The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netinet6/frag6.c

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    1 /*      $FreeBSD: releng/5.2/sys/netinet6/frag6.c 121684 2003-10-29 15:07:04Z ume $     */
    2 /*      $KAME: frag6.c,v 1.33 2002/01/07 11:34:48 kjc Exp $     */
    3 
    4 /*
    5  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
    6  * All rights reserved.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 3. Neither the name of the project nor the names of its contributors
   17  *    may be used to endorse or promote products derived from this software
   18  *    without specific prior written permission.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  */
   32 
   33 #include "opt_random_ip_id.h"
   34 
   35 #include <sys/param.h>
   36 #include <sys/systm.h>
   37 #include <sys/malloc.h>
   38 #include <sys/mbuf.h>
   39 #include <sys/domain.h>
   40 #include <sys/protosw.h>
   41 #include <sys/socket.h>
   42 #include <sys/errno.h>
   43 #include <sys/time.h>
   44 #include <sys/kernel.h>
   45 #include <sys/syslog.h>
   46 
   47 #include <net/if.h>
   48 #include <net/route.h>
   49 
   50 #include <netinet/in.h>
   51 #include <netinet/in_var.h>
   52 #include <netinet/ip6.h>
   53 #include <netinet6/ip6_var.h>
   54 #include <netinet/icmp6.h>
   55 #include <netinet/in_systm.h>   /* for ECN definitions */
   56 #include <netinet/ip.h>         /* for ECN definitions */
   57 
   58 #include <net/net_osdep.h>
   59 
   60 /*
   61  * Define it to get a correct behavior on per-interface statistics.
   62  * You will need to perform an extra routing table lookup, per fragment,
   63  * to do it.  This may, or may not be, a performance hit.
   64  */
   65 #define IN6_IFSTAT_STRICT
   66 
   67 static void frag6_enq __P((struct ip6asfrag *, struct ip6asfrag *));
   68 static void frag6_deq __P((struct ip6asfrag *));
   69 static void frag6_insque __P((struct ip6q *, struct ip6q *));
   70 static void frag6_remque __P((struct ip6q *));
   71 static void frag6_freef __P((struct ip6q *));
   72 
   73 static struct mtx ip6qlock;
   74 /*
   75  * These fields all protected by ip6qlock.
   76  */
   77 static u_int frag6_nfragpackets;
   78 static u_int frag6_nfrags;
   79 static struct   ip6q ip6q;      /* ip6 reassemble queue */
   80 
   81 #define IP6Q_LOCK_INIT()        mtx_init(&ip6qlock, "ip6qlock", NULL, MTX_DEF);
   82 #define IP6Q_LOCK()             mtx_lock(&ip6qlock)
   83 #define IP6Q_TRYLOCK()          mtx_trylock(&ip6qlock)
   84 #define IP6Q_LOCK_ASSERT()      mtx_assert(&ip6qlock, MA_OWNED)
   85 #define IP6Q_UNLOCK()           mtx_unlock(&ip6qlock)
   86 
   87 static MALLOC_DEFINE(M_FTABLE, "fragment", "fragment reassembly header");
   88 
   89 /*
   90  * Initialise reassembly queue and fragment identifier.
   91  */
   92 void
   93 frag6_init()
   94 {
   95 
   96         ip6_maxfragpackets = nmbclusters / 4;
   97         ip6_maxfrags = nmbclusters / 4;
   98 
   99         IP6Q_LOCK_INIT();
  100 
  101 #ifndef RANDOM_IP_ID
  102         ip6_id = arc4random();
  103 #endif
  104         ip6q.ip6q_next = ip6q.ip6q_prev = &ip6q;
  105 }
  106 
  107 /*
  108  * In RFC2460, fragment and reassembly rule do not agree with each other,
  109  * in terms of next header field handling in fragment header.
  110  * While the sender will use the same value for all of the fragmented packets,
  111  * receiver is suggested not to check the consistency.
  112  *
  113  * fragment rule (p20):
  114  *      (2) A Fragment header containing:
  115  *      The Next Header value that identifies the first header of
  116  *      the Fragmentable Part of the original packet.
