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
27static 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
49u32 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(m: 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
75static 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 */
105static 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(sk) || !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 reason: 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(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 */
148static 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
164static 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, pmtu: 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, pmtu: icsk->icsk_pmtu_cookie);
184}
185
186static 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(sk) / 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(sk);
198 return jiffies_to_msecs(j: 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 */
213static 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(j: 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. */
241static 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), timeout: 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, flag: SOCK_DEAD)) {
271 const bool alive = icsk->icsk_rto < tcp_rto_max(sk);
272
273 retry_until = tcp_orphan_retries(sk, alive);
274 do_reset = alive ||
275 !retransmits_timed_out(sk, boundary: retry_until, timeout: 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, boundary: 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, op: BPF_SOCK_OPS_RTO_CB,
289 arg1: icsk->icsk_retransmits,
290 arg2: icsk->icsk_rto, arg3: (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 */
307void 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_delack_timeout(icsk), jiffies)) {
326 sk_reset_timer(sk, timer: &icsk->icsk_delack_timer,
327 expires: icsk_delack_timeout(icsk));
328 return;
329 }
330 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
331
332 if (inet_csk_ack_scheduled(sk)) {
333 if (!inet_csk_in_pingpong_mode(sk)) {
334 /* Delayed ACK missed: inflate ATO. */
335 icsk->icsk_ack.ato = min_t(u32, icsk->icsk_ack.ato << 1, icsk->icsk_rto);
336 } else {
337 /* Delayed ACK missed: leave pingpong mode and
338 * deflate ATO.
339 */
340 inet_csk_exit_pingpong_mode(sk);
341 icsk->icsk_ack.ato = TCP_ATO_MIN;
342 }
343 tcp_mstamp_refresh(tp);
344 tcp_send_ack(sk);
345 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
346 }
347}
348
349
350/**
351 * tcp_delack_timer() - The TCP delayed ACK timeout handler
352 * @t: Pointer to the timer. (gets casted to struct sock *)
353 *
354 * This function gets (indirectly) called when the kernel timer for a TCP packet
355 * of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
356 *
357 * Returns: Nothing (void)
358 */
359static void tcp_delack_timer(struct timer_list *t)
360{
361 struct inet_connection_sock *icsk =
362 timer_container_of(icsk, t, icsk_delack_timer);
363 struct sock *sk = &icsk->icsk_inet.sk;
364
365 /* Avoid taking socket spinlock if there is no ACK to send.
366 * The compressed_ack check is racy, but a separate hrtimer
367 * will take care of it eventually.
368 */
369 if (!(smp_load_acquire(&icsk->icsk_ack.pending) & ICSK_ACK_TIMER) &&
370 !READ_ONCE(tcp_sk(sk)->compressed_ack))
371 goto out;
372
373 bh_lock_sock(sk);
374 if (!sock_owned_by_user(sk)) {
375 tcp_delack_timer_handler(sk);
376 } else {
377 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
378 /* deleguate our work to tcp_release_cb() */
379 if (!test_and_set_bit(nr: TCP_DELACK_TIMER_DEFERRED, addr: &sk->sk_tsq_flags))
380 sock_hold(sk);
381 }
382 bh_unlock_sock(sk);
383out:
384 sock_put(sk);
385}
386
387static void tcp_probe_timer(struct sock *sk)
388{
389 struct inet_connection_sock *icsk = inet_csk(sk);
390 struct sk_buff *skb = tcp_send_head(sk);
391 struct tcp_sock *tp = tcp_sk(sk);
392 int max_probes;
393
394 if (tp->packets_out || !skb) {
395 WRITE_ONCE(icsk->icsk_probes_out, 0);
396 icsk->icsk_probes_tstamp = 0;
397 return;
398 }
399
400 /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
401 * long as the receiver continues to respond probes. We support this by
402 * default and reset icsk_probes_out with incoming ACKs. But if the
403 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
404 * kill the socket when the retry count and the time exceeds the
405 * corresponding system limit. We also implement similar policy when
406 * we use RTO to probe window in tcp_retransmit_timer().
