/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * 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: ip6_forward.c,v 1.69 2001/05/17 03:48:30 itojun Exp $
 */

#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_ipstealth.h"
#include "opt_sctp.h"

#include <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 <sys/errno.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/syslog.h>

#include <net/if.h>
#include <net/if_var.h>
#include <net/if_private.h>
#include <net/netisr.h>
#include <net/route.h>
#include <net/route/nhop.h>
#include <net/pfil.h>

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_var.h>
#include <netinet6/in6_var.h>
#include <netinet/ip6.h>
#include <netinet6/in6_fib.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>

#include <netinet/in_pcb.h>

#include <netipsec/ipsec_support.h>

#if defined(SCTP) || defined(SCTP_SUPPORT)
#include <netinet/sctp_crc32.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 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 ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
        struct sockaddr_in6 dst;
        struct nhop_object *nh = NULL;
        int error, type = 0, code = 0;
        struct mbuf *mcopy = NULL;
        struct ifnet *origifp;  /* maybe unnecessary */
        u_int32_t inzone, outzone;
        struct in6_addr odst;
        struct m_tag *fwd_tag;
        char ip6bufs[INET6_ADDRSTRLEN], ip6bufd[INET6_ADDRSTRLEN];

        /*
         * 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 the 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) ||
            IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_dst)) {
                IP6STAT_INC(ip6s_cantforward);
                /* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
                if (V_ip6_log_cannot_forward && ip6_log_ratelimit()) {
                        log(LOG_DEBUG,
                            "cannot forward "
                            "from %s to %s nxt %d received on %s\n",
                            ip6_sprintf(ip6bufs, &ip6->ip6_src),
                            ip6_sprintf(ip6bufd, &ip6->ip6_dst),
                            ip6->ip6_nxt,
                            if_name(m->m_pkthdr.rcvif));
                }
                m_freem(m);
                return;
        }

        if (
#ifdef IPSTEALTH
            V_ip6stealth == 0 &&
#endif
            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);
                return;
        }

        /*
         * 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_NOWAIT);
#ifdef IPSTEALTH
        if (V_ip6stealth == 0)
#endif
                ip6->ip6_hlim -= IPV6_HLIMDEC;

#if defined(IPSEC) || defined(IPSEC_SUPPORT)
        if (IPSEC_ENABLED(ipv6)) {
                if ((error = IPSEC_FORWARD(ipv6, m)) != 0) {
                        /* mbuf consumed by IPsec */
                        m_freem(mcopy);
                        if (error != EINPROGRESS)
                                IP6STAT_INC(ip6s_cantforward);
                        return;
                }
                /* No IPsec processing required */
        }
#endif
        /*
         * ip6_forward() operates with IPv6 addresses with deembedded scope.
         *
         * There are 3 sources of IPv6 destination address:
         *
         * 1) ip6_input(), where ip6_dst contains deembedded address.
         *   In order to deal with forwarding of link-local packets,
         *   calculate the scope based on input interface (RFC 4007, clause 9).
         * 2) packet filters changing ip6_dst directly. It would embed scope
         *   for LL addresses, so in6_localip() performs properly.
         * 3) packet filters attaching PACKET_TAG_IPFORWARD would embed
         *   scope for the nexthop.
         */
        bzero(&dst, sizeof(struct sockaddr_in6));
        dst.sin6_family = AF_INET6;
        dst.sin6_addr = ip6->ip6_dst;
        dst.sin6_scope_id = in6_get_unicast_scopeid(&ip6->ip6_dst, m->m_pkthdr.rcvif);
again:
        nh = fib6_lookup(M_GETFIB(m), &dst.sin6_addr, dst.sin6_scope_id,
            NHR_REF, m->m_pkthdr.flowid);
        if (nh == NULL) {
                IP6STAT_INC(ip6s_noroute);
                in6_ifstat_inc(m->m_pkthdr.rcvif, ifs6_in_noroute);
                if (mcopy) {
                        icmp6_error(mcopy, ICMP6_DST_UNREACH,
                        ICMP6_DST_UNREACH_NOROUTE, 0);
                }
                goto bad;
        }

        if (nh->nh_flags & (NHF_BLACKHOLE | NHF_REJECT)) {
                IP6STAT_INC(ip6s_cantforward);
                if (mcopy != NULL) {
                        if (nh->nh_flags & NHF_REJECT) {
                                icmp6_error(mcopy, ICMP6_DST_UNREACH,
                                    ICMP6_DST_UNREACH_REJECT, 0);
                        } else
                                m_freem(mcopy);
                }
                goto bad;
        }

