netdev - Re: tun netns BUG()

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Message-ID: <20090703090355.GA25768@gondor.apana.org.au>
Date:	Fri, 3 Jul 2009 17:03:55 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"David S. Miller" <davem@...emloft.net>
Cc:	dwmw2@...radead.org, netdev@...r.kernel.org,
	johannes@...solutions.net
Subject: Re: tun netns BUG()

On Fri, Jul 03, 2009 at 04:35:01PM +0800, Herbert Xu wrote:
> 
> This just turns a wide-open race into a less likely one (that's
> why it appears to fix the problem).  The crux of the issue is that 
> __tun_get(tfile) != NULL has nothing to do with whether the device
> has been unregistered.

tun: Fix device unregister race

It is currently possible for an asynchronous device unregister
to cause the same tun device to be unregistered twice.  This
is because the unregister in tun_chr_close only checks whether
__tun_get(tfile) != NULL.  This however has nothing to do with
whether the device has already been unregistered.  All it tells
you is whether __tun_detach has been called.

This patch fixes this by using the most obvious thing to test
whether the device has been unregistered.

It also moves __tun_detach outside of rtnl_unlock since nothing
that it does requires that lock.

Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 11a0ba4..b393536 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1324,20 +1324,22 @@ static int tun_chr_close(struct inode *inode, struct file *file)
 	struct tun_file *tfile = file->private_data;
 	struct tun_struct *tun;
 
-
-	rtnl_lock();
 	tun = __tun_get(tfile);
 	if (tun) {
-		DBG(KERN_INFO "%s: tun_chr_close\n", tun->dev->name);
+		struct net_device *dev = tun->dev;
+
+		DBG(KERN_INFO "%s: tun_chr_close\n", dev->name);
 
 		__tun_detach(tun);
 
 		/* If desireable, unregister the netdevice. */
-		if (!(tun->flags & TUN_PERSIST))
-			unregister_netdevice(tun->dev);
-
+		if (!(tun->flags & TUN_PERSIST)) {
+			rtnl_lock();
+			if (dev->reg_state == NETREG_REGISTERED)
+				unregister_netdevice(dev);
+			rtnl_unlock();
+		}
 	}
-	rtnl_unlock();
 
 	tun = tfile->tun;
 	if (tun)

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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