp->rx_opt.dsack = 0;
5375 
5376 	/*  Queue data for delivery to the user.
5377 	 *  Packets in sequence go to the receive queue.
5378 	 *  Out of sequence packets to the out_of_order_queue.
5379 	 */
5380 	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
5381 		if (tcp_receive_window(tp) == 0) {
5382 			/* Some stacks are known to send bare FIN packets
5383 			 * in a loop even if we send RWIN 0 in our ACK.
5384 			 * Accepting this FIN does not hurt memory pressure
5385 			 * because the FIN flag will simply be merged to the
5386 			 * receive queue tail skb in most cases.
5387 			 */
5388 			if (!skb->len &&
5389 			    (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
5390 				goto queue_and_out;
5391 
5392 			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5393 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5394 			goto out_of_window;
5395 		}
5396 
5397 		/* Ok. In sequence. In window. */
5398 queue_and_out:
5399 		if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
5400 			/* TODO: maybe ratelimit these WIN 0 ACK ? */
5401 			inet_csk(sk)->icsk_ack.pending |=
5402 					(ICSK_ACK_NOMEM | ICSK_ACK_NOW);
5403 			inet_csk_schedule_ack(sk);
5404 			sk->sk_data_ready(sk);
5405 
5406 			if (skb_queue_len(&sk->sk_receive_queue) && skb->len) {
5407 				reason = SKB_DROP_REASON_PROTO_MEM;
5408 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
5409 				goto drop;
5410 			}
5411 			sk_forced_mem_schedule(sk, skb->truesize);
5412 		}
5413 
5414 		eaten = tcp_queue_rcv(sk, skb, &fragstolen);
5415 		if (skb->len)
5416 			tcp_event_data_recv(sk, skb);
5417 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
5418 			tcp_fin(sk);
5419 
5420 		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5421 			tcp_ofo_queue(sk);
5422 
5423 			/* RFC5681. 4.2. SHOULD send immediate ACK, when
5424 			 * gap in queue is filled.
5425 			 */
5426 			if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5427 				inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
5428 		}
5429 
5430 		if (tp->rx_opt.num_sacks)
5431 			tcp_sack_remove(tp);
5432 
5433 		tcp_fast_path_check(sk);
5434 
5435 		if (eaten > 0)
5436 			kfree_skb_partial(skb, fragstolen);
5437 		if (!sock_flag(sk, SOCK_DEAD))
5438 			tcp_data_ready(sk);
5439 		return;
5440 	}
5441 
5442 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
5443 		tcp_rcv_spurious_retrans(sk, skb);
5444 		/* A retransmit, 2nd most common case.  Force an immediate ack. */
5445 		reason = SKB_DROP_REASON_TCP_OLD_DATA;
5446 		NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
5447 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
5448 
5449 out_of_window:
5450 		tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
5451 		inet_csk_schedule_ack(sk);
5452 drop:
5453 		tcp_drop_reason(sk, skb, reason);
5454 		return;
5455 	}
5456 
5457 	/* Out of window. F.e. zero window probe. */
5458 	if (!before(TCP_SKB_CB(skb)->seq,
5459 		    tp->rcv_nxt + tcp_receive_window(tp))) {
5460 		reason = SKB_DROP_REASON_TCP_OVERWINDOW;
5461 		goto out_of_window;
5462 	}
5463 
5464 	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5465 		/* Partial packet, seq < rcv_next < end_seq */
5466 		tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
5467 
5468 		/* If window is closed, drop tail of packet. But after
5469 		 * remembering D-SACK for its head made in previous line.
5470 		 */
5471 		if (!tcp_receive_window(tp)) {
5472 			reason = SKB_DROP_REASON_TCP_ZEROWINDOW;
5473 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
5474 			goto out_of_window;
5475 		}
5476 		goto queue_and_out;
5477 	}
5478 
5479 	tcp_data_queue_ofo(sk, skb);
5480 }
5481 
5482 static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
5483 {
5484 	if (list)
5485 		return !skb_queue_is_last(list, skb) ? skb->next : NULL;
5486 
5487 	return skb_rb_next(skb);
5488 }
5489 
5490 static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
5491 					struct sk_buff_head *list,
5492 					struct rb_root *root)
5493 {
5494 	struct sk_buff *next = tcp_skb_next(skb, list);
5495 
5496 	if (list)
5497 		__skb_unlink(skb, list);
5498 	else
5499 		rb_erase(&skb->rbnode, root);
5500 
5501 	__kfree_skb(skb);
5502 	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
5503 
5504 	return next;
5505 }
5506 
5507 /* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
5508 void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
5509 {
5510 	struct rb_node **p = &root->rb_node;
5511 	struct rb_node *parent = NULL;
5512 	struct sk_buff *skb1;
5513 
5514 	while (*p) {
5515 		parent = *p;
5516 		skb1 = rb_to_skb(parent);
5517 		if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
5518 			p = &parent->rb_left;
5519 		else
5520 			p = &parent->rb_right;
5521 	}
5522 	rb_link_node(&skb->rbnode, parent, p);
5523 	rb_insert_color(&skb->rbnode, root);
5524 }
5525 
5526 /* Collapse contiguous sequence of skbs head..tail with
5527  * sequence numbers start..end.
5528  *
5529  * If tail is NULL, this means until the end of the queue.
5530  *
5531  * Segments with FIN/SYN are not collapsed (only because this
5532  * simplifies code)
5533  */
5534 static void
5535 tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
5536 	     struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
5537 {
5538 	struct sk_buff *skb = head, *n;
5539 	struct sk_buff_head tmp;
5540 	bool end_of_skbs;
5541 
5542 	/* First, check that queue is collapsible and find
5543 	 * the point where collapsing can be useful.
5544 	 */
5545 restart:
5546 	for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
5547 		n = tcp_skb_next(skb, list);
5548 
5549 		if (!skb_frags_readable(skb))
5550 			goto skip_this;
5551 
5552 		/* No new bits? It is possible on ofo queue. */
5553 		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5554 			skb = tcp_collapse_one(sk, skb, list, root);
5555 			if (!skb)
5556 				break;
5557 			goto restart;
5558 		}
5559 
5560 		/* The first skb to collapse is:
5561 		 * - not SYN/FIN and
5562 		 * - bloated or contains data before "start" or
5563 		 *   overlaps to the next one and mptcp allow collapsing.
5564 		 */
5565 		if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
5566 		    (tcp_win_from_space(sk, skb->truesize) > skb->len ||
5567 		     before(TCP_SKB_CB(skb)->seq, start))) {
5568 			end_of_skbs = false;
5569 			break;
5570 		}
5571 
5572 		if (n && n != tail && skb_frags_readable(n) &&
5573 		    tcp_skb_can_collapse_rx(skb, n) &&
5574 		    TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
5575 			end_of_skbs = false;
5576 			break;
5577 		}
5578 
5579 skip_this:
5580 		/* Decided to skip this, advance start seq. */
5581 		start = TCP_SKB_CB(skb)->end_seq;
5582 	}
5583 	if (end_of_skbs ||
5584 	    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) ||
5585 	    !skb_frags_readable(skb))
5586 		return;
5587 
5588 	__skb_queue_head_init(&tmp);
5589 
5590 	while (before(start, end)) {
5591 		int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
5592 		struct sk_buff *nskb;
5593 
5594 		nskb = alloc_skb(copy, GFP_ATOMIC);
5595 		if (!nskb)
5596 			break;
5597 
5598 		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
5599 		skb_copy_decrypted(nskb, skb);
5600 		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
5601 		if (list)
5602 			__skb_queue_before(list, skb, nskb);
5603 		else
5604 			__skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
5605 		skb_set_owner_r(nskb, sk);
5606 		mptcp_skb_ext_move(nskb, skb);
5607 
5608 		/* Copy data, releasing collapsed skbs. */
5609 		while (copy > 0) {
5610 			int offset = start - TCP_SKB_CB(skb)->seq;
5611 			int size = TCP_SKB_CB(skb)->end_seq - start;
5612 
5613 			BUG_ON(offset < 0);
5614 			if (size > 0) {
5615 				size = min(copy, size);
5616 				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
5617 					BUG();
5618 				TCP_SKB_CB(nskb)->end_seq += size;
5619 				copy -= size;
5620 				start += size;
5621 			}
5622 			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
5623 				skb = tcp_collapse_one(sk, skb, list, root);
5624 				if (!skb ||
5625 				    skb == tail ||
5626 				    !tcp_skb_can_collapse_rx(nskb, skb) ||
5627 				    (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) ||
5628 				    !skb_frags_readable(skb))
5629 					goto end;
5630 			}
5631 		}
5632 	}
5633 end:
5634 	skb_queue_walk_safe(&tmp, skb, n)
5635 		tcp_rbtree_insert(root, skb);
5636 }
5637 
5638 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
5639  * and tcp_collapse() them until all the queue is collapsed.
5640  */
5641 static void tcp_collapse_ofo_queue(struct sock *sk)
5642 {
5643 	struct tcp_sock *tp = tcp_sk(sk);
5644 	u32 range_truesize, sum_tiny = 0;
5645 	struct sk_buff *skb, *head;
5646 	u32 start, end;
5647 
5648 	skb = skb_rb_first(&tp->out_of_order_queue);
5649 new_range:
5650 	if (!skb) {
5651 		tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
5652 		return;
5653 	}
5654 	start = TCP_SKB_CB(skb)->seq;
5655 	end = TCP_SKB_CB(skb)->end_seq;
5656 	range_truesize = skb->truesize;
5657 
5658 	for (head = skb;;) {
5659 		skb = skb_rb_next(skb);
5660 
5661 		/* Range is terminated when we see a gap or when
5662 		 * we are at the queue end.
5663 		 */
5664 		if (!skb ||
5665 		    after(TCP_SKB_CB(skb)->seq, end) ||
5666 		    before(TCP_SKB_CB(skb)->end_seq, start)) {
5667 			/* Do not attempt collapsing tiny skbs */
5668 			if (range_truesize != head->truesize ||
5669 			    end - start >= SKB_WITH_OVERHEAD(PAGE_SIZE)) {
5670 				tcp_collapse(sk, NULL, &tp->out_of_order_queue,
5671 					     head, skb, start, end);
5672 			} else {
5673 				sum_tiny += range_truesize;
5674 				if (sum_tiny > sk->sk_rcvbuf >> 3)
5675 					return;
5676 			}
5677 			goto new_range;
5678 		}
5679 
5680 		range_truesize += skb->truesize;
5681 		if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
5682 			start = TCP_SKB_CB(skb)->seq;
5683 		if (after(TCP_SKB_CB(skb)->end_seq, end))
5684 			end = TCP_SKB_CB(skb)->end_seq;
5685 	}
5686 }
5687 
5688 /*
5689  * Clean the out-of-order queue to make room.
