Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753655Ab3COIYO (ORCPT ); Fri, 15 Mar 2013 04:24:14 -0400 Received: from mga02.intel.com ([134.134.136.20]:12561 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752357Ab3COIYL (ORCPT ); Fri, 15 Mar 2013 04:24:11 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,849,1355126400"; d="scan'208";a="302641178" Date: Fri, 15 Mar 2013 08:24:03 +0000 From: Chris Wilson To: Ben Widawsky Cc: Tommi Rantala , David Airlie , Daniel Vetter , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Dave Jones Subject: Re: [Intel-gfx] [PATCH] drm/i915: Sanity check incoming ioctl data for a NULL pointer Message-ID: <20130315082403.GA29916@cantiga.alporthouse.com> Mail-Followup-To: Chris Wilson , Ben Widawsky , Tommi Rantala , David Airlie , Daniel Vetter , intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Dave Jones References: <1363265997-29023-1-git-send-email-chris@chris-wilson.co.uk> <20130315045004.GA14747@bwidawsk.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130315045004.GA14747@bwidawsk.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2831 Lines: 70 On Thu, Mar 14, 2013 at 09:50:04PM -0700, Ben Widawsky wrote: > On Thu, Mar 14, 2013 at 12:59:57PM +0000, Chris Wilson wrote: > > In order to prevent a potential NULL deference with hostile userspace, > > we need to check whether the ioctl was passed an invalid args pointer. > > > > Reported-by: Tommi Rantala > > Link: http://lkml.kernel.org/r/CA+ydwtpuBvbwxbt-tdgPUvj1EU7itmCHo_2B3w13HkD5+jWKow@mail.gmail.com > > Signed-off-by: Chris Wilson > > --- > > drivers/gpu/drm/i915/i915_gem_execbuffer.c | 11 +++++++++-- > > 1 file changed, 9 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c > > index 365e41a..9f5602e 100644 > > --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c > > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c > > @@ -1103,7 +1103,11 @@ i915_gem_execbuffer(struct drm_device *dev, void *data, > > struct drm_i915_gem_exec_object2 *exec2_list = NULL; > > int ret, i; > > > > - if (args->buffer_count < 1) { > > + if (args == NULL) > > + return -EINVAL; > > + > > + if (args->buffer_count < 1 || > > + args->buffer_count > INT_MAX / sizeof(*exec2_list)) { > > DRM_DEBUG("execbuf with %d buffers\n", args->buffer_count); > > return -EINVAL; > > } > > @@ -1182,8 +1186,11 @@ i915_gem_execbuffer2(struct drm_device *dev, void *data, > > struct drm_i915_gem_exec_object2 *exec2_list = NULL; > > int ret; > > > > + if (args == NULL) > > + return -EINVAL; > > + > > if (args->buffer_count < 1 || > > - args->buffer_count > UINT_MAX / sizeof(*exec2_list)) { > > + args->buffer_count > INT_MAX / sizeof(*exec2_list)) { > > DRM_DEBUG("execbuf2 with %d buffers\n", args->buffer_count); > > return -EINVAL; > > } > > Why did you change UINT_MAX to INT_MAX? Because we check later against INT_MAX, and I didn't like the confusion. If we are going to pick an arbitrary limit, lets at least be consistent. > TBH, I'm confused what we're > trying to achieve, and why we need anything other than: > if (!args->buffer_count) Because we then promptly do a u32 multiply and we need to be sure that userspace can't trigger an overflow there and cause us to read unallocated memory later. > > I'm also not seeing how the NULL checks are needed since at least it > seems to be for execbuffer (IOW) we could never have NULL args. That's what I thought too. Looking at the stack trace, the empirical evidence is that we need the check. -Chris -- Chris Wilson, Intel Open Source Technology Centre -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/