The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_reass.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 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_input.c 8.12 (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_tcpdebug.h"
   38 
   39 #include <sys/param.h>
   40 #include <sys/kernel.h>
   41 #include <sys/malloc.h>
   42 #include <sys/mbuf.h>
   43 #include <sys/socket.h>
   44 #include <sys/socketvar.h>
   45 #include <sys/sysctl.h>
   46 #include <sys/syslog.h>
   47 #include <sys/systm.h>
   48 
   49 #include <vm/uma.h>
   50 
   51 #include <net/if.h>
   52 #include <net/route.h>
   53 #include <net/vnet.h>
   54 
   55 #include <netinet/in.h>
   56 #include <netinet/in_pcb.h>
   57 #include <netinet/in_systm.h>
   58 #include <netinet/in_var.h>
   59 #include <netinet/ip.h>
   60 #include <netinet/ip_var.h>
   61 #include <netinet/ip_options.h>
   62 #include <netinet/ip6.h>
   63 #include <netinet6/in6_pcb.h>
   64 #include <netinet6/ip6_var.h>
   65 #include <netinet6/nd6.h>
   66 #include <netinet/tcp.h>
   67 #include <netinet/tcp_fsm.h>
   68 #include <netinet/tcp_seq.h>
   69 #include <netinet/tcp_timer.h>
   70 #include <netinet/tcp_var.h>
   71 #include <netinet6/tcp6_var.h>
   72 #include <netinet/tcpip.h>
   73 #ifdef TCPDEBUG
   74 #include <netinet/tcp_debug.h>
   75 #endif /* TCPDEBUG */
   76 
   77 static int tcp_reass_sysctl_maxseg(SYSCTL_HANDLER_ARGS);
   78 static int tcp_reass_sysctl_qsize(SYSCTL_HANDLER_ARGS);
   79 
   80 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
   81     "TCP Segment Reassembly Queue");
   82 
   83 static int tcp_reass_maxseg = 0;
   84 SYSCTL_VNET_PROC(_net_inet_tcp_reass, OID_AUTO, maxsegments,
   85     CTLTYPE_INT | CTLFLAG_RDTUN,
   86     &tcp_reass_maxseg, 0, &tcp_reass_sysctl_maxseg, "I",
   87     "Global maximum number of TCP Segments in Reassembly Queue");
   88 
   89 static int tcp_reass_qsize = 0;
   90 SYSCTL_PROC(_net_inet_tcp_reass, OID_AUTO, cursegments,
   91     CTLTYPE_INT | CTLFLAG_RD,
   92     &tcp_reass_qsize, 0, &tcp_reass_sysctl_qsize, "I",
   93     "Global number of TCP Segments currently in Reassembly Queue");
   94 
   95 static int tcp_reass_overflows = 0;
   96 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, overflows,
   97     CTLTYPE_INT | CTLFLAG_RD,
   98     &tcp_reass_overflows, 0,
   99     "Global number of TCP Segment Reassembly Queue Overflows");
  100 
  101 static uma_zone_t tcp_reass_zone;
  102 
  103 /* Initialize TCP reassembly queue */
  104 static void
  105 tcp_reass_zone_change(void *tag)
  106 {
  107 
  108         tcp_reass_maxseg = nmbclusters / 16;
  109         uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg);
  110 }
  111 
  112 void
  113 tcp_reass_global_init(void)
  114 {
  115 
  116         tcp_reass_maxseg = nmbclusters / 16;
  117         TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments",
  118             &tcp_reass_maxseg);
  119         tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent),
  120             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  121         uma_zone_set_max(tcp_reass_zone, tcp_reass_maxseg);
  122         EVENTHANDLER_REGISTER(nmbclusters_change,
  123             tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);
  124 }
  125 
  126 void
  127 tcp_reass_flush(struct tcpcb *tp)
  128 {
  129         struct tseg_qent *qe;
  130 
  131         INP_WLOCK_ASSERT(tp->t_inpcb);
  132 
  133         while ((qe = LIST_FIRST(&tp->t_segq)) != NULL) {
  134                 LIST_REMOVE(qe, tqe_q);
  135                 m_freem(qe->tqe_m);
  136                 uma_zfree(tcp_reass_zone, qe);
  137                 tp->t_segqlen--;
  138         }
  139 
  140         KASSERT((tp->t_segqlen == 0),
  141             ("TCP reass queue %p segment count is %d instead of 0 after flush.",
  142             tp, tp->t_segqlen));
  143 }
  144 
  145 static int
  146 tcp_reass_sysctl_maxseg(SYSCTL_HANDLER_ARGS)
  147 {
  148         tcp_reass_maxseg = uma_zone_get_max(tcp_reass_zone);
  149         return (sysctl_handle_int(oidp, arg1, arg2, req));
  150 }
  151 
  152 static int
  153 tcp_reass_sysctl_qsize(SYSCTL_HANDLER_ARGS)
  154 {
  155         tcp_reass_qsize = uma_zone_get_cur(tcp_reass_zone);
  156         return (sysctl_handle_int(oidp, arg1, arg2, req));
  157 }
  158 
  159 int
