Re: [PATCH] drm/atomic: fix out of bounds read in for_each_*_in_state helpers

[Jani Nikula]

On Mon, 25 May 2015, Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> wrote:
> On Mon, 25 May 2015, Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> wrote:
>> On 05/25/2015 04:12 PM, Jani Nikula wrote:
>>> On Mon, 25 May 2015, Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx> wrote:
>>>> for_each_*_in_state validate array index after
>>>> access to array elements, thus perform out of bounds read.
>>>>
>>>> Fix this by validating index in the first place and read
>>>> array element iff validation was successful.
>>>>
>>>> Fixes: df63b9994eaf ("drm/atomic: Add for_each_{connector,crtc,plane}_in_state helper macros")
>>>> Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
>>>> ---
>>>>  include/drm/drm_atomic.h | 24 ++++++++++++------------
>>>>  1 file changed, 12 insertions(+), 12 deletions(-)
>>>>
>>>> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
>>>> index c1571034..3f13b91 100644
>>>> --- a/include/drm/drm_atomic.h
>>>> +++ b/include/drm/drm_atomic.h
>>>> @@ -77,26 +77,26 @@ int __must_check drm_atomic_async_commit(struct drm_atomic_state *state);
>>>>  
>>>>  #define for_each_connector_in_state(state, connector, connector_state, __i) \
>>>>  	for ((__i) = 0;							\
>>>> -	     (connector) = (state)->connectors[__i],			\
>>>> -	     (connector_state) = (state)->connector_states[__i],	\
>>>> -	     (__i) < (state)->num_connector;				\
>>>> +	     (__i) < (state)->num_connector &&				\
>>>> +	     ((connector) = (state)->connectors[__i],			\
>>>> +	     (connector_state) = (state)->connector_states[__i], 1); 	\
>>> 
>>> This will stop at the first NULL connector/connector_state. Similarly
>>> for the loops below.
>>> 
>>
>> This will stop iff (__i) >= (state)->num_connector, because the result of expression:
>> 	 ((connector) = (state)->connectors[__i], (connector_state) = (state)->connector_states[__i], 1)
>> is always 1.
>
> Why do you think it'll always be 1?

That might be because there's the 1 at the end. *blush*.

I do wonder if this is too subtle in general, or if it's just too subtle
for me.

BR,
Jani.

>
> BR,
> Jani.
>
>
>>
>>
>
> -- 
> Jani Nikula, Intel Open Source Technology Center

-- 
Jani Nikula, Intel Open Source Technology Center
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