tuntap: forbid changing mq flag for persistent device
We currently allow changing the mq flag (IFF_MULTI_QUEUE) for a persistent
device. This will result a mismatch between the number the queues in netdev and
tuntap. This is because we only allocate a 1q netdevice when IFF_MULTI_QUEUE was
not specified, so when we set the IFF_MULTI_QUEUE and try to attach more queues
later, netif_set_real_num_tx_queues() may fail which result a single queue
netdevice with multiple sockets attached.
Solve this by disallowing changing the mq flag for persistent device.
Bug was introduced by commit edfb6a148ce62e5e19354a1dcd9a34e00815c2a1
(tuntap: reduce memory using of queues).
Reported-by: Sriram Narasimhan <sriram.narasimhan@hp.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index f042b03..89776c5 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1585,6 +1585,10 @@
else
return -EINVAL;
+ if (!!(ifr->ifr_flags & IFF_MULTI_QUEUE) !=
+ !!(tun->flags & TUN_TAP_MQ))
+ return -EINVAL;
+
if (tun_not_capable(tun))
return -EPERM;
err = security_tun_dev_open(tun->security);
