예제 #1
0
파일: ip6_forward.c 프로젝트: Algozjb/xnu
struct mbuf *
ip6_forward(struct mbuf *m, struct route_in6 *ip6forward_rt,
    int srcrt)
{
	struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);
	struct sockaddr_in6 *dst;
	struct rtentry *rt;
	int error, type = 0, code = 0;
	boolean_t proxy = FALSE;
	struct mbuf *mcopy = NULL;
	struct ifnet *ifp, *origifp;	/* maybe unnecessary */
	u_int32_t inzone, outzone;
	struct in6_addr src_in6, dst_in6;
#if IPSEC
	struct secpolicy *sp = NULL;
#endif
	struct timeval timenow;
	unsigned int ifscope = IFSCOPE_NONE;
#if PF
	struct pf_mtag *pf_mtag;
#endif /* PF */

	getmicrotime(&timenow);
#if PF
	pf_mtag = pf_find_mtag(m);
	if (pf_mtag != NULL && pf_mtag->pftag_rtableid != IFSCOPE_NONE)
		ifscope = pf_mtag->pftag_rtableid;

	/*
	 * If the caller provides a route which is on a different interface
	 * than the one specified for scoped forwarding, discard the route
	 * and do a lookup below.
	 */
	if (ifscope != IFSCOPE_NONE && (rt = ip6forward_rt->ro_rt) != NULL) {
		RT_LOCK(rt);
		if (rt->rt_ifp->if_index != ifscope) {
			RT_UNLOCK(rt);
			rtfree(rt);
			rt = ip6forward_rt->ro_rt = NULL;
		} else {
			RT_UNLOCK(rt);
		}
	}
#endif /* PF */

#if IPSEC
	/*
	 * Check AH/ESP integrity.
	 */
	/*
	 * Don't increment ip6s_cantforward because this is the check
	 * before forwarding packet actually.
	 */
	if (ipsec_bypass == 0) {
		if (ipsec6_in_reject(m, NULL)) {
			IPSEC_STAT_INCREMENT(ipsec6stat.in_polvio);
			m_freem(m);
			return (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.ip6s_cantforward++;
		/* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard) */
		if (ip6_log_time + ip6_log_interval < timenow.tv_sec) {
			ip6_log_time = timenow.tv_sec;
			log(LOG_DEBUG,
			    "cannot forward "
			    "from %s to %s nxt %d received on %s\n",
			    ip6_sprintf(&ip6->ip6_src),
			    ip6_sprintf(&ip6->ip6_dst),
			    ip6->ip6_nxt,
			    if_name(m->m_pkthdr.rcvif));
		}
		m_freem(m);
		return (NULL);
	}

	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);
		return (NULL);
	}

	/*
	 * See if the destination is a proxied address, and if so pretend
	 * that it's for us.  This is mostly to handle NUD probes against
	 * the proxied addresses.  We filter for ICMPv6 here and will let
	 * icmp6_input handle the rest.
	 */
	if (!srcrt && nd6_prproxy) {
		VERIFY(!IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst));
		proxy = nd6_prproxy_isours(m, ip6, ip6forward_rt, ifscope);
		/*
		 * Don't update hop limit while proxying; RFC 4389 4.1.
		 * Also skip IPsec forwarding path processing as this
		 * packet is not to be forwarded.
		 */
		if (proxy)
			goto skip_ipsec;
	}

	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_copy(m, 0, imin(m->m_pkthdr.len, ICMPV6_PLD_MAXLEN));

#if IPSEC
	if (ipsec_bypass != 0)
		goto skip_ipsec;
	/* get a security policy for this packet */
	sp = ipsec6_getpolicybyaddr(m, IPSEC_DIR_OUTBOUND, IP_FORWARDING,
	    &error);
	if (sp == NULL) {
		IPSEC_STAT_INCREMENT(ipsec6stat.out_inval);
		ip6stat.ip6s_cantforward++;
		if (mcopy) {
#if 0
			/* XXX: what icmp ? */
#else
			m_freem(mcopy);
#endif
		}
		m_freem(m);
		return (NULL);
	}

	error = 0;

