/usr/lib/x86_64-linux-gnu/lua/5.1/socket/core.so is in lua-socket 3.0~rc1+git+321c0c9-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/lua/5.1/socket/../../../liblua5.1-socket.so.2.0.0