source: rtems-libbsd/freebsd/sys/netinet6/frag6.c @ 7eeb079

#include <machine/rtems-bsd-kernel-space.h>

/*-
 * 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.
 *
 *      $KAME: frag6.c,v 1.33 2002/01/07 11:34:48 kjc Exp $
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <rtems/bsd/sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <rtems/bsd/sys/errno.h>
#include <rtems/bsd/sys/time.h>
#include <sys/kernel.h>
#include <sys/syslog.h>

#include <net/if.h>
#include <net/route.h>
#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet/icmp6.h>
#include <netinet/in_systm.h>   /* for ECN definitions */
#include <netinet/ip.h>         /* for ECN definitions */

#include <security/mac/mac_framework.h>

/*
 * Define it to get a correct behavior on per-interface statistics.
 * You will need to perform an extra routing table lookup, per fragment,
 * to do it.  This may, or may not be, a performance hit.
 */
#define IN6_IFSTAT_STRICT

static void frag6_enq(struct ip6asfrag *, struct ip6asfrag *);
static void frag6_deq(struct ip6asfrag *);
static void frag6_insque(struct ip6q *, struct ip6q *);
static void frag6_remque(struct ip6q *);
static void frag6_freef(struct ip6q *);

static struct mtx ip6qlock;
/*
 * These fields all protected by ip6qlock.
 */
static VNET_DEFINE(u_int, frag6_nfragpackets);
static VNET_DEFINE(u_int, frag6_nfrags);
static VNET_DEFINE(struct ip6q, ip6q);  /* ip6 reassemble queue */

#define V_frag6_nfragpackets            VNET(frag6_nfragpackets)
#define V_frag6_nfrags                  VNET(frag6_nfrags)
#define V_ip6q                          VNET(ip6q)

#define IP6Q_LOCK_INIT()        mtx_init(&ip6qlock, "ip6qlock", NULL, MTX_DEF);
#define IP6Q_LOCK()             mtx_lock(&ip6qlock)
#define IP6Q_TRYLOCK()          mtx_trylock(&ip6qlock)
#define IP6Q_LOCK_ASSERT()      mtx_assert(&ip6qlock, MA_OWNED)
#define IP6Q_UNLOCK()           mtx_unlock(&ip6qlock)

static MALLOC_DEFINE(M_FTABLE, "fragment", "fragment reassembly header");

/*
 * Initialise reassembly queue and fragment identifier.
 */
static void
frag6_change(void *tag)
{

        V_ip6_maxfragpackets = nmbclusters / 4;
        V_ip6_maxfrags = nmbclusters / 4;
}

void
frag6_init(void)
{

        V_ip6_maxfragpackets = nmbclusters / 4;
        V_ip6_maxfrags = nmbclusters / 4;
        V_ip6q.ip6q_next = V_ip6q.ip6q_prev = &V_ip6q;

        if (!IS_DEFAULT_VNET(curvnet))
                return;

        EVENTHANDLER_REGISTER(nmbclusters_change,
            frag6_change, NULL, EVENTHANDLER_PRI_ANY);

        IP6Q_LOCK_INIT();
}

/*
 * 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)
{
        struct mbuf *m = *mp, *t;
        struct ip6_hdr *ip6;
        struct ip6_frag *ip6f;
        struct ip6q *q6;
        struct ip6asfrag *af6, *ip6af, *af6dwn;
#ifdef IN6_IFSTAT_STRICT
        struct in6_ifaddr *ia;
#endif
        int offset = *offp, nxt, i, next;
        int first_frag = 0;
        int fragoff, frgpartlen;        /* must be larger than u_int16_t */
        struct ifnet *dstifp;
        u_int8_t ecn, ecn0;
#if 0
        char ip6buf[INET6_ADDRSTRLEN];
#endif

        ip6 = mtod(m, struct ip6_hdr *);
#ifndef PULLDOWN_TEST
        IP6_EXTHDR_CHECK(m, offset, sizeof(struct ip6_frag), IPPROTO_DONE);
        ip6f = (struct ip6_frag *)((caddr_t)ip6 + offset);
#else
        IP6_EXTHDR_GET(ip6f, struct ip6_frag *, m, offset, sizeof(*ip6f));
        if (ip6f == NULL)
                return (IPPROTO_DONE);
#endif

