/*      $NetBSD: frag6.c,v 1.78 2024/04/19 05:04:06 ozaki-r 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/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: frag6.c,v 1.78 2024/04/19 05:04:06 ozaki-r Exp $");

#ifdef _KERNEL_OPT
#include "opt_net_mpsafe.h"
#endif

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/kmem.h>
#include <sys/kernel.h>
#include <sys/syslog.h>

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

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/ip6_private.h>
#include <netinet/icmp6.h>

/*
 * IPv6 reassembly queue structure. Each fragment being reassembled is
 * attached to one of these structures.
 *
 * XXX: Would be better to use TAILQ.
 */
struct  ip6q {
        u_int32_t       ip6q_head;
        u_int16_t       ip6q_len;
        u_int8_t        ip6q_nxt;       /* ip6f_nxt in first fragment */
        u_int8_t        ip6q_hlim;
        struct ip6asfrag *ip6q_down;
        struct ip6asfrag *ip6q_up;
        u_int32_t       ip6q_ident;
        u_int8_t        ip6q_ttl;
        struct in6_addr ip6q_src, ip6q_dst;
        struct ip6q     *ip6q_next;
        struct ip6q     *ip6q_prev;
        int             ip6q_unfrglen;  /* len of unfragmentable part */
        int             ip6q_nfrag;     /* # of fragments */
        int             ip6q_ipsec;     /* IPsec flags */
};

struct  ip6asfrag {
        u_int32_t       ip6af_head;
        u_int16_t       ip6af_len;
        u_int8_t        ip6af_nxt;
        u_int8_t        ip6af_hlim;
        /* must not override the above members during reassembling */
        struct ip6asfrag *ip6af_down;
        struct ip6asfrag *ip6af_up;
        struct mbuf     *ip6af_m;
        int             ip6af_offset;   /* offset in ip6af_m to next header */
        int             ip6af_frglen;   /* fragmentable part length */
        int             ip6af_off;      /* fragment offset */
        bool            ip6af_mff;      /* more fragment bit in frag off */
};

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 int frag6_drainwanted;

static u_int frag6_nfragpackets;
static u_int frag6_nfrags;
static struct ip6q ip6q;        /* ip6 reassembly queue */

/* Protects ip6q */
static kmutex_t frag6_lock __cacheline_aligned;

/*
 * Initialise reassembly queue and fragment identifier.
 */
void
frag6_init(void)
{

        ip6q.ip6q_next = ip6q.ip6q_prev = &ip6q;
        mutex_init(&frag6_lock, MUTEX_DEFAULT, IPL_NONE);
}

static void
frag6_dropfrag(struct ip6q *q6)
{
        frag6_remque(q6);
        frag6_nfrags -= q6->ip6q_nfrag;
        kmem_intr_free(q6, sizeof(*q6));
        frag6_nfragpackets--;
}

/*
 * IPv6 fragment input.
 *
 * 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?
 *
 * XXX: It would be better to use a pool, rather than kmem.
 */
int
frag6_input(struct mbuf **mp, int *offp, int proto)
{
        struct rtentry *rt;
        struct mbuf *m = *mp, *t;
        struct ip6_hdr *ip6;
        struct ip6_frag *ip6f;
        struct ip6q *q6;
        struct ip6asfrag *af6, *ip6af, *af6dwn;
        int offset = *offp, nxt, i, next;
        int ipsecflags = m->m_flags & (M_DECRYPTED|M_AUTHIPHDR);
        int first_frag = 0;
        int fragoff, frgpartlen;        /* must be larger than u_int16_t */
        struct ifnet *dstifp;
        static struct route ro;
        union {
                struct sockaddr         dst;
                struct sockaddr_in6     dst6;
        } u;

        ip6 = mtod(m, struct ip6_hdr *);
        IP6_EXTHDR_GET(ip6f, struct ip6_frag *, m, offset, sizeof(*ip6f));
        if (ip6f == NULL)
                return IPPROTO_DONE;

        dstifp = NULL;
        /* find the destination interface of the packet. */
        sockaddr_in6_init(&u.dst6, &ip6->ip6_dst, 0, 0, 0);
        if ((rt = rtcache_lookup(&ro, &u.dst)) != NULL)
                dstifp = ((struct in6_ifaddr *)rt->rt_ifa)->ia_ifp;

