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_syn_retries __read_mostly = TCP_SYN_RETRIES; 26 int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES; 27 int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME; 28 int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES; 29 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL; 30 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1; 31 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2; 32 int sysctl_tcp_orphan_retries __read_mostly; 33 int sysctl_tcp_thin_linear_timeouts __read_mostly; 34 35 static void tcp_write_timer(unsigned long); 36 static void tcp_delack_timer(unsigned long); 37 static void tcp_keepalive_timer (unsigned long data); 38 39 void 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 } 44 EXPORT_SYMBOL(tcp_init_xmit_timers); 45 46 static 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 */ 66 static 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_too_many_orphans(sk, shift)) { 81 if (net_ratelimit()) 82 printk(KERN_INFO "Out of socket memory\n"); 83 84 /* Catch exceptional cases, when connection requires reset. 85 * 1. Last segment was sent recently. */ 86 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 87 /* 2. Window is closed. */ 88 (!tp->snd_wnd && !tp->packets_out)) 89 do_reset = 1; 90 if (do_reset) 91 tcp_send_active_reset(sk, GFP_ATOMIC); 92 tcp_done(sk); 93 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); 94 return 1; 95 } 96 return 0; 97 } 98 99 /* Calculate maximal number or retries on an orphaned socket. */ 100 static int tcp_orphan_retries(struct sock *sk, int alive) 101 { 102 int retries = sysctl_tcp_orphan_retries; /* May be zero. */ 103 104 /* We know from an ICMP that something is wrong. */ 105 if (sk->sk_err_soft && !alive) 106 retries = 0; 107 108 /* However, if socket sent something recently, select some safe 109 * number of retries. 8 corresponds to >100 seconds with minimal 110 * RTO of 200msec. */ 111 if (retries == 0 && alive) 112 retries = 8; 113 return retries; 114 } 115 116 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) 117 { 118 /* Black hole detection */ 119 if (sysctl_tcp_mtu_probing) { 120 if (!icsk->icsk_mtup.enabled) { 121 icsk->icsk_mtup.enabled = 1; 122 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 123 } else { 124 struct tcp_sock *tp = tcp_sk(sk); 125 int mss; 126 127 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; 128 mss = min(sysctl_tcp_base_mss, mss); 129 mss = max(mss, 68 - tp->tcp_header_len); 130 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 131 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 132 } 133 } 134 } 135 136 /* This function calculates a "timeout" which is equivalent to the timeout of a 137 * TCP connection after "boundary" unsuccessful, exponentially backed-off 138 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if 139 * syn_set flag is set. 140 */ 141 static bool retransmits_timed_out(struct sock *sk, 142 unsigned int boundary, 143 unsigned int timeout, 144 bool syn_set) 145 { 146 unsigned int linear_backoff_thresh, start_ts; 147 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN; 148 149 if (!inet_csk(sk)->icsk_retransmits) 150 return false; 151 152 if (unlikely(!tcp_sk(sk)->retrans_stamp)) 153 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when; 154 else 155 start_ts = tcp_sk(sk)->retrans_stamp; 156 157 if (likely(timeout == 0)) { 158 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base); 159 160 if (boundary <= linear_backoff_thresh) 161 timeout = ((2 << boundary) - 1) * rto_base; 162 else 163 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base + 164 (boundary - linear_backoff_thresh) * TCP_RTO_MAX; 165 } 166 return (tcp_time_stamp - start_ts) >= timeout; 167 } 168 169 /* A write timeout has occurred. Process the after effects. */ 170 static int tcp_write_timeout(struct sock *sk) 171 { 172 struct inet_connection_sock *icsk = inet_csk(sk); 173 int retry_until; 174 bool do_reset, syn_set = 0; 175 176 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 177 if (icsk->icsk_retransmits) 