        dstifp = NULL;
#ifdef IN6_IFSTAT_STRICT
        /* find the destination interface of the packet. */
        if ((ia = ip6_getdstifaddr(m)) != NULL) {
                dstifp = ia->ia_ifp;
                ifa_free(&ia->ia_ifa);
        }
#else
        /* we are violating the spec, this is not the destination interface */
        if ((m->m_flags & M_PKTHDR) != 0)
                dstifp = m->m_pkthdr.rcvif;
#endif

        /* jumbo payload can't contain a fragment header */
        if (ip6->ip6_plen == 0) {
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER, offset);
                in6_ifstat_inc(dstifp, ifs6_reass_fail);
                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));
                in6_ifstat_inc(dstifp, ifs6_reass_fail);
                return IPPROTO_DONE;
        }

        IP6STAT_INC(ip6s_fragments);
        in6_ifstat_inc(dstifp, ifs6_reass_reqd);

        /* offset now points to data portion */
        offset += sizeof(struct ip6_frag);

        /*
         * RFC 6946: Handle "atomic" fragments (offset and m bit set to 0)
         * upfront, unrelated to any reassembly.  Just skip the fragment header.
         */
        if ((ip6f->ip6f_offlg & ~IP6F_RESERVED_MASK) == 0) {
                /* XXX-BZ we want dedicated counters for this. */
                IP6STAT_INC(ip6s_reassembled);
                in6_ifstat_inc(dstifp, ifs6_reass_ok);
                *offp = offset;
                return (ip6f->ip6f_nxt);
        }

        IP6Q_LOCK();

        /*
         * Enforce upper bound on number of fragments.
         * If maxfrag is 0, never accept fragments.
         * If maxfrag is -1, accept all fragments without limitation.
         */
        if (V_ip6_maxfrags < 0)
                ;
        else if (V_frag6_nfrags >= (u_int)V_ip6_maxfrags)
                goto dropfrag;

        for (q6 = V_ip6q.ip6q_next; q6 != &V_ip6q; q6 = q6->ip6q_next)
                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)
#ifdef MAC
                    && mac_ip6q_match(m, q6)
#endif
                    )
                        break;

        if (q6 == &V_ip6q) {
                /*
                 * 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 (V_ip6_maxfragpackets < 0)
                        ;
                else if (V_frag6_nfragpackets >= (u_int)V_ip6_maxfragpackets)
                        goto dropfrag;
                V_frag6_nfragpackets++;
                q6 = (struct ip6q *)malloc(sizeof(struct ip6q), M_FTABLE,
                    M_NOWAIT);
                if (q6 == NULL)
                        goto dropfrag;
                bzero(q6, sizeof(*q6));
#ifdef MAC
                if (mac_ip6q_init(q6, M_NOWAIT) != 0) {
                        free(q6, M_FTABLE);
                        goto dropfrag;
                }
                mac_ip6q_create(m, q6);
#endif
                frag6_insque(q6, &V_ip6q);

                /* ip6q_nxt will be filled afterwards, from 1st fragment */
                q6->ip6q_down   = q6->ip6q_up = (struct ip6asfrag *)q6;
#ifdef notyet
                q6->ip6q_nxtp   = (u_char *)nxtp;
#endif
                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.
         */
        fragoff = ntohs(ip6f->ip6f_offlg & IP6F_OFF_MASK);
        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) {
                        icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                            offset - sizeof(struct ip6_frag) +
                            offsetof(struct ip6_frag, ip6f_offlg));
                        IP6Q_UNLOCK();
                        return (IPPROTO_DONE);
                }
        } else if (fragoff + frgpartlen > IPV6_MAXPACKET) {
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                    offset - sizeof(struct ip6_frag) +
                    offsetof(struct ip6_frag, ip6f_offlg));
                IP6Q_UNLOCK();
                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) {
                for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
                     af6 = af6dwn) {
                        af6dwn = af6->ip6af_down;