        /* 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);
                goto done;
        }

        /*
         * Check whether fragment packet's fragment length is non-zero and
         * multiple of 8 octets.
         * sizeof(struct ip6_frag) == 8
         * sizeof(struct ip6_hdr) = 40
         */
        frgpartlen = sizeof(struct ip6_hdr) + ntohs(ip6->ip6_plen) - offset
            - sizeof(struct ip6_frag);
        if ((frgpartlen == 0) ||
            ((ip6f->ip6f_offlg & IP6F_MORE_FRAG) && (frgpartlen & 0x7) != 0)) {
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                    offsetof(struct ip6_hdr, ip6_plen));
                in6_ifstat_inc(dstifp, ifs6_reass_fail);
                goto done;
        }

        IP6_STATINC(IP6_STAT_FRAGMENTS);
        in6_ifstat_inc(dstifp, ifs6_reass_reqd);

        /* 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.
         *
         * XXX: Would be better to remove this fragment header entirely,
         * for us not to get confused later when looking back at the
         * previous headers in the chain.
         */
        fragoff = ntohs(ip6f->ip6f_offlg & IP6F_OFF_MASK);
        if (fragoff == 0 && !(ip6f->ip6f_offlg & IP6F_MORE_FRAG)) {
                IP6_STATINC(IP6_STAT_REASSEMBLED);
                in6_ifstat_inc(dstifp, ifs6_reass_ok);
                *offp = offset;
                rtcache_unref(rt, &ro);
                return ip6f->ip6f_nxt;
        }

        mutex_enter(&frag6_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 (ip6_maxfrags < 0)
                ;
        else if (frag6_nfrags >= (u_int)ip6_maxfrags)
                goto dropfrag;

        for (q6 = ip6q.ip6q_next; q6 != &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))
                        break;

        if (q6 != &ip6q) {
                /* All fragments must have the same IPsec flags. */
                if (q6->ip6q_ipsec != ipsecflags) {
                        goto dropfrag;
                }
        }

        if (q6 == &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 (ip6_maxfragpackets < 0)
                        ;
                else if (frag6_nfragpackets >= (u_int)ip6_maxfragpackets)
                        goto dropfrag;
                frag6_nfragpackets++;

                q6 = kmem_intr_zalloc(sizeof(struct ip6q), KM_NOSLEEP);
                if (q6 == NULL) {
                        goto dropfrag;
                }
                frag6_insque(q6, &ip6q);

                /* ip6q_nxt will be filled afterwards, from 1st fragment */
                q6->ip6q_down   = q6->ip6q_up = (struct ip6asfrag *)q6;
                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_unfrglen = -1; /* The 1st fragment has not arrived. */
                q6->ip6q_nfrag = 0;
                q6->ip6q_ipsec = ipsecflags;
        }

        /*
         * 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.
         */
        if (q6->ip6q_unfrglen >= 0) {
                /* The 1st fragment has already arrived. */
                if (q6->ip6q_unfrglen + fragoff + frgpartlen > IPV6_MAXPACKET) {
                        mutex_exit(&frag6_lock);
                        icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                            offset - sizeof(struct ip6_frag) +
                            offsetof(struct ip6_frag, ip6f_offlg));
                        goto done;
                }
        } else if (fragoff + frgpartlen > IPV6_MAXPACKET) {
                mutex_exit(&frag6_lock);
                icmp6_error(m, ICMP6_PARAM_PROB, ICMP6_PARAMPROB_HEADER,
                    offset - sizeof(struct ip6_frag) +
                    offsetof(struct ip6_frag, ip6f_offlg));
                goto 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 = af6->ip6af_m;
                                struct ip6_hdr *ip6err;
                                int erroff = af6->ip6af_offset;

                                /* dequeue the fragment. */
                                frag6_deq(af6);
                                kmem_intr_free(af6, sizeof(struct ip6asfrag));