178 dst_negative_advice(sk); 179 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; 180 syn_set = 1; 181 } else { 182 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) { 183 /* Black hole detection */ 184 tcp_mtu_probing(icsk, sk); 185 186 dst_negative_advice(sk); 187 } 188 189 retry_until = sysctl_tcp_retries2; 190 if (sock_flag(sk, SOCK_DEAD)) { 191 const int alive = (icsk->icsk_rto < TCP_RTO_MAX); 192 193 retry_until = tcp_orphan_retries(sk, alive); 194 do_reset = alive || 195 !retransmits_timed_out(sk, retry_until, 0, 0); 196 197 if (tcp_out_of_resources(sk, do_reset)) 198 return 1; 199 } 200 } 201 202 if (retransmits_timed_out(sk, retry_until, 203 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) { 204 /* Has it gone just too far? */ 205 tcp_write_err(sk); 206 return 1; 207 } 208 return 0; 209 } 210 211 static void tcp_delack_timer(unsigned long data) 212 { 213 struct sock *sk = (struct sock *)data; 214 struct tcp_sock *tp = tcp_sk(sk); 215 struct inet_connection_sock *icsk = inet_csk(sk); 216 217 bh_lock_sock(sk); 218 if (sock_owned_by_user(sk)) { 219 /* Try again later. */ 220 icsk->icsk_ack.blocked = 1; 221 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 222 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN); 223 goto out_unlock; 224 } 225 226 sk_mem_reclaim_partial(sk); 227 228 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 229 goto out; 230 231 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 232 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 233 goto out; 234 } 235 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 236 237 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 238 struct sk_buff *skb; 239 240 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); 241 242 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 243 sk_backlog_rcv(sk, skb); 244 245 tp->ucopy.memory = 0; 246 } 247 248 if (inet_csk_ack_scheduled(sk)) { 249 if (!icsk->icsk_ack.pingpong) { 250 /* Delayed ACK missed: inflate ATO. */ 251 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 252 } else { 253 /* Delayed ACK missed: leave pingpong mode and 254 * deflate ATO. 255 */ 256 icsk->icsk_ack.pingpong = 0; 257 icsk->icsk_ack.ato = TCP_ATO_MIN; 258 } 259 tcp_send_ack(sk); 260 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS); 261 } 262 263 out: 264 if (tcp_memory_pressure) 265 sk_mem_reclaim(sk); 266 out_unlock: 267 bh_unlock_sock(sk); 268 sock_put(sk); 269 } 270 271 static void tcp_probe_timer(struct sock *sk) 272 { 273 struct inet_connection_sock *icsk = inet_csk(sk); 274 struct tcp_sock *tp = tcp_sk(sk); 275 int max_probes; 276 277 if (tp->packets_out || !tcp_send_head(sk)) { 278 icsk->icsk_probes_out = 0; 279 return; 280 } 281 282 /* *WARNING* RFC 1122 forbids this 283 * 284 * It doesn't AFAIK, because we kill the retransmit timer -AK 285 * 286 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing 287 * this behaviour in Solaris down as a bug fix. [AC] 288 * 289 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs 290 * even if they advertise zero window. Hence, connection is killed only 291 * if we received no ACKs for normal connection timeout. It is not killed 292 * only because window stays zero for some time, window may be zero 293 * until armageddon and even later. We are in full accordance 294 * with RFCs, only probe timer combines both retransmission timeout 295 * and probe timeout in one bottle. --ANK 296 */ 297 max_probes = sysctl_tcp_retries2; 298 299 if (sock_flag(sk, SOCK_DEAD)) { 300 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX); 301 302 max_probes = tcp_orphan_retries(sk, alive); 303 304 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes)) 305 return; 306 } 307 308 if (icsk->icsk_probes_out > max_probes) { 309 tcp_write_err(sk); 310 } else { 311 /* Only send another probe if we didn't close things up. */ 312 tcp_send_probe0(sk); 313 } 314 } 315 316 /* 317 * The TCP retransmit timer. 