tcp_timewait.c revision 186222
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: head/sys/netinet/tcp_timewait.c 186222 2008-12-17 12:52:34Z bz $"); 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#include <sys/vimage.h> 54 55#include <vm/uma.h> 56 57#include <net/route.h> 58#include <net/if.h> 59 60#include <netinet/in.h> 61#include <netinet/in_systm.h> 62#include <netinet/ip.h> 63#ifdef INET6 64#include <netinet/ip6.h> 65#endif 66#include <netinet/in_pcb.h> 67#ifdef INET6 68#include <netinet6/in6_pcb.h> 69#endif 70#include <netinet/in_var.h> 71#include <netinet/ip_var.h> 72#ifdef INET6 73#include <netinet6/ip6_var.h> 74#include <netinet6/scope6_var.h> 75#include <netinet6/nd6.h> 76#endif 77#include <netinet/ip_icmp.h> 78#include <netinet/tcp.h> 79#include <netinet/tcp_fsm.h> 80#include <netinet/tcp_seq.h> 81#include <netinet/tcp_timer.h> 82#include <netinet/tcp_var.h> 83#ifdef INET6 84#include <netinet6/tcp6_var.h> 85#endif 86#include <netinet/tcpip.h> 87#ifdef TCPDEBUG 88#include <netinet/tcp_debug.h> 89#endif 90#include <netinet6/ip6protosw.h> 91#include <netinet/vinet.h> 92 93#include <machine/in_cksum.h> 94 95#include <security/mac/mac_framework.h> 96 97static uma_zone_t tcptw_zone; 98static int maxtcptw; 99 100/* 101 * The timed wait queue contains references to each of the TCP sessions 102 * currently in the TIME_WAIT state. The queue pointers, including the 103 * queue pointers in each tcptw structure, are protected using the global 104 * tcbinfo lock, which must be held over queue iteration and modification. 105 */ 106#ifdef VIMAGE_GLOBALS 107static TAILQ_HEAD(, tcptw) twq_2msl; 108int nolocaltimewait; 109#endif 110 111static void tcp_tw_2msl_reset(struct tcptw *, int); 112static void tcp_tw_2msl_stop(struct tcptw *); 113 114static int 115tcptw_auto_size(void) 116{ 117 INIT_VNET_INET(curvnet); 118 int halfrange; 119 120 /* 121 * Max out at half the ephemeral port range so that TIME_WAIT 122 * sockets don't tie up too many ephemeral ports. 123 */ 124 if (V_ipport_lastauto > V_ipport_firstauto) 125 halfrange = (V_ipport_lastauto - V_ipport_firstauto) / 2; 126 else 127 halfrange = (V_ipport_firstauto - V_ipport_lastauto) / 2; 128 /* Protect against goofy port ranges smaller than 32. */ 129 return (imin(imax(halfrange, 32), maxsockets / 5)); 130} 131 132static int 133sysctl_maxtcptw(SYSCTL_HANDLER_ARGS) 134{ 135 int error, new; 136 137 if (maxtcptw == 0) 138 new = tcptw_auto_size(); 139 else 140 new = maxtcptw; 141 error = sysctl_handle_int(oidp, &new, 0, req); 142 if (error == 0 && req->newptr) 143 if (new >= 32) { 144 maxtcptw = new; 145 uma_zone_set_max(tcptw_zone, maxtcptw); 146 } 147 return (error); 148} 149 150SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxtcptw, CTLTYPE_INT|CTLFLAG_RW, 151 &maxtcptw, 0, sysctl_maxtcptw, "IU", 152 "Maximum number of compressed TCP TIME_WAIT entries"); 153 154SYSCTL_V_INT(V_NET, vnet_inet, _net_inet_tcp, OID_AUTO, nolocaltimewait, 155 CTLFLAG_RW, nolocaltimewait, 0, 156 "Do not create compressed TCP TIME_WAIT entries for local connections"); 157 158void 159tcp_tw_zone_change(void) 160{ 161 162 if (maxtcptw == 0) 163 uma_zone_set_max(tcptw_zone, tcptw_auto_size()); 164} 165 166void 167tcp_tw_init(void) 168{ 169 INIT_VNET_INET(curvnet); 170 171 tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw), 172 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE); 173 TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw); 174 if (maxtcptw == 0) 175 uma_zone_set_max(tcptw_zone, tcptw_auto_size()); 176 else 177 uma_zone_set_max(tcptw_zone, maxtcptw); 178 TAILQ_INIT(&V_twq_2msl); 179} 180 181/* 182 * Move a TCP connection into TIME_WAIT state. 