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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
26static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
27{
28 struct inet_connection_sock *icsk = inet_csk(sk);
29 u32 elapsed, start_ts;
30 s32 remaining;
31
32 start_ts = tcp_sk(sk)->retrans_stamp;
33 if (!icsk->icsk_user_timeout)
34 return icsk->icsk_rto;
35 elapsed = tcp_time_stamp(tcp_sk(sk)) - start_ts;
36 remaining = icsk->icsk_user_timeout - elapsed;
37 if (remaining <= 0)
38 return 1; /* user timeout has passed; fire ASAP */
39
40 return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(remaining));
41}
42
43/**
44 * tcp_write_err() - close socket and save error info
45 * @sk: The socket the error has appeared on.
46 *
47 * Returns: Nothing (void)
48 */
49
50static void tcp_write_err(struct sock *sk)
51{
52 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
53 sk->sk_error_report(sk);
54
55 tcp_write_queue_purge(sk);
56 tcp_done(sk);
57 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
58}
59
60/**
61 * tcp_out_of_resources() - Close socket if out of resources
62 * @sk: pointer to current socket
63 * @do_reset: send a last packet with reset flag
64 *
65 * Do not allow orphaned sockets to eat all our resources.
66 * This is direct violation of TCP specs, but it is required
67 * to prevent DoS attacks. It is called when a retransmission timeout
68 * or zero probe timeout occurs on orphaned socket.
69 *
70 * Also close if our net namespace is exiting; in that case there is no
71 * hope of ever communicating again since all netns interfaces are already
72 * down (or about to be down), and we need to release our dst references,
73 * which have been moved to the netns loopback interface, so the namespace
74 * can finish exiting. This condition is only possible if we are a kernel
75 * socket, as those do not hold references to the namespace.
76 *
77 * Criteria is still not confirmed experimentally and may change.
78 * We kill the socket, if:
79 * 1. If number of orphaned sockets exceeds an administratively configured
80 * limit.
81 * 2. If we have strong memory pressure.
82 * 3. If our net namespace is exiting.
83 */
84static int tcp_out_of_resources(struct sock *sk, bool do_reset)
85{
86 struct tcp_sock *tp = tcp_sk(sk);
87 int shift = 0;
88
89 /* If peer does not open window for long time, or did not transmit
90 * anything for long time, penalize it. */
91 if ((s32)(tcp_jiffies32 - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
92 shift++;
93
94 /* If some dubious ICMP arrived, penalize even more. */
95 if (sk->sk_err_soft)
96 shift++;
97
98 if (tcp_check_oom(sk, shift)) {
99 /* Catch exceptional cases, when connection requires reset.
100 * 1. Last segment was sent recently. */
101 if ((s32)(tcp_jiffies32 - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
102 /* 2. Window is closed. */
103 (!tp->snd_wnd && !tp->packets_out))
104 do_reset = true;
105 if (do_reset)
106 tcp_send_active_reset(sk, GFP_ATOMIC);
107 tcp_done(sk);
108 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
109 return 1;
110 }
111
112 if (!check_net(sock_net(sk))) {
113 /* Not possible to send reset; just close */
114 tcp_done(sk);
115 return 1;
116 }
117
118 return 0;
119}
120
121/**
122 * tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket
123 * @sk: Pointer to the current socket.
124 * @alive: bool, socket alive state
125 */
126static int tcp_orphan_retries(struct sock *sk, bool alive)
127{
128 int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */
129
130 /* We know from an ICMP that something is wrong. */
131 if (sk->sk_err_soft && !alive)
132 retries = 0;
133
134 /* However, if socket sent something recently, select some safe
135 * number of retries. 8 corresponds to >100 seconds with minimal
136 * RTO of 200msec. */
137 if (retries == 0 && alive)
138 retries = 8;
139 return retries;
140}
141
142static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
143{
144 const struct net *net = sock_net(sk);
145 int mss;
146
147 /* Black hole detection */
148 if (!net->ipv4.sysctl_tcp_mtu_probing)
149 return;
150
151 if (!icsk->icsk_mtup.enabled) {
152 icsk->icsk_mtup.enabled = 1;
153 icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
154 } else {
155 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
156 mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
157 mss = max(mss, net->ipv4.sysctl_tcp_mtu_probe_floor);
158 mss = max(mss, net->ipv4.sysctl_tcp_min_snd_mss);
159 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
160 }
161 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
162}
163
164static unsigned int tcp_model_timeout(struct sock *sk,
165 unsigned int boundary,
166 unsigned int rto_base)
167{
168 unsigned int linear_backoff_thresh, timeout;
169
170 linear_backoff_thresh = ilog2(TCP_RTO_MAX / rto_base);
171 if (boundary <= linear_backoff_thresh)
172 timeout = ((2 << boundary) - 1) * rto_base;
173 else
174 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
175 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
176 return jiffies_to_msecs(timeout);
177}
178/**
179 * retransmits_timed_out() - returns true if this connection has timed out
180 * @sk: The current socket
181 * @boundary: max number of retransmissions
182 * @timeout: A custom timeout value.
