bridge: multicast port group RCU fix

The recently introduced bridge mulitcast port group list was only
partially using RCU correctly. It was missing rcu_dereference()
and missing the necessary barrier on deletion.

The code should have used one of the standard list methods (list or hlist)
instead of open coding a RCU based link list.
Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_forward.c

@@ -217,7 +217,7 @@ static void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 	prev = NULL;
 
 	rp = rcu_dereference(br->router_list.first);
-	p = mdst ? mdst->ports : NULL;
+	p = mdst ? rcu_dereference(mdst->ports) : NULL;
 	while (p || rp) {
 		lport = p ? p->port : NULL;
 		rport = rp ? hlist_entry(rp, struct net_bridge_port, rlist) :
@@ -231,7 +231,7 @@ static void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 			goto out;
 
 		if ((unsigned long)lport >= (unsigned long)port)
-			p = p->next;
+			p = rcu_dereference(p->next);
 		if ((unsigned long)rport >= (unsigned long)port)
 			rp = rcu_dereference(rp->next);
 	}

net/bridge/br_multicast.c

@@ -259,7 +259,7 @@ static void br_multicast_del_pg(struct net_bridge *br,
 		if (p != pg)
 			continue;
 
-		*pp = p->next;
+		rcu_assign_pointer(*pp, p->next);
 		hlist_del_init(&p->mglist);
 		del_timer(&p->timer);
 		del_timer(&p->query_timer);