Index: in_mcast.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/in_mcast.c,v
retrieving revision 1.1
diff -u -p -r1.1 in_mcast.c
--- in_mcast.c	12 Jun 2007 16:24:53 -0000	1.1
+++ in_mcast.c	3 Jul 2007 17:10:01 -0000
@@ -967,11 +967,40 @@ inp_join_group(struct inpcb *inp, struct
 		struct ip_mreq_source	 mreqs;
 
 		if (sopt->sopt_name == IP_ADD_MEMBERSHIP) {
-			error = sooptcopyin(sopt, &mreqs,
-			    sizeof(struct ip_mreq),
-			    sizeof(struct ip_mreq));
 			/*
-			 * Do argument switcharoo from ip_mreq into
+			 * Handle the case where a struct ip_mreqn
+			 * was passed to the IP_ADD_MEMBERSHIP ioctl to
+			 * specify an interface index. This is an
+			 * undocumented modification of the IPv4 ASM API
+			 * obtained from Linux.
+			 */
+			if (sopt->sopt_valsize == sizeof(struct ip_mreqn)) {
+				struct ip_mreqn *mreqn =
+				    (struct ip_mreqn *)&mreqs;
+
+				error = sooptcopyin(sopt, mreqn,
+				    sizeof(struct ip_mreqn),
+				    sizeof(struct ip_mreqn));
+				if (error)
+					return (error);
+
+				if (mreqn->imr_ifindex < 0 ||
+				    if_index < mreqn->imr_ifindex)
+					return (EINVAL);
+				if (mreqn->imr_ifindex == 0) {
+					ifp = NULL;
+				} else {
+					ifp = ifnet_byindex(mreqn->imr_ifindex);
+					if (ifp == NULL)
+						return (EADDRNOTAVAIL);
+				}
+			} else {
+				error = sooptcopyin(sopt, &mreqs,
+				    sizeof(struct ip_mreq),
+				    sizeof(struct ip_mreq));
+			}
+			/*
+			 * Do argument switcharoo from ip_mreq[n] into
 			 * ip_mreq_source to avoid using two instances.
 			 */
 			mreqs.imr_interface = mreqs.imr_sourceaddr;
@@ -995,29 +1024,48 @@ inp_join_group(struct inpcb *inp, struct
 		}
 
 		/*
-		 * Obtain ifp. If no interface address was provided,
-		 * use the interface of the route to the given multicast
-		 * address (usually this is the default route).
+		 * If ifp was not already overridden, obtain it.
+		 *
+		 * If no interface address was provided, use the interface
+		 * of the route in the unicast FIB for the given multicast
+		 * destination; usually, this is the default route.
+		 *
+		 * If this lookup fails, attempt to use the first non-loopback
+		 * interface with multicast capability in the system as a
+		 * last resort. The legacy IPv4 ASM API requires that we do
+		 * this in order to allow groups to be joined when the routing
+		 * table has not yet been populated during boot.
+		 *
+		 * If all of these conditions fail, return EADDRNOTAVAIL, and
+		 * reject the IPv4 multicast join.
 		 */
-		if (mreqs.imr_interface.s_addr != INADDR_ANY) {
+		if (ifp == NULL && mreqs.imr_interface.s_addr != INADDR_ANY) {
 			INADDR_TO_IFP(mreqs.imr_interface, ifp);
-		} else {
+		} else if (ifp == NULL) {
 			struct route ro;
 
 			ro.ro_rt = NULL;
 			*(struct sockaddr_in *)&ro.ro_dst = gsa->sin;
 			rtalloc_ign(&ro, RTF_CLONING);
-			if (ro.ro_rt == NULL) {
-#ifdef DIAGNOSTIC
-				printf("%s: no route to %s\n", __func__,
-				    inet_ntoa(gsa->sin.sin_addr));
-#endif
-				return (EADDRNOTAVAIL);
+			if (ro.ro_rt != NULL) {
+				ifp = ro.ro_rt->rt_ifp;
+				KASSERT(ifp != NULL, ("%s: null ifp",
+				    __func__));
+				RTFREE(ro.ro_rt);
+			} else {
+				struct in_ifaddr *ia;
+				struct ifnet *mfp = NULL;
+				TAILQ_FOREACH(ia, &in_ifaddrhead, ia_link) {
+					mfp = ia->ia_ifp;
+					if (!(mfp->if_flags & IFF_LOOPBACK) &&
+					     (mfp->if_flags & IFF_MULTICAST)) {
+						ifp = mfp;
+						break;
+					}
+				}
 			}
-			ifp = ro.ro_rt->rt_ifp;
-			KASSERT(ifp != NULL, ("%s: null ifp", __func__));
-			RTFREE(ro.ro_rt);
 		}
+
 #ifdef DIAGNOSTIC
 		if (bootverbose) {
 			printf("%s: imr_interface = %s, ifp = %p\n",
@@ -1207,12 +1255,42 @@ inp_leave_group(struct inpcb *inp, struc
 	case IP_DROP_MEMBERSHIP:
 	case IP_DROP_SOURCE_MEMBERSHIP:
 		if (sopt->sopt_name == IP_DROP_MEMBERSHIP) {
-			error = sooptcopyin(sopt, &mreqs,
-			    sizeof(struct ip_mreq),
-			    sizeof(struct ip_mreq));
+			/*
+			 * Handle the case where a struct ip_mreqn
+			 * was passed to the IP_DROP_MEMBERSHIP ioctl to
+			 * specify an interface index. This is an
+			 * undocumented modification of the IPv4 ASM API
+			 * obtained from Linux.
+			 */
+			if (sopt->sopt_valsize == sizeof(struct ip_mreqn)) {
+				struct ip_mreqn *mreqn =
+				    (struct ip_mreqn *)&mreqs;
+
+				error = sooptcopyin(sopt, mreqn,
+				    sizeof(struct ip_mreqn),
+				    sizeof(struct ip_mreqn));
+				if (error)
+					return (error);
+
+				if (mreqn->imr_ifindex < 0 ||
+				    if_index < mreqn->imr_ifindex)
+					return (EINVAL);
+				if (mreqn->imr_ifindex == 0) {
+					ifp = NULL;
+				} else {
+					ifp = ifnet_byindex(mreqn->imr_ifindex);
+					if (ifp == NULL)
+						return (EADDRNOTAVAIL);
+				}
+			} else {
+				error = sooptcopyin(sopt, &mreqs,
+				    sizeof(struct ip_mreq),
+				    sizeof(struct ip_mreq));
+			}
+
 			/*
 			 * Swap interface and sourceaddr arguments,
-			 * as ip_mreq and ip_mreq_source are laid
+			 * as ip_mreq[n] and ip_mreq_source are laid
 			 * out differently.
 			 */
 			mreqs.imr_interface = mreqs.imr_sourceaddr;
@@ -1235,7 +1313,7 @@ inp_leave_group(struct inpcb *inp, struc
 			ssa->sin.sin_addr = mreqs.imr_sourceaddr;
 		}
 
-		if (gsa->sin.sin_addr.s_addr != INADDR_ANY)
+		if (ifp == NULL && gsa->sin.sin_addr.s_addr != INADDR_ANY)
 			INADDR_TO_IFP(mreqs.imr_interface, ifp);
 
 #ifdef DIAGNOSTIC