linux-hardening - Re: [PATCH][next] drm/i915/uapi: Replace fake flex-array with flexible-array member

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Date:   Tue, 21 Mar 2023 08:43:07 +0000
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/i915/uapi: Replace fake flex-array with
 flexible-array member


On 20/03/2023 17:36, Kees Cook wrote:
> On Fri, Mar 17, 2023 at 12:18:01PM -0600, Gustavo A. R. Silva wrote:
>> Zero-length arrays as fake flexible arrays are deprecated and we are
>> moving towards adopting C99 flexible-array members instead.
>>
>> Address the following warning found with GCC-13 and
>> -fstrict-flex-arrays=3 enabled:
>> drivers/gpu/drm/i915/gem/i915_gem_context.c: In function ‘set_proto_ctx_engines.isra’:
>> drivers/gpu/drm/i915/gem/i915_gem_context.c:769:41: warning: array subscript n is outside array bounds of ‘struct i915_engine_class_instance[0]’ [-Warray-bounds=]
>>    769 |                 if (copy_from_user(&ci, &user->engines[n], sizeof(ci))) {
>>        |                                         ^~~~~~~~~~~~~~~~~
>> ./include/uapi/drm/i915_drm.h:2494:43: note: while referencing ‘engines’
>>   2494 |         struct i915_engine_class_instance engines[0];
>>
>> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
>> routines on memcpy() and help us make progress towards globally
>> enabling -fstrict-flex-arrays=3 [1].
>>
>> Link: https://github.com/KSPP/linux/issues/21
>> Link: https://github.com/KSPP/linux/issues/271
>> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> 
> Reviewed-by: Kees Cook <keescook@...omium.org>

Flexible array member is even consistent with the rest of our uapi, 
pushed to drm-intel-gt-next, thanks!

Regards,

Tvrtko