183 * tcbinfo is locked. 184 * inp is locked, and is unlocked before returning. 185 */ 186void 187tcp_twstart(struct tcpcb *tp) 188{ 189#if defined(INVARIANTS) || defined(INVARIANT_SUPPORT) 190 INIT_VNET_INET(tp->t_vnet); 191#endif 192 struct tcptw *tw; 193 struct inpcb *inp = tp->t_inpcb; 194 int acknow; 195 struct socket *so; 196 197 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); /* tcp_tw_2msl_reset(). */ 198 INP_WLOCK_ASSERT(inp); 199 200 if (V_nolocaltimewait && in_localip(inp->inp_faddr)) { 201 tp = tcp_close(tp); 202 if (tp != NULL) 203 INP_WUNLOCK(inp); 204 return; 205 } 206 207 tw = uma_zalloc(tcptw_zone, M_NOWAIT); 208 if (tw == NULL) { 209 tw = tcp_tw_2msl_scan(1); 210 if (tw == NULL) { 211 tp = tcp_close(tp); 212 if (tp != NULL) 213 INP_WUNLOCK(inp); 214 return; 215 } 216 } 217 tw->tw_inpcb = inp; 218 219 /* 220 * Recover last window size sent. 221 */ 222 tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale; 223 224 /* 225 * Set t_recent if timestamps are used on the connection. 226 */ 227 if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) == 228 (TF_REQ_TSTMP|TF_RCVD_TSTMP)) { 229 tw->t_recent = tp->ts_recent; 230 tw->ts_offset = tp->ts_offset; 231 } else { 232 tw->t_recent = 0; 233 tw->ts_offset = 0; 234 } 235 236 tw->snd_nxt = tp->snd_nxt; 237 tw->rcv_nxt = tp->rcv_nxt; 238 tw->iss = tp->iss; 239 tw->irs = tp->irs; 240 tw->t_starttime = tp->t_starttime; 241 tw->tw_time = 0; 242 243/* XXX 244 * If this code will 245 * be used for fin-wait-2 state also, then we may need 246 * a ts_recent from the last segment. 247 */ 248 acknow = tp->t_flags & TF_ACKNOW; 249 250 /* 251 * First, discard tcpcb state, which includes stopping its timers and 252 * freeing it. tcp_discardcb() used to also release the inpcb, but 253 * that work is now done in the caller. 254 * 255 * Note: soisdisconnected() call used to be made in tcp_discardcb(), 256 * and might not be needed here any longer. 257 */ 258 tcp_discardcb(tp); 259 so = inp->inp_socket; 260 soisdisconnected(so); 261 tw->tw_cred = crhold(so->so_cred); 262 SOCK_LOCK(so); 263 tw->tw_so_options = so->so_options; 264 SOCK_UNLOCK(so); 265 if (acknow) 266 tcp_twrespond(tw, TH_ACK); 267 inp->inp_ppcb = tw; 268 inp->inp_vflag |= INP_TIMEWAIT; 269 tcp_tw_2msl_reset(tw, 0); 270 271 /* 272 * If the inpcb owns the sole reference to the socket, then we can 273 * detach and free the socket as it is not needed in time wait. 274 */ 275 if (inp->inp_vflag & INP_SOCKREF) { 276 KASSERT(so->so_state & SS_PROTOREF, 277 ("tcp_twstart: !SS_PROTOREF")); 278 inp->inp_vflag &= ~INP_SOCKREF; 279 INP_WUNLOCK(inp); 280 ACCEPT_LOCK(); 281 SOCK_LOCK(so); 282 so->so_state &= ~SS_PROTOREF; 283 sofree(so); 284 } else 285 INP_WUNLOCK(inp); 286} 287 288#if 0 289/* 290 * The appromixate rate of ISN increase of Microsoft TCP stacks; 291 * the actual rate is slightly higher due to the addition of 292 * random positive increments. 