sys/netinet/tcp_timewait.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. Neither the name of the University nor the names of its contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  *      @(#)tcp_subr.c  8.2 (Berkeley) 5/24/95
  32  */
  33
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include "opt_inet.h"
  38 #include "opt_inet6.h"
  39 #include "opt_tcpdebug.h"
  40
  41 #include <sys/param.h>
  42 #include <sys/systm.h>
  43 #include <sys/callout.h>
  44 #include <sys/kernel.h>
  45 #include <sys/sysctl.h>
  46 #include <sys/malloc.h>
  47 #include <sys/mbuf.h>
  48 #include <sys/priv.h>
  49 #include <sys/proc.h>
  50 #include <sys/socket.h>
  51 #include <sys/socketvar.h>
  52 #ifndef INVARIANTS
  53 #include <sys/syslog.h>
  54 #endif
  55 #include <sys/protosw.h>
  56 #include <sys/random.h>
  57
  58 #include <vm/uma.h>
  59
  60 #include <net/route.h>
  61 #include <net/if.h>
  62 #include <net/if_var.h>
  63 #include <net/vnet.h>
  64
  65 #include <netinet/in.h>
  66 #include <netinet/in_pcb.h>
  67 #include <netinet/in_systm.h>
  68 #include <netinet/in_var.h>
  69 #include <netinet/ip.h>
  70 #include <netinet/ip_icmp.h>
  71 #include <netinet/ip_var.h>
  72 #ifdef INET6
  73 #include <netinet/ip6.h>
  74 #include <netinet6/in6_pcb.h>
  75 #include <netinet6/ip6_var.h>
  76 #include <netinet6/scope6_var.h>
  77 #include <netinet6/nd6.h>
  78 #endif
  79 #include <netinet/tcp.h>
  80 #include <netinet/tcp_fsm.h>
  81 #include <netinet/tcp_seq.h>
  82 #include <netinet/tcp_timer.h>
  83 #include <netinet/tcp_var.h>
  84 #ifdef INET6
  85 #include <netinet6/tcp6_var.h>
  86 #endif
  87 #include <netinet/tcpip.h>
  88 #ifdef TCPDEBUG
  89 #include <netinet/tcp_debug.h>
  90 #endif
  91 #ifdef INET6
  92 #include <netinet6/ip6protosw.h>
  93 #endif
  94
  95 #include <machine/in_cksum.h>
  96
  97 #include <security/mac/mac_framework.h>
  98
  99 static VNET_DEFINE(uma_zone_t, tcptw_zone);
 100 #define V_tcptw_zone            VNET(tcptw_zone)
 101 static int      maxtcptw;
 102
 103 /*
 104  * The timed wait queue contains references to each of the TCP sessions
 105  * currently in the TIME_WAIT state.  The queue pointers, including the
 106  * queue pointers in each tcptw structure, are protected using the global
 107  * timewait lock, which must be held over queue iteration and modification.