  117  *              -> next header field is same for all fragments
  118  *
  119  * reassembly rule (p21):
  120  *      The Next Header field of the last header of the Unfragmentable
  121  *      Part is obtained from the Next Header field of the first
  122  *      fragment's Fragment header.
  123  *              -> should grab it from the first fragment only
  124  *
  125  * The following note also contradicts with fragment rule - noone is going to
  126  * send different fragment with different next header field.
  127  *
  128  * additional note (p22):
  129  *      The Next Header values in the Fragment headers of different
  130  *      fragments of the same original packet may differ.  Only the value
  131  *      from the Offset zero fragment packet is used for reassembly.
  132  *              -> should grab it from the first fragment only
  133  *
  134  * There is no explicit reason given in the RFC.  Historical reason maybe?
  135  */
  136 /*
  137  * Fragment input
  138  */
  139 int
  140 frag6_input(mp, offp, proto)
  141         struct mbuf **mp;
  142         int *offp, proto;
  143 {
  144         struct mbuf *m = *mp, *t;
  145         struct ip6_hdr *ip6;
  146         struct ip6_frag *ip6f;
  147         struct ip6q *q6;
  148         struct ip6asfrag *af6, *ip6af, *af6dwn;
  149 #ifdef IN6_IFSTAT_STRICT
  150         struct in6_ifaddr *ia;
  151 #endif
  152         int offset = *offp, nxt, i, next;
  153         int first_frag = 0;
  154         int fragoff, frgpartlen;        /* must be larger than u_int16_t */
  155         struct ifnet *dstifp;
  156         u_int8_t ecn, ecn0;
  157 
  158         ip6 = mtod(m, struct ip6_hdr *);
  159 #ifndef PULLDOWN_TEST
  160         IP6_EXTHDR_CHECK(m, offset, sizeof(struct ip6_frag), IPPROTO_DONE);
  161         ip6f = (struct ip6_frag *)((caddr_t)ip6 + offset);
  162 #else
  163         IP6_EXTHDR_GET(ip6f, struct ip6_frag *, m, offset, sizeof(*ip6f));
  164         if (ip6f == NULL)
  165                 return (IPPROTO_DONE);
  166 #endif
  167 
  168         dstifp = NULL;
  169 #ifdef IN6_IFSTAT_STRICT
  170         /* find the destination interface of the packet. */
  171         if ((ia = ip6_getdstifaddr(m)) != NULL)
  172                 dstifp = ia->ia_ifp;
  173 #else
  174         /* we are violating the spec, this is not the destination interface */
  175         if ((m->m_flags & M_PKTHDR) != 0)
  176                 dstifp = m->m_pkthdr.rcvif;
  177 #endif
  178 
  179         /* jumbo payload can't contain a fragment header */
  180         if (ip6->ip6_plen == 0) {
  181                 icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER, offset);
  182                 in6_ifstat_inc(dstifp, ifs6_reass_fail);
  183                 return IPPROTO_DONE;
  184         }
  185 
  186         /*
  187          * check whether fragment packet's fragment length is
  188          * multiple of 8 octets.
  189          * sizeof(struct ip6_frag) == 8
  190          * sizeof(struct ip6_hdr) = 40
  191          */
  192         if ((ip6f->ip6f_offlg & IP6F_MORE_FRAG) &&
  193             (((ntohs(ip6->ip6_plen) - offset) & 0x7) != 0)) {
  194                 icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
  195                     offsetof(struct ip6_hdr, ip6_plen));
  196                 in6_ifstat_inc(dstifp, ifs6_reass_fail);
  197                 return IPPROTO_DONE;
  198         }
  199 
  200         ip6stat.ip6s_fragments++;
  201         in6_ifstat_inc(dstifp, ifs6_reass_reqd);
  202 
  203         /* offset now points to data portion */
  204         offset += sizeof(struct ip6_frag);
  205 
  206         IP6Q_LOCK();
  207 
  208         /*
  209          * Enforce upper bound on number of fragments.
  210          * If maxfrag is 0, never accept fragments.
  211          * If maxfrag is -1, accept all fragments without limitation.
