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 * Version: $Id: tcp_timer.c,v 1.88 2002/02/01 22:01:04 davem Exp $ 9 * 10 * Authors: Ross Biro 11 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 12 * Mark Evans, <evansmp@uhura.aston.ac.uk> 13 * Corey Minyard <wf-rch!minyard@relay.EU.net> 14 * Florian La Roche, <flla@stud.uni-sb.de> 15 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 16 * Linus Torvalds, <torvalds@cs.helsinki.fi> 17 * Alan Cox, <gw4pts@gw4pts.ampr.org> 18 * Matthew Dillon, <dillon@apollo.west.oic.com> 19 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 20 * Jorge Cwik, <jorge@laser.satlink.net> 21 */ 22 23 #include <linux/module.h> 24 #include <net/tcp.h> 25 26 int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES; 27 int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES; 28 int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME; 29 int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES; 30 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL; 31 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1; 32 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2; 33 int sysctl_tcp_orphan_retries __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 45 EXPORT_SYMBOL(tcp_init_xmit_timers); 46 47 static void tcp_write_err(struct sock *sk) 48 { 49 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; 50 sk->sk_error_report(sk); 51 52 tcp_done(sk); 53 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONTIMEOUT); 54 } 55 56 /* Do not allow orphaned sockets to eat all our resources. 57 * This is direct violation of TCP specs, but it is required 58 * to prevent DoS attacks. It is called when a retransmission timeout 59 * or zero probe timeout occurs on orphaned socket. 60 * 61 * Criteria is still not confirmed experimentally and may change. 62 * We kill the socket, if: 63 * 1. If number of orphaned sockets exceeds an administratively configured 64 * limit. 65 * 2. If we have strong memory pressure. 66 */ 67 static int tcp_out_of_resources(struct sock *sk, int do_reset) 68 { 69 struct tcp_sock *tp = tcp_sk(sk); 70 int orphans = atomic_read(&tcp_orphan_count); 71 72 /* If peer does not open window for long time, or did not transmit 73 * anything for long time, penalize it. */ 74 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset) 75 orphans <<= 1; 76 77 /* If some dubious ICMP arrived, penalize even more. */ 78 if (sk->sk_err_soft) 79 orphans <<= 1; 80 81 if (tcp_too_many_orphans(sk, orphans)) { 82 if (net_ratelimit()) 83 printk(KERN_INFO "Out of socket memory\n"); 84 85 /* Catch exceptional cases, when connection requires reset. 86 * 1. Last segment was sent recently. */ 87 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 88 /* 2. Window is closed. */ 89 (!tp->snd_wnd && !tp->packets_out)) 90 do_reset = 1; 91 if (do_reset) 92 tcp_send_active_reset(sk, GFP_ATOMIC); 93 tcp_done(sk); 94 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONMEMORY); 95 return 1; 96 } 97 return 0; 98 } 99 100 /* Calculate maximal number or retries on an orphaned socket. */ 101 static int tcp_orphan_retries(struct sock *sk, int alive) 102 { 103 int retries = sysctl_tcp_orphan_retries; /* May be zero. */ 104 105 /* We know from an ICMP that something is wrong. */ 106 if (sk->sk_err_soft && !alive) 107 retries = 0; 108 109 /* However, if socket sent something recently, select some safe 110 * number of retries. 