 108  *
 109  * Rules on tcptw usage:
 110  *  - a inpcb is always freed _after_ its tcptw
 111  *  - a tcptw relies on its inpcb reference counting for memory stability
 112  *  - a tcptw is dereferenceable only while its inpcb is locked
 113  */
 114 static VNET_DEFINE(TAILQ_HEAD(, tcptw), twq_2msl);
 115 #define V_twq_2msl              VNET(twq_2msl)
 116
 117 /* Global timewait lock */
 118 static VNET_DEFINE(struct rwlock, tw_lock);
 119 #define V_tw_lock               VNET(tw_lock)
 120
 121 #define TW_LOCK_INIT(tw, d)     rw_init_flags(&(tw), (d), 0)
 122 #define TW_LOCK_DESTROY(tw)     rw_destroy(&(tw))
 123 #define TW_RLOCK(tw)            rw_rlock(&(tw))
 124 #define TW_WLOCK(tw)            rw_wlock(&(tw))
 125 #define TW_RUNLOCK(tw)          rw_runlock(&(tw))
 126 #define TW_WUNLOCK(tw)          rw_wunlock(&(tw))
 127 #define TW_LOCK_ASSERT(tw)      rw_assert(&(tw), RA_LOCKED)
 128 #define TW_RLOCK_ASSERT(tw)     rw_assert(&(tw), RA_RLOCKED)
 129 #define TW_WLOCK_ASSERT(tw)     rw_assert(&(tw), RA_WLOCKED)
 130 #define TW_UNLOCK_ASSERT(tw)    rw_assert(&(tw), RA_UNLOCKED)
 131
 132 static void     tcp_tw_2msl_reset(struct tcptw *, int);
 133 static void     tcp_tw_2msl_stop(struct tcptw *, int);
 134 static int      tcp_twrespond(struct tcptw *, int);
 135
 136 static int
 137 tcptw_auto_size(void)
 138 {
 139         int halfrange;
 140
 141         /*
 142          * Max out at half the ephemeral port range so that TIME_WAIT
 143          * sockets don't tie up too many ephemeral ports.
 144          */
 145         if (V_ipport_lastauto > V_ipport_firstauto)
 146                 halfrange = (V_ipport_lastauto - V_ipport_firstauto) / 2;
 147         else
 148                 halfrange = (V_ipport_firstauto - V_ipport_lastauto) / 2;
 149         /* Protect against goofy port ranges smaller than 32. */
 150         return (imin(imax(halfrange, 32), maxsockets / 5));
 151 }
 152
 153 static int
 154 sysctl_maxtcptw(SYSCTL_HANDLER_ARGS)
 155 {
 156         int error, new;
 157
 158         if (maxtcptw == 0)
 159                 new = tcptw_auto_size();
 160         else
 161                 new = maxtcptw;
 162         error = sysctl_handle_int(oidp, &new, 0, req);
 163         if (error == 0 && req->newptr)
 164                 if (new >= 32) {
 165                         maxtcptw = new;
 166                         uma_zone_set_max(V_tcptw_zone, maxtcptw);
 167                 }
 168         return (error);
 169 }
 170
 171 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxtcptw, CTLTYPE_INT|CTLFLAG_RW,
 172     &maxtcptw, 0, sysctl_maxtcptw, "IU",
 173     "Maximum number of compressed TCP TIME_WAIT entries");
 174
 175 VNET_DEFINE(int, nolocaltimewait) = 0;
 176 #define V_nolocaltimewait       VNET(nolocaltimewait)
 177 SYSCTL_INT(_net_inet_tcp, OID_AUTO, nolocaltimewait, CTLFLAG_VNET | CTLFLAG_RW,
 178     &VNET_NAME(nolocaltimewait), 0,
 179     "Do not create compressed TCP TIME_WAIT entries for local connections");
 180
 181 void
 182 tcp_tw_zone_change(void)
 183 {
 184
 185         if (maxtcptw == 0)
 186                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
 187 }
 188
 189 void
 190 tcp_tw_init(void)
 191 {
 192
 193         V_tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw),
 194             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
 195         TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw);
 196         if (maxtcptw == 0)
 197                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
 198         else
 199                 uma_zone_set_max(V_tcptw_zone, maxtcptw);
 200         TAILQ_INIT(&V_twq_2msl);
 201         TW_LOCK_INIT(V_tw_lock, "tcptw");
 202 }
 203
 204 #ifdef VIMAGE
 205 void
 206 tcp_tw_destroy(void)
 207 {
 208         struct tcptw *tw;
 209
 210         INP_INFO_RLOCK(&V_tcbinfo);
 211         while ((tw = TAILQ_FIRST(&V_twq_2msl)) != NULL)
 212                 tcp_twclose(tw, 0);
 213         INP_INFO_RUNLOCK(&V_tcbinfo);
 214
 215         TW_LOCK_DESTROY(V_tw_lock);
 216         uma_zdestroy(V_tcptw_zone);
 217 }
 218 #endif
 219
 220 /*
 221  * Move a TCP connection into TIME_WAIT state.
