net: dsa: Deny enslaving VLAN devices into VLAN aware bridge

VLAN devices on top of a DSA network device which is already part of a
bridge and with said bridge being VLAN aware should not be allowed to be
enslaved into that bridge. For one, this duplicates functionality
offered by the VLAN aware bridge which supports tagged and untagged VLAN
frames processing and it would make things needlessly complex to e.g.:
propagate FDB/MDB accordingly.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/slave.c

@@ -1408,16 +1408,49 @@ static int dsa_slave_changeupper(struct net_device *dev,
 	return err;
 }
 
+static int dsa_slave_upper_vlan_check(struct net_device *dev,
+				      struct netdev_notifier_changeupper_info *
+				      info)
+{
+	struct netlink_ext_ack *ext_ack;
+	struct net_device *slave;
+	struct dsa_port *dp;
+
+	ext_ack = netdev_notifier_info_to_extack(&info->info);
+
+	if (!is_vlan_dev(dev))
+		return NOTIFY_DONE;
+
+	slave = vlan_dev_real_dev(dev);
+	if (!dsa_slave_dev_check(slave))
+		return NOTIFY_DONE;
+
+	dp = dsa_slave_to_port(slave);
+	if (!dp->bridge_dev)
+		return NOTIFY_DONE;
+
+	/* Deny enslaving a VLAN device into a VLAN-aware bridge */
+	if (br_vlan_enabled(dp->bridge_dev) &&
+	    netif_is_bridge_master(info->upper_dev) && info->linking) {
+		NL_SET_ERR_MSG_MOD(ext_ack,
+				   "Cannot enslave VLAN device into VLAN aware bridge");
+		return notifier_from_errno(-EINVAL);
+	}
+
+	return NOTIFY_DONE;
+}
+
 static int dsa_slave_netdevice_event(struct notifier_block *nb,
 				     unsigned long event, void *ptr)
 {
 	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 
+	if (event == NETDEV_CHANGEUPPER) {
 		if (!dsa_slave_dev_check(dev))
-		return NOTIFY_DONE;
+			return dsa_slave_upper_vlan_check(dev, ptr);
 
-	if (event == NETDEV_CHANGEUPPER)
 		return dsa_slave_changeupper(dev, ptr);
+	}
 
 	return NOTIFY_DONE;
 }