1 // SPDX-License-Identifier: GPL-2.0-only
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 #include <linux/module.h>
23 #include <linux/gfp.h>
24 #include <net/tcp.h>
25 #include <net/rstreason.h>
26
tcp_clamp_rto_to_user_timeout(const struct sock * sk)27 static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
28 {
29 const struct inet_connection_sock *icsk = inet_csk(sk);
30 const struct tcp_sock *tp = tcp_sk(sk);
31 u32 elapsed, user_timeout;
32 s32 remaining;
33
34 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
35 if (!user_timeout)
36 return icsk->icsk_rto;
37
38 elapsed = tcp_time_stamp_ts(tp) - tp->retrans_stamp;
39 if (tp->tcp_usec_ts)
40 elapsed /= USEC_PER_MSEC;
41
42 remaining = user_timeout - elapsed;
43 if (remaining <= 0)
44 return 1; /* user timeout has passed; fire ASAP */
45
46 return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(remaining));
47 }
48
tcp_clamp_probe0_to_user_timeout(const struct sock * sk,u32 when)49 u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when)
50 {
51 const struct inet_connection_sock *icsk = inet_csk(sk);
52 u32 remaining, user_timeout;
53 s32 elapsed;
54
55 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
56 if (!user_timeout || !icsk->icsk_probes_tstamp)
57 return when;
58
59 elapsed = tcp_jiffies32 - icsk->icsk_probes_tstamp;
60 if (unlikely(elapsed < 0))
61 elapsed = 0;
62 remaining = msecs_to_jiffies(user_timeout) - elapsed;
63 remaining = max_t(u32, remaining, TCP_TIMEOUT_MIN);
64
65 return min_t(u32, remaining, when);
66 }
67
68 /**
69 * tcp_write_err() - close socket and save error info
70 * @sk: The socket the error has appeared on.
71 *
72 * Returns: Nothing (void)
73 */
74
tcp_write_err(struct sock * sk)75 static void tcp_write_err(struct sock *sk)
76 {
77 tcp_done_with_error(sk, READ_ONCE(sk->sk_err_soft) ? : ETIMEDOUT);
78 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
79 }
80
81 /**
82 * tcp_out_of_resources() - Close socket if out of resources
83 * @sk: pointer to current socket
84 * @do_reset: send a last packet with reset flag
85 *
86 * Do not allow orphaned sockets to eat all our resources.
87 * This is direct violation of TCP specs, but it is required
88 * to prevent DoS attacks. It is called when a retransmission timeout
89 * or zero probe timeout occurs on orphaned socket.
90 *
91 * Also close if our net namespace is exiting; in that case there is no
92 * hope of ever communicating again since all netns interfaces are already
93 * down (or about to be down), and we need to release our dst references,
94 * which have been moved to the netns loopback interface, so the namespace
95 * can finish exiting. This condition is only possible if we are a kernel
96 * socket, as those do not hold references to the namespace.
97 *
98 * Criteria is still not confirmed experimentally and may change.
99 * We kill the socket, if:
100 * 1. If number of orphaned sockets exceeds an administratively configured
101 * limit.
102 * 2. If we have strong memory pressure.
103 * 3. If our net namespace is exiting.
104 */
tcp_out_of_resources(struct sock * sk,bool do_reset)105 static int tcp_out_of_resources(struct sock *sk, bool do_reset)
106 {
107 struct tcp_sock *tp = tcp_sk(sk);
108 int shift = 0;
109
110 /* If peer does not open window for long time, or did not transmit
111 * anything for long time, penalize it. */
112 if ((s32)(tcp_jiffies32 - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
113 shift++;
114
115 /* If some dubious ICMP arrived, penalize even more. */
116 if (READ_ONCE(sk->sk_err_soft))
117 shift++;
118
119 if (tcp_check_oom(sk, shift)) {
120 /* Catch exceptional cases, when connection requires reset.
