linux-kernel - Re: [PATCH 2/2] mkiss: Fix use after free in sixpack

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Message-Id: <20151218.160345.1312134246949260423.davem@davemloft.net>
Date:	Fri, 18 Dec 2015 16:03:45 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ralf@...ux-mips.org
Cc:	gnomes@...rguk.ukuu.org.uk, dvyukov@...gle.com,
	ajk@...nets.uni-bremen.de, linux-hams@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, jslaby@...e.com,
	syzkaller@...glegroups.com, kcc@...gle.com, glider@...gle.com,
	sasha.levin@...cle.com, edumazet@...gle.com
Subject: Re: [PATCH 2/2] mkiss: Fix use after free in sixpack_close().

From: Ralf Baechle <ralf@...ux-mips.org>
Date: Thu, 17 Dec 2015 22:35:31 +0100

> On Thu, Dec 17, 2015 at 04:05:49PM -0500, David Miller wrote:
> 
>> Subject: [PATCH 2/2] mkiss: Fix use after free in sixpack_close().
> 
> Make that subject "... mkiss_close()."

Durrr... indeed.  Thanks for catching that.

Committed as follows:

====================
[PATCH] mkiss: Fix use after free in mkiss_close().

Need to do the unregister_device() after all references to the driver
private have been done.

Signed-off-by: David S. Miller <davem@...emloft.net>
---
 drivers/net/hamradio/mkiss.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/hamradio/mkiss.c b/drivers/net/hamradio/mkiss.c
index 216bfd3..0b72b9d 100644
--- a/drivers/net/hamradio/mkiss.c
+++ b/drivers/net/hamradio/mkiss.c
@@ -798,13 +798,13 @@ static void mkiss_close(struct tty_struct *tty)
 	if (!atomic_dec_and_test(&ax->refcnt))
 		down(&ax->dead_sem);
 
-	unregister_netdev(ax->dev);
-
 	/* Free all AX25 frame buffers. */
 	kfree(ax->rbuff);
 	kfree(ax->xbuff);
 
 	ax->tty = NULL;
+
+	unregister_netdev(ax->dev);
 }
 
 /* Perform I/O control on an active ax25 channel. */
-- 
2.4.1

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