Messages in this thread Patch in this message | | | Subject | Re: [PATCH] drm/simple_kms_helper: Fix NULL pointer dereference with no active CRTC | From | Oleksandr Andrushchenko <> | Date | Mon, 19 Feb 2018 16:58:43 +0200 |
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On 02/19/2018 04:30 PM, Daniel Vetter wrote: > 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? Yes, it does work if this is what you mean: diff --git a/drivers/gpu/drm/drm_simple_kms_helper.c b/drivers/gpu/drm/drm_simple_kms_helper.c index a05eca9cec8b..c48858bb2823 100644 --- a/drivers/gpu/drm/drm_simple_kms_helper.c +++ b/drivers/gpu/drm/drm_simple_kms_helper.c @@ -122,14 +122,6 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane, crtc_state = drm_atomic_get_new_crtc_state(plane_state->state, &pipe->crtc);
- 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, - &clip.x2, &clip.y2); - ret = drm_atomic_helper_check_plane_state(plane_state, crtc_state, &clip, DRM_PLANE_HELPER_NO_SCALING, @@ -138,6 +130,13 @@ static int drm_simple_kms_plane_atomic_check(struct drm_plane *plane, if (ret) return ret;
+ if (!plane_state->visible || !crtc_state->enable) + return 0; /* nothing to check when disabling or disabled */ + + if (plane_state->visible && crtc_state->enable) + drm_mode_get_hv_timing(&crtc_state->mode, + &clip.x2, &clip.y2); + if (!plane_state->visible) return -EINVAL;
> 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. It doesn't look at it at the moment > 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. At list with the change above it passes my test which failed before. Although I cannot confirm it works for others, but it certainly does for me. > -Daniel Do you want me to send v1 with the code above? Thank you, Oleksandr
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