        /*
         * 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).
         * [draft-ietf-ipngwg-icmp-v3-04.txt, Section 3.1]
         */
        outzone = in6_get_unicast_scopeid(&ip6->ip6_src, nh->nh_ifp);
        inzone = in6_get_unicast_scopeid(&ip6->ip6_src, m->m_pkthdr.rcvif);
        if (inzone != outzone) {
                IP6STAT_INC(ip6s_cantforward);
                IP6STAT_INC(ip6s_badscope);
                in6_ifstat_inc(nh->nh_ifp, ifs6_in_discard);

                if (V_ip6_log_cannot_forward && ip6_log_ratelimit()) {
                        log(LOG_DEBUG,
                            "cannot forward "
                            "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
                            ip6_sprintf(ip6bufs, &ip6->ip6_src),
                            ip6_sprintf(ip6bufd, &ip6->ip6_dst),
                            ip6->ip6_nxt,
                            if_name(m->m_pkthdr.rcvif), if_name(nh->nh_ifp));
                }
                if (mcopy)
                        icmp6_error(mcopy, ICMP6_DST_UNREACH,
                                    ICMP6_DST_UNREACH_BEYONDSCOPE, 0);
                goto bad;
        }

        /*
         * 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.
         */
        inzone = in6_get_unicast_scopeid(&ip6->ip6_dst, m->m_pkthdr.rcvif);
        outzone = in6_get_unicast_scopeid(&ip6->ip6_dst, nh->nh_ifp);

        if (inzone != outzone) {
                IP6STAT_INC(ip6s_cantforward);
                IP6STAT_INC(ip6s_badscope);
                goto bad;
        }

        if (nh->nh_flags & NHF_GATEWAY) {
                /* Store gateway address in deembedded form */
                dst.sin6_addr = nh->gw6_sa.sin6_addr;
                dst.sin6_scope_id = ntohs(in6_getscope(&dst.sin6_addr));
                in6_clearscope(&dst.sin6_addr);
        }

        /*
         * 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 (V_ip6_sendredirects && nh->nh_ifp == m->m_pkthdr.rcvif && !srcrt &&
            (nh->nh_flags & NHF_REDIRECT) == 0)
                type = ND_REDIRECT;

        /*
         * Fake scoped addresses. Note that even link-local source or
         * destinaion 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 ((nh->nh_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
                {
                        printf("ip6_forward: outgoing interface is loopback. "
                               "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
                               ip6_sprintf(ip6bufs, &ip6->ip6_src),
                               ip6_sprintf(ip6bufd, &ip6->ip6_dst),
                               ip6->ip6_nxt, if_name(m->m_pkthdr.rcvif),
                               if_name(nh->nh_ifp));
                }

                /* we can just use rcvif in forwarding. */
                origifp = m->m_pkthdr.rcvif;
        }
        else
                origifp = nh->nh_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);

        /* Jump over all PFIL processing if hooks are not active. */
        if (!PFIL_HOOKED_OUT(V_inet6_pfil_head))
                goto pass;

        odst = ip6->ip6_dst;
        /* Run through list of hooks for forwarded packets. */
        if (pfil_mbuf_fwd(V_inet6_pfil_head, &m, nh->nh_ifp,
            NULL) != PFIL_PASS)
                goto freecopy;
        ip6 = mtod(m, struct ip6_hdr *);

        /* See if destination IP address was changed by packet filter. */
        if (!IN6_ARE_ADDR_EQUAL(&odst, &ip6->ip6_dst)) {
                m->m_flags |= M_SKIP_FIREWALL;
                /* If destination is now ourself drop to ip6_input(). */
                if (in6_localip(&ip6->ip6_dst))
                        m->m_flags |= M_FASTFWD_OURS;
                else {
                        NH_FREE(nh);

                        /* Update address and scopeid. Assume scope is embedded */
                        dst.sin6_scope_id = ntohs(in6_getscope(&ip6->ip6_dst));
                        dst.sin6_addr = ip6->ip6_dst;
                        in6_clearscope(&dst.sin6_addr);
                        goto again;     /* Redo the routing table lookup. */
                }
        }

