[PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not supported

[Mario Limonciello]

On 10/29/2024 18:32, Antonio Quartulli wrote:
> acpi_evaluate_object() may return AE_NOT_FOUND (failure), which
> would result in dereferencing buffer.pointer (obj) while being NULL.
> 
> Bail out also when status is AE_NOT_FOUND with a proper error message.
> 
> This fixes 1 FORWARD_NULL issue reported by Coverity
> Report: CID 1600951:  Null pointer dereferences  (FORWARD_NULL)
> 
> Signed-off-by: Antonio Quartulli <antonio at mandelbit.com>

I'm not really sure how realistic this failure is.  Can you share the 
full call trace that Coverity identified?

amdgpu_atif_pci_probe_handle() will check whether the handle is 
available in the first place.  We'll never this this far if that failed.

Because of that I don't follow how this could return AE_NOT_FOUND.
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> index cce85389427f..f10c3261a4ab 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> @@ -172,10 +172,13 @@ static union acpi_object *amdgpu_atif_call(struct amdgpu_atif *atif,
>   				      &buffer);
>   	obj = (union acpi_object *)buffer.pointer;
>   
> -	/* Fail if calling the method fails and ATIF is supported */
> -	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
> -		DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
> -				 acpi_format_exception(status));
> +	/* Fail if calling the method fails */
> +	if (ACPI_FAILURE(status)) {
> +		if (status != AE_NOT_FOUND)
> +			DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
> +					 acpi_format_exception(status));
> +		else
> +			DRM_DEBUG_DRIVER("ATIF not supported\n");
>   		kfree(obj);
>   		return NULL;
>   	}