  212          */
  213         if (ip6_maxfrags < 0)
  214                 ;
  215         else if (frag6_nfrags >= (u_int)ip6_maxfrags)
  216                 goto dropfrag;
  217 
  218         for (q6 = ip6q.ip6q_next; q6 != &ip6q; q6 = q6->ip6q_next)
  219                 if (ip6f->ip6f_ident == q6->ip6q_ident &&
  220                     IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &q6->ip6q_src) &&
  221                     IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &q6->ip6q_dst))
  222                         break;
  223 
  224         if (q6 == &ip6q) {
  225                 /*
  226                  * the first fragment to arrive, create a reassembly queue.
  227                  */
  228                 first_frag = 1;
  229 
  230                 /*
  231                  * Enforce upper bound on number of fragmented packets
  232                  * for which we attempt reassembly;
  233                  * If maxfragpackets is 0, never accept fragments.
  234                  * If maxfragpackets is -1, accept all fragments without
  235                  * limitation.
  236                  */
  237                 if (ip6_maxfragpackets < 0)
  238                         ;
  239                 else if (frag6_nfragpackets >= (u_int)ip6_maxfragpackets)
  240                         goto dropfrag;
  241                 frag6_nfragpackets++;
  242                 q6 = (struct ip6q *)malloc(sizeof(struct ip6q), M_FTABLE,
  243                     M_NOWAIT);
  244                 if (q6 == NULL)
  245                         goto dropfrag;
  246                 bzero(q6, sizeof(*q6));
  247 
  248                 frag6_insque(q6, &ip6q);
  249 
  250                 /* ip6q_nxt will be filled afterwards, from 1st fragment */
  251                 q6->ip6q_down   = q6->ip6q_up = (struct ip6asfrag *)q6;
  252 #ifdef notyet
  253                 q6->ip6q_nxtp   = (u_char *)nxtp;
  254 #endif
  255                 q6->ip6q_ident  = ip6f->ip6f_ident;
  256                 q6->ip6q_arrive = 0; /* Is it used anywhere? */
  257                 q6->ip6q_ttl    = IPV6_FRAGTTL;
  258                 q6->ip6q_src    = ip6->ip6_src;
  259                 q6->ip6q_dst    = ip6->ip6_dst;
  260                 q6->ip6q_unfrglen = -1; /* The 1st fragment has not arrived. */
  261 
  262                 q6->ip6q_nfrag = 0;
  263         }
  264 
  265         /*
  266          * If it's the 1st fragment, record the length of the
  267          * unfragmentable part and the next header of the fragment header.
  268          */
  269         fragoff = ntohs(ip6f->ip6f_offlg & IP6F_OFF_MASK);
  270         if (fragoff == 0) {
  271                 q6->ip6q_unfrglen = offset - sizeof(struct ip6_hdr) -
  272                     sizeof(struct ip6_frag);
  273                 q6->ip6q_nxt = ip6f->ip6f_nxt;
  274         }
  275 
  276         /*
  277          * Check that the reassembled packet would not exceed 65535 bytes
  278          * in size.
  279          * If it would exceed, discard the fragment and return an ICMP error.
  280          */
  281         frgpartlen = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) - offset;
  282         if (q6->ip6q_unfrglen >= 0) {
  283                 /* The 1st fragment has already arrived. */
  284                 if (q6->ip6q_unfrglen + fragoff + frgpartlen > IPV6_MAXPACKET) {
  285                         icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
  286                             offset - sizeof(struct ip6_frag) +
  287                             offsetof(struct ip6_frag, ip6f_offlg));
  288                         IP6Q_UNLOCK();
  289                         return (IPPROTO_DONE);
  290                 }
  291         } else if (fragoff + frgpartlen > IPV6_MAXPACKET) {
  292                 icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
  293                     offset - sizeof(struct ip6_frag) +
  294                     offsetof(struct ip6_frag, ip6f_offlg));
  295                 IP6Q_UNLOCK();
  296                 return (IPPROTO_DONE);
  297         }
  298         /*
  299          * If it's the first fragment, do the above check for each
  300          * fragment already stored in the reassembly queue.