5690  * We drop high sequences packets to :
5691  * 1) Let a chance for holes to be filled.
5692  *    This means we do not drop packets from ooo queue if their sequence
5693  *    is before incoming packet sequence.
5694  * 2) not add too big latencies if thousands of packets sit there.
5695  *    (But if application shrinks SO_RCVBUF, we could still end up
5696  *     freeing whole queue here)
5697  * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
5698  *
5699  * Return true if queue has shrunk.
5700  */
5701 static bool tcp_prune_ofo_queue(struct sock *sk, const struct sk_buff *in_skb)
5702 {
5703 	struct tcp_sock *tp = tcp_sk(sk);
5704 	struct rb_node *node, *prev;
5705 	bool pruned = false;
5706 	int goal;
5707 
5708 	if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
5709 		return false;
5710 
5711 	goal = sk->sk_rcvbuf >> 3;
5712 	node = &tp->ooo_last_skb->rbnode;
5713 
5714 	do {
5715 		struct sk_buff *skb = rb_to_skb(node);
5716 
5717 		/* If incoming skb would land last in ofo queue, stop pruning. */
5718 		if (after(TCP_SKB_CB(in_skb)->seq, TCP_SKB_CB(skb)->seq))
5719 			break;
5720 		pruned = true;
5721 		prev = rb_prev(node);
5722 		rb_erase(node, &tp->out_of_order_queue);
5723 		goal -= skb->truesize;
5724 		tcp_drop_reason(sk, skb, SKB_DROP_REASON_TCP_OFO_QUEUE_PRUNE);
5725 		tp->ooo_last_skb = rb_to_skb(prev);
5726 		if (!prev || goal <= 0) {
5727 			if (tcp_can_ingest(sk, in_skb) &&
5728 			    !tcp_under_memory_pressure(sk))
5729 				break;
5730 			goal = sk->sk_rcvbuf >> 3;
5731 		}
5732 		node = prev;
5733 	} while (node);
5734 
5735 	if (pruned) {
5736 		NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
5737 		/* Reset SACK state.  A conforming SACK implementation will
5738 		 * do the same at a timeout based retransmit.  When a connection
5739 		 * is in a sad state like this, we care only about integrity
5740 		 * of the connection not performance.
5741 		 */
5742 		if (tp->rx_opt.sack_ok)
5743 			tcp_sack_reset(&tp->rx_opt);
5744 	}
5745 	return pruned;
5746 }
5747 
5748 /* Reduce allocated memory if we can, trying to get
5749  * the socket within its memory limits again.
5750  *
5751  * Return less than zero if we should start dropping frames
5752  * until the socket owning process reads some of the data
5753  * to stabilize the situation.
5754  */
5755 static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb)
5756 {
5757 	struct tcp_sock *tp = tcp_sk(sk);
5758 
5759 	/* Do nothing if our queues are empty. */
5760 	if (!atomic_read(&sk->sk_rmem_alloc))
5761 		return -1;
5762 
5763 	NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
5764 
5765 	if (!tcp_can_ingest(sk, in_skb))
5766 		tcp_clamp_window(sk);
5767 	else if (tcp_under_memory_pressure(sk))
5768 		tcp_adjust_rcv_ssthresh(sk);
5769 
5770 	if (tcp_can_ingest(sk, in_skb))
5771 		return 0;
5772 
5773 	tcp_collapse_ofo_queue(sk);
5774 	if (!skb_queue_empty(&sk->sk_receive_queue))
5775 		tcp_collapse(sk, &sk->sk_receive_queue, NULL,
5776 			     skb_peek(&sk->sk_receive_queue),
5777 			     NULL,
5778 			     tp->copied_seq, tp->rcv_nxt);
5779 
5780 	if (tcp_can_ingest(sk, in_skb))
5781 		return 0;
5782 
5783 	/* Collapsing did not help, destructive actions follow.
5784 	 * This must not ever occur. */
5785 
5786 	tcp_prune_ofo_queue(sk, in_skb);
5787 
5788 	if (tcp_can_ingest(sk, in_skb))
5789 		return 0;
5790 
5791 	/* If we are really being abused, tell the caller to silently
5792 	 * drop receive data on the floor.  It will get retransmitted
5793 	 * and hopefully then we'll have sufficient space.
5794 	 */
5795 	NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
5796 
5797 	/* Massive buffer overcommit. */
5798 	tp->pred_flags = 0;
5799 	return -1;
5800 }
5801 
5802 static bool tcp_should_expand_sndbuf(struct sock *sk)
5803 {
5804 	const struct tcp_sock *tp = tcp_sk(sk);
5805 
5806 	/* If the user specified a specific send buffer setting, do
5807 	 * not modify it.
5808 	 */
5809 	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
5810 		return false;
5811 
5812 	/* If we are under global TCP memory pressure, do not expand.  */
5813 	if (tcp_under_memory_pressure(sk)) {
5814 		int unused_mem = sk_unused_reserved_mem(sk);
5815 
5816 		/* Adjust sndbuf according to reserved mem. But make sure
5817 		 * it never goes below SOCK_MIN_SNDBUF.
5818 		 * See sk_stream_moderate_sndbuf() for more details.
5819 		 */
5820 		if (unused_mem > SOCK_MIN_SNDBUF)
5821 			WRITE_ONCE(sk->sk_sndbuf, unused_mem);
5822 
5823 		return false;
5824 	}
5825 
5826 	/* If we are under soft global TCP memory pressure, do not expand.  */
5827 	if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
5828 		return false;
5829 
5830 	/* If we filled the congestion window, do not expand.  */
5831 	if (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp))
5832 		return false;
5833 
5834 	return true;
5835 }
5836 
5837 static void tcp_new_space(struct sock *sk)
5838 {
5839 	struct tcp_sock *tp = tcp_sk(sk);
5840 
5841 	if (tcp_should_expand_sndbuf(sk)) {
5842 		tcp_sndbuf_expand(sk);
5843 		tp->snd_cwnd_stamp = tcp_jiffies32;
5844 	}
5845 
5846 	INDIRECT_CALL_1(sk->sk_write_space, sk_stream_write_space, sk);
5847 }
5848 
5849 /* Caller made space either from:
5850  * 1) Freeing skbs in rtx queues (after tp->snd_una has advanced)
5851  * 2) Sent skbs from output queue (and thus advancing tp->snd_nxt)
5852  *
5853  * We might be able to generate EPOLLOUT to the application if:
5854  * 1) Space consumed in output/rtx queues is below sk->sk_sndbuf/2
5855  * 2) notsent amount (tp->write_seq - tp->snd_nxt) became
5856  *    small enough that tcp_stream_memory_free() decides it
5857  *    is time to generate EPOLLOUT.
5858  */
5859 void tcp_check_space(struct sock *sk)
5860 {
5861 	/* pairs with tcp_poll() */
5862 	smp_mb();
5863 	if (sk->sk_socket &&
5864 	    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
5865 		tcp_new_space(sk);
5866 		if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
5867 			tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
5868 	}
5869 }
5870 
5871 static inline void tcp_data_snd_check(struct sock *sk)
5872 {
5873 	tcp_push_pending_frames(sk);
5874 	tcp_check_space(sk);
5875 }
5876 
5877 /*
5878  * Check if sending an ack is needed.
5879  */
5880 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
5881 {
5882 	struct tcp_sock *tp = tcp_sk(sk);
5883 	unsigned long rtt, delay;
5884 
5885 	    /* More than one full frame received... */
5886 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
5887 	     /* ... and right edge of window advances far enough.
5888 	      * (tcp_recvmsg() will send ACK otherwise).
5889 	      * If application uses SO_RCVLOWAT, we want send ack now if
5890 	      * we have not received enough bytes to satisfy the condition.
5891 	      */
5892 	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
5893 	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||
5894 	    /* We ACK each frame or... */
5895 	    tcp_in_quickack_mode(sk) ||
5896 	    /* Protocol state mandates a one-time immediate ACK */
5897 	    inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
5898 		/* If we are running from __release_sock() in user context,
5899 		 * Defer the ack until tcp_release_cb().
5900 		 */
5901 		if (sock_owned_by_user_nocheck(sk) &&
5902 		    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_backlog_ack_defer)) {
5903 			set_bit(TCP_ACK_DEFERRED, &sk->sk_tsq_flags);
5904 			return;
5905 		}
5906 send_now:
5907 		tcp_send_ack(sk);
5908 		return;
5909 	}
5910 
5911 	if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
5912 		tcp_send_delayed_ack(sk);
5913 		return;
5914 	}
5915 
5916 	if (!tcp_is_sack(tp) ||
5917 	    tp->compressed_ack >= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr))
5918 		goto send_now;
5919 
5920 	if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
5921 		tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
5922 		tp->dup_ack_counter = 0;
5923 	}
5924 	if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) {
5925 		tp->dup_ack_counter++;
5926 		goto send_now;
5927 	}
5928 	tp->compressed_ack++;
5929 	if (hrtimer_is_queued(&tp->compressed_ack_timer))
5930 		return;
5931 
5932 	/* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
5933 
5934 	rtt = tp->rcv_rtt_est.rtt_us;
5935 	if (tp->srtt_us && tp->srtt_us < rtt)
5936 		rtt = tp->srtt_us;
5937 
5938 	delay = min_t(unsigned long,
5939 		      READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns),
5940 		      rtt * (NSEC_PER_USEC >> 3)/20);
5941 	sock_hold(sk);
5942 	hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay),
5943 			       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns),
5944 			       HRTIMER_MODE_REL_PINNED_SOFT);
5945 }
5946 
5947 static inline void tcp_ack_snd_check(struct sock *sk)
5948 {
5949 	if (!inet_csk_ack_scheduled(sk)) {
5950 		/* We sent a data segment already. */
5951 		return;
5952 	}
5953 	__tcp_ack_snd_check(sk, 1);
5954 }
5955 
5956 /*
5957  *	This routine is only called when we have urgent data
5958  *	signaled. Its the 'slow' part of tcp_urg. It could be
5959  *	moved inline now as tcp_urg is only called from one
5960  *	place. We handle URGent data wrong. We have to - as
5961  *	BSD still doesn't use the correction from RFC961.
