FreeBSD/Linux Kernel Cross Reference
sys/netinet6/frag6.c

     /*      $OpenBSD: frag6.c,v 1.87 2022/02/22 01:15:02 guenther Exp $     */
     /*      $KAME: frag6.c,v 1.40 2002/05/27 21:40:31 itojun Exp $  */
     
     /*
      * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the project nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/mbuf.h>
    #include <sys/socket.h>
    #include <sys/errno.h>
    #include <sys/time.h>
    #include <sys/kernel.h>
    #include <sys/pool.h>
    #include <sys/mutex.h>
    
    #include <net/if.h>
    #include <net/if_var.h>
    #include <net/route.h>
    
    #include <netinet/in.h>
    #include <netinet6/in6_var.h>
    #include <netinet/ip6.h>
    #include <netinet6/ip6_var.h>
    #include <netinet/icmp6.h>
    #include <netinet/ip.h>         /* for ECN definitions */
    
    /* Protects `frag6_queue', `frag6_nfragpackets' and `frag6_nfrags'. */
    struct mutex frag6_mutex = MUTEX_INITIALIZER(IPL_SOFTNET);
    
    u_int frag6_nfragpackets;
    u_int frag6_nfrags;
    TAILQ_HEAD(ip6q_head, ip6q) frag6_queue;        /* ip6 reassemble queue */
    
    void frag6_freef(struct ip6q *);
    void frag6_unlink(struct ip6q *, struct ip6q_head *);
    
    struct pool ip6af_pool;
    struct pool ip6q_pool;
    
    /*
     * Initialise reassembly queue and pools.
     */
    void
    frag6_init(void)
    {
            pool_init(&ip6af_pool, sizeof(struct ip6asfrag),
                0, IPL_SOFTNET, 0, "ip6af", NULL);
            pool_init(&ip6q_pool, sizeof(struct ip6q),
                0, IPL_SOFTNET, 0, "ip6q", NULL);
    
            TAILQ_INIT(&frag6_queue);
    }
    
    /*
     * In RFC2460, fragment and reassembly rule do not agree with each other,
     * in terms of next header field handling in fragment header.
     * While the sender will use the same value for all of the fragmented packets,
     * receiver is suggested not to check the consistency.
     *
     * fragment rule (p20):
     *      (2) A Fragment header containing:
     *      The Next Header value that identifies the first header of
     *      the Fragmentable Part of the original packet.
     *              -> next header field is same for all fragments
     *
     * reassembly rule (p21):
     *      The Next Header field of the last header of the Unfragmentable
     *      Part is obtained from the Next Header field of the first
     *      fragment's Fragment header.
     *              -> should grab it from the first fragment only
     *
     * The following note also contradicts with fragment rule - noone is going to
    * send different fragment with different next header field.
    *
    * additional note (p22):
    *      The Next Header values in the Fragment headers of different
    *      fragments of the same original packet may differ.  Only the value
    *      from the Offset zero fragment packet is used for reassembly.
    *              -> should grab it from the first fragment only
    *
    * There is no explicit reason given in the RFC.  Historical reason maybe?
    */
   /*
    * Fragment input
    */
   int
   frag6_input(struct mbuf **mp, int *offp, int proto, int af)
   {
           struct mbuf *m = *mp, *t;
           struct ip6_hdr *ip6;
           struct ip6_frag *ip6f;
           struct ip6q *q6;
           struct ip6asfrag *af6, *ip6af, *naf6, *paf6;
           int offset = *offp, nxt, i, next;
           int first_frag = 0;
           int fragoff, frgpartlen;        /* must be larger than u_int16_t */
           u_int8_t ecn, ecn0;
   
           ip6 = mtod(m, struct ip6_hdr *);
           IP6_EXTHDR_GET(ip6f, struct ip6_frag *, m, offset, sizeof(*ip6f));
           if (ip6f == NULL)
                   return IPPROTO_DONE;
   
           /* jumbo payload can't contain a fragment header */
           if (ip6->ip6_plen == 0) {
                   icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER, offset);
                   return IPPROTO_DONE;
           }
   
