The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
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: releng/9.2/sys/netinet/tcp_timewait.c 247658 2013-03-02 17:51:22Z flo $");
   34 
   35 #include "opt_inet.h"
   36 #include "opt_inet6.h"
   37 #include "opt_tcpdebug.h"
   38 
   39 #include <sys/param.h>
   40 #include <sys/systm.h>
   41 #include <sys/callout.h>
   42 #include <sys/kernel.h>
   43 #include <sys/sysctl.h>
   44 #include <sys/malloc.h>
   45 #include <sys/mbuf.h>
   46 #include <sys/priv.h>
   47 #include <sys/proc.h>
   48 #include <sys/socket.h>
   49 #include <sys/socketvar.h>
   50 #include <sys/protosw.h>
   51 #include <sys/random.h>
   52 
   53 #include <vm/uma.h>
   54 
   55 #include <net/route.h>
   56 #include <net/if.h>
   57 #include <net/vnet.h>
   58 
   59 #include <netinet/in.h>
   60 #include <netinet/in_pcb.h>
   61 #include <netinet/in_systm.h>
   62 #include <netinet/in_var.h>
   63 #include <netinet/ip.h>
   64 #include <netinet/ip_icmp.h>
   65 #include <netinet/ip_var.h>
   66 #ifdef INET6
   67 #include <netinet/ip6.h>
   68 #include <netinet6/in6_pcb.h>
   69 #include <netinet6/ip6_var.h>
   70 #include <netinet6/scope6_var.h>
   71 #include <netinet6/nd6.h>
   72 #endif
   73 #include <netinet/tcp.h>
   74 #include <netinet/tcp_fsm.h>
   75 #include <netinet/tcp_seq.h>
   76 #include <netinet/tcp_timer.h>
   77 #include <netinet/tcp_var.h>
   78 #ifdef INET6
   79 #include <netinet6/tcp6_var.h>
   80 #endif
   81 #include <netinet/tcpip.h>
   82 #ifdef TCPDEBUG
   83 #include <netinet/tcp_debug.h>
   84 #endif
   85 #ifdef INET6
   86 #include <netinet6/ip6protosw.h>
   87 #endif
   88 
   89 #include <machine/in_cksum.h>
   90 
   91 #include <security/mac/mac_framework.h>
   92 
   93 static VNET_DEFINE(uma_zone_t, tcptw_zone);
   94 #define V_tcptw_zone                    VNET(tcptw_zone)
   95 static int      maxtcptw;
   96 
   97 /*
   98  * The timed wait queue contains references to each of the TCP sessions
   99  * currently in the TIME_WAIT state.  The queue pointers, including the
  100  * queue pointers in each tcptw structure, are protected using the global
  101  * tcbinfo lock, which must be held over queue iteration and modification.
  102  */
  103 static VNET_DEFINE(TAILQ_HEAD(, tcptw), twq_2msl);
  104 #define V_twq_2msl                      VNET(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 (V_ipport_lastauto > V_ipport_firstauto)
  119                 halfrange = (V_ipport_lastauto - V_ipport_firstauto) / 2;
  120         else
  121                 halfrange = (V_ipport_firstauto - V_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(V_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 VNET_DEFINE(int, nolocaltimewait) = 0;
  149 #define V_nolocaltimewait       VNET(nolocaltimewait)
  150 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, nolocaltimewait, CTLFLAG_RW,
  151     &VNET_NAME(nolocaltimewait), 0,
  152     "Do not create compressed TCP TIME_WAIT entries for local connections");
  153 
  154 void
  155 tcp_tw_zone_change(void)
  156 {
  157 
  158         if (maxtcptw == 0)
  159                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
  160 }
  161 
  162 void
  163 tcp_tw_init(void)
  164 {
  165 
  166         V_tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw),
  167             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  168         TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw);
  169         if (maxtcptw == 0)
  170                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
  171         else
  172                 uma_zone_set_max(V_tcptw_zone, maxtcptw);
  173         TAILQ_INIT(&V_twq_2msl);
  174 }
  175 
  176 #ifdef VIMAGE
  177 void
  178 tcp_tw_destroy(void)
  179 {
  180         struct tcptw *tw;
  181 
  182         INP_INFO_WLOCK(&V_tcbinfo);
  183         while((tw = TAILQ_FIRST(&V_twq_2msl)) != NULL)
  184                 tcp_twclose(tw, 0);
  185         INP_INFO_WUNLOCK(&V_tcbinfo);
  186 
  187         uma_zdestroy(V_tcptw_zone);
  188 }
  189 #endif
  190 
  191 /*
  192  * Move a TCP connection into TIME_WAIT state.