5962  *	For 1003.1g we should support a new option TCP_STDURG to permit
5963  *	either form (or just set the sysctl tcp_stdurg).
5964  */
5965 
5966 static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5967 {
5968 	struct tcp_sock *tp = tcp_sk(sk);
5969 	u32 ptr = ntohs(th->urg_ptr);
5970 
5971 	if (ptr && !READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_stdurg))
5972 		ptr--;
5973 	ptr += ntohl(th->seq);
5974 
5975 	/* Ignore urgent data that we've already seen and read. */
5976 	if (after(tp->copied_seq, ptr))
5977 		return;
5978 
5979 	/* Do not replay urg ptr.
5980 	 *
5981 	 * NOTE: interesting situation not covered by specs.
5982 	 * Misbehaving sender may send urg ptr, pointing to segment,
5983 	 * which we already have in ofo queue. We are not able to fetch
5984 	 * such data and will stay in TCP_URG_NOTYET until will be eaten
5985 	 * by recvmsg(). Seems, we are not obliged to handle such wicked
5986 	 * situations. But it is worth to think about possibility of some
5987 	 * DoSes using some hypothetical application level deadlock.
5988 	 */
5989 	if (before(ptr, tp->rcv_nxt))
5990 		return;
5991 
5992 	/* Do we already have a newer (or duplicate) urgent pointer? */
5993 	if (tp->urg_data && !after(ptr, tp->urg_seq))
5994 		return;
5995 
5996 	/* Tell the world about our new urgent pointer. */
5997 	sk_send_sigurg(sk);
5998 
5999 	/* We may be adding urgent data when the last byte read was
6000 	 * urgent. To do this requires some care. We cannot just ignore
6001 	 * tp->copied_seq since we would read the last urgent byte again
6002 	 * as data, nor can we alter copied_seq until this data arrives
6003 	 * or we break the semantics of SIOCATMARK (and thus sockatmark())
6004 	 *
6005 	 * NOTE. Double Dutch. Rendering to plain English: author of comment
6006 	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
6007 	 * and expect that both A and B disappear from stream. This is _wrong_.
6008 	 * Though this happens in BSD with high probability, this is occasional.
6009 	 * Any application relying on this is buggy. Note also, that fix "works"
6010 	 * only in this artificial test. Insert some normal data between A and B and we will
6011 	 * decline of BSD again. Verdict: it is better to remove to trap
6012 	 * buggy users.
6013 	 */
6014 	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
6015 	    !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
6016 		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
6017 		tp->copied_seq++;
6018 		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
6019 			__skb_unlink(skb, &sk->sk_receive_queue);
6020 			__kfree_skb(skb);
6021 		}
6022 	}
6023 
6024 	WRITE_ONCE(tp->urg_data, TCP_URG_NOTYET);
6025 	WRITE_ONCE(tp->urg_seq, ptr);
6026 
6027 	/* Disable header prediction. */
6028 	tp->pred_flags = 0;
6029 }
6030 
6031 /* This is the 'fast' part of urgent handling. */
6032 static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
6033 {
6034 	struct tcp_sock *tp = tcp_sk(sk);
6035 
6036 	/* Check if we get a new urgent pointer - normally not. */
6037 	if (unlikely(th->urg))
6038 		tcp_check_urg(sk, th);
6039 
6040 	/* Do we wait for any urgent data? - normally not... */
6041 	if (unlikely(tp->urg_data == TCP_URG_NOTYET)) {
6042 		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
6043 			  th->syn;
6044 
6045 		/* Is the urgent pointer pointing into this packet? */
6046 		if (ptr < skb->len) {
6047 			u8 tmp;
6048 			if (skb_copy_bits(skb, ptr, &tmp, 1))
6049 				BUG();
6050 			WRITE_ONCE(tp->urg_data, TCP_URG_VALID | tmp);
6051 			if (!sock_flag(sk, SOCK_DEAD))
6052 				sk->sk_data_ready(sk);
6053 		}
6054 	}
6055 }
6056 
6057 /* Accept RST for rcv_nxt - 1 after a FIN.
6058  * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
6059  * FIN is sent followed by a RST packet. The RST is sent with the same
6060  * sequence number as the FIN, and thus according to RFC 5961 a challenge
6061  * ACK should be sent. However, Mac OSX rate limits replies to challenge
6062  * ACKs on the closed socket. In addition middleboxes can drop either the
6063  * challenge ACK or a subsequent RST.
6064  */
6065 static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
6066 {
6067 	const struct tcp_sock *tp = tcp_sk(sk);
6068 
6069 	return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
6070 			(1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
6071 					       TCPF_CLOSING));
6072 }
6073 
6074 /* Does PAWS and seqno based validation of an incoming segment, flags will
6075  * play significant role here.
6076  */
6077 static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
6078 				  const struct tcphdr *th, int syn_inerr)
6079 {
6080 	struct tcp_sock *tp = tcp_sk(sk);
6081 	bool accecn_reflector = false;
6082 	SKB_DR(reason);
6083 
6084 	/* RFC1323: H1. Apply PAWS check first. */
6085 	if (!tcp_fast_parse_options(sock_net(sk), skb, th, tp) ||
6086 	    !tp->rx_opt.saw_tstamp ||
6087 	    tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW))
6088 		goto step1;
6089 
6090 	reason = tcp_disordered_ack_check(sk, skb);
6091 	if (!reason)
6092 		goto step1;
6093 	/* Reset is accepted even if it did not pass PAWS. */
6094 	if (th->rst)
6095 		goto step1;
6096 	if (unlikely(th->syn))
6097 		goto syn_challenge;
6098 
6099 	/* Old ACK are common, increment PAWS_OLD_ACK
6100 	 * and do not send a dupack.
6101 	 */
6102 	if (reason == SKB_DROP_REASON_TCP_RFC7323_PAWS_ACK) {
6103 		NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWS_OLD_ACK);
6104 		goto discard;
6105 	}
6106 	NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
6107 	if (!tcp_oow_rate_limited(sock_net(sk), skb,
6108 				  LINUX_MIB_TCPACKSKIPPEDPAWS,
6109 				  &tp->last_oow_ack_time))
6110 		tcp_send_dupack(sk, skb);
6111 	goto discard;
6112 
6113 step1:
6114 	/* Step 1: check sequence number */
6115 	reason = tcp_sequence(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
6116 	if (reason) {
6117 		/* RFC793, page 37: "In all states except SYN-SENT, all reset
6118 		 * (RST) segments are validated by checking their SEQ-fields."
6119 		 * And page 69: "If an incoming segment is not acceptable,
6120 		 * an acknowledgment should be sent in reply (unless the RST
6121 		 * bit is set, if so drop the segment and return)".
6122 		 */
6123 		if (!th->rst) {
6124 			if (th->syn)
6125 				goto syn_challenge;
6126 
6127 			if (reason == SKB_DROP_REASON_TCP_INVALID_SEQUENCE ||
6128 			    reason == SKB_DROP_REASON_TCP_INVALID_END_SEQUENCE)
6129 				NET_INC_STATS(sock_net(sk),
6130 					      LINUX_MIB_BEYOND_WINDOW);
6131 			if (!tcp_oow_rate_limited(sock_net(sk), skb,
6132 						  LINUX_MIB_TCPACKSKIPPEDSEQ,
6133 						  &tp->last_oow_ack_time))
6134 				tcp_send_dupack(sk, skb);
6135 		} else if (tcp_reset_check(sk, skb)) {
6136 			goto reset;
6137 		}
6138 		goto discard;
6139 	}
6140 
6141 	/* Step 2: check RST bit */
6142 	if (th->rst) {
6143 		/* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
6144 		 * FIN and SACK too if available):
6145 		 * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
6146 		 * the right-most SACK block,
6147 		 * then
6148 		 *     RESET the connection
6149 		 * else
6150 		 *     Send a challenge ACK
6151 		 */
6152 		if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
6153 		    tcp_reset_check(sk, skb))
6154 			goto reset;
6155 
6156 		if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
6157 			struct tcp_sack_block *sp = &tp->selective_acks[0];
6158 			int max_sack = sp[0].end_seq;
6159 			int this_sack;
6160 
6161 			for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
6162 			     ++this_sack) {
6163 				max_sack = after(sp[this_sack].end_seq,
6164 						 max_sack) ?
6165 					sp[this_sack].end_seq : max_sack;
6166 			}
6167 
6168 			if (TCP_SKB_CB(skb)->seq == max_sack)
6169 				goto reset;
6170 		}
6171 
6172 		/* Disable TFO if RST is out-of-order
6173 		 * and no data has been received
6174 		 * for current active TFO socket
6175 		 */
6176 		if (tp->syn_fastopen && !tp->data_segs_in &&
6177 		    sk->sk_state == TCP_ESTABLISHED)
6178 			tcp_fastopen_active_disable(sk);
6179 		tcp_send_challenge_ack(sk, false);
6180 		SKB_DR_SET(reason, TCP_RESET);
6181 		goto discard;
6182 	}
6183 
6184 	/* step 3: check security and precedence [ignored] */
6185 
6186 	/* step 4: Check for a SYN
6187 	 * RFC 5961 4.2 : Send a challenge ack
6188 	 */
6189 	if (th->syn) {
6190 		if (tcp_ecn_mode_accecn(tp)) {
6191 			accecn_reflector = true;
6192 			if (tp->rx_opt.accecn &&
6193 			    tp->saw_accecn_opt < TCP_ACCECN_OPT_COUNTER_SEEN) {
6194 				u8 saw_opt = tcp_accecn_option_init(skb, tp->rx_opt.accecn);
6195 
6196 				tcp_accecn_saw_opt_fail_recv(tp, saw_opt);
6197 				tcp_accecn_opt_demand_min(sk, 1);
6198 			}
6199 		}
6200 		if (sk->sk_state == TCP_SYN_RECV && sk->sk_socket && th->ack &&
6201 		    TCP_SKB_CB(skb)->seq + 1 == TCP_SKB_CB(skb)->end_seq &&
6202 		    TCP_SKB_CB(skb)->seq + 1 == tp->rcv_nxt &&
6203 		    TCP_SKB_CB(skb)->ack_seq == tp->snd_nxt)
6204 			goto pass;
6205 syn_challenge:
6206 		if (syn_inerr)
6207 			TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6208 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
6209 		tcp_send_challenge_ack(sk, accecn_reflector);
6210 		SKB_DR_SET(reason, TCP_INVALID_SYN);
6211 		goto discard;
6212 	}
6213 
6214 pass:
6215 	bpf_skops_parse_hdr(sk, skb);
6216 
6217 	return true;
6218 
6219 discard:
6220 	tcp_drop_reason(sk, skb, reason);
6221 	return false;
6222 
6223 reset:
6224 	tcp_reset(sk, skb);
6225 	__kfree_skb(skb);
6226 	return false;
6227 }
6228 
6229 /*
6230  *	TCP receive function for the ESTABLISHED state.