 222  *    tcbinfo is locked.
 223  *    inp is locked, and is unlocked before returning.
 224  */
 225 void
 226 tcp_twstart(struct tcpcb *tp)
 227 {
 228         struct tcptw *tw;
 229         struct inpcb *inp = tp->t_inpcb;
 230         int acknow;
 231         struct socket *so;
 232 #ifdef INET6
 233         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
 234 #endif
 235
 236         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 237         INP_WLOCK_ASSERT(inp);
 238
 239         /* A dropped inp should never transition to TIME_WAIT state. */
 240         KASSERT((inp->inp_flags & INP_DROPPED) == 0, ("tcp_twstart: "
 241             "(inp->inp_flags & INP_DROPPED) != 0"));
 242
 243         if (V_nolocaltimewait) {
 244                 int error = 0;
 245 #ifdef INET6
 246                 if (isipv6)
 247                         error = in6_localaddr(&inp->in6p_faddr);
 248 #endif
 249 #if defined(INET6) && defined(INET)
 250                 else
 251 #endif
 252 #ifdef INET
 253                         error = in_localip(inp->inp_faddr);
 254 #endif
 255                 if (error) {
 256                         tp = tcp_close(tp);
 257                         if (tp != NULL)
 258                                 INP_WUNLOCK(inp);
 259                         return;
 260                 }
 261         }
 262
 263
 264         /*
 265          * For use only by DTrace.  We do not reference the state
 266          * after this point so modifying it in place is not a problem.
 267          */
 268         tcp_state_change(tp, TCPS_TIME_WAIT);
 269
 270         tw = uma_zalloc(V_tcptw_zone, M_NOWAIT);
 271         if (tw == NULL) {
 272                 /*
 273                  * Reached limit on total number of TIMEWAIT connections
 274                  * allowed. Remove a connection from TIMEWAIT queue in LRU
 275                  * fashion to make room for this connection.
 276                  *
 277                  * XXX:  Check if it possible to always have enough room
 278                  * in advance based on guarantees provided by uma_zalloc().
 279                  */
 280                 tw = tcp_tw_2msl_scan(1);
 281                 if (tw == NULL) {
 282                         tp = tcp_close(tp);
 283                         if (tp != NULL)
 284                                 INP_WUNLOCK(inp);
 285                         return;
 286                 }
 287         }
 288         /*
 289          * The tcptw will hold a reference on its inpcb until tcp_twclose
 290          * is called
 291          */
 292         tw->tw_inpcb = inp;
 293         in_pcbref(inp); /* Reference from tw */
 294
 295         /*
 296          * Recover last window size sent.
 297          */
 298         if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
 299                 tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
 300         else
 301                 tw->last_win = 0;
 302
 303         /*
 304          * Set t_recent if timestamps are used on the connection.
 305          */
 306         if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
 307             (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
 308                 tw->t_recent = tp->ts_recent;
 309                 tw->ts_offset = tp->ts_offset;
 310         } else {
 311                 tw->t_recent = 0;
 312                 tw->ts_offset = 0;
 313         }
 314
 315         tw->snd_nxt = tp->snd_nxt;
 316         tw->rcv_nxt = tp->rcv_nxt;
 317         tw->iss     = tp->iss;
 318         tw->irs     = tp->irs;
 319         tw->t_starttime = tp->t_starttime;
 320         tw->tw_time = 0;
 321
 322 /* XXX
 323  * If this code will
 324  * be used for fin-wait-2 state also, then we may need
 325  * a ts_recent from the last segment.
 326  */
 327         acknow = tp->t_flags & TF_ACKNOW;
 328
 329         /*
 330          * First, discard tcpcb state, which includes stopping its timers and
 331          * freeing it.  tcp_discardcb() used to also release the inpcb, but
 332          * that work is now done in the caller.