        /* See if local, if yes, send it to netisr. */
        if (m->m_flags & M_FASTFWD_OURS) {
                if (m->m_pkthdr.rcvif == NULL)
                        m->m_pkthdr.rcvif = V_loif;
                if (m->m_pkthdr.csum_flags & CSUM_DELAY_DATA_IPV6) {
                        m->m_pkthdr.csum_flags |=
                            CSUM_DATA_VALID_IPV6 | CSUM_PSEUDO_HDR;
                        m->m_pkthdr.csum_data = 0xffff;
                }
#if defined(SCTP) || defined(SCTP_SUPPORT)
                if (m->m_pkthdr.csum_flags & CSUM_SCTP_IPV6)
                        m->m_pkthdr.csum_flags |= CSUM_SCTP_VALID;
#endif
                error = netisr_queue(NETISR_IPV6, m);
                goto out;
        }
        /* Or forward to some other address? */
        if ((m->m_flags & M_IP6_NEXTHOP) &&
            (fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL)) != NULL) {
                struct sockaddr_in6 *gw6 = (struct sockaddr_in6 *)(fwd_tag + 1);

                /* Update address and scopeid. Assume scope is embedded */
                dst.sin6_scope_id = ntohs(in6_getscope(&gw6->sin6_addr));
                dst.sin6_addr = gw6->sin6_addr;
                in6_clearscope(&dst.sin6_addr);

                m->m_flags |= M_SKIP_FIREWALL;
                m->m_flags &= ~M_IP6_NEXTHOP;
                m_tag_delete(m, fwd_tag);
                NH_FREE(nh);
                goto again;
        }

pass:
        /* See if the size was changed by the packet filter. */
        /* TODO: change to nh->nh_mtu */
        if (m->m_pkthdr.len > in6_ifmtu(nh->nh_ifp)) {
                in6_ifstat_inc(nh->nh_ifp, ifs6_in_toobig);
                if (mcopy)
                        icmp6_error(mcopy, ICMP6_PACKET_TOO_BIG, 0,
                            in6_ifmtu(nh->nh_ifp));
                goto bad;
        }

        /*
         * If TCP/UDP header still needs a valid checksum and interface will not
         * calculate it for us, do it here.
         */
        if (__predict_false(m->m_pkthdr.csum_flags & CSUM_DELAY_DATA_IPV6 &
            ~nh->nh_ifp->if_hwassist)) {
                int offset = ip6_lasthdr(m, 0, IPPROTO_IPV6, NULL);

                if (offset < sizeof(struct ip6_hdr) || offset > m->m_pkthdr.len)
                        goto bad;
                in6_delayed_cksum(m, m->m_pkthdr.len - offset, offset);
                m->m_pkthdr.csum_flags &= ~CSUM_DELAY_DATA_IPV6;
        }
#if defined(SCTP) || defined(SCTP_SUPPORT)
        if (__predict_false(m->m_pkthdr.csum_flags & CSUM_IP6_SCTP &
            ~nh->nh_ifp->if_hwassist)) {
                int offset = ip6_lasthdr(m, 0, IPPROTO_IPV6, NULL);

                sctp_delayed_cksum(m, offset);
                m->m_pkthdr.csum_flags &= ~CSUM_IP6_SCTP;
        }
#endif

        /* Currently LLE layer stores embedded IPv6 addresses */
        if (IN6_IS_SCOPE_LINKLOCAL(&dst.sin6_addr)) {
                in6_set_unicast_scopeid(&dst.sin6_addr, dst.sin6_scope_id);
                dst.sin6_scope_id = 0;
        }
        error = nd6_output_ifp(nh->nh_ifp, origifp, m, &dst, NULL);
        if (error) {
                in6_ifstat_inc(nh->nh_ifp, ifs6_out_discard);
                IP6STAT_INC(ip6s_cantforward);
        } else {
                IP6STAT_INC(ip6s_forward);
                in6_ifstat_inc(nh->nh_ifp, ifs6_out_forward);
                if (type)
                        IP6STAT_INC(ip6s_redirectsent);
                else {
                        if (mcopy)
                                goto freecopy;
                }
        }

        if (mcopy == NULL)
                goto out;
        switch (error) {
        case 0:
                if (type == ND_REDIRECT) {
                        icmp6_redirect_output(mcopy, nh);
                        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;
bad:
        m_freem(m);
out:
        if (nh != NULL)
                NH_FREE(nh);
}