samples: net: openthread: border_router: Fix packet forwarding bug

This commit fixes an issue introduced in #97531. Multicast routes added
by application are now set to have a prefix length of 16 bits instead of
128. This will allow multicast routing to all IPv6 addresses from those
groups.

For the OpenThread multicast listener callback, route length will be set
to 128 bits, as a MLD event is expected when an address is subscribed.
Route lookup has been removed since one will always be found as the
application registers multicast routes with same scope, but with a
smaller prefix length.

Fixed issue regarding packet forwarding and BBR state. Previously, code
was covering only the case wehn BBR was secondary and packet was
received from backbone interface. A secondary BBR should not forward a
multicast packet from OT interface to backbone interface and vice versa.

Improved unicast forwarding function to return from the beginning if the
packet has a multicast destination.

Signed-off-by: Cristian Bulacu <[email protected]>

Author: Cristib05

subsys/net/l2/openthread/openthread_border_router.c

@@ -282,11 +282,8 @@ static void ot_bbr_multicast_listener_handler(void *context,
 	memcpy(recv_addr.s6_addr, address->mFields.m32, sizeof(otIp6Address));
 
 	if (event == OT_BACKBONE_ROUTER_MULTICAST_LISTENER_ADDED) {
-		entry = net_route_mcast_lookup(&recv_addr);
-		if (entry == NULL) {
-			entry = net_route_mcast_add(ot_context->iface, &recv_addr,
-						    NUM_BITS(struct in6_addr));
-		}
+		entry = net_route_mcast_add(ot_context->iface, &recv_addr,
+					    NUM_BITS(struct in6_addr));
 		if (entry != NULL) {
 			/*
 			 * No need to perform mcast_lookup explicitly as it's already done in
@@ -466,14 +463,15 @@ static bool openthread_border_router_can_forward_multicast(struct net_pkt *pkt)
 	}
 
 	if (net_ipv6_is_addr_mcast_raw(hdr->dst)) {
+		/* A secondary BBR should not forward onto an external iface
+		 * or from external network.
+		 */
+		if (otBackboneRouterGetState(instance) == OT_BACKBONE_ROUTER_STATE_SECONDARY ||
+		    otBackboneRouterGetState(instance) == OT_BACKBONE_ROUTER_STATE_DISABLED) {
+			return false;
+		}
 		/* AIL to Thread network message */
 		if (net_pkt_orig_iface(pkt) == ail_iface_ptr) {
-			if (otBackboneRouterGetState(instance) ==
-			    OT_BACKBONE_ROUTER_STATE_SECONDARY ||
-			    otBackboneRouterGetState(instance) ==
-			    OT_BACKBONE_ROUTER_STATE_DISABLED) {
-				return false;
-			}
 			if (openthread_border_router_has_multicast_listener(hdr->dst)) {
 				return true;
 			}
@@ -510,6 +508,10 @@ static bool openthread_border_router_check_unicast_packet_forwarding_policy(stru
 		return false;
 	}
 
+	if (net_ipv6_is_addr_mcast_raw(hdr->dst)) {
+		return false;
+	}
+
 	/*
 	 * This is the case when a packet from OpenThread stack is sent via UDP platform.
 	 * Packet will be eventually returned to OpenThread interface, but it won't have
@@ -594,8 +596,8 @@ static void openthread_border_router_add_route_to_multicast_groups(void)
 
 	ARRAY_FOR_EACH(mcast_group_idx, i) {
 
-		net_ipv6_addr_create(&addr, (0xff << 8) | mcast_group_idx[i], 0, 0, 0, 0, 0, 0, 1);
-		entry = net_route_mcast_add(ail_iface_ptr, &addr, NUM_BITS(struct in6_addr));
+		net_ipv6_addr_create(&addr, (0xff << 8) | mcast_group_idx[i], 0, 0, 0, 0, 0, 0, 0);
+		entry = net_route_mcast_add(ail_iface_ptr, &addr, 16);
 		if (entry != NULL) {
 			mcast_addr = net_if_ipv6_maddr_add(ail_iface_ptr,
 							   (const struct in6_addr *)&addr);