/*      $OpenBSD: ip6_forward.c,v 1.129 2025/09/16 09:18:55 florian Exp $       */
/*      $KAME: ip6_forward.c,v 1.75 2001/06/29 12:42:13 jinmei 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 "pf.h"

#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/syslog.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/route.h>
#if NPF > 0
#include <net/pfvar.h>
#endif

#include <netinet/in.h>
#include <netinet6/in6_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>
#include <netinet/udp.h>
#include <netinet/tcp.h>
#ifdef IPSEC
#include <netinet/ip_ipsp.h>
#endif

/*
 * Forward a packet.  If some error occurs return the sender
 * an icmp packet.  Note we can't always generate a meaningful
 * icmp message because icmp doesn't have a large enough repertoire
 * of codes and types.
 *
 * If not forwarding, just drop the packet.  This could be confusing
 * if ip6_forwarding was zero but some routing protocol was advancing
 * us as a gateway to somewhere.  However, we must let the routing
 * protocol deal with that.
 *
 */

void
ip6_forward(struct mbuf *m, struct route *ro, int flags)
{
        struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
        struct route iproute;
        struct rtentry *rt;
        struct sockaddr *dst;
        struct ifnet *ifp = NULL;
        u_int rtableid = m->m_pkthdr.ph_rtableid;
        u_int ifidx = m->m_pkthdr.ph_ifidx;
        u_int8_t loopcnt = m->m_pkthdr.ph_loopcnt;
        u_int icmp_len;
        char icmp_buf[MHLEN];
        CTASSERT(sizeof(struct ip6_hdr) + sizeof(struct tcphdr) +
            MAX_TCPOPTLEN <= sizeof(icmp_buf));
        u_short mflags, pfflags;
        struct mbuf *mcopy;
        int error = 0, type = 0, code = 0, destmtu = 0;
        u_int orig_rtableid;
#ifdef IPSEC
        struct tdb *tdb = NULL;
#endif /* IPSEC */

        /*
         * Do not forward packets to multicast destination (should be handled
         * by ip6_mforward().
         * Do not forward packets with unspecified source.  It was discussed
         * in July 2000, on ipngwg mailing list.
         */
        if ((m->m_flags & (M_BCAST|M_MCAST)) != 0 ||
            IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
            IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
                ip6stat_inc(ip6s_cantforward);
                m_freem(m);
                goto done;
        }

        if (ip6->ip6_hlim <= IPV6_HLIMDEC) {
                icmp6_error(m, ICMP6_TIME_EXCEEDED,
                                ICMP6_TIME_EXCEED_TRANSIT, 0);
                goto done;
        }
        ip6->ip6_hlim -= IPV6_HLIMDEC;

        /*
         * Save at most ICMPV6_PLD_MAXLEN (= the min IPv6 MTU -
         * size of IPv6 + ICMPv6 headers) bytes of the packet in case
         * we need to generate an ICMP6 message to the src.
         * Thanks to M_EXT, in most cases copy will not occur.
         * For small packets copy original onto stack instead of mbuf.
         *
         * For final protocol header like TCP or UDP, full header chain in
         * ICMP6 packet is not necessary.  In this case only copy small
         * part of original packet and save it on stack instead of mbuf.
         * Although this violates RFC 4443 2.4. (c), it avoids additional
         * mbuf allocations.  Also pf nat and rdr do not affect the shared
         * mbuf cluster.
         *
         * It is important to save it before IPsec processing as IPsec
         * processing may modify the mbuf.
         */
        switch (ip6->ip6_nxt) {
        case IPPROTO_TCP:
                icmp_len = sizeof(struct ip6_hdr) + sizeof(struct tcphdr) +
                    MAX_TCPOPTLEN;
                break;
        case IPPROTO_UDP:
                icmp_len = sizeof(struct ip6_hdr) + sizeof(struct udphdr);
                break;
        case IPPROTO_ESP:
                icmp_len = sizeof(struct ip6_hdr) + 2 * sizeof(u_int32_t);
                break;
        default:
                icmp_len = ICMPV6_PLD_MAXLEN;
                break;
        }
        if (icmp_len > m->m_pkthdr.len)
                icmp_len = m->m_pkthdr.len;
        if (icmp_len <= sizeof(icmp_buf)) {
                mflags = m->m_flags;
                pfflags = m->m_pkthdr.pf.flags;
                m_copydata(m, 0, icmp_len, icmp_buf);
                mcopy = NULL;
        } else {
                mcopy = m_copym(m, 0, icmp_len, M_NOWAIT);
                icmp_len = 0;
        }

        orig_rtableid = m->m_pkthdr.ph_rtableid;
#if NPF > 0
reroute:
#endif

#ifdef IPSEC
        if (ipsec_in_use) {
                error = ip6_output_ipsec_lookup(m, NULL, &tdb);
                if (error) {
                        /*
                         * -EINVAL is used to indicate that the packet should
                         * be silently dropped, typically because we've asked
                         * key management for an SA.
                         */
                        if (error == -EINVAL) /* Should silently drop packet */
                                error = 0;

                        m_freem(m);
                        goto freecopy;
                }
        }
#endif /* IPSEC */

        if (ro == NULL) {
                ro = &iproute;
                ro->ro_rt = NULL;
        }
        rt = route6_mpath(ro, &ip6->ip6_dst, &ip6->ip6_src,
            m->m_pkthdr.ph_rtableid);
        if (rt == NULL) {
                ip6stat_inc(ip6s_noroute);
                type = ICMP6_DST_UNREACH;
                code = ICMP6_DST_UNREACH_NOROUTE;
                m_freem(m);
                goto icmperror;
        }
        dst = &ro->ro_dstsa;

        /*
         * Scope check: if a packet can't be delivered to its destination
         * for the reason that the destination is beyond the scope of the
         * source address, discard the packet and return an icmp6 destination
         * unreachable error with Code 2 (beyond scope of source address).
         * [draft-ietf-ipngwg-icmp-v3-00.txt, Section 3.1]
         */
        if (in6_addr2scopeid(ifidx, &ip6->ip6_src) !=
            in6_addr2scopeid(rt->rt_ifidx, &ip6->ip6_src)) {
                ip6stat_inc(ip6s_cantforward);
                ip6stat_inc(ip6s_badscope);
                type = ICMP6_DST_UNREACH;
                code = ICMP6_DST_UNREACH_BEYONDSCOPE;
                m_freem(m);
                goto icmperror;
        }

#ifdef IPSEC
        /*
         * Check if the packet needs encapsulation.
         * ipsp_process_packet will never come back to here.
         */
        if (tdb != NULL) {
                /* Callee frees mbuf */
                error = ip6_output_ipsec_send(tdb, m, ro, orig_rtableid, 0, 1);
                rt = ro->ro_rt;
                if (error)
                        goto senderr;
                goto freecopy;
        }
#endif /* IPSEC */

        if (rt->rt_flags & RTF_GATEWAY)
                dst = rt->rt_gateway;

        /*
         * If we are to forward the packet using the same interface
         * as one we got the packet from, perhaps we should send a redirect
         * to sender to shortcut a hop.
         * Only send redirect if source is sending directly to us,
         * and if packet was not source routed (or has any options).
         * Also, don't send redirect if forwarding using a route
         * modified by a redirect.
         */
        ifp = if_get(rt->rt_ifidx);
        if (ifp == NULL) {
                m_freem(m);
                goto freecopy;
        }
        if (rt->rt_ifidx == ifidx &&
            !ISSET(rt->rt_flags, RTF_DYNAMIC|RTF_MODIFIED) &&
            !ISSET(flags, IPV6_REDIRECT) &&
            atomic_load_int(&ip6_sendredirects)) {
                if ((ifp->if_flags & IFF_POINTOPOINT) &&
                    nd6_is_addr_neighbor(&ro->ro_dstsin6, ifp)) {
                        /*
                         * If the incoming interface is equal to the outgoing
                         * one, the link attached to the interface is
                         * point-to-point, and the IPv6 destination is
                         * regarded as on-link on the link, then it will be
                         * highly probable that the destination address does
                         * not exist on the link and that the packet is going
                         * to loop.  Thus, we immediately drop the packet and
                         * send an ICMPv6 error message.
                         * For other routing loops, we dare to let the packet
                         * go to the loop, so that a remote diagnosing host
                         * can detect the loop by traceroute.
                         * type/code is based on suggestion by Rich Draves.
                         * not sure if it is the best pick.
                         */
                        type = ICMP6_DST_UNREACH;
                        code = ICMP6_DST_UNREACH_ADDR;
                        m_freem(m);
                        goto icmperror;
                }
                type = ND_REDIRECT;
        }

        /*
         * Fake scoped addresses. Note that even link-local source or
         * destination can appear, if the originating node just sends the
         * packet to us (without address resolution for the destination).
         * Since both icmp6_error and icmp6_redirect_output fill the embedded
         * link identifiers, we can do this stuff after making a copy for
         * returning an error.
         */
        if (IN6_IS_SCOPE_EMBED(&ip6->ip6_src))
                ip6->ip6_src.s6_addr16[1] = 0;
        if (IN6_IS_SCOPE_EMBED(&ip6->ip6_dst))
                ip6->ip6_dst.s6_addr16[1] = 0;

