/usr/lib/ruby/ is in ruby-json 1.8.3-1build4.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/json/
/usr/lib/ruby/vendor_ruby/json.rb
/usr/lib/ruby/vendor_ruby/json/add/
/usr/lib/ruby/vendor_ruby/json/add/bigdecimal.rb
/usr/lib/ruby/vendor_ruby/json/add/complex.rb
/usr/lib/ruby/vendor_ruby/json/add/core.rb
/usr/lib/ruby/vendor_ruby/json/add/date.rb
/usr/lib/ruby/vendor_ruby/json/add/date_time.rb
/usr/lib/ruby/vendor_ruby/json/add/exception.rb
/usr/lib/ruby/vendor_ruby/json/add/ostruct.rb
/usr/lib/ruby/vendor_ruby/json/add/range.rb
/usr/lib/ruby/vendor_ruby/json/add/rational.rb
/usr/lib/ruby/vendor_ruby/json/add/regexp.rb
/usr/lib/ruby/vendor_ruby/json/add/struct.rb
/usr/lib/ruby/vendor_ruby/json/add/symbol.rb
/usr/lib/ruby/vendor_ruby/json/add/time.rb
/usr/lib/ruby/vendor_ruby/json/common.rb
/usr/lib/ruby/vendor_ruby/json/ext.rb
/usr/lib/ruby/vendor_ruby/json/generic_object.rb
/usr/lib/ruby/vendor_ruby/json/pure/
/usr/lib/ruby/vendor_ruby/json/pure.rb
/usr/lib/ruby/vendor_ruby/json/pure/generator.rb
/usr/lib/ruby/vendor_ruby/json/pure/parser.rb
/usr/lib/ruby/vendor_ruby/json/version.rb