407 */
408 if (!icsk->icsk_probes_tstamp) {
409 icsk->icsk_probes_tstamp = tcp_jiffies32;
410 } else {
411 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
412
413 if (user_timeout &&
414 (s32)(tcp_jiffies32 - icsk->icsk_probes_tstamp) >=
415 msecs_to_jiffies(m: user_timeout))
416 goto abort;
417 }
418 max_probes = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_retries2);
419 if (sock_flag(sk, flag: SOCK_DEAD)) {
420 unsigned int rto_max = tcp_rto_max(sk);
421 const bool alive = inet_csk_rto_backoff(icsk, max_when: rto_max) < rto_max;
422
423 max_probes = tcp_orphan_retries(sk, alive);
424 if (!alive && icsk->icsk_backoff >= max_probes)
425 goto abort;
426 if (tcp_out_of_resources(sk, do_reset: true))
427 return;
428 }
429
430 if (icsk->icsk_probes_out >= max_probes) {
431abort: tcp_write_err(sk);
432 } else {
433 /* Only send another probe if we didn't close things up. */
434 tcp_send_probe0(sk);
435 }
436}
437
438static void tcp_update_rto_stats(struct sock *sk)
439{
440 struct inet_connection_sock *icsk = inet_csk(sk);
441 struct tcp_sock *tp = tcp_sk(sk);
442
443 if (!icsk->icsk_retransmits) {
444 tp->total_rto_recoveries++;
445 tp->rto_stamp = tcp_time_stamp_ms(tp);
446 }
447 WRITE_ONCE(icsk->icsk_retransmits, icsk->icsk_retransmits + 1);
448 tp->total_rto++;
449}
450
451/*
452 * Timer for Fast Open socket to retransmit SYNACK. Note that the
453 * sk here is the child socket, not the parent (listener) socket.
454 */
455static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
456{
457 struct inet_connection_sock *icsk = inet_csk(sk);
458 struct tcp_sock *tp = tcp_sk(sk);
459 int max_retries;
460
461 req->rsk_ops->syn_ack_timeout(req);
462
463 /* Add one more retry for fastopen.
464 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()
465 */
466 max_retries = READ_ONCE(icsk->icsk_syn_retries) ? :
467 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;
468
469 if (req->num_timeout >= max_retries) {
470 tcp_write_err(sk);
471 return;
472 }
473 /* Lower cwnd after certain SYNACK timeout like tcp_init_transfer() */
474 if (icsk->icsk_retransmits == 1)
475 tcp_enter_loss(sk);
476 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
477 * returned from rtx_syn_ack() to make it more persistent like
478 * regular retransmit because if the child socket has been accepted
479 * it's not good to give up too easily.
480 */
481 tcp_rtx_synack(sk, req);
482 req->num_timeout++;
483 tcp_update_rto_stats(sk);
484 if (!tp->retrans_stamp)
485 tp->retrans_stamp = tcp_time_stamp_ts(tp);
486 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
487 when: req->timeout << req->num_timeout, pace_delay: false);
488}
489
490static bool tcp_rtx_probe0_timed_out(const struct sock *sk,
491 const struct sk_buff *skb,
492 u32 rtx_delta)
493{
494 const struct inet_connection_sock *icsk = inet_csk(sk);
495 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
496 const struct tcp_sock *tp = tcp_sk(sk);
497 int timeout = tcp_rto_max(sk) * 2;
498 s32 rcv_delta;
499
500 if (user_timeout) {
501 /* If user application specified a TCP_USER_TIMEOUT,
502 * it does not want win 0 packets to 'reset the timer'
503 * while retransmits are not making progress.
504 */
505 if (rtx_delta > user_timeout)
506 return true;
507 timeout = min_t(u32, timeout, msecs_to_jiffies(user_timeout));
508 }
509 /* Note: timer interrupt might have been delayed by at least one jiffy,
510 * and tp->rcv_tstamp might very well have been written recently.
511 * rcv_delta can thus be negative.
512 */
513 rcv_delta = icsk_timeout(icsk) - tp->rcv_tstamp;
514 if (rcv_delta <= timeout)
515 return false;
516
517 return msecs_to_jiffies(m: rtx_delta) > timeout;
518}
519
520/**
521 * tcp_retransmit_timer() - The TCP retransmit timeout handler
522 * @sk: Pointer to the current socket.
523 *
524 * This function gets called when the kernel timer for a TCP packet
525 * of this socket expires.
526 *
527 * It handles retransmission, timer adjustment and other necessary measures.
528 *
529 * Returns: Nothing (void)
530 */
531void tcp_retransmit_timer(struct sock *sk)
532{
533 struct tcp_sock *tp = tcp_sk(sk);
534 struct net *net = sock_net(sk);
535 struct inet_connection_sock *icsk = inet_csk(sk);
536 struct request_sock *req;
537 struct sk_buff *skb;
538
539 req = rcu_dereference_protected(tp->fastopen_rsk,
540 lockdep_sock_is_held(sk));
541 if (req) {
542 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
543 sk->sk_state != TCP_FIN_WAIT1);
544 tcp_fastopen_synack_timer(sk, req);
545 /* Before we receive ACK to our SYN-ACK don't retransmit
546 * anything else (e.g., data or FIN segments).
547 */
548 return;
549 }
550
551 if (!tp->packets_out)
552 return;
553
554 skb = tcp_rtx_queue_head(sk);
555 if (WARN_ON_ONCE(!skb))
556 return;
557
558 if (!tp->snd_wnd && !sock_flag(sk, flag: SOCK_DEAD) &&
559 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
560 /* Receiver dastardly shrinks window. Our retransmits
561 * become zero probes, but we should not timeout this
562 * connection. If the socket is an orphan, time it out,
563 * we cannot allow such beasts to hang infinitely.
564 */
565 struct inet_sock *inet = inet_sk(sk);
566 u32 rtx_delta;
567
568 rtx_delta = tcp_time_stamp_ts(tp) - (tp->retrans_stamp ?:
569 tcp_skb_timestamp_ts(usec_ts: tp->tcp_usec_ts, skb));
570 if (tp->tcp_usec_ts)
571 rtx_delta /= USEC_PER_MSEC;
572
573 if (sk->sk_family == AF_INET) {
574 net_dbg_ratelimited("Probing zero-window on %pI4:%u/%u, seq=%u:%u, recv %ums ago, lasting %ums\n",
575 &inet->inet_daddr, ntohs(inet->inet_dport),
576 inet->inet_num, tp->snd_una, tp->snd_nxt,
577 jiffies_to_msecs(jiffies - tp->rcv_tstamp),
578 rtx_delta);
579 }
580#if IS_ENABLED(CONFIG_IPV6)
581 else if (sk->sk_family == AF_INET6) {
582 net_dbg_ratelimited("Probing zero-window on %pI6:%u/%u, seq=%u:%u, recv %ums ago, lasting %ums\n",
583 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
584 inet->inet_num, tp->snd_una, tp->snd_nxt,
585 jiffies_to_msecs(jiffies - tp->rcv_tstamp),
586 rtx_delta);
587 }
588#endif
589 if (tcp_rtx_probe0_timed_out(sk, skb, rtx_delta)) {
590 tcp_write_err(sk);
591 goto out;
592 }
593 tcp_enter_loss(sk);
594 tcp_retransmit_skb(sk, skb, segs: 1);
595 __sk_dst_reset(sk);
596 goto out_reset_timer;
597 }
598
599 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
600 if (tcp_write_timeout(sk))
601 goto out;
602
603 if (icsk->icsk_retransmits == 0) {
604 int mib_idx = 0;
605
606 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
607 if (tcp_is_sack(tp))
608 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
609 else
610 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
611 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
612 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
613 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
614 tp->sacked_out) {
615 if (tcp_is_sack(tp))
616 mib_idx = LINUX_MIB_TCPSACKFAILURES;
617 else
618 mib_idx = LINUX_MIB_TCPRENOFAILURES;
619 }
620 if (mib_idx)
621 __NET_INC_STATS(sock_net(sk), mib_idx);
622 }
623
624 tcp_enter_loss(sk);
625
626 tcp_update_rto_stats(sk);
627 if (tcp_retransmit_skb(sk, skb: tcp_rtx_queue_head(sk), segs: 1) > 0) {
628 /* Retransmission failed because of local congestion,
629 * Let senders fight for local resources conservatively.
630 */
631 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
632 TCP_RESOURCE_PROBE_INTERVAL,
633 pace_delay: false);
634 goto out;
635 }
636
637 /* Increase the timeout each time we retransmit. Note that
638 * we do not increase the rtt estimate. rto is initialized
639 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
640 * that doubling rto each time is the least we can get away with.
641 * In KA9Q, Karn uses this for the first few times, and then
642 * goes to quadratic. netBSD doubles, but only goes up to *64,
643 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
644 * defined in the protocol as the maximum possible RTT. I guess
645 * we'll have to use something other than TCP to talk to the
646 * University of Mars.
647 *
648 * PAWS allows us longer timeouts and large windows, so once
649 * implemented ftp to mars will work nicely. We will have to fix
650 * the 120 second clamps though!