121 * 1. Last segment was sent recently. */
122 if ((s32)(tcp_jiffies32 - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
123 /* 2. Window is closed. */
124 (!tp->snd_wnd && !tp->packets_out))
125 do_reset = true;
126 if (do_reset)
127 tcp_send_active_reset(sk, GFP_ATOMIC,
128 SK_RST_REASON_TCP_ABORT_ON_MEMORY);
129 tcp_done(sk);
130 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
131 return 1;
132 }
133
134 if (!check_net(sock_net(sk))) {
135 /* Not possible to send reset; just close */
136 tcp_done(sk);
137 return 1;
138 }
139
140 return 0;
141 }
142
143 /**
144 * tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket
145 * @sk: Pointer to the current socket.
146 * @alive: bool, socket alive state
147 */
tcp_orphan_retries(struct sock * sk,bool alive)148 static int tcp_orphan_retries(struct sock *sk, bool alive)
149 {
150 int retries = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_orphan_retries); /* May be zero. */
151
152 /* We know from an ICMP that something is wrong. */
153 if (READ_ONCE(sk->sk_err_soft) && !alive)
154 retries = 0;
155
156 /* However, if socket sent something recently, select some safe
157 * number of retries. 8 corresponds to >100 seconds with minimal
158 * RTO of 200msec. */
159 if (retries == 0 && alive)
160 retries = 8;
161 return retries;
162 }
163
tcp_mtu_probing(struct inet_connection_sock * icsk,struct sock * sk)164 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
165 {
166 const struct net *net = sock_net(sk);
167 int mss;
168
169 /* Black hole detection */
170 if (!READ_ONCE(net->ipv4.sysctl_tcp_mtu_probing))
171 return;
172
173 if (!icsk->icsk_mtup.enabled) {
174 icsk->icsk_mtup.enabled = 1;
175 icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
176 } else {
177 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
178 mss = min(READ_ONCE(net->ipv4.sysctl_tcp_base_mss), mss);
179 mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_mtu_probe_floor));
180 mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_min_snd_mss));
181 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
182 }
183 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
184 }
185
tcp_model_timeout(struct sock * sk,unsigned int boundary,unsigned int rto_base)186 static unsigned int tcp_model_timeout(struct sock *sk,
187 unsigned int boundary,
188 unsigned int rto_base)
189 {
190 unsigned int linear_backoff_thresh, timeout;
191
192 linear_backoff_thresh = ilog2(TCP_RTO_MAX / rto_base);
193 if (boundary <= linear_backoff_thresh)
194 timeout = ((2 << boundary) - 1) * rto_base;
195 else
196 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
197 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
198 return jiffies_to_msecs(timeout);
199 }
200 /**
201 * retransmits_timed_out() - returns true if this connection has timed out
202 * @sk: The current socket
203 * @boundary: max number of retransmissions
204 * @timeout: A custom timeout value.
205 * If set to 0 the default timeout is calculated and used.
206 * Using TCP_RTO_MIN and the number of unsuccessful retransmits.
207 *
208 * The default "timeout" value this function can calculate and use
209 * is equivalent to the timeout of a TCP Connection
210 * after "boundary" unsuccessful, exponentially backed-off
211 * retransmissions with an initial RTO of TCP_RTO_MIN.