  301          */
  302         if (fragoff == 0) {
  303                 for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  304                      af6 = af6dwn) {
  305                         af6dwn = af6->ip6af_down;
  306 
  307                         if (q6->ip6q_unfrglen + af6->ip6af_off + af6->ip6af_frglen >
  308                             IPV6_MAXPACKET) {
  309                                 struct mbuf *merr = IP6_REASS_MBUF(af6);
  310                                 struct ip6_hdr *ip6err;
  311                                 int erroff = af6->ip6af_offset;
  312 
  313                                 /* dequeue the fragment. */
  314                                 frag6_deq(af6);
  315                                 free(af6, M_FTABLE);
  316 
  317                                 /* adjust pointer. */
  318                                 ip6err = mtod(merr, struct ip6_hdr *);
  319 
  320                                 /*
  321                                  * Restore source and destination addresses
  322                                  * in the erroneous IPv6 header.
  323                                  */
  324                                 ip6err->ip6_src = q6->ip6q_src;
  325                                 ip6err->ip6_dst = q6->ip6q_dst;
  326 
  327                                 icmp6_error(merr, ICMP6_PARAM_PROB,
  328                                     ICMP6_PARAMPROB_HEADER,
  329                                     erroff - sizeof(struct ip6_frag) +
  330                                     offsetof(struct ip6_frag, ip6f_offlg));
  331                         }
  332                 }
  333         }
  334 
  335         ip6af = (struct ip6asfrag *)malloc(sizeof(struct ip6asfrag), M_FTABLE,
  336             M_NOWAIT);
  337         if (ip6af == NULL)
  338                 goto dropfrag;
  339         bzero(ip6af, sizeof(*ip6af));
  340         ip6af->ip6af_head = ip6->ip6_flow;
  341         ip6af->ip6af_len = ip6->ip6_plen;
  342         ip6af->ip6af_nxt = ip6->ip6_nxt;
  343         ip6af->ip6af_hlim = ip6->ip6_hlim;
  344         ip6af->ip6af_mff = ip6f->ip6f_offlg & IP6F_MORE_FRAG;
  345         ip6af->ip6af_off = fragoff;
  346         ip6af->ip6af_frglen = frgpartlen;
  347         ip6af->ip6af_offset = offset;
  348         IP6_REASS_MBUF(ip6af) = m;
  349 
  350         if (first_frag) {
  351                 af6 = (struct ip6asfrag *)q6;
  352                 goto insert;
  353         }
  354 
  355         /*
  356          * Handle ECN by comparing this segment with the first one;
  357          * if CE is set, do not lose CE.
  358          * drop if CE and not-ECT are mixed for the same packet.
  359          */
  360         ecn = (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
  361         ecn0 = (ntohl(q6->ip6q_down->ip6af_head) >> 20) & IPTOS_ECN_MASK;
  362         if (ecn == IPTOS_ECN_CE) {
  363                 if (ecn0 == IPTOS_ECN_NOTECT) {
  364                         free(ip6af, M_FTABLE);
  365                         goto dropfrag;
  366                 }
  367                 if (ecn0 != IPTOS_ECN_CE)
  368                         q6->ip6q_down->ip6af_head |= htonl(IPTOS_ECN_CE << 20);
  369         }
  370         if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT) {
  371                 free(ip6af, M_FTABLE);
  372                 goto dropfrag;
  373         }
  374 
  375         /*
  376          * Find a segment which begins after this one does.
  377          */
  378         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  379              af6 = af6->ip6af_down)
  380                 if (af6->ip6af_off > ip6af->ip6af_off)
  381                         break;
  382 
  383 #if 0
  384         /*
  385          * If there is a preceding segment, it may provide some of
  386          * our data already.  If so, drop the data from the incoming
  387          * segment.  If it provides all of our data, drop us.
  388          */
  389         if (af6->ip6af_up != (struct ip6asfrag *)q6) {
  390                 i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
  391                         - ip6af->ip6af_off;
  392                 if (i > 0) {
  393                         if (i >= ip6af->ip6af_frglen)
  394                                 goto dropfrag;
  395                         m_adj(IP6_REASS_MBUF(ip6af), i);
  396                         ip6af->ip6af_off += i;
  397                         ip6af->ip6af_frglen -= i;
  398                 }
  399         }
  400 
  401         /*
  402          * While we overlap succeeding segments trim them or,
  403          * if they are completely covered, dequeue them.