183 * If set to 0 the default timeout is calculated and used.
184 * Using TCP_RTO_MIN and the number of unsuccessful retransmits.
185 *
186 * The default "timeout" value this function can calculate and use
187 * is equivalent to the timeout of a TCP Connection
188 * after "boundary" unsuccessful, exponentially backed-off
189 * retransmissions with an initial RTO of TCP_RTO_MIN.
190 */
191static bool retransmits_timed_out(struct sock *sk,
192 unsigned int boundary,
193 unsigned int timeout)
194{
195 unsigned int start_ts;
196
197 if (!inet_csk(sk)->icsk_retransmits)
198 return false;
199
200 start_ts = tcp_sk(sk)->retrans_stamp;
201 if (likely(timeout == 0)) {
202 unsigned int rto_base = TCP_RTO_MIN;
203
204 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
205 rto_base = tcp_timeout_init(sk);
206 timeout = tcp_model_timeout(sk, boundary, rto_base);
207 }
208
209 return (s32)(tcp_time_stamp(tcp_sk(sk)) - start_ts - timeout) >= 0;
210}
211
212/* A write timeout has occurred. Process the after effects. */
213static int tcp_write_timeout(struct sock *sk)
214{
215 struct inet_connection_sock *icsk = inet_csk(sk);
216 struct tcp_sock *tp = tcp_sk(sk);
217 struct net *net = sock_net(sk);
218 bool expired = false, do_reset;
219 int retry_until;
220
221 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
222 if (icsk->icsk_retransmits) {
223 dst_negative_advice(sk);
224 } else {
225 sk_rethink_txhash(sk);
226 }
227 retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
228 expired = icsk->icsk_retransmits >= retry_until;
229 } else {
230 if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0)) {
231 /* Black hole detection */
232 tcp_mtu_probing(icsk, sk);
233
234 dst_negative_advice(sk);
235 } else {
236 sk_rethink_txhash(sk);
237 }
238
239 retry_until = net->ipv4.sysctl_tcp_retries2;
240 if (sock_flag(sk, SOCK_DEAD)) {
241 const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
242
243 retry_until = tcp_orphan_retries(sk, alive);
244 do_reset = alive ||
245 !retransmits_timed_out(sk, retry_until, 0);
246
247 if (tcp_out_of_resources(sk, do_reset))
248 return 1;
249 }
250 }
251 if (!expired)
252 expired = retransmits_timed_out(sk, retry_until,
253 icsk->icsk_user_timeout);
254 tcp_fastopen_active_detect_blackhole(sk, expired);
255
256 if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTO_CB_FLAG))
257 tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RTO_CB,
258 icsk->icsk_retransmits,
259 icsk->icsk_rto, (int)expired);
260
261 if (expired) {
262 /* Has it gone just too far? */
263 tcp_write_err(sk);
264 return 1;
265 }
266
267 return 0;
268}
269
270/* Called with BH disabled */
271void tcp_delack_timer_handler(struct sock *sk)
272{
273 struct inet_connection_sock *icsk = inet_csk(sk);
274
275 sk_mem_reclaim_partial(sk);
276
277 if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
278 !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
279 goto out;
280
281 if (time_after(icsk->icsk_ack.timeout, jiffies)) {
282 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
283 goto out;
284 }
285 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
286
287 if (inet_csk_ack_scheduled(sk)) {
288 if (!inet_csk_in_pingpong_mode(sk)) {
289 /* Delayed ACK missed: inflate ATO. */
290 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
291 } else {
292 /* Delayed ACK missed: leave pingpong mode and
293 * deflate ATO.
294 */
295 inet_csk_exit_pingpong_mode(sk);
296 icsk->icsk_ack.ato = TCP_ATO_MIN;
297 }
298 tcp_mstamp_refresh(tcp_sk(sk));
299 tcp_send_ack(sk);
300 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
301 }
302
303out:
304 if (tcp_under_memory_pressure(sk))
305 sk_mem_reclaim(sk);
306}
307
308
309/**
310 * tcp_delack_timer() - The TCP delayed ACK timeout handler
311 * @data: Pointer to the current socket. (gets casted to struct sock *)
312 *
313 * This function gets (indirectly) called when the kernel timer for a TCP packet
314 * of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
315 *
316 * Returns: Nothing (void)
317 */
318static void tcp_delack_timer(struct timer_list *t)
319{
320 struct inet_connection_sock *icsk =
321 from_timer(icsk, t, icsk_delack_timer);
322 struct sock *sk = &icsk->icsk_inet.sk;
323
324 bh_lock_sock(sk);
325 if (!sock_owned_by_user(sk)) {
326 tcp_delack_timer_handler(sk);
327 } else {
328 icsk->icsk_ack.blocked = 1;
329 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
330 /* deleguate our work to tcp_release_cb() */
331 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags))
332 sock_hold(sk);
333 }
334 bh_unlock_sock(sk);
335 sock_put(sk);
336}
337
338static void tcp_probe_timer(struct sock *sk)
339{
340 struct inet_connection_sock *icsk = inet_csk(sk);
341 struct sk_buff *skb = tcp_send_head(sk);
342 struct tcp_sock *tp = tcp_sk(sk);
343 int max_probes;
344
345 if (tp->packets_out || !skb) {
346 icsk->icsk_probes_out = 0;
347 return;
348 }
349
350 /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
351 * long as the receiver continues to respond probes. We support this by
352 * default and reset icsk_probes_out with incoming ACKs. But if the
353 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
354 * kill the socket when the retry count and the time exceeds the
355 * corresponding system limit. We also implement similar policy when
356 * we use RTO to probe window in tcp_retransmit_timer().
