Revert "bridge: only expire the mdb entry when query is received"

While this commit was a good attempt to fix issues occuring when no
multicast querier is present, this commit still has two more issues:

1) There are cases where mdb entries do not expire even if there is a
querier present. The bridge will unnecessarily continue flooding
multicast packets on the according ports.

2) Never removing an mdb entry could be exploited for a Denial of
Service by an attacker on the local link, slowly, but steadily eating up
all memory.

Actually, this commit became obsolete with
"bridge: disable snooping if there is no querier" (b00589af)
which included fixes for a few more cases.

Therefore reverting the following commits (the commit stated in the
commit message plus three of its follow up fixes):

====================
Revert "bridge: update mdb expiration timer upon reports."
This reverts commit f144febd.
Revert "bridge: do not call setup_timer() multiple times"
This reverts commit 1faabf2a.
Revert "bridge: fix some kernel warning in multicast timer"
This reverts commit c7e8e8a8.
Revert "bridge: only expire the mdb entry when query is received"
This reverts commit 9f00b2e7.
====================

CC: Cong Wang <amwang@redhat.com>
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Reviewed-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_mdb.c

@@ -453,7 +453,7 @@ static int __br_mdb_del(struct net_bridge *br, struct br_mdb_entry *entry)
 		call_rcu_bh(&p->rcu, br_multicast_free_pg);
 		err = 0;
 
-		if (!mp->ports && !mp->mglist && mp->timer_armed &&
+		if (!mp->ports && !mp->mglist &&
 		    netif_running(br->dev))
 			mod_timer(&mp->timer, jiffies);
 		break;

net/bridge/br_multicast.c

@@ -272,7 +272,7 @@ static void br_multicast_del_pg(struct net_bridge *br,
 		del_timer(&p->timer);
 		call_rcu_bh(&p->rcu, br_multicast_free_pg);
 
-		if (!mp->ports && !mp->mglist && mp->timer_armed &&
+		if (!mp->ports && !mp->mglist &&
 		    netif_running(br->dev))
 			mod_timer(&mp->timer, jiffies);
 
@@ -611,9 +611,6 @@ struct net_bridge_mdb_entry *br_multicast_new_group(struct net_bridge *br,
 		break;
 
 	default:
-		/* If we have an existing entry, update it's expire timer */
-		mod_timer(&mp->timer,
-			  jiffies + br->multicast_membership_interval);
 		goto out;
 	}
 
@@ -623,7 +620,6 @@ struct net_bridge_mdb_entry *br_multicast_new_group(struct net_bridge *br,
 
 	mp->br = br;
 	mp->addr = *group;
-
 	setup_timer(&mp->timer, br_multicast_group_expired,
 		    (unsigned long)mp);
 
@@ -663,6 +659,7 @@ static int br_multicast_add_group(struct net_bridge *br,
 	struct net_bridge_mdb_entry *mp;
 	struct net_bridge_port_group *p;
 	struct net_bridge_port_group __rcu **pp;
+	unsigned long now = jiffies;
 	int err;
 
 	spin_lock(&br->multicast_lock);
@@ -677,18 +674,15 @@ static int br_multicast_add_group(struct net_bridge *br,
 
 	if (!port) {
 		mp->mglist = true;
+		mod_timer(&mp->timer, now + br->multicast_membership_interval);
 		goto out;
 	}
 
 	for (pp = &mp->ports;
 	     (p = mlock_dereference(*pp, br)) != NULL;
 	     pp = &p->next) {
-		if (p->port == port) {
-			/* We already have a portgroup, update the timer.  */
-			mod_timer(&p->timer,
-				  jiffies + br->multicast_membership_interval);
-			goto out;
-		}
+		if (p->port == port)
+			goto found;
 		if ((unsigned long)p->port < (unsigned long)port)
 			break;
 	}
@@ -699,6 +693,8 @@ static int br_multicast_add_group(struct net_bridge *br,
 	rcu_assign_pointer(*pp, p);
 	br_mdb_notify(br->dev, port, group, RTM_NEWMDB);
 
+found:
+	mod_timer(&p->timer, now + br->multicast_membership_interval);
 out:
 	err = 0;
 
@@ -1198,9 +1194,6 @@ static int br_ip4_multicast_query(struct net_bridge *br,
 	if (!mp)
 		goto out;
 
-	mod_timer(&mp->timer, now + br->multicast_membership_interval);
-	mp->timer_armed = true;
-
 	max_delay *= br->multicast_last_member_count;
 
 	if (mp->mglist &&
@@ -1277,9 +1270,6 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 	if (!mp)
 		goto out;
 
-	mod_timer(&mp->timer, now + br->multicast_membership_interval);
-	mp->timer_armed = true;
-
 	max_delay *= br->multicast_last_member_count;
 	if (mp->mglist &&
 	    (timer_pending(&mp->timer) ?
@@ -1365,7 +1355,7 @@ static void br_multicast_leave_group(struct net_bridge *br,
 			call_rcu_bh(&p->rcu, br_multicast_free_pg);
 			br_mdb_notify(br->dev, port, group, RTM_DELMDB);
 
-			if (!mp->ports && !mp->mglist && mp->timer_armed &&
+			if (!mp->ports && !mp->mglist &&
 			    netif_running(br->dev))
 				mod_timer(&mp->timer, jiffies);
 		}
@@ -1377,12 +1367,30 @@ static void br_multicast_leave_group(struct net_bridge *br,
 		     br->multicast_last_member_interval;
 
 	if (!port) {
-		if (mp->mglist && mp->timer_armed &&
+		if (mp->mglist &&
 		    (timer_pending(&mp->timer) ?
 		     time_after(mp->timer.expires, time) :
 		     try_to_del_timer_sync(&mp->timer) >= 0)) {
 			mod_timer(&mp->timer, time);
 		}
+
+		goto out;
+	}
+
+	for (p = mlock_dereference(mp->ports, br);
+	     p != NULL;
+	     p = mlock_dereference(p->next, br)) {
+		if (p->port != port)
+			continue;
+
+		if (!hlist_unhashed(&p->mglist) &&
+		    (timer_pending(&p->timer) ?
+		     time_after(p->timer.expires, time) :
+		     try_to_del_timer_sync(&p->timer) >= 0)) {
+			mod_timer(&p->timer, time);
+		}
+
+		break;
 	}
 out:
 	spin_unlock(&br->multicast_lock);
@@ -1805,7 +1813,6 @@ void br_multicast_stop(struct net_bridge *br)
 		hlist_for_each_entry_safe(mp, n, &mdb->mhash[i],
 					  hlist[ver]) {
 			del_timer(&mp->timer);
-			mp->timer_armed = false;
 			call_rcu_bh(&mp->rcu, br_multicast_free_group);
 		}
 	}

net/bridge/br_private.h

@@ -126,7 +126,6 @@ struct net_bridge_mdb_entry
 	struct timer_list		timer;
 	struct br_ip			addr;
 	bool				mglist;
-	bool				timer_armed;
 };
 
 struct net_bridge_mdb_htable