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 25 int sysctl_tcp_thin_linear_timeouts __read_mostly; 26 27 /** 28 * tcp_write_err() - close socket and save error info 29 * @sk: The socket the error has appeared on. 30 * 31 * Returns: Nothing (void) 32 */ 33 34 static void tcp_write_err(struct sock *sk) 35 { 36 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; 37 sk->sk_error_report(sk); 38 39 tcp_done(sk); 40 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); 41 } 42 43 /** 44 * tcp_out_of_resources() - Close socket if out of resources 45 * @sk: pointer to current socket 46 * @do_reset: send a last packet with reset flag 47 * 48 * Do not allow orphaned sockets to eat all our resources. 49 * This is direct violation of TCP specs, but it is required 50 * to prevent DoS attacks. It is called when a retransmission timeout 51 * or zero probe timeout occurs on orphaned socket. 52 * 53 * Criteria is still not confirmed experimentally and may change. 54 * We kill the socket, if: 55 * 1. If number of orphaned sockets exceeds an administratively configured 56 * limit. 57 * 2. If we have strong memory pressure. 58 */ 59 static int tcp_out_of_resources(struct sock *sk, bool do_reset) 60 { 61 struct tcp_sock *tp = tcp_sk(sk); 62 int shift = 0; 63 64 /* If peer does not open window for long time, or did not transmit 65 * anything for long time, penalize it. */ 66 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset) 67 shift++; 68 69 /* If some dubious ICMP arrived, penalize even more. */ 70 if (sk->sk_err_soft) 71 shift++; 72 73 if (tcp_check_oom(sk, shift)) { 74 /* Catch exceptional cases, when connection requires reset. 75 * 1. Last segment was sent recently. */ 76 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 77 /* 2. Window is closed. */ 78 (!tp->snd_wnd && !tp->packets_out)) 79 do_reset = true; 80 if (do_reset) 81 tcp_send_active_reset(sk, GFP_ATOMIC); 82 tcp_done(sk); 83 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); 84 return 1; 85 } 86 return 0; 87 } 88 89 /** 90 * tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket 91 * @sk: Pointer to the current socket. 92 * @alive: bool, socket alive state 93 */ 94 static int tcp_orphan_retries(struct sock *sk, bool alive) 95 { 96 int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */ 97 98 /* We know from an ICMP that something is wrong. */ 99 if (sk->sk_err_soft && !alive) 100 retries = 0; 101 102 /* However, if socket sent something recently, select some safe 103 * number of retries. 8 corresponds to >100 seconds with minimal 104 * RTO of 200msec. */ 105 if (retries == 0 && alive) 106 retries = 8; 107 return retries; 108 } 109 110 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) 111 { 112 struct net *net = sock_net(sk); 113 114 /* Black hole detection */ 115 if (net->ipv4.sysctl_tcp_mtu_probing) { 116 if (!icsk->icsk_mtup.enabled) { 117 icsk->icsk_mtup.enabled = 1; 118 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp; 119 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 120 } else { 121 struct net *net = sock_net(sk); 122 struct tcp_sock *tp = tcp_sk(sk); 123 int mss; 124 125 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; 126 mss = min(net->ipv4.sysctl_tcp_base_mss, mss); 127 mss = max(mss, 68 - tp->tcp_header_len); 128 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 129 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 130 } 131 } 132 } 133 134 135 /** 136 * retransmits_timed_out() - returns true if this connection has timed out 137 * @sk: The current socket 138 * @boundary: max number of retransmissions 139 * @timeout: A custom timeout value. 140 * If set to 0 the default timeout is calculated and used. 141 * Using TCP_RTO_MIN and the number of unsuccessful retransmits. 