Commit f85ba780 authored Apr 27, 2009 by David Woodhouse Committed by David S. Miller Apr 27, 2009

tun: add IFF_TUN_EXCL flag to avoid opening a persistent device.



When creating a certain types of VPN, NetworkManager will first attempt
to find an available tun device by iterating through 'vpn%d' until it
finds one that isn't already busy. Then it'll set that to be persistent
and owned by the otherwise unprivileged user that the VPN dæmon itself
runs as.

There's a race condition here -- during the period where the vpn%d
device is created and we're waiting for the VPN dæmon to actually
connect and use it, if we try to create _another_ device we could end up
re-using the same one -- because trying to open it again doesn't get
-EBUSY as it would while it's _actually_ busy.

So solve this, we add an IFF_TUN_EXCL flag which causes tun_set_iff() to
fail if it would be opening an existing persistent tundevice -- so that
we can make sure we're getting an entirely _new_ device.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 0456b4f8

drivers/net/tun.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -874,6 +874,8 @@ static int tun_set_iff(struct net net, struct file file, struct ifreq *ifr)

		dev = __dev_get_by_name(net, ifr->ifr_name);
		if (dev) {
		if (ifr->ifr_flags & IFF_TUN_EXCL)
		return -EBUSY;
		if ((ifr->ifr_flags & IFF_TUN) && dev->netdev_ops == &tun_netdev_ops)
		tun = netdev_priv(dev);
		else if ((ifr->ifr_flags & IFF_TAP) && dev->netdev_ops == &tap_netdev_ops)

include/linux/if_tun.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -55,6 +55,7 @@
		#define IFF_NO_PI 0x1000
		#define IFF_ONE_QUEUE 0x2000
		#define IFF_VNET_HDR 0x4000
		#define IFF_TUN_EXCL 0x8000

		/* Features for GSO (TUNSETOFFLOAD). */
		#define TUN_F_CSUM 0x01 /* You can hand me unchecksummed packets. */

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