651 */
652
653out_reset_timer:
654 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
655 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
656 * might be increased if the stream oscillates between thin and thick,
657 * thus the old value might already be too high compared to the value
658 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
659 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
660 * exponential backoff behaviour to avoid continue hammering
661 * linear-timeout retransmissions into a black hole
662 */
663 if (sk->sk_state == TCP_ESTABLISHED &&
664 (tp->thin_lto || READ_ONCE(net->ipv4.sysctl_tcp_thin_linear_timeouts)) &&
665 tcp_stream_is_thin(tp) &&
666 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
667 icsk->icsk_backoff = 0;
668 icsk->icsk_rto = clamp(__tcp_set_rto(tp),
669 tcp_rto_min(sk),
670 tcp_rto_max(sk));
671 } else if (sk->sk_state != TCP_SYN_SENT ||
672 tp->total_rto >
673 READ_ONCE(net->ipv4.sysctl_tcp_syn_linear_timeouts)) {
674 /* Use normal (exponential) backoff unless linear timeouts are
675 * activated.
676 */
677 icsk->icsk_backoff++;
678 icsk->icsk_rto = min(icsk->icsk_rto << 1, tcp_rto_max(sk));
679 }
680 tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
681 when: tcp_clamp_rto_to_user_timeout(sk), pace_delay: false);
682 if (retransmits_timed_out(sk, READ_ONCE(net->ipv4.sysctl_tcp_retries1) + 1, timeout: 0))
683 __sk_dst_reset(sk);
684
685out:;
686}
687
688/* Called with bottom-half processing disabled.
689 * Called by tcp_write_timer() and tcp_release_cb().
690 */
691void tcp_write_timer_handler(struct sock *sk)
692{
693 struct inet_connection_sock *icsk = inet_csk(sk);
694 int event;
695
696 if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
697 !icsk->icsk_pending)
698 return;
699
700 if (time_after(icsk_timeout(icsk), jiffies)) {
701 sk_reset_timer(sk, timer: &icsk->icsk_retransmit_timer,
702 expires: icsk_timeout(icsk));
703 return;
704 }
705 tcp_mstamp_refresh(tcp_sk(sk));
706 event = icsk->icsk_pending;
707
708 switch (event) {
709 case ICSK_TIME_REO_TIMEOUT:
710 tcp_rack_reo_timeout(sk);
711 break;
712 case ICSK_TIME_LOSS_PROBE:
713 tcp_send_loss_probe(sk);
714 break;
715 case ICSK_TIME_RETRANS:
716 smp_store_release(&icsk->icsk_pending, 0);
717 tcp_retransmit_timer(sk);
718 break;
719 case ICSK_TIME_PROBE0:
720 smp_store_release(&icsk->icsk_pending, 0);
721 tcp_probe_timer(sk);
722 break;
723 }
724}
725
726static void tcp_write_timer(struct timer_list *t)
727{
728 struct inet_connection_sock *icsk =
729 timer_container_of(icsk, t, icsk_retransmit_timer);
730 struct sock *sk = &icsk->icsk_inet.sk;
731
732 /* Avoid locking the socket when there is no pending event. */
733 if (!smp_load_acquire(&icsk->icsk_pending))
734 goto out;
735
736 bh_lock_sock(sk);
737 if (!sock_owned_by_user(sk)) {
738 tcp_write_timer_handler(sk);
739 } else {
740 /* delegate our work to tcp_release_cb() */
741 if (!test_and_set_bit(nr: TCP_WRITE_TIMER_DEFERRED, addr: &sk->sk_tsq_flags))
742 sock_hold(sk);
743 }
744 bh_unlock_sock(sk);
745out:
746 sock_put(sk);
747}
748
749void tcp_syn_ack_timeout(const struct request_sock *req)
750{
751 struct net *net = read_pnet(pnet: &inet_rsk(sk: req)->ireq_net);
752
753 __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
754}
755EXPORT_IPV6_MOD(tcp_syn_ack_timeout);
756
757void tcp_reset_keepalive_timer(struct sock *sk, unsigned long len)
758{
759 sk_reset_timer(sk, timer: &sk->sk_timer, expires: jiffies + len);
760}
761
762static void tcp_delete_keepalive_timer(struct sock *sk)
763{
764 sk_stop_timer(sk, timer: &sk->sk_timer);
765}
766
767void tcp_set_keepalive(struct sock *sk, int val)
768{
769 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
770 return;
771
772 if (val && !sock_flag(sk, flag: SOCK_KEEPOPEN))
773 tcp_reset_keepalive_timer(sk, len: keepalive_time_when(tcp_sk(sk)));