  404          */
  405         while (af6 != (struct ip6asfrag *)q6 &&
  406                ip6af->ip6af_off + ip6af->ip6af_frglen > af6->ip6af_off) {
  407                 i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
  408                 if (i < af6->ip6af_frglen) {
  409                         af6->ip6af_frglen -= i;
  410                         af6->ip6af_off += i;
  411                         m_adj(IP6_REASS_MBUF(af6), i);
  412                         break;
  413                 }
  414                 af6 = af6->ip6af_down;
  415                 m_freem(IP6_REASS_MBUF(af6->ip6af_up));
  416                 frag6_deq(af6->ip6af_up);
  417         }
  418 #else
  419         /*
  420          * If the incoming framgent overlaps some existing fragments in
  421          * the reassembly queue, drop it, since it is dangerous to override
  422          * existing fragments from a security point of view.
  423          * We don't know which fragment is the bad guy - here we trust
  424          * fragment that came in earlier, with no real reason.
  425          */
  426         if (af6->ip6af_up != (struct ip6asfrag *)q6) {
  427                 i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
  428                         - ip6af->ip6af_off;
  429                 if (i > 0) {
  430 #if 0                           /* suppress the noisy log */
  431                         log(LOG_ERR, "%d bytes of a fragment from %s "
  432                             "overlaps the previous fragment\n",
  433                             i, ip6_sprintf(&q6->ip6q_src));
  434 #endif
  435                         free(ip6af, M_FTABLE);
  436                         goto dropfrag;
  437                 }
  438         }
  439         if (af6 != (struct ip6asfrag *)q6) {
  440                 i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
  441                 if (i > 0) {
  442 #if 0                           /* suppress the noisy log */
  443                         log(LOG_ERR, "%d bytes of a fragment from %s "
  444                             "overlaps the succeeding fragment",
  445                             i, ip6_sprintf(&q6->ip6q_src));
  446 #endif
  447                         free(ip6af, M_FTABLE);
  448                         goto dropfrag;
  449                 }
  450         }
  451 #endif
  452 
  453 insert:
  454 
  455         /*
  456          * Stick new segment in its place;
  457          * check for complete reassembly.
  458          * Move to front of packet queue, as we are
  459          * the most recently active fragmented packet.
  460          */
  461         frag6_enq(ip6af, af6->ip6af_up);
  462         frag6_nfrags++;
  463         q6->ip6q_nfrag++;
  464 #if 0 /* xxx */
  465         if (q6 != ip6q.ip6q_next) {
  466                 frag6_remque(q6);
  467                 frag6_insque(q6, &ip6q);
  468         }
  469 #endif
  470         next = 0;
  471         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  472              af6 = af6->ip6af_down) {
  473                 if (af6->ip6af_off != next) {
  474                         IP6Q_UNLOCK();
  475                         return IPPROTO_DONE;
  476                 }
  477                 next += af6->ip6af_frglen;
  478         }
  479         if (af6->ip6af_up->ip6af_mff) {
  480                 IP6Q_UNLOCK();
  481                 return IPPROTO_DONE;
  482         }
  483 
  484         /*
  485          * Reassembly is complete; concatenate fragments.
  486          */
  487         ip6af = q6->ip6q_down;
  488         t = m = IP6_REASS_MBUF(ip6af);
  489         af6 = ip6af->ip6af_down;
  490         frag6_deq(ip6af);
  491         while (af6 != (struct ip6asfrag *)q6) {
  492                 af6dwn = af6->ip6af_down;
  493                 frag6_deq(af6);
  494                 while (t->m_next)
  495                         t = t->m_next;
  496                 t->m_next = IP6_REASS_MBUF(af6);
  497                 m_adj(t->m_next, af6->ip6af_offset);
  498                 free(af6, M_FTABLE);
  499                 af6 = af6dwn;
  500         }
  501 
  502         /* adjust offset to point where the original next header starts */
  503         offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
  504         free(ip6af, M_FTABLE);
  505         ip6 = mtod(m, struct ip6_hdr *);
  506         ip6->ip6_plen = htons((u_short)next + offset - sizeof(struct ip6_hdr));
  507         ip6->ip6_src = q6->ip6q_src;
  508         ip6->ip6_dst = q6->ip6q_dst;
  509         nxt = q6->ip6q_nxt;
  510 #ifdef notyet
  511         *q6->ip6q_nxtp = (u_char)(nxt & 0xff);
  512 #endif
  513 
  514         /*
  515          * Delete frag6 header with as a few cost as possible.
  516          */
  517         if (offset < m->m_len) {
  518                 ovbcopy((caddr_t)ip6, (caddr_t)ip6 + sizeof(struct ip6_frag),
  519                         offset);
  520                 m->m_data += sizeof(struct ip6_frag);
  521                 m->m_len -= sizeof(struct ip6_frag);
  522         } else {
  523                 /* this comes with no copy if the boundary is on cluster */
  524                 if ((t = m_split(m, offset, M_DONTWAIT)) == NULL) {
  525                         frag6_remque(q6);
  526                         frag6_nfrags -= q6->ip6q_nfrag;
  527                         free(q6, M_FTABLE);
  528                         frag6_nfragpackets--;
  529                         goto dropfrag;
  530                 }
  531                 m_adj(t, sizeof(struct ip6_frag));
  532                 m_cat(m, t);
  533         }
  534 
  535         /*
  536          * Store NXT to the original.
  537          */
  538         {
  539                 char *prvnxtp = ip6_get_prevhdr(m, offset); /* XXX */
  540                 *prvnxtp = nxt;
  541         }
  542 
  543         frag6_remque(q6);
  544         frag6_nfrags -= q6->ip6q_nfrag;
  545         free(q6, M_FTABLE);
  546         frag6_nfragpackets--;
  547 
  548         if (m->m_flags & M_PKTHDR) { /* Isn't it always true? */
  549                 int plen = 0;
  550                 for (t = m; t; t = t->m_next)
  551                         plen += t->m_len;
  552                 m->m_pkthdr.len = plen;
  553         }
  554 
  555         ip6stat.ip6s_reassembled++;
  556         in6_ifstat_inc(dstifp, ifs6_reass_ok);
  557 
  558         /*
  559          * Tell launch routine the next header
  560          */
  561 
  562         *mp = m;
  563         *offp = offset;
  564 
  565         IP6Q_UNLOCK();
  566         return nxt;
  567 
  568  dropfrag:
  569         IP6Q_UNLOCK();
  570         in6_ifstat_inc(dstifp, ifs6_reass_fail);
  571         ip6stat.ip6s_fragdropped++;
  572         m_freem(m);
  573         return IPPROTO_DONE;
  574 }
  575 
  576 /*
  577  * Free a fragment reassembly header and all
  578  * associated datagrams.
  579  */
  580 void
  581 frag6_freef(q6)
  582         struct ip6q *q6;
  583 {
  584         struct ip6asfrag *af6, *down6;
  585 
  586         IP6Q_LOCK_ASSERT();
  587 
  588         for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
  589              af6 = down6) {
  590                 struct mbuf *m = IP6_REASS_MBUF(af6);
  591 
  592                 down6 = af6->ip6af_down;
  593                 frag6_deq(af6);
  594 
  595                 /*
  596                  * Return ICMP time exceeded error for the 1st fragment.
  597                  * Just free other fragments.
  598                  */
  599                 if (af6->ip6af_off == 0) {
  600                         struct ip6_hdr *ip6;
  601 
  602                         /* adjust pointer */
  603                         ip6 = mtod(m, struct ip6_hdr *);
  604 
  605                         /* restore source and destination addresses */
  606                         ip6->ip6_src = q6->ip6q_src;
  607                         ip6->ip6_dst = q6->ip6q_dst;
  608 
  609                         icmp6_error(m, ICMP6_TIME_EXCEEDED,
  610                                     ICMP6_TIME_EXCEED_REASSEMBLY, 0);
  611                 } else
  612                         m_freem(m);
  613                 free(af6, M_FTABLE);
  614         }
  615         frag6_remque(q6);
  616         frag6_nfrags -= q6->ip6q_nfrag;
  617         free(q6, M_FTABLE);
  618         frag6_nfragpackets--;
  619 }
  620 
  621 /*
  622  * Put an ip fragment on a reassembly chain.