142 * @syn_set: true if the SYN Bit was set. 143 * 144 * The default "timeout" value this function can calculate and use 145 * is equivalent to the timeout of a TCP Connection 146 * after "boundary" unsuccessful, exponentially backed-off 147 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if 148 * syn_set flag is set. 149 * 150 */ 151 static bool retransmits_timed_out(struct sock *sk, 152 unsigned int boundary, 153 unsigned int timeout, 154 bool syn_set) 155 { 156 unsigned int linear_backoff_thresh, start_ts; 157 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN; 158 159 if (!inet_csk(sk)->icsk_retransmits) 160 return false; 161 162 start_ts = tcp_sk(sk)->retrans_stamp; 163 if (unlikely(!start_ts)) 164 start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk)); 165 166 if (likely(timeout == 0)) { 167 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base); 168 169 if (boundary <= linear_backoff_thresh) 170 timeout = ((2 << boundary) - 1) * rto_base; 171 else 172 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base + 173 (boundary - linear_backoff_thresh) * TCP_RTO_MAX; 174 } 175 return (tcp_time_stamp - start_ts) >= timeout; 176 } 177 178 /* A write timeout has occurred. Process the after effects. */ 179 static int tcp_write_timeout(struct sock *sk) 180 { 181 struct inet_connection_sock *icsk = inet_csk(sk); 182 struct tcp_sock *tp = tcp_sk(sk); 183 struct net *net = sock_net(sk); 184 int retry_until; 185 bool do_reset, syn_set = false; 186 187 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 188 if (icsk->icsk_retransmits) { 189 dst_negative_advice(sk); 190 if (tp->syn_fastopen || tp->syn_data) 191 tcp_fastopen_cache_set(sk, 0, NULL, true, 0); 192 if (tp->syn_data && icsk->icsk_retransmits == 1) 193 NET_INC_STATS(sock_net(sk), 194 LINUX_MIB_TCPFASTOPENACTIVEFAIL); 195 } 196 retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries; 197 syn_set = true; 198 } else { 199 if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0, 0)) { 200 /* Some middle-boxes may black-hole Fast Open _after_ 201 * the handshake. Therefore we conservatively disable 202 * Fast Open on this path on recurring timeouts with 203 * few or zero bytes acked after Fast Open. 204 */ 205 if (tp->syn_data_acked && 206 tp->bytes_acked <= tp->rx_opt.mss_clamp) { 207 tcp_fastopen_cache_set(sk, 0, NULL, true, 0); 208 if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1) 209 NET_INC_STATS(sock_net(sk), 210 LINUX_MIB_TCPFASTOPENACTIVEFAIL); 211 } 212 /* Black hole detection */ 213 tcp_mtu_probing(icsk, sk); 214 215 dst_negative_advice(sk); 216 } 217 218 retry_until = net->ipv4.sysctl_tcp_retries2; 219 if (sock_flag(sk, SOCK_DEAD)) { 220 const bool alive = icsk->icsk_rto < TCP_RTO_MAX; 221 222 retry_until = tcp_orphan_retries(sk, alive); 223 do_reset = alive || 224 !retransmits_timed_out(sk, retry_until, 0, 0); 225 226 if (tcp_out_of_resources(sk, do_reset)) 227 return 1; 228 } 229 } 230 231 if (retransmits_timed_out(sk, retry_until, 232 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) { 233 /* Has it gone just too far? */ 234 tcp_write_err(sk); 235 return 1; 236 } 237 return 0; 238 } 239 240 /* Called with BH disabled */ 241 void tcp_delack_timer_handler(struct sock *sk) 242 { 243 struct tcp_sock *tp = tcp_sk(sk); 244 struct inet_connection_sock *icsk = inet_csk(sk); 245 246 sk_mem_reclaim_partial(sk); 247 248 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 249 goto out; 250 251 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 252 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 253 goto out; 254 } 255 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 256 257 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 258 struct sk_buff *skb; 259 260 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); 261 262 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 263 sk_backlog_rcv(sk, skb); 264 265 tp->ucopy.memory = 0; 266 } 267 268 if (inet_csk_ack_scheduled(sk)) { 269 if (!icsk->icsk_ack.pingpong) { 270 /* Delayed ACK missed: inflate ATO. */ 271 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 272 } else { 273 /* Delayed ACK missed: leave pingpong mode and 274 * deflate ATO. 275 */ 276 icsk->icsk_ack.pingpong = 0; 277 icsk->icsk_ack.ato = TCP_ATO_MIN; 278 } 279 tcp_send_ack(sk); 280 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS); 281 } 282 283 out: 284 if (tcp_under_memory_pressure(sk)) 285 sk_mem_reclaim(sk); 286 } 287 288 289 /** 290 * tcp_delack_timer() - The TCP delayed ACK timeout handler 291 * @data: Pointer to the current socket. (gets casted to struct sock *) 292 * 293 * This function gets (indirectly) called when the kernel timer for a TCP packet 294 * of this socket expires. Calls tcp_delack_timer_handler() to do the actual work. 295 * 296 * Returns: Nothing (void) 297 */ 298 static void tcp_delack_timer(unsigned long data) 299 { 300 struct sock *sk = (struct sock *)data; 301 302 bh_lock_sock(sk); 303 if (!sock_owned_by_user(sk)) { 304 tcp_delack_timer_handler(sk); 305 } else { 306 inet_csk(sk)->icsk_ack.blocked = 1; 307 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 308 /* deleguate our work to tcp_release_cb() */ 309 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) 310 sock_hold(sk); 311 } 312 bh_unlock_sock(sk); 313 sock_put(sk); 314 } 315 316 static void tcp_probe_timer(struct sock *sk) 317 { 318 struct inet_connection_sock *icsk = inet_csk(sk); 319 struct tcp_sock *tp = tcp_sk(sk); 320 int max_probes; 321 u32 start_ts; 322 323 if (tp->packets_out || !tcp_send_head(sk)) { 324 icsk->icsk_probes_out = 0; 325 return; 326 } 327 328 /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as 329 * long as the receiver continues to respond probes. We support this by 330 * default and reset icsk_probes_out with incoming ACKs. But if the 331 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we 332 * kill the socket when the retry count and the time exceeds the 333 * corresponding system limit. We also implement similar policy when 334 * we use RTO to probe window in tcp_retransmit_timer(). 335 */ 336 start_ts = tcp_skb_timestamp(tcp_send_head(sk)); 337 if (!start_ts) 338 skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp); 339 else if (icsk->icsk_user_timeout && 340 (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout) 341 goto abort; 342 343 max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2; 344 if (sock_flag(sk, SOCK_DEAD)) { 345 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX; 346 347 max_probes = tcp_orphan_retries(sk, alive); 348 if (!alive && icsk->icsk_backoff >= max_probes) 349 goto abort; 350 if (tcp_out_of_resources(sk, true)) 351 return; 352 } 353 354 if (icsk->icsk_probes_out > max_probes) { 355 abort: tcp_write_err(sk); 356 } else { 357 /* Only send another probe if we didn't close things up. */ 358 tcp_send_probe0(sk); 359 } 360 } 361 362 /* 363 * Timer for Fast Open socket to retransmit SYNACK. Note that the 364 * sk here is the child socket, not the parent (listener) socket. 365 */ 366 static void tcp_fastopen_synack_timer(struct sock *sk) 367 { 368 struct inet_connection_sock *icsk = inet_csk(sk); 369 int max_retries = icsk->icsk_syn_retries ? : 370 sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */ 371 struct request_sock *req; 372 373 req = tcp_sk(sk)->fastopen_rsk; 374 req->rsk_ops->syn_ack_timeout(req); 375 376 if (req->num_timeout >= max_retries) { 377 tcp_write_err(sk); 378 return; 379 } 380 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error 381 * returned from rtx_syn_ack() to make it more persistent like 382 * regular retransmit because if the child socket has been accepted 383 * it's not good to give up too easily. 384 */ 385 inet_rtx_syn_ack(sk, req); 386 req->num_timeout++; 387 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 388 TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX); 389 } 390 391 392 /** 393 * tcp_retransmit_timer() - The TCP retransmit timeout handler 394 * @sk: Pointer to the current socket. 395 * 396 * This function gets called when the kernel timer for a TCP packet 397 * of this socket expires. 398 * 399 * It handles retransmission, timer adjustment and other necesarry measures. 400 * 401 * Returns: Nothing (void) 402 */ 403 void tcp_retransmit_timer(struct sock *sk) 404 { 405 struct tcp_sock *tp = tcp_sk(sk); 406 struct net *net = sock_net(sk); 407 struct inet_connection_sock *icsk = inet_csk(sk); 408 409 if (tp->fastopen_rsk) { 410 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && 411 sk->sk_state != TCP_FIN_WAIT1); 412 tcp_fastopen_synack_timer(sk); 413 /* Before we receive ACK to our SYN-ACK don't retransmit 414 * anything else (e.g., data or FIN segments). 