/usr/lib/x86_64-linux-gnu/libgdm.so.1 is in libgdm1 3.10.0.1-0ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgdm.so.1.0.0
/usr/lib/x86_64-linux-gnu/libgdm.so.1.0.0