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