           /*
            * check whether fragment packet's fragment length is
            * multiple of 8 octets.
            * sizeof(struct ip6_frag) == 8
            * sizeof(struct ip6_hdr) = 40
            */
           if ((ip6f->ip6f_offlg & IP6F_MORE_FRAG) &&
               (((ntohs(ip6->ip6_plen) - offset) & 0x7) != 0)) {
                   icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                       offsetof(struct ip6_hdr, ip6_plen));
                   return IPPROTO_DONE;
           }
   
           ip6stat_inc(ip6s_fragments);
   
           /* offset now points to data portion */
           offset += sizeof(struct ip6_frag);
   
           /*
            * RFC6946:  A host that receives an IPv6 packet which includes
            * a Fragment Header with the "Fragment Offset" equal to 0 and
            * the "M" bit equal to 0 MUST process such packet in isolation
            * from any other packets/fragments.
            */
           fragoff = ntohs(ip6f->ip6f_offlg & IP6F_OFF_MASK);
           if (fragoff == 0 && !(ip6f->ip6f_offlg & IP6F_MORE_FRAG)) {
                   ip6stat_inc(ip6s_reassembled);
                   *offp = offset;
                   return ip6f->ip6f_nxt;
           }
   
           /* Ignore empty non atomic fragment, do not classify as overlapping. */
           if (sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) <= offset) {
                   m_freem(m);
                   return IPPROTO_DONE;
           }
   
           mtx_enter(&frag6_mutex);
   
           /*
            * Enforce upper bound on number of fragments.
            * If maxfrag is 0, never accept fragments.
            * If maxfrag is -1, accept all fragments without limitation.
            */
           if (ip6_maxfrags >= 0 && frag6_nfrags >= (u_int)ip6_maxfrags) {
                   mtx_leave(&frag6_mutex);
                   goto dropfrag;
           }
   
           TAILQ_FOREACH(q6, &frag6_queue, ip6q_queue)
                   if (ip6f->ip6f_ident == q6->ip6q_ident &&
                       IN6_ARE_ADDR_EQUAL(&ip6->ip6_src, &q6->ip6q_src) &&
                       IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &q6->ip6q_dst))
                           break;
   
           if (q6 == NULL) {
                   /*
                    * the first fragment to arrive, create a reassembly queue.
                    */
                   first_frag = 1;
   
                   /*
                    * Enforce upper bound on number of fragmented packets
                    * for which we attempt reassembly;
                    * If maxfragpackets is 0, never accept fragments.
                    * If maxfragpackets is -1, accept all fragments without
                    * limitation.
                    */
                   if (ip6_maxfragpackets >= 0 &&
                       frag6_nfragpackets >= (u_int)ip6_maxfragpackets) {
                           mtx_leave(&frag6_mutex);
                           goto dropfrag;
                   }
                   frag6_nfragpackets++;
                   q6 = pool_get(&ip6q_pool, PR_NOWAIT | PR_ZERO);
                   if (q6 == NULL) {
                           mtx_leave(&frag6_mutex);
                           goto dropfrag;
                   }
   
                   TAILQ_INSERT_HEAD(&frag6_queue, q6, ip6q_queue);
   
                   /* ip6q_nxt will be filled afterwards, from 1st fragment */
                   LIST_INIT(&q6->ip6q_asfrag);
                   q6->ip6q_ident  = ip6f->ip6f_ident;
                   q6->ip6q_ttl    = IPV6_FRAGTTL;
                   q6->ip6q_src    = ip6->ip6_src;
                   q6->ip6q_dst    = ip6->ip6_dst;
                   q6->ip6q_ecn    = (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
                   q6->ip6q_unfrglen = -1; /* The 1st fragment has not arrived. */
                   q6->ip6q_nfrag = 0;
           }
   
           /*
            * If it's the 1st fragment, record the length of the
            * unfragmentable part and the next header of the fragment header.
            */
           if (fragoff == 0) {
                   q6->ip6q_unfrglen = offset - sizeof(struct ip6_hdr) -
                       sizeof(struct ip6_frag);
                   q6->ip6q_nxt = ip6f->ip6f_nxt;
           }
   
