From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:60781)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1RzCyz-0007uz-0p
	for qemu-devel@nongnu.org; Sun, 19 Feb 2012 15:03:42 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1RzCyx-0007KC-UX
	for qemu-devel@nongnu.org; Sun, 19 Feb 2012 15:03:40 -0500
Received: from mx1.redhat.com ([209.132.183.28]:42386)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1RzCyx-0007K6-J4
	for qemu-devel@nongnu.org; Sun, 19 Feb 2012 15:03:39 -0500
Received: from int-mx09.intmail.prod.int.phx2.redhat.com
	(int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22])
	by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q1JK3cBL012030
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK)
	for <qemu-devel@nongnu.org>; Sun, 19 Feb 2012 15:03:38 -0500
Date: Sun, 19 Feb 2012 22:03:43 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20120219200343.GA24464@redhat.com>
References: <cover.1329416075.git.mst@redhat.com>
	<f9fbea93081f7b7aa7e4f1814cf9f6dfbd6f907d.1329416075.git.mst@redhat.com>
	<alpine.LNX.2.00.1202162323260.2192@linmac>
	<4F3D6966.8090401@redhat.com> <20120217100810.GB31366@redhat.com>
	<m3ehttmydl.fsf@blackfin.pond.sub.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <m3ehttmydl.fsf@blackfin.pond.sub.org>
Subject: Re: [Qemu-devel] [PATCH 2/2] pci: rewrite devaddr parsing
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Markus Armbruster <armbru@redhat.com>
Cc: Eric Blake <eblake@redhat.com>, qemu-devel@nongnu.org

On Fri, Feb 17, 2012 at 01:35:02PM +0100, Markus Armbruster wrote:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
> 
> > On Thu, Feb 16, 2012 at 01:39:02PM -0700, Eric Blake wrote:
> >> On 02/16/2012 12:23 PM, malc wrote:
> >> > On Thu, 16 Feb 2012, Michael S. Tsirkin wrote:
> >> > 
> >> >> Use scanf instead of manual string scanning.
> >> >>
> >> >> +
> >> >> +    /* Parse [[<domain>:]<bus>:]<slot> */
> >> >> +    sscanf(addr, "%x:%x:%x%n", &dom, &bus, &slot, &n);
> >> > 
> >> > sscanf can fail.
> >> 
> >> Worse, the *scanf family has undefined behavior on integer overflow.  If
> >> addr contains "100000000000000:0:0", there's no telling whether it will
> >> be diagnosed as a parse error, or silently accepted and truncated, in
> >> which case, there's no telling what dom will contain.
> >> 
> >> I cringe any time I see someone using scanf to parse numbers from
> >> arbitrary user input; I barely tolerate it for parsing things generated
> >> by the kernel, but even there, I won't ever use scanf myself.
> >> Same goes
> >> for atoi.  _Only_ strtol and friends can robustly parse arbitrary input
> >> into integers.
> >
> > Seems easy to fix: I'll just set maximum field width of 8.
> 
> Nope.  Functional change: "000000001.2" is no longer accepted.

OK, there's an easy way to fix with
%*[0]%8x

> > Any other issues?
> 
> Yes.
> 
> 1. More functional changes, e.g.
> 
>    * "1" is no longer rejected when funcp != NULL
> 
>    Probably more.  I'd be particularly wary of sscanf()'s appetite for
>    space.

BTW strtoul that we currently use skips whitespace
silently too. We probably should validate input with
%*[0-9a-f.:] beforehand to address this.

> 2. Diffstat: 1 files changed, 38 insertions(+), 43 deletions(-)
> 
> Why bother?