6231  *
6232  *	It is split into a fast path and a slow path. The fast path is
6233  * 	disabled when:
6234  *	- A zero window was announced from us - zero window probing
6235  *        is only handled properly in the slow path.
6236  *	- Out of order segments arrived.
6237  *	- Urgent data is expected.
6238  *	- There is no buffer space left
6239  *	- Unexpected TCP flags/window values/header lengths are received
6240  *	  (detected by checking the TCP header against pred_flags)
6241  *	- Data is sent in both directions. Fast path only supports pure senders
6242  *	  or pure receivers (this means either the sequence number or the ack
6243  *	  value must stay constant)
6244  *	- Unexpected TCP option.
6245  *
6246  *	When these conditions are not satisfied it drops into a standard
6247  *	receive procedure patterned after RFC793 to handle all cases.
6248  *	The first three cases are guaranteed by proper pred_flags setting,
6249  *	the rest is checked inline. Fast processing is turned on in
6250  *	tcp_data_queue when everything is OK.
6251  */
6252 void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
6253 {
6254 	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
6255 	const struct tcphdr *th = (const struct tcphdr *)skb->data;
6256 	struct tcp_sock *tp = tcp_sk(sk);
6257 	unsigned int len = skb->len;
6258 
6259 	/* TCP congestion window tracking */
6260 	trace_tcp_probe(sk, skb);
6261 
6262 	tcp_mstamp_refresh(tp);
6263 	if (unlikely(!rcu_access_pointer(sk->sk_rx_dst)))
6264 		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
6265 	/*
6266 	 *	Header prediction.
6267 	 *	The code loosely follows the one in the famous
6268 	 *	"30 instruction TCP receive" Van Jacobson mail.
6269 	 *
6270 	 *	Van's trick is to deposit buffers into socket queue
6271 	 *	on a device interrupt, to call tcp_recv function
6272 	 *	on the receive process context and checksum and copy
6273 	 *	the buffer to user space. smart...
6274 	 *
6275 	 *	Our current scheme is not silly either but we take the
6276 	 *	extra cost of the net_bh soft interrupt processing...
6277 	 *	We do checksum and copy also but from device to kernel.
6278 	 */
6279 
6280 	tp->rx_opt.saw_tstamp = 0;
6281 	tp->rx_opt.accecn = 0;
6282 
6283 	/*	pred_flags is 0xS?10 << 16 + snd_wnd
6284 	 *	if header_prediction is to be made
6285 	 *	'S' will always be tp->tcp_header_len >> 2
6286 	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
6287 	 *  turn it off	(when there are holes in the receive
6288 	 *	 space for instance)
6289 	 *	PSH flag is ignored.
6290 	 */
6291 
6292 	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
6293 	    TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
6294 	    !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
6295 		int tcp_header_len = tp->tcp_header_len;
6296 		s32 delta = 0;
6297 		int flag = 0;
6298 
6299 		/* Timestamp header prediction: tcp_header_len
6300 		 * is automatically equal to th->doff*4 due to pred_flags
6301 		 * match.
6302 		 */
6303 
6304 		/* Check timestamp */
6305 		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
6306 			/* No? Slow path! */
6307 			if (!tcp_parse_aligned_timestamp(tp, th))
6308 				goto slow_path;
6309 
6310 			delta = tp->rx_opt.rcv_tsval -
6311 				tp->rx_opt.ts_recent;
6312 			/* If PAWS failed, check it more carefully in slow path */
6313 			if (delta < 0)
6314 				goto slow_path;
6315 
6316 			/* DO NOT update ts_recent here, if checksum fails
6317 			 * and timestamp was corrupted part, it will result
6318 			 * in a hung connection since we will drop all
6319 			 * future packets due to the PAWS test.
6320 			 */
6321 		}
6322 
6323 		if (len <= tcp_header_len) {
6324 			/* Bulk data transfer: sender */
6325 			if (len == tcp_header_len) {
6326 				/* Predicted packet is in window by definition.
6327 				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
6328 				 * Hence, check seq<=rcv_wup reduces to:
6329 				 */
6330 				if (tcp_header_len ==
6331 				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
6332 				    tp->rcv_nxt == tp->rcv_wup)
6333 					flag |= __tcp_replace_ts_recent(tp,
6334 									delta);
6335 
6336 				tcp_ecn_received_counters(sk, skb, 0);
6337 
6338 				/* We know that such packets are checksummed
6339 				 * on entry.
6340 				 */
6341 				tcp_ack(sk, skb, flag);
6342 				__kfree_skb(skb);
6343 				tcp_data_snd_check(sk);
6344 				/* When receiving pure ack in fast path, update
6345 				 * last ts ecr directly instead of calling
6346 				 * tcp_rcv_rtt_measure_ts()
6347 				 */
6348 				tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
6349 				return;
6350 			} else { /* Header too small */
6351 				reason = SKB_DROP_REASON_PKT_TOO_SMALL;
6352 				TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6353 				goto discard;
6354 			}
6355 		} else {
6356 			int eaten = 0;
6357 			bool fragstolen = false;
6358 
6359 			if (tcp_checksum_complete(skb))
6360 				goto csum_error;
6361 
6362 			if (after(TCP_SKB_CB(skb)->end_seq,
6363 				  tp->rcv_nxt + tcp_receive_window(tp)))
6364 				goto validate;
6365 
6366 			if ((int)skb->truesize > sk->sk_forward_alloc)
6367 				goto step5;
6368 
6369 			/* Predicted packet is in window by definition.
6370 			 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
6371 			 * Hence, check seq<=rcv_wup reduces to:
6372 			 */
6373 			if (tcp_header_len ==
6374 			    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
6375 			    tp->rcv_nxt == tp->rcv_wup)
6376 				flag |= __tcp_replace_ts_recent(tp,
6377 								delta);
6378 
6379 			tcp_rcv_rtt_measure_ts(sk, skb);
6380 
6381 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
6382 
6383 			/* Bulk data transfer: receiver */
6384 			tcp_cleanup_skb(skb);
6385 			__skb_pull(skb, tcp_header_len);
6386 			tcp_ecn_received_counters(sk, skb,
6387 						  len - tcp_header_len);
6388 			eaten = tcp_queue_rcv(sk, skb, &fragstolen);
6389 
6390 			tcp_event_data_recv(sk, skb);
6391 
6392 			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
6393 				/* Well, only one small jumplet in fast path... */
6394 				tcp_ack(sk, skb, flag | FLAG_DATA);
6395 				tcp_data_snd_check(sk);
6396 				if (!inet_csk_ack_scheduled(sk))
6397 					goto no_ack;
6398 			} else {
6399 				tcp_update_wl(tp, TCP_SKB_CB(skb)->seq);
6400 			}
6401 
6402 			__tcp_ack_snd_check(sk, 0);
6403 no_ack:
6404 			if (eaten)
6405 				kfree_skb_partial(skb, fragstolen);
6406 			tcp_data_ready(sk);
6407 			return;
6408 		}
6409 	}
6410 
6411 slow_path:
6412 	if (len < (th->doff << 2) || tcp_checksum_complete(skb))
6413 		goto csum_error;
6414 
6415 	if (!th->ack && !th->rst && !th->syn) {
6416 		reason = SKB_DROP_REASON_TCP_FLAGS;
6417 		goto discard;
6418 	}
6419 
6420 	/*
6421 	 *	Standard slow path.
6422 	 */
6423 validate:
6424 	if (!tcp_validate_incoming(sk, skb, th, 1))
6425 		return;
6426 
6427 step5:
6428 	tcp_ecn_received_counters_payload(sk, skb);
6429 
6430 	reason = tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT);
6431 	if ((int)reason < 0) {
6432 		reason = -reason;
6433 		goto discard;
6434 	}
6435 	tcp_rcv_rtt_measure_ts(sk, skb);
6436 
6437 	/* Process urgent data. */
6438 	tcp_urg(sk, skb, th);
6439 
6440 	/* step 7: process the segment text */
6441 	tcp_data_queue(sk, skb);
6442 
6443 	tcp_data_snd_check(sk);
6444 	tcp_ack_snd_check(sk);
6445 	return;
6446 
6447 csum_error:
6448 	reason = SKB_DROP_REASON_TCP_CSUM;
6449 	trace_tcp_bad_csum(skb);
6450 	TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
6451 	TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
6452 
6453 discard:
6454 	tcp_drop_reason(sk, skb, reason);
6455 }
6456 EXPORT_IPV6_MOD(tcp_rcv_established);
6457 
6458 void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb)
6459 {
6460 	struct inet_connection_sock *icsk = inet_csk(sk);
6461 	struct tcp_sock *tp = tcp_sk(sk);
6462 
6463 	tcp_mtup_init(sk);
6464 	icsk->icsk_af_ops->rebuild_header(sk);
6465 	tcp_init_metrics(sk);
6466 
6467 	/* Initialize the congestion window to start the transfer.
6468 	 * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
6469 	 * retransmitted. In light of RFC6298 more aggressive 1sec
6470 	 * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
6471 	 * retransmission has occurred.