8 corresponds to >100 seconds with minimal 111 * RTO of 200msec. */ 112 if (retries == 0 && alive) 113 retries = 8; 114 return retries; 115 } 116 117 /* A write timeout has occurred. Process the after effects. */ 118 static int tcp_write_timeout(struct sock *sk) 119 { 120 struct inet_connection_sock *icsk = inet_csk(sk); 121 struct tcp_sock *tp = tcp_sk(sk); 122 int retry_until; 123 int mss; 124 125 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 126 if (icsk->icsk_retransmits) 127 dst_negative_advice(&sk->sk_dst_cache); 128 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; 129 } else { 130 if (icsk->icsk_retransmits >= sysctl_tcp_retries1) { 131 /* Black hole detection */ 132 if (sysctl_tcp_mtu_probing) { 133 if (!icsk->icsk_mtup.enabled) { 134 icsk->icsk_mtup.enabled = 1; 135 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 136 } else { 137 mss = min(sysctl_tcp_base_mss, 138 tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)/2); 139 mss = max(mss, 68 - tp->tcp_header_len); 140 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 141 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 142 } 143 } 144 145 dst_negative_advice(&sk->sk_dst_cache); 146 } 147 148 retry_until = sysctl_tcp_retries2; 149 if (sock_flag(sk, SOCK_DEAD)) { 150 const int alive = (icsk->icsk_rto < TCP_RTO_MAX); 151 152 retry_until = tcp_orphan_retries(sk, alive); 153 154 if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until)) 155 return 1; 156 } 157 } 158 159 if (icsk->icsk_retransmits >= retry_until) { 160 /* Has it gone just too far? */ 161 tcp_write_err(sk); 162 return 1; 163 } 164 return 0; 165 } 166 167 static void tcp_delack_timer(unsigned long data) 168 { 169 struct sock *sk = (struct sock*)data; 170 struct tcp_sock *tp = tcp_sk(sk); 171 struct inet_connection_sock *icsk = inet_csk(sk); 172 173 bh_lock_sock(sk); 174 if (sock_owned_by_user(sk)) { 175 /* Try again later. */ 176 icsk->icsk_ack.blocked = 1; 177 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOCKED); 178 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN); 179 goto out_unlock; 180 } 181 182 sk_stream_mem_reclaim(sk); 183 184 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 185 goto out; 186 187 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 188 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 189 goto out; 190 } 191 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 192 193 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 194 struct sk_buff *skb; 195 196 NET_INC_STATS_BH(LINUX_MIB_TCPSCHEDULERFAILED); 197 198 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 199 sk->sk_backlog_rcv(sk, skb); 200 201 tp->ucopy.memory = 0; 202 } 203 204 if (inet_csk_ack_scheduled(sk)) { 205 if (!icsk->icsk_ack.pingpong) { 206 /* Delayed ACK missed: inflate ATO. */ 207 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 208 } else { 209 /* Delayed ACK missed: leave pingpong mode and 210 * deflate ATO. 211 */ 212 icsk->icsk_ack.pingpong = 0; 213 icsk->icsk_ack.ato = TCP_ATO_MIN; 214 } 215 tcp_send_ack(sk); 216 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKS); 217 } 218 TCP_CHECK_TIMER(sk); 219 220 out: 221 if (tcp_memory_pressure) 222 sk_stream_mem_reclaim(sk); 223 out_unlock: 224 bh_unlock_sock(sk); 225 sock_put(sk); 226 } 227 228 static void tcp_probe_timer(struct sock *sk) 229 { 230 struct inet_connection_sock *icsk = inet_csk(sk); 231 struct tcp_sock *tp = tcp_sk(sk); 232 int max_probes; 233 234 if (tp->packets_out || !tcp_send_head(sk)) { 235 icsk->icsk_probes_out = 0; 236 return; 237 } 238 239 /* *WARNING* RFC 1122 forbids this 240 * 241 * It doesn't AFAIK, because we kill the retransmit timer -AK 242 * 243 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing 244 * this behaviour in Solaris down as a bug fix. [AC] 245 * 246 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs 247 * even if they advertise zero window. Hence, connection is killed only 248 * if we received no ACKs for normal connection timeout. It is not killed 249 * only because window stays zero for some time, window may be zero 250 * until armageddon and even later. We are in full accordance 251 * with RFCs, only