bridge: switchdev: Allow device drivers to install locked FDB entries

When the bridge is offloaded to hardware, FDB entries are learned and
aged-out by the hardware. Some device drivers synchronize the hardware
and software FDBs by generating switchdev events towards the bridge.

When a port is locked, the hardware must not learn autonomously, as
otherwise any host will blindly gain authorization. Instead, the
hardware should generate events regarding hosts that are trying to gain
authorization and their MAC addresses should be notified by the device
driver as locked FDB entries towards the bridge driver.

Allow device drivers to notify the bridge driver about such entries by
extending the 'switchdev_notifier_fdb_info' structure with the 'locked'
bit. The bit can only be set by device drivers and not by the bridge
driver.

Prevent a locked entry from being installed if MAB is not enabled on the
bridge port.

If an entry already exists in the bridge driver, reject the locked entry
if the current entry does not have the "locked" flag set or if it points
to a different port. The same semantics are implemented in the software
data path.

Signed-off-by: Hans J. Schultz <[e-mail]>
Signed-off-by: Ido Schimmel <[e-mail]>
Reviewed-by: Petr Machata <[e-mail]>
Signed-off-by: Petr Machata <[e-mail]>
Reviewed-by: Vladimir Oltean <[e-mail]>
Acked-by: Nikolay Aleksandrov <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/switchdev.h

···
 	u16 vid;
 	u8 added_by_user:1,
 	   is_local:1,
+	   locked:1,
 	   offloaded:1;
 };
 

net/bridge/br.c

···
 	case SWITCHDEV_FDB_ADD_TO_BRIDGE:
 		fdb_info = ptr;
 		err = br_fdb_external_learn_add(br, p, fdb_info->addr,
-						fdb_info->vid, false);
+						fdb_info->vid,
+						fdb_info->locked, false);
 		if (err) {
 			err = notifier_from_errno(err);
 			break;

net/bridge/br_fdb.c

···
 					   "FDB entry towards bridge must be permanent");
 			return -EINVAL;
 		}
-		err = br_fdb_external_learn_add(br, p, addr, vid, true);
+		err = br_fdb_external_learn_add(br, p, addr, vid, false, true);
 	} else {
 		spin_lock_bh(&br->hash_lock);
 		err = fdb_add_entry(br, p, addr, ndm, nlh_flags, vid, nfea_tb);
···
 }
 
 int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
-			      const unsigned char *addr, u16 vid,
+			      const unsigned char *addr, u16 vid, bool locked,
 			      bool swdev_notify)
 {
 	struct net_bridge_fdb_entry *fdb;
···
 	int err = 0;
 
 	trace_br_fdb_external_learn_add(br, p, addr, vid);
+
+	if (locked && (!p || !(p->flags & BR_PORT_MAB)))
+		return -EINVAL;
 
 	spin_lock_bh(&br->hash_lock);
 
···
 		if (!p)
 			flags |= BIT(BR_FDB_LOCAL);
 
+		if (locked)
+			flags |= BIT(BR_FDB_LOCKED);
+
 		fdb = fdb_create(br, p, addr, vid, flags);
 		if (!fdb) {
 			err = -ENOMEM;
···
 		}
 		fdb_notify(br, fdb, RTM_NEWNEIGH, swdev_notify);
 	} else {
+		if (locked &&
+		    (!test_bit(BR_FDB_LOCKED, &fdb->flags) ||
+		     READ_ONCE(fdb->dst) != p)) {
+			err = -EINVAL;
+			goto err_unlock;
+		}
+
 		fdb->updated = jiffies;
 
 		if (READ_ONCE(fdb->dst) != p) {
···
 		} else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
 			/* Take over SW learned entry */
 			set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
+			modified = true;
+		}
+
+		if (locked != test_bit(BR_FDB_LOCKED, &fdb->flags)) {
+			change_bit(BR_FDB_LOCKED, &fdb->flags);
 			modified = true;
 		}
 

net/bridge/br_private.h

···
 void br_fdb_unsync_static(struct net_bridge *br, struct net_bridge_port *p);
 int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
 			      const unsigned char *addr, u16 vid,
-			      bool swdev_notify);
+			      bool locked, bool swdev_notify);
 int br_fdb_external_learn_del(struct net_bridge *br, struct net_bridge_port *p,
 			      const unsigned char *addr, u16 vid,
 			      bool swdev_notify);

net/bridge/br_switchdev.c

···
 	item->added_by_user = test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags);
 	item->offloaded = test_bit(BR_FDB_OFFLOADED, &fdb->flags);
 	item->is_local = test_bit(BR_FDB_LOCAL, &fdb->flags);
+	item->locked = false;
 	item->info.dev = (!p || item->is_local) ? br->dev : p->dev;
 	item->info.ctx = ctx;
 }
···
 			const struct net_bridge_fdb_entry *fdb, int type)
 {
 	struct switchdev_notifier_fdb_info item;
+
+	if (test_bit(BR_FDB_LOCKED, &fdb->flags))
+		return;
 
 	br_switchdev_fdb_populate(br, &item, fdb, NULL);