318 */ 319 320 void tcp_retransmit_timer(struct sock *sk) 321 { 322 struct tcp_sock *tp = tcp_sk(sk); 323 struct inet_connection_sock *icsk = inet_csk(sk); 324 325 if (!tp->packets_out) 326 goto out; 327 328 WARN_ON(tcp_write_queue_empty(sk)); 329 330 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 331 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 332 /* Receiver dastardly shrinks window. Our retransmits 333 * become zero probes, but we should not timeout this 334 * connection. If the socket is an orphan, time it out, 335 * we cannot allow such beasts to hang infinitely. 336 */ 337 struct inet_sock *inet = inet_sk(sk); 338 if (sk->sk_family == AF_INET) { 339 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 340 &inet->inet_daddr, ntohs(inet->inet_dport), 341 inet->inet_num, tp->snd_una, tp->snd_nxt); 342 } 343 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) 344 else if (sk->sk_family == AF_INET6) { 345 struct ipv6_pinfo *np = inet6_sk(sk); 346 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 347 &np->daddr, ntohs(inet->inet_dport), 348 inet->inet_num, tp->snd_una, tp->snd_nxt); 349 } 350 #endif 351 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 352 tcp_write_err(sk); 353 goto out; 354 } 355 tcp_enter_loss(sk, 0); 356 tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); 357 __sk_dst_reset(sk); 358 goto out_reset_timer; 359 } 360 361 if (tcp_write_timeout(sk)) 362 goto out; 363 364 if (icsk->icsk_retransmits == 0) { 365 int mib_idx; 366 367 if (icsk->icsk_ca_state == TCP_CA_Recovery) { 368 if (tcp_is_sack(tp)) 369 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 370 else 371 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 372 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 373 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 374 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || 375 tp->sacked_out) { 376 if (tcp_is_sack(tp)) 377 mib_idx = LINUX_MIB_TCPSACKFAILURES; 378 else 379 mib_idx = LINUX_MIB_TCPRENOFAILURES; 380 } else { 381 mib_idx = LINUX_MIB_TCPTIMEOUTS; 382 } 383 NET_INC_STATS_BH(sock_net(sk), mib_idx); 384 } 385 386 if (tcp_use_frto(sk)) { 387 tcp_enter_frto(sk); 388 } else { 389 tcp_enter_loss(sk, 0); 390 } 391 392 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) { 393 /* Retransmission failed because of local congestion, 394 * do not backoff. 395 */ 396 if (!icsk->icsk_retransmits) 397 icsk->icsk_retransmits = 1; 398 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 399 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 400 TCP_RTO_MAX); 401 goto out; 402 } 403 404 /* Increase the timeout each time we retransmit. Note that 405 * we do not increase the rtt estimate. rto is initialized 406 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 407 * that doubling rto each time is the least we can get away with. 408 * In KA9Q, Karn uses this for the first few times, and then 409 * goes to quadratic. netBSD doubles, but only goes up to *64, 410 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 411 * defined in the protocol as the maximum possible RTT. I guess 412 * we'll have to use something other than TCP to talk to the 413 * University of Mars. 414 * 415 * PAWS allows us longer timeouts and large windows, so once 416 * implemented ftp to mars will work nicely. We will have to fix 417 * the 120 second clamps though! 418 */ 419 icsk->icsk_backoff++; 420 icsk->icsk_retransmits++; 421 422 out_reset_timer: 423 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is 424 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this 425 * might be increased if the stream oscillates between thin and thick, 426 * thus the old value might already be too high compared to the value 427 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without 428 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating 429 * exponential backoff behaviour to avoid continue hammering 430 * linear-timeout retransmissions into a black hole 431 */ 432 if (sk->sk_state == TCP_ESTABLISHED && 433 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) && 434 tcp_stream_is_thin(tp) && 435 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { 436 icsk->icsk_backoff = 0; 437 