357 */
358 if (icsk->icsk_user_timeout) {
359 u32 elapsed = tcp_model_timeout(sk, icsk->icsk_probes_out,
360 tcp_probe0_base(sk));
361
362 if (elapsed >= icsk->icsk_user_timeout)
363 goto abort;
364 }
365
366 max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2;
367 if (sock_flag(sk, SOCK_DEAD)) {
368 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
369
370 max_probes = tcp_orphan_retries(sk, alive);
371 if (!alive && icsk->icsk_backoff >= max_probes)
372 goto abort;
373 if (tcp_out_of_resources(sk, true))
374 return;
375 }
376
377 if (icsk->icsk_probes_out >= max_probes) {
378abort: tcp_write_err(sk);
379 } else {
380 /* Only send another probe if we didn't close things up. */
381 tcp_send_probe0(sk);
382 }
383}
384
385/*
386 * Timer for Fast Open socket to retransmit SYNACK. Note that the
387 * sk here is the child socket, not the parent (listener) socket.
388 */
389static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
390{
391 struct inet_connection_sock *icsk = inet_csk(sk);
392 int max_retries = icsk->icsk_syn_retries ? :
393 sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
394 struct tcp_sock *tp = tcp_sk(sk);
395
396 req->rsk_ops->syn_ack_timeout(req);
397
398 if (req->num_timeout >= max_retries) {
399 tcp_write_err(sk);
400 return;
401 }
402 /* Lower cwnd after certain SYNACK timeout like tcp_init_transfer() */
403 if (icsk->icsk_retransmits == 1)
404 tcp_enter_loss(sk);
405 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
406 * returned from rtx_syn_ack() to make it more persistent like
407 * regular retransmit because if the child socket has been accepted
408 * it's not good to give up too easily.
409 */
410 inet_rtx_syn_ack(sk, req);
411 req->num_timeout++;
412 icsk->icsk_retransmits++;
413 if (!tp->retrans_stamp)
414 tp->retrans_stamp = tcp_time_stamp(tp);
415 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
416 TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
417}
418
419
420/**
421 * tcp_retransmit_timer() - The TCP retransmit timeout handler
422 * @sk: Pointer to the current socket.
423 *
424 * This function gets called when the kernel timer for a TCP packet
425 * of this socket expires.
426 *
427 * It handles retransmission, timer adjustment and other necesarry measures.
428 *
429 * Returns: Nothing (void)
430 */
431void tcp_retransmit_timer(struct sock *sk)
432{
433 struct tcp_sock *tp = tcp_sk(sk);
434 struct net *net = sock_net(sk);
435 struct inet_connection_sock *icsk = inet_csk(sk);
436 struct request_sock *req;
437
438 req = rcu_dereference_protected(tp->fastopen_rsk,
439 lockdep_sock_is_held(sk));
440 if (req) {
441 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
442 sk->sk_state != TCP_FIN_WAIT1);
443 tcp_fastopen_synack_timer(sk, req);
444 /* Before we receive ACK to our SYN-ACK don't retransmit
445 * anything else (e.g., data or FIN segments).
446 */
447 return;
448 }
449 if (!tp->packets_out || WARN_ON_ONCE(tcp_rtx_queue_empty(sk)))
450 return;
451
452 tp->tlp_high_seq = 0;
453
454 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
455 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
456 /* Receiver dastardly shrinks window. Our retransmits
457 * become zero probes, but we should not timeout this
458 * connection. If the socket is an orphan, time it out,
459 * we cannot allow such beasts to hang infinitely.
460 */
461 struct inet_sock *inet = inet_sk(sk);
462 if (sk->sk_family == AF_INET) {
463 net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
464 &inet->inet_daddr,
465 ntohs(inet->inet_dport),
466 inet->inet_num,
467 tp->snd_una, tp->snd_nxt);
468 }
469#if IS_ENABLED(CONFIG_IPV6)
470 else if (sk->sk_family == AF_INET6) {
471 net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
472 &sk->sk_v6_daddr,
473 ntohs(inet->inet_dport),
474 inet->inet_num,
475 tp->snd_una, tp->snd_nxt);
476 }
477#endif
478 if (tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX) {
479 tcp_write_err(sk);
480 goto out;
481 }
482 tcp_enter_loss(sk);
483 tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1);
484 __sk_dst_reset(sk);
485 goto out_reset_timer;
486 }
487
488 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
489 if (tcp_write_timeout(sk))
490 goto out;
491
492 if (icsk->icsk_retransmits == 0) {
493 int mib_idx = 0;
494
495 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
496 if (tcp_is_sack(tp))
497 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
498 else
499 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
500 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
501 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
502 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
503 tp->sacked_out) {
504 if (tcp_is_sack(tp))
505 mib_idx = LINUX_MIB_TCPSACKFAILURES;
506 else
507 mib_idx = LINUX_MIB_TCPRENOFAILURES;
508 }
509 if (mib_idx)
510 __NET_INC_STATS(sock_net(sk), mib_idx);
511 }
512
513 tcp_enter_loss(sk);
514
515 icsk->icsk_retransmits++;
516 if (tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1) > 0) {
517 /* Retransmission failed because of local congestion,
518 * Let senders fight for local resources conservatively.