293 * 294 * Most other new OSes use semi-randomized ISN values, so we 295 * do not need to worry about them. 296 */ 297#define MS_ISN_BYTES_PER_SECOND 250000 298 299/* 300 * Determine if the ISN we will generate has advanced beyond the last 301 * sequence number used by the previous connection. If so, indicate 302 * that it is safe to recycle this tw socket by returning 1. 303 */ 304int 305tcp_twrecycleable(struct tcptw *tw) 306{ 307 INIT_VNET_INET(curvnet); 308 tcp_seq new_iss = tw->iss; 309 tcp_seq new_irs = tw->irs; 310 311 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 312 new_iss += (ticks - tw->t_starttime) * (ISN_BYTES_PER_SECOND / hz); 313 new_irs += (ticks - tw->t_starttime) * (MS_ISN_BYTES_PER_SECOND / hz); 314 315 if (SEQ_GT(new_iss, tw->snd_nxt) && SEQ_GT(new_irs, tw->rcv_nxt)) 316 return (1); 317 else 318 return (0); 319} 320#endif 321 322/* 323 * Returns 1 if the TIME_WAIT state was killed and we should start over, 324 * looking for a pcb in the listen state. Returns 0 otherwise. 325 */ 326int 327tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th, 328 struct mbuf *m, int tlen) 329{ 330#if defined(INVARIANTS) || defined(INVARIANT_SUPPORT) 331 INIT_VNET_INET(curvnet); 332#endif 333 struct tcptw *tw; 334 int thflags; 335 tcp_seq seq; 336#ifdef INET6 337 int isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0; 338#else 339 const int isipv6 = 0; 340#endif 341 342 /* tcbinfo lock required for tcp_twclose(), tcp_tw_2msl_reset(). */ 343 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 344 INP_WLOCK_ASSERT(inp); 345 346 /* 347 * XXXRW: Time wait state for inpcb has been recycled, but inpcb is 348 * still present. This is undesirable, but temporarily necessary 349 * until we work out how to handle inpcb's who's timewait state has 350 * been removed. 351 */ 352 tw = intotw(inp); 353 if (tw == NULL) 354 goto drop; 355 356 thflags = th->th_flags; 357 358 /* 359 * NOTE: for FIN_WAIT_2 (to be added later), 360 * must validate sequence number before accepting RST 361 */ 362 363 /* 364 * If the segment contains RST: 365 * Drop the segment - see Stevens, vol. 2, p. 964 and 366 * RFC 1337. 367 */ 368 if (thflags & TH_RST) 369 goto drop; 370 371#if 0 372/* PAWS not needed at the moment */ 373 /* 374 * RFC 1323 PAWS: If we have a timestamp reply on this segment 375 * and it's less than ts_recent, drop it. 376 */ 377 if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent && 378 TSTMP_LT(to.to_tsval, tp->ts_recent)) { 379 if ((thflags & TH_ACK) == 0) 380 goto drop; 381 goto ack; 382 } 383 /* 384 * ts_recent is never updated because we never accept new segments. 385 */ 386#endif 387 388 /* 389 * If a new connection request is received 390 * while in TIME_WAIT, drop the old connection 391 * and start over if the sequence numbers 392 * are above the previous ones. 393 */ 394 if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) { 395 tcp_twclose(tw, 0); 396 return (1); 397 } 398 399 /* 400 * Drop the the segment if it does not contain an ACK. 401 */ 402 if ((thflags & TH_ACK) == 0) 403 goto drop; 404 405 /* 406 * Reset the 2MSL timer if this is a duplicate FIN. 407 */ 408 if (thflags & TH_FIN) { 409 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0); 410 if (seq + 1 == tw->rcv_nxt) 411 tcp_tw_2msl_reset(tw, 1); 412 } 413 414 /* 415 * Acknowledge the segment if it has data or is not a duplicate ACK. 416 */ 417 if (thflags != TH_ACK || tlen != 0 || 418 th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt) 419 tcp_twrespond(tw, TH_ACK); 420 goto drop; 421 422 /* 423 * Generate a RST, dropping incoming segment. 