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); 438 } else { 439 /* Use normal (exponential) backoff */ 440 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 441 } 442 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 443 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0)) 444 __sk_dst_reset(sk); 445 446 out:; 447 } 448 449 static void tcp_write_timer(unsigned long data) 450 { 451 struct sock *sk = (struct sock *)data; 452 struct inet_connection_sock *icsk = inet_csk(sk); 453 int event; 454 455 bh_lock_sock(sk); 456 if (sock_owned_by_user(sk)) { 457 /* Try again later */ 458 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20)); 459 goto out_unlock; 460 } 461 462 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 463 goto out; 464 465 if (time_after(icsk->icsk_timeout, jiffies)) { 466 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 467 goto out; 468 } 469 470 event = icsk->icsk_pending; 471 icsk->icsk_pending = 0; 472 473 switch (event) { 474 case ICSK_TIME_RETRANS: 475 tcp_retransmit_timer(sk); 476 break; 477 case ICSK_TIME_PROBE0: 478 tcp_probe_timer(sk); 479 break; 480 } 481 482 out: 483 sk_mem_reclaim(sk); 484 out_unlock: 485 bh_unlock_sock(sk); 486 sock_put(sk); 487 } 488 489 /* 490 * Timer for listening sockets 491 */ 492 493 static void tcp_synack_timer(struct sock *sk) 494 { 495 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL, 496 TCP_TIMEOUT_INIT, TCP_RTO_MAX); 497 } 498 499 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req) 500 { 501 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS); 502 } 503 EXPORT_SYMBOL(tcp_syn_ack_timeout); 504 505 void tcp_set_keepalive(struct sock *sk, int val) 506 { 507 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 508 return; 509 510 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 511 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 512 else if (!val) 513 inet_csk_delete_keepalive_timer(sk); 514 } 515 516 517 static void tcp_keepalive_timer (unsigned long data) 518 { 519 struct sock *sk = (struct sock *) data; 520 struct inet_connection_sock *icsk = inet_csk(sk); 521 struct tcp_sock *tp = tcp_sk(sk); 522 u32 elapsed; 523 524 /* Only process if socket is not in use. */ 525 bh_lock_sock(sk); 526 if (sock_owned_by_user(sk)) { 527 /* Try again later. */ 528 inet_csk_reset_keepalive_timer (sk, HZ/20); 529 goto out; 530 } 531 532 if (sk->sk_state == TCP_LISTEN) { 533 tcp_synack_timer(sk); 534 goto out; 535 } 536 537 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 538 if (tp->linger2 >= 0) { 539 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 540 541 if (tmo > 0) { 542 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 543 goto out; 544 } 545 } 546 tcp_send_active_reset(sk, GFP_ATOMIC); 547 goto death; 548 } 549 550 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 551 goto out; 552 553 elapsed = keepalive_time_when(tp); 554 555 /* It is alive without keepalive 8) */ 556 if (tp->packets_out || tcp_send_head(sk)) 557 goto resched; 558 559 elapsed = keepalive_time_elapsed(tp); 560 561 if (elapsed >= keepalive_time_when(tp)) { 562 /* If the TCP_USER_TIMEOUT option is enabled, use that 563 * to determine when to timeout instead. 564 */ 565 if ((icsk->icsk_user_timeout != 0 && 566 elapsed >= icsk->icsk_user_timeout && 567 icsk->icsk_probes_out > 0) || 568 (icsk->icsk_user_timeout == 0 && 569 icsk->icsk_probes_out >= keepalive_probes(tp))) { 570 tcp_send_active_reset(sk, GFP_ATOMIC); 571 tcp_write_err(sk); 572 goto out; 573 } 574 if (tcp_write_wakeup(sk) <= 0) { 575 icsk->icsk_probes_out++; 576 elapsed = keepalive_intvl_when(tp); 577 } else { 578 /* If keepalive was lost due to local congestion, 579 * try harder. 580 */ 581 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 582 } 583 } else { 584 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 585 elapsed = keepalive_time_when(tp) - elapsed; 586 } 587 588 sk_mem_reclaim(sk); 589 590 resched: 591 inet_csk_reset_keepalive_timer (sk, elapsed); 592 goto out; 593 594 death: 595 tcp_done(sk); 596 597 out: 598 bh_unlock_sock(sk); 599 sock_put(sk); 600 } 601