                        if (q6->ip6q_unfrglen + af6->ip6af_off + af6->ip6af_frglen >
                            IPV6_MAXPACKET) {
                                struct mbuf *merr = IP6_REASS_MBUF(af6);
                                struct ip6_hdr *ip6err;
                                int erroff = af6->ip6af_offset;

                                /* dequeue the fragment. */
                                frag6_deq(af6);
                                free(af6, M_FTABLE);

                                /* 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 = (struct ip6asfrag *)malloc(sizeof(struct ip6asfrag), M_FTABLE,
            M_NOWAIT);
        if (ip6af == NULL)
                goto dropfrag;
        bzero(ip6af, sizeof(*ip6af));
        ip6af->ip6af_mff = ip6f->ip6f_offlg & IP6F_MORE_FRAG;
        ip6af->ip6af_off = fragoff;
        ip6af->ip6af_frglen = frgpartlen;
        ip6af->ip6af_offset = offset;
        IP6_REASS_MBUF(ip6af) = m;

        if (first_frag) {
                af6 = (struct ip6asfrag *)q6;
                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) {
                        free(ip6af, M_FTABLE);
                        goto dropfrag;
                }
                if (ecn0 != IPTOS_ECN_CE)
                        q6->ip6q_ecn = IPTOS_ECN_CE;
        }
        if (ecn == IPTOS_ECN_NOTECT && ecn0 != IPTOS_ECN_NOTECT) {
                free(ip6af, M_FTABLE);
                goto dropfrag;
        }

        /*
         * Find a segment which begins after this one does.
         */
        for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
             af6 = af6->ip6af_down)
                if (af6->ip6af_off > ip6af->ip6af_off)
                        break;

#if 0
        /*
         * If there is a preceding segment, it may provide some of
         * our data already.  If so, drop the data from the incoming
         * segment.  If it provides all of our data, drop us.
         */
        if (af6->ip6af_up != (struct ip6asfrag *)q6) {
                i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
                        - ip6af->ip6af_off;
                if (i > 0) {
                        if (i >= ip6af->ip6af_frglen)
                                goto dropfrag;
                        m_adj(IP6_REASS_MBUF(ip6af), i);
                        ip6af->ip6af_off += i;
                        ip6af->ip6af_frglen -= i;
                }
        }

        /*
         * While we overlap succeeding segments trim them or,
         * if they are completely covered, dequeue them.
         */
        while (af6 != (struct ip6asfrag *)q6 &&
               ip6af->ip6af_off + ip6af->ip6af_frglen > af6->ip6af_off) {
                i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
                if (i < af6->ip6af_frglen) {
                        af6->ip6af_frglen -= i;
                        af6->ip6af_off += i;
                        m_adj(IP6_REASS_MBUF(af6), i);
                        break;
                }
                af6 = af6->ip6af_down;
                m_freem(IP6_REASS_MBUF(af6->ip6af_up));
                frag6_deq(af6->ip6af_up);
        }
#else
        /*
         * If the incoming framgent overlaps some existing fragments in
         * the reassembly queue, drop it, since it is dangerous to override
         * existing fragments from a security point of view.
         * We don't know which fragment is the bad guy - here we trust
         * fragment that came in earlier, with no real reason.
         *
         * Note: due to changes after disabling this part, mbuf passed to
         * m_adj() below now does not meet the requirement.
         */
        if (af6->ip6af_up != (struct ip6asfrag *)q6) {
                i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
                        - ip6af->ip6af_off;
                if (i > 0) {
#if 0                           /* suppress the noisy log */
                        log(LOG_ERR, "%d bytes of a fragment from %s "
                            "overlaps the previous fragment\n",
                            i, ip6_sprintf(ip6buf, &q6->ip6q_src));
#endif
                        free(ip6af, M_FTABLE);
                        goto dropfrag;
                }
        }
        if (af6 != (struct ip6asfrag *)q6) {
                i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
                if (i > 0) {
#if 0                           /* suppress the noisy log */
                        log(LOG_ERR, "%d bytes of a fragment from %s "
                            "overlaps the succeeding fragment",
                            i, ip6_sprintf(ip6buf, &q6->ip6q_src));
#endif
                        free(ip6af, M_FTABLE);
                        goto dropfrag;
                }
        }
#endif

insert:
#ifdef MAC
        if (!first_frag)
                mac_ip6q_update(m, q6);
#endif