#if NPF > 0
        if (pf_test(AF_INET6, PF_FWD, ifp, &m) != PF_PASS) {
                m_freem(m);
                goto senderr;
        }
        if (m == NULL)
                goto senderr;
        ip6 = mtod(m, struct ip6_hdr *);
        if ((m->m_pkthdr.pf.flags & (PF_TAG_REROUTE | PF_TAG_GENERATED)) ==
            (PF_TAG_REROUTE | PF_TAG_GENERATED)) {
                /* already rerun the route lookup, go on */
                m->m_pkthdr.pf.flags &= ~(PF_TAG_GENERATED | PF_TAG_REROUTE);
        } else if (m->m_pkthdr.pf.flags & PF_TAG_REROUTE) {
                /* tag as generated to skip over pf_test on rerun */
                m->m_pkthdr.pf.flags |= PF_TAG_GENERATED;
                SET(flags, IPV6_REDIRECT);
                if (ro == &iproute)
                        rtfree(ro->ro_rt);
                ro = NULL;
                if_put(ifp);
                ifp = NULL;
                goto reroute;
        }
#endif

#ifdef IPSEC
        if (ISSET(flags, IPV6_FORWARDING) &&
            ISSET(flags, IPV6_FORWARDING_IPSEC) &&
            !ISSET(m->m_pkthdr.ph_tagsset, PACKET_TAG_IPSEC_IN_DONE)) {
                error = EHOSTUNREACH;
                goto senderr;
        }
#endif

        error = if_output_tso(ifp, &m, dst, rt, ifp->if_mtu);
        if (error)
                ip6stat_inc(ip6s_cantforward);
        else if (m == NULL)
                ip6stat_inc(ip6s_forward);
        if (error || m == NULL)
                goto senderr;

        type = ICMP6_PACKET_TOO_BIG;
        destmtu = ifp->if_mtu;
        m_freem(m);
        goto icmperror;

senderr:
        if (mcopy == NULL && icmp_len == 0)
                goto done;

        switch (error) {
        case 0:
                if (type == ND_REDIRECT) {
                        if (icmp_len != 0) {
                                mcopy = m_gethdr(M_DONTWAIT, MT_DATA);
                                if (mcopy == NULL)
                                        goto done;
                                mcopy->m_len = mcopy->m_pkthdr.len = icmp_len;
                                mcopy->m_flags |= (mflags & M_COPYFLAGS);
                                mcopy->m_pkthdr.ph_rtableid = rtableid;
                                mcopy->m_pkthdr.ph_ifidx = ifidx;
                                mcopy->m_pkthdr.ph_loopcnt = loopcnt;
                                mcopy->m_pkthdr.pf.flags |=
                                    (pfflags & PF_TAG_GENERATED);
                                memcpy(mcopy->m_data, icmp_buf, icmp_len);
                        }
                        if (mcopy != NULL) {
                                icmp6_redirect_output(mcopy, rt);
                                ip6stat_inc(ip6s_redirectsent);
                        }
                        goto done;
                }
                goto freecopy;

        case EMSGSIZE:
                type = ICMP6_PACKET_TOO_BIG;
                if (rt != NULL) {
                        u_int rtmtu;

                        rtmtu = atomic_load_int(&rt->rt_mtu);
                        if (rtmtu != 0) {
                                destmtu = rtmtu;
                        } else {
                                struct ifnet *destifp;

                                destifp = if_get(rt->rt_ifidx);
                                if (destifp != NULL)
                                        destmtu = destifp->if_mtu;
                                if_put(destifp);
                        }
                }
                ip6stat_inc(ip6s_cantfrag);
                if (destmtu == 0)
                        goto freecopy;
                break;

        case EACCES:
                /*
                 * pf(4) blocked the packet. There is no need to send an ICMP
                 * packet back since pf(4) takes care of it.
                 */
                goto freecopy;

        case ENOBUFS:
                /* Tell source to slow down like source quench in IP? */
                goto freecopy;

        case ENETUNREACH:       /* shouldn't happen, checked above */
        case EHOSTUNREACH:
        case ENETDOWN:
        case EHOSTDOWN:
        default:
                type = ICMP6_DST_UNREACH;
                code = ICMP6_DST_UNREACH_ADDR;
                break;
        }
 icmperror:
        if (icmp_len != 0) {
                mcopy = m_gethdr(M_DONTWAIT, MT_DATA);
                if (mcopy == NULL)
                        goto done;
                mcopy->m_len = mcopy->m_pkthdr.len = icmp_len;
                mcopy->m_flags |= (mflags & M_COPYFLAGS);
                mcopy->m_pkthdr.ph_rtableid = rtableid;
                mcopy->m_pkthdr.ph_ifidx = ifidx;
                mcopy->m_pkthdr.ph_loopcnt = loopcnt;
                mcopy->m_pkthdr.pf.flags |= (pfflags & PF_TAG_GENERATED);
                memcpy(mcopy->m_data, icmp_buf, icmp_len);
        }
        if (mcopy != NULL)
                icmp6_error(mcopy, type, code, destmtu);
        goto done;

 freecopy:
        m_freem(mcopy);
 done:
        if (ro == &iproute)
                rtfree(ro->ro_rt);
        if_put(ifp);
#ifdef IPSEC
        tdb_unref(tdb);
#endif /* IPSEC */
}