  193  *    tcbinfo is locked.
  194  *    inp is locked, and is unlocked before returning.
  195  */
  196 void
  197 tcp_twstart(struct tcpcb *tp)
  198 {
  199         struct tcptw *tw;
  200         struct inpcb *inp = tp->t_inpcb;
  201         int acknow;
  202         struct socket *so;
  203 #ifdef INET6
  204         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
  205 #endif
  206 
  207         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);      /* tcp_tw_2msl_reset(). */
  208         INP_WLOCK_ASSERT(inp);
  209 
  210         if (V_nolocaltimewait) {
  211                 int error = 0;
  212 #ifdef INET6
  213                 if (isipv6)
  214                         error = in6_localaddr(&inp->in6p_faddr);
  215 #endif
  216 #if defined(INET6) && defined(INET)
  217                 else
  218 #endif
  219 #ifdef INET
  220                         error = in_localip(inp->inp_faddr);
  221 #endif
  222                 if (error) {
  223                         tp = tcp_close(tp);
  224                         if (tp != NULL)
  225                                 INP_WUNLOCK(inp);
  226                         return;
  227                 }
  228         }
  229 
  230         tw = uma_zalloc(V_tcptw_zone, M_NOWAIT);
  231         if (tw == NULL) {
  232                 tw = tcp_tw_2msl_scan(1);
  233                 if (tw == NULL) {
  234                         tp = tcp_close(tp);
  235                         if (tp != NULL)
  236                                 INP_WUNLOCK(inp);
  237                         return;
  238                 }
  239         }
  240         tw->tw_inpcb = inp;
  241 
  242         /*
  243          * Recover last window size sent.
  244          */
  245         if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
  246                 tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
  247         else
  248                 tw->last_win = 0;
  249 
  250         /*
  251          * Set t_recent if timestamps are used on the connection.
  252          */
  253         if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
  254             (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
  255                 tw->t_recent = tp->ts_recent;
  256                 tw->ts_offset = tp->ts_offset;
  257         } else {
  258                 tw->t_recent = 0;
  259                 tw->ts_offset = 0;
  260         }
  261 
  262         tw->snd_nxt = tp->snd_nxt;
  263         tw->rcv_nxt = tp->rcv_nxt;
  264         tw->iss     = tp->iss;
  265         tw->irs     = tp->irs;
  266         tw->t_starttime = tp->t_starttime;
  267         tw->tw_time = 0;
  268 
  269 /* XXX
  270  * If this code will
  271  * be used for fin-wait-2 state also, then we may need
  272  * a ts_recent from the last segment.
  273  */
  274         acknow = tp->t_flags & TF_ACKNOW;
  275 
  276         /*
  277          * First, discard tcpcb state, which includes stopping its timers and
  278          * freeing it.  tcp_discardcb() used to also release the inpcb, but
  279          * that work is now done in the caller.
  280          *
  281          * Note: soisdisconnected() call used to be made in tcp_discardcb(),
  282          * and might not be needed here any longer.
  283          */
  284         tcp_discardcb(tp);
  285         so = inp->inp_socket;
  286         soisdisconnected(so);
  287         tw->tw_cred = crhold(so->so_cred);
  288         SOCK_LOCK(so);
  289         tw->tw_so_options = so->so_options;
  290         SOCK_UNLOCK(so);
  291         if (acknow)
  292                 tcp_twrespond(tw, TH_ACK);
  293         inp->inp_ppcb = tw;
  294         inp->inp_flags |= INP_TIMEWAIT;
  295         tcp_tw_2msl_reset(tw, 0);
  296 
  297         /*
  298          * If the inpcb owns the sole reference to the socket, then we can
  299          * detach and free the socket as it is not needed in time wait.