415 */ 416 return; 417 } 418 if (!tp->packets_out) 419 goto out; 420 421 WARN_ON(tcp_write_queue_empty(sk)); 422 423 tp->tlp_high_seq = 0; 424 425 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 426 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 427 /* Receiver dastardly shrinks window. Our retransmits 428 * become zero probes, but we should not timeout this 429 * connection. If the socket is an orphan, time it out, 430 * we cannot allow such beasts to hang infinitely. 431 */ 432 struct inet_sock *inet = inet_sk(sk); 433 if (sk->sk_family == AF_INET) { 434 net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 435 &inet->inet_daddr, 436 ntohs(inet->inet_dport), 437 inet->inet_num, 438 tp->snd_una, tp->snd_nxt); 439 } 440 #if IS_ENABLED(CONFIG_IPV6) 441 else if (sk->sk_family == AF_INET6) { 442 net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 443 &sk->sk_v6_daddr, 444 ntohs(inet->inet_dport), 445 inet->inet_num, 446 tp->snd_una, tp->snd_nxt); 447 } 448 #endif 449 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 450 tcp_write_err(sk); 451 goto out; 452 } 453 tcp_enter_loss(sk); 454 tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1); 455 __sk_dst_reset(sk); 456 goto out_reset_timer; 457 } 458 459 if (tcp_write_timeout(sk)) 460 goto out; 461 462 if (icsk->icsk_retransmits == 0) { 463 int mib_idx; 464 465 if (icsk->icsk_ca_state == TCP_CA_Recovery) { 466 if (tcp_is_sack(tp)) 467 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 468 else 469 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 470 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 471 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 472 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || 473 tp->sacked_out) { 474 if (tcp_is_sack(tp)) 475 mib_idx = LINUX_MIB_TCPSACKFAILURES; 476 else 477 mib_idx = LINUX_MIB_TCPRENOFAILURES; 478 } else { 479 mib_idx = LINUX_MIB_TCPTIMEOUTS; 480 } 481 __NET_INC_STATS(sock_net(sk), mib_idx); 482 } 483 484 tcp_enter_loss(sk); 485 486 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1) > 0) { 487 /* Retransmission failed because of local congestion, 488 * do not backoff. 489 */ 490 if (!icsk->icsk_retransmits) 491 icsk->icsk_retransmits = 1; 492 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 493 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 494 TCP_RTO_MAX); 495 goto out; 496 } 497 498 /* Increase the timeout each time we retransmit. Note that 499 * we do not increase the rtt estimate. rto is initialized 500 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 501 * that doubling rto each time is the least we can get away with. 502 * In KA9Q, Karn uses this for the first few times, and then 503 * goes to quadratic. netBSD doubles, but only goes up to *64, 504 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 505 * defined in the protocol as the maximum possible RTT. I guess 506 * we'll have to use something other than TCP to talk to the 507 * University of Mars. 508 * 509 * PAWS allows us longer timeouts and large windows, so once 510 * implemented ftp to mars will work nicely. We will have to fix 511 * the 120 second clamps though! 512 */ 513 icsk->icsk_backoff++; 514 icsk->icsk_retransmits++; 515 516 out_reset_timer: 517 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is 518 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this 519 * might be increased if the stream oscillates between thin and thick, 520 * thus the old value might already be too high compared to the value 521 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without 522 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating 523 * exponential backoff behaviour to avoid continue hammering 524 * linear-timeout retransmissions into a black hole 525 */ 526 if (sk->sk_state == TCP_ESTABLISHED && 527 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) && 528 tcp_stream_is_thin(tp) && 529 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { 530 icsk->icsk_backoff = 0; 531 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); 532 } else { 533 /* Use normal (exponential) backoff */ 534 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 535 } 536 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 537 if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0, 0)) 538 __sk_dst_reset(sk); 539 540 out:; 541 } 542 543 /* Called with bottom-half processing disabled. 