6472 	 */
6473 	if (tp->total_retrans > 1 && tp->undo_marker)
6474 		tcp_snd_cwnd_set(tp, 1);
6475 	else
6476 		tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, __sk_dst_get(sk)));
6477 	tp->snd_cwnd_stamp = tcp_jiffies32;
6478 
6479 	bpf_skops_established(sk, bpf_op, skb);
6480 	/* Initialize congestion control unless BPF initialized it already: */
6481 	if (!icsk->icsk_ca_initialized)
6482 		tcp_init_congestion_control(sk);
6483 	tcp_init_buffer_space(sk);
6484 }
6485 
6486 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
6487 {
6488 	struct tcp_sock *tp = tcp_sk(sk);
6489 	struct inet_connection_sock *icsk = inet_csk(sk);
6490 
6491 	tcp_ao_finish_connect(sk, skb);
6492 	tcp_set_state(sk, TCP_ESTABLISHED);
6493 	icsk->icsk_ack.lrcvtime = tcp_jiffies32;
6494 
6495 	if (skb) {
6496 		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
6497 		security_inet_conn_established(sk, skb);
6498 		sk_mark_napi_id(sk, skb);
6499 	}
6500 
6501 	tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb);
6502 
6503 	/* Prevent spurious tcp_cwnd_restart() on first data
6504 	 * packet.
6505 	 */
6506 	tp->lsndtime = tcp_jiffies32;
6507 
6508 	if (sock_flag(sk, SOCK_KEEPOPEN))
6509 		tcp_reset_keepalive_timer(sk, keepalive_time_when(tp));
6510 
6511 	if (!tp->rx_opt.snd_wscale)
6512 		__tcp_fast_path_on(tp, tp->snd_wnd);
6513 	else
6514 		tp->pred_flags = 0;
6515 }
6516 
6517 static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
6518 				    struct tcp_fastopen_cookie *cookie)
6519 {
6520 	struct tcp_sock *tp = tcp_sk(sk);
6521 	struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
6522 	u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
6523 	bool syn_drop = false;
6524 
6525 	if (mss == READ_ONCE(tp->rx_opt.user_mss)) {
6526 		struct tcp_options_received opt;
6527 
6528 		/* Get original SYNACK MSS value if user MSS sets mss_clamp */
6529 		tcp_clear_options(&opt);
6530 		opt.user_mss = opt.mss_clamp = 0;
6531 		tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
6532 		mss = opt.mss_clamp;
6533 	}
6534 
6535 	if (!tp->syn_fastopen) {
6536 		/* Ignore an unsolicited cookie */
6537 		cookie->len = -1;
6538 	} else if (tp->total_retrans) {
6539 		/* SYN timed out and the SYN-ACK neither has a cookie nor
6540 		 * acknowledges data. Presumably the remote received only
6541 		 * the retransmitted (regular) SYNs: either the original
6542 		 * SYN-data or the corresponding SYN-ACK was dropped.
6543 		 */
6544 		syn_drop = (cookie->len < 0 && data);
6545 	} else if (cookie->len < 0 && !tp->syn_data) {
6546 		/* We requested a cookie but didn't get it. If we did not use
6547 		 * the (old) exp opt format then try so next time (try_exp=1).
6548 		 * Otherwise we go back to use the RFC7413 opt (try_exp=2).
6549 		 */
6550 		try_exp = tp->syn_fastopen_exp ? 2 : 1;
6551 	}
6552 
6553 	tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
6554 
6555 	if (data) { /* Retransmit unacked data in SYN */
6556 		if (tp->total_retrans)
6557 			tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED;
6558 		else
6559 			tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
6560 		skb_rbtree_walk_from(data)
6561 			 tcp_mark_skb_lost(sk, data);
6562 		tcp_non_congestion_loss_retransmit(sk);
6563 		NET_INC_STATS(sock_net(sk),
6564 				LINUX_MIB_TCPFASTOPENACTIVEFAIL);
6565 		return true;
6566 	}
6567 	tp->syn_data_acked = tp->syn_data;
6568 	if (tp->syn_data_acked) {
6569 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
6570 		/* SYN-data is counted as two separate packets in tcp_ack() */
6571 		if (tp->delivered > 1)
6572 			--tp->delivered;
6573 	}
6574 
6575 	tcp_fastopen_add_skb(sk, synack);
6576 
6577 	return false;
6578 }
6579 
6580 static void smc_check_reset_syn(struct tcp_sock *tp)
6581 {
6582 #if IS_ENABLED(CONFIG_SMC)
6583 	if (static_branch_unlikely(&tcp_have_smc)) {
6584 		if (tp->syn_smc && !tp->rx_opt.smc_ok)
6585 			tp->syn_smc = 0;
6586 	}
6587 #endif
6588 }
6589 
6590 static void tcp_try_undo_spurious_syn(struct sock *sk)
6591 {
6592 	struct tcp_sock *tp = tcp_sk(sk);
6593 	u32 syn_stamp;
6594 
6595 	/* undo_marker is set when SYN or SYNACK times out. The timeout is
6596 	 * spurious if the ACK's timestamp option echo value matches the
6597 	 * original SYN timestamp.
6598 	 */
6599 	syn_stamp = tp->retrans_stamp;
6600 	if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp &&
6601 	    syn_stamp == tp->rx_opt.rcv_tsecr)
6602 		tp->undo_marker = 0;
6603 }
6604 
6605 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
6606 					 const struct tcphdr *th)
6607 {
6608 	struct inet_connection_sock *icsk = inet_csk(sk);
6609 	struct tcp_sock *tp = tcp_sk(sk);
6610 	struct tcp_fastopen_cookie foc = { .len = -1 };
6611 	int saved_clamp = tp->rx_opt.mss_clamp;
6612 	bool fastopen_fail;
6613 	SKB_DR(reason);
6614 
6615 	tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
6616 	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
6617 		tp->rx_opt.rcv_tsecr -= tp->tsoffset;
6618 
6619 	if (th->ack) {
6620 		/* rfc793:
6621 		 * "If the state is SYN-SENT then
6622 		 *    first check the ACK bit
6623 		 *      If the ACK bit is set
6624 		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
6625 		 *        a reset (unless the RST bit is set, if so drop
6626 		 *        the segment and return)"
6627 		 */
6628 		if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
6629 		    after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
6630 			/* Previous FIN/ACK or RST/ACK might be ignored. */
6631 			if (icsk->icsk_retransmits == 0)
6632 				tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
6633 						     TCP_TIMEOUT_MIN, false);
6634 			SKB_DR_SET(reason, TCP_INVALID_ACK_SEQUENCE);
6635 			goto reset_and_undo;
6636 		}
6637 
6638 		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
6639 		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
6640 			     tcp_time_stamp_ts(tp))) {
6641 			NET_INC_STATS(sock_net(sk),
6642 					LINUX_MIB_PAWSACTIVEREJECTED);
6643 			SKB_DR_SET(reason, TCP_RFC7323_PAWS);
6644 			goto reset_and_undo;
6645 		}
6646 
6647 		/* Now ACK is acceptable.
6648 		 *
6649 		 * "If the RST bit is set
6650 		 *    If the ACK was acceptable then signal the user "error:
6651 		 *    connection reset", drop the segment, enter CLOSED state,
6652 		 *    delete TCB, and return."
6653 		 */
6654 
6655 		if (th->rst) {
6656 			tcp_reset(sk, skb);
6657 consume:
6658 			__kfree_skb(skb);
6659 			return 0;
6660 		}
6661 
6662 		/* rfc793:
6663 		 *   "fifth, if neither of the SYN or RST bits is set then
6664 		 *    drop the segment and return."
6665 		 *
6666 		 *    See note below!
6667 		 *                                        --ANK(990513)
6668 		 */
6669 		if (!th->syn) {
6670 			SKB_DR_SET(reason, TCP_FLAGS);
6671 			goto discard_and_undo;
6672 		}
6673 		/* rfc793:
6674 		 *   "If the SYN bit is on ...
6675 		 *    are acceptable then ...
6676 		 *    (our SYN has been ACKed), change the connection
6677 		 *    state to ESTABLISHED..."
6678 		 */
6679 
6680 		if (tcp_ecn_mode_any(tp))
6681 			tcp_ecn_rcv_synack(sk, skb, th,
6682 					   TCP_SKB_CB(skb)->ip_dsfield);
6683 
6684 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
6685 		tcp_try_undo_spurious_syn(sk);
6686 		tcp_ack(sk, skb, FLAG_SLOWPATH);
6687 
6688 		/* Ok.. it's good. Set up sequence numbers and
6689 		 * move to established.
6690 		 */
6691 		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6692 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6693 
6694 		/* RFC1323: The window in SYN & SYN/ACK segments is
6695 		 * never scaled.
6696 		 */
6697 		tp->snd_wnd = ntohs(th->window);
6698 
6699 		if (!tp->rx_opt.wscale_ok) {
6700 			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
6701 			WRITE_ONCE(tp->window_clamp,
6702 				   min(tp->window_clamp, 65535U));
6703 		}
6704 
6705 		if (tp->rx_opt.saw_tstamp) {
6706 			tp->rx_opt.tstamp_ok	   = 1;
6707 			tp->tcp_header_len =
6708 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6709 			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
6710 			tcp_store_ts_recent(tp);
6711 		} else {
6712 			tp->tcp_header_len = sizeof(struct tcphdr);
6713 		}
6714 
6715 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6716 		tcp_initialize_rcv_mss(sk);
6717 
6718 		/* Remember, tcp_poll() does not lock socket!
6719 		 * Change state from SYN-SENT only after copied_seq
6720 		 * is initialized. */
6721 		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6722 
6723 		smc_check_reset_syn(tp);
6724 
6725 		smp_mb();
6726 
6727 		tcp_finish_connect(sk, skb);
6728 
6729 		fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
6730 				tcp_rcv_fastopen_synack(sk, skb, &foc);
6731 
6732 		if (!sock_flag(sk, SOCK_DEAD)) {
6733 			sk->sk_state_change(sk);
6734 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
6735 		}
6736 		if (fastopen_fail)
6737 			return -1;
6738 		if (sk->sk_write_pending ||
6739 		    READ_ONCE(icsk->icsk_accept_queue.rskq_defer_accept) ||
6740 		    inet_csk_in_pingpong_mode(sk)) {
6741 			/* Save one ACK. Data will be ready after
6742 			 * several ticks, if write_pending is set.
6743 			 *
6744 			 * It may be deleted, but with this feature tcpdumps
6745 			 * look so _wonderfully_ clever, that I was not able
6746 			 * to stand against the temptation 8)     --ANK
6747 			 */
6748 			inet_csk_schedule_ack(sk);
6749 			tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
6750 			tcp_reset_xmit_timer(sk, ICSK_TIME_DACK,
6751 					     TCP_DELACK_MAX, false);
6752 			goto consume;
6753 		}
6754 		tcp_send_ack_reflect_ect(sk, tcp_ecn_mode_accecn(tp));
6755 		return -1;
6756 	}
6757 
6758 	/* No ACK in the segment */
6759 
6760 	if (th->rst) {
6761 		/* rfc793:
6762 		 * "If the RST bit is set
6763 		 *
6764 		 *      Otherwise (no ACK) drop the segment and return."
