bridge br_multicast: BUG: unable to handle kernel NULL pointer dereference

On Tue, Jul 06, 2010 at 08:48:35AM +0800, Herbert Xu wrote:
>
> bridge: Restore NULL check in br_mdb_ip_get

Resend with proper attribution.

bridge: Restore NULL check in br_mdb_ip_get

Somewhere along the line the NULL check in br_mdb_ip_get went
AWOL, causing crashes when we receive an IGMP packet with no
multicast table allocated.

This patch restores it and ensures all br_mdb_*_get functions
use it.

Reported-by: Frank Arnold <frank.arnold@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Thanks,
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_multicast.c

@@ -99,6 +99,15 @@ static struct net_bridge_mdb_entry *__br_mdb_ip_get(
 	return NULL;
 }
 
+static struct net_bridge_mdb_entry *br_mdb_ip_get(
+	struct net_bridge_mdb_htable *mdb, struct br_ip *dst)
+{
+	if (!mdb)
+		return NULL;
+
+	return __br_mdb_ip_get(mdb, dst, br_ip_hash(mdb, dst));
+}
+
 static struct net_bridge_mdb_entry *br_mdb_ip4_get(
 	struct net_bridge_mdb_htable *mdb, __be32 dst)
 {
@@ -107,7 +116,7 @@ static struct net_bridge_mdb_entry *br_mdb_ip4_get(
 	br_dst.u.ip4 = dst;
 	br_dst.proto = htons(ETH_P_IP);
 
-	return __br_mdb_ip_get(mdb, &br_dst, __br_ip4_hash(mdb, dst));
+	return br_mdb_ip_get(mdb, &br_dst);
 }
 
 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
@@ -119,23 +128,17 @@ static struct net_bridge_mdb_entry *br_mdb_ip6_get(
 	ipv6_addr_copy(&br_dst.u.ip6, dst);
 	br_dst.proto = htons(ETH_P_IPV6);
 
-	return __br_mdb_ip_get(mdb, &br_dst, __br_ip6_hash(mdb, dst));
+	return br_mdb_ip_get(mdb, &br_dst);
 }
 #endif
 
-static struct net_bridge_mdb_entry *br_mdb_ip_get(
-	struct net_bridge_mdb_htable *mdb, struct br_ip *dst)
-{
-	return __br_mdb_ip_get(mdb, dst, br_ip_hash(mdb, dst));
-}
-
 struct net_bridge_mdb_entry *br_mdb_get(struct net_bridge *br,
 					struct sk_buff *skb)
 {
 	struct net_bridge_mdb_htable *mdb = br->mdb;
 	struct br_ip ip;
 
-	if (!mdb || br->multicast_disabled)
+	if (br->multicast_disabled)
 		return NULL;
 
 	if (BR_INPUT_SKB_CB(skb)->igmp)