 333          *
 334          * Note: soisdisconnected() call used to be made in tcp_discardcb(),
 335          * and might not be needed here any longer.
 336          */
 337         tcp_discardcb(tp);
 338         so = inp->inp_socket;
 339         soisdisconnected(so);
 340         tw->tw_cred = crhold(so->so_cred);
 341         SOCK_LOCK(so);
 342         tw->tw_so_options = so->so_options;
 343         SOCK_UNLOCK(so);
 344         if (acknow)
 345                 tcp_twrespond(tw, TH_ACK);
 346         inp->inp_ppcb = tw;
 347         inp->inp_flags |= INP_TIMEWAIT;
 348         TCPSTATES_INC(TCPS_TIME_WAIT);
 349         tcp_tw_2msl_reset(tw, 0);
 350
 351         /*
 352          * If the inpcb owns the sole reference to the socket, then we can
 353          * detach and free the socket as it is not needed in time wait.
 354          */
 355         if (inp->inp_flags & INP_SOCKREF) {
 356                 KASSERT(so->so_state & SS_PROTOREF,
 357                     ("tcp_twstart: !SS_PROTOREF"));
 358                 inp->inp_flags &= ~INP_SOCKREF;
 359                 INP_WUNLOCK(inp);
 360                 SOCK_LOCK(so);
 361                 so->so_state &= ~SS_PROTOREF;
 362                 sofree(so);
 363         } else
 364                 INP_WUNLOCK(inp);
 365 }
 366
 367 /*
 368  * Returns 1 if the TIME_WAIT state was killed and we should start over,
 369  * looking for a pcb in the listen state.  Returns 0 otherwise.
 370  */
 371 int
 372 tcp_twcheck(struct inpcb *inp, struct tcpopt *to __unused, struct tcphdr *th,
 373     struct mbuf *m, int tlen)
 374 {
 375         struct tcptw *tw;
 376         int thflags;
 377         tcp_seq seq;
 378
 379         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 380         INP_WLOCK_ASSERT(inp);
 381
 382         /*
 383          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
 384          * still present.  This is undesirable, but temporarily necessary
 385          * until we work out how to handle inpcb's who's timewait state has
 386          * been removed.
 387          */
 388         tw = intotw(inp);
 389         if (tw == NULL)
 390                 goto drop;
 391
 392         thflags = th->th_flags;
 393
 394         /*
 395          * NOTE: for FIN_WAIT_2 (to be added later),
 396          * must validate sequence number before accepting RST
 397          */
 398
 399         /*
 400          * If the segment contains RST:
 401          *      Drop the segment - see Stevens, vol. 2, p. 964 and
 402          *      RFC 1337.
 403          */
 404         if (thflags & TH_RST)
 405                 goto drop;
 406
 407 #if 0
 408 /* PAWS not needed at the moment */
 409         /*
 410          * RFC 1323 PAWS: If we have a timestamp reply on this segment
 411          * and it's less than ts_recent, drop it.
 412          */
 413         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
 414             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
 415                 if ((thflags & TH_ACK) == 0)
 416                         goto drop;
 417                 goto ack;
 418         }
 419         /*
 420          * ts_recent is never updated because we never accept new segments.
 421          */
 422 #endif
 423
 424         /*
 425          * If a new connection request is received
 426          * while in TIME_WAIT, drop the old connection
 427          * and start over if the sequence numbers
 428          * are above the previous ones.
 429          */
 430         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
 431                 tcp_twclose(tw, 0);
 432                 return (1);
 433         }
 434
 435         /*
 436          * Drop the segment if it does not contain an ACK.
 437          */
 438         if ((thflags & TH_ACK) == 0)
 439                 goto drop;
 440
 441         /*
 442          * Reset the 2MSL timer if this is a duplicate FIN.