6765 		 */
6766 		SKB_DR_SET(reason, TCP_RESET);
6767 		goto discard_and_undo;
6768 	}
6769 
6770 	/* PAWS check. */
6771 	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
6772 	    tcp_paws_reject(&tp->rx_opt, 0)) {
6773 		SKB_DR_SET(reason, TCP_RFC7323_PAWS);
6774 		goto discard_and_undo;
6775 	}
6776 	if (th->syn) {
6777 		/* We see SYN without ACK. It is attempt of
6778 		 * simultaneous connect with crossed SYNs.
6779 		 * Particularly, it can be connect to self.
6780 		 */
6781 #ifdef CONFIG_TCP_AO
6782 		struct tcp_ao_info *ao;
6783 
6784 		ao = rcu_dereference_protected(tp->ao_info,
6785 					       lockdep_sock_is_held(sk));
6786 		if (ao) {
6787 			WRITE_ONCE(ao->risn, th->seq);
6788 			ao->rcv_sne = 0;
6789 		}
6790 #endif
6791 		tcp_set_state(sk, TCP_SYN_RECV);
6792 
6793 		if (tp->rx_opt.saw_tstamp) {
6794 			tp->rx_opt.tstamp_ok = 1;
6795 			tcp_store_ts_recent(tp);
6796 			tp->tcp_header_len =
6797 				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
6798 		} else {
6799 			tp->tcp_header_len = sizeof(struct tcphdr);
6800 		}
6801 
6802 		WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1);
6803 		WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
6804 		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
6805 
6806 		/* RFC1323: The window in SYN & SYN/ACK segments is
6807 		 * never scaled.
6808 		 */
6809 		tp->snd_wnd    = ntohs(th->window);
6810 		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
6811 		tp->max_window = tp->snd_wnd;
6812 
6813 		tcp_ecn_rcv_syn(tp, th, skb);
6814 
6815 		tcp_mtup_init(sk);
6816 		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
6817 		tcp_initialize_rcv_mss(sk);
6818 
6819 		tcp_send_synack(sk);
6820 #if 0
6821 		/* Note, we could accept data and URG from this segment.
6822 		 * There are no obstacles to make this (except that we must
6823 		 * either change tcp_recvmsg() to prevent it from returning data
6824 		 * before 3WHS completes per RFC793, or employ TCP Fast Open).
6825 		 *
6826 		 * However, if we ignore data in ACKless segments sometimes,
6827 		 * we have no reasons to accept it sometimes.
6828 		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
6829 		 * is not flawless. So, discard packet for sanity.
6830 		 * Uncomment this return to process the data.
6831 		 */
6832 		return -1;
6833 #else
6834 		goto consume;
6835 #endif
6836 	}
6837 	/* "fifth, if neither of the SYN or RST bits is set then
6838 	 * drop the segment and return."
6839 	 */
6840 
6841 discard_and_undo:
6842 	tcp_clear_options(&tp->rx_opt);
6843 	tp->rx_opt.mss_clamp = saved_clamp;
6844 	tcp_drop_reason(sk, skb, reason);
6845 	return 0;
6846 
6847 reset_and_undo:
6848 	tcp_clear_options(&tp->rx_opt);
6849 	tp->rx_opt.mss_clamp = saved_clamp;
6850 	/* we can reuse/return @reason to its caller to handle the exception */
6851 	return reason;
6852 }
6853 
6854 static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
6855 {
6856 	struct tcp_sock *tp = tcp_sk(sk);
6857 	struct request_sock *req;
6858 
6859 	/* If we are still handling the SYNACK RTO, see if timestamp ECR allows
6860 	 * undo. If peer SACKs triggered fast recovery, we can't undo here.
6861 	 */
6862 	if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss && !tp->packets_out)
6863 		tcp_try_undo_recovery(sk);
6864 
6865 	tcp_update_rto_time(tp);
6866 	WRITE_ONCE(inet_csk(sk)->icsk_retransmits, 0);
6867 	/* In tcp_fastopen_synack_timer() on the first SYNACK RTO we set
6868 	 * retrans_stamp but don't enter CA_Loss, so in case that happened we
6869 	 * need to zero retrans_stamp here to prevent spurious
6870 	 * retransmits_timed_out(). However, if the ACK of our SYNACK caused us
6871 	 * to enter CA_Recovery then we need to leave retrans_stamp as it was
6872 	 * set entering CA_Recovery, for correct retransmits_timed_out() and
6873 	 * undo behavior.
6874 	 */
6875 	tcp_retrans_stamp_cleanup(sk);
6876 
6877 	/* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1,
6878 	 * we no longer need req so release it.
6879 	 */
6880 	req = rcu_dereference_protected(tp->fastopen_rsk,
6881 					lockdep_sock_is_held(sk));
6882 	reqsk_fastopen_remove(sk, req, false);
6883 
6884 	/* Re-arm the timer because data may have been sent out.
6885 	 * This is similar to the regular data transmission case
6886 	 * when new data has just been ack'ed.
6887 	 *
6888 	 * (TFO) - we could try to be more aggressive and
6889 	 * retransmitting any data sooner based on when they
6890 	 * are sent out.
6891 	 */
6892 	tcp_rearm_rto(sk);
6893 }
6894 
6895 /*
6896  *	This function implements the receiving procedure of RFC 793 for
6897  *	all states except ESTABLISHED and TIME_WAIT.
6898  *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
6899  *	address independent.
6900  */
6901 
6902 enum skb_drop_reason
6903 tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
6904 {
6905 	struct tcp_sock *tp = tcp_sk(sk);
6906 	struct inet_connection_sock *icsk = inet_csk(sk);
6907 	const struct tcphdr *th = tcp_hdr(skb);
6908 	struct request_sock *req;
6909 	int queued = 0;
6910 	SKB_DR(reason);
6911 
6912 	switch (sk->sk_state) {
6913 	case TCP_CLOSE:
6914 		SKB_DR_SET(reason, TCP_CLOSE);
6915 		goto discard;
6916 
6917 	case TCP_LISTEN:
6918 		if (th->ack)
6919 			return SKB_DROP_REASON_TCP_FLAGS;
6920 
6921 		if (th->rst) {
6922 			SKB_DR_SET(reason, TCP_RESET);
6923 			goto discard;
6924 		}
6925 		if (th->syn) {
6926 			if (th->fin) {
6927 				SKB_DR_SET(reason, TCP_FLAGS);
6928 				goto discard;
6929 			}
6930 			/* It is possible that we process SYN packets from backlog,
6931 			 * so we need to make sure to disable BH and RCU right there.
6932 			 */
6933 			rcu_read_lock();
6934 			local_bh_disable();
6935 			icsk->icsk_af_ops->conn_request(sk, skb);
6936 			local_bh_enable();
6937 			rcu_read_unlock();
6938 
6939 			consume_skb(skb);
6940 			return 0;
6941 		}
6942 		SKB_DR_SET(reason, TCP_FLAGS);
6943 		goto discard;
6944 
6945 	case TCP_SYN_SENT:
6946 		tp->rx_opt.saw_tstamp = 0;
6947 		tcp_mstamp_refresh(tp);
6948 		queued = tcp_rcv_synsent_state_process(sk, skb, th);
6949 		if (queued >= 0)
6950 			return queued;
6951 
6952 		/* Do step6 onward by hand. */
6953 		tcp_urg(sk, skb, th);
6954 		__kfree_skb(skb);
6955 		tcp_data_snd_check(sk);
6956 		return 0;
6957 	}
6958 
6959 	tcp_mstamp_refresh(tp);
6960 	tp->rx_opt.saw_tstamp = 0;
6961 	req = rcu_dereference_protected(tp->fastopen_rsk,
6962 					lockdep_sock_is_held(sk));
6963 	if (req) {
6964 		bool req_stolen;
6965 
6966 		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
6967 		    sk->sk_state != TCP_FIN_WAIT1);
6968 
6969 		SKB_DR_SET(reason, TCP_FASTOPEN);
6970 		if (!tcp_check_req(sk, skb, req, true, &req_stolen, &reason))
6971 			goto discard;
6972 	}
6973 
6974 	if (!th->ack && !th->rst && !th->syn) {
6975 		SKB_DR_SET(reason, TCP_FLAGS);
6976 		goto discard;
6977 	}
6978 	if (!tcp_validate_incoming(sk, skb, th, 0))
6979 		return 0;
6980 
6981 	/* step 5: check the ACK field */
6982 	reason = tcp_ack(sk, skb, FLAG_SLOWPATH |
6983 				  FLAG_UPDATE_TS_RECENT |
6984 				  FLAG_NO_CHALLENGE_ACK);
6985 
6986 	if ((int)reason <= 0) {
6987 		if (sk->sk_state == TCP_SYN_RECV) {
6988 			/* send one RST */
6989 			if (!reason)
6990 				return SKB_DROP_REASON_TCP_OLD_ACK;
6991 			return -reason;
6992 		}
6993 		/* accept old ack during closing */
6994 		if ((int)reason < 0) {
6995 			tcp_send_challenge_ack(sk, false);
6996 			reason = -reason;
6997 			goto discard;
6998 		}
6999 	}
7000 	SKB_DR_SET(reason, NOT_SPECIFIED);
7001 	switch (sk->sk_state) {
7002 	case TCP_SYN_RECV:
7003 		tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
7004 		if (!tp->srtt_us)
7005 			tcp_synack_rtt_meas(sk, req);
7006 
7007 		if (tp->rx_opt.tstamp_ok)
7008 			tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
7009 
7010 		if (req) {
7011 			tcp_rcv_synrecv_state_fastopen(sk);
7012 		} else {
7013 			tcp_try_undo_spurious_syn(sk);
7014 			tp->retrans_stamp = 0;
7015 			tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB,
7016 					  skb);
7017 			WRITE_ONCE(tp->copied_seq, tp->rcv_nxt);
7018 		}
7019 		tcp_ao_established(sk);
7020 		smp_mb();
7021 		tcp_set_state(sk, TCP_ESTABLISHED);
7022 		sk->sk_state_change(sk);
7023 
7024 		/* Note, that this wakeup is only for marginal crossed SYN case.
