/usr/lib/ruby/ is in ruby-bson 1.10.0-1+deb8u1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/bson/
/usr/lib/ruby/vendor_ruby/bson/bson_ruby.rb
/usr/lib/ruby/vendor_ruby/bson/bson_java.rb
/usr/lib/ruby/vendor_ruby/bson/bson_c.rb
/usr/lib/ruby/vendor_ruby/bson/ordered_hash.rb
/usr/lib/ruby/vendor_ruby/bson/exceptions.rb
/usr/lib/ruby/vendor_ruby/bson/byte_buffer.rb
/usr/lib/ruby/vendor_ruby/bson/support/
/usr/lib/ruby/vendor_ruby/bson/support/hash_with_indifferent_access.rb
/usr/lib/ruby/vendor_ruby/bson/grow.rb
/usr/lib/ruby/vendor_ruby/bson/types/
/usr/lib/ruby/vendor_ruby/bson/types/binary.rb
/usr/lib/ruby/vendor_ruby/bson/types/object_id.rb
/usr/lib/ruby/vendor_ruby/bson/types/regex.rb
/usr/lib/ruby/vendor_ruby/bson/types/code.rb
/usr/lib/ruby/vendor_ruby/bson/types/dbref.rb
/usr/lib/ruby/vendor_ruby/bson/types/timestamp.rb
/usr/lib/ruby/vendor_ruby/bson/types/min_max_keys.rb
/usr/lib/ruby/vendor_ruby/bson.rb