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>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 3da557830937..70aa628834f0 100644
--- 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();