Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/netinet/tcp_timewait.c
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1 /*- 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 4. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * @(#)tcp_subr.c 8.2 (Berkeley) 5/24/95 30 */ 31 32 #include <sys/cdefs.h> 33 __FBSDID("$FreeBSD$"); 34 35 #include "opt_inet.h" 36 #include "opt_inet6.h" 37 #include "opt_mac.h" 38 #include "opt_tcpdebug.h" 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/callout.h> 43 #include <sys/kernel.h> 44 #include <sys/sysctl.h> 45 #include <sys/malloc.h> 46 #include <sys/mbuf.h> 47 #include <sys/priv.h> 48 #include <sys/proc.h> 49 #include <sys/socket.h> 50 #include <sys/socketvar.h> 51 #include <sys/protosw.h> 52 #include <sys/random.h> 53 54 #include <vm/uma.h> 55 56 #include <net/route.h> 57 #include <net/if.h> 58 59 #include <netinet/in.h> 60 #include <netinet/in_systm.h> 61 #include <netinet/ip.h> 62 #ifdef INET6 63 #include <netinet/ip6.h> 64 #endif 65 #include <netinet/in_pcb.h> 66 #ifdef INET6 67 #include <netinet6/in6_pcb.h> 68 #endif 69 #include <netinet/in_var.h> 70 #include <netinet/ip_var.h> 71 #ifdef INET6 72 #include <netinet6/ip6_var.h> 73 #include <netinet6/scope6_var.h> 74 #include <netinet6/nd6.h> 75 #endif 76 #include <netinet/ip_icmp.h> 77 #include <netinet/tcp.h> 78 #include <netinet/tcp_fsm.h> 79 #include <netinet/tcp_seq.h> 80 #include <netinet/tcp_timer.h> 81 #include <netinet/tcp_var.h> 82 #ifdef INET6 83 #include <netinet6/tcp6_var.h> 84 #endif 85 #include <netinet/tcpip.h> 86 #ifdef TCPDEBUG 87 #include <netinet/tcp_debug.h> 88 #endif 89 #include <netinet6/ip6protosw.h> 90 91 #include <machine/in_cksum.h> 92 93 #include <security/mac/mac_framework.h> 94 95 static uma_zone_t tcptw_zone; 96 static int maxtcptw; 97 98 /* 99 * The timed wait queue contains references to each of the TCP sessions 100 * currently in the TIME_WAIT state. The queue pointers, including the 101 * queue pointers in each tcptw structure, are protected using the global 102 * tcbinfo lock, which must be held over queue iteration and modification. 103 */ 104 static TAILQ_HEAD(, tcptw) twq_2msl; 105 106 static void tcp_tw_2msl_reset(struct tcptw *, int); 107 static void tcp_tw_2msl_stop(struct tcptw *); 108 109 static int 110 tcptw_auto_size(void) 111 { 112 int halfrange; 113 114 /* 115 * Max out at half the ephemeral port range so that TIME_WAIT 116 * sockets don't tie up too many ephemeral ports. 117 */ 118 if (ipport_lastauto > ipport_firstauto) 119 halfrange = (ipport_lastauto - ipport_firstauto) / 2; 120 else 121 halfrange = (ipport_firstauto - ipport_lastauto) / 2; 122 /* Protect against goofy port ranges smaller than 32. */ 123 return (imin(imax(halfrange, 32), maxsockets / 5)); 124 } 125 126 static int 127 sysctl_maxtcptw(SYSCTL_HANDLER_ARGS) 128 { 129 int error, new; 130 131 if (maxtcptw == 0) 132 new = tcptw_auto_size(); 133 else 134 new = maxtcptw; 135 error = sysctl_handle_int(oidp, &new, 0, req); 136 if (error == 0 && req->newptr) 137 if (new >= 32) { 138 maxtcptw = new; 139 uma_zone_set_max(tcptw_zone, maxtcptw); 