  300          */
  301         if (inp->inp_flags & INP_SOCKREF) {
  302                 KASSERT(so->so_state & SS_PROTOREF,
  303                     ("tcp_twstart: !SS_PROTOREF"));
  304                 inp->inp_flags &= ~INP_SOCKREF;
  305                 INP_WUNLOCK(inp);
  306                 ACCEPT_LOCK();
  307                 SOCK_LOCK(so);
  308                 so->so_state &= ~SS_PROTOREF;
  309                 sofree(so);
  310         } else
  311                 INP_WUNLOCK(inp);
  312 }
  313 
  314 #if 0
  315 /*
  316  * The appromixate rate of ISN increase of Microsoft TCP stacks;
  317  * the actual rate is slightly higher due to the addition of
  318  * random positive increments.
  319  *
  320  * Most other new OSes use semi-randomized ISN values, so we
  321  * do not need to worry about them.
  322  */
  323 #define MS_ISN_BYTES_PER_SECOND         250000
  324 
  325 /*
  326  * Determine if the ISN we will generate has advanced beyond the last
  327  * sequence number used by the previous connection.  If so, indicate
  328  * that it is safe to recycle this tw socket by returning 1.
  329  */
  330 int
  331 tcp_twrecycleable(struct tcptw *tw)
  332 {
  333         tcp_seq new_iss = tw->iss;
  334         tcp_seq new_irs = tw->irs;
  335 
  336         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  337         new_iss += (ticks - tw->t_starttime) * (ISN_BYTES_PER_SECOND / hz);
  338         new_irs += (ticks - tw->t_starttime) * (MS_ISN_BYTES_PER_SECOND / hz);
  339 
  340         if (SEQ_GT(new_iss, tw->snd_nxt) && SEQ_GT(new_irs, tw->rcv_nxt))
  341                 return (1);
  342         else
  343                 return (0);
  344 }
  345 #endif
  346 
  347 /*
  348  * Returns 1 if the TIME_WAIT state was killed and we should start over,
  349  * looking for a pcb in the listen state.  Returns 0 otherwise.
  350  */
  351 int
  352 tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
  353     struct mbuf *m, int tlen)
  354 {
  355         struct tcptw *tw;
  356         int thflags;
  357         tcp_seq seq;
  358 
  359         /* tcbinfo lock required for tcp_twclose(), tcp_tw_2msl_reset(). */
  360         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  361         INP_WLOCK_ASSERT(inp);
  362 
  363         /*
  364          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
  365          * still present.  This is undesirable, but temporarily necessary
  366          * until we work out how to handle inpcb's who's timewait state has
  367          * been removed.
  368          */
  369         tw = intotw(inp);
  370         if (tw == NULL)
  371                 goto drop;
  372 
  373         thflags = th->th_flags;
  374 
  375         /*
  376          * NOTE: for FIN_WAIT_2 (to be added later),
  377          * must validate sequence number before accepting RST
  378          */
  379 
  380         /*
  381          * If the segment contains RST:
  382          *      Drop the segment - see Stevens, vol. 2, p. 964 and
  383          *      RFC 1337.
  384          */
  385         if (thflags & TH_RST)
  386                 goto drop;
  387 
  388 #if 0
  389 /* PAWS not needed at the moment */
  390         /*
  391          * RFC 1323 PAWS: If we have a timestamp reply on this segment
  392          * and it's less than ts_recent, drop it.
  393          */
  394         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
  395             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
  396                 if ((thflags & TH_ACK) == 0)
  397                         goto drop;
  398                 goto ack;
  399         }
  400         /*
  401          * ts_recent is never updated because we never accept new segments.
  402          */
  403 #endif
  404 
  405         /*
  406          * If a new connection request is received
  407          * while in TIME_WAIT, drop the old connection
  408          * and start over if the sequence numbers
  409          * are above the previous ones.
  410          */
  411         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
  412                 tcp_twclose(tw, 0);
  413                 return (1);
  414         }
  415 
  416         /*
  417          * Drop the segment if it does not contain an ACK.
