* 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. *
* 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.
ip6_forward(m, srcrt)	struct mbuf *m;	int srcrt;{	struct ip6_hdr *ip6 = mtod(m, struct ip6_hdr *);	struct sockaddr_in6 *dst;	struct rtentry *rt;	int error, type = 0, code = 0;	struct mbuf *mcopy = NULL;	long time_second = time.tv_sec;	struct ifnet *origifp;	/* maybe unnecessary */#ifdef IPSEC_IPV6FWD	struct secpolicy *sp = NULL;#endif#ifdef IPSEC_IPV6FWD	/*	 * Check AH/ESP integrity.	 */	/*	 * Don't increment ip6s_cantforward because this is the check	 * before forwarding packet actually.	 */	if (ipsec6_in_reject(m, NULL)) {		ipsec6stat.in_polvio++;		m_freem(m);		return;	}#endif /*IPSEC_IPV6FWD*/	/*	 * 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 < time_second) {			ip6_log_time = time_second;			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,			    m->m_pkthdr.rcvif->if_xname);		}		m_freem(m);		return;	}	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;	}	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));#ifdef IPSEC_IPV6FWD	/* get a security policy for this packet */	sp = ipsec6_getpolicybyaddr(m, IPSEC_DIR_OUTBOUND, 0, &error);	if (sp == NULL) {		ipsec6stat.out_inval++;		ip6stat.ip6s_cantforward++;		if (mcopy) {#if 0			/* XXX: what icmp ? */#else			m_freem(mcopy);#endif		}		m_freem(m);		return;	}	error = 0;	/* check policy */	switch (sp->policy) {	case IPSEC_POLICY_DISCARD:		/*		 * This packet is just discarded.		 */		ipsec6stat.out_polvio++;		ip6stat.ip6s_cantforward++;		key_freesp(sp);		if (mcopy) {#if 0			/* XXX: what icmp ? */#else			m_freem(mcopy);#endif		}		m_freem(m);		return;	case IPSEC_POLICY_BYPASS:	case IPSEC_POLICY_NONE:		/* no need to do IPsec. */		key_freesp(sp);		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);			if (mcopy) {#if 0				/* XXX: what icmp ? */#else				m_freem(mcopy);#endif			}			m_freem(m);			return;		}		/* do IPsec */		break;	case IPSEC_POLICY_ENTRUST:	default:		/* should be panic ?? */		printf("ip6_forward: Invalid policy found. %d\n", sp->policy);		key_freesp(sp);		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.ro = NULL;	/* update at ipsec6_output_tunnel() */	state.dst = NULL;	/* update at ipsec6_output_tunnel() */	error = ipsec6_output_tunnel(&state, sp, 0);	m = state.m;#if 0	/* XXX allocate a route (ro, dst) again later */	ro = (struct route_in6 *)state.ro;	dst = (struct sockaddr_in6 *)state.dst;#endif	key_freesp(sp);	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;	}    }    skip_ipsec:#endif /* IPSEC_IPV6FWD */	dst = &ip6_forward_rt.ro_dst;	if (!srcrt) {		/*		 * ip6_forward_rt.ro_dst.sin6_addr is equal to ip6->ip6_dst		 */		if (ip6_forward_rt.ro_rt == 0 ||		    (ip6_forward_rt.ro_rt->rt_flags & RTF_UP) == 0) {			if (ip6_forward_rt.ro_rt) {				RTFREE(ip6_forward_rt.ro_rt);				ip6_forward_rt.ro_rt = 0;			}			/* this probably fails but give it a try again */			rtalloc((struct route *)&ip6_forward_rt);		}		if (ip6_forward_rt.ro_rt == 0) {			ip6stat.ip6s_noroute++;			/* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_noroute) */			if (mcopy) {				icmp6_error(mcopy, ICMP6_DST_UNREACH,					    ICMP6_DST_UNREACH_NOROUTE, 0);			}			m_freem(m);			return;		}	} else if ((rt = ip6_forward_rt.ro_rt) == 0 ||		 !IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &dst->sin6_addr)) {		