140 } 141 return (error); 142 } 143 144 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxtcptw, CTLTYPE_INT|CTLFLAG_RW, 145 &maxtcptw, 0, sysctl_maxtcptw, "IU", 146 "Maximum number of compressed TCP TIME_WAIT entries"); 147 148 static int nolocaltimewait = 0; 149 SYSCTL_INT(_net_inet_tcp, OID_AUTO, nolocaltimewait, CTLFLAG_RW, 150 &nolocaltimewait, 0, 151 "Do not create compressed TCP TIME_WAIT entries for local connections"); 152 153 void 154 tcp_tw_zone_change(void) 155 { 156 157 if (maxtcptw == 0) 158 uma_zone_set_max(tcptw_zone, tcptw_auto_size()); 159 } 160 161 void 162 tcp_tw_init(void) 163 { 164 165 tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw), 166 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE); 167 TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw); 168 if (maxtcptw == 0) 169 uma_zone_set_max(tcptw_zone, tcptw_auto_size()); 170 else 171 uma_zone_set_max(tcptw_zone, maxtcptw); 172 TAILQ_INIT(&twq_2msl); 173 } 174 175 /* 176 * Move a TCP connection into TIME_WAIT state. 177 * tcbinfo is locked. 178 * inp is locked, and is unlocked before returning. 179 */ 180 void 181 tcp_twstart(struct tcpcb *tp) 182 { 183 struct tcptw *tw; 184 struct inpcb *inp = tp->t_inpcb; 185 int acknow; 186 struct socket *so; 187 188 INP_INFO_WLOCK_ASSERT(&tcbinfo); /* tcp_tw_2msl_reset(). */ 189 INP_WLOCK_ASSERT(inp); 190 191 if (nolocaltimewait && in_localip(inp->inp_faddr)) { 192 tp = tcp_close(tp); 193 if (tp != NULL) 194 INP_WUNLOCK(inp); 195 return; 196 } 197 198 tw = uma_zalloc(tcptw_zone, M_NOWAIT); 199 if (tw == NULL) { 200 tw = tcp_tw_2msl_scan(1); 201 if (tw == NULL) { 202 tp = tcp_close(tp); 203 if (tp != NULL) 204 INP_WUNLOCK(inp); 205 return; 206 } 207 } 208 tw->tw_inpcb = inp; 209 210 /* 211 * Recover last window size sent. 212 */ 213 KASSERT(SEQ_GEQ(tp->rcv_adv, tp->rcv_nxt), 214 ("tcp_twstart negative window: tp %p rcv_nxt %u rcv_adv %u", tp, 215 tp->rcv_adv, tp->rcv_nxt)); 216 tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale; 217 218 /* 219 * Set t_recent if timestamps are used on the connection. 220 */ 221 if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) == 222 (TF_REQ_TSTMP|TF_RCVD_TSTMP)) { 223 tw->t_recent = tp->ts_recent; 224 tw->ts_offset = tp->ts_offset; 225 } else { 226 tw->t_recent = 0; 227 tw->ts_offset = 0; 228 } 229 230 tw->snd_nxt = tp->snd_nxt; 231 tw->rcv_nxt = tp->rcv_nxt; 232 tw->iss = tp->iss; 233 tw->irs = tp->irs; 234 tw->t_starttime = tp->t_starttime; 235 tw->tw_time = 0; 236 237 /* XXX 238 * If this code will 239 * be used for fin-wait-2 state also, then we may need 240 * a ts_recent from the last segment. 241 */ 242 acknow = tp->t_flags & TF_ACKNOW; 243 244 /* 245 * First, discard tcpcb state, which includes stopping its timers and 246 * freeing it. tcp_discardcb() used to also release the inpcb, but 247 * that work is now done in the caller. 248 * 249 * Note: soisdisconnected() call used to be made in tcp_discardcb(), 250 * and might not be needed here any longer. 