	/* check policy */
	switch (sp->policy) {
	case IPSEC_POLICY_DISCARD:
        case IPSEC_POLICY_GENERATE:
		/*
		 * This packet is just discarded.
		 */
		IPSEC_STAT_INCREMENT(ipsec6stat.out_polvio);
		ip6stat.ip6s_cantforward++;
		key_freesp(sp, KEY_SADB_UNLOCKED);
		if (mcopy) {
#if 0
			/* XXX: what icmp ? */
#else
			m_freem(mcopy);
#endif
		}
		m_freem(m);
		return (NULL);

	case IPSEC_POLICY_BYPASS:
	case IPSEC_POLICY_NONE:
		/* no need to do IPsec. */
		key_freesp(sp, KEY_SADB_UNLOCKED);
		goto skip_ipsec;

	case IPSEC_POLICY_IPSEC:
		if (sp->req == NULL) {
			/* XXX should be panic ? */
			printf("ip6_forward: No IPsec request specified.\n");
			ip6stat.ip6s_cantforward++;
			key_freesp(sp, KEY_SADB_UNLOCKED);
			if (mcopy) {
#if 0
				/* XXX: what icmp ? */
#else
				m_freem(mcopy);
#endif
			}
			m_freem(m);
			return (NULL);
		}
		/* do IPsec */
		break;

	case IPSEC_POLICY_ENTRUST:
	default:
		/* should be panic ?? */
		printf("ip6_forward: Invalid policy found. %d\n", sp->policy);
		key_freesp(sp, KEY_SADB_UNLOCKED);
		goto skip_ipsec;
	}

    {
	struct ipsec_output_state state;

	/*
	 * All the extension headers will become inaccessible
	 * (since they can be encrypted).
	 * Don't panic, we need no more updates to extension headers
	 * on inner IPv6 packet (since they are now encapsulated).
	 *
	 * IPv6 [ESP|AH] IPv6 [extension headers] payload
	 */
	bzero(&state, sizeof(state));
	state.m = m;
	state.dst = NULL;	/* update at ipsec6_output_tunnel() */

	error = ipsec6_output_tunnel(&state, sp, 0);
	key_freesp(sp, KEY_SADB_UNLOCKED);
	if (state.tunneled == 4)
		return (NULL);  /* packet is gone - sent over IPv4 */
		
	m = state.m;
	if (state.ro.ro_rt) {
		rtfree(state.ro.ro_rt);
		state.ro.ro_rt = NULL;
	}
	if (error) {
		/* mbuf is already reclaimed in ipsec6_output_tunnel. */
		switch (error) {
		case EHOSTUNREACH:
		case ENETUNREACH:
		case EMSGSIZE:
		case ENOBUFS:
		case ENOMEM:
			break;
		default:
			printf("ip6_output (ipsec): error code %d\n", error);
			/* fall through */
		case ENOENT:
			/* don't show these error codes to the user */
			break;
		}
		ip6stat.ip6s_cantforward++;
		if (mcopy) {
#if 0
			/* XXX: what icmp ? */
#else
			m_freem(mcopy);
#endif
		}
		m_freem(m);
		return (NULL);
	}
    }
    skip_ipsec:
#endif /* IPSEC */

	dst = (struct sockaddr_in6 *)&ip6forward_rt->ro_dst;
	if ((rt = ip6forward_rt->ro_rt) != NULL) {
		RT_LOCK(rt);
		/* Take an extra ref for ourselves */
		RT_ADDREF_LOCKED(rt);
	}

