media: v4l2-ctrls.c/uvc: zero v4l2_event

Control events can leak kernel memory since they do not fully zero the
event. The same code is present in both v4l2-ctrls.c and uvc_ctrl.c, so
fix both.

It appears that all other event code is properly zeroing the structure,
it's these two places.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reported-by: syzbot+4f021cf3697781dbd9fb@syzkaller.appspotmail.com
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/usb/uvc/uvc_ctrl.c

@@ -1212,7 +1212,7 @@ static void uvc_ctrl_fill_event(struct uvc_video_chain *chain,
 
 	__uvc_query_v4l2_ctrl(chain, ctrl, mapping, &v4l2_ctrl);
 
-	memset(ev->reserved, 0, sizeof(ev->reserved));
+	memset(ev, 0, sizeof(*ev));
 	ev->type = V4L2_EVENT_CTRL;
 	ev->id = v4l2_ctrl.id;
 	ev->u.ctrl.value = value;

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

@@ -1387,7 +1387,7 @@ static u32 user_flags(const struct v4l2_ctrl *ctrl)
 
 static void fill_event(struct v4l2_event *ev, struct v4l2_ctrl *ctrl, u32 changes)
 {
-	memset(ev->reserved, 0, sizeof(ev->reserved));
+	memset(ev, 0, sizeof(*ev));
 	ev->type = V4L2_EVENT_CTRL;
 	ev->id = ctrl->id;
 	ev->u.ctrl.changes = changes;