/usr/share/doc/linux-tools-4.2.0-21-generic/changelog.Debian.gz is in linux-tools-4.2.0-21-generic 4.2.0-21.25~14.04.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/linux-tools-4.2.0-21-generic/../linux-lts-wily-tools-4.2.0-21/changelog.Debian.gz