net: bridge: fix net device refcount tracking issue in error path

I left one dev_put() in br_add_if() error path and sure enough
syzbot found its way.

As the tracker is allocated in new_nbp(), we must make sure
to properly free it.

We have to call dev_put_track(dev, &p->dev_tracker) before
@p object is freed, of course. This is not an issue because
br_add_if() owns a reference on @dev.

Fixes: b2dcdc7f ("net: bridge: add net device refcount tracker")
Signed-off-by: NEric Dumazet <edumazet@google.com>
Reported-by: Nsyzbot <syzkaller@googlegroups.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/bridge/br_if.c

@@ -615,6 +615,7 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	err = dev_set_allmulti(dev, 1);
 	if (err) {
 		br_multicast_del_port(p);
+		dev_put_track(dev, &p->dev_tracker);
 		kfree(p);	/* kobject not yet init'd, manually free */
 		goto err1;
 	}
@@ -724,10 +725,10 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
 	sysfs_remove_link(br->ifobj, p->dev->name);
 err2:
 	br_multicast_del_port(p);
+	dev_put_track(dev, &p->dev_tracker);
 	kobject_put(&p->kobj);
 	dev_set_allmulti(dev, -1);
 err1:
-	dev_put(dev);
 	return err;
 }