[ 3.5.y.z extended stable ] Patch "netpoll: fix NULL pointer dereference in netpoll_cleanup" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    netpoll: fix NULL pointer dereference in netpoll_cleanup

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 13534dcb11dc5b3338f6aa3fc2df623425a37bbe Mon Sep 17 00:00:00 2001
From: Nikolay Aleksandrov <nikolay at redhat.com>
Date: Thu, 19 Sep 2013 15:02:35 +0200
Subject: [PATCH] netpoll: fix NULL pointer dereference in netpoll_cleanup

commit d0fe8c888b1fd1a2f84b9962cabcb98a70988aec upstream.

I've been hitting a NULL ptr deref while using netconsole because the
np->dev check and the pointer manipulation in netpoll_cleanup are done
without rtnl and the following sequence happens when having a netconsole
over a vlan and we remove the vlan while disabling the netconsole:
	CPU 1					CPU2
					removes vlan and calls the notifier
enters store_enabled(), calls
netdev_cleanup which checks np->dev
and then waits for rtnl
					executes the netconsole netdev
					release notifier making np->dev
					== NULL and releases rtnl
continues to dereference a member of
np->dev which at this point is == NULL

Signed-off-by: Nikolay Aleksandrov <nikolay at redhat.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/core/netpoll.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index f9f40b9..5e81c49 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -920,15 +920,14 @@ EXPORT_SYMBOL_GPL(__netpoll_cleanup);

 void netpoll_cleanup(struct netpoll *np)
 {
-	if (!np->dev)
-		return;
-
 	rtnl_lock();
+	if (!np->dev)
+		goto out;
 	__netpoll_cleanup(np);
-	rtnl_unlock();
-
 	dev_put(np->dev);
 	np->dev = NULL;
+out:
+	rtnl_unlock();
 }
 EXPORT_SYMBOL(netpoll_cleanup);

--
1.8.3.2