212 */
retransmits_timed_out(struct sock * sk,unsigned int boundary,unsigned int timeout)213 static bool retransmits_timed_out(struct sock *sk,
214 unsigned int boundary,
215 unsigned int timeout)
216 {
217 struct tcp_sock *tp = tcp_sk(sk);
218 unsigned int start_ts, delta;
219
220 if (!inet_csk(sk)->icsk_retransmits)
221 return false;
222
223 start_ts = tp->retrans_stamp;
224 if (likely(timeout == 0)) {
225 unsigned int rto_base = TCP_RTO_MIN;
226
227 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
228 rto_base = tcp_timeout_init(sk);
229 timeout = tcp_model_timeout(sk, boundary, rto_base);
230 }
231
232 if (tp->tcp_usec_ts) {
233 /* delta maybe off up to a jiffy due to timer granularity. */
234 delta = tp->tcp_mstamp - start_ts + jiffies_to_usecs(1);
235 return (s32)(delta - timeout * USEC_PER_MSEC) >= 0;
236 }
237 return (s32)(tcp_time_stamp_ts(tp) - start_ts - timeout) >= 0;
238 }
239
240 /* A write timeout has occurred. Process the after effects. */
tcp_write_timeout(struct sock * sk)241 static int tcp_write_timeout(struct sock *sk)
242 {
243 struct inet_connection_sock *icsk = inet_csk(sk);
244 struct tcp_sock *tp = tcp_sk(sk);
245 struct net *net = sock_net(sk);
246 bool expired = false, do_reset;
247 int retry_until, max_retransmits;
248
249 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
250 if (icsk->icsk_retransmits)
251 __dst_negative_advice(sk);
252 /* Paired with WRITE_ONCE() in tcp_sock_set_syncnt() */
253 retry_until = READ_ONCE(icsk->icsk_syn_retries) ? :
254 READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);
255
256 max_retransmits = retry_until;
257 if (sk->sk_state == TCP_SYN_SENT)
258 max_retransmits += READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts);
259
260 expired = icsk->icsk_retransmits >= max_retransmits;
261 } else {
262 if (retransmits_timed_out(sk, READ_ONCE(net->ipv4.sysctl_tcp_retries1), 0)) {
263 /* Black hole detection */
264 tcp_mtu_probing(icsk, sk);
265
266 __dst_negative_advice(sk);
267 }
268
269 retry_until = READ_ONCE(net->ipv4.sysctl_tcp_retries2);
270 if (sock_flag(sk, SOCK_DEAD)) {
271 const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
272
273 retry_until = tcp_orphan_retries(sk, alive);
274 do_reset = alive ||
275 !retransmits_timed_out(sk, retry_until, 0);
276
277 if (tcp_out_of_resources(sk, do_reset))
278 return 1;
279 }
280 }
281 if (!expired)
282 expired = retransmits_timed_out(sk, retry_until,
283 READ_ONCE(icsk->icsk_user_timeout));
284 tcp_fastopen_active_detect_blackhole(sk, expired);
285 mptcp_active_detect_blackhole(sk, expired);
286
287 if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTO_CB_FLAG))
288 tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RTO_CB,
289 icsk->icsk_retransmits,
290 icsk->icsk_rto, (int)expired);
291
292 if (expired) {
293 /* Has it gone just too far? */
294 tcp_write_err(sk);
295 return 1;
296 }
297
298 if (sk_rethink_txhash(sk)) {
299 tp->timeout_rehash++;
300 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH);
301 }
302
303 return 0;
304 }
305
306 /* Called with BH disabled */
tcp_delack_timer_handler(struct sock * sk)307 void tcp_delack_timer_handler(struct sock *sk)
308 {
309 struct inet_connection_sock *icsk = inet_csk(sk);
310 struct tcp_sock *tp = tcp_sk(sk);
311
312 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
313 return;
314
315 /* Handling the sack compression case */
316 if (tp->compressed_ack) {
317 tcp_mstamp_refresh(tp);
318 tcp_sack_compress_send_ack(sk);
319 return;
320 }
321
322 if (!(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
323 return;
324
325 if (time_after(icsk->icsk_ack.timeout, jiffies)) {
326 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
327 return;
328 }
329 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
330
331 if (inet_csk_ack_scheduled(sk)) {
332 if (!inet_csk_in_pingpong_mode(sk)) {
333 /* Delayed ACK missed: inflate ATO. */
334 icsk->icsk_ack.ato = min_t(u32, icsk->icsk_ack.ato << 1, icsk->icsk_rto);
335 } else {
336 /* Delayed ACK missed: leave pingpong mode and
337 * deflate ATO.
