inherit_resources with cancan

application_controller.rb

class ApplicationController < ActionController::Base

  # Add this to your application_controller
  def self.authorized_inherited_resources
    inherit_resources

    before_filter :authorize_resource_with_cancan
    define_method(:authorize_resource_with_cancan) do
      case action_name.to_sym
      when :new, :create
        authorize!(action_name.to_sym, build_resource)
      when :show, :edit, :destroy
        authorize!(action_name.to_sym, resource)
      else
        authorize!(action_name.to_sym, resource_class)
      end
    end
  end
end

Nice!