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: releng/10.0/sys/netinet/tcp_reass.c 265124 2014-04-30 04:04:42Z delphij $");
   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_qsize(SYSCTL_HANDLER_ARGS);
   78 
   79 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass, CTLFLAG_RW, 0,
   80     "TCP Segment Reassembly Queue");
   81 
   82 static VNET_DEFINE(int, tcp_reass_maxseg) = 0;
   83 #define V_tcp_reass_maxseg              VNET(tcp_reass_maxseg)
   84 SYSCTL_VNET_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RDTUN,
   85     &VNET_NAME(tcp_reass_maxseg), 0,
   86     "Global maximum number of TCP Segments in Reassembly Queue");
   87 
   88 SYSCTL_VNET_PROC(_net_inet_tcp_reass, OID_AUTO, cursegments,
   89     (CTLTYPE_INT | CTLFLAG_RD), NULL, 0, &tcp_reass_sysctl_qsize, "I",
   90     "Global number of TCP Segments currently in Reassembly Queue");
   91 
   92 static VNET_DEFINE(int, tcp_reass_overflows) = 0;
   93 #define V_tcp_reass_overflows           VNET(tcp_reass_overflows)
   94 SYSCTL_VNET_INT(_net_inet_tcp_reass, OID_AUTO, overflows,
   95     CTLTYPE_INT | CTLFLAG_RD,
   96     &VNET_NAME(tcp_reass_overflows), 0,
   97     "Global number of TCP Segment Reassembly Queue Overflows");
   98 
   99 static VNET_DEFINE(uma_zone_t, tcp_reass_zone);
  100 #define V_tcp_reass_zone                VNET(tcp_reass_zone)
  101 
  102 /* Initialize TCP reassembly queue */
  103 static void
  104 tcp_reass_zone_change(void *tag)
  105 {
  106 
  107         /* Set the zone limit and read back the effective value. */
  108         V_tcp_reass_maxseg = nmbclusters / 16;
  109         V_tcp_reass_maxseg = uma_zone_set_max(V_tcp_reass_zone,
  110             V_tcp_reass_maxseg);
  111 }
  112 
  113 void
  114 tcp_reass_init(void)
  115 {
  116 
  117         V_tcp_reass_maxseg = nmbclusters / 16;
  118         TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments",
  119             &V_tcp_reass_maxseg);
  120         V_tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent),
  121             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  122         /* Set the zone limit and read back the effective value. */
  123         V_tcp_reass_maxseg = uma_zone_set_max(V_tcp_reass_zone,
  124             V_tcp_reass_maxseg);
  125         EVENTHANDLER_REGISTER(nmbclusters_change,
  126             tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);
  127 }
  128 
  129 #ifdef VIMAGE
  130 void
  131 tcp_reass_destroy(void)
  132 {
  133 
  134         uma_zdestroy(V_tcp_reass_zone);
  135 }
  136 #endif
  137 
  138 void
  139 tcp_reass_flush(struct tcpcb *tp)
  140 {
  141         struct tseg_qent *qe;
  142 
  143         INP_WLOCK_ASSERT(tp->t_inpcb);
  144 
  145         while ((qe = LIST_FIRST(&tp->t_segq)) != NULL) {
  146                 LIST_REMOVE(qe, tqe_q);
  147                 m_freem(qe->tqe_m);
  148                 uma_zfree(V_tcp_reass_zone, qe);
  149                 tp->t_segqlen--;
  150         }
  151 
  152         KASSERT((tp->t_segqlen == 0),
  153             ("TCP reass queue %p segment count is %d instead of 0 after flush.",
  154             tp, tp->t_segqlen));
  155 }
  156 
  157 static int
  158 tcp_reass_sysctl_qsize(SYSCTL_HANDLER_ARGS)
  159 {
  160         int qsize;
  161 
  162         qsize = uma_zone_get_cur(V_tcp_reass_zone);
  163         return (sysctl_handle_int(oidp, &qsize, 0, req));
  164 }
  165 
  166 int
  167 tcp_reass(struct tcpcb *tp, struct tcphdr *th, int *tlenp, struct mbuf *m)
  168 {
  169         struct tseg_qent *q;
  170         struct tseg_qent *p = NULL;
  171         struct tseg_qent *nq;
  172         struct tseg_qent *te = NULL;
  173         struct socket *so = tp->t_inpcb->inp_socket;
  174         char *s = NULL;
  175         int flags;
  176         struct tseg_qent tqs;
  177 
  178         INP_WLOCK_ASSERT(tp->t_inpcb);
  179 
  180         /*
  181          * XXX: tcp_reass() is rather inefficient with its data structures
  182          * and should be rewritten (see NetBSD for optimizations).