	if (!srcrt) {
		/*
		 * ip6forward_rt->ro_dst.sin6_addr is equal to ip6->ip6_dst
		 */
		if (rt == NULL || !(rt->rt_flags & RTF_UP) ||
		    rt->generation_id != route_generation) {
			if (rt != NULL) {
				/* Release extra ref */
				RT_REMREF_LOCKED(rt);
				RT_UNLOCK(rt);
				rtfree(rt);
				ip6forward_rt->ro_rt = NULL;
			}
			/* this probably fails but give it a try again */
			rtalloc_scoped_ign((struct route *)ip6forward_rt,
			    RTF_PRCLONING, ifscope);
			if ((rt = ip6forward_rt->ro_rt) != NULL) {
				RT_LOCK(rt);
				/* Take an extra ref for ourselves */
				RT_ADDREF_LOCKED(rt);
			}
		}

		if (rt == NULL) {
			ip6stat.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);
			m_freem(m);
			return (NULL);
		}
		RT_LOCK_ASSERT_HELD(rt);
	} else if (rt == NULL || !(rt->rt_flags & RTF_UP) ||
	    !IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &dst->sin6_addr) ||
	    rt->generation_id != route_generation) {
		if (rt != NULL) {
			/* Release extra ref */
			RT_REMREF_LOCKED(rt);
			RT_UNLOCK(rt);
			rtfree(rt);
			ip6forward_rt->ro_rt = NULL;
		}
		bzero(dst, sizeof(*dst));
		dst->sin6_len = sizeof(struct sockaddr_in6);
		dst->sin6_family = AF_INET6;
		dst->sin6_addr = ip6->ip6_dst;

		rtalloc_scoped_ign((struct route *)ip6forward_rt,
		    RTF_PRCLONING, ifscope);
		if ((rt = ip6forward_rt->ro_rt) == NULL) {
			ip6stat.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);
			m_freem(m);
			return (NULL);
		}
		RT_LOCK(rt);
		/* Take an extra ref for ourselves */
		RT_ADDREF_LOCKED(rt);
	}

	/*
	 * 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) unless we are proxying (source address is link local
	 * for NUDs.)  We use a local copy of ip6_src, since in6_setscope()
	 * will possibly modify its first argument.
	 * [draft-ietf-ipngwg-icmp-v3-04.txt, Section 3.1]
	 */
	src_in6 = ip6->ip6_src;
	if (in6_setscope(&src_in6, rt->rt_ifp, &outzone)) {
		/* XXX: this should not happen */
		ip6stat.ip6s_cantforward++;
		ip6stat.ip6s_badscope++;
		m_freem(m);
		return (NULL);
	}
	if (in6_setscope(&src_in6, m->m_pkthdr.rcvif, &inzone)) {
		ip6stat.ip6s_cantforward++;
		ip6stat.ip6s_badscope++;
		m_freem(m);
		return (NULL);
	}

	if (inzone != outzone && !proxy) {
		ip6stat.ip6s_cantforward++;
		ip6stat.ip6s_badscope++;
		in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard);

		if (ip6_log_time + ip6_log_interval < timenow.tv_sec) {
			ip6_log_time = timenow.tv_sec;
			log(LOG_DEBUG,
			    "cannot forward "
			    "src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
			    ip6_sprintf(&ip6->ip6_src),
			    ip6_sprintf(&ip6->ip6_dst),
			    ip6->ip6_nxt,
			    if_name(m->m_pkthdr.rcvif), if_name(rt->rt_ifp));
		}
		/* Release extra ref */
		RT_REMREF_LOCKED(rt);
		RT_UNLOCK(rt);
		if (mcopy) {
			icmp6_error(mcopy, ICMP6_DST_UNREACH,
				    ICMP6_DST_UNREACH_BEYONDSCOPE, 0);
		}
		m_freem(m);
		return (NULL);
	}