        /*
         * 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.
         */
        frag6_enq(ip6af, af6->ip6af_up);
        V_frag6_nfrags++;
        q6->ip6q_nfrag++;
#if 0 /* xxx */
        if (q6 != V_ip6q.ip6q_next) {
                frag6_remque(q6);
                frag6_insque(q6, &V_ip6q);
        }
#endif
        next = 0;
        for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
             af6 = af6->ip6af_down) {
                if (af6->ip6af_off != next) {
                        IP6Q_UNLOCK();
                        return IPPROTO_DONE;
                }
                next += af6->ip6af_frglen;
        }
        if (af6->ip6af_up->ip6af_mff) {
                IP6Q_UNLOCK();
                return IPPROTO_DONE;
        }

        /*
         * Reassembly is complete; concatenate fragments.
         */
        ip6af = q6->ip6q_down;
        t = m = IP6_REASS_MBUF(ip6af);
        af6 = ip6af->ip6af_down;
        frag6_deq(ip6af);
        while (af6 != (struct ip6asfrag *)q6) {
                af6dwn = af6->ip6af_down;
                frag6_deq(af6);
                while (t->m_next)
                        t = t->m_next;
                t->m_next = IP6_REASS_MBUF(af6);
                m_adj(t->m_next, af6->ip6af_offset);
                free(af6, M_FTABLE);
                af6 = af6dwn;
        }

        /* adjust offset to point where the original next header starts */
        offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
        free(ip6af, M_FTABLE);
        ip6 = mtod(m, struct ip6_hdr *);
        ip6->ip6_plen = htons((u_short)next + offset - sizeof(struct ip6_hdr));
        if (q6->ip6q_ecn == IPTOS_ECN_CE)
                ip6->ip6_flow |= htonl(IPTOS_ECN_CE << 20);
        nxt = q6->ip6q_nxt;
#ifdef notyet
        *q6->ip6q_nxtp = (u_char)(nxt & 0xff);
#endif

        /* Delete frag6 header */
        if (m->m_len >= offset + sizeof(struct ip6_frag)) {
                /* This is the only possible case with !PULLDOWN_TEST */
                ovbcopy((caddr_t)ip6, (caddr_t)ip6 + sizeof(struct ip6_frag),
                    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) {
                        frag6_remque(q6);
                        V_frag6_nfrags -= q6->ip6q_nfrag;
#ifdef MAC
                        mac_ip6q_destroy(q6);
#endif
                        free(q6, M_FTABLE);
                        V_frag6_nfragpackets--;
                        goto dropfrag;
                }
                m_adj(t, sizeof(struct ip6_frag));
                m_cat(m, t);
        }

        /*
         * Store NXT to the original.
         */
        {
                char *prvnxtp = ip6_get_prevhdr(m, offset); /* XXX */
                *prvnxtp = nxt;
        }

        frag6_remque(q6);
        V_frag6_nfrags -= q6->ip6q_nfrag;
#ifdef MAC
        mac_ip6q_reassemble(q6, m);
        mac_ip6q_destroy(q6);
#endif
        free(q6, M_FTABLE);
        V_frag6_nfragpackets--;

        if (m->m_flags & M_PKTHDR) { /* Isn't it always true? */
                int plen = 0;
                for (t = m; t; t = t->m_next)
                        plen += t->m_len;
                m->m_pkthdr.len = plen;
        }

        IP6STAT_INC(ip6s_reassembled);
        in6_ifstat_inc(dstifp, ifs6_reass_ok);

        /*
         * Tell launch routine the next header
         */

        *mp = m;
        *offp = offset;

        IP6Q_UNLOCK();
        return nxt;

 dropfrag:
        IP6Q_UNLOCK();
        in6_ifstat_inc(dstifp, ifs6_reass_fail);
        IP6STAT_INC(ip6s_fragdropped);
        m_freem(m);
        return IPPROTO_DONE;
}