  623  * Like insque, but pointers in middle of structure.
  624  */
  625 void
  626 frag6_enq(af6, up6)
  627         struct ip6asfrag *af6, *up6;
  628 {
  629 
  630         IP6Q_LOCK_ASSERT();
  631 
  632         af6->ip6af_up = up6;
  633         af6->ip6af_down = up6->ip6af_down;
  634         up6->ip6af_down->ip6af_up = af6;
  635         up6->ip6af_down = af6;
  636 }
  637 
  638 /*
  639  * To frag6_enq as remque is to insque.
  640  */
  641 void
  642 frag6_deq(af6)
  643         struct ip6asfrag *af6;
  644 {
  645 
  646         IP6Q_LOCK_ASSERT();
  647 
  648         af6->ip6af_up->ip6af_down = af6->ip6af_down;
  649         af6->ip6af_down->ip6af_up = af6->ip6af_up;
  650 }
  651 
  652 void
  653 frag6_insque(new, old)
  654         struct ip6q *new, *old;
  655 {
  656 
  657         IP6Q_LOCK_ASSERT();
  658 
  659         new->ip6q_prev = old;
  660         new->ip6q_next = old->ip6q_next;
  661         old->ip6q_next->ip6q_prev= new;
  662         old->ip6q_next = new;
  663 }
  664 
  665 void
  666 frag6_remque(p6)
  667         struct ip6q *p6;
  668 {
  669 
  670         IP6Q_LOCK_ASSERT();
  671 
  672         p6->ip6q_prev->ip6q_next = p6->ip6q_next;
  673         p6->ip6q_next->ip6q_prev = p6->ip6q_prev;
  674 }
  675 
  676 /*
  677  * IPv6 reassembling timer processing;
  678  * if a timer expires on a reassembly
  679  * queue, discard it.
  680  */
  681 void
  682 frag6_slowtimo()
  683 {
  684         struct ip6q *q6;
  685         int s = splnet();
  686 
  687         IP6Q_LOCK();
  688         q6 = ip6q.ip6q_next;
  689         if (q6)
  690                 while (q6 != &ip6q) {
  691                         --q6->ip6q_ttl;
  692                         q6 = q6->ip6q_next;
  693                         if (q6->ip6q_prev->ip6q_ttl == 0) {
  694                                 ip6stat.ip6s_fragtimeout++;
  695                                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  696                                 frag6_freef(q6->ip6q_prev);
  697                         }
  698                 }
  699         /*
  700          * If we are over the maximum number of fragments
  701          * (due to the limit being lowered), drain off
  702          * enough to get down to the new limit.
  703          */
  704         while (frag6_nfragpackets > (u_int)ip6_maxfragpackets &&
  705             ip6q.ip6q_prev) {
  706                 ip6stat.ip6s_fragoverflow++;
  707                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  708                 frag6_freef(ip6q.ip6q_prev);
  709         }
  710         IP6Q_UNLOCK();
  711 
  712 #if 0
  713         /*
  714          * Routing changes might produce a better route than we last used;
  715          * make sure we notice eventually, even if forwarding only for one
  716          * destination and the cache is never replaced.
  717          */
  718         if (ip6_forward_rt.ro_rt) {
  719                 RTFREE(ip6_forward_rt.ro_rt);
  720                 ip6_forward_rt.ro_rt = 0;
  721         }
  722         if (ipsrcchk_rt.ro_rt) {
  723                 RTFREE(ipsrcchk_rt.ro_rt);
  724                 ipsrcchk_rt.ro_rt = 0;
  725         }
  726 #endif
  727 
  728         splx(s);
  729 }
  730 
  731 /*
  732  * Drain off all datagram fragments.
  733  */
  734 void
  735 frag6_drain()
  736 {
  737 
  738         if (IP6Q_TRYLOCK() == 0)
  739                 return;
  740         while (ip6q.ip6q_next != &ip6q) {
  741                 ip6stat.ip6s_fragdropped++;
  742                 /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
  743                 frag6_freef(ip6q.ip6q_next);
  744         }
  745         IP6Q_UNLOCK();
  746 }

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