	/*
	 * 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;
	if (in6_setscope(&dst_in6, m->m_pkthdr.rcvif, &inzone) != 0 ||
	    in6_setscope(&dst_in6, rt->rt_ifp, &outzone) != 0 ||
	    inzone != outzone) {
		ip6stat.ip6s_cantforward++;
		ip6stat.ip6s_badscope++;
		m_freem(m);
		return (NULL);
	}

	if (m->m_pkthdr.len > rt->rt_ifp->if_mtu) {
		in6_ifstat_inc(rt->rt_ifp, ifs6_in_toobig);
		if (mcopy) {
			uint32_t mtu;
#if IPSEC
			struct secpolicy *sp2;
			int ipsecerror;
			size_t ipsechdrsiz;
#endif

			mtu = rt->rt_ifp->if_mtu;
#if IPSEC
			/*
			 * When we do IPsec tunnel ingress, we need to play
			 * with the link value (decrement IPsec header size
			 * from mtu value).  The code is much simpler than v4
			 * case, as we have the outgoing interface for
			 * encapsulated packet as "rt->rt_ifp".
			 */
			sp2 = ipsec6_getpolicybyaddr(mcopy, IPSEC_DIR_OUTBOUND,
				IP_FORWARDING, &ipsecerror);
			if (sp2) {
				ipsechdrsiz = ipsec6_hdrsiz(mcopy,
					IPSEC_DIR_OUTBOUND, NULL);
				if (ipsechdrsiz < mtu)
					mtu -= ipsechdrsiz;
				key_freesp(sp2, KEY_SADB_UNLOCKED);
			}
			/*
			 * if mtu becomes less than minimum MTU,
			 * tell minimum MTU (and I'll need to fragment it).
			 */
			if (mtu < IPV6_MMTU)
				mtu = IPV6_MMTU;
#endif
			/* Release extra ref */
			RT_REMREF_LOCKED(rt);
			RT_UNLOCK(rt);
			icmp6_error(mcopy, ICMP6_PACKET_TOO_BIG, 0, mtu);
		} else {
			/* Release extra ref */
			RT_REMREF_LOCKED(rt);
			RT_UNLOCK(rt);
		}
		m_freem(m);
		return (NULL);
 	}

	if (rt->rt_flags & RTF_GATEWAY)
		dst = (struct sockaddr_in6 *)(void *)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 (!proxy &&
	    ip6_sendredirects && rt->rt_ifp == m->m_pkthdr.rcvif && !srcrt &&
	    (rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0) {
		if ((rt->rt_ifp->if_flags & IFF_POINTOPOINT) != 0) {
			/*
			 * If the incoming interface is equal to the outgoing
			 * one, and the link attached to the interface is
			 * point-to-point, then it will be highly probable
			 * that a routing loop occurs. Thus, we immediately
			 * drop the packet and send an ICMPv6 error message.
			 *
			 * type/code is based on suggestion by Rich Draves.
			 * not sure if it is the best pick.
			 */
			RT_REMREF_LOCKED(rt);	/* Release extra ref */
			RT_UNLOCK(rt);
			icmp6_error(mcopy, ICMP6_DST_UNREACH,
				    ICMP6_DST_UNREACH_ADDR, 0);
			m_freem(m);
			return (NULL);
		}
		type = ND_REDIRECT;
	}

#if IPFW2
	/*
	 * Check with the firewall...
	 */
	if (ip6_fw_enable && ip6_fw_chk_ptr) {
		u_short port = 0;
		ifp = rt->rt_ifp;
		/* Drop the lock but retain the extra ref */
		RT_UNLOCK(rt);
		/* If ipfw says divert, we have to just drop packet */
		if (ip6_fw_chk_ptr(&ip6, ifp, &port, &m)) {
			m_freem(m);
			goto freecopy;
		}
		if (!m) {
			goto freecopy;
		}
		/* We still have the extra ref on rt */
		RT_LOCK(rt);
	}
#endif

	/*
	 * 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 ((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
		{
			printf("ip6_forward: outgoing interface is loopback. "
				"src %s, dst %s, nxt %d, rcvif %s, outif %s\n",
				ip6_sprintf(&ip6->ip6_src),
				ip6_sprintf(&ip6->ip6_dst),
				ip6->ip6_nxt, if_name(m->m_pkthdr.rcvif),
				if_name(rt->rt_ifp));
		}