           /*
            * Check that the reassembled packet would not exceed 65535 bytes
            * in size.
            * If it would exceed, discard the fragment and return an ICMP error.
            */
           frgpartlen = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) - offset;
           if (q6->ip6q_unfrglen >= 0) {
                   /* The 1st fragment has already arrived. */
                   if (q6->ip6q_unfrglen + fragoff + frgpartlen > IPV6_MAXPACKET) {
                           mtx_leave(&frag6_mutex);
                           icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                               offset - sizeof(struct ip6_frag) +
                               offsetof(struct ip6_frag, ip6f_offlg));
                           return (IPPROTO_DONE);
                   }
           } else if (fragoff + frgpartlen > IPV6_MAXPACKET) {
                   mtx_leave(&frag6_mutex);
                   icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                               offset - sizeof(struct ip6_frag) +
                                   offsetof(struct ip6_frag, ip6f_offlg));
                   return (IPPROTO_DONE);
           }
           /*
            * If it's the first fragment, do the above check for each
            * fragment already stored in the reassembly queue.
            */
           if (fragoff == 0) {
                   LIST_FOREACH_SAFE(af6, &q6->ip6q_asfrag, ip6af_list, naf6) {
                           if (q6->ip6q_unfrglen + af6->ip6af_off +
                               af6->ip6af_frglen > IPV6_MAXPACKET) {
                                   struct mbuf *merr = af6->ip6af_m;
                                   struct ip6_hdr *ip6err;
                                   int erroff = af6->ip6af_offset;
   
                                   /* dequeue the fragment. */
                                   LIST_REMOVE(af6, ip6af_list);
                                   pool_put(&ip6af_pool, af6);
   
                                   /* adjust pointer. */
                                   ip6err = mtod(merr, struct ip6_hdr *);
   
                                   /*
                                    * Restore source and destination addresses
                                    * in the erroneous IPv6 header.
                                    */
                                   ip6err->ip6_src = q6->ip6q_src;
                                   ip6err->ip6_dst = q6->ip6q_dst;
   
                                   icmp6_error(merr, ICMP6_PARAM_PROB,
                                       ICMP6_PARAMPROB_HEADER,
                                       erroff - sizeof(struct ip6_frag) +
                                       offsetof(struct ip6_frag, ip6f_offlg));
                           }
                   }
           }
   
           ip6af = pool_get(&ip6af_pool, PR_NOWAIT | PR_ZERO);
           if (ip6af == NULL) {
                   mtx_leave(&frag6_mutex);
                   goto dropfrag;
           }
           ip6af->ip6af_mff = ip6f->ip6f_offlg & IP6F_MORE_FRAG;
           ip6af->ip6af_off = fragoff;
           ip6af->ip6af_frglen = frgpartlen;
           ip6af->ip6af_offset = offset;
           ip6af->ip6af_m = m;
   
           if (first_frag) {
                   paf6 = NULL;
                   goto insert;
           }
   
           /*
            * Handle ECN by comparing this segment with the first one;
            * if CE is set, do not lose CE.
            * drop if CE and not-ECT are mixed for the same packet.
            */
           ecn = (ntohl(ip6->ip6_flow) >> 20) & IPTOS_ECN_MASK;
           ecn0 = q6->ip6q_ecn;
           if (ecn == IPTOS_ECN_CE) {
                   if (ecn0 == IPTOS_ECN_NOTECT) {
                           mtx_leave(&frag6_mutex);
                           pool_put(&ip6af_pool, ip6af);
                           goto dropfrag;
                   }
                   if (ecn0 != IPTOS_ECN_CE)
                           q6->ip6q_ecn = IPTOS_ECN_CE;
           }
           if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT) {
                   mtx_leave(&frag6_mutex);
                   pool_put(&ip6af_pool, ip6af);
                   goto dropfrag;
           }
   
           /*
            * Find a segment which begins after this one does.
            */
           for (paf6 = NULL, af6 = LIST_FIRST(&q6->ip6q_asfrag);
               af6 != NULL;
               paf6 = af6, af6 = LIST_NEXT(af6, ip6af_list))
                   if (af6->ip6af_off > ip6af->ip6af_off)
                           break;
   
