/usr/lib/ is in ruby-rack-mount 0.8.3-2.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/rack/
/usr/lib/ruby/vendor_ruby/rack/mount/
/usr/lib/ruby/vendor_ruby/rack/mount/analysis/
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/
/usr/lib/ruby/vendor_ruby/rack/mount/analysis/histogram.rb
/usr/lib/ruby/vendor_ruby/rack/mount/analysis/splitting.rb
/usr/lib/ruby/vendor_ruby/rack/mount/code_generation.rb
/usr/lib/ruby/vendor_ruby/rack/mount/generatable_regexp.rb
/usr/lib/ruby/vendor_ruby/rack/mount/multimap.rb
/usr/lib/ruby/vendor_ruby/rack/mount/prefix.rb
/usr/lib/ruby/vendor_ruby/rack/mount/regexp_with_named_groups.rb
/usr/lib/ruby/vendor_ruby/rack/mount/route.rb
/usr/lib/ruby/vendor_ruby/rack/mount/route_set.rb
/usr/lib/ruby/vendor_ruby/rack/mount/strexp/
/usr/lib/ruby/vendor_ruby/rack/mount/strexp/parser.rb
/usr/lib/ruby/vendor_ruby/rack/mount/strexp/parser.y
/usr/lib/ruby/vendor_ruby/rack/mount/strexp/tokenizer.rb
/usr/lib/ruby/vendor_ruby/rack/mount/strexp/tokenizer.rex
/usr/lib/ruby/vendor_ruby/rack/mount/strexp.rb
/usr/lib/ruby/vendor_ruby/rack/mount/utils.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/alternation.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/anchor.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/atom.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/character.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/character_class.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/collection.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/expression.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/group.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/options.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/parser.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/tokenizer.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin/version.rb
/usr/lib/ruby/vendor_ruby/rack/mount/vendor/regin/regin.rb
/usr/lib/ruby/vendor_ruby/rack/mount/version.rb
/usr/lib/ruby/vendor_ruby/rack/mount.rb