544 Called by tcp_write_timer() */ 545 void tcp_write_timer_handler(struct sock *sk) 546 { 547 struct inet_connection_sock *icsk = inet_csk(sk); 548 int event; 549 550 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 551 goto out; 552 553 if (time_after(icsk->icsk_timeout, jiffies)) { 554 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 555 goto out; 556 } 557 558 event = icsk->icsk_pending; 559 560 switch (event) { 561 case ICSK_TIME_EARLY_RETRANS: 562 tcp_resume_early_retransmit(sk); 563 break; 564 case ICSK_TIME_LOSS_PROBE: 565 tcp_send_loss_probe(sk); 566 break; 567 case ICSK_TIME_RETRANS: 568 icsk->icsk_pending = 0; 569 tcp_retransmit_timer(sk); 570 break; 571 case ICSK_TIME_PROBE0: 572 icsk->icsk_pending = 0; 573 tcp_probe_timer(sk); 574 break; 575 } 576 577 out: 578 sk_mem_reclaim(sk); 579 } 580 581 static void tcp_write_timer(unsigned long data) 582 { 583 struct sock *sk = (struct sock *)data; 584 585 bh_lock_sock(sk); 586 if (!sock_owned_by_user(sk)) { 587 tcp_write_timer_handler(sk); 588 } else { 589 /* delegate our work to tcp_release_cb() */ 590 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) 591 sock_hold(sk); 592 } 593 bh_unlock_sock(sk); 594 sock_put(sk); 595 } 596 597 void tcp_syn_ack_timeout(const struct request_sock *req) 598 { 599 struct net *net = read_pnet(&inet_rsk(req)->ireq_net); 600 601 __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS); 602 } 603 EXPORT_SYMBOL(tcp_syn_ack_timeout); 604 605 void tcp_set_keepalive(struct sock *sk, int val) 606 { 607 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 608 return; 609 610 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 611 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 612 else if (!val) 613 inet_csk_delete_keepalive_timer(sk); 614 } 615 616 617 static void tcp_keepalive_timer (unsigned long data) 618 { 619 struct sock *sk = (struct sock *) data; 620 struct inet_connection_sock *icsk = inet_csk(sk); 621 struct tcp_sock *tp = tcp_sk(sk); 622 u32 elapsed; 623 624 /* Only process if socket is not in use. */ 625 bh_lock_sock(sk); 626 if (sock_owned_by_user(sk)) { 627 /* Try again later. */ 628 inet_csk_reset_keepalive_timer (sk, HZ/20); 629 goto out; 630 } 631 632 if (sk->sk_state == TCP_LISTEN) { 633 pr_err("Hmm... keepalive on a LISTEN ???\n"); 634 goto out; 635 } 636 637 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 638 if (tp->linger2 >= 0) { 639 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 640 641 if (tmo > 0) { 642 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 643 goto out; 644 } 645 } 646 tcp_send_active_reset(sk, GFP_ATOMIC); 647 goto death; 648 } 649 650 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 651 goto out; 652 653 elapsed = keepalive_time_when(tp); 654 655 /* It is alive without keepalive 8) */ 656 if (tp->packets_out || tcp_send_head(sk)) 657 goto resched; 658 659 elapsed = keepalive_time_elapsed(tp); 660 661 if (elapsed >= keepalive_time_when(tp)) { 662 /* If the TCP_USER_TIMEOUT option is enabled, use that 663 * to determine when to timeout instead. 664 */ 665 if ((icsk->icsk_user_timeout != 0 && 666 elapsed >= icsk->icsk_user_timeout && 667 icsk->icsk_probes_out > 0) || 668 (icsk->icsk_user_timeout == 0 && 669 icsk->icsk_probes_out >= keepalive_probes(tp))) { 670 tcp_send_active_reset(sk, GFP_ATOMIC); 671 tcp_write_err(sk); 672 goto out; 673 } 674 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) { 675 icsk->icsk_probes_out++; 676 elapsed = keepalive_intvl_when(tp); 677 } else { 678 /* If keepalive was lost due to local congestion, 679 * try harder. 680 */ 681 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 682 } 683 } else { 684 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 685 elapsed = keepalive_time_when(tp) - elapsed; 686 } 687 688 sk_mem_reclaim(sk); 689 690 resched: 691 inet_csk_reset_keepalive_timer (sk, elapsed); 692 goto out; 693 694 death: 695 tcp_done(sk); 696 697 out: 698 bh_unlock_sock(sk); 699 sock_put(sk); 700 } 701 702 void tcp_init_xmit_timers(struct sock *sk) 703 { 704 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 705 &tcp_keepalive_timer); 706 } 707