251 */ 252 tcp_discardcb(tp); 253 so = inp->inp_socket; 254 soisdisconnected(so); 255 tw->tw_cred = crhold(so->so_cred); 256 SOCK_LOCK(so); 257 tw->tw_so_options = so->so_options; 258 SOCK_UNLOCK(so); 259 if (acknow) 260 tcp_twrespond(tw, TH_ACK); 261 inp->inp_ppcb = tw; 262 inp->inp_flags |= INP_TIMEWAIT; 263 tcp_tw_2msl_reset(tw, 0); 264 265 /* 266 * If the inpcb owns the sole reference to the socket, then we can 267 * detach and free the socket as it is not needed in time wait. 268 */ 269 if (inp->inp_flags & INP_SOCKREF) { 270 KASSERT(so->so_state & SS_PROTOREF, 271 ("tcp_twstart: !SS_PROTOREF")); 272 inp->inp_flags &= ~INP_SOCKREF; 273 INP_WUNLOCK(inp); 274 ACCEPT_LOCK(); 275 SOCK_LOCK(so); 276 so->so_state &= ~SS_PROTOREF; 277 sofree(so); 278 } else 279 INP_WUNLOCK(inp); 280 } 281 282 #if 0 283 /* 284 * The appromixate rate of ISN increase of Microsoft TCP stacks; 285 * the actual rate is slightly higher due to the addition of 286 * random positive increments. 287 * 288 * Most other new OSes use semi-randomized ISN values, so we 289 * do not need to worry about them. 290 */ 291 #define MS_ISN_BYTES_PER_SECOND 250000 292 293 /* 294 * Determine if the ISN we will generate has advanced beyond the last 295 * sequence number used by the previous connection. If so, indicate 296 * that it is safe to recycle this tw socket by returning 1. 297 */ 298 int 299 tcp_twrecycleable(struct tcptw *tw) 300 { 301 tcp_seq new_iss = tw->iss; 302 tcp_seq new_irs = tw->irs; 303 304 INP_INFO_WLOCK_ASSERT(&tcbinfo); 305 new_iss += (ticks - tw->t_starttime) * (ISN_BYTES_PER_SECOND / hz); 306 new_irs += (ticks - tw->t_starttime) * (MS_ISN_BYTES_PER_SECOND / hz); 307 308 if (SEQ_GT(new_iss, tw->snd_nxt) && SEQ_GT(new_irs, tw->rcv_nxt)) 309 return (1); 310 else 311 return (0); 312 } 313 #endif 314 315 /* 316 * Returns 1 if the TIME_WAIT state was killed and we should start over, 317 * looking for a pcb in the listen state. Returns 0 otherwise. 318 */ 319 int 320 tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th, 321 struct mbuf *m, int tlen) 322 { 323 struct tcptw *tw; 324 int thflags; 325 tcp_seq seq; 326 327 /* tcbinfo lock required for tcp_twclose(), tcp_tw_2msl_reset(). */ 328 INP_INFO_WLOCK_ASSERT(&tcbinfo); 329 INP_WLOCK_ASSERT(inp); 330 331 /* 332 * XXXRW: Time wait state for inpcb has been recycled, but inpcb is 333 * still present. This is undesirable, but temporarily necessary 334 * until we work out how to handle inpcb's who's timewait state has 335 * been removed. 336 */ 337 tw = intotw(inp); 338 if (tw == NULL) 339 goto drop; 340 341 thflags = th->th_flags; 342 343 /* 344 * NOTE: for FIN_WAIT_2 (to be added later), 345 * must validate sequence number before accepting RST 346 */ 347 348 /* 349 * If the segment contains RST: 350 * Drop the segment - see Stevens, vol. 2, p. 964 and 351 * RFC 1337. 352 */ 353 if (thflags & TH_RST) 354 goto drop; 355 356 #if 0 357 /* PAWS not needed at the moment */ 358 /* 359 * RFC 1323 PAWS: If we have a timestamp reply on this segment 360 * and it's less than ts_recent, drop it. 361 */ 362 if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent && 363 TSTMP_LT(to.to_tsval, tp->ts_recent)) { 364 if ((thflags & TH_ACK) == 0) 365 goto drop; 366 goto ack; 367 } 368 /* 369 * ts_recent is never updated because we never accept new segments. 