Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934176AbcKVSG0 (ORCPT ); Tue, 22 Nov 2016 13:06:26 -0500 Received: from mga07.intel.com ([134.134.136.100]:27244 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932768AbcKVSGZ (ORCPT ); Tue, 22 Nov 2016 13:06:25 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.31,533,1473145200"; d="scan'208";a="8031676" Date: Tue, 22 Nov 2016 20:06:19 +0200 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: Rob Clark Cc: Liviu Dudau , Jani Nikula , Daniel Vetter , Eric Engestrom , LKML , DRI devel Subject: Re: [PATCH] drm: check for NULL parameter in exported drm_get_format_name() function. Message-ID: <20161122180619.GE31595@intel.com> References: <20161122164106.31852-1-Liviu.Dudau@arm.com> <20161122165017.GC31595@intel.com> <20161122173157.GD31595@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2692 Lines: 64 On Tue, Nov 22, 2016 at 12:35:53PM -0500, Rob Clark wrote: > On Tue, Nov 22, 2016 at 12:31 PM, Ville Syrj?l? > wrote: > > On Tue, Nov 22, 2016 at 12:23:59PM -0500, Rob Clark wrote: > >> On Tue, Nov 22, 2016 at 11:50 AM, Ville Syrj?l? > >> wrote: > >> > On Tue, Nov 22, 2016 at 04:41:06PM +0000, Liviu Dudau wrote: > >> >> drm_get_format_name() de-references the buf parameter without checking > >> >> if the pointer was not NULL. Given that the function is EXPORT-ed, lets > >> >> sanitise the parameters before proceeding. > >> >> > >> >> Fixes: b3c11ac267d461d3d5 ("drm: move allocation out of drm_get_format_name()) > >> >> Cc: Eric Engestrom > >> >> Cc: Rob Clark > >> >> Cc: Jani Nikula > >> >> Cc: Daniel Vetter > >> >> > >> >> Signed-off-by: Liviu Dudau > >> >> --- > >> >> drivers/gpu/drm/drm_fourcc.c | 3 +++ > >> >> 1 file changed, 3 insertions(+) > >> >> > >> >> diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c > >> >> index 90d2cc8..0a3ff0b 100644 > >> >> --- a/drivers/gpu/drm/drm_fourcc.c > >> >> +++ b/drivers/gpu/drm/drm_fourcc.c > >> >> @@ -85,6 +85,9 @@ EXPORT_SYMBOL(drm_mode_legacy_fb_format); > >> >> */ > >> >> const char *drm_get_format_name(uint32_t format, struct drm_format_name_buf *buf) > >> >> { > >> >> + if (!buf) > >> >> + return NULL; > >> >> + > >> > > >> > Seems rather pointless to me. Why would you ever pass NULL to this guy? > >> > >> perhaps BUG_ON(!buf)... > > > > And how does that differ from just buf->foo? > > it gets you a file and line # in the error splat.. not that > drm_get_format_name() is such a big function that it would be > difficult to decipher the null deref crash, but if we added anything > it should be BUG_ON() to make it clear that passing null isn't a > caller error. Yeah, BUG_ON() at least documents the intent, so it's better than the null check. But for something like this even BUG_ON() is just wasted bytes IMO. BUG_ON() can be useful for those weird bugs where somewhere deep down you hit a null pointer and you can't figure out where the bad pointer came from. So you might sprinkle a few BUG_ONs() further up to catch it sooner. Esp. if you can't reproduce the bug yourself and have to rely on user(s) to find it for you. Even WARN_ON() w/ or w/o an early bailout might be a decent idea sometimes since it might have a slightly higher chance of keeping the kernel in working condition, but IMO just blindly throwing it around everywhere is not a good approach. -- Ville Syrj?l? Intel OTC