338 */
339 inet_csk_exit_pingpong_mode(sk);
340 icsk->icsk_ack.ato = TCP_ATO_MIN;
341 }
342 tcp_mstamp_refresh(tp);
343 tcp_send_ack(sk);
344 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
345 }
346 }
347
348
349 /**
350 * tcp_delack_timer() - The TCP delayed ACK timeout handler
351 * @t: Pointer to the timer. (gets casted to struct sock *)
352 *
353 * This function gets (indirectly) called when the kernel timer for a TCP packet
354 * of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
355 *
356 * Returns: Nothing (void)
357 */
tcp_delack_timer(struct timer_list * t)358 static void tcp_delack_timer(struct timer_list *t)
359 {
360 struct inet_connection_sock *icsk =
361 from_timer(icsk, t, icsk_delack_timer);
362 struct sock *sk = &icsk->icsk_inet.sk;
363
364 bh_lock_sock(sk);
365 if (!sock_owned_by_user(sk)) {
366 tcp_delack_timer_handler(sk);
367 } else {
368 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
369 /* deleguate our work to tcp_release_cb() */
370 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags))
371 sock_hold(sk);
372 }
373 bh_unlock_sock(sk);
374 sock_put(sk);
375 }
376
tcp_probe_timer(struct sock * sk)377 static void tcp_probe_timer(struct sock *sk)
378 {
379 struct inet_connection_sock *icsk = inet_csk(sk);
380 struct sk_buff *skb = tcp_send_head(sk);
381 struct tcp_sock *tp = tcp_sk(sk);
382 int max_probes;
383
384 if (tp->packets_out || !skb) {
385 icsk->icsk_probes_out = 0;
386 icsk->icsk_probes_tstamp = 0;
387 return;
388 }
389
390 /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
391 * long as the receiver continues to respond probes. We support this by
392 * default and reset icsk_probes_out with incoming ACKs. But if the
393 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
394 * kill the socket when the retry count and the time exceeds the
395 * corresponding system limit. We also implement similar policy when
396 * we use RTO to probe window in tcp_retransmit_timer().
397 */
398 if (!icsk->icsk_probes_tstamp) {
399 icsk->icsk_probes_tstamp = tcp_jiffies32;
400 } else {
401 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
402
403 if (user_timeout &&
404 (s32)(tcp_jiffies32 - icsk->icsk_probes_tstamp) >=
405 msecs_to_jiffies(user_timeout))
406 goto abort;
407 }
408 max_probes = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_retries2);
409 if (sock_flag(sk, SOCK_DEAD)) {
410 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
411
412 max_probes = tcp_orphan_retries(sk, alive);
413 if (!alive && icsk->icsk_backoff >= max_probes)
414 goto abort;
415 if (tcp_out_of_resources(sk, true))
416 return;
417 }
418
419 if (icsk->icsk_probes_out >= max_probes) {
420 abort: tcp_write_err(sk);
421 } else {
422 /* Only send another probe if we didn't close things up. */
423 tcp_send_probe0(sk);
424 }
425 }
426
tcp_update_rto_stats(struct sock * sk)427 static void tcp_update_rto_stats(struct sock *sk)
428 {
429 struct inet_connection_sock *icsk = inet_csk(sk);
430 struct tcp_sock *tp = tcp_sk(sk);
431
432 if (!icsk->icsk_retransmits) {
433 tp->total_rto_recoveries++;
434 tp->rto_stamp = tcp_time_stamp_ms(tp);
435 }
436 icsk->icsk_retransmits++;
437 tp->total_rto++;
438 }
439
440 /*
441 * Timer for Fast Open socket to retransmit SYNACK. Note that the
442 * sk here is the child socket, not the parent (listener) socket.
