media: v4l2-ctrl: Lock main_hdl on operations of requests_queued.

There's a race condition between the list_del_init in the
v4l2_ctrl_request_complete, and the list_add_tail in the
v4l2_ctrl_request_queue, since they can be called in different thread
and the requests_queued list is not protected by a lock. This can lead
to that the v4l2_ctrl_handler is still in the requests_queued list while
the request_is_queued is already set to false, which would cause
use-after-free if the v4l2_ctrl_handler is later released.

Fix this by locking the ->lock of main_hdl (which is the owner of the
requests_queued list) when doing list operations on the
->requests_queued list.
Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/v4l2-core/v4l2-ctrls.c

@@ -3302,6 +3302,7 @@ static void v4l2_ctrl_request_queue(struct media_request_object *obj)
 	struct v4l2_ctrl_handler *prev_hdl = NULL;
 	struct v4l2_ctrl_ref *ref_ctrl, *ref_ctrl_prev = NULL;
 
+	mutex_lock(main_hdl->lock);
 	if (list_empty(&main_hdl->requests_queued))
 		goto queue;
 
@@ -3333,18 +3334,22 @@ static void v4l2_ctrl_request_queue(struct media_request_object *obj)
 queue:
 	list_add_tail(&hdl->requests_queued, &main_hdl->requests_queued);
 	hdl->request_is_queued = true;
+	mutex_unlock(main_hdl->lock);
 }
 
 static void v4l2_ctrl_request_unbind(struct media_request_object *obj)
 {
 	struct v4l2_ctrl_handler *hdl =
 		container_of(obj, struct v4l2_ctrl_handler, req_obj);
+	struct v4l2_ctrl_handler *main_hdl = obj->priv;
 
 	list_del_init(&hdl->requests);
+	mutex_lock(main_hdl->lock);
 	if (hdl->request_is_queued) {
 		list_del_init(&hdl->requests_queued);
 		hdl->request_is_queued = false;
 	}
+	mutex_unlock(main_hdl->lock);
 }
 
 static void v4l2_ctrl_request_release(struct media_request_object *obj)
@@ -4298,9 +4303,11 @@ void v4l2_ctrl_request_complete(struct media_request *req,
 		v4l2_ctrl_unlock(ctrl);
 	}
 
+	mutex_lock(main_hdl->lock);
 	WARN_ON(!hdl->request_is_queued);
 	list_del_init(&hdl->requests_queued);
 	hdl->request_is_queued = false;
+	mutex_unlock(main_hdl->lock);
 	media_request_object_complete(obj);
 	media_request_object_put(obj);
 }