/usr/lib/ruby/vendor_ruby/ is in ruby-ferret 0.11.6-3build1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/1.8/
/usr/lib/ruby/vendor_ruby/1.8/x86_64-linux/
/usr/lib/ruby/vendor_ruby/1.8/x86_64-linux/ferret_ext.so
/usr/lib/ruby/vendor_ruby/ferret/
/usr/lib/ruby/vendor_ruby/ferret.rb
/usr/lib/ruby/vendor_ruby/ferret/browser/
/usr/lib/ruby/vendor_ruby/ferret/browser.rb
/usr/lib/ruby/vendor_ruby/ferret/browser/s/
/usr/lib/ruby/vendor_ruby/ferret/browser/s/global.js
/usr/lib/ruby/vendor_ruby/ferret/browser/s/style.css
/usr/lib/ruby/vendor_ruby/ferret/browser/views/
/usr/lib/ruby/vendor_ruby/ferret/browser/views/document/
/usr/lib/ruby/vendor_ruby/ferret/browser/views/document/list.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/views/document/show.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/views/error/
/usr/lib/ruby/vendor_ruby/ferret/browser/views/error/index.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/views/help/
/usr/lib/ruby/vendor_ruby/ferret/browser/views/help/index.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/views/home/
/usr/lib/ruby/vendor_ruby/ferret/browser/views/home/index.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/views/layout.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/views/term/
/usr/lib/ruby/vendor_ruby/ferret/browser/views/term-vector/
/usr/lib/ruby/vendor_ruby/ferret/browser/views/term-vector/index.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/views/term/index.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/views/term/termdocs.rhtml
/usr/lib/ruby/vendor_ruby/ferret/browser/webrick.rb
/usr/lib/ruby/vendor_ruby/ferret/document.rb
/usr/lib/ruby/vendor_ruby/ferret/field_infos.rb
/usr/lib/ruby/vendor_ruby/ferret/index.rb
/usr/lib/ruby/vendor_ruby/ferret/number_tools.rb
/usr/lib/ruby/vendor_ruby/ferret_version.rb