           /*
            * RFC 5722, Errata 3089:  When reassembling an IPv6 datagram, if one
            * or more its constituent fragments is determined to be an overlapping
            * fragment, the entire datagram (and any constituent fragments) MUST
            * be silently discarded.
            */
           if (paf6 != NULL) {
                   i = (paf6->ip6af_off + paf6->ip6af_frglen) - ip6af->ip6af_off;
                   if (i > 0)
                           goto flushfrags;
           }
           if (af6 != NULL) {
                   i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
                   if (i > 0)
                           goto flushfrags;
           }
   
    insert:
           /*
            * Stick new segment in its place;
            * check for complete reassembly.
            * Move to front of packet queue, as we are
            * the most recently active fragmented packet.
            */
           if (paf6 != NULL)
                   LIST_INSERT_AFTER(paf6, ip6af, ip6af_list);
           else
                   LIST_INSERT_HEAD(&q6->ip6q_asfrag, ip6af, ip6af_list);
           frag6_nfrags++;
           q6->ip6q_nfrag++;
           next = 0;
           for (paf6 = NULL, af6 = LIST_FIRST(&q6->ip6q_asfrag);
               af6 != NULL;
               paf6 = af6, af6 = LIST_NEXT(af6, ip6af_list)) {
                   if (af6->ip6af_off != next) {
                           mtx_leave(&frag6_mutex);
                           return IPPROTO_DONE;
                   }
                   next += af6->ip6af_frglen;
           }
           if (paf6->ip6af_mff) {
                   mtx_leave(&frag6_mutex);
                   return IPPROTO_DONE;
           }
   
           /*
            * Reassembly is complete; concatenate fragments.
            */
           ip6af = LIST_FIRST(&q6->ip6q_asfrag);
           LIST_REMOVE(ip6af, ip6af_list);
           t = m = ip6af->ip6af_m;
           while ((af6 = LIST_FIRST(&q6->ip6q_asfrag)) != NULL) {
                   LIST_REMOVE(af6, ip6af_list);
                   while (t->m_next)
                           t = t->m_next;
                   t->m_next = af6->ip6af_m;
                   m_adj(t->m_next, af6->ip6af_offset);
                   m_removehdr(t->m_next);
                   pool_put(&ip6af_pool, af6);
           }
   
           /* adjust offset to point where the original next header starts */
           offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
           pool_put(&ip6af_pool, ip6af);
           ip6 = mtod(m, struct ip6_hdr *);
           ip6->ip6_plen = htons((u_short)next + offset - sizeof(struct ip6_hdr));
           ip6->ip6_src = q6->ip6q_src;
           ip6->ip6_dst = q6->ip6q_dst;
           if (q6->ip6q_ecn == IPTOS_ECN_CE)
                   ip6->ip6_flow |= htonl(IPTOS_ECN_CE << 20);
           nxt = q6->ip6q_nxt;
   
           /* Delete frag6 header */
           if (frag6_deletefraghdr(m, offset) != 0) {
                   TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
                   frag6_nfrags -= q6->ip6q_nfrag;
                   frag6_nfragpackets--;
                   mtx_leave(&frag6_mutex);
                   pool_put(&ip6q_pool, q6);
                   goto dropfrag;
           }
   
           TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
           frag6_nfrags -= q6->ip6q_nfrag;
           frag6_nfragpackets--;
   
           mtx_leave(&frag6_mutex);
   
           pool_put(&ip6q_pool, q6);
   
           m_calchdrlen(m);
   
           /*
            * Restore NXT to the original.
            */
           {
                   int prvnxt = ip6_get_prevhdr(m, offset);
                   uint8_t *prvnxtp;
   
                   IP6_EXTHDR_GET(prvnxtp, uint8_t *, m, prvnxt,
                       sizeof(*prvnxtp));
                   if (prvnxtp == NULL)
                           goto dropfrag;
                   *prvnxtp = nxt;
           }
   
           ip6stat_inc(ip6s_reassembled);
   
           /*
            * Tell launch routine the next header
            */
   
           *mp = m;
           *offp = offset;
   
           return nxt;
   
    flushfrags:
           TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
           frag6_nfrags -= q6->ip6q_nfrag;
           frag6_nfragpackets--;
   
           mtx_leave(&frag6_mutex);
   
           pool_put(&ip6af_pool, ip6af);
   
           while ((af6 = LIST_FIRST(&q6->ip6q_asfrag)) != NULL) {
                   LIST_REMOVE(af6, ip6af_list);
                   m_freem(af6->ip6af_m);
                   pool_put(&ip6af_pool, af6);
           }
           ip6stat_add(ip6s_fragdropped, q6->ip6q_nfrag + 1);
           pool_put(&ip6q_pool, q6);
           m_freem(m);
           return IPPROTO_DONE;
   
    dropfrag:
           ip6stat_inc(ip6s_fragdropped);
           m_freem(m);
           return IPPROTO_DONE;
   }
   
