You can use a login library (ion_auth) and create a new column in the respective table "user_records" then in the GC function use :
// load user Id
$user = $this->ion_auth->user()->row();
// when adding new records - adds the user id to the new record - field user_records
$crud->change_field_type('user_records', 'hidden', $user->id);
// users can see only there records
$crud->where('user_records', $user->id);
first : loads the user_id
second : when a user adds a new record the user_records will auto take the value from $user->id
third : users can see only there records
dont forget to include user_records in the add_fields
hope this can help a bit