On Tue, Feb 13, 2018 at 10:44:16AM +0200, 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
drivers/gpu/drm/drm_simple_kms_helper.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c index 9ca8a4a59b74..a05eca9cec8b 100644 --- a/drivers/gpu/drm/drm_simple_kms_helper.c +++ b/drivers/gpu/drm/drm_simple_kms_helper.c @@ -121,8 +121,10 @@ 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 || !crtc_state->enable)
/* nothing to check when disabling or disabled or no CRTC set */return 0;if (crtc_state->enable) drm_mode_get_hv_timing(&crtc_state->mode,
Hm, this is a bit annoying, since the can_position = false parameter to drm_atomic_helper_check_plane_state is supposed to catch all this. Would moving all the checks after the call to that helper, and gating them on plane_state->visible also work?
We'd need to add a guarantee to drm_atomic_helper_check_plane_state that it can cope with crtc_state == NULL, but I think that's a good idea anyway. Atm it shouldn't end up looking at the crtc_state pointer in that case.
Otherwise we'll just go with your fix, but it feels all a bit too fragile, hence why I want to explore more robust options a bit. -Daniel