[PATCH] drm/gma500: Fix potential NULL pointer dereference

[Ville Syrjälä]

On Mon, Jun 25, 2018 at 07:18:44AM -0500, Gustavo A. R. Silva wrote:
> fb is being dereferenced before it is null checked, hence there
> is a potential null pointer dereference.
> 
> Fix this by moving the pointer dereference after fb has been
> properly null checked at line 74: if (!fb)

I don't remember if set_base w/ fb==NULL is even legal. But as long as
the check is there this seems sane. Pushed to drm-misc-next. Thanks for
the patch.

> 
> Addresses-Coverity-ID: 1470169 ("Dereference before null check")
> Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com>
> ---
>  drivers/gpu/drm/gma500/gma_display.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/gma500/gma_display.c b/drivers/gpu/drm/gma500/gma_display.c
> index c8f071c..f767579 100644
> --- a/drivers/gpu/drm/gma500/gma_display.c
> +++ b/drivers/gpu/drm/gma500/gma_display.c
> @@ -60,7 +60,7 @@ int gma_pipe_set_base(struct drm_crtc *crtc, int x, int y,
>  	struct drm_psb_private *dev_priv = dev->dev_private;
>  	struct gma_crtc *gma_crtc = to_gma_crtc(crtc);
>  	struct drm_framebuffer *fb = crtc->primary->fb;
> -	struct gtt_range *gtt = to_gtt_range(fb->obj[0]);
> +	struct gtt_range *gtt;
>  	int pipe = gma_crtc->pipe;
>  	const struct psb_offset *map = &dev_priv->regmap[pipe];
>  	unsigned long start, offset;
> @@ -76,6 +76,8 @@ int gma_pipe_set_base(struct drm_crtc *crtc, int x, int y,
>  		goto gma_pipe_cleaner;
>  	}
>  
> +	gtt = to_gtt_range(fb->obj[0]);
> +
>  	/* We are displaying this buffer, make sure it is actually loaded
>  	   into the GTT */
>  	ret = psb_gtt_pin(gtt);
> -- 
> 2.7.4
> 
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-- 
Ville Syrjälä
Intel