                                /* 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 = kmem_intr_zalloc(sizeof(struct ip6asfrag), KM_NOSLEEP);
        if (ip6af == NULL) {
                goto dropfrag;
        }
        ip6af->ip6af_head = ip6->ip6_flow;
        ip6af->ip6af_len = ip6->ip6_plen;
        ip6af->ip6af_nxt = ip6->ip6_nxt;
        ip6af->ip6af_hlim = ip6->ip6_hlim;
        ip6af->ip6af_mff = (ip6f->ip6f_offlg & IP6F_MORE_FRAG) != 0;
        ip6af->ip6af_off = fragoff;
        ip6af->ip6af_frglen = frgpartlen;
        ip6af->ip6af_offset = offset;
        ip6af->ip6af_m = m;

        if (first_frag) {
                af6 = (struct ip6asfrag *)q6;
                goto insert;
        }

        /*
         * 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 the incoming fragment overlaps some existing fragments in
         * the reassembly queue - drop it as per RFC 5722.
         */
        if (af6->ip6af_up != (struct ip6asfrag *)q6) {
                i = af6->ip6af_up->ip6af_off + af6->ip6af_up->ip6af_frglen
                        - ip6af->ip6af_off;
                if (i > 0) {
                        kmem_intr_free(ip6af, sizeof(struct ip6asfrag));
                        goto dropfrag;
                }
        }
        if (af6 != (struct ip6asfrag *)q6) {
                i = (ip6af->ip6af_off + ip6af->ip6af_frglen) - af6->ip6af_off;
                if (i > 0) {
                        kmem_intr_free(ip6af, sizeof(struct ip6asfrag));
                        goto dropfrag;
                }
        }

insert:
        /*
         * Stick new segment in its place.
         */
        frag6_enq(ip6af, af6->ip6af_up);
        frag6_nfrags++;
        q6->ip6q_nfrag++;

        /*
         * Check for complete reassembly.
         */
        next = 0;
        for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
             af6 = af6->ip6af_down) {
                if (af6->ip6af_off != next) {
                        mutex_exit(&frag6_lock);
                        goto done;
                }
                next += af6->ip6af_frglen;
        }
        if (af6->ip6af_up->ip6af_mff) {
                mutex_exit(&frag6_lock);
                goto done;
        }

        /*
         * Reassembly is complete; concatenate fragments.
         */
        ip6af = q6->ip6q_down;
        t = m = ip6af->ip6af_m;
        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 = af6->ip6af_m;
                m_adj(t->m_next, af6->ip6af_offset);
                m_remove_pkthdr(t->m_next);
                kmem_intr_free(af6, sizeof(struct ip6asfrag));
                af6 = af6dwn;
        }

        /* adjust offset to point where the original next header starts */
        offset = ip6af->ip6af_offset - sizeof(struct ip6_frag);
        kmem_intr_free(ip6af, sizeof(struct ip6asfrag));
        next += offset - sizeof(struct ip6_hdr);
        if ((u_int)next > IPV6_MAXPACKET) {
                frag6_dropfrag(q6);
                goto dropfrag;
        }
        ip6 = mtod(m, struct ip6_hdr *);
        ip6->ip6_plen = htons(next);
        ip6->ip6_src = q6->ip6q_src;
        ip6->ip6_dst = q6->ip6q_dst;
        nxt = q6->ip6q_nxt;

        /*
         * Delete frag6 header.
         */
        if (m->m_len >= offset + sizeof(struct ip6_frag)) {
                memmove((char *)ip6 + sizeof(struct ip6_frag), ip6, 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_dropfrag(q6);
                        goto dropfrag;
                }
                m_adj(t, sizeof(struct ip6_frag));
                m_cat(m, t);
        }

        frag6_dropfrag(q6);

        {
                KASSERT(m->m_flags & M_PKTHDR);
                int plen = 0;
                for (t = m; t; t = t->m_next) {
                        plen += t->m_len;
                }
                m->m_pkthdr.len = plen;
                /* XXX XXX: clear csum_flags? */
        }