424 * Make ACK acceptable to originator of segment. 425 * Don't bother to respond if destination was broadcast/multicast. 426 */ 427 if (m->m_flags & (M_BCAST|M_MCAST)) 428 goto drop; 429 if (isipv6) { 430#ifdef INET6 431 struct ip6_hdr *ip6; 432 433 /* IPv6 anycast check is done at tcp6_input() */ 434 ip6 = mtod(m, struct ip6_hdr *); 435 if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) || 436 IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) 437 goto drop; 438#endif 439 } else { 440 struct ip *ip; 441 442 ip = mtod(m, struct ip *); 443 if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) || 444 IN_MULTICAST(ntohl(ip->ip_src.s_addr)) || 445 ip->ip_src.s_addr == htonl(INADDR_BROADCAST) || 446 in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) 447 goto drop; 448 } 449 if (thflags & TH_ACK) { 450 tcp_respond(NULL, 451 mtod(m, void *), th, m, 0, th->th_ack, TH_RST); 452 } else { 453 seq = th->th_seq + (thflags & TH_SYN ? 1 : 0); 454 tcp_respond(NULL, 455 mtod(m, void *), th, m, seq, 0, TH_RST|TH_ACK); 456 } 457 INP_WUNLOCK(inp); 458 return (0); 459 460drop: 461 INP_WUNLOCK(inp); 462 m_freem(m); 463 return (0); 464} 465 466void 467tcp_twclose(struct tcptw *tw, int reuse) 468{ 469 INIT_VNET_INET(curvnet); 470 struct socket *so; 471 struct inpcb *inp; 472 473 /* 474 * At this point, we are in one of two situations: 475 * 476 * (1) We have no socket, just an inpcb<->twtcp pair. We can free 477 * all state. 478 * 479 * (2) We have a socket -- if we own a reference, release it and 480 * notify the socket layer. 481 */ 482 inp = tw->tw_inpcb; 483 KASSERT((inp->inp_vflag & INP_TIMEWAIT), ("tcp_twclose: !timewait")); 484 KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw")); 485 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); /* tcp_tw_2msl_stop(). */ 486 INP_WLOCK_ASSERT(inp); 487 488 tw->tw_inpcb = NULL; 489 tcp_tw_2msl_stop(tw); 490 inp->inp_ppcb = NULL; 491 in_pcbdrop(inp); 492 493 so = inp->inp_socket; 494 if (so != NULL) { 495 /* 496 * If there's a socket, handle two cases: first, we own a 497 * strong reference, which we will now release, or we don't 498 * in which case another reference exists (XXXRW: think 499 * about this more), and we don't need to take action. 500 */ 501 if (inp->inp_vflag & INP_SOCKREF) { 502 inp->inp_vflag &= ~INP_SOCKREF; 503 INP_WUNLOCK(inp); 504 ACCEPT_LOCK(); 505 SOCK_LOCK(so); 506 KASSERT(so->so_state & SS_PROTOREF, 507 ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF")); 508 so->so_state &= ~SS_PROTOREF; 509 sofree(so); 510 } else { 511 /* 512 * If we don't own the only reference, the socket and 513 * inpcb need to be left around to be handled by 514 * tcp_usr_detach() later. 