443 */
tcp_fastopen_synack_timer(struct sock * sk,struct request_sock * req)444 static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
445 {
446 struct inet_connection_sock *icsk = inet_csk(sk);
447 struct tcp_sock *tp = tcp_sk(sk);
448 int max_retries;
449
450 req->rsk_ops->syn_ack_timeout(req);
451
452 /* Add one more retry for fastopen.
453 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()
454 */
455 max_retries = READ_ONCE(icsk->icsk_syn_retries) ? :
456 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;
457
458 if (req->num_timeout >= max_retries) {
459 tcp_write_err(sk);
460 return;
461 }
462 /* Lower cwnd after certain SYNACK timeout like tcp_init_transfer() */
463 if (icsk->icsk_retransmits == 1)
464 tcp_enter_loss(sk);
465 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
466 * returned from rtx_syn_ack() to make it more persistent like
467 * regular retransmit because if the child socket has been accepted
468 * it's not good to give up too easily.
469 */
470 inet_rtx_syn_ack(sk, req);
471 req->num_timeout++;
472 tcp_update_rto_stats(sk);
473 if (!tp->retrans_stamp)
474 tp->retrans_stamp = tcp_time_stamp_ts(tp);
475 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
476 req->timeout << req->num_timeout, TCP_RTO_MAX);
477 }
478
tcp_rtx_probe0_timed_out(const struct sock * sk,const struct sk_buff * skb,u32 rtx_delta)479 static bool tcp_rtx_probe0_timed_out(const struct sock *sk,
480 const struct sk_buff *skb,
481 u32 rtx_delta)
482 {
483 const struct inet_connection_sock *icsk = inet_csk(sk);
484 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
485 const struct tcp_sock *tp = tcp_sk(sk);
486 int timeout = TCP_RTO_MAX * 2;
487 s32 rcv_delta;
488
489 if (user_timeout) {
490 /* If user application specified a TCP_USER_TIMEOUT,
491 * it does not want win 0 packets to 'reset the timer'
492 * while retransmits are not making progress.
493 */
494 if (rtx_delta > user_timeout)
495 return true;
496 timeout = min_t(u32, timeout, msecs_to_jiffies(user_timeout));
497 }
498 /* Note: timer interrupt might have been delayed by at least one jiffy,
499 * and tp->rcv_tstamp might very well have been written recently.
500 * rcv_delta can thus be negative.
501 */
502 rcv_delta = icsk->icsk_timeout - tp->rcv_tstamp;
503 if (rcv_delta <= timeout)
504 return false;
505
506 return msecs_to_jiffies(rtx_delta) > timeout;
507 }
508
509 /**
510 * tcp_retransmit_timer() - The TCP retransmit timeout handler
511 * @sk: Pointer to the current socket.
512 *
513 * This function gets called when the kernel timer for a TCP packet
514 * of this socket expires.
515 *
516 * It handles retransmission, timer adjustment and other necessary measures.
517 *
518 * Returns: Nothing (void)
519 */
tcp_retransmit_timer(struct sock * sk)520 void tcp_retransmit_timer(struct sock *sk)
521 {
522 struct tcp_sock *tp = tcp_sk(sk);
523 struct net *net = sock_net(sk);
524 struct inet_connection_sock *icsk = inet_csk(sk);
525 struct request_sock *req;
526 struct sk_buff *skb;
527
528 req = rcu_dereference_protected(tp->fastopen_rsk,
529 lockdep_sock_is_held(sk));
530 if (req) {
531 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
532 sk->sk_state != TCP_FIN_WAIT1);
533 tcp_fastopen_synack_timer(sk, req);
534 /* Before we receive ACK to our SYN-ACK don't retransmit
535 * anything else (e.g., data or FIN segments).
536 */
537 return;
538 }
539
540 if (!tp->packets_out)
541 return;
542
543 skb = tcp_rtx_queue_head(sk);
544 if (WARN_ON_ONCE(!skb))
545 return;
546
547 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
548 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
549 /* Receiver dastardly shrinks window. Our retransmits
550 * become zero probes, but we should not timeout this
551 * connection. If the socket is an orphan, time it out,
552 * we cannot allow such beasts to hang infinitely.
