[patch 021/108] tun: Fix unregister race

[Greg KH]

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

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

From: Eric W. Biederman <ebiederm@xxxxxxxxxxxxxxxxxx>

[ 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@xxxxxxxxxxxxxxxxxx>
Tested-by: David Woodhouse <David.Woodhouse@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 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)


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