macvtap: Close a race between macvtap_open and macvtap_dellink.

There is a small window in macvtap_open between looking up a
networking device and calling macvtap_set_queue in which
macvtap_del_queues called from macvtap_dellink.   After
calling macvtap_del_queues it is totally incorrect to
allow macvtap_set_queue to proceed so prevent success by
reporting that all of the available queues are in use.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 3da557830937dee2c7edeea3326ee88c6b7e158b..70aa628834f03e7d9ee7b4f2ac629333a6627169 100644 (file)
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -231,6 +231,8 @@ static void macvtap_del_queues(struct net_device *dev)
                }
        }
        BUG_ON(vlan->numvtaps != 0);
+       /* guarantee that any future macvtap_set_queue will fail */
+       vlan->numvtaps = MAX_MACVTAP_QUEUES;
        spin_unlock(&macvtap_lock);
 
        synchronize_rcu();