/usr/share/man/man3/XShmAttach.3.gz is in libxext-dev 2:1.3.2-1ubuntu0.0.14.04.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man3/XShm.3.gz
/usr/share/man/man3/XShm.3.gz