Re: [PATCH] drm/msm: Fix NULL deref in adreno_load_gpu

[Jordan Crouse <jcrouse@codeaurora.org>]

On Thu, Dec 14, 2017 at 11:11:50AM +0530, Archit Taneja wrote:
> The msm/kms driver should work even if there is no GPU device specified
> in DT. Currently, we get a NULL dereference crash in adreno_load_gpu
> since the driver assumes that priv->gpu_pdev is non-NULL.
> 
> Perform an additional check on priv->gpu_pdev before trying to retrieve
> the msm_gpu pointer from it.
> 
> Fixes: eec874ce5ff1 (drm/msm/adreno: load gpu at probe/bind time)
> 
> Signed-off-by: Archit Taneja <architt@codeaurora.org>
> ---
>  drivers/gpu/drm/msm/adreno/adreno_device.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c b/drivers/gpu/drm/msm/adreno/adreno_device.c
> index 05022ea2a007..ac60cf3c794e 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_device.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
> @@ -124,10 +124,17 @@ const struct adreno_info *adreno_info(struct adreno_rev rev)
>  struct msm_gpu *adreno_load_gpu(struct drm_device *dev)
>  {
>  	struct msm_drm_private *priv = dev->dev_private;
> -	struct platform_device *pdev = priv->gpu_pdev;
> -	struct msm_gpu *gpu = platform_get_drvdata(priv->gpu_pdev);
> +	struct platform_device *pdev;
> +	struct msm_gpu *gpu;
>  	int ret;
>  
> +	pdev = priv->gpu_pdev;
> +	if (!pdev) {
> +		dev_dbg(dev->dev, "no adreno platform device found\n");
> +		return NULL;
> +	}
> +
> +	gpu = platform_get_drvdata(pdev);
>  	if (!gpu) {
>  		dev_err(dev->dev, "no adreno device\n");
>  		return NULL;

Obviously correct fix but I can't help but think that we should share the same
error message, so something like:

struct msm_gpu *gpu = NULL;

.. 

if (priv->gpu_pdev)
   gpu = platform_get_drvdata(priv->gpu_pdev);

if (!gpu) {
	dev_err(dev->dev, "No GPU device was was found\n");
 	return NULL;
}

(also, I can't help but think maybe that dev_err should be a ONCE so you don't
get a nasty message every time you open the file descriptor).

Jordan

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