515 */ 516 INP_WUNLOCK(inp); 517 } 518 } else 519 in_pcbfree(inp); 520 V_tcpstat.tcps_closed++; 521 crfree(tw->tw_cred); 522 tw->tw_cred = NULL; 523 if (reuse) 524 return; 525 uma_zfree(tcptw_zone, tw); 526} 527 528int 529tcp_twrespond(struct tcptw *tw, int flags) 530{ 531 INIT_VNET_INET(curvnet); 532 struct inpcb *inp = tw->tw_inpcb; 533 struct tcphdr *th; 534 struct mbuf *m; 535 struct ip *ip = NULL; 536 u_int hdrlen, optlen; 537 int error; 538 struct tcpopt to; 539#ifdef INET6 540 struct ip6_hdr *ip6 = NULL; 541 int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6; 542#endif 543 544 INP_WLOCK_ASSERT(inp); 545 546 m = m_gethdr(M_DONTWAIT, MT_DATA); 547 if (m == NULL) 548 return (ENOBUFS); 549 m->m_data += max_linkhdr; 550 551#ifdef MAC 552 mac_inpcb_create_mbuf(inp, m); 553#endif 554 555#ifdef INET6 556 if (isipv6) { 557 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr); 558 ip6 = mtod(m, struct ip6_hdr *); 559 th = (struct tcphdr *)(ip6 + 1); 560 tcpip_fillheaders(inp, ip6, th); 561 } else 562#endif 563 { 564 hdrlen = sizeof(struct tcpiphdr); 565 ip = mtod(m, struct ip *); 566 th = (struct tcphdr *)(ip + 1); 567 tcpip_fillheaders(inp, ip, th); 568 } 569 to.to_flags = 0; 570 571 /* 572 * Send a timestamp and echo-reply if both our side and our peer 573 * have sent timestamps in our SYN's and this is not a RST. 574 */ 575 if (tw->t_recent && flags == TH_ACK) { 576 to.to_flags |= TOF_TS; 577 to.to_tsval = ticks + tw->ts_offset; 578 to.to_tsecr = tw->t_recent; 579 } 580 optlen = tcp_addoptions(&to, (u_char *)(th + 1)); 581 582 m->m_len = hdrlen + optlen; 583 m->m_pkthdr.len = m->m_len; 584 585 KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small")); 586 587 th->th_seq = htonl(tw->snd_nxt); 588 th->th_ack = htonl(tw->rcv_nxt); 589 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2; 590 th->th_flags = flags; 591 th->th_win = htons(tw->last_win); 592 593#ifdef INET6 594 if (isipv6) { 595 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr), 596 sizeof(struct tcphdr) + optlen); 597 ip6->ip6_hlim = in6_selecthlim(inp, NULL); 598 error = ip6_output(m, inp->in6p_outputopts, NULL, 599 (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp); 600 } else 601#endif 602 { 603 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr, 604 htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP)); 605 m->m_pkthdr.csum_flags = CSUM_TCP; 606 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum); 607 ip->ip_len = m->m_pkthdr.len; 608 if (V_path_mtu_discovery) 609 ip->ip_off |= IP_DF; 610 error = ip_output(m, inp->inp_options, NULL, 611 ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 612 NULL, inp); 613 } 614 if (flags & TH_ACK) 615 V_tcpstat.tcps_sndacks++; 616 else 617 V_tcpstat.tcps_sndctrl++; 618 V_tcpstat.tcps_sndtotal++; 619 return (error); 620} 621 622static void 623tcp_tw_2msl_reset(struct tcptw *tw, int rearm) 624{ 625 INIT_VNET_INET(curvnet); 626 627 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 628 INP_WLOCK_ASSERT(tw->tw_inpcb); 629 if (rearm) 630 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl); 631 tw->tw_time = ticks + 2 * tcp_msl; 632 TAILQ_INSERT_TAIL(&V_twq_2msl, tw, tw_2msl); 633} 634 635static void 636tcp_tw_2msl_stop(struct tcptw *tw) 637{ 638 INIT_VNET_INET(curvnet); 639 640 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 641 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl); 642} 643 644struct tcptw * 645tcp_tw_2msl_scan(int reuse) 646{ 647 INIT_VNET_INET(curvnet); 648 struct tcptw *tw; 649 650 INP_INFO_WLOCK_ASSERT(&V_tcbinfo); 651 for (;;) { 652 tw = TAILQ_FIRST(&V_twq_2msl); 653 if (tw == NULL || (!reuse && tw->tw_time > ticks)) 654 break; 655 INP_WLOCK(tw->tw_inpcb); 656 tcp_twclose(tw, reuse); 657 if (reuse) 658 return (tw); 659 } 660 return (NULL); 661} 662