7025 		 * Passively open sockets are not waked up, because
7026 		 * sk->sk_sleep == NULL and sk->sk_socket == NULL.
7027 		 */
7028 		if (sk->sk_socket)
7029 			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
7030 
7031 		tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
7032 		tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
7033 		tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
7034 
7035 		if (!inet_csk(sk)->icsk_ca_ops->cong_control)
7036 			tcp_update_pacing_rate(sk);
7037 
7038 		/* Prevent spurious tcp_cwnd_restart() on first data packet */
7039 		tp->lsndtime = tcp_jiffies32;
7040 
7041 		tcp_initialize_rcv_mss(sk);
7042 		if (tcp_ecn_mode_accecn(tp))
7043 			tcp_accecn_third_ack(sk, skb, tp->syn_ect_snt);
7044 		tcp_fast_path_on(tp);
7045 		if (sk->sk_shutdown & SEND_SHUTDOWN)
7046 			tcp_shutdown(sk, SEND_SHUTDOWN);
7047 
7048 		break;
7049 
7050 	case TCP_FIN_WAIT1: {
7051 		int tmo;
7052 
7053 		if (req)
7054 			tcp_rcv_synrecv_state_fastopen(sk);
7055 
7056 		if (tp->snd_una != tp->write_seq)
7057 			break;
7058 
7059 		tcp_set_state(sk, TCP_FIN_WAIT2);
7060 		WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | SEND_SHUTDOWN);
7061 
7062 		sk_dst_confirm(sk);
7063 
7064 		if (!sock_flag(sk, SOCK_DEAD)) {
7065 			/* Wake up lingering close() */
7066 			sk->sk_state_change(sk);
7067 			break;
7068 		}
7069 
7070 		if (READ_ONCE(tp->linger2) < 0) {
7071 			tcp_done(sk);
7072 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
7073 			return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
7074 		}
7075 		if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
7076 		    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
7077 			/* Receive out of order FIN after close() */
7078 			if (tp->syn_fastopen && th->fin)
7079 				tcp_fastopen_active_disable(sk);
7080 			tcp_done(sk);
7081 			NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
7082 			return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
7083 		}
7084 
7085 		tmo = tcp_fin_time(sk);
7086 		if (tmo > TCP_TIMEWAIT_LEN) {
7087 			tcp_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
7088 		} else if (th->fin || sock_owned_by_user(sk)) {
7089 			/* Bad case. We could lose such FIN otherwise.
7090 			 * It is not a big problem, but it looks confusing
7091 			 * and not so rare event. We still can lose it now,
7092 			 * if it spins in bh_lock_sock(), but it is really
7093 			 * marginal case.
7094 			 */
7095 			tcp_reset_keepalive_timer(sk, tmo);
7096 		} else {
7097 			tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
7098 			goto consume;
7099 		}
7100 		break;
7101 	}
7102 
7103 	case TCP_CLOSING:
7104 		if (tp->snd_una == tp->write_seq) {
7105 			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
7106 			goto consume;
7107 		}
7108 		break;
7109 
7110 	case TCP_LAST_ACK:
7111 		if (tp->snd_una == tp->write_seq) {
7112 			tcp_update_metrics(sk);
7113 			tcp_done(sk);
7114 			goto consume;
7115 		}
7116 		break;
7117 	}
7118 
7119 	/* step 6: check the URG bit */
7120 	tcp_urg(sk, skb, th);
7121 
7122 	/* step 7: process the segment text */
7123 	switch (sk->sk_state) {
7124 	case TCP_CLOSE_WAIT:
7125 	case TCP_CLOSING:
7126 	case TCP_LAST_ACK:
7127 		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
7128 			/* If a subflow has been reset, the packet should not
7129 			 * continue to be processed, drop the packet.
7130 			 */
7131 			if (sk_is_mptcp(sk) && !mptcp_incoming_options(sk, skb))
7132 				goto discard;
7133 			break;
7134 		}
7135 		fallthrough;
7136 	case TCP_FIN_WAIT1:
7137 	case TCP_FIN_WAIT2:
7138 		/* RFC 793 says to queue data in these states,
7139 		 * RFC 1122 says we MUST send a reset.
7140 		 * BSD 4.4 also does reset.
7141 		 */
7142 		if (sk->sk_shutdown & RCV_SHUTDOWN) {
7143 			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
7144 			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
7145 				NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
7146 				tcp_reset(sk, skb);
7147 				return SKB_DROP_REASON_TCP_ABORT_ON_DATA;
7148 			}
7149 		}
7150 		fallthrough;
7151 	case TCP_ESTABLISHED:
7152 		tcp_data_queue(sk, skb);
7153 		queued = 1;
7154 		break;
7155 	}
7156 
7157 	/* tcp_data could move socket to TIME-WAIT */
7158 	if (sk->sk_state != TCP_CLOSE) {
7159 		tcp_data_snd_check(sk);
7160 		tcp_ack_snd_check(sk);
7161 	}
7162 
7163 	if (!queued) {
7164 discard:
7165 		tcp_drop_reason(sk, skb, reason);
7166 	}
7167 	return 0;
7168 
7169 consume:
7170 	__kfree_skb(skb);
7171 	return 0;
7172 }
7173 EXPORT_IPV6_MOD(tcp_rcv_state_process);
7174 
7175 static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
7176 {
7177 	struct inet_request_sock *ireq = inet_rsk(req);
7178 
7179 	if (family == AF_INET)
7180 		net_dbg_ratelimited("drop open request from %pI4/%u\n",
7181 				    &ireq->ir_rmt_addr, port);
7182 #if IS_ENABLED(CONFIG_IPV6)
7183 	else if (family == AF_INET6)
7184 		net_dbg_ratelimited("drop open request from %pI6/%u\n",
7185 				    &ireq->ir_v6_rmt_addr, port);
7186 #endif
7187 }
7188 
7189 /* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
7190  *
7191  * If we receive a SYN packet with these bits set, it means a
7192  * network is playing bad games with TOS bits. In order to
7193  * avoid possible false congestion notifications, we disable
7194  * TCP ECN negotiation.
7195  *
7196  * Exception: tcp_ca wants ECN. This is required for DCTCP
7197  * congestion control: Linux DCTCP asserts ECT on all packets,
7198  * including SYN, which is most optimal solution; however,
7199  * others, such as FreeBSD do not.
7200  *
7201  * Exception: At least one of the reserved bits of the TCP header (th->res1) is
7202  * set, indicating the use of a future TCP extension (such as AccECN). See
7203  * RFC8311 §4.3 which updates RFC3168 to allow the development of such
7204  * extensions.
7205  */
7206 static void tcp_ecn_create_request(struct request_sock *req,
7207 				   const struct sk_buff *skb,
7208 				   const struct sock *listen_sk,
7209 				   const struct dst_entry *dst)
7210 {
7211 	const struct tcphdr *th = tcp_hdr(skb);
7212 	const struct net *net = sock_net(listen_sk);
7213 	bool th_ecn = th->ece && th->cwr;
7214 	bool ect, ecn_ok;
7215 	u32 ecn_ok_dst;
7216 
7217 	if (tcp_accecn_syn_requested(th) &&
7218 	    READ_ONCE(net->ipv4.sysctl_tcp_ecn) >= 3) {
7219 		inet_rsk(req)->ecn_ok = 1;
7220 		tcp_rsk(req)->accecn_ok = 1;
7221 		tcp_rsk(req)->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield &
7222 					    INET_ECN_MASK;
7223 		return;
7224 	}
7225 
7226 	if (!th_ecn)
7227 		return;
7228 
7229 	ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
7230 	ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
7231 	ecn_ok = READ_ONCE(net->ipv4.sysctl_tcp_ecn) || ecn_ok_dst;
7232 
7233 	if (((!ect || th->res1 || th->ae) && ecn_ok) ||
7234 	    tcp_ca_needs_ecn(listen_sk) ||
7235 	    (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
7236 	    tcp_bpf_ca_needs_ecn((struct sock *)req))
7237 		inet_rsk(req)->ecn_ok = 1;
7238 }
7239 
7240 static void tcp_openreq_init(struct request_sock *req,
7241 			     const struct tcp_options_received *rx_opt,
7242 			     struct sk_buff *skb, const struct sock *sk)
7243 {
7244 	struct inet_request_sock *ireq = inet_rsk(req);
7245 
7246 	req->rsk_rcv_wnd = 0;		/* So that tcp_send_synack() knows! */
7247 	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
7248 	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
7249 	tcp_rsk(req)->snt_synack = 0;
7250 	tcp_rsk(req)->snt_tsval_first = 0;
7251 	tcp_rsk(req)->last_oow_ack_time = 0;
7252 	tcp_rsk(req)->accecn_ok = 0;
7253 	tcp_rsk(req)->saw_accecn_opt = TCP_ACCECN_OPT_NOT_SEEN;
7254 	tcp_rsk(req)->accecn_fail_mode = 0;
7255 	tcp_rsk(req)->syn_ect_rcv = 0;
7256 	tcp_rsk(req)->syn_ect_snt = 0;
7257 	req->mss = rx_opt->mss_clamp;
7258 	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
7259 	ireq->tstamp_ok = rx_opt->tstamp_ok;
7260 	ireq->sack_ok = rx_opt->sack_ok;
7261 	ireq->snd_wscale = rx_opt->snd_wscale;
7262 	ireq->wscale_ok = rx_opt->wscale_ok;
7263 	ireq->acked = 0;
7264 	ireq->ecn_ok = 0;
7265 	ireq->ir_rmt_port = tcp_hdr(skb)->source;
7266 	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
7267 	ireq->ir_mark = inet_request_mark(sk, skb);
7268 #if IS_ENABLED(CONFIG_SMC)
7269 	ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_hs_congested &&
7270 			tcp_sk(sk)->smc_hs_congested(sk));
7271 #endif
7272 }
7273 
7274 /*
7275  * Return true if a syncookie should be sent
7276  */
7277 static bool tcp_syn_flood_action(struct sock *sk, const char *proto)
7278 {
7279 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
7280 	const char *msg = "Dropping request";
7281 	struct net *net = sock_net(sk);
7282 	bool want_cookie = false;
7283 	u8 syncookies;
7284 
7285 	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
7286 
7287 #ifdef CONFIG_SYN_COOKIES
7288 	if (syncookies) {
7289 		msg = "Sending cookies";
7290 		want_cookie = true;
7291 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
7292 	} else
7293 #endif
7294 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
7295 
7296 	if (syncookies != 2 && !READ_ONCE(queue->synflood_warned)) {
7297 		WRITE_ONCE(queue->synflood_warned, 1);
7298 		if (IS_ENABLED(CONFIG_IPV6) && sk->sk_family == AF_INET6) {
7299 			net_info_ratelimited("%s: Possible SYN flooding on port [%pI6c]:%u. %s.\n",
7300 					proto, inet6_rcv_saddr(sk),
7301 					sk->sk_num, msg);
7302 		} else {
7303 			net_info_ratelimited("%s: Possible SYN flooding on port %pI4:%u. %s.\n",
7304 					proto, &sk->sk_rcv_saddr,
7305 					sk->sk_num, msg);
7306 		}
7307 	}
7308 
7309 	return want_cookie;
7310 }
7311 
7312 static void tcp_reqsk_record_syn(const struct sock *sk,
7313 				 struct request_sock *req,
7314 				 const struct sk_buff *skb)
7315 {
7316 	if (tcp_sk(sk)->save_syn) {
7317 		u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
7318 		struct saved_syn *saved_syn;
7319 		u32 mac_hdrlen;
7320 		void *base;
7321 
7322 		if (tcp_sk(sk)->save_syn == 2) {  /* Save full header. */
7323 			base = skb_mac_header(skb);
7324 			mac_hdrlen = skb_mac_header_len(skb);
7325 			len += mac_hdrlen;
7326 		} else {
7327 			base = skb_network_header(skb);
7328 			mac_hdrlen = 0;
7329 		}
7330 
7331 		saved_syn = kmalloc(struct_size(saved_syn, data, len),
7332 				    GFP_ATOMIC);
7333 		if (saved_syn) {
7334 			saved_syn->mac_hdrlen = mac_hdrlen;
7335 			saved_syn->network_hdrlen = skb_network_header_len(skb);
7336 			saved_syn->tcp_hdrlen = tcp_hdrlen(skb);
7337 			memcpy(saved_syn->data, base, len);
7338 			req->saved_syn = saved_syn;
7339 		}
7340 	}
7341 }
7342 
7343 /* If a SYN cookie is required and supported, returns a clamped MSS value to be
7344  * used for SYN cookie generation.