probe timer combines both retransmission timeout 252 * and probe timeout in one bottle. --ANK 253 */ 254 max_probes = sysctl_tcp_retries2; 255 256 if (sock_flag(sk, SOCK_DEAD)) { 257 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX); 258 259 max_probes = tcp_orphan_retries(sk, alive); 260 261 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes)) 262 return; 263 } 264 265 if (icsk->icsk_probes_out > max_probes) { 266 tcp_write_err(sk); 267 } else { 268 /* Only send another probe if we didn't close things up. */ 269 tcp_send_probe0(sk); 270 } 271 } 272 273 /* 274 * The TCP retransmit timer. 275 */ 276 277 static void tcp_retransmit_timer(struct sock *sk) 278 { 279 struct tcp_sock *tp = tcp_sk(sk); 280 struct inet_connection_sock *icsk = inet_csk(sk); 281 282 if (!tp->packets_out) 283 goto out; 284 285 BUG_TRAP(!tcp_write_queue_empty(sk)); 286 287 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 288 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 289 /* Receiver dastardly shrinks window. Our retransmits 290 * become zero probes, but we should not timeout this 291 * connection. If the socket is an orphan, time it out, 292 * we cannot allow such beasts to hang infinitely. 293 */ 294 #ifdef TCP_DEBUG 295 if (1) { 296 struct inet_sock *inet = inet_sk(sk); 297 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Treason uncloaked! Peer %u.%u.%u.%u:%u/%u shrinks window %u:%u. Repaired.\n", 298 NIPQUAD(inet->daddr), ntohs(inet->dport), 299 inet->num, tp->snd_una, tp->snd_nxt); 300 } 301 #endif 302 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 303 tcp_write_err(sk); 304 goto out; 305 } 306 tcp_enter_loss(sk, 0); 307 tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); 308 __sk_dst_reset(sk); 309 goto out_reset_timer; 310 } 311 312 if (tcp_write_timeout(sk)) 313 goto out; 314 315 if (icsk->icsk_retransmits == 0) { 316 if (icsk->icsk_ca_state == TCP_CA_Disorder || 317 icsk->icsk_ca_state == TCP_CA_Recovery) { 318 if (tp->rx_opt.sack_ok) { 319 if (icsk->icsk_ca_state == TCP_CA_Recovery) 320 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERYFAIL); 321 else 322 NET_INC_STATS_BH(LINUX_MIB_TCPSACKFAILURES); 323 } else { 324 if (icsk->icsk_ca_state == TCP_CA_Recovery) 325 NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERYFAIL); 326 else 327 NET_INC_STATS_BH(LINUX_MIB_TCPRENOFAILURES); 328 } 329 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 330 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSFAILURES); 331 } else { 332 NET_INC_STATS_BH(LINUX_MIB_TCPTIMEOUTS); 333 } 334 } 335 336 if (tcp_use_frto(sk)) { 337 tcp_enter_frto(sk); 338 } else { 339 tcp_enter_loss(sk, 0); 340 } 341 342 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) { 343 /* Retransmission failed because of local congestion, 344 * do not backoff. 345 */ 346 if (!icsk->icsk_retransmits) 347 icsk->icsk_retransmits = 1; 348 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 349 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 350 TCP_RTO_MAX); 351 goto out; 352 } 353 354 /* Increase the timeout each time we retransmit. Note that 355 * we do not increase the rtt estimate. rto is initialized 356 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 357 * that doubling rto each time is the least we can get away with. 358 * In KA9Q, Karn uses this for the first few times, and then 359 * goes to quadratic. netBSD doubles, but only goes up to *64, 360 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 361 * defined in the protocol as the maximum possible RTT. I guess 362 * we'll have to use something other than TCP to talk to the 363 * University of Mars. 364 * 365 * PAWS allows us longer timeouts and large windows, so once 366 * implemented ftp to mars will work nicely. We will have to fix 367 * the 120 second clamps though! 