/*      $OpenBSD: frag6.c,v 1.95 2025/07/24 22:57:24 mvs 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/errno.h>
#include <sys/pool.h>
#include <sys/mutex.h>

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

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


/*
 * Locks used to protect global variables in this file:
 *      Q       frag6_mutex
 */

struct mutex frag6_mutex = MUTEX_INITIALIZER(IPL_SOFTNET);

u_int frag6_nfragpackets;                       /* [Q] */
u_int frag6_nfrags;                             /* [Q] */
TAILQ_HEAD(ip6q_head, ip6q) frag6_queue;        /* [Q] 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 netstack *ns)
{
        struct mbuf *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(*mp, struct ip6_hdr *);
        ip6f = ip6_exthdr_get(mp, offset, sizeof(*ip6f));
        if (ip6f == NULL)
                return IPPROTO_DONE;

        /* jumbo payload can't contain a fragment header */
        if (ip6->ip6_plen == 0) {
                icmp6_error(*mp, 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(*mp, 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_freemp(mp);
                return IPPROTO_DONE;
        }

        mtx_enter(&frag6_mutex);

        /*
         * Enforce upper bound on number of fragments.
         * If maxfrag is 0, never accept fragments.
         */
        if (frag6_nfrags >= atomic_load_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 (frag6_nfragpackets >=
                    atomic_load_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(*mp, 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(*mp, 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 = *mp;

        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 = *mp = 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);
        next += offset - sizeof(struct ip6_hdr);
        if ((u_int)next > IPV6_MAXPACKET) {
                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;
        }
        ip6 = mtod(*mp, struct ip6_hdr *);
        ip6->ip6_plen = htons(next);
        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(*mp, 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(*mp);

        /*
         * Restore NXT to the original.
         */
        {
                int prvnxt = ip6_get_prevhdr(*mp, offset);
                uint8_t *prvnxtp;

                prvnxtp = ip6_exthdr_get(mp, prvnxt, sizeof(*prvnxtp));
                if (prvnxtp == NULL)
                        goto dropfrag;
                *prvnxtp = nxt;
        }

        ip6stat_inc(ip6s_reassembled);

        /*
         * Tell launch routine the next header
         */
        *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_freemp(mp);
        return IPPROTO_DONE;

 dropfrag:
        ip6stat_inc(ip6s_fragdropped);
        m_freemp(mp);
        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_SHARED();
                        icmp6_error(m, ICMP6_TIME_EXCEEDED,
                                    ICMP6_TIME_EXCEED_REASSEMBLY, 0);
                        NET_UNLOCK_SHARED();
                } 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;
        u_int ip6_maxfragpackets_local = atomic_load_int(&ip6_maxfragpackets);

        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 > ip6_maxfragpackets_local &&
            !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);
        }
}