        /*
         * Restore NXT to the original.
         */
        {
                const 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;
        }

        IP6_STATINC(IP6_STAT_REASSEMBLED);
        in6_ifstat_inc(dstifp, ifs6_reass_ok);
        rtcache_unref(rt, &ro);
        mutex_exit(&frag6_lock);

        /*
         * Tell launch routine the next header.
         */
        *mp = m;
        *offp = offset;
        return nxt;

 dropfrag:
        mutex_exit(&frag6_lock);
        in6_ifstat_inc(dstifp, ifs6_reass_fail);
        IP6_STATINC(IP6_STAT_FRAGDROPPED);
        m_freem(m);
 done:
        rtcache_unref(rt, &ro);
        return IPPROTO_DONE;
}

int
ip6_reass_packet(struct mbuf **mp, int offset)
{

        if (frag6_input(mp, &offset, IPPROTO_IPV6) == IPPROTO_DONE) {
                *mp = NULL;
                return EINVAL;
        }
        return 0;
}

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

        KASSERT(mutex_owned(&frag6_lock));

        for (af6 = q6->ip6q_down; af6 != (struct ip6asfrag *)q6;
             af6 = down6) {
                struct mbuf *m = af6->ip6af_m;

                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);
                }
                kmem_intr_free(af6, sizeof(struct ip6asfrag));
        }

        frag6_dropfrag(q6);
}

/*
 * 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)
{

        KASSERT(mutex_owned(&frag6_lock));

        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)
{

        KASSERT(mutex_owned(&frag6_lock));

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

/*
 * Insert newq after oldq.
 */
void
frag6_insque(struct ip6q *newq, struct ip6q *oldq)
{

        KASSERT(mutex_owned(&frag6_lock));

        newq->ip6q_prev = oldq;
        newq->ip6q_next = oldq->ip6q_next;
        oldq->ip6q_next->ip6q_prev = newq;
        oldq->ip6q_next = newq;
}

/*
 * Unlink p6.
 */
void
frag6_remque(struct ip6q *p6)
{

        KASSERT(mutex_owned(&frag6_lock));

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

void
frag6_fasttimo(void)
{

        SOFTNET_KERNEL_LOCK_UNLESS_NET_MPSAFE();

        if (frag6_drainwanted) {
                frag6_drain();
                frag6_drainwanted = 0;
        }

        SOFTNET_KERNEL_UNLOCK_UNLESS_NET_MPSAFE();
}

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

        SOFTNET_KERNEL_LOCK_UNLESS_NET_MPSAFE();

        mutex_enter(&frag6_lock);
        q6 = ip6q.ip6q_next;
        if (q6) {
                while (q6 != &ip6q) {
                        --q6->ip6q_ttl;
                        q6 = q6->ip6q_next;
                        if (q6->ip6q_prev->ip6q_ttl == 0) {
                                IP6_STATINC(IP6_STAT_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 (frag6_nfragpackets > (u_int)ip6_maxfragpackets &&
            ip6q.ip6q_prev) {
                IP6_STATINC(IP6_STAT_FRAGOVERFLOW);
                /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                frag6_freef(ip6q.ip6q_prev);
        }
        mutex_exit(&frag6_lock);

        SOFTNET_KERNEL_UNLOCK_UNLESS_NET_MPSAFE();

#if 0
        /*
         * Routing changes might produce a better route than we last used;
         * make sure we notice eventually, even if forwarding only for one
         * destination and the cache is never replaced.
         */
        rtcache_free(&ip6_forward_rt);
        rtcache_free(&ipsrcchk_rt);
#endif
}

void
frag6_drainstub(void)
{
        frag6_drainwanted = 1;
}

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

        if (mutex_tryenter(&frag6_lock)) {
                while (ip6q.ip6q_next != &ip6q) {
                        IP6_STATINC(IP6_STAT_FRAGDROPPED);
                        /* XXX in6_ifstat_inc(ifp, ifs6_reass_fail) */
                        frag6_freef(ip6q.ip6q_next);
                }
                mutex_exit(&frag6_lock);
        }
}