370 */ 371 #endif 372 373 /* 374 * If a new connection request is received 375 * while in TIME_WAIT, drop the old connection 376 * and start over if the sequence numbers 377 * are above the previous ones. 378 */ 379 if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) { 380 tcp_twclose(tw, 0); 381 return (1); 382 } 383 384 /* 385 * Drop the segment if it does not contain an ACK. 386 */ 387 if ((thflags & TH_ACK) == 0) 388 goto drop; 389 390 /* 391 * Reset the 2MSL timer if this is a duplicate FIN. 392 */ 393 if (thflags & TH_FIN) { 394 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0); 395 if (seq + 1 == tw->rcv_nxt) 396 tcp_tw_2msl_reset(tw, 1); 397 } 398 399 /* 400 * Acknowledge the segment if it has data or is not a duplicate ACK. 401 */ 402 if (thflags != TH_ACK || tlen != 0 || 403 th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt) 404 tcp_twrespond(tw, TH_ACK); 405 drop: 406 INP_WUNLOCK(inp); 407 m_freem(m); 408 return (0); 409 } 410 411 void 412 tcp_twclose(struct tcptw *tw, int reuse) 413 { 414 struct socket *so; 415 struct inpcb *inp; 416 417 /* 418 * At this point, we are in one of two situations: 419 * 420 * (1) We have no socket, just an inpcb<->twtcp pair. We can free 421 * all state. 422 * 423 * (2) We have a socket -- if we own a reference, release it and 424 * notify the socket layer. 425 */ 426 inp = tw->tw_inpcb; 427 KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait")); 428 KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw")); 429 INP_INFO_WLOCK_ASSERT(&tcbinfo); /* tcp_tw_2msl_stop(). */ 430 INP_WLOCK_ASSERT(inp); 431 432 tw->tw_inpcb = NULL; 433 tcp_tw_2msl_stop(tw); 434 inp->inp_ppcb = NULL; 435 in_pcbdrop(inp); 436 437 so = inp->inp_socket; 438 if (so != NULL) { 439 /* 440 * If there's a socket, handle two cases: first, we own a 441 * strong reference, which we will now release, or we don't 442 * in which case another reference exists (XXXRW: think 443 * about this more), and we don't need to take action. 444 */ 445 if (inp->inp_flags & INP_SOCKREF) { 446 inp->inp_flags &= ~INP_SOCKREF; 447 INP_WUNLOCK(inp); 448 ACCEPT_LOCK(); 449 SOCK_LOCK(so); 450 KASSERT(so->so_state & SS_PROTOREF, 451 ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF")); 452 so->so_state &= ~SS_PROTOREF; 453 sofree(so); 454 } else { 455 /* 456 * If we don't own the only reference, the socket and 457 * inpcb need to be left around to be handled by 458 * tcp_usr_detach() later. 459 */ 460 INP_WUNLOCK(inp); 461 } 462 } else 463 in_pcbfree(inp); 464 tcpstat.tcps_closed++; 465 crfree(tw->tw_cred); 466 tw->tw_cred = NULL; 467 if (reuse) 468 return; 469 uma_zfree(tcptw_zone, tw); 470 } 471 472 int 473 tcp_twrespond(struct tcptw *tw, int flags) 474 { 475 struct inpcb *inp = tw->tw_inpcb; 476 struct tcphdr *th; 477 struct mbuf *m; 478 struct ip *ip = NULL; 479 u_int hdrlen, optlen; 480 int error; 481 struct tcpopt to; 482 #ifdef INET6 483 struct ip6_hdr *ip6 = NULL; 484 int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6; 485 #endif 