  418          */
  419         if ((thflags & TH_ACK) == 0)
  420                 goto drop;
  421 
  422         /*
  423          * Reset the 2MSL timer if this is a duplicate FIN.
  424          */
  425         if (thflags & TH_FIN) {
  426                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
  427                 if (seq + 1 == tw->rcv_nxt)
  428                         tcp_tw_2msl_reset(tw, 1);
  429         }
  430 
  431         /*
  432          * Acknowledge the segment if it has data or is not a duplicate ACK.
  433          */
  434         if (thflags != TH_ACK || tlen != 0 ||
  435             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
  436                 tcp_twrespond(tw, TH_ACK);
  437 drop:
  438         INP_WUNLOCK(inp);
  439         m_freem(m);
  440         return (0);
  441 }
  442 
  443 void
  444 tcp_twclose(struct tcptw *tw, int reuse)
  445 {
  446         struct socket *so;
  447         struct inpcb *inp;
  448 
  449         /*
  450          * At this point, we are in one of two situations:
  451          *
  452          * (1) We have no socket, just an inpcb<->twtcp pair.  We can free
  453          *     all state.
  454          *
  455          * (2) We have a socket -- if we own a reference, release it and
  456          *     notify the socket layer.
  457          */
  458         inp = tw->tw_inpcb;
  459         KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait"));
  460         KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw"));
  461         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);      /* tcp_tw_2msl_stop(). */
  462         INP_WLOCK_ASSERT(inp);
  463 
  464         tw->tw_inpcb = NULL;
  465         tcp_tw_2msl_stop(tw);
  466         inp->inp_ppcb = NULL;
  467         in_pcbdrop(inp);
  468 
  469         so = inp->inp_socket;
  470         if (so != NULL) {
  471                 /*
  472                  * If there's a socket, handle two cases: first, we own a
  473                  * strong reference, which we will now release, or we don't
  474                  * in which case another reference exists (XXXRW: think
  475                  * about this more), and we don't need to take action.
  476                  */
  477                 if (inp->inp_flags & INP_SOCKREF) {
  478                         inp->inp_flags &= ~INP_SOCKREF;
  479                         INP_WUNLOCK(inp);
  480                         ACCEPT_LOCK();
  481                         SOCK_LOCK(so);
  482                         KASSERT(so->so_state & SS_PROTOREF,
  483                             ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF"));
  484                         so->so_state &= ~SS_PROTOREF;
  485                         sofree(so);
  486                 } else {
  487                         /*
  488                          * If we don't own the only reference, the socket and
  489                          * inpcb need to be left around to be handled by
  490                          * tcp_usr_detach() later.
  491                          */
  492                         INP_WUNLOCK(inp);
  493                 }
  494         } else
  495                 in_pcbfree(inp);
  496         TCPSTAT_INC(tcps_closed);
  497         crfree(tw->tw_cred);
  498         tw->tw_cred = NULL;
  499         if (reuse)
  500                 return;
  501         uma_zfree(V_tcptw_zone, tw);
  502 }
  503 
  504 int
  505 tcp_twrespond(struct tcptw *tw, int flags)
  506 {
  507         struct inpcb *inp = tw->tw_inpcb;
  508 #if defined(INET6) || defined(INET)
  509         struct tcphdr *th = NULL;
  510 #endif
  511         struct mbuf *m;
  512 #ifdef INET
  513         struct ip *ip = NULL;
  514 #endif
  515         u_int hdrlen, optlen;
  516         int error = 0;                  /* Keep compiler happy */
  517         struct tcpopt to;
  518 #ifdef INET6
  519         struct ip6_hdr *ip6 = NULL;
  520         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
  521 #endif
  522         hdrlen = 0;                     /* Keep compiler happy */
  523 
  524         INP_WLOCK_ASSERT(inp);
  525 
  526         m = m_gethdr(M_DONTWAIT, MT_DATA);
  527         if (m == NULL)
  528                 return (ENOBUFS);
  529         m->m_data += max_linkhdr;
  530 
  531 #ifdef MAC
  532         mac_inpcb_create_mbuf(inp, m);
  533 #endif
  534 
  535 #ifdef INET6
  536         if (isipv6) {
  537                 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
  538                 ip6 = mtod(m, struct ip6_hdr *);
  539                 th = (struct tcphdr *)(ip6 + 1);
  540                 tcpip_fillheaders(inp, ip6, th);
  541         }
  542 #endif
  543 #if defined(INET6) && defined(INET)
  544         else
  545 #endif
  546 #ifdef INET
  547         {
  548                 hdrlen = sizeof(struct tcpiphdr);
  549                 ip = mtod(m, struct ip *);
  550                 th = (struct tcphdr *)(ip + 1);
  551                 tcpip_fillheaders(inp, ip, th);
  552         }
  553 #endif
  554         to.to_flags = 0;
  555 
  556         /*
  557          * Send a timestamp and echo-reply if both our side and our peer
  558          * have sent timestamps in our SYN's and this is not a RST.
