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>

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>
David Woodhouse · David S. Miller
1 parent 0456b4f8b7
Showing 2 changed files with 3 additions and 0 deletions Side-by-side Diff
drivers/net/tun.c
include/linux/if_tun.h
@@ -874,6 +874,8 @@
  
 	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)
@@ -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. */
...	...	@@ -874,6 +874,8 @@
874	874
875	875	dev = __dev_get_by_name(net, ifr->ifr_name);
876	876	if (dev) {
	877	+ if (ifr->ifr_flags & IFF_TUN_EXCL)
	878	+ return -EBUSY;
877	879	if ((ifr->ifr_flags & IFF_TUN) && dev->netdev_ops == &tun_netdev_ops)
878	880	tun = netdev_priv(dev);
879	881	else if ((ifr->ifr_flags & IFF_TAP) && dev->netdev_ops == &tap_netdev_ops)
...	...	@@ -55,6 +55,7 @@
55	55	#define IFF_NO_PI 0x1000
56	56	#define IFF_ONE_QUEUE 0x2000
57	57	#define IFF_VNET_HDR 0x4000
	58	+#define IFF_TUN_EXCL 0x8000
58	59
59	60	/* Features for GSO (TUNSETOFFLOAD). */
60	61	#define TUN_F_CSUM 0x01 /* You can hand me unchecksummed packets. */