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