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

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Date:   Sun, 21 Aug 2016 14:06:02 -0700
From:   Joe Perches <joe@...ches.com>
To:     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 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)) {