7345  */
7346 u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
7347 			  const struct tcp_request_sock_ops *af_ops,
7348 			  struct sock *sk, struct tcphdr *th)
7349 {
7350 	struct tcp_sock *tp = tcp_sk(sk);
7351 	u16 mss;
7352 
7353 	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
7354 	    !inet_csk_reqsk_queue_is_full(sk))
7355 		return 0;
7356 
7357 	if (!tcp_syn_flood_action(sk, rsk_ops->slab_name))
7358 		return 0;
7359 
7360 	if (sk_acceptq_is_full(sk)) {
7361 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
7362 		return 0;
7363 	}
7364 
7365 	mss = tcp_parse_mss_option(th, READ_ONCE(tp->rx_opt.user_mss));
7366 	if (!mss)
7367 		mss = af_ops->mss_clamp;
7368 
7369 	return mss;
7370 }
7371 EXPORT_IPV6_MOD_GPL(tcp_get_syncookie_mss);
7372 
7373 int tcp_conn_request(struct request_sock_ops *rsk_ops,
7374 		     const struct tcp_request_sock_ops *af_ops,
7375 		     struct sock *sk, struct sk_buff *skb)
7376 {
7377 	struct tcp_fastopen_cookie foc = { .len = -1 };
7378 	struct tcp_options_received tmp_opt;
7379 	const struct tcp_sock *tp = tcp_sk(sk);
7380 	struct net *net = sock_net(sk);
7381 	struct sock *fastopen_sk = NULL;
7382 	struct request_sock *req;
7383 	bool want_cookie = false;
7384 	struct dst_entry *dst;
7385 	struct flowi fl;
7386 	u8 syncookies;
7387 	u32 isn;
7388 
7389 #ifdef CONFIG_TCP_AO
7390 	const struct tcp_ao_hdr *aoh;
7391 #endif
7392 
7393 	isn = __this_cpu_read(tcp_tw_isn);
7394 	if (isn) {
7395 		/* TW buckets are converted to open requests without
7396 		 * limitations, they conserve resources and peer is
7397 		 * evidently real one.
7398 		 */
7399 		__this_cpu_write(tcp_tw_isn, 0);
7400 	} else {
7401 		syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
7402 
7403 		if (syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) {
7404 			want_cookie = tcp_syn_flood_action(sk,
7405 							   rsk_ops->slab_name);
7406 			if (!want_cookie)
7407 				goto drop;
7408 		}
7409 	}
7410 
7411 	if (sk_acceptq_is_full(sk)) {
7412 		NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
7413 		goto drop;
7414 	}
7415 
7416 	req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
7417 	if (!req)
7418 		goto drop;
7419 
7420 	req->syncookie = want_cookie;
7421 	tcp_rsk(req)->af_specific = af_ops;
7422 	tcp_rsk(req)->ts_off = 0;
7423 	tcp_rsk(req)->req_usec_ts = false;
7424 #if IS_ENABLED(CONFIG_MPTCP)
7425 	tcp_rsk(req)->is_mptcp = 0;
7426 #endif
7427 
7428 	tcp_clear_options(&tmp_opt);
7429 	tmp_opt.mss_clamp = af_ops->mss_clamp;
7430 	tmp_opt.user_mss  = READ_ONCE(tp->rx_opt.user_mss);
7431 	tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
7432 			  want_cookie ? NULL : &foc);
7433 
7434 	if (want_cookie && !tmp_opt.saw_tstamp)
7435 		tcp_clear_options(&tmp_opt);
7436 
7437 	if (IS_ENABLED(CONFIG_SMC) && want_cookie)
7438 		tmp_opt.smc_ok = 0;
7439 
7440 	tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
7441 	tcp_openreq_init(req, &tmp_opt, skb, sk);
7442 	inet_rsk(req)->no_srccheck = inet_test_bit(TRANSPARENT, sk);
7443 
7444 	/* Note: tcp_v6_init_req() might override ir_iif for link locals */
7445 	inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
7446 
7447 	dst = af_ops->route_req(sk, skb, &fl, req, isn);
7448 	if (!dst)
7449 		goto drop_and_free;
7450 
7451 	if (tmp_opt.tstamp_ok) {
7452 		tcp_rsk(req)->req_usec_ts = dst_tcp_usec_ts(dst);
7453 		tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
7454 	}
7455 	if (!want_cookie && !isn) {
7456 		int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog);
7457 
7458 		/* Kill the following clause, if you dislike this way. */
7459 		if (!syncookies &&
7460 		    (max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
7461 		     (max_syn_backlog >> 2)) &&
7462 		    !tcp_peer_is_proven(req, dst)) {
7463 			/* Without syncookies last quarter of
7464 			 * backlog is filled with destinations,
7465 			 * proven to be alive.
7466 			 * It means that we continue to communicate
7467 			 * to destinations, already remembered
7468 			 * to the moment of synflood.
7469 			 */
7470 			pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
7471 				    rsk_ops->family);
7472 			goto drop_and_release;
7473 		}
7474 
7475 		isn = af_ops->init_seq(skb);
7476 	}
7477 
7478 	tcp_ecn_create_request(req, skb, sk, dst);
7479 
7480 	if (want_cookie) {
7481 		isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
7482 		if (!tmp_opt.tstamp_ok)
7483 			inet_rsk(req)->ecn_ok = 0;
7484 	}
7485 
7486 #ifdef CONFIG_TCP_AO
7487 	if (tcp_parse_auth_options(tcp_hdr(skb), NULL, &aoh))
7488 		goto drop_and_release; /* Invalid TCP options */
7489 	if (aoh) {
7490 		tcp_rsk(req)->used_tcp_ao = true;
7491 		tcp_rsk(req)->ao_rcv_next = aoh->keyid;
7492 		tcp_rsk(req)->ao_keyid = aoh->rnext_keyid;
7493 
7494 	} else {
7495 		tcp_rsk(req)->used_tcp_ao = false;
7496 	}
7497 #endif
7498 	tcp_rsk(req)->snt_isn = isn;
7499 	tcp_rsk(req)->txhash = net_tx_rndhash();
7500 	tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
7501 	tcp_openreq_init_rwin(req, sk, dst);
7502 	sk_rx_queue_set(req_to_sk(req), skb);
7503 	if (!want_cookie) {
7504 		tcp_reqsk_record_syn(sk, req, skb);
7505 		fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
7506 	}
7507 	if (fastopen_sk) {
7508 		af_ops->send_synack(fastopen_sk, dst, &fl, req,
7509 				    &foc, TCP_SYNACK_FASTOPEN, skb);
7510 		/* Add the child socket directly into the accept queue */
7511 		if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
7512 			reqsk_fastopen_remove(fastopen_sk, req, false);
7513 			bh_unlock_sock(fastopen_sk);
7514 			sock_put(fastopen_sk);
7515 			goto drop_and_free;
7516 		}
7517 		sk->sk_data_ready(sk);
7518 		bh_unlock_sock(fastopen_sk);
7519 		sock_put(fastopen_sk);
7520 	} else {
7521 		tcp_rsk(req)->tfo_listener = false;
7522 		if (!want_cookie) {
7523 			req->timeout = tcp_timeout_init((struct sock *)req);
7524 			if (unlikely(!inet_csk_reqsk_queue_hash_add(sk, req,
7525 								    req->timeout))) {
7526 				reqsk_free(req);
7527 				dst_release(dst);
7528 				return 0;
7529 			}
7530 
7531 		}
7532 		af_ops->send_synack(sk, dst, &fl, req, &foc,
7533 				    !want_cookie ? TCP_SYNACK_NORMAL :
7534 						   TCP_SYNACK_COOKIE,
7535 				    skb);
7536 		if (want_cookie) {
7537 			reqsk_free(req);
7538 			return 0;
7539 		}
7540 	}
7541 	reqsk_put(req);
7542 	return 0;
7543 
7544 drop_and_release:
7545 	dst_release(dst);
7546 drop_and_free:
7547 	__reqsk_free(req);
7548 drop:
7549 	tcp_listendrop(sk);
7550 	return 0;
7551 }
7552 EXPORT_IPV6_MOD(tcp_conn_request);
7553