/usr/lib/x86_64-linux-gnu/libnilfs.so is in nilfs-tools 2.2.3-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libnilfs.so.0.2.1
/usr/lib/x86_64-linux-gnu/libnilfs.so.0.2.1