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

	ifp = rt->rt_ifp;
	/* Drop the lock but retain the extra ref */
	RT_UNLOCK(rt);

	/*
	 * If this is to be processed locally, let ip6_input have it.
	 */
	if (proxy) {
		VERIFY(m->m_pkthdr.aux_flags & MAUXF_PROXY_DST);
		/* Release extra ref */
		RT_REMREF(rt);
		if (mcopy != NULL)
			m_freem(mcopy);
		return (m);
	}

#if PF
	/* Invoke outbound packet filter */
	error = pf_af_hook(ifp, NULL, &m, AF_INET6, FALSE, NULL);

	if (error != 0 || m == NULL) {
		if (m != NULL) {
			panic("%s: unexpected packet %p\n", __func__, m);
			/* NOTREACHED */
		}
		/* Already freed by callee */
		goto senderr;
	}
	ip6 = mtod(m, struct ip6_hdr *);
#endif /* PF */

	error = nd6_output(ifp, origifp, m, dst, rt, NULL);
	if (error) {
		in6_ifstat_inc(ifp, ifs6_out_discard);
		ip6stat.ip6s_cantforward++;
	} else {
		ip6stat.ip6s_forward++;
		in6_ifstat_inc(ifp, ifs6_out_forward);
		if (type)
			ip6stat.ip6s_redirectsent++;
		else {
			if (mcopy) {
				goto freecopy;
			}
		}
	}
#if PF
senderr:
#endif /* PF */
	if (mcopy == NULL) {
		/* Release extra ref */
		RT_REMREF(rt);
		return (NULL);
	}
	switch (error) {
	case 0:
#if 1
		if (type == ND_REDIRECT) {
			icmp6_redirect_output(mcopy, rt);
			/* Release extra ref */
			RT_REMREF(rt);
			return (NULL);
		}
#endif
		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);
	/* Release extra ref */
	RT_REMREF(rt);
	return (NULL);

 freecopy:
	m_freem(mcopy);
	/* Release extra ref */
	RT_REMREF(rt);
	return (NULL);
}
예제 #2
0
파일: in_arp.c 프로젝트: SbIm/xnu-env
__private_extern__ errno_t
arp_route_to_gateway_route(const struct sockaddr *net_dest, route_t hint0,
     route_t *out_route)
{
	struct timeval timenow;
	route_t rt = hint0, hint = hint0;
	errno_t error = 0;

	*out_route = NULL;

	/*
	 * Next hop determination.  Because we may involve the gateway route
	 * in addition to the original route, locking is rather complicated.
	 * The general concept is that regardless of whether the route points
	 * to the original route or to the gateway route, this routine takes
	 * an extra reference on such a route.  This extra reference will be
	 * released at the end.
	 *
	 * Care must be taken to ensure that the "hint0" route never gets freed
	 * via rtfree(), since the caller may have stored it inside a struct
	 * route with a reference held for that placeholder.
	 */
	if (rt != NULL) {
		unsigned int ifindex;

		RT_LOCK_SPIN(rt);
		ifindex = rt->rt_ifp->if_index;
		RT_ADDREF_LOCKED(rt);
		if (!(rt->rt_flags & RTF_UP)) {
			RT_REMREF_LOCKED(rt);
			RT_UNLOCK(rt);
			/* route is down, find a new one */
			hint = rt = rtalloc1_scoped((struct sockaddr *)
			    (size_t)net_dest, 1, 0, ifindex);
			if (hint != NULL) {
				RT_LOCK_SPIN(rt);
				ifindex = rt->rt_ifp->if_index;
			} else {
				senderr(EHOSTUNREACH);
			}
		}

		/*
		 * We have a reference to "rt" by now; it will either
		 * be released or freed at the end of this routine.
		 */
		RT_LOCK_ASSERT_HELD(rt);
		if (rt->rt_flags & RTF_GATEWAY) {
			struct rtentry *gwrt = rt->rt_gwroute;
			struct sockaddr_in gw;