 443          */
 444         if (thflags & TH_FIN) {
 445                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
 446                 if (seq + 1 == tw->rcv_nxt)
 447                         tcp_tw_2msl_reset(tw, 1);
 448         }
 449
 450         /*
 451          * Acknowledge the segment if it has data or is not a duplicate ACK.
 452          */
 453         if (thflags != TH_ACK || tlen != 0 ||
 454             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
 455                 tcp_twrespond(tw, TH_ACK);
 456 drop:
 457         INP_WUNLOCK(inp);
 458         m_freem(m);
 459         return (0);
 460 }
 461
 462 void
 463 tcp_twclose(struct tcptw *tw, int reuse)
 464 {
 465         struct socket *so;
 466         struct inpcb *inp;
 467
 468         /*
 469          * At this point, we are in one of two situations:
 470          *
 471          * (1) We have no socket, just an inpcb<->twtcp pair.  We can free
 472          *     all state.
 473          *
 474          * (2) We have a socket -- if we own a reference, release it and
 475          *     notify the socket layer.
 476          */
 477         inp = tw->tw_inpcb;
 478         KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait"));
 479         KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw"));
 480         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);      /* in_pcbfree() */
 481         INP_WLOCK_ASSERT(inp);
 482
 483         tcp_tw_2msl_stop(tw, reuse);
 484         inp->inp_ppcb = NULL;
 485         in_pcbdrop(inp);
 486
 487         so = inp->inp_socket;
 488         if (so != NULL) {
 489                 /*
 490                  * If there's a socket, handle two cases: first, we own a
 491                  * strong reference, which we will now release, or we don't
 492                  * in which case another reference exists (XXXRW: think
 493                  * about this more), and we don't need to take action.
 494                  */
 495                 if (inp->inp_flags & INP_SOCKREF) {
 496                         inp->inp_flags &= ~INP_SOCKREF;
 497                         INP_WUNLOCK(inp);
 498                         SOCK_LOCK(so);
 499                         KASSERT(so->so_state & SS_PROTOREF,
 500                             ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF"));
 501                         so->so_state &= ~SS_PROTOREF;
 502                         sofree(so);
 503                 } else {
 504                         /*
 505                          * If we don't own the only reference, the socket and
 506                          * inpcb need to be left around to be handled by
 507                          * tcp_usr_detach() later.
 508                          */
 509                         INP_WUNLOCK(inp);
 510                 }
 511         } else {
 512                 /*
 513                  * The socket has been already cleaned-up for us, only free the
 514                  * inpcb.
 515                  */
 516                 in_pcbfree(inp);
 517         }
 518         TCPSTAT_INC(tcps_closed);
 519 }
 520
 521 static int
 522 tcp_twrespond(struct tcptw *tw, int flags)
 523 {
 524         struct inpcb *inp = tw->tw_inpcb;
 525 #if defined(INET6) || defined(INET)
 526         struct tcphdr *th = NULL;
 527 #endif
 528         struct mbuf *m;
 529 #ifdef INET
 530         struct ip *ip = NULL;
 531 #endif
 532         u_int hdrlen, optlen;
 533         int error = 0;                  /* Keep compiler happy */
 534         struct tcpopt to;
 535 #ifdef INET6
 536         struct ip6_hdr *ip6 = NULL;
 537         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
 538 #endif
 539         hdrlen = 0;                     /* Keep compiler happy */
 540
 541         INP_WLOCK_ASSERT(inp);
 542
 543         m = m_gethdr(M_NOWAIT, MT_DATA);
 544         if (m == NULL)
 545                 return (ENOBUFS);
 546         m->m_data += max_linkhdr;
 547
 548 #ifdef MAC
 549         mac_inpcb_create_mbuf(inp, m);
 550 #endif
 551
 552 #ifdef INET6
 553         if (isipv6) {
 554                 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
 555                 ip6 = mtod(m, struct ip6_hdr *);
 556                 th = (struct tcphdr *)(ip6 + 1);
 557                 tcpip_fillheaders(inp, ip6, th);
 558         }
 559 #endif
 560 #if defined(INET6) && defined(INET)
 561         else
 562 #endif
 563 #ifdef INET
 564         {
 565                 hdrlen = sizeof(struct tcpiphdr);
 566                 ip = mtod(m, struct ip *);
 567                 th = (struct tcphdr *)(ip + 1);
 568                 tcpip_fillheaders(inp, ip, th);
 569         }
 570 #endif
 571         to.to_flags = 0;
 572
 573         /*
 574          * Send a timestamp and echo-reply if both our side and our peer
 575          * have sent timestamps in our SYN's and this is not a RST.
