staging: dpaa2-switch: prevent joining a bridge while VLAN uppers are…

… present

Each time a switch port joins a bridge, it will start to use a FDB table
common with all the other switch ports that are under the same bridge.
This means that any VLAN added prior to a bridge join, will retain its
previous FDB table destination. With this patch, I choose to restrict
when a switch port can change it's upper device (either join or leave)
so that the driver does not have to delete all the previously installed
VLANs from the previous FDB and add them into the new one.

Thus, in the PRECHANGEUPPER  notification we check if there are any VLAN
type upper devices and if that's true, deny the CHANGEUPPER.

This way, the user is not restricted in the topology but rather in the
order in which the setup is done: it must first create the bridging
domain layout and after that add the necessary VLAN devices if
necessary. The teardown is similar, the VLAN devices will need to be
destroyed prior to a change in the bridging layout.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Link: https://lore.kernel.org/r/20210310121452.552070-15-ciorneiioana@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fsl-dpaa2/ethsw/ethsw.c

@@ -1590,6 +1590,21 @@ static int dpaa2_switch_port_bridge_leave(struct net_device *netdev)
 					  BRIDGE_VLAN_INFO_UNTAGGED | BRIDGE_VLAN_INFO_PVID);
 }
 
+static int dpaa2_switch_prevent_bridging_with_8021q_upper(struct net_device *netdev)
+{
+	struct net_device *upper_dev;
+	struct list_head *iter;
+
+	/* RCU read lock not necessary because we have write-side protection
+	 * (rtnl_mutex), however a non-rcu iterator does not exist.
+	 */
+	netdev_for_each_upper_dev_rcu(netdev, upper_dev, iter)
+		if (is_vlan_dev(upper_dev))
+			return -EOPNOTSUPP;
+
+	return 0;
+}
+
 static int dpaa2_switch_port_netdevice_event(struct notifier_block *nb,
 					     unsigned long event, void *ptr)
 {
@@ -1607,10 +1622,22 @@ static int dpaa2_switch_port_netdevice_event(struct notifier_block *nb,
 	switch (event) {
 	case NETDEV_PRECHANGEUPPER:
 		upper_dev = info->upper_dev;
-		if (netif_is_bridge_master(upper_dev) && !br_vlan_enabled(upper_dev)) {
+		if (!netif_is_bridge_master(upper_dev))
+			break;
+
+		if (!br_vlan_enabled(upper_dev)) {
 			NL_SET_ERR_MSG_MOD(extack, "Cannot join a VLAN-unaware bridge");
 			err = -EOPNOTSUPP;
+			goto out;
+		}
+
+		err = dpaa2_switch_prevent_bridging_with_8021q_upper(netdev);
+		if (err) {
+			NL_SET_ERR_MSG_MOD(extack,
+					   "Cannot join a bridge while VLAN uppers are present");
+			goto out;
 		}
+
 		break;
 	case NETDEV_CHANGEUPPER:
 		upper_dev = info->upper_dev;
@@ -1623,6 +1650,7 @@ static int dpaa2_switch_port_netdevice_event(struct notifier_block *nb,
 		break;
 	}
 
+out:
 	return notifier_from_errno(err);
 }