linux-kernel - [ 07/48] netpoll: fix NULL pointer dereference in netpoll

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Message-Id: <20131011193638.078000526@linuxfoundation.org>
Date:	Fri, 11 Oct 2013 12:36:14 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Nikolay Aleksandrov <nikolay@...hat.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 07/48] netpoll: fix NULL pointer dereference in netpoll_cleanup

3.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Nikolay Aleksandrov <nikolay@...hat.com>

[ Upstream commit d0fe8c888b1fd1a2f84b9962cabcb98a70988aec ]

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@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/netpoll.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- 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);
 


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