[PATCH] drm/amdgpu/acpi: Add NULL check for event->device_class in amdgpu_atif_handler

[Alex Deucher]

On Tue, Jul 2, 2024 at 4:50 AM Srinivasan Shanmugam
<srinivasan.shanmugam at amd.com> wrote:
>
> This commit addresses a NULL dereference issue in the
> amdgpu_atif_handler function.
>
> The issue arises when event->device_class is NULL and is passed to the
> DRM_DEBUG_DRIVER macro, which attempts to print the NULL string with the
> %s format specifier. This constitutes undefined behavior.
>
> To resolve this, a conditional check is added to ensure that
> event->device_class is not NULL before it is passed to the
> DRM_DEBUG_DRIVER macro. If it is NULL, the string "NULL" is printed
> instead, thereby preventing the NULL dereference.

I don't think this can ever be NULL.  Not sure there is a way to indicate that.

Alex

>
> Fixes the below:
> In function ‘amdgpu_atif_handler’,
>     inlined from ‘amdgpu_acpi_event’ at drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c:1215:9:
> ./include/drm/drm_print.h:536:49: warning: ‘%s’ directive argument is null [-Wformat-overflow=]
>   536 | #define __drm_dbg(cat, fmt, ...)                ___drm_dbg(NULL, cat, fmt, ##__VA_ARGS__)
>       |                                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ./include/drm/drm_print.h:582:9: note: in expansion of macro ‘__drm_dbg’
>   582 |         __drm_dbg(DRM_UT_DRIVER, fmt, ##__VA_ARGS__)
>       |         ^~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c:452:9: note: in expansion of macro ‘DRM_DEBUG_DRIVER’
>   452 |         DRM_DEBUG_DRIVER("event, device_class = %s, type = %#x\n",
>       |         ^~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c: In function ‘amdgpu_acpi_event’:
> drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c:452:49: note: format string is defined here
>   452 |         DRM_DEBUG_DRIVER("event, device_class = %s, type = %#x\n",
>       |
>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Christian König <christian.koenig at amd.com>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> index f85ace0384d2..27131ff30579 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> @@ -450,7 +450,7 @@ static int amdgpu_atif_handler(struct amdgpu_device *adev,
>         int count;
>
>         DRM_DEBUG_DRIVER("event, device_class = %s, type = %#x\n",
> -                       event->device_class, event->type);
> +                       event->device_class ? event->device_class : "NULL", event->type);
>
>         if (strcmp(event->device_class, ACPI_VIDEO_CLASS) != 0)
>                 return NOTIFY_DONE;
> --
> 2.34.1
>