net: if: check for multicast address already registered

Add a check to stop a multicast address to be registered multiple times.
This can happen if the application is using net_if_ipv6_maddr_add()
directly.

Tested on the existing bluetooth/ipsp sample:

<wrn> net_if: Multicast address ff02::1 is is already registered.

Signed-off-by: Fabio Baltieri <[email protected]>

Author: fabiobaltieri

subsys/net/ip/net_if.c

@@ -1672,6 +1672,12 @@ struct net_if_mcast_addr *net_if_ipv6_maddr_add(struct net_if *iface,
 		return NULL;
 	}
 
+	if (net_if_ipv6_maddr_lookup(addr, &iface)) {
+		NET_WARN("Multicast address %s is is already registered.",
+			log_strdup(net_sprint_ipv6_addr(addr)));
+		return NULL;
+	}
+
 	for (i = 0; i < NET_IF_MAX_IPV6_MADDR; i++) {
 		if (ipv6->mcast[i].is_used) {
 			continue;

tests/net/iface/src/main.c

@@ -718,6 +718,14 @@ static void test_v6_addr_add(void)
 	zassert_true(ret, "Cannot add IPv6 address");
 }
 
+static void test_v6_addr_add_mcast_twice(void)
+{
+	struct net_if_mcast_addr *maddr;
+
+	maddr = net_if_ipv6_maddr_add(iface1, &in6addr_mcast);
+	zassert_equal(maddr, NULL, "Address was added twice");
+}
+
 static void test_v6_addr_lookup(void)
 {
 	int ret;
@@ -859,6 +867,7 @@ void test_main(void)
 			 ztest_user_unit_test(test_v4_addr_lookup_user),
 			 ztest_unit_test(test_v4_addr_rm_user_from_userspace),
 			 ztest_unit_test(test_v6_addr_add),
+			 ztest_unit_test(test_v6_addr_add_mcast_twice),
 			 ztest_unit_test(test_v6_addr_lookup),
 			 ztest_unit_test(test_v6_addr_rm),
 			 ztest_unit_test(test_v6_addr_add_user_from_userspace),