net: bridge: mcast: fix stale ipv6 hdr pointer when handling v6 query

We get a pointer to the ipv6 hdr in br_ip6_multicast_query but we may
call pskb_may_pull afterwards and end up using a stale pointer.
So use the header directly, it's just 1 place where it's needed.

Fixes: 08b202b6 ("bridge br_multicast: IPv6 MLD support.")
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Tested-by: Martin Weinelt <martin@linuxlounge.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_multicast.c

@@ -1279,7 +1279,6 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 				  u16 vid)
 {
 	unsigned int transport_len = ipv6_transport_len(skb);
-	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
 	struct mld_msg *mld;
 	struct net_bridge_mdb_entry *mp;
 	struct mld2_query *mld2q;
@@ -1323,7 +1322,7 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 
 	if (is_general_query) {
 		saddr.proto = htons(ETH_P_IPV6);
-		saddr.u.ip6 = ip6h->saddr;
+		saddr.u.ip6 = ipv6_hdr(skb)->saddr;
 
 		br_multicast_query_received(br, port, &br->ip6_other_query,
 					    &saddr, max_delay);