net: dsa: Avoid cross-chip syncing of VLAN filtering

Changes to VLAN filtering are not applicable to cross-chip
notifications.

On a system like this:

.-----.   .-----.   .-----.
| sw1 +---+ sw2 +---+ sw3 |
'-1-2-'   '-1-2-'   '-1-2-'

Before this change, upon sw1p1 leaving a bridge, a call to
dsa_port_vlan_filtering would also be made to sw2p1 and sw3p1.

In this scenario:

.---------.   .-----.   .-----.
|   sw1   +---+ sw2 +---+ sw3 |
'-1-2-3-4-'   '-1-2-'   '-1-2-'

When sw1p4 would leave a bridge, dsa_port_vlan_filtering would be
called for sw2 and sw3 with a non-existing port - leading to array
out-of-bounds accesses and crashes on mv88e6xxx.

Fixes: d371b7c9 ("net: dsa: Unset vlan_filtering when ports leave the bridge")
Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/switch.c

@@ -180,9 +180,11 @@ static int dsa_switch_bridge_leave(struct dsa_switch *ds,
 						info->sw_index, info->port,
 						info->bridge);
 
-	err = dsa_switch_sync_vlan_filtering(ds, info);
-	if (err)
-		return err;
+	if (ds->dst->index == info->tree_index && ds->index == info->sw_index) {
+		err = dsa_switch_sync_vlan_filtering(ds, info);
+		if (err)
+			return err;
+	}
 
 	return dsa_tag_8021q_bridge_leave(ds, info);
 }