 576          */
 577         if (tw->t_recent && flags == TH_ACK) {
 578                 to.to_flags |= TOF_TS;
 579                 to.to_tsval = tcp_ts_getticks() + tw->ts_offset;
 580                 to.to_tsecr = tw->t_recent;
 581         }
 582         optlen = tcp_addoptions(&to, (u_char *)(th + 1));
 583
 584         m->m_len = hdrlen + optlen;
 585         m->m_pkthdr.len = m->m_len;
 586
 587         KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small"));
 588
 589         th->th_seq = htonl(tw->snd_nxt);
 590         th->th_ack = htonl(tw->rcv_nxt);
 591         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
 592         th->th_flags = flags;
 593         th->th_win = htons(tw->last_win);
 594
 595         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
 596 #ifdef INET6
 597         if (isipv6) {
 598                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
 599                 th->th_sum = in6_cksum_pseudo(ip6,
 600                     sizeof(struct tcphdr) + optlen, IPPROTO_TCP, 0);
 601                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
 602                 error = ip6_output(m, inp->in6p_outputopts, NULL,
 603                     (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp);
 604         }
 605 #endif
 606 #if defined(INET6) && defined(INET)
 607         else
 608 #endif
 609 #ifdef INET
 610         {
 611                 m->m_pkthdr.csum_flags = CSUM_TCP;
 612                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
 613                     htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP));
 614                 ip->ip_len = htons(m->m_pkthdr.len);
 615                 if (V_path_mtu_discovery)
 616                         ip->ip_off |= htons(IP_DF);
 617                 error = ip_output(m, inp->inp_options, NULL,
 618                     ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
 619                     NULL, inp);
 620         }
 621 #endif
 622         if (flags & TH_ACK)
 623                 TCPSTAT_INC(tcps_sndacks);
 624         else
 625                 TCPSTAT_INC(tcps_sndctrl);
 626         TCPSTAT_INC(tcps_sndtotal);
 627         return (error);
 628 }
 629
 630 static void
 631 tcp_tw_2msl_reset(struct tcptw *tw, int rearm)
 632 {
 633
 634         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 635         INP_WLOCK_ASSERT(tw->tw_inpcb);
 636
 637         TW_WLOCK(V_tw_lock);
 638         if (rearm)
 639                 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
 640         tw->tw_time = ticks + 2 * tcp_msl;
 641         TAILQ_INSERT_TAIL(&V_twq_2msl, tw, tw_2msl);
 642         TW_WUNLOCK(V_tw_lock);
 643 }
 644
 645 static void
 646 tcp_tw_2msl_stop(struct tcptw *tw, int reuse)
 647 {
 648         struct ucred *cred;
 649         struct inpcb *inp;
 650         int released;
 651
 652         INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 653
 654         TW_WLOCK(V_tw_lock);
 655         inp = tw->tw_inpcb;
 656         tw->tw_inpcb = NULL;
 657
 658         TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
 659         cred = tw->tw_cred;
 660         tw->tw_cred = NULL;
 661         TW_WUNLOCK(V_tw_lock);
 662
 663         if (cred != NULL)
 664                 crfree(cred);
 665
 666         released = in_pcbrele_wlocked(inp);
 667         KASSERT(!released, ("%s: inp should not be released here", __func__));
 668
 669         if (!reuse)
 670                 uma_zfree(V_tcptw_zone, tw);
 671         TCPSTATES_DEC(TCPS_TIME_WAIT);
 672 }
 673
 674 struct tcptw *
 675 tcp_tw_2msl_scan(int reuse)
 676 {
 677         struct tcptw *tw;
 678         struct inpcb *inp;
 679
 680 #ifdef INVARIANTS
 681         if (reuse) {
 682                 /*
 683                  * Exclusive pcbinfo lock is not required in reuse case even if
 684                  * two inpcb locks can be acquired simultaneously:
 685                  *  - the inpcb transitioning to TIME_WAIT state in
 686                  *    tcp_tw_start(),
 687                  *  - the inpcb closed by tcp_twclose().
