[patch 021/108] tun: Fix unregister race

Greg KH
2009-07-01T00:52:42Z

[-- Attachment #1: tun-fix-unregister-race.patch --]
[-- Type: text/plain, Size: 1722 bytes --]

2.6.30-stable review patch. If anyone has any objections, please let us know.

------------------

From: Eric W. Biederman <ebiederm@aristanetworks.com>

[ Upstream commit f0a4d0e5b5bfd271e6737f7c095994835b70d450 ]

It is possible for tun_chr_close to race with dellink on the
a tun device. In which case if __tun_get runs before dellink
but dellink runs before tun_chr_close calls unregister_netdevice
we will attempt to unregister the netdevice after it is already
gone.

The two cases are already serialized on the rtnl_lock, so I have
gone for the cheap simple fix of moving rtnl_lock to cover __tun_get
in tun_chr_close. Eliminating the possibility of the tun device
being unregistered between __tun_get and unregister_netdevice in
tun_chr_close.

Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Tested-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/net/tun.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1275,21 +1275,22 @@ static int tun_chr_open(struct inode *in
static int tun_chr_close(struct inode *inode, struct file *file)
{
struct tun_file *tfile = file->private_data;
- struct tun_struct *tun = __tun_get(tfile);
+ struct tun_struct *tun;

+ rtnl_lock();
+ tun = __tun_get(tfile);
if (tun) {
DBG(KERN_INFO "%s: tun_chr_close\n", tun->dev->name);

- rtnl_lock();
__tun_detach(tun);

/* If desireable, unregister the netdevice. */
if (!(tun->flags & TUN_PERSIST))
unregister_netdevice(tun->dev);

- rtnl_unlock();
}
+ rtnl_unlock();

tun = tfile->tun;
if (tun)