[PATCH net] net: Fix the rollback test in dev_change_name()

[Jarek Poplawski <jarkao2@gmail.com>]

On Mon, Nov 02, 2009 at 12:05:49AM -0800, David Miller wrote:
> From: Jarek Poplawski <jarkao2@gmail.com>
> Date: Sat, 31 Oct 2009 00:50:09 +0100
> 
> > I don't think so: err stores the previous ret meaning rollback and
> > is checked for this later. But somebody forgot err can store previous
> > (positive) value here, so IMHO you're right: there is a bug in this
> > place ;-)
> 
> Just not the one Eric is specifically fixing :-)

Since this bug looks quite serious (consider -stable), here is a
proposal in case we forget what is Eric specifically fixing. ;-)

Thanks,
Jarek P.

---------------->
From: Eric Dumazet <eric.dumazet@gmail.com>

net: Fix the rollback test in dev_change_name()

In dev_change_name() an err variable is used for storing the original
call_netdevice_notifiers() errno (negative) and testing for a rollback
error later, but the test for non-zero is wrong, because the err might
have positive value as well - from dev_alloc_name(). It means the
rollback for a netdevice with a number > 0 will never happen. (The err
test is reordered btw. to make it more readable.)

Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
---

 net/core/dev.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index b8f74cf..fe10551 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -942,14 +942,15 @@ rollback:
 	ret = notifier_to_errno(ret);
 
 	if (ret) {
-		if (err) {
-			printk(KERN_ERR
-			       "%s: name change rollback failed: %d.\n",
-			       dev->name, ret);
-		} else {
+		/* err >= 0 after dev_alloc_name() or stores the first errno */
+		if (err >= 0) {
 			err = ret;
 			memcpy(dev->name, oldname, IFNAMSIZ);
 			goto rollback;
+		} else {
+			printk(KERN_ERR
+			       "%s: name change rollback failed: %d.\n",
+			       dev->name, ret);
 		}
 	}