Re: [PATCH v4] drm: Fix drm_pending_vblank_event leak in error path for out_fence_ptr

[Melissa Wen <mwen@igalia.com>]

On 26/08/2026 13:46, 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.

LGTM. Thanks!

Reviewed-by: Melissa Wen <mwen@igalia.com>

>
> Reported-by: sashiko-bot@kernel.org
> Closes: https://sashiko.dev/#/patchset/20260727-drm_crtc_atomic_commit_leak-v1-1-23d9948a9d7c@igalia.com?part=1
> Fixes: 92c715fca907 ("drm/atomic: Fix double free in drm_atomic_state_default_clear")
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
> ---
> Changes in v4:
> - Rename label to err_free_event.
> - Use crtc_state->event instead of a local variable e.
> - Link to v3: https://patch.msgid.link/20260817-drm_pending_vblank_event_leak-v3-1-7582b24447d0@igalia.com
>
> 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@igalia.com
>
> 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@igalia.com
> ---
>   drivers/gpu/drm/drm_atomic_uapi.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
> index ae7667d1072d..8c0eea2fed4a 100644
> --- a/drivers/gpu/drm/drm_atomic_uapi.c
> +++ b/drivers/gpu/drm/drm_atomic_uapi.c
> @@ -1458,10 +1458,12 @@ static int prepare_signaling(struct drm_device *dev,
>   			struct dma_fence *fence;
>   			struct drm_out_fence_state *f;
>   
> +			ret = -ENOMEM;
> +
>   			f = krealloc(*fence_state, sizeof(**fence_state) *
>   				     (*num_fences + 1), GFP_KERNEL);
>   			if (!f)
> -				return -ENOMEM;
> +				goto err_free_event;
>   
>   			memset(&f[*num_fences], 0, sizeof(*f));
>   
> @@ -1470,12 +1472,12 @@ static int prepare_signaling(struct drm_device *dev,
>   
>   			fence = drm_crtc_create_fence(crtc);
>   			if (!fence)
> -				return -ENOMEM;
> +				goto err_free_event;
>   
>   			ret = setup_out_fence(&f[(*num_fences)++], fence);
>   			if (ret) {
>   				dma_fence_put(fence);
> -				return ret;
> +				goto err_free_event;
>   			}
>   
>   			crtc_state->event->base.fence = fence;
> @@ -1531,6 +1533,11 @@ static int prepare_signaling(struct drm_device *dev,
>   	}
>   
>   	return 0;
> +
> +err_free_event:
> +	drm_event_cancel_free(dev, &crtc_state->event->base);
> +	crtc_state->event = NULL;
> +	return ret;
>   }
>   
>   static void complete_signaling(struct drm_device *dev,
>
> ---
> base-commit: 4d4be202165e832d74849b4a68e289a2a377039c
> change-id: 20260728-drm_pending_vblank_event_leak-a36cedb296ba
>
> Best regards,
> --
> Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
>