  160 tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
  161 {
  162         struct tseg_qent *q;
  163         struct tseg_qent *p = NULL;
  164         struct tseg_qent *nq;
  165         struct tseg_qent *te = NULL;
  166         struct socket *so = tp->t_inpcb->inp_socket;
  167         char *s = NULL;
  168         int flags;
  169         struct tseg_qent tqs;
  170 
  171         INP_WLOCK_ASSERT(tp->t_inpcb);
  172 
  173         /*
  174          * XXX: tcp_reass() is rather inefficient with its data structures
  175          * and should be rewritten (see NetBSD for optimizations).
  176          */
  177 
  178         /*
  179          * Call with th==NULL after become established to
  180          * force pre-ESTABLISHED data up to user socket.
  181          */
  182         if (th == NULL)
  183                 goto present;
  184 
  185         /*
  186          * Limit the number of segments that can be queued to reduce the
  187          * potential for mbuf exhaustion. For best performance, we want to be
  188          * able to queue a full window's worth of segments. The size of the
  189          * socket receive buffer determines our advertised window and grows
  190          * automatically when socket buffer autotuning is enabled. Use it as the
  191          * basis for our queue limit.
  192          * Always let the missing segment through which caused this queue.
  193          * NB: Access to the socket buffer is left intentionally unlocked as we
  194          * can tolerate stale information here.
  195          *
  196          * XXXLAS: Using sbspace(so->so_rcv) instead of so->so_rcv.sb_hiwat
  197          * should work but causes packets to be dropped when they shouldn't.
  198          * Investigate why and re-evaluate the below limit after the behaviour
  199          * is understood.
  200          */
  201         if ((th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) &&
  202             tp->t_segqlen >= (so->so_rcv.sb_hiwat / tp->t_maxseg) + 1) {
  203                 tcp_reass_overflows++;
  204                 TCPSTAT_INC(tcps_rcvmemdrop);
  205                 m_freem(m);
  206                 *tlenp = 0;
  207                 if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
  208                         log(LOG_DEBUG, "%s; %s: queue limit reached, "
  209                             "segment dropped\n", s, __func__);
  210                         free(s, M_TCPLOG);
  211                 }
  212                 return (0);
  213         }
  214 
  215         /*
  216          * Allocate a new queue entry. If we can't, or hit the zone limit
  217          * just drop the pkt.
  218          *
  219          * Use a temporary structure on the stack for the missing segment
  220          * when the zone is exhausted. Otherwise we may get stuck.
  221          */
  222         te = uma_zalloc(tcp_reass_zone, M_NOWAIT);
  223         if (te == NULL) {
  224                 if (th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) {
  225                         TCPSTAT_INC(tcps_rcvmemdrop);
  226                         m_freem(m);
  227                         *tlenp = 0;
  228                         if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
  229                             NULL))) {
  230                                 log(LOG_DEBUG, "%s; %s: global zone limit "
  231                                     "reached, segment dropped\n", s, __func__);
  232                                 free(s, M_TCPLOG);
  233                         }
  234                         return (0);
  235                 } else {
  236                         bzero(&tqs, sizeof(struct tseg_qent));
  237                         te = &tqs;
  238                         if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
  239                             NULL))) {
  240                                 log(LOG_DEBUG,
  241                                     "%s; %s: global zone limit reached, using "
  242                                     "stack for missing segment\n", s, __func__);
  243                                 free(s, M_TCPLOG);
  244                         }
  245                 }
  246         }
  247         tp->t_segqlen++;
  248 
  249         /*
  250          * Find a segment which begins after this one does.
