/usr/share/doc/linux-image-extra-4.2.0-42-generic/changelog.Debian.gz is in linux-image-extra-4.2.0-42-generic 4.2.0-42.49~14.04.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/linux-image-extra-4.2.0-42-generic/../linux-image-4.2.0-42-generic/changelog.Debian.gz