519 */
520 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
521 TCP_RESOURCE_PROBE_INTERVAL,
522 TCP_RTO_MAX);
523 goto out;
524 }
525
526 /* Increase the timeout each time we retransmit. Note that
527 * we do not increase the rtt estimate. rto is initialized
528 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
529 * that doubling rto each time is the least we can get away with.
530 * In KA9Q, Karn uses this for the first few times, and then
531 * goes to quadratic. netBSD doubles, but only goes up to *64,
532 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
533 * defined in the protocol as the maximum possible RTT. I guess
534 * we'll have to use something other than TCP to talk to the
535 * University of Mars.
536 *
537 * PAWS allows us longer timeouts and large windows, so once
538 * implemented ftp to mars will work nicely. We will have to fix
539 * the 120 second clamps though!
540 */
541 icsk->icsk_backoff++;
542
543out_reset_timer:
544 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
545 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
546 * might be increased if the stream oscillates between thin and thick,
547 * thus the old value might already be too high compared to the value
548 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
549 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
550 * exponential backoff behaviour to avoid continue hammering
551 * linear-timeout retransmissions into a black hole
552 */
553 if (sk->sk_state == TCP_ESTABLISHED &&
554 (tp->thin_lto || net->ipv4.sysctl_tcp_thin_linear_timeouts) &&
555 tcp_stream_is_thin(tp) &&
556 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
557 icsk->icsk_backoff = 0;
558 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
559 } else {
560 /* Use normal (exponential) backoff */
561 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
562 }
563 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
564 tcp_clamp_rto_to_user_timeout(sk), TCP_RTO_MAX);
565 if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0))
566 __sk_dst_reset(sk);
567
568out:;
569}
570
571/* Called with bottom-half processing disabled.
572 Called by tcp_write_timer() */
573void tcp_write_timer_handler(struct sock *sk)
574{
575 struct inet_connection_sock *icsk = inet_csk(sk);
576 int event;
577
578 if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
579 !icsk->icsk_pending)
580 goto out;
581
582 if (time_after(icsk->icsk_timeout, jiffies)) {
583 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
584 goto out;
585 }
586
587 tcp_mstamp_refresh(tcp_sk(sk));
588 event = icsk->icsk_pending;
589
590 switch (event) {
591 case ICSK_TIME_REO_TIMEOUT:
592 tcp_rack_reo_timeout(sk);
593 break;
594 case ICSK_TIME_LOSS_PROBE:
595 tcp_send_loss_probe(sk);
596 break;
597 case ICSK_TIME_RETRANS:
598 icsk->icsk_pending = 0;
599 tcp_retransmit_timer(sk);
600 break;
601 case ICSK_TIME_PROBE0:
602 icsk->icsk_pending = 0;
603 tcp_probe_timer(sk);
604 break;
605 }
606
607out:
608 sk_mem_reclaim(sk);
609}
610
611static void tcp_write_timer(struct timer_list *t)
612{
613 struct inet_connection_sock *icsk =
614 from_timer(icsk, t, icsk_retransmit_timer);
615 struct sock *sk = &icsk->icsk_inet.sk;
616
617 bh_lock_sock(sk);
618 if (!sock_owned_by_user(sk)) {
619 tcp_write_timer_handler(sk);
620 } else {
621 /* delegate our work to tcp_release_cb() */
622 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &sk->sk_tsq_flags))
623 sock_hold(sk);
624 }
625 bh_unlock_sock(sk);
626 sock_put(sk);
627}
628
629void tcp_syn_ack_timeout(const struct request_sock *req)
630{
631 struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
632
633 __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
634}
635EXPORT_SYMBOL(tcp_syn_ack_timeout);
636
637void tcp_set_keepalive(struct sock *sk, int val)
638{
639 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
640 return;
641
642 if (val && !sock_flag(sk, SOCK_KEEPOPEN))
643 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
644 else if (!val)
645 inet_csk_delete_keepalive_timer(sk);
646}
647EXPORT_SYMBOL_GPL(tcp_set_keepalive);
648
649
650static void tcp_keepalive_timer (struct timer_list *t)
651{
652 struct sock *sk = from_timer(sk, t, sk_timer);
653 struct inet_connection_sock *icsk = inet_csk(sk);
654 struct tcp_sock *tp = tcp_sk(sk);
655 u32 elapsed;
656
657 /* Only process if socket is not in use. */
658 bh_lock_sock(sk);
659 if (sock_owned_by_user(sk)) {
660 /* Try again later. */
661 inet_csk_reset_keepalive_timer (sk, HZ/20);
662 goto out;
663 }
664
665 if (sk->sk_state == TCP_LISTEN) {
666 pr_err("Hmm... keepalive on a LISTEN ???\n");
667 goto out;
668 }
669
670 tcp_mstamp_refresh(tp);
671 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
672 if (tp->linger2 >= 0) {
673 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
674
675 if (tmo > 0) {
676 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
677 goto out;
678 }
679 }
680 tcp_send_active_reset(sk, GFP_ATOMIC);
681 goto death;
682 }
683
684 if (!sock_flag(sk, SOCK_KEEPOPEN) ||
685 ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
686 goto out;
687
688 elapsed = keepalive_time_when(tp);
689
690 /* It is alive without keepalive 8) */
691 if (tp->packets_out || !tcp_write_queue_empty(sk))
692 goto resched;
693
694 elapsed = keepalive_time_elapsed(tp);
695
696 if (elapsed >= keepalive_time_when(tp)) {
697 /* If the TCP_USER_TIMEOUT option is enabled, use that
698 * to determine when to timeout instead.