368 */ 369 icsk->icsk_backoff++; 370 icsk->icsk_retransmits++; 371 372 out_reset_timer: 373 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 374 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 375 if (icsk->icsk_retransmits > sysctl_tcp_retries1) 376 __sk_dst_reset(sk); 377 378 out:; 379 } 380 381 static void tcp_write_timer(unsigned long data) 382 { 383 struct sock *sk = (struct sock*)data; 384 struct inet_connection_sock *icsk = inet_csk(sk); 385 int event; 386 387 bh_lock_sock(sk); 388 if (sock_owned_by_user(sk)) { 389 /* Try again later */ 390 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20)); 391 goto out_unlock; 392 } 393 394 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 395 goto out; 396 397 if (time_after(icsk->icsk_timeout, jiffies)) { 398 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 399 goto out; 400 } 401 402 event = icsk->icsk_pending; 403 icsk->icsk_pending = 0; 404 405 switch (event) { 406 case ICSK_TIME_RETRANS: 407 tcp_retransmit_timer(sk); 408 break; 409 case ICSK_TIME_PROBE0: 410 tcp_probe_timer(sk); 411 break; 412 } 413 TCP_CHECK_TIMER(sk); 414 415 out: 416 sk_stream_mem_reclaim(sk); 417 out_unlock: 418 bh_unlock_sock(sk); 419 sock_put(sk); 420 } 421 422 /* 423 * Timer for listening sockets 424 */ 425 426 static void tcp_synack_timer(struct sock *sk) 427 { 428 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL, 429 TCP_TIMEOUT_INIT, TCP_RTO_MAX); 430 } 431 432 void tcp_set_keepalive(struct sock *sk, int val) 433 { 434 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 435 return; 436 437 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 438 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 439 else if (!val) 440 inet_csk_delete_keepalive_timer(sk); 441 } 442 443 444 static void tcp_keepalive_timer (unsigned long data) 445 { 446 struct sock *sk = (struct sock *) data; 447 struct inet_connection_sock *icsk = inet_csk(sk); 448 struct tcp_sock *tp = tcp_sk(sk); 449 __u32 elapsed; 450 451 /* Only process if socket is not in use. */ 452 bh_lock_sock(sk); 453 if (sock_owned_by_user(sk)) { 454 /* Try again later. */ 455 inet_csk_reset_keepalive_timer (sk, HZ/20); 456 goto out; 457 } 458 459 if (sk->sk_state == TCP_LISTEN) { 460 tcp_synack_timer(sk); 461 goto out; 462 } 463 464 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 465 if (tp->linger2 >= 0) { 466 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 467 468 if (tmo > 0) { 469 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 470 goto out; 471 } 472 } 473 tcp_send_active_reset(sk, GFP_ATOMIC); 474 goto death; 475 } 476 477 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 478 goto out; 479 480 elapsed = keepalive_time_when(tp); 481 482 /* It is alive without keepalive 8) */ 483 if (tp->packets_out || tcp_send_head(sk)) 484 goto resched; 485 486 elapsed = tcp_time_stamp - tp->rcv_tstamp; 487 488 if (elapsed >= keepalive_time_when(tp)) { 489 if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) || 490 (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) { 491 tcp_send_active_reset(sk, GFP_ATOMIC); 492 tcp_write_err(sk); 493 goto out; 494 } 495 if (tcp_write_wakeup(sk) <= 0) { 496 icsk->icsk_probes_out++; 497 elapsed = keepalive_intvl_when(tp); 498 } else { 499 /* If keepalive was lost due to local congestion, 500 * try harder. 501 */ 502 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 503 } 504 } else { 505 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 506 elapsed = keepalive_time_when(tp) - elapsed; 507 } 508 509 TCP_CHECK_TIMER(sk); 510 sk_stream_mem_reclaim(sk); 511 512 resched: 513 inet_csk_reset_keepalive_timer (sk, elapsed); 514 goto out; 515 516 death: 517 tcp_done(sk); 518 519 out: 520 bh_unlock_sock(sk); 521 sock_put(sk); 522 } 523