  559          */
  560         if (tw->t_recent && flags == TH_ACK) {
  561                 to.to_flags |= TOF_TS;
  562                 to.to_tsval = tcp_ts_getticks() + tw->ts_offset;
  563                 to.to_tsecr = tw->t_recent;
  564         }
  565         optlen = tcp_addoptions(&to, (u_char *)(th + 1));
  566 
  567         m->m_len = hdrlen + optlen;
  568         m->m_pkthdr.len = m->m_len;
  569 
  570         KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small"));
  571 
  572         th->th_seq = htonl(tw->snd_nxt);
  573         th->th_ack = htonl(tw->rcv_nxt);
  574         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
  575         th->th_flags = flags;
  576         th->th_win = htons(tw->last_win);
  577 
  578         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
  579 #ifdef INET6
  580         if (isipv6) {
  581                 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
  582                 th->th_sum = in6_cksum_pseudo(ip6,
  583                     sizeof(struct tcphdr) + optlen, IPPROTO_TCP, 0);
  584                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
  585                 error = ip6_output(m, inp->in6p_outputopts, NULL,
  586                     (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp);
  587         }
  588 #endif
  589 #if defined(INET6) && defined(INET)
  590         else
  591 #endif
  592 #ifdef INET
  593         {
  594                 m->m_pkthdr.csum_flags = CSUM_TCP;
  595                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
  596                     htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP));
  597                 ip->ip_len = m->m_pkthdr.len;
  598                 if (V_path_mtu_discovery)
  599                         ip->ip_off |= IP_DF;
  600                 error = ip_output(m, inp->inp_options, NULL,
  601                     ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
  602                     NULL, inp);
  603         }
  604 #endif
  605         if (flags & TH_ACK)
  606                 TCPSTAT_INC(tcps_sndacks);
  607         else
  608                 TCPSTAT_INC(tcps_sndctrl);
  609         TCPSTAT_INC(tcps_sndtotal);
  610         return (error);
  611 }
  612 
  613 static void
  614 tcp_tw_2msl_reset(struct tcptw *tw, int rearm)
  615 {
  616 
  617         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  618         INP_WLOCK_ASSERT(tw->tw_inpcb);
  619         if (rearm)
  620                 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
  621         tw->tw_time = ticks + 2 * tcp_msl;
  622         TAILQ_INSERT_TAIL(&V_twq_2msl, tw, tw_2msl);
  623 }
  624 
  625 static void
  626 tcp_tw_2msl_stop(struct tcptw *tw)
  627 {
  628 
  629         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  630         TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
  631 }
  632 
  633 struct tcptw *
  634 tcp_tw_2msl_scan(int reuse)
  635 {
  636         struct tcptw *tw;
  637 
  638         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  639         for (;;) {
  640                 tw = TAILQ_FIRST(&V_twq_2msl);
  641                 if (tw == NULL || (!reuse && (tw->tw_time - ticks) > 0))
  642                         break;
  643                 INP_WLOCK(tw->tw_inpcb);
  644                 tcp_twclose(tw, reuse);
  645                 if (reuse)
  646                         return (tw);
  647         }
  648         return (NULL);
  649 }

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