linux-kernel - Re: [PATCH] drm/atomic: fix out of bounds read in for_each_*_in

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Date:	Mon, 25 May 2015 16:25:58 +0300
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	Jani Nikula <jani.nikula@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>
Cc:	Ander Conselvan de Oliveira 
	<ander.conselvan.de.oliveira@...el.com>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/atomic: fix out of bounds read in for_each_*_in_state
 helpers

On 05/25/2015 04:12 PM, Jani Nikula wrote:
> On Mon, 25 May 2015, Andrey Ryabinin <a.ryabinin@...sung.com> 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@...sung.com>
>> ---
>>  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.


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