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Commit f85ba780 authored by David Woodhouse's avatar David Woodhouse Committed by David S. Miller
Browse files

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: default avatarDavid Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0456b4f8

drivers/net/tun.c

+2 −0
Original line number Original line 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);

	dev = __dev_get_by_name(net, ifr->ifr_name);

	if (dev) {

	if (dev) {

		if (ifr->ifr_flags & IFF_TUN_EXCL)

			return -EBUSY;

		if ((ifr->ifr_flags & IFF_TUN) && dev->netdev_ops == &tun_netdev_ops)

		if ((ifr->ifr_flags & IFF_TUN) && dev->netdev_ops == &tun_netdev_ops)

			tun = netdev_priv(dev);

			tun = netdev_priv(dev);

		else if ((ifr->ifr_flags & IFF_TAP) && dev->netdev_ops == &tap_netdev_ops)

		else if ((ifr->ifr_flags & IFF_TAP) && dev->netdev_ops == &tap_netdev_ops)

include/linux/if_tun.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -55,6 +55,7 @@ 
#define IFF_NO_PI	0x1000

#define IFF_NO_PI	0x1000

#define IFF_ONE_QUEUE	0x2000

#define IFF_ONE_QUEUE	0x2000

#define IFF_VNET_HDR	0x4000

#define IFF_VNET_HDR	0x4000

#define IFF_TUN_EXCL	0x8000





/* Features for GSO (TUNSETOFFLOAD). */

/* Features for GSO (TUNSETOFFLOAD). */

#define TUN_F_CSUM	0x01	/* You can hand me unchecksummed packets. */

#define TUN_F_CSUM	0x01	/* You can hand me unchecksummed packets. */