486 487 INP_WLOCK_ASSERT(inp); 488 489 m = m_gethdr(M_DONTWAIT, MT_DATA); 490 if (m == NULL) 491 return (ENOBUFS); 492 m->m_data += max_linkhdr; 493 494 #ifdef MAC 495 mac_create_mbuf_from_inpcb(inp, m); 496 #endif 497 498 #ifdef INET6 499 if (isipv6) { 500 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr); 501 ip6 = mtod(m, struct ip6_hdr *); 502 th = (struct tcphdr *)(ip6 + 1); 503 tcpip_fillheaders(inp, ip6, th); 504 } else 505 #endif 506 { 507 hdrlen = sizeof(struct tcpiphdr); 508 ip = mtod(m, struct ip *); 509 th = (struct tcphdr *)(ip + 1); 510 tcpip_fillheaders(inp, ip, th); 511 } 512 to.to_flags = 0; 513 514 /* 515 * Send a timestamp and echo-reply if both our side and our peer 516 * have sent timestamps in our SYN's and this is not a RST. 517 */ 518 if (tw->t_recent && flags == TH_ACK) { 519 to.to_flags |= TOF_TS; 520 to.to_tsval = tcp_ts_getticks() + tw->ts_offset; 521 to.to_tsecr = tw->t_recent; 522 } 523 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 524 525 m->m_len = hdrlen + optlen; 526 m->m_pkthdr.len = m->m_len; 527 528 KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small")); 529 530 th->th_seq = htonl(tw->snd_nxt); 531 th->th_ack = htonl(tw->rcv_nxt); 532 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 533 th->th_flags = flags; 534 th->th_win = htons(tw->last_win); 535 536 #ifdef INET6 537 if (isipv6) { 538 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr), 539 sizeof(struct tcphdr) + optlen); 540 ip6->ip6_hlim = in6_selecthlim(inp, NULL); 541 error = ip6_output(m, inp->in6p_outputopts, NULL, 542 (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp); 543 } else 544 #endif 545 { 546 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 547 htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP)); 548 m->m_pkthdr.csum_flags = CSUM_TCP; 549 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 550 ip->ip_len = m->m_pkthdr.len; 551 if (path_mtu_discovery) 552 ip->ip_off |= IP_DF; 553 error = ip_output(m, inp->inp_options, NULL, 554 ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 555 NULL, inp); 556 } 557 if (flags & TH_ACK) 558 tcpstat.tcps_sndacks++; 559 else 560 tcpstat.tcps_sndctrl++; 561 tcpstat.tcps_sndtotal++; 562 return (error); 563 } 564 565 static void 566 tcp_tw_2msl_reset(struct tcptw *tw, int rearm) 567 { 568 569 INP_INFO_WLOCK_ASSERT(&tcbinfo); 570 INP_WLOCK_ASSERT(tw->tw_inpcb); 571 if (rearm) 572 TAILQ_REMOVE(&twq_2msl, tw, tw_2msl); 573 tw->tw_time = ticks + 2 * tcp_msl; 574 TAILQ_INSERT_TAIL(&twq_2msl, tw, tw_2msl); 575 } 576 577 static void 578 tcp_tw_2msl_stop(struct tcptw *tw) 579 { 580 581 INP_INFO_WLOCK_ASSERT(&tcbinfo); 582 TAILQ_REMOVE(&twq_2msl, tw, tw_2msl); 583 } 584 585 struct tcptw * 586 tcp_tw_2msl_scan(int reuse) 587 { 588 struct tcptw *tw; 589 590 INP_INFO_WLOCK_ASSERT(&tcbinfo); 591 for (;;) { 592 tw = TAILQ_FIRST(&twq_2msl); 593 if (tw == NULL || (!reuse && (tw->tw_time - ticks) > 0)) 594 break; 595 INP_WLOCK(tw->tw_inpcb); 596 tcp_twclose(tw, reuse); 597 if (reuse) 598 return (tw); 599 } 600 return (NULL); 601 }
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