699 */
700 if ((icsk->icsk_user_timeout != 0 &&
701 elapsed >= msecs_to_jiffies(icsk->icsk_user_timeout) &&
702 icsk->icsk_probes_out > 0) ||
703 (icsk->icsk_user_timeout == 0 &&
704 icsk->icsk_probes_out >= keepalive_probes(tp))) {
705 tcp_send_active_reset(sk, GFP_ATOMIC);
706 tcp_write_err(sk);
707 goto out;
708 }
709 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
710 icsk->icsk_probes_out++;
711 elapsed = keepalive_intvl_when(tp);
712 } else {
713 /* If keepalive was lost due to local congestion,
714 * try harder.
715 */
716 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
717 }
718 } else {
719 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
720 elapsed = keepalive_time_when(tp) - elapsed;
721 }
722
723 sk_mem_reclaim(sk);
724
725resched:
726 inet_csk_reset_keepalive_timer (sk, elapsed);
727 goto out;
728
729death:
730 tcp_done(sk);
731
732out:
733 bh_unlock_sock(sk);
734 sock_put(sk);
735}
736
737static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer)
738{
739 struct tcp_sock *tp = container_of(timer, struct tcp_sock, compressed_ack_timer);
740 struct sock *sk = (struct sock *)tp;
741
742 bh_lock_sock(sk);
743 if (!sock_owned_by_user(sk)) {
744 if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
745 tcp_send_ack(sk);
746 } else {
747 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED,
748 &sk->sk_tsq_flags))
749 sock_hold(sk);
750 }
751 bh_unlock_sock(sk);
752
753 sock_put(sk);
754
755 return HRTIMER_NORESTART;
756}
757
758void tcp_init_xmit_timers(struct sock *sk)
759{
760 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
761 &tcp_keepalive_timer);
762 hrtimer_init(&tcp_sk(sk)->pacing_timer, CLOCK_MONOTONIC,
763 HRTIMER_MODE_ABS_PINNED_SOFT);
764 tcp_sk(sk)->pacing_timer.function = tcp_pace_kick;
765
766 hrtimer_init(&tcp_sk(sk)->compressed_ack_timer, CLOCK_MONOTONIC,
767 HRTIMER_MODE_REL_PINNED_SOFT);
768 tcp_sk(sk)->compressed_ack_timer.function = tcp_compressed_ack_kick;
769}
1/*
2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
5 *
6 * Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors: Ross Biro
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
19 */
20
21#include <linux/module.h>
22#include <linux/gfp.h>
23#include <net/tcp.h>
24
25int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
26int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
27int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
28int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
29int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
30int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
31int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
32int sysctl_tcp_orphan_retries __read_mostly;
33int sysctl_tcp_thin_linear_timeouts __read_mostly;
34
35static void tcp_write_timer(unsigned long);
36static void tcp_delack_timer(unsigned long);
37static void tcp_keepalive_timer (unsigned long data);
38
39void tcp_init_xmit_timers(struct sock *sk)
40{
41 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
42 &tcp_keepalive_timer);
43}
44EXPORT_SYMBOL(tcp_init_xmit_timers);
45
46static void tcp_write_err(struct sock *sk)
47{
48 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
49 sk->sk_error_report(sk);
50
51 tcp_done(sk);
52 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
53}
54
55/* Do not allow orphaned sockets to eat all our resources.
56 * This is direct violation of TCP specs, but it is required
57 * to prevent DoS attacks. It is called when a retransmission timeout
58 * or zero probe timeout occurs on orphaned socket.
59 *
60 * Criteria is still not confirmed experimentally and may change.
61 * We kill the socket, if:
62 * 1. If number of orphaned sockets exceeds an administratively configured
63 * limit.
64 * 2. If we have strong memory pressure.
