WordPress - Restrict Media access per user

functions.php

/* Restrict users viewing their own attachments */
add_filