net: bridge: fix a null pointer dereference in br_afspec

We might call br_afspec() with p == NULL which is a valid use case if
the action is on the bridge device itself, but the bridge tunnel code
dereferences the p pointer without checking, so check if p is null
first.

Reported-by: Gustavo A. R. Silva <[email protected]>
Fixes: efa5356 ("bridge: per vlan dst_metadata netlink support")
Signed-off-by: Nikolay Aleksandrov <[email protected]>
Acked-by: Roopa Prabhu <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Nikolay Aleksandrov

net/bridge/br_netlink.c

@@ -595,7 +595,7 @@ static int br_afspec(struct net_bridge *br,
 		err = 0;
 		switch (nla_type(attr)) {
 		case IFLA_BRIDGE_VLAN_TUNNEL_INFO:
-			if (!(p->flags & BR_VLAN_TUNNEL))
+			if (!p || !(p->flags & BR_VLAN_TUNNEL))
 				return -EINVAL;
 			err = br_parse_vlan_tunnel_info(attr, &tinfo_curr);
 			if (err)