if (ip6_forward_rt.ro_rt) {			RTFREE(ip6_forward_rt.ro_rt);			ip6_forward_rt.ro_rt = 0;		}		bzero(dst, sizeof(*dst));		dst->sin6_len = sizeof(struct sockaddr_in6);		dst->sin6_family = AF_INET6;		dst->sin6_addr = ip6->ip6_dst;		rtalloc((struct route *)&ip6_forward_rt);		if (ip6_forward_rt.ro_rt == 0) {			ip6stat.ip6s_noroute++;			/* XXX in6_ifstat_inc(rt->rt_ifp, ifs6_in_noroute) */			if (mcopy) {				icmp6_error(mcopy, ICMP6_DST_UNREACH,					    ICMP6_DST_UNREACH_NOROUTE, 0);			}			m_freem(m);			return;		}	}	rt = ip6_forward_rt.ro_rt;	/*	 * 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.rcvif, &ip6->ip6_src) !=	    in6_addr2scopeid(rt->rt_ifp, &ip6->ip6_src)) {		ip6stat.ip6s_cantforward++;		ip6stat.ip6s_badscope++;		in6_ifstat_inc(rt->rt_ifp, ifs6_in_discard);		if (ip6_log_time + ip6_log_interval < time_second) {			ip6_log_time = time_second;			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,			    m->m_pkthdr.rcvif->if_xname, rt->rt_ifp->if_xname);		}		if (mcopy)			icmp6_error(mcopy, ICMP6_DST_UNREACH,				    ICMP6_DST_UNREACH_BEYONDSCOPE, 0);		m_freem(m);		return;	}	if (m->m_pkthdr.len > rt->rt_ifp->if_mtu) {		in6_ifstat_inc(rt->rt_ifp, ifs6_in_toobig);		if (mcopy) {			u_long mtu;#ifdef IPSEC_IPV6FWD			struct secpolicy *sp;			int ipsecerror;			size_t ipsechdrsiz;#endif			mtu = rt->rt_ifp->if_mtu;#ifdef IPSEC_IPV6FWD			/*			 * When we do IPsec tunnel ingress, we need to play			 * with if_mtu 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".			 */			sp = ipsec6_getpolicybyaddr(mcopy, IPSEC_DIR_OUTBOUND,				IP_FORWARDING, &ipsecerror);			if (sp) {				ipsechdrsiz = ipsec6_hdrsiz(mcopy,					IPSEC_DIR_OUTBOUND, NULL);				if (ipsechdrsiz < mtu)					mtu -= ipsechdrsiz;			}			/*			 * 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			icmp6_error(mcopy, ICMP6_PACKET_TOO_BIG, 0, mtu);		}		m_freem(m);		return; 	}	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 == 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.			 */			icmp6_error(mcopy, ICMP6_DST_UNREACH,				    ICMP6_DST_UNREACH_ADDR, 0);			m_freem(m);			return;		}		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 ((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		{			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, m->m_pkthdr.rcvif->if_xname,			       rt->rt_ifp->if_xname);		}		/* we can just use rcvif in forwarding. */		origifp = m->m_pkthdr.rcvif;	}	else		origifp = rt->rt_ifp;	if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_src))		ip6->ip6_src.s6_addr16[1] = 0;	if (IN6_IS_SCOPE_LINKLOCAL(&ip6->ip6_dst))		ip6->ip6_dst.s6_addr16[1] = 0;#ifdef OLDIP6OUTPUT	error = (*rt->rt_ifp->if_output)(rt->rt_ifp, m,					 (struct sockaddr *)dst,					 ip6_forward_rt.ro_rt);#else	error = nd6_output(rt->rt_ifp, origifp, m, dst, rt);#endif	if (error) {		in6_ifstat_inc(rt->rt_ifp, ifs6_out_discard);		ip6stat.ip6s_cantforward++;	} else {		ip6stat.ip6s_forward++;		in6_ifstat_inc(rt->rt_ifp, ifs6_out_forward);		if (type)			ip6stat.ip6s_redirectsent++;		else {			if (mcopy)				goto freecopy;		}	}	if (mcopy == NULL)		return;	switch (error) {	case 0:#if 1		if (type == ND_REDIRECT) {			icmp6_redirect_output(mcopy, rt);			return;		}#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);	return; freecopy:	m_freem(mcopy);	return;}