553 */
554 struct inet_sock *inet = inet_sk(sk);
555 u32 rtx_delta;
556
557 rtx_delta = tcp_time_stamp_ts(tp) - (tp->retrans_stamp ?:
558 tcp_skb_timestamp_ts(tp->tcp_usec_ts, skb));
559 if (tp->tcp_usec_ts)
560 rtx_delta /= USEC_PER_MSEC;
561
562 if (sk->sk_family == AF_INET) {
563 net_dbg_ratelimited("Probing zero-window on %pI4:%u/%u, seq=%u:%u, recv %ums ago, lasting %ums\n",
564 &inet->inet_daddr, ntohs(inet->inet_dport),
565 inet->inet_num, tp->snd_una, tp->snd_nxt,
566 jiffies_to_msecs(jiffies - tp->rcv_tstamp),
567 rtx_delta);
568 }
569 #if IS_ENABLED(CONFIG_IPV6)
570 else if (sk->sk_family == AF_INET6) {
571 net_dbg_ratelimited("Probing zero-window on %pI6:%u/%u, seq=%u:%u, recv %ums ago, lasting %ums\n",
572 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
573 inet->inet_num, tp->snd_una, tp->snd_nxt,
574 jiffies_to_msecs(jiffies - tp->rcv_tstamp),
575 rtx_delta);
576 }
577 #endif
578 if (tcp_rtx_probe0_timed_out(sk, skb, rtx_delta)) {
579 tcp_write_err(sk);
580 goto out;
581 }
582 tcp_enter_loss(sk);
583 tcp_retransmit_skb(sk, skb, 1);
584 __sk_dst_reset(sk);
585 goto out_reset_timer;
586 }
587
588 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
589 if (tcp_write_timeout(sk))
590 goto out;
591
592 if (icsk->icsk_retransmits == 0) {
593 int mib_idx = 0;
594
595 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
596 if (tcp_is_sack(tp))
597 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
598 else
599 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
600 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
601 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
602 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
603 tp->sacked_out) {
604 if (tcp_is_sack(tp))
605 mib_idx = LINUX_MIB_TCPSACKFAILURES;
606 else
607 mib_idx = LINUX_MIB_TCPRENOFAILURES;
608 }
609 if (mib_idx)
610 __NET_INC_STATS(sock_net(sk), mib_idx);
611 }
612
613 tcp_enter_loss(sk);
614
615 tcp_update_rto_stats(sk);
616 if (tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1) > 0) {
617 /* Retransmission failed because of local congestion,
618 * Let senders fight for local resources conservatively.
619 */
620 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
621 TCP_RESOURCE_PROBE_INTERVAL,
622 TCP_RTO_MAX);
623 goto out;
624 }
625
626 /* Increase the timeout each time we retransmit. Note that
627 * we do not increase the rtt estimate. rto is initialized
628 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
629 * that doubling rto each time is the least we can get away with.
630 * In KA9Q, Karn uses this for the first few times, and then
631 * goes to quadratic. netBSD doubles, but only goes up to *64,
632 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
633 * defined in the protocol as the maximum possible RTT. I guess
634 * we'll have to use something other than TCP to talk to the
635 * University of Mars.
636 *
637 * PAWS allows us longer timeouts and large windows, so once
638 * implemented ftp to mars will work nicely. We will have to fix
639 * the 120 second clamps though!
640 */
641
642 out_reset_timer:
643 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
644 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
645 * might be increased if the stream oscillates between thin and thick,
646 * thus the old value might already be too high compared to the value
647 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
648 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
649 * exponential backoff behaviour to avoid continue hammering
650 * linear-timeout retransmissions into a black hole
651 */
652 if (sk->sk_state == TCP_ESTABLISHED &&
653 (tp->thin_lto || READ_ONCE(net->ipv4.sysctl_tcp_thin_linear_timeouts)) &&
654 tcp_stream_is_thin(tp) &&
655 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
656 icsk->icsk_backoff = 0;
657 icsk->icsk_rto = clamp(__tcp_set_rto(tp),
658 tcp_rto_min(sk),
659 TCP_RTO_MAX);
660 } else if (sk->sk_state != TCP_SYN_SENT ||
661 tp->total_rto >
662 READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts)) {
663 /* Use normal (exponential) backoff unless linear timeouts are
664 * activated.
