bridge: join all-snoopers multicast address

Next to snooping IGMP/MLD queries RFC4541, section 2.1.1.a) recommends
to snoop multicast router advertisements to detect multicast routers.

Multicast router advertisements are sent to an "all-snoopers"
multicast address. To be able to receive them reliably, we need to
join this group.

Otherwise other snooping switches might refrain from forwarding these
advertisements to us.

Signed-off-by: Linus Lüssing <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/uapi/linux/in.h

···
 #define	IN_LOOPBACK(a)		((((long int) (a)) & 0xff000000) == 0x7f000000)
 
 /* Defines for Multicast INADDR */
-#define INADDR_UNSPEC_GROUP   	0xe0000000U	/* 224.0.0.0   */
-#define INADDR_ALLHOSTS_GROUP 	0xe0000001U	/* 224.0.0.1   */
-#define INADDR_ALLRTRS_GROUP    0xe0000002U	/* 224.0.0.2 */
-#define INADDR_MAX_LOCAL_GROUP  0xe00000ffU	/* 224.0.0.255 */
+#define INADDR_UNSPEC_GROUP		0xe0000000U	/* 224.0.0.0   */
+#define INADDR_ALLHOSTS_GROUP		0xe0000001U	/* 224.0.0.1   */
+#define INADDR_ALLRTRS_GROUP		0xe0000002U	/* 224.0.0.2 */
+#define INADDR_ALLSNOOPERS_GROUP	0xe000006aU	/* 224.0.0.106 */
+#define INADDR_MAX_LOCAL_GROUP		0xe00000ffU	/* 224.0.0.255 */
 #endif
 
 /* <asm/byteorder.h> contains the htonl type stuff.. */

net/bridge/br_multicast.c

···
 	INIT_HLIST_HEAD(&br->mdb_list);
 }
 
+static void br_ip4_multicast_join_snoopers(struct net_bridge *br)
+{
+	struct in_device *in_dev = in_dev_get(br->dev);
+
+	if (!in_dev)
+		return;
+
+	ip_mc_inc_group(in_dev, htonl(INADDR_ALLSNOOPERS_GROUP));
+	in_dev_put(in_dev);
+}
+
+#if IS_ENABLED(CONFIG_IPV6)
+static void br_ip6_multicast_join_snoopers(struct net_bridge *br)
+{
+	struct in6_addr addr;
+
+	ipv6_addr_set(&addr, htonl(0xff020000), 0, 0, htonl(0x6a));
+	ipv6_dev_mc_inc(br->dev, &addr);
+}
+#else
+static inline void br_ip6_multicast_join_snoopers(struct net_bridge *br)
+{
+}
+#endif
+
+static void br_multicast_join_snoopers(struct net_bridge *br)
+{
+	br_ip4_multicast_join_snoopers(br);
+	br_ip6_multicast_join_snoopers(br);
+}
+
+static void br_ip4_multicast_leave_snoopers(struct net_bridge *br)
+{
+	struct in_device *in_dev = in_dev_get(br->dev);
+
+	if (WARN_ON(!in_dev))
+		return;
+
+	ip_mc_dec_group(in_dev, htonl(INADDR_ALLSNOOPERS_GROUP));
+	in_dev_put(in_dev);
+}
+
+#if IS_ENABLED(CONFIG_IPV6)
+static void br_ip6_multicast_leave_snoopers(struct net_bridge *br)
+{
+	struct in6_addr addr;
+
+	ipv6_addr_set(&addr, htonl(0xff020000), 0, 0, htonl(0x6a));
+	ipv6_dev_mc_dec(br->dev, &addr);
+}
+#else
+static inline void br_ip6_multicast_leave_snoopers(struct net_bridge *br)
+{
+}
+#endif
+
+static void br_multicast_leave_snoopers(struct net_bridge *br)
+{
+	br_ip4_multicast_leave_snoopers(br);
+	br_ip6_multicast_leave_snoopers(br);
+}
+
 static void __br_multicast_open(struct net_bridge *br,
 				struct bridge_mcast_own_query *query)
 {
···
 
 void br_multicast_open(struct net_bridge *br)
 {
+	if (br_opt_get(br, BROPT_MULTICAST_ENABLED))
+		br_multicast_join_snoopers(br);
+
 	__br_multicast_open(br, &br->ip4_own_query);
 #if IS_ENABLED(CONFIG_IPV6)
 	__br_multicast_open(br, &br->ip6_own_query);
···
 	del_timer_sync(&br->ip6_other_query.timer);
 	del_timer_sync(&br->ip6_own_query.timer);
 #endif
+
+	if (br_opt_get(br, BROPT_MULTICAST_ENABLED))
+		br_multicast_leave_snoopers(br);
 }
 
 void br_multicast_dev_del(struct net_bridge *br)
···
 
 	br_mc_disabled_update(br->dev, val);
 	br_opt_toggle(br, BROPT_MULTICAST_ENABLED, !!val);
-	if (!br_opt_get(br, BROPT_MULTICAST_ENABLED))
+	if (!br_opt_get(br, BROPT_MULTICAST_ENABLED)) {
+		br_multicast_leave_snoopers(br);
 		goto unlock;
+	}
 
 	if (!netif_running(br->dev))
 		goto unlock;

net/ipv6/mcast.c

···
 {
 	return __ipv6_dev_mc_inc(dev, addr, MCAST_EXCLUDE);
 }
+EXPORT_SYMBOL(ipv6_dev_mc_inc);
 
 /*
  *	device multicast group del
···
 
 	return err;
 }
+EXPORT_SYMBOL(ipv6_dev_mc_dec);
 
 /*
  *	check if the interface/address pair is valid