Re: [PATCH v6 3/5] media: uvcvideo: Remove dangling pointers

Ricardo Ribalda
2024-12-04T00:10:30Z

On Tue, 3 Dec 2024 at 22:20, Ricardo Ribalda <ribalda@chromium.org> wrote:
>
> When an async control is written, we copy a pointer to the file handle
> that started the operation. That pointer will be used when the device is
> done. Which could be anytime in the future.
>
> If the user closes that file descriptor, its structure will be freed,
> and there will be one dangling pointer per pending async control, that
> the driver will try to use.
>
> Clean all the dangling pointers during release().
>
> To avoid adding a performance penalty in the most common case (no async
> operation), a counter has been introduced with some logic to make sure
> that it is properly handled.
>
> Cc: stable@vger.kernel.org
> Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
> Reviewed-by: Hans de Goede <hdegoede@redhat.com>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
> drivers/media/usb/uvc/uvc_ctrl.c | 58 ++++++++++++++++++++++++++++++++++++++--
> drivers/media/usb/uvc/uvc_v4l2.c | 2 ++
> drivers/media/usb/uvc/uvcvideo.h | 9 ++++++-
> 3 files changed, 66 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 42b0a0cdc51c..def502195528 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1579,6 +1579,40 @@ static void uvc_ctrl_send_slave_event(struct uvc_video_chain *chain,
> uvc_ctrl_send_event(chain, handle, ctrl, mapping, val, changes);
> }
>
> +static void uvc_ctrl_set_handle(struct uvc_fh *handle, struct uvc_control *ctrl,
> + struct uvc_fh *new_handle)
> +{
> + lockdep_assert_held(&handle->chain->ctrl_mutex);
> +
> + if (new_handle) {
> + if (ctrl->handle)
> + dev_warn_ratelimited(&handle->stream->dev->udev->dev,
> + "UVC non compliance: Setting an async control with a pending operation.");
> +
> + if (new_handle == ctrl->handle)
> + return;
> +
> + if (ctrl->handle) {
> + WARN_ON(!ctrl->handle->pending_async_ctrls);
> + if (ctrl->handle->pending_async_ctrls)
> + ctrl->handle->pending_async_ctrls--;
> + }
> +
> + ctrl->handle = new_handle;
> + handle->pending_async_ctrls++;
> + return;
> + }
> +
> + /* Cannot clear the handle for a control not owned by us.*/
> + if (WARN_ON(ctrl->handle != handle))
> + return;
> +
> + ctrl->handle = NULL;
> + if (WARN_ON(!handle->pending_async_ctrls))
> + return;
> + handle->pending_async_ctrls--;
> +}

Laurent,

If I have to redo the patch... would you be open to have two functions:
uvc_ctrl_set_handle(struct uvc_fh *handle, struct uvc_control *ctrl)
uvc_ctrl_clear_handle(struct uvc_fh *handle, struct uvc_control *ctrl)

instead of this one? It might be me, but it looks uglier than before.

If you like this code just disregard this message.

Regards!

> +
> void uvc_ctrl_status_event(struct uvc_video_chain *chain,
> struct uvc_control *ctrl, const u8 *data)
> {
> @@ -1589,7 +1623,8 @@ void uvc_ctrl_status_event(struct uvc_video_chain *chain,
> mutex_lock(&chain->ctrl_mutex);
>
> handle = ctrl->handle;
> - ctrl->handle = NULL;
> + if (handle)
> + uvc_ctrl_set_handle(handle, ctrl, NULL);
>
> list_for_each_entry(mapping, &ctrl->info.mappings, list) {
> s32 value = __uvc_ctrl_get_value(mapping, data);
> @@ -1863,7 +1898,7 @@ static int uvc_ctrl_commit_entity(struct uvc_device *dev,
>
> if (!rollback && handle &&
> ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS)
> - ctrl->handle = handle;
> + uvc_ctrl_set_handle(handle, ctrl, handle);
> }
>
> return 0;
> @@ -2772,6 +2807,25 @@ int uvc_ctrl_init_device(struct uvc_device *dev)
> return 0;
> }
>
> +void uvc_ctrl_cleanup_fh(struct uvc_fh *handle)
> +{
> + struct uvc_entity *entity;
> +
> + guard(mutex)(&handle->chain->ctrl_mutex);
> +
> + if (!handle->pending_async_ctrls)
> + return;
> +
> + list_for_each_entry(entity, &handle->chain->dev->entities, list)
> + for (unsigned int i = 0; i < entity->ncontrols; ++i) {
> + if (entity->controls[i].handle != handle)
> + continue;
> + uvc_ctrl_set_handle(handle, &entity->controls[i], NULL);
> + }
> +
> + WARN_ON(handle->pending_async_ctrls);
> +}
> +
> /*
> * Cleanup device controls.
> */
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 97c5407f6603..b425306a3b8c 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -652,6 +652,8 @@ static int uvc_v4l2_release(struct file *file)
>
> uvc_dbg(stream->dev, CALLS, "%s\n", __func__);
>
> + uvc_ctrl_cleanup_fh(handle);
> +
> /* Only free resources if this is a privileged handle. */
> if (uvc_has_privileges(handle))
> uvc_queue_release(&stream->queue);
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index 07f9921d83f2..92ecdd188587 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -337,7 +337,11 @@ struct uvc_video_chain {
> struct uvc_entity *processing; /* Processing unit */
> struct uvc_entity *selector; /* Selector unit */
>
> - struct mutex ctrl_mutex; /* Protects ctrl.info */
> + struct mutex ctrl_mutex; /*
> + * Protects ctrl.info,
> + * ctrl.handle and
> + * uvc_fh.pending_async_ctrls
> + */
>
> struct v4l2_prio_state prio; /* V4L2 priority state */
> u32 caps; /* V4L2 chain-wide caps */
> @@ -612,6 +616,7 @@ struct uvc_fh {
> struct uvc_video_chain *chain;
> struct uvc_streaming *stream;
> enum uvc_handle_state state;
> + unsigned int pending_async_ctrls;
> };
>
> struct uvc_driver {
> @@ -797,6 +802,8 @@ int uvc_ctrl_is_accessible(struct uvc_video_chain *chain, u32 v4l2_id,
> int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
> struct uvc_xu_control_query *xqry);
>
> +void uvc_ctrl_cleanup_fh(struct uvc_fh *handle);
> +
> /* Utility functions */
> struct usb_host_endpoint *uvc_find_endpoint(struct usb_host_interface *alts,
> u8 epaddr);
>
> --
> 2.47.0.338.g60cca15819-goog
>

--
Ricardo Ribalda