665 */
666 icsk->icsk_backoff++;
667 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
668 }
669 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
670 tcp_clamp_rto_to_user_timeout(sk), TCP_RTO_MAX);
671 if (retransmits_timed_out(sk, READ_ONCE(net->ipv4.sysctl_tcp_retries1) + 1, 0))
672 __sk_dst_reset(sk);
673
674 out:;
675 }
676
677 /* Called with bottom-half processing disabled.
678 Called by tcp_write_timer() */
tcp_write_timer_handler(struct sock * sk)679 void tcp_write_timer_handler(struct sock *sk)
680 {
681 struct inet_connection_sock *icsk = inet_csk(sk);
682 int event;
683
684 if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
685 !icsk->icsk_pending)
686 return;
687
688 if (time_after(icsk->icsk_timeout, jiffies)) {
689 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
690 return;
691 }
692
693 tcp_mstamp_refresh(tcp_sk(sk));
694 event = icsk->icsk_pending;
695
696 switch (event) {
697 case ICSK_TIME_REO_TIMEOUT:
698 tcp_rack_reo_timeout(sk);
699 break;
700 case ICSK_TIME_LOSS_PROBE:
701 tcp_send_loss_probe(sk);
702 break;
703 case ICSK_TIME_RETRANS:
704 icsk->icsk_pending = 0;
705 tcp_retransmit_timer(sk);
706 break;
707 case ICSK_TIME_PROBE0:
708 icsk->icsk_pending = 0;
709 tcp_probe_timer(sk);
710 break;
711 }
712 }
713
tcp_write_timer(struct timer_list * t)714 static void tcp_write_timer(struct timer_list *t)
715 {
716 struct inet_connection_sock *icsk =
717 from_timer(icsk, t, icsk_retransmit_timer);
718 struct sock *sk = &icsk->icsk_inet.sk;
719
720 bh_lock_sock(sk);
721 if (!sock_owned_by_user(sk)) {
722 tcp_write_timer_handler(sk);
723 } else {
724 /* delegate our work to tcp_release_cb() */
725 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &sk->sk_tsq_flags))
726 sock_hold(sk);
727 }
728 bh_unlock_sock(sk);
729 sock_put(sk);
730 }
731
tcp_syn_ack_timeout(const struct request_sock * req)732 void tcp_syn_ack_timeout(const struct request_sock *req)
733 {
734 struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
735
736 __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
737 }
738 EXPORT_SYMBOL(tcp_syn_ack_timeout);
739
tcp_set_keepalive(struct sock * sk,int val)740 void tcp_set_keepalive(struct sock *sk, int val)
741 {
742 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
743 return;
744
745 if (val && !sock_flag(sk, SOCK_KEEPOPEN))
746 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
747 else if (!val)
748 inet_csk_delete_keepalive_timer(sk);
749 }
750 EXPORT_SYMBOL_GPL(tcp_set_keepalive);
751
752
tcp_keepalive_timer(struct timer_list * t)753 static void tcp_keepalive_timer (struct timer_list *t)
754 {
755 struct sock *sk = from_timer(sk, t, sk_timer);
756 struct inet_connection_sock *icsk = inet_csk(sk);
757 struct tcp_sock *tp = tcp_sk(sk);
758 u32 elapsed;
759
760 /* Only process if socket is not in use. */
761 bh_lock_sock(sk);
762 if (sock_owned_by_user(sk)) {
763 /* Try again later. */
764 inet_csk_reset_keepalive_timer (sk, HZ/20);
765 goto out;
766 }
767
768 if (sk->sk_state == TCP_LISTEN) {
769 pr_err("Hmm... keepalive on a LISTEN ???\n");
770 goto out;
771 }
772
