From f85ba78068ac137fe9c1f50d25405d2783d75c77 Mon Sep 17 00:00:00 2001 From: David Woodhouse Date: Mon, 27 Apr 2009 03:23:54 -0700 Subject: [PATCH] tun: add IFF_TUN_EXCL flag to avoid opening a persistent device. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: David S. Miller --- drivers/net/tun.c | 2 ++ include/linux/if_tun.h | 1 + 2 files changed, 3 insertions(+) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 589f0ca668d6..94622e5fb936 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -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) diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h index 049d6c9428db..915ba5789f0e 100644 --- a/include/linux/if_tun.h +++ b/include/linux/if_tun.h @@ -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. */