net: bridge: sync fdb to new unicast-filtering ports

Since commit 2796d0c6 ("bridge: Automatically manage
port promiscuous mode.")
bridges with `vlan_filtering 1` and only 1 auto-port don't
set IFF_PROMISC for unicast-filtering-capable ports.

Normally on port changes `br_manage_promisc` is called to
update the promisc flags and unicast filters if necessary,
but it cannot distinguish between *new* ports and ones
losing their promisc flag, and new ports end up not
receiving the MAC address list.

Fix this by calling `br_fdb_sync_static` in `br_add_if`
after the port promisc flags are updated and the unicast
filter was supposed to have been filled.

Fixes: 2796d0c6 ("bridge: Automatically manage port promiscuous mode.")
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_if.c

@@ -562,7 +562,7 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	struct net_bridge_port *p;
 	int err = 0;
 	unsigned br_hr, dev_hr;
-	bool changed_addr;
+	bool changed_addr, fdb_synced = false;
 
 	/* Don't allow bridging non-ethernet like devices. */
 	if ((dev->flags & IFF_LOOPBACK) ||
@@ -652,6 +652,19 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	list_add_rcu(&p->list, &br->port_list);
 
 	nbp_update_port_count(br);
+	if (!br_promisc_port(p) && (p->dev->priv_flags & IFF_UNICAST_FLT)) {
+		/* When updating the port count we also update all ports'
+		 * promiscuous mode.
+		 * A port leaving promiscuous mode normally gets the bridge's
+		 * fdb synced to the unicast filter (if supported), however,
+		 * `br_port_clear_promisc` does not distinguish between
+		 * non-promiscuous ports and *new* ports, so we need to
+		 * sync explicitly here.
+		 */
+		fdb_synced = br_fdb_sync_static(br, p) == 0;
+		if (!fdb_synced)
+			netdev_err(dev, "failed to sync bridge static fdb addresses to this port\n");
+	}
 
 	netdev_update_features(br->dev);
 
@@ -701,6 +714,8 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	return 0;
 
 err7:
+	if (fdb_synced)
+		br_fdb_unsync_static(br, p);
 	list_del_rcu(&p->list);
 	br_fdb_delete_by_port(br, p, 0, 1);
 	nbp_update_port_count(br);