bridge: make br_fdb_delete also check if the port matches

Before this patch the user-specified bridge port was ignored when
deleting an fdb entry and thus one could delete an entry that belonged
to any port.
Example (eth0 and eth1 are br0 ports):
bridge fdb add 00:11:22:33:44:55 dev eth0 master
bridge fdb del 00:11:22:33:44:55 dev eth1 master
(succeeds)

after the patch:
bridge fdb add 00:11:22:33:44:55 dev eth0 master
bridge fdb del 00:11:22:33:44:55 dev eth1 master
RTNETLINK answers: No such file or directory

Based on a patch by Wilson Kok.

Reported-by: Wilson Kok <wkok@cumulusnetworks.com>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_fdb.c

@@ -873,13 +873,15 @@ out:
 	return err;
 }
 
-static int fdb_delete_by_addr(struct net_bridge *br, const u8 *addr, u16 vlan)
+static int fdb_delete_by_addr_and_port(struct net_bridge_port *p,
+				       const u8 *addr, u16 vlan)
 {
+	struct net_bridge *br = p->br;
 	struct hlist_head *head = &br->hash[br_mac_hash(addr, vlan)];
 	struct net_bridge_fdb_entry *fdb;
 
 	fdb = fdb_find(head, addr, vlan);
-	if (!fdb)
+	if (!fdb || fdb->dst != p)
 		return -ENOENT;
 
 	fdb_delete(br, fdb);
@@ -892,7 +894,7 @@ static int __br_fdb_delete(struct net_bridge_port *p,
 	int err;
 
 	spin_lock_bh(&p->br->hash_lock);
-	err = fdb_delete_by_addr(p->br, addr, vid);
+	err = fdb_delete_by_addr_and_port(p, addr, vid);
 	spin_unlock_bh(&p->br->hash_lock);
 
 	return err;