  251          */
  252         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
  253                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
  254                         break;
  255                 p = q;
  256         }
  257 
  258         /*
  259          * If there is a preceding segment, it may provide some of
  260          * our data already.  If so, drop the data from the incoming
  261          * segment.  If it provides all of our data, drop us.
  262          */
  263         if (p != NULL) {
  264                 int i;
  265                 /* conversion to int (in i) handles seq wraparound */
  266                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
  267                 if (i > 0) {
  268                         if (i >= *tlenp) {
  269                                 TCPSTAT_INC(tcps_rcvduppack);
  270                                 TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
  271                                 m_freem(m);
  272                                 if (te != &tqs)
  273                                         uma_zfree(tcp_reass_zone, te);
  274                                 tp->t_segqlen--;
  275                                 /*
  276                                  * Try to present any queued data
  277                                  * at the left window edge to the user.
  278                                  * This is needed after the 3-WHS
  279                                  * completes.
  280                                  */
  281                                 goto present;   /* ??? */
  282                         }
  283                         m_adj(m, i);
  284                         *tlenp -= i;
  285                         th->th_seq += i;
  286                 }
  287         }
  288         tp->t_rcvoopack++;
  289         TCPSTAT_INC(tcps_rcvoopack);
  290         TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
  291 
  292         /*
  293          * While we overlap succeeding segments trim them or,
  294          * if they are completely covered, dequeue them.
  295          */
  296         while (q) {
  297                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
  298                 if (i <= 0)
  299                         break;
  300                 if (i < q->tqe_len) {
  301                         q->tqe_th->th_seq += i;
  302                         q->tqe_len -= i;
  303                         m_adj(q->tqe_m, i);
  304                         break;
  305                 }
  306 
  307                 nq = LIST_NEXT(q, tqe_q);
  308                 LIST_REMOVE(q, tqe_q);
  309                 m_freem(q->tqe_m);
  310                 uma_zfree(tcp_reass_zone, q);
  311                 tp->t_segqlen--;
  312                 q = nq;
  313         }
  314 
  315         /* Insert the new segment queue entry into place. */
  316         te->tqe_m = m;
  317         te->tqe_th = th;
  318         te->tqe_len = *tlenp;
  319 
  320         if (p == NULL) {
  321                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
  322         } else {
  323                 KASSERT(te != &tqs, ("%s: temporary stack based entry not "
  324                     "first element in queue", __func__));
  325                 LIST_INSERT_AFTER(p, te, tqe_q);
  326         }
  327 
  328 present:
  329         /*
  330          * Present data to user, advancing rcv_nxt through
  331          * completed sequence space.
  332          */
  333         if (!TCPS_HAVEESTABLISHED(tp->t_state))
  334                 return (0);
  335         q = LIST_FIRST(&tp->t_segq);
  336         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
  337                 return (0);
  338         SOCKBUF_LOCK(&so->so_rcv);
  339         do {
  340                 tp->rcv_nxt += q->tqe_len;
  341                 flags = q->tqe_th->th_flags & TH_FIN;
  342                 nq = LIST_NEXT(q, tqe_q);
  343                 LIST_REMOVE(q, tqe_q);
  344                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
  345                         m_freem(q->tqe_m);
  346                 else
  347                         sbappendstream_locked(&so->so_rcv, q->tqe_m);
  348                 if (q != &tqs)
  349                         uma_zfree(tcp_reass_zone, q);
  350                 tp->t_segqlen--;
  351                 q = nq;
  352         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
  353         ND6_HINT(tp);
  354         sorwakeup_locked(so);
  355         return (flags);
  356 }

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