/usr/lib/x86_64-linux-gnu/libbd_mdraid.so is in libblockdev-mdraid-dev 2.16-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libbd_mdraid.so.2.0.0
/usr/lib/x86_64-linux-gnu/libbd_mdraid.so.2.0.0