/*      $NetBSD: ip6_forward.c,v 1.103 2024/06/29 13:00:44 riastradh Exp $      */
/*      $KAME: ip6_forward.c,v 1.109 2002/09/11 08:10:17 sakane 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: ip6_forward.c,v 1.103 2024/06/29 13:00:44 riastradh Exp $");

#ifdef _KERNEL_OPT
#include "opt_gateway.h"
#include "opt_ipsec.h"
#endif

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

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

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/ip_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/ip6_private.h>
#include <netinet6/scope6_var.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>

#ifdef IPSEC
#include <netipsec/ipsec.h>
#include <netipsec/ipsec6.h>
#include <netipsec/key.h>
#endif

extern percpu_t *ip6_forward_rt_percpu;

extern pfil_head_t *inet6_pfil_hook;    /* XXX */

static void __printflike(4, 5)
ip6_cantforward(const struct ip6_hdr *ip6, const struct ifnet *srcifp,
    const struct ifnet *dstifp, const char *fmt, ...)
{
        char sbuf[INET6_ADDRSTRLEN], dbuf[INET6_ADDRSTRLEN];
        char reason[256];
        va_list ap;
        net_stat_ref_t ip6s;

        /* update statistics */
        ip6s = IP6_STAT_GETREF();
        _NET_STATINC_REF(ip6s, IP6_STAT_CANTFORWARD);
        if (dstifp)
                _NET_STATINC_REF(ip6s, IP6_STAT_BADSCOPE);
        IP6_STAT_PUTREF();

        if (dstifp)
                in6_ifstat_inc(dstifp, ifs6_in_discard);

        if (ip6_log_time + ip6_log_interval >= time_uptime)
                return;
        ip6_log_time = time_uptime;

        va_start(ap, fmt);
        vsnprintf(reason, sizeof(reason), fmt, ap);
        va_end(ap);

        log(LOG_DEBUG, "Cannot forward from %s@%s to %s@%s nxt %d (%s)\n",
            IN6_PRINT(sbuf, &ip6->ip6_src), srcifp ? if_name(srcifp) : "?",
            IN6_PRINT(dbuf, &ip6->ip6_dst), dstifp ? if_name(dstifp) : "?",
            ip6->ip6_nxt, reason);
}

/*
 * 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 ipforwarding 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, int srcrt, struct ifnet *rcvif)
{
        struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
        const struct sockaddr_in6 *dst;
        struct rtentry *rt = NULL;
        int error = 0, type = 0, code = 0;
        struct mbuf *mcopy = NULL;
        struct ifnet *origifp;  /* maybe unnecessary */
        uint32_t inzone, outzone;
        struct in6_addr src_in6, dst_in6;
        struct route *ro = NULL;
#ifdef IPSEC
        int needipsec = 0;
        struct secpolicy *sp = NULL;
#endif

        /*
         * Clear any in-bound checksum flags for this packet.
         */
        m->m_pkthdr.csum_flags = 0;

        /*
         * 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)) {
                ip6_cantforward(ip6, rcvif, NULL,
                    ((m->m_flags & (M_BCAST|M_MCAST)) != 0) ? "bcast/mcast" :
                    IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ? "mcast/dst" :
                    "unspec/src");
                goto drop;
        }

        if (ip6->ip6_hlim <= IPV6_HLIMDEC) {
                /* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
                icmp6_error(m, ICMP6_TIME_EXCEEDED,
                                ICMP6_TIME_EXCEED_TRANSIT, 0);
                goto out;
        }
        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.
         *
         * It is important to save it before IPsec processing as IPsec
         * processing may modify the mbuf.
         */
        mcopy = m_copym(m, 0, imin(m->m_pkthdr.len, ICMPV6_PLD_MAXLEN),
            M_DONTWAIT);

