Fixing Segmentation fault on aliasing

lib/cancan/ability.rb

@@ -172,10 +172,16 @@ module CanCan
     # This way one can use params[:action] in the controller to determine the permission.
     def alias_action(*args)
       target = args.pop[:to]
+      validate_target(target)
       aliased_actions[target] ||= []
       aliased_actions[target] += args
     end
 
+    # User shouldn't specify targets with names of real actions or it will cause Seg fault
+    def validate_target(target)
+      raise Error, "You can't specify target (#{target}) as alias because it is real action name" if aliased_actions.values.flatten.include? target
+    end
+
     # Returns a hash of aliased actions. The key is the target and the value is an array of actions aliasing the key.
     def aliased_actions
       @aliased_actions ||= default_alias_actions

spec/cancan/ability_spec.rb

@@ -87,6 +87,10 @@ describe CanCan::Ability do
     @ability.can?(:increment, 123).should be_true
   end
 
+  it "should raise an Error if alias target is an exist action" do
+    lambda{ @ability.alias_action :show, :to => :show }.should raise_error(CanCan::Error, "You can't specify target (show) as alias because it is real action name")
+  end
+
   it "should always call block with arguments when passing no arguments to can" do
     @ability.can do |action, object_class, object|
       action.should == :foo