 688                  *
 689                  * It is because only inpcbs in FIN_WAIT2 or CLOSING states can
 690                  * transition in TIME_WAIT state.  Then a pcbcb cannot be in
 691                  * TIME_WAIT list and transitioning to TIME_WAIT state at same
 692                  * time.
 693                  */
 694                 INP_INFO_RLOCK_ASSERT(&V_tcbinfo);
 695         }
 696 #endif
 697
 698         for (;;) {
 699                 TW_RLOCK(V_tw_lock);
 700                 tw = TAILQ_FIRST(&V_twq_2msl);
 701                 if (tw == NULL || (!reuse && (tw->tw_time - ticks) > 0)) {
 702                         TW_RUNLOCK(V_tw_lock);
 703                         break;
 704                 }
 705                 KASSERT(tw->tw_inpcb != NULL, ("%s: tw->tw_inpcb == NULL",
 706                     __func__));
 707
 708                 inp = tw->tw_inpcb;
 709                 in_pcbref(inp);
 710                 TW_RUNLOCK(V_tw_lock);
 711
 712                 if (INP_INFO_TRY_RLOCK(&V_tcbinfo)) {
 713
 714                         INP_WLOCK(inp);
 715                         tw = intotw(inp);
 716                         if (in_pcbrele_wlocked(inp)) {
 717                                 if (__predict_true(tw == NULL)) {
 718                                         INP_INFO_RUNLOCK(&V_tcbinfo);
 719                                         continue;
 720                                 } else {
 721                                         /* This should not happen as in TIMEWAIT
 722                                          * state the inp should not be destroyed
 723                                          * before its tcptw. If INVARIANTS is
 724                                          * defined panic.
 725                                          */
 726 #ifdef INVARIANTS
 727                                         panic("%s: Panic before an infinite "
 728                                             "loop: INP_TIMEWAIT && (INP_FREED "
 729                                             "|| inp last reference) && tw != "
 730                                             "NULL", __func__);
 731 #else
 732                                         log(LOG_ERR, "%s: Avoid an infinite "
 733                                             "loop: INP_TIMEWAIT && (INP_FREED "
 734                                             "|| inp last reference) && tw != "
 735                                             "NULL", __func__);
 736 #endif
 737                                         INP_INFO_RUNLOCK(&V_tcbinfo);
 738                                         break;
 739                                 }
 740                         }
 741
 742                         if (tw == NULL) {
 743                                 /* tcp_twclose() has already been called */
 744                                 INP_WUNLOCK(inp);
 745                                 INP_INFO_RUNLOCK(&V_tcbinfo);
 746                                 continue;
 747                         }
 748
 749                         tcp_twclose(tw, reuse);
 750                         INP_INFO_RUNLOCK(&V_tcbinfo);
 751                         if (reuse)
 752                             return tw;
 753                 } else {
 754                         /* INP_INFO lock is busy, continue later. */
 755                         INP_WLOCK(inp);
 756                         if (!in_pcbrele_wlocked(inp))
 757                                 INP_WUNLOCK(inp);
 758                         break;
 759                 }
 760         }
 761
 762         return NULL;
 763 }