/usr/lib/x86_64-linux-gnu/libb2.so is in libb2-dev 0.97+git20171226-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libb2.so.1.0.3
/usr/lib/x86_64-linux-gnu/libb2.so.1.0.3