From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH] drm/i915/ppgtt: Prevent NULL deref in reset
	ioctl
Date: Fri, 20 Dec 2013 15:11:09 +0100
Message-ID: <20131220141044.GA23400@phenom.ffwll.local>
References: <1387495360-15114-1-git-send-email-benjamin.widawsky@intel.com>
	<CAKMK7uGscQU=frnJxnEzCcznazSnw-=0SxH_Ca0mdpVpGcypzQ@mail.gmail.com>
	<20131220065556.GA31581@bwidawsk.net>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <intel-gfx-bounces@lists.freedesktop.org>
Received: from mail-ea0-f176.google.com (mail-ea0-f176.google.com
	[209.85.215.176])
	by gabe.freedesktop.org (Postfix) with ESMTP id EF840FA33E
	for <intel-gfx@lists.freedesktop.org>;
	Fri, 20 Dec 2013 06:10:27 -0800 (PST)
Received: by mail-ea0-f176.google.com with SMTP id h14so1073871eaj.35
	for <intel-gfx@lists.freedesktop.org>;
	Fri, 20 Dec 2013 06:10:25 -0800 (PST)
Content-Disposition: inline
In-Reply-To: <20131220065556.GA31581@bwidawsk.net>
List-Unsubscribe: <http://lists.freedesktop.org/mailman/options/intel-gfx>,
	<mailto:intel-gfx-request@lists.freedesktop.org?subject=unsubscribe>
List-Archive: <http://lists.freedesktop.org/archives/intel-gfx>
List-Post: <mailto:intel-gfx@lists.freedesktop.org>
List-Help: <mailto:intel-gfx-request@lists.freedesktop.org?subject=help>
List-Subscribe: <http://lists.freedesktop.org/mailman/listinfo/intel-gfx>,
	<mailto:intel-gfx-request@lists.freedesktop.org?subject=subscribe>
Sender: intel-gfx-bounces@lists.freedesktop.org
Errors-To: intel-gfx-bounces@lists.freedesktop.org
To: Ben Widawsky <ben@bwidawsk.net>
Cc: Intel GFX <intel-gfx@lists.freedesktop.org>, Ben Widawsky <benjamin.widawsky@intel.com>
List-Id: intel-gfx@lists.freedesktop.org

On Thu, Dec 19, 2013 at 10:55:56PM -0800, Ben Widawsky wrote:
> On Fri, Dec 20, 2013 at 07:05:10AM +0100, Daniel Vetter wrote:
> > On Fri, Dec 20, 2013 at 12:22 AM, Ben Widawsky
> > <benjamin.widawsky@intel.com> wrote:
> > >         ctx = i915_gem_context_get(file->driver_priv, args->ctx_id);
> > > -       if (IS_ERR(ctx)) {
> > > +       if (IS_ERR_OR_NULL(ctx)) {
> > 
> > We now have half the callers check for IS_ERR and the others not.
> > Afaics i915_gem_context_get can only return NULL or a real context
> > though. Also from a quite read the expected error for a lookup failure
> > is ENOENT (and there seems to be a testcase for this).
> > -Daniel
> 
> 
> To your first point:
> I think checking null is always the right thing currently, but for
> future proofing, IS_ERR_OR_NULL is really the right thing. After his
> patch, I believe only i915_gem_context_destroy_ioctl is still incorrect.

Using IS_ERR_OR_NULL on a return value which can never contain an
encoded errno value is imo confusing, more so when it's inconsitently
applied.

> To the second:
> This is only based on my memory, so feel free to change whatever you
> need. When I retuned -ENXIO, the test failed.
> 
> It should be:
> return ctx ? PTR_ERR(ctx) : -ENOENT;

On a cursory read that's been the semantics before your patch. And there
seems to be a testcase in gem_reset_stat for this, have you run all
subtests?

> I had
> return ctx ? PTR_ERR(ctx) : -ENXIO;
> which made the subtest fail. However, as we've noted, this itself was
> not correct. Try the return above.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch