media: uvcvideo: Remove dangling pointers

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: [email protected]
Fixes: e5225c8 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
Reviewed-by: Hans de Goede <[email protected]>
Signed-off-by: Ricardo Ribalda <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Laurent Pinchart <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>

Author: ribalda

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--;
+}
+
 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 +2807,26 @@ 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.
  */

drivers/media/usb/uvc/uvc_v4l2.c

@@ -671,6 +671,8 @@ 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);

drivers/media/usb/uvc/uvcvideo.h

@@ -338,7 +338,11 @@ 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 */
@@ -613,6 +617,7 @@ 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 {
@@ -798,6 +803,8 @@ 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);