predicate builder should not recurse for determining where columns.

Thanks to Ben Murphy for reporting this

CVE-2012-2661

activerecord/lib/active_record/associations/association_scope.rb

@@ -87,7 +87,7 @@ def add_constraints(scope)
 
             conditions.each do |condition|
               if options[:through] && condition.is_a?(Hash)
-                condition = { table.name => condition }
+                condition = disambiguate_condition(table, condition)
               end
 
               scope = scope.where(interpolate(condition))
@@ -126,6 +126,21 @@ def table_name_for(reflection)
         end
       end
 
+      def disambiguate_condition(table, condition)
+        if condition.is_a?(Hash)
+          Hash[
+            condition.map do |k, v|
+              if v.is_a?(Hash)
+                [k, v]
+              else
+                [table.table_alias || table.name, { k => v }]
+              end
+            end
+          ]
+        else
+          condition
+        end
+      end
     end
   end
 end

activerecord/lib/active_record/relation/predicate_builder.rb

@@ -1,16 +1,16 @@
 module ActiveRecord
   class PredicateBuilder # :nodoc:
-    def self.build_from_hash(engine, attributes, default_table)
+    def self.build_from_hash(engine, attributes, default_table, check_column = true)
       predicates = attributes.map do |column, value|
         table = default_table
 
         if value.is_a?(Hash)
           table = Arel::Table.new(column, engine)
-          build_from_hash(engine, value, table)
+          build_from_hash(engine, value, table, false)
         else
           column = column.to_s
 
-          if column.include?('.')
+          if check_column && column.include?('.')
             table_name, column = column.split('.', 2)
             table = Arel::Table.new(table_name, engine)
           end

activerecord/test/cases/relation/where_test.rb

@@ -0,0 +1,19 @@
+require "cases/helper"
+require 'models/post'
+
+module ActiveRecord
+  class WhereTest < ActiveRecord::TestCase
+    fixtures :posts
+
+    def test_where_error
+      assert_raises(ActiveRecord::StatementInvalid) do
+        Post.where(:id => { 'posts.author_id' => 10 }).first
+      end
+    end
+
+    def test_where_with_table_name
+      post = Post.first
+      assert_equal post, Post.where(:posts => { 'id' => post.id }).first
+    end
+  end
+end