  183          */
  184 
  185         /*
  186          * Call with th==NULL after become established to
  187          * force pre-ESTABLISHED data up to user socket.
  188          */
  189         if (th == NULL)
  190                 goto present;
  191 
  192         /*
  193          * Limit the number of segments that can be queued to reduce the
  194          * potential for mbuf exhaustion. For best performance, we want to be
  195          * able to queue a full window's worth of segments. The size of the
  196          * socket receive buffer determines our advertised window and grows
  197          * automatically when socket buffer autotuning is enabled. Use it as the
  198          * basis for our queue limit.
  199          * Always let the missing segment through which caused this queue.
  200          * NB: Access to the socket buffer is left intentionally unlocked as we
  201          * can tolerate stale information here.
  202          *
  203          * XXXLAS: Using sbspace(so->so_rcv) instead of so->so_rcv.sb_hiwat
  204          * should work but causes packets to be dropped when they shouldn't.
  205          * Investigate why and re-evaluate the below limit after the behaviour
  206          * is understood.
  207          */
  208         if ((th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) &&
  209             tp->t_segqlen >= (so->so_rcv.sb_hiwat / tp->t_maxseg) + 1) {
  210                 V_tcp_reass_overflows++;
  211                 TCPSTAT_INC(tcps_rcvmemdrop);
  212                 m_freem(m);
  213                 *tlenp = 0;
  214                 if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
  215                         log(LOG_DEBUG, "%s; %s: queue limit reached, "
  216                             "segment dropped\n", s, __func__);
  217                         free(s, M_TCPLOG);
  218                 }
  219                 return (0);
  220         }
  221 
  222         /*
  223          * Allocate a new queue entry. If we can't, or hit the zone limit
  224          * just drop the pkt.
  225          *
  226          * Use a temporary structure on the stack for the missing segment
  227          * when the zone is exhausted. Otherwise we may get stuck.
  228          */
  229         te = uma_zalloc(V_tcp_reass_zone, M_NOWAIT);
  230         if (te == NULL) {
  231                 if (th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) {
  232                         TCPSTAT_INC(tcps_rcvmemdrop);
  233                         m_freem(m);
  234                         *tlenp = 0;
  235                         if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
  236                             NULL))) {
  237                                 log(LOG_DEBUG, "%s; %s: global zone limit "
  238                                     "reached, segment dropped\n", s, __func__);
  239                                 free(s, M_TCPLOG);
  240                         }
  241                         return (0);
  242                 } else {
  243                         bzero(&tqs, sizeof(struct tseg_qent));
  244                         te = &tqs;
  245                         if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
  246                             NULL))) {
  247                                 log(LOG_DEBUG,
  248                                     "%s; %s: global zone limit reached, using "
  249                                     "stack for missing segment\n", s, __func__);
  250                                 free(s, M_TCPLOG);
  251                         }
  252                 }
  253         }
  254         tp->t_segqlen++;
  255 
  256         /*
  257          * Find a segment which begins after this one does.