   /*
    * Delete fragment header after the unfragmentable header portions.
    */
   int
   frag6_deletefraghdr(struct mbuf *m, int offset)
   {
           struct mbuf *t;
   
           if (m->m_len >= offset + sizeof(struct ip6_frag)) {
                   memmove(mtod(m, caddr_t) + sizeof(struct ip6_frag),
                       mtod(m, caddr_t), offset);
                   m->m_data += sizeof(struct ip6_frag);
                   m->m_len -= sizeof(struct ip6_frag);
           } else {
                   /* this comes with no copy if the boundary is on cluster */
                   if ((t = m_split(m, offset, M_DONTWAIT)) == NULL)
                           return (ENOBUFS);
                   m_adj(t, sizeof(struct ip6_frag));
                   m_cat(m, t);
           }
   
           return (0);
   }
   
   /*
    * Free a fragment reassembly header and all
    * associated datagrams.
    * The header must not be in any queue.
    */
   void
   frag6_freef(struct ip6q *q6)
   {
           struct ip6asfrag *af6;
   
           while ((af6 = LIST_FIRST(&q6->ip6q_asfrag)) != NULL) {
                   struct mbuf *m = af6->ip6af_m;
   
                   LIST_REMOVE(af6, ip6af_list);
   
                   /*
                    * Return ICMP time exceeded error for the 1st fragment.
                    * Just free other fragments.
                    */
                   if (af6->ip6af_off == 0) {
                           struct ip6_hdr *ip6;
   
                           /* adjust pointer */
                           ip6 = mtod(m, struct ip6_hdr *);
   
                           /* restore source and destination addresses */
                           ip6->ip6_src = q6->ip6q_src;
                           ip6->ip6_dst = q6->ip6q_dst;
   
                           NET_LOCK();
                           icmp6_error(m, ICMP6_TIME_EXCEEDED,
                                       ICMP6_TIME_EXCEED_REASSEMBLY, 0);
                           NET_UNLOCK();
                   } else
                           m_freem(m);
                   pool_put(&ip6af_pool, af6);
           }
           pool_put(&ip6q_pool, q6);
   }
   
   /*
    * Unlinks a fragment reassembly header from the reassembly queue
    * and inserts it into a given remove queue.
    */
   void
   frag6_unlink(struct ip6q *q6, struct ip6q_head *rmq6)
   {
           MUTEX_ASSERT_LOCKED(&frag6_mutex);
   
           TAILQ_REMOVE(&frag6_queue, q6, ip6q_queue);
           TAILQ_INSERT_HEAD(rmq6, q6, ip6q_queue);
           frag6_nfrags -= q6->ip6q_nfrag;
           frag6_nfragpackets--;
   }
   
   /*
    * IPv6 reassembling timer processing;
    * if a timer expires on a reassembly
    * queue, discard it.
    */
   void
   frag6_slowtimo(void)
   {
           struct ip6q_head rmq6;
           struct ip6q *q6, *nq6;
   
           TAILQ_INIT(&rmq6);
   
           mtx_enter(&frag6_mutex);
   
           TAILQ_FOREACH_SAFE(q6, &frag6_queue, ip6q_queue, nq6) {
                   if (--q6->ip6q_ttl == 0) {
                           ip6stat_inc(ip6s_fragtimeout);
                           frag6_unlink(q6, &rmq6);
                   }
           }
   
           /*
            * If we are over the maximum number of fragments
            * (due to the limit being lowered), drain off
            * enough to get down to the new limit.
            */
           while (frag6_nfragpackets > (u_int)ip6_maxfragpackets &&
               !TAILQ_EMPTY(&frag6_queue)) {
                   ip6stat_inc(ip6s_fragoverflow);
                   frag6_unlink(TAILQ_LAST(&frag6_queue, ip6q_head), &rmq6);
           }
   
           mtx_leave(&frag6_mutex);
   
           while ((q6 = TAILQ_FIRST(&rmq6)) != NULL) {
                   TAILQ_REMOVE(&rmq6, q6, ip6q_queue);
                   frag6_freef(q6);
           }
   }

Cache object: 621255ff548765f2adc68854b50e2f00