65 */
66static int tcp_out_of_resources(struct sock *sk, int do_reset)
67{
68 struct tcp_sock *tp = tcp_sk(sk);
69 int shift = 0;
70
71 /* If peer does not open window for long time, or did not transmit
72 * anything for long time, penalize it. */
73 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
74 shift++;
75
76 /* If some dubious ICMP arrived, penalize even more. */
77 if (sk->sk_err_soft)
78 shift++;
79
80 if (tcp_check_oom(sk, shift)) {
81 /* Catch exceptional cases, when connection requires reset.
82 * 1. Last segment was sent recently. */
83 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
84 /* 2. Window is closed. */
85 (!tp->snd_wnd && !tp->packets_out))
86 do_reset = 1;
87 if (do_reset)
88 tcp_send_active_reset(sk, GFP_ATOMIC);
89 tcp_done(sk);
90 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
91 return 1;
92 }
93 return 0;
94}
95
96/* Calculate maximal number or retries on an orphaned socket. */
97static int tcp_orphan_retries(struct sock *sk, int alive)
98{
99 int retries = sysctl_tcp_orphan_retries; /* May be zero. */
100
101 /* We know from an ICMP that something is wrong. */
102 if (sk->sk_err_soft && !alive)
103 retries = 0;
104
105 /* However, if socket sent something recently, select some safe
106 * number of retries. 8 corresponds to >100 seconds with minimal
107 * RTO of 200msec. */
108 if (retries == 0 && alive)
109 retries = 8;
110 return retries;
111}
112
113static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
114{
115 /* Black hole detection */
116 if (sysctl_tcp_mtu_probing) {
117 if (!icsk->icsk_mtup.enabled) {
118 icsk->icsk_mtup.enabled = 1;
119 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
120 } else {
121 struct tcp_sock *tp = tcp_sk(sk);
122 int mss;
123
124 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
125 mss = min(sysctl_tcp_base_mss, mss);
126 mss = max(mss, 68 - tp->tcp_header_len);
127 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
128 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
129 }
130 }
131}
132
133/* This function calculates a "timeout" which is equivalent to the timeout of a
134 * TCP connection after "boundary" unsuccessful, exponentially backed-off
135 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
136 * syn_set flag is set.
137 */
138static bool retransmits_timed_out(struct sock *sk,
139 unsigned int boundary,
140 unsigned int timeout,
141 bool syn_set)
142{
143 unsigned int linear_backoff_thresh, start_ts;
144 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
145
146 if (!inet_csk(sk)->icsk_retransmits)
147 return false;
148
149 if (unlikely(!tcp_sk(sk)->retrans_stamp))
150 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
151 else
152 start_ts = tcp_sk(sk)->retrans_stamp;
153
154 if (likely(timeout == 0)) {
155 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
156
157 if (boundary <= linear_backoff_thresh)
158 timeout = ((2 << boundary) - 1) * rto_base;
159 else
160 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
161 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
162 }
163 return (tcp_time_stamp - start_ts) >= timeout;
164}
165
166/* A write timeout has occurred. Process the after effects. */
167static int tcp_write_timeout(struct sock *sk)
168{
169 struct inet_connection_sock *icsk = inet_csk(sk);
170 int retry_until;
171 bool do_reset, syn_set = false;
172
173 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
174 if (icsk->icsk_retransmits)
175 dst_negative_advice(sk);
176 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
177 syn_set = true;
178 } else {
179 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
180 /* Black hole detection */
181 tcp_mtu_probing(icsk, sk);
182
183 dst_negative_advice(sk);
184 }
185
186 retry_until = sysctl_tcp_retries2;
187 if (sock_flag(sk, SOCK_DEAD)) {
188 const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
189
190 retry_until = tcp_orphan_retries(sk, alive);
191 do_reset = alive ||
192 !retransmits_timed_out(sk, retry_until, 0, 0);
193
194 if (tcp_out_of_resources(sk, do_reset))
195 return 1;
196 }
197 }
198
199 if (retransmits_timed_out(sk, retry_until,
200 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
201 /* Has it gone just too far? */
202 tcp_write_err(sk);
203 return 1;
204 }
205 return 0;
206}
207
208static void tcp_delack_timer(unsigned long data)
209{
210 struct sock *sk = (struct sock *)data;
211 struct tcp_sock *tp = tcp_sk(sk);
212 struct inet_connection_sock *icsk = inet_csk(sk);
213
214 bh_lock_sock(sk);
215 if (sock_owned_by_user(sk)) {
216 /* Try again later. */
217 icsk->icsk_ack.blocked = 1;
218 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
219 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
220 goto out_unlock;
221 }
222
223 sk_mem_reclaim_partial(sk);
224
225 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
226 goto out;
227
228 if (time_after(icsk->icsk_ack.timeout, jiffies)) {
229 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
230 goto out;
231 }
232 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
233
234 if (!skb_queue_empty(&tp->ucopy.prequeue)) {
235 struct sk_buff *skb;
236
237 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
238
239 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
240 sk_backlog_rcv(sk, skb);
241
242 tp->ucopy.memory = 0;
243 }
244
245 if (inet_csk_ack_scheduled(sk)) {
246 if (!icsk->icsk_ack.pingpong) {
247 /* Delayed ACK missed: inflate ATO. */
248 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
249 } else {
250 /* Delayed ACK missed: leave pingpong mode and
251 * deflate ATO.
