Re: [PATCH v1] drm/simple_kms_helper: Fix NULL pointer dereference with no active CRTC

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>]

On 02/22/2018 08:09 AM, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>
> It is possible that drm_simple_kms_plane_atomic_check called
> with no CRTC set, e.g. when user-space application sets CRTC_ID/FB_ID
> to 0 before doing any actual drawing. This leads to NULL pointer
> dereference because in this case new CRTC state is NULL and must be
> checked before accessing.
>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>
> ---
> Changes since initial:
> - re-worked checks for null CRTC as suggested by Daniel Vetter
> ---
>   drivers/gpu/drm/drm_simple_kms_helper.c | 10 +++-------
>   1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c
> index 9ca8a4a59b74..4a1dbd88b1ec 100644
> --- a/drivers/gpu/drm/drm_simple_kms_helper.c
> +++ b/drivers/gpu/drm/drm_simple_kms_helper.c
> @@ -121,12 +121,6 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
>   	pipe = container_of(plane, struct drm_simple_display_pipe, plane);
>   	crtc_state = drm_atomic_get_new_crtc_state(plane_state->state,
>   						   &pipe->crtc);
> -	if (!crtc_state->enable)
> -		return 0; /* nothing to check when disabling or disabled */
> -
> -	if (crtc_state->enable)
> -		drm_mode_get_hv_timing(&crtc_state->mode,
> -				       &clip.x2, &clip.y2);
>   
>   	ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state,
>   						  &clip,
> @@ -137,7 +131,9 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane,
>   		return ret;
>   
>   	if (!plane_state->visible)
> -		return -EINVAL;
Daniel, I have put your R-b tag, but I had removed suggested
"WARN_ON(crtc_state && crtc_state->enable);"
here as it fires each time when crtc_state is not NULL.
Please let me know if this is not ok and you want me to remove
your R-b tag.
> +		return 0;
> +
> +	drm_mode_get_hv_timing(&crtc_state->mode, &clip.x2, &clip.y2);
>   
>   	if (!pipe->funcs || !pipe->funcs->check)
>   		return 0;
Thank you,
Oleksandr