774 else if (!val)
775 tcp_delete_keepalive_timer(sk);
776}
777EXPORT_IPV6_MOD_GPL(tcp_set_keepalive);
778
779static void tcp_keepalive_timer(struct timer_list *t)
780{
781 struct sock *sk = timer_container_of(sk, t, sk_timer);
782 struct inet_connection_sock *icsk = inet_csk(sk);
783 struct tcp_sock *tp = tcp_sk(sk);
784 u32 elapsed;
785
786 /* Only process if socket is not in use. */
787 bh_lock_sock(sk);
788 if (sock_owned_by_user(sk)) {
789 /* Try again later. */
790 tcp_reset_keepalive_timer(sk, HZ/20);
791 goto out;
792 }
793
794 if (sk->sk_state == TCP_LISTEN) {
795 pr_err("Hmm... keepalive on a LISTEN ???\n");
796 goto out;
797 }
798
799 tcp_mstamp_refresh(tp);
800 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, flag: SOCK_DEAD)) {
801 if (READ_ONCE(tp->linger2) >= 0) {
802 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
803
804 if (tmo > 0) {
805 tcp_time_wait(sk, state: TCP_FIN_WAIT2, timeo: tmo);
806 goto out;
807 }
808 }
809 tcp_send_active_reset(sk, GFP_ATOMIC, reason: SK_RST_REASON_TCP_STATE);
810 goto death;
811 }
812
813 if (!sock_flag(sk, flag: SOCK_KEEPOPEN) ||
814 ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
815 goto out;
816
817 elapsed = keepalive_time_when(tp);
818
819 /* It is alive without keepalive 8) */
820 if (tp->packets_out || !tcp_write_queue_empty(sk))
821 goto resched;
822
823 elapsed = keepalive_time_elapsed(tp);
824
825 if (elapsed >= keepalive_time_when(tp)) {
826 u32 user_timeout = READ_ONCE(icsk->icsk_user_timeout);
827
828 /* If the TCP_USER_TIMEOUT option is enabled, use that
829 * to determine when to timeout instead.
830 */
831 if ((user_timeout != 0 &&
832 elapsed >= msecs_to_jiffies(m: user_timeout) &&
833 icsk->icsk_probes_out > 0) ||
834 (user_timeout == 0 &&
835 icsk->icsk_probes_out >= keepalive_probes(tp))) {
836 tcp_send_active_reset(sk, GFP_ATOMIC,
837 reason: SK_RST_REASON_TCP_KEEPALIVE_TIMEOUT);
838 tcp_write_err(sk);
839 goto out;
840 }
841 if (tcp_write_wakeup(sk, mib: LINUX_MIB_TCPKEEPALIVE) <= 0) {
842 WRITE_ONCE(icsk->icsk_probes_out, icsk->icsk_probes_out + 1);
843 elapsed = keepalive_intvl_when(tp);
844 } else {
845 /* If keepalive was lost due to local congestion,
846 * try harder.
847 */
848 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
849 }
850 } else {
851 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
852 elapsed = keepalive_time_when(tp) - elapsed;
853 }
854
855resched:
856 tcp_reset_keepalive_timer(sk, len: elapsed);
857 goto out;
858
859death:
860 tcp_done(sk);
861
862out:
863 bh_unlock_sock(sk);
864 sock_put(sk);
865}
866
867static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer)
868{
869 struct tcp_sock *tp = container_of(timer, struct tcp_sock, compressed_ack_timer);
870 struct sock *sk = (struct sock *)tp;
871
872 bh_lock_sock(sk);
873 if (!sock_owned_by_user(sk)) {
874 if (tp->compressed_ack) {
875 /* Since we have to send one ack finally,
876 * subtract one from tp->compressed_ack to keep
877 * LINUX_MIB_TCPACKCOMPRESSED accurate.
878 */
879 tp->compressed_ack--;
880 tcp_mstamp_refresh(tp);
881 tcp_send_ack(sk);
882 }
883 } else {
884 if (!test_and_set_bit(nr: TCP_DELACK_TIMER_DEFERRED,
885 addr: &sk->sk_tsq_flags))
886 sock_hold(sk);
887 }
888 bh_unlock_sock(sk);
889
890 sock_put(sk);
891
892 return HRTIMER_NORESTART;
893}
894
895void tcp_init_xmit_timers(struct sock *sk)
896{
897 inet_csk_init_xmit_timers(sk, retransmit_handler: &tcp_write_timer, delack_handler: &tcp_delack_timer,
898 keepalive_handler: &tcp_keepalive_timer);
899 hrtimer_setup(timer: &tcp_sk(sk)->pacing_timer, function: tcp_pace_kick, CLOCK_MONOTONIC,
900 mode: HRTIMER_MODE_ABS_PINNED_SOFT);
901
902 hrtimer_setup(timer: &tcp_sk(sk)->compressed_ack_timer, function: tcp_compressed_ack_kick, CLOCK_MONOTONIC,
903 mode: HRTIMER_MODE_REL_PINNED_SOFT);
904}
905