  258          */
  259         LIST_FOREACH(q, &tp->t_segq, tqe_q) {
  260                 if (SEQ_GT(q->tqe_th->th_seq, th->th_seq))
  261                         break;
  262                 p = q;
  263         }
  264 
  265         /*
  266          * If there is a preceding segment, it may provide some of
  267          * our data already.  If so, drop the data from the incoming
  268          * segment.  If it provides all of our data, drop us.
  269          */
  270         if (p != NULL) {
  271                 int i;
  272                 /* conversion to int (in i) handles seq wraparound */
  273                 i = p->tqe_th->th_seq + p->tqe_len - th->th_seq;
  274                 if (i > 0) {
  275                         if (i >= *tlenp) {
  276                                 TCPSTAT_INC(tcps_rcvduppack);
  277                                 TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
  278                                 m_freem(m);
  279                                 if (te != &tqs)
  280                                         uma_zfree(V_tcp_reass_zone, te);
  281                                 tp->t_segqlen--;
  282                                 /*
  283                                  * Try to present any queued data
  284                                  * at the left window edge to the user.
  285                                  * This is needed after the 3-WHS
  286                                  * completes.
  287                                  */
  288                                 goto present;   /* ??? */
  289                         }
  290                         m_adj(m, i);
  291                         *tlenp -= i;
  292                         th->th_seq += i;
  293                 }
  294         }
  295         tp->t_rcvoopack++;
  296         TCPSTAT_INC(tcps_rcvoopack);
  297         TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
  298 
  299         /*
  300          * While we overlap succeeding segments trim them or,
  301          * if they are completely covered, dequeue them.
  302          */
  303         while (q) {
  304                 int i = (th->th_seq + *tlenp) - q->tqe_th->th_seq;
  305                 if (i <= 0)
  306                         break;
  307                 if (i < q->tqe_len) {
  308                         q->tqe_th->th_seq += i;
  309                         q->tqe_len -= i;
  310                         m_adj(q->tqe_m, i);
  311                         break;
  312                 }
  313 
  314                 nq = LIST_NEXT(q, tqe_q);
  315                 LIST_REMOVE(q, tqe_q);
  316                 m_freem(q->tqe_m);
  317                 uma_zfree(V_tcp_reass_zone, q);
  318                 tp->t_segqlen--;
  319                 q = nq;
  320         }
  321 
  322         /* Insert the new segment queue entry into place. */
  323         te->tqe_m = m;
  324         te->tqe_th = th;
  325         te->tqe_len = *tlenp;
  326 
  327         if (p == NULL) {
  328                 LIST_INSERT_HEAD(&tp->t_segq, te, tqe_q);
  329         } else {
  330                 KASSERT(te != &tqs, ("%s: temporary stack based entry not "
  331                     "first element in queue", __func__));
  332                 LIST_INSERT_AFTER(p, te, tqe_q);
  333         }
  334 
  335 present:
  336         /*
  337          * Present data to user, advancing rcv_nxt through
  338          * completed sequence space.
  339          */
  340         if (!TCPS_HAVEESTABLISHED(tp->t_state))
  341                 return (0);
  342         q = LIST_FIRST(&tp->t_segq);
  343         if (!q || q->tqe_th->th_seq != tp->rcv_nxt)
  344                 return (0);
  345         SOCKBUF_LOCK(&so->so_rcv);
  346         do {
  347                 tp->rcv_nxt += q->tqe_len;
  348                 flags = q->tqe_th->th_flags & TH_FIN;
  349                 nq = LIST_NEXT(q, tqe_q);
  350                 LIST_REMOVE(q, tqe_q);
  351                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
  352                         m_freem(q->tqe_m);
  353                 else
  354                         sbappendstream_locked(&so->so_rcv, q->tqe_m);
  355                 if (q != &tqs)
  356                         uma_zfree(V_tcp_reass_zone, q);
  357                 tp->t_segqlen--;
  358                 q = nq;
  359         } while (q && q->tqe_th->th_seq == tp->rcv_nxt);
  360         ND6_HINT(tp);
  361         sorwakeup_locked(so);
  362         return (flags);
  363 }

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