Switch to on-by-default XSS escaping for rails.

  This consists of:

  * String#html_safe! a method to mark a string as 'safe'
  * ActionView::SafeBuffer a string subclass which escapes anything unsafe which is concatenated to it
  * Calls to String#html_safe! throughout the rails helpers
  * a 'raw' helper which lets you concatenate trusted HTML from non-safety-aware sources (e.g. presantized strings in the DB)
  * New ERB implementation based on erubis which uses a SafeBuffer instead of a String

Hat tip to Django for the inspiration.

1 files changed, 25 insertions, 3 deletions

diff --git a/actionpack/lib/action_view/template/handlers/erb.rb b/actionpack/lib/action_view/template/handlers/erb.rb
index aab7baf442..a780ab8d85 100644
--- a/actionpack/lib/action_view/template/handlers/erb.rb
+++ b/actionpack/lib/action_view/template/handlers/erb.rb
@@ -1,7 +1,31 @@
 require 'active_support/core_ext/class/attribute_accessors'
+require 'active_support/core_ext/string/output_safety'
+require 'erubis'
 
 module ActionView
   module TemplateHandlers
+    class Erubis < ::Erubis::Eruby
+      def add_preamble(src)
+        src << "@output_buffer = ActionView::SafeBuffer.new;"
+      end
+
+      def add_text(src, text)
+        src << "@output_buffer << ('" << escape_text(text) << "'.html_safe!);"
+      end
+
+      def add_expr_literal(src, code)
+        src << '@output_buffer << ((' << code << ').to_s);'
+      end
+
+      def add_expr_escaped(src, code)
+        src << '@output_buffer << ' << escaped_expr(code) << ';'
+      end
+
+      def add_postamble(src)
+        src << '@output_buffer.to_s'
+      end
+    end
+
     class ERB < TemplateHandler
       include Compilable
 
@@ -15,11 +39,9 @@ module ActionView
       self.default_format = Mime::HTML
 
       def compile(template)
-        require 'erb'
-
         magic = $1 if template.source =~ /\A(<%#.*coding[:=]\s*(\S+)\s*-?%>)/
         erb = "#{magic}<% __in_erb_template=true %>#{template.source}"
-        ::ERB.new(erb, nil, erb_trim_mode, '@output_buffer').src
+        Erubis.new(erb, :trim=>(self.class.erb_trim_mode == "-")).src
       end
     end
   end