			/* If there's no gateway rt, look it up */
			if (gwrt == NULL) {
				gw = *((struct sockaddr_in *)rt->rt_gateway);
				RT_UNLOCK(rt);
				goto lookup;
			}
			/* Become a regular mutex */
			RT_CONVERT_LOCK(rt);

			/*
			 * Take gwrt's lock while holding route's lock;
			 * this is okay since gwrt never points back
			 * to "rt", so no lock ordering issues.
			 */
			RT_LOCK_SPIN(gwrt);
			if (!(gwrt->rt_flags & RTF_UP)) {
				struct rtentry *ogwrt;

				rt->rt_gwroute = NULL;
				RT_UNLOCK(gwrt);
				gw = *((struct sockaddr_in *)rt->rt_gateway);
				RT_UNLOCK(rt);
				rtfree(gwrt);
lookup:
				gwrt = rtalloc1_scoped(
				    (struct sockaddr *)&gw, 1, 0, ifindex);

				RT_LOCK(rt);
				/*
				 * Bail out if the route is down, no route
				 * to gateway, circular route, or if the
				 * gateway portion of "rt" has changed.
				 */
				if (!(rt->rt_flags & RTF_UP) ||
				    gwrt == NULL || gwrt == rt ||
				    !equal(SA(&gw), rt->rt_gateway)) {
					if (gwrt == rt) {
						RT_REMREF_LOCKED(gwrt);
						gwrt = NULL;
					}
					RT_UNLOCK(rt);
					if (gwrt != NULL)
						rtfree(gwrt);
					senderr(EHOSTUNREACH);
				}

				/* Remove any existing gwrt */
				ogwrt = rt->rt_gwroute;
				if ((rt->rt_gwroute = gwrt) != NULL)
					RT_ADDREF(gwrt);

				/* Clean up "rt" now while we can */
				if (rt == hint0) {
					RT_REMREF_LOCKED(rt);
					RT_UNLOCK(rt);
				} else {
					RT_UNLOCK(rt);
					rtfree(rt);
				}
				rt = gwrt;
				/* Now free the replaced gwrt */
				if (ogwrt != NULL)
					rtfree(ogwrt);
				/* If still no route to gateway, bail out */
				if (rt == NULL)
					senderr(EHOSTUNREACH);
			} else {
				RT_ADDREF_LOCKED(gwrt);
				RT_UNLOCK(gwrt);
				/* Clean up "rt" now while we can */
				if (rt == hint0) {
					RT_REMREF_LOCKED(rt);
					RT_UNLOCK(rt);
				} else {
					RT_UNLOCK(rt);
					rtfree(rt);
				}
				rt = gwrt;
			}

			/* rt == gwrt; if it is now down, give up */
			RT_LOCK_SPIN(rt);
			if (!(rt->rt_flags & RTF_UP)) {
				RT_UNLOCK(rt);
				senderr(EHOSTUNREACH);
			}
		}

		if (rt->rt_flags & RTF_REJECT) {
			getmicrotime(&timenow);
			if (rt->rt_rmx.rmx_expire == 0 ||
			    timenow.tv_sec < rt->rt_rmx.rmx_expire) {
				RT_UNLOCK(rt);
				senderr(rt == hint ? EHOSTDOWN : EHOSTUNREACH);
			}
		}

		/* Become a regular mutex */
		RT_CONVERT_LOCK(rt);

		/* Caller is responsible for cleaning up "rt" */
		*out_route = rt;
	}
	return (0);

bad:
	/* Clean up route (either it is "rt" or "gwrt") */
	if (rt != NULL) {
		RT_LOCK_SPIN(rt);
		if (rt == hint0) {
			RT_REMREF_LOCKED(rt);
			RT_UNLOCK(rt);
		} else {
			RT_UNLOCK(rt);
			rtfree(rt);
		}
	}
	return (error);
}