#ifdef IPSEC
        if (ipsec_used) {
                /* Check the security policy (SP) for the packet */
                sp = ipsec6_check_policy(m, NULL, 0, &needipsec, &error);
                if (error != 0) {
                        /*
                         * Hack: -EINVAL is used to signal that a packet
                         * should be silently discarded.  This is typically
                         * because we asked key management for an SA and
                         * it was delayed (e.g. kicked up to IKE).
                         */
                        if (error == -EINVAL)
                                error = 0;
                        m_freem(m);
                        IP6_STATINC(IP6_STAT_IPSECDROP_OUT);
                        goto freecopy;
                }
        }
#endif

        ro = rtcache_percpu_getref(ip6_forward_rt_percpu);
        if (srcrt) {
                union {
                        struct sockaddr         dst;
                        struct sockaddr_in6     dst6;
                } u;

                sockaddr_in6_init(&u.dst6, &ip6->ip6_dst, 0, 0, 0);
                rt = rtcache_lookup(ro, &u.dst);
                if (rt == NULL) {
                        IP6_STATINC(IP6_STAT_NOROUTE);
                        /* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_noroute) */
                        if (mcopy) {
                                icmp6_error(mcopy, ICMP6_DST_UNREACH,
                                            ICMP6_DST_UNREACH_NOROUTE, 0);
                        }
                        goto drop;
                }
        } else if ((rt = rtcache_validate(ro)) == NULL &&
                   (rt = rtcache_update(ro, 1)) == NULL) {
                /*
                 * rtcache_getdst(ip6_forward_rt)->sin6_addr was equal to
                 * ip6->ip6_dst
                 */
                IP6_STATINC(IP6_STAT_NOROUTE);
                /* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_noroute) */
                if (mcopy) {
                        icmp6_error(mcopy, ICMP6_DST_UNREACH,
                            ICMP6_DST_UNREACH_NOROUTE, 0);
                }
                goto drop;
        }
        dst = satocsin6(rtcache_getdst(ro));

        /*
         * Source 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).  We use a local copy of ip6_src, since in6_setscope()
         * will possibly modify its first argument.
         * [draft-ietf-ipngwg-icmp-v3-07, Section 3.1]
         */
        src_in6 = ip6->ip6_src;
        inzone = outzone = ~0;
        if (in6_setscope(&src_in6, rt->rt_ifp, &outzone) != 0 ||
            in6_setscope(&src_in6, rcvif, &inzone) != 0 ||
            inzone != outzone) {
                ip6_cantforward(ip6, rcvif, rt->rt_ifp,
                    "src[%s] inzone %d outzone %d",
                    in6_getscopename(&ip6->ip6_src), inzone, outzone);
                if (mcopy)
                        icmp6_error(mcopy, ICMP6_DST_UNREACH,
                                    ICMP6_DST_UNREACH_BEYONDSCOPE, 0);
                goto drop;
        }

#ifdef IPSEC
        /*
         * If we need to encapsulate the packet, do it here.
         * ipsec6_process_packet will send the packet using ip6_output.
         */
        if (needipsec) {
                int s = splsoftnet();
                error = ipsec6_process_packet(m, sp->req, 0);
                splx(s);
                /* m is freed */
                if (mcopy)
                        goto freecopy;
                goto out;
        }
#endif

        /*
         * Destination scope check: if a packet is going to break the scope
         * zone of packet's destination address, discard it.  This case should
         * usually be prevented by appropriately-configured routing table, but
         * we need an explicit check because we may mistakenly forward the
         * packet to a different zone by (e.g.) a default route.
         */
        dst_in6 = ip6->ip6_dst;
        inzone = outzone = ~0;
        if (in6_setscope(&dst_in6, rcvif, &inzone) != 0 ||
            in6_setscope(&dst_in6, rt->rt_ifp, &outzone) != 0 ||
            inzone != outzone) {
                ip6_cantforward(ip6, rcvif, rt->rt_ifp,
                    "dst[%s] inzone %d outzone %d",
                    in6_getscopename(&ip6->ip6_dst), inzone, outzone);
                if (mcopy)
                        icmp6_error(mcopy, ICMP6_DST_UNREACH,
                                    ICMP6_DST_UNREACH_BEYONDSCOPE, 0);
                goto drop;
        }

        if (m->m_pkthdr.len > rt->rt_ifp->if_mtu) {
                IP6_STATINC(IP6_STAT_TOOBIG);
                in6_ifstat_inc(rt->rt_ifp, ifs6_in_toobig);
                if (mcopy)
                        icmp6_error(mcopy, ICMP6_PACKET_TOO_BIG, 0,
                            rt->rt_ifp->if_mtu);
                goto drop;
        }

