From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753478AbcD0IH2 (ORCPT <rfc822;w@1wt.eu>);
	Wed, 27 Apr 2016 04:07:28 -0400
Received: from mail2-relais-roc.national.inria.fr ([192.134.164.83]:55144 "EHLO
	mail2-relais-roc.national.inria.fr" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1752262AbcD0IHV (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 27 Apr 2016 04:07:21 -0400
X-IronPort-AV: E=Sophos;i="5.24,540,1454972400"; 
   d="scan'208";a="215999339"
Date: Wed, 27 Apr 2016 10:07:05 +0200 (CEST)
From: Julia Lawall <julia.lawall@lip6.fr>
X-X-Sender: jll@hadrien
To: Dan Carpenter <dan.carpenter@oracle.com>
cc: Kees Cook <keescook@google.com>, Pengfei Wang <wpengfeinudt@gmail.com>,
        "security@kernel.org" <security@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: Double-Fetch bug in Linux-4.5/drivers/scsi/aacraid/commctrl.c
In-Reply-To: <20160427080105.GI17913@mwanda>
Message-ID: <alpine.DEB.2.10.1604271005530.3100@hadrien>
References: <0484FFD3-4BAB-43B9-AD56-B4A098C3E8AE@gmail.com> <CAGXu5jLYkLpMzvwm+mFBfoaNMqkTpXhrt_c7kJN0SvQVqJqyYw@mail.gmail.com> <alpine.DEB.2.02.1604270741260.2223@localhost6.localdomain6> <20160427080105.GI17913@mwanda>
User-Agent: Alpine 2.10 (DEB 1266 2009-07-14)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org



On Wed, 27 Apr 2016, Dan Carpenter wrote:

> On Wed, Apr 27, 2016 at 07:42:04AM +0200, Julia Lawall wrote:
> >
> >
> > On Tue, 26 Apr 2016, Kees Cook wrote:
> >
> > > On Mon, Apr 25, 2016 at 7:50 AM, Pengfei Wang <wpengfeinudt@gmail.com> wrote:
> > > > Hello,
> > > >
> > > > I found this Double-Fetch bug in Linux-4.5/drivers/scsi/aacraid/commctrl.c
> > > > when I was examining the source code.
> > >
> > > Thanks for these reports! I wrote a coccinelle script to find these,
> > > but it requires some manual checking. For what it's worth, it found
> > > your report as well:
> > >
> > > ./drivers/scsi/aacraid/commctrl.c:116:5-19: potentially dangerous
> > > second copy_from_user()
> > >
> > > So I should probably get this added to the coccicheck run... Maybe it
> > > can get some clean up from Julia. :)
> >
> > I looked a bit at the results, and didn't see anything obvious.  What is
> > the problem, exactly, and what would be a characteristic of a false
> > positive?
> >
>
>
> 	copy_from_user(dest, src, sizeof(dest));
>
> 	if (dest.extra > MAX_SIZE)
> 		return -EINVAL;
>
> 	copy_from_user(dest, src, sizeof(dest) + dest.extra);
>
> 	for (i = 0; i < dest.extra; i++) {
> 		dest.foo[i] = xxx;
>
>
> We get dest.extra from the user, we verify the size, then we copy more
> data from the user but that over writes dest.extra again.  We use
> dest.extra a second time without checking that it's still <= MAX_SIZE.

OK, so the problem is when data that was checked on the first copy is used
after the second copy?  It would probably be possible to get rid of a lot
of false positives with that.

thanks,
julia