/*
 * Free a fragment reassembly header and all
 * associated datagrams.
 */
void
frag6_freef(struct ip6q *q6)
{
        struct ip6asfrag *af6, *down6;

        IP6Q_LOCK_ASSERT();

        for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
             af6 = down6) {
                struct mbuf *m = IP6_REASS_MBUF(af6);

                down6 = af6->ip6af_down;
                frag6_deq(af6);

                /*
                 * 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;

                        icmp6_error(m, ICMP6_TIME_EXCEEDED,
                                    ICMP6_TIME_EXCEED_REASSEMBLY, 0);
                } else
                        m_freem(m);
                free(af6, M_FTABLE);
        }
        frag6_remque(q6);
        V_frag6_nfrags -= q6->ip6q_nfrag;
#ifdef MAC
        mac_ip6q_destroy(q6);
#endif
        free(q6, M_FTABLE);
        V_frag6_nfragpackets--;
}

/*
 * Put an ip fragment on a reassembly chain.
 * Like insque, but pointers in middle of structure.
 */
void
frag6_enq(struct ip6asfrag *af6, struct ip6asfrag *up6)
{

        IP6Q_LOCK_ASSERT();

        af6->ip6af_up = up6;
        af6->ip6af_down = up6->ip6af_down;
        up6->ip6af_down->ip6af_up = af6;
        up6->ip6af_down = af6;
}

/*
 * To frag6_enq as remque is to insque.
 */
void
frag6_deq(struct ip6asfrag *af6)
{

        IP6Q_LOCK_ASSERT();

        af6->ip6af_up->ip6af_down = af6->ip6af_down;
        af6->ip6af_down->ip6af_up = af6->ip6af_up;
}

void
frag6_insque(struct ip6q *new, struct ip6q *old)
{

        IP6Q_LOCK_ASSERT();

        new->ip6q_prev = old;
        new->ip6q_next = old->ip6q_next;
        old->ip6q_next->ip6q_prev= new;
        old->ip6q_next = new;
}

void
frag6_remque(struct ip6q *p6)
{

        IP6Q_LOCK_ASSERT();

        p6->ip6q_prev->ip6q_next = p6->ip6q_next;
        p6->ip6q_next->ip6q_prev = p6->ip6q_prev;
}

/*
 * IPv6 reassembling timer processing;
 * if a timer expires on a reassembly
 * queue, discard it.
 */
void
frag6_slowtimo(void)
{
        VNET_ITERATOR_DECL(vnet_iter);
        struct ip6q *q6;

        VNET_LIST_RLOCK_NOSLEEP();
        IP6Q_LOCK();
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                q6 = V_ip6q.ip6q_next;
                if (q6)
                        while (q6 != &V_ip6q) {
                                --q6->ip6q_ttl;
                                q6 = q6->ip6q_next;
                                if (q6->ip6q_prev->ip6q_ttl == 0) {
                                        IP6STAT_INC(ip6s_fragtimeout);
                                        /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                                        frag6_freef(q6->ip6q_prev);
                                }
                        }
                /*
                 * 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 (V_frag6_nfragpackets > (u_int)V_ip6_maxfragpackets &&
                    V_ip6q.ip6q_prev) {
                        IP6STAT_INC(ip6s_fragoverflow);
                        /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                        frag6_freef(V_ip6q.ip6q_prev);
                }
                CURVNET_RESTORE();
        }
        IP6Q_UNLOCK();
        VNET_LIST_RUNLOCK_NOSLEEP();
}

/*
 * Drain off all datagram fragments.
 */
void
frag6_drain(void)
{
        VNET_ITERATOR_DECL(vnet_iter);

        VNET_LIST_RLOCK_NOSLEEP();
        if (IP6Q_TRYLOCK() == 0) {
                VNET_LIST_RUNLOCK_NOSLEEP();
                return;
        }
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                while (V_ip6q.ip6q_next != &V_ip6q) {
                        IP6STAT_INC(ip6s_fragdropped);
                        /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                        frag6_freef(V_ip6q.ip6q_next);
                }
                CURVNET_RESTORE();
        }
        IP6Q_UNLOCK();
        VNET_LIST_RUNLOCK_NOSLEEP();
}