252 */
253 icsk->icsk_ack.pingpong = 0;
254 icsk->icsk_ack.ato = TCP_ATO_MIN;
255 }
256 tcp_send_ack(sk);
257 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
258 }
259
260out:
261 if (sk_under_memory_pressure(sk))
262 sk_mem_reclaim(sk);
263out_unlock:
264 bh_unlock_sock(sk);
265 sock_put(sk);
266}
267
268static void tcp_probe_timer(struct sock *sk)
269{
270 struct inet_connection_sock *icsk = inet_csk(sk);
271 struct tcp_sock *tp = tcp_sk(sk);
272 int max_probes;
273
274 if (tp->packets_out || !tcp_send_head(sk)) {
275 icsk->icsk_probes_out = 0;
276 return;
277 }
278
279 /* *WARNING* RFC 1122 forbids this
280 *
281 * It doesn't AFAIK, because we kill the retransmit timer -AK
282 *
283 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
284 * this behaviour in Solaris down as a bug fix. [AC]
285 *
286 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
287 * even if they advertise zero window. Hence, connection is killed only
288 * if we received no ACKs for normal connection timeout. It is not killed
289 * only because window stays zero for some time, window may be zero
290 * until armageddon and even later. We are in full accordance
291 * with RFCs, only probe timer combines both retransmission timeout
292 * and probe timeout in one bottle. --ANK
293 */
294 max_probes = sysctl_tcp_retries2;
295
296 if (sock_flag(sk, SOCK_DEAD)) {
297 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
298
299 max_probes = tcp_orphan_retries(sk, alive);
300
301 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
302 return;
303 }
304
305 if (icsk->icsk_probes_out > max_probes) {
306 tcp_write_err(sk);
307 } else {
308 /* Only send another probe if we didn't close things up. */
309 tcp_send_probe0(sk);
310 }
311}
312
313/*
314 * The TCP retransmit timer.
315 */
316
317void tcp_retransmit_timer(struct sock *sk)
318{
319 struct tcp_sock *tp = tcp_sk(sk);
320 struct inet_connection_sock *icsk = inet_csk(sk);
321
322 if (tp->early_retrans_delayed) {
323 tcp_resume_early_retransmit(sk);
324 return;
325 }
326
327 if (!tp->packets_out)
328 goto out;
329
330 WARN_ON(tcp_write_queue_empty(sk));
331
332 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
333 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
334 /* Receiver dastardly shrinks window. Our retransmits
335 * become zero probes, but we should not timeout this
336 * connection. If the socket is an orphan, time it out,
337 * we cannot allow such beasts to hang infinitely.
338 */
339 struct inet_sock *inet = inet_sk(sk);
340 if (sk->sk_family == AF_INET) {
341 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
342 &inet->inet_daddr,
343 ntohs(inet->inet_dport), inet->inet_num,
344 tp->snd_una, tp->snd_nxt);
345 }
346#if IS_ENABLED(CONFIG_IPV6)
347 else if (sk->sk_family == AF_INET6) {
348 struct ipv6_pinfo *np = inet6_sk(sk);
349 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
350 &np->daddr,
351 ntohs(inet->inet_dport), inet->inet_num,
352 tp->snd_una, tp->snd_nxt);
353 }
354#endif
355 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
356 tcp_write_err(sk);
357 goto out;
358 }
359 tcp_enter_loss(sk, 0);
360 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
361 __sk_dst_reset(sk);
362 goto out_reset_timer;
363 }
364
365 if (tcp_write_timeout(sk))
366 goto out;
367
368 if (icsk->icsk_retransmits == 0) {
369 int mib_idx;
370
371 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
372 if (tcp_is_sack(tp))
373 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
374 else
375 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
376 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
377 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
378 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
379 tp->sacked_out) {
380 if (tcp_is_sack(tp))
381 mib_idx = LINUX_MIB_TCPSACKFAILURES;
382 else
383 mib_idx = LINUX_MIB_TCPRENOFAILURES;
384 } else {
385 mib_idx = LINUX_MIB_TCPTIMEOUTS;
386 }
387 NET_INC_STATS_BH(sock_net(sk), mib_idx);
388 }
389
390 if (tcp_use_frto(sk)) {
391 tcp_enter_frto(sk);
392 } else {
393 tcp_enter_loss(sk, 0);
394 }
395
396 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
397 /* Retransmission failed because of local congestion,
398 * do not backoff.
399 */
400 if (!icsk->icsk_retransmits)
401 icsk->icsk_retransmits = 1;
402 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
403 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
404 TCP_RTO_MAX);
405 goto out;
406 }
407
408 /* Increase the timeout each time we retransmit. Note that
409 * we do not increase the rtt estimate. rto is initialized
410 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
411 * that doubling rto each time is the least we can get away with.
412 * In KA9Q, Karn uses this for the first few times, and then
413 * goes to quadratic. netBSD doubles, but only goes up to *64,
414 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
415 * defined in the protocol as the maximum possible RTT. I guess
416 * we'll have to use something other than TCP to talk to the
417 * University of Mars.
