Re: [PATCH v3] drm: Fix drm_pending_vblank_event leak in error path for out_fence_ptr

[Melissa Wen]

On 17/08/2026 23:36, Thadeu Lima de Souza Cascardo wrote:
> When an out_fence_ptr is provided but DRM_MODE_PAGE_FLIP_EVENT is not
> set, a drm_pending_vblank_event will be allocated. If later, there is an
> allocation failure or another failure at setup_out_fence(), that event
> will not have base.fence set and it will not be released at
> complete_signaling().
>
> Release the event and set crtc_state->event to NULL just like in the
> DRM_MODE_PAGE_FLIP_EVENT case when there is a failure at
> drm_event_reserve_init(). That is, prepare_signaling() releases the
> event and there is nothing to be done at complete_signaling(). Use
> drm_event_cancel_free() as that will also undo drm_event_reserve_init()
> in case it has been called.
>
> Reported-by: sashiko-bot@xxxxxxxxxx
> Closes: https://sashiko.dev/#/patchset/20260727-drm_crtc_atomic_commit_leak-v1-1-23d9948a9d7c@xxxxxxxxxx?part=1
> Fixes: 92c715fca907 ("drm/atomic: Fix double free in drm_atomic_state_default_clear")
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxx>
> ---
> Changes in v3:
> - Use a label for the common exit pattern.
> - Link to v2: https://patch.msgid.link/20260729-drm_pending_vblank_event_leak-v2-1-a5074aae07df@xxxxxxxxxx
>
> Changes in v2:
> - Fix UAF when DRM_MODE_PAGE_FLIP_EVENT is used.
> - Link to v1: https://patch.msgid.link/20260728-drm_pending_vblank_event_leak-v1-1-08429b920b16@xxxxxxxxxx
> ---
>   drivers/gpu/drm/drm_atomic_uapi.c | 19 +++++++++++++------
>   1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> index 1050dddadb17..0aba33824595 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -1426,6 +1426,7 @@ static int prepare_signaling(struct drm_device *dev,
>   	struct drm_crtc_state *crtc_state;
>   	struct drm_connector *conn;
>   	struct drm_connector_state *conn_state;
> +	struct drm_pending_vblank_event *e;
>   	int i, c = 0, ret;
>   
>   	if (arg->flags & DRM_MODE_ATOMIC_TEST_ONLY)
> @@ -1437,8 +1438,6 @@ static int prepare_signaling(struct drm_device *dev,
>   		fence_ptr = get_out_fence_for_crtc(crtc_state->state, crtc);
>   
>   		if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT || fence_ptr) {
> -			struct drm_pending_vblank_event *e;
> -
>   			e = create_vblank_event(crtc, arg->user_data);
>   			if (!e)
>   				return -ENOMEM;
> @@ -1447,7 +1446,7 @@ static int prepare_signaling(struct drm_device *dev,
>   		}
>   
>   		if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT) {
> -			struct drm_pending_vblank_event *e = crtc_state->event;
> +			e = crtc_state->event;
>   
>   			if (!file_priv)
>   				continue;
> @@ -1464,11 +1463,14 @@ static int prepare_signaling(struct drm_device *dev,
>   		if (fence_ptr) {
>   			struct dma_fence *fence;
>   			struct drm_out_fence_state *f;
> +			e = crtc_state->event;
> +
> +			ret = -ENOMEM;
>   
>   			f = krealloc(*fence_state, sizeof(**fence_state) *
>   				     (*num_fences + 1), GFP_KERNEL);
>   			if (!f)
> -				return -ENOMEM;
> +				goto error;
>   
>   			memset(&f[*num_fences], 0, sizeof(*f));
>   
> @@ -1477,12 +1479,12 @@ static int prepare_signaling(struct drm_device *dev,
>   
>   			fence = drm_crtc_create_fence(crtc);
>   			if (!fence)
> -				return -ENOMEM;
> +				goto error;
>   
>   			ret = setup_out_fence(&f[(*num_fences)++], fence);
>   			if (ret) {
>   				dma_fence_put(fence);
> -				return ret;
> +				goto error;
>   			}
>   
>   			crtc_state->event->base.fence = fence;
> @@ -1538,6 +1540,11 @@ static int prepare_signaling(struct drm_device *dev,
>   	}
>   
>   	return 0;
> +
> +error:
> +	drm_event_cancel_free(dev, &e->base);

I think it's clearer to name the error handle as `err_free_event`, and 
to use `&crtc_state->event` directly instead of `&e` here.

With this,
Reviewed-by: Melissa Wen <mwen@xxxxxxxxxx>

Thanks!

> +	crtc_state->event = NULL;
> +	return ret;
>   }
>   
>   static void complete_signaling(struct drm_device *dev,
>
> ---
> base-commit: 5d2584e2ffaabf2d420edcb2d120209e151f8dce
> change-id: 20260728-drm_pending_vblank_event_leak-a36cedb296ba
>
> Best regards,
> --
> Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxx>