[PATCH 1/2] bridge: fix smatch warning / potential null pointer dereference

["Linus Lüssing" <linus.luessing@web.de>]

 "New smatch warnings:
  net/bridge/br_multicast.c:1368 br_ip6_multicast_query() error:
    we previously assumed 'group' could be null (see line 1349)"

In the rare (sort of broken) case of a query having a Maximum
Response Delay of zero, we could create a potential null pointer
dereference.

Fixing this by skipping the multicast specific MLD Query parsing again
if no multicast group address is available.

Introduced by dc4eb53a996a78bfb8ea07b47423ff5a3aadc362
("bridge: adhere to querier election mechanism specified by RFCs")

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
---
 net/bridge/br_multicast.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index cd3cf39..876e5fb 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1373,6 +1373,8 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 		br_multicast_query_received(br, port, &br->ip6_other_query,
 					    &saddr, max_delay);
 		goto out;
+	} else if (!group) {
+		goto out;
 	}
 
 	mp = br_mdb_ip6_get(mlock_dereference(br->mdb, br), group, vid);
-- 
1.7.10.4