418 *
419 * PAWS allows us longer timeouts and large windows, so once
420 * implemented ftp to mars will work nicely. We will have to fix
421 * the 120 second clamps though!
422 */
423 icsk->icsk_backoff++;
424 icsk->icsk_retransmits++;
425
426out_reset_timer:
427 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
428 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
429 * might be increased if the stream oscillates between thin and thick,
430 * thus the old value might already be too high compared to the value
431 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
432 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
433 * exponential backoff behaviour to avoid continue hammering
434 * linear-timeout retransmissions into a black hole
435 */
436 if (sk->sk_state == TCP_ESTABLISHED &&
437 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
438 tcp_stream_is_thin(tp) &&
439 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
440 icsk->icsk_backoff = 0;
441 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
442 } else {
443 /* Use normal (exponential) backoff */
444 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
445 }
446 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
447 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
448 __sk_dst_reset(sk);
449
450out:;
451}
452
453static void tcp_write_timer(unsigned long data)
454{
455 struct sock *sk = (struct sock *)data;
456 struct inet_connection_sock *icsk = inet_csk(sk);
457 int event;
458
459 bh_lock_sock(sk);
460 if (sock_owned_by_user(sk)) {
461 /* Try again later */
462 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
463 goto out_unlock;
464 }
465
466 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
467 goto out;
468
469 if (time_after(icsk->icsk_timeout, jiffies)) {
470 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
471 goto out;
472 }
473
474 event = icsk->icsk_pending;
475 icsk->icsk_pending = 0;
476
477 switch (event) {
478 case ICSK_TIME_RETRANS:
479 tcp_retransmit_timer(sk);
480 break;
481 case ICSK_TIME_PROBE0:
482 tcp_probe_timer(sk);
483 break;
484 }
485
486out:
487 sk_mem_reclaim(sk);
488out_unlock:
489 bh_unlock_sock(sk);
490 sock_put(sk);
491}
492
493/*
494 * Timer for listening sockets
495 */
496
497static void tcp_synack_timer(struct sock *sk)
498{
499 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
500 TCP_TIMEOUT_INIT, TCP_RTO_MAX);
501}
502
503void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
504{
505 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
506}
507EXPORT_SYMBOL(tcp_syn_ack_timeout);
508
509void tcp_set_keepalive(struct sock *sk, int val)
510{
511 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
512 return;
513
514 if (val && !sock_flag(sk, SOCK_KEEPOPEN))
515 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
516 else if (!val)
517 inet_csk_delete_keepalive_timer(sk);
518}
519
520
521static void tcp_keepalive_timer (unsigned long data)
522{
523 struct sock *sk = (struct sock *) data;
524 struct inet_connection_sock *icsk = inet_csk(sk);
525 struct tcp_sock *tp = tcp_sk(sk);
526 u32 elapsed;
527
528 /* Only process if socket is not in use. */
529 bh_lock_sock(sk);
530 if (sock_owned_by_user(sk)) {
531 /* Try again later. */
532 inet_csk_reset_keepalive_timer (sk, HZ/20);
533 goto out;
534 }
535
536 if (sk->sk_state == TCP_LISTEN) {
537 tcp_synack_timer(sk);
538 goto out;
539 }
540
541 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
542 if (tp->linger2 >= 0) {
543 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
544
545 if (tmo > 0) {
546 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
547 goto out;
548 }
549 }
550 tcp_send_active_reset(sk, GFP_ATOMIC);
551 goto death;
552 }
553
554 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
555 goto out;
556
557 elapsed = keepalive_time_when(tp);
558
559 /* It is alive without keepalive 8) */
560 if (tp->packets_out || tcp_send_head(sk))
561 goto resched;
562
563 elapsed = keepalive_time_elapsed(tp);
564
565 if (elapsed >= keepalive_time_when(tp)) {
566 /* If the TCP_USER_TIMEOUT option is enabled, use that
567 * to determine when to timeout instead.
568 */
569 if ((icsk->icsk_user_timeout != 0 &&
570 elapsed >= icsk->icsk_user_timeout &&
571 icsk->icsk_probes_out > 0) ||
572 (icsk->icsk_user_timeout == 0 &&
573 icsk->icsk_probes_out >= keepalive_probes(tp))) {
574 tcp_send_active_reset(sk, GFP_ATOMIC);
575 tcp_write_err(sk);
576 goto out;
577 }
578 if (tcp_write_wakeup(sk) <= 0) {
579 icsk->icsk_probes_out++;
580 elapsed = keepalive_intvl_when(tp);
581 } else {
582 /* If keepalive was lost due to local congestion,
583 * try harder.
584 */
585 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
586 }
587 } else {
588 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
589 elapsed = keepalive_time_when(tp) - elapsed;
590 }
591
592 sk_mem_reclaim(sk);
593
594resched:
595 inet_csk_reset_keepalive_timer (sk, elapsed);
596 goto out;
597
598death:
599 tcp_done(sk);
600
601out:
602 bh_unlock_sock(sk);
603 sock_put(sk);
604}