Rails 4 Strong parameters : permit all attributes?

You can call the bang version of permit.

params.require(:user).permit!

Strong Params README on Github

Source code for reference:

def permit!
  each_pair do |key, value|
    convert_hashes_to_parameters(key, value)
    self[key].permit! if self[key].respond_to? :permit!
  end

  @permitted = true
  self
end