linux-kernel - Re: [PATCH 1/1] drm/radeon: avoid NULL dereference, si_get_vce_clock

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Date:   Sun, 21 Aug 2016 23:20:06 +0200
From:   Heinrich Schuchardt <xypron.debian@....de>
To:     Joe Perches <joe@...ches.com>,
        Heinrich Schuchardt <xypron.glpk@....de>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>
Cc:     David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] drm/radeon: avoid NULL dereference,
 si_get_vce_clock_voltage

On 08/21/2016 11:06 PM, Joe Perches wrote:
> On Sun, 2016-08-21 at 22:52 +0200, Heinrich Schuchardt wrote:
>> It does not make sense to check if table is NULL
>> and afterwards to dereference it without
>> considering the result.
> 
> This makes no sense.
> 
>> The inconsistency was indicated by cppcheck.
> 
> Perhaps this is a defect in cppcheck?
> 
>> An actual NULL pointer dereference was not observed.
> []
>> diff --git a/drivers/gpu/drm/radeon/si_dpm.c b/drivers/gpu/drm/radeon/si_dpm.c
> []
>> @@ -2962,7 +2962,7 @@ static int si_get_vce_clock_voltage(struct radeon_device *rdev,
>>  		&rdev->pm.dpm.dyn_state.vce_clock_voltage_dependency_table;
>>  
>>  	if (((evclk == 0) && (ecclk == 0)) ||
>> -	    (table && (table->count == 0))) {
> 
> Here table is only dereferenced if table is non-null
> 
>> +	    table == NULL || table->count == 0) {
>>  		*voltage = 0;
>>  		return 0;
>>  	}
> 
> Perhaps the unnecessary parentheses can be reduce though.
> 
>  	if ((evclk == 0 && ecclk == 0) || (table && table->count == 0)) {
> 
The possible NULL pointer dereference would occur here:

2970        for (i = 0; i < table->count; i++) {