filelock: UnixFileLock truncates and chmods any regular file another user renames or hard-links onto the lock path

UnixFileLock, the backend of FileLock and AsyncFileLock on Unix, empties whatever regular file it finds at the lock path once it holds the flock a kernel lock on an open file. With an explicit mode it also chmods that file sets its permission bits, whether or not this acquire created it. Another...