/usr/src/linux-headers-4.4.0-141-generic/Kbuild is in linux-headers-4.4.0-141-generic 4.4.0-141.167.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-4.4.0-141-generic/../linux-headers-4.4.0-141/Kbuild