/* $NetBSD: ip6_forward.c,v 1.103 2024/06/29 13:00:44 riastradh Exp $ */

/* $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. ([email protected])
* 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;
}