From: Eric W. Biederman <ebiederm@aristanetworks.com>
Date: Mon, 8 Jun 2009 07:44:31 +0000 (-0700)
Subject: tun: Fix unregister race
X-Git-Tag: MMI-PSA29.97-13-9~27597^2~191
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=f0a4d0e5b5bfd271e6737f7c095994835b70d450;p=GitHub%2FMotorolaMobilityLLC%2Fkernel-slsi.git

tun: Fix unregister race

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>
---

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index d83ccb8c982b..811d3517fce0 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1322,21 +1322,22 @@ static int tun_chr_open(struct inode *inode, struct file * file)
 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)