773 tcp_mstamp_refresh(tp);
774 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
775 if (READ_ONCE(tp->linger2) >= 0) {
776 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
777
778 if (tmo > 0) {
779 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
780 goto out;
781 }
782 }
783 tcp_send_active_reset(sk, GFP_ATOMIC, SK_RST_REASON_TCP_STATE);
784 goto death;
785 }
786
787 if (!sock_flag(sk, SOCK_KEEPOPEN) ||
788 ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
789 goto out;
790
791 elapsed = keepalive_time_when(tp);
792
793 /* It is alive without keepalive 8) */
794 if (tp->packets_out || !tcp_write_queue_empty(sk))
795 goto resched;
796
797 elapsed = keepalive_time_elapsed(tp);
798
799 if (elapsed >= keepalive_time_when(tp)) {
800 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
801
802 /* If the TCP_USER_TIMEOUT option is enabled, use that
803 * to determine when to timeout instead.
804 */
805 if ((user_timeout != 0 &&
806 elapsed >= msecs_to_jiffies(user_timeout) &&
807 icsk->icsk_probes_out > 0) ||
808 (user_timeout == 0 &&
809 icsk->icsk_probes_out >= keepalive_probes(tp))) {
810 tcp_send_active_reset(sk, GFP_ATOMIC,
811 SK_RST_REASON_TCP_KEEPALIVE_TIMEOUT);
812 tcp_write_err(sk);
813 goto out;
814 }
815 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
816 icsk->icsk_probes_out++;
817 elapsed = keepalive_intvl_when(tp);
818 } else {
819 /* If keepalive was lost due to local congestion,
820 * try harder.
821 */
822 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
823 }
824 } else {
825 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
826 elapsed = keepalive_time_when(tp) - elapsed;
827 }
828
829 resched:
830 inet_csk_reset_keepalive_timer (sk, elapsed);
831 goto out;
832
833 death:
834 tcp_done(sk);
835
836 out:
837 bh_unlock_sock(sk);
838 sock_put(sk);
839 }
840
tcp_compressed_ack_kick(struct hrtimer * timer)841 static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer)
842 {
843 struct tcp_sock *tp = container_of(timer, struct tcp_sock, compressed_ack_timer);
844 struct sock *sk = (struct sock *)tp;
845
846 bh_lock_sock(sk);
847 if (!sock_owned_by_user(sk)) {
848 if (tp->compressed_ack) {
849 /* Since we have to send one ack finally,
850 * subtract one from tp->compressed_ack to keep
851 * LINUX_MIB_TCPACKCOMPRESSED accurate.
852 */
853 tp->compressed_ack--;
854 tcp_send_ack(sk);
855 }
856 } else {
857 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED,
858 &sk->sk_tsq_flags))
859 sock_hold(sk);
860 }
861 bh_unlock_sock(sk);
862
863 sock_put(sk);
864
865 return HRTIMER_NORESTART;
866 }
867
tcp_init_xmit_timers(struct sock * sk)868 void tcp_init_xmit_timers(struct sock *sk)
869 {
870 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
871 &tcp_keepalive_timer);
872 hrtimer_init(&tcp_sk(sk)->pacing_timer, CLOCK_MONOTONIC,
873 HRTIMER_MODE_ABS_PINNED_SOFT);
874 tcp_sk(sk)->pacing_timer.function = tcp_pace_kick;
875
876 hrtimer_init(&tcp_sk(sk)->compressed_ack_timer, CLOCK_MONOTONIC,
877 HRTIMER_MODE_REL_PINNED_SOFT);
878 tcp_sk(sk)->compressed_ack_timer.function = tcp_compressed_ack_kick;
879 }
880