        if (rt->rt_flags & RTF_GATEWAY)
                dst = (struct sockaddr_in6 *)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.
         */
        if (rt->rt_ifp == rcvif && !srcrt && ip6_sendredirects &&
            (rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0) {
                if ((rt->rt_ifp->if_flags & IFF_POINTOPOINT) &&
                    nd6_is_addr_neighbor(satocsin6(rtcache_getdst(ro)),
                                         rt->rt_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.
                         */
                        icmp6_error(mcopy, ICMP6_DST_UNREACH,
                                    ICMP6_DST_UNREACH_ADDR, 0);
                        goto drop;
                }
                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 ((rt->rt_ifp->if_flags & IFF_LOOPBACK) != 0) {
                /*
                 * See corresponding comments in ip6_output.
                 * XXX: but is it possible that ip6_forward() sends a packet
                 *      to a loopback interface? I don't think so, and thus
                 *      I bark here. (jinmei@kame.net)
                 * XXX: it is common to route invalid packets to loopback.
                 *      also, the codepath will be visited on use of ::1 in
                 *      rthdr. (itojun)
                 */
#if 1
                if (0)
#else
                if ((rt->rt_flags & (RTF_BLACKHOLE|RTF_REJECT)) == 0)
#endif
                {
                        char ip6bufs[INET6_ADDRSTRLEN];
                        char ip6bufd[INET6_ADDRSTRLEN];

                        printf("ip6_forward: outgoing interface is loopback. "
                               "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
                               IN6_PRINT(ip6bufs, &ip6->ip6_src),
                               IN6_PRINT(ip6bufd, &ip6->ip6_dst),
                               ip6->ip6_nxt, if_name(rcvif),
                               if_name(rt->rt_ifp));
                }

                /* we can just use rcvif in forwarding. */
                origifp = rcvif;
        } else {
                origifp = rt->rt_ifp;
        }

        /*
         * clear embedded scope identifiers if necessary.
         * in6_clearscope will touch the addresses only when necessary.
         */
        in6_clearscope(&ip6->ip6_src);
        in6_clearscope(&ip6->ip6_dst);

        /*
         * Run through list of hooks for output packets.
         */
        if ((error = pfil_run_hooks(inet6_pfil_hook, &m, rt->rt_ifp,
            PFIL_OUT)) != 0) {
                IP6_STATINC(IP6_STAT_PFILDROP_OUT);
                goto senderr;
        }
        if (m == NULL) {
                IP6_STATINC(IP6_STAT_PFILDROP_OUT);
                goto freecopy;
        }
        ip6 = mtod(m, struct ip6_hdr *);

        error = ip6_if_output(rt->rt_ifp, origifp, m, dst, rt);
        if (error) {
                in6_ifstat_inc(rt->rt_ifp, ifs6_out_discard);
                IP6_STATINC(IP6_STAT_CANTFORWARD);
        } else {
                IP6_STATINC(IP6_STAT_FORWARD);
                in6_ifstat_inc(rt->rt_ifp, ifs6_out_forward);
                if (type)
                        IP6_STATINC(IP6_STAT_REDIRECTSENT);
                else {
#ifdef GATEWAY
                        /* Need to release rt here */
                        rtcache_unref(rt, ro);
                        rt = NULL;
                        if (mcopy->m_flags & M_CANFASTFWD)
                                ip6flow_create(ro, mcopy);
#endif
                        if (mcopy)
                                goto freecopy;
                }
        }

senderr:
        if (mcopy == NULL)
                goto out;
        switch (error) {
        case 0:
                if (type == ND_REDIRECT) {
                        icmp6_redirect_output(mcopy, rt);
                        goto out;
                }
                goto freecopy;

        case EMSGSIZE:
                /* xxx MTU is constant in PPP? */
                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;
        }
        icmp6_error(mcopy, type, code, 0);
        goto out;

freecopy:
        m_freem(mcopy);
        goto out;

drop:
        m_freem(m);

out:
#ifdef IPSEC
        if (sp != NULL)
                KEY_SP_UNREF(&sp);
#endif
        rtcache_unref(rt, ro);
        if (ro != NULL)
                rtcache_percpu_putref(ip6_forward_rt_percpu);
        return;
}