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Use route cache function in IP input.

Instaed of passing a struct rtentry from ip_input() to ip_forward()
and then embed it into a struct route for ip_output(), start with
struct route and pass it along.  Then the route cache is used
consistently.  Also the route cache hit and missed counters should
reflect reality after this commit.

There is a small difference in the code.  in_ouraddr() checks for
NULL and not rtisvalid().  Previous discussion showed that the route
RTF_UP flag should only be considered for multipath routing.
Otherwise it does not mean anything.  Especially the local and
broadcast check in in_ouraddr() should not be affected by interface
link status.

When doing cache lookups, route must be valid, but after rtalloc_mpath()
lookup, use any route that route_mpath() returns.

OK claudio@

/*	$OpenBSD: ip6_forward.c,v 1.117 2024/04/16 12:56:39 bluhm 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/kernel.h>
#include <sys/syslog.h>

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

#include <netinet/in.h>
#include <netinet/ip_var.h>
#include <netinet6/in6_var.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet/icmp6.h>
#include <netinet6/nd6.h>

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

#ifdef IPSEC
#include <netinet/ip_ipsp.h>
#include <netinet/ip_ah.h>
#include <netinet/ip_esp.h>
#include <netinet/udp.h>
#endif
#include <netinet/tcp.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>

/*
 * 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, struct route *ro, int srcrt)
{
	struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
	struct route iproute;
	struct rtentry *rt;
	struct sockaddr *dst;
	struct ifnet *ifp = NULL;
	int error = 0, type = 0, code = 0, destmtu = 0;
	struct mbuf *mcopy;
#ifdef IPSEC
	struct tdb *tdb = NULL;
#endif /* IPSEC */
	char src6[INET6_ADDRSTRLEN], dst6[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 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)) {
		time_t uptime;

		ip6stat_inc(ip6s_cantforward);
		uptime = getuptime();

		if (ip6_log_time + ip6_log_interval < uptime) {
			ip6_log_time = uptime;
			inet_ntop(AF_INET6, &ip6->ip6_src, src6, sizeof(src6));
			inet_ntop(AF_INET6, &ip6->ip6_dst, dst6, sizeof(dst6));
			log(LOG_DEBUG,
			    "cannot forward "
			    "from %s to %s nxt %d received on interface %u\n",
			    src6, dst6,
			    ip6->ip6_nxt,
			    m->m_pkthdr.ph_ifidx);
		}
		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.
	 *
	 * 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);

#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);
		if (mcopy != NULL) {
			icmp6_error(mcopy, ICMP6_DST_UNREACH,
				    ICMP6_DST_UNREACH_NOROUTE, 0);
		}
		m_freem(m);
		goto done;
	}
	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(m->m_pkthdr.ph_ifidx, &ip6->ip6_src) !=
	    in6_addr2scopeid(rt->rt_ifidx, &ip6->ip6_src)) {
		time_t uptime;

		ip6stat_inc(ip6s_cantforward);
		ip6stat_inc(ip6s_badscope);
		uptime = getuptime();

		if (ip6_log_time + ip6_log_interval < uptime) {
			ip6_log_time = uptime;
			inet_ntop(AF_INET6, &ip6->ip6_src, src6, sizeof(src6));
			inet_ntop(AF_INET6, &ip6->ip6_dst, dst6, sizeof(dst6));
			log(LOG_DEBUG,
			    "cannot forward "
			    "src %s, dst %s, nxt %d, rcvif %u, outif %u\n",
			    src6, dst6,
			    ip6->ip6_nxt,
			    m->m_pkthdr.ph_ifidx, rt->rt_ifidx);
		}
		if (mcopy != NULL)
			icmp6_error(mcopy, ICMP6_DST_UNREACH,
				    ICMP6_DST_UNREACH_BEYONDSCOPE, 0);
		m_freem(m);
		goto done;
	}

#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, 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 == m->m_pkthdr.ph_ifidx && !srcrt &&
	    ip6_sendredirects &&
	    (rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0) {
		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.
			 */
			if (mcopy != NULL)
				icmp6_error(mcopy, ICMP6_DST_UNREACH,
				    ICMP6_DST_UNREACH_ADDR, 0);
			m_freem(m);
			goto done;
		}
		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;
		srcrt = 1;
		if (ro == &iproute)
			rtfree(ro->ro_rt);
		ro = NULL;
		if_put(ifp);
		ifp = NULL;
		goto reroute;
	}
#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;

	if (mcopy != NULL)
		icmp6_error(mcopy, ICMP6_PACKET_TOO_BIG, 0, ifp->if_mtu);
	m_freem(m);
	goto done;

senderr:
	if (mcopy == NULL)
		goto done;

	switch (error) {
	case 0:
		if (type == ND_REDIRECT) {
			icmp6_redirect_output(mcopy, rt);
			ip6stat_inc(ip6s_redirectsent);
			goto done;
		}
		goto freecopy;

	case EMSGSIZE:
		type = ICMP6_PACKET_TOO_BIG;
		code = 0;
		if (rt != NULL) {
			if (rt->rt_mtu) {
				destmtu = rt->rt_mtu;
			} 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;
	}
	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 */
}