Commit 8e6d91ae authored May 28, 2013 by Jason Wang Committed by David S. Miller May 29, 2013

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 edfb6a14
(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>

parent 456db6a4

drivers/net/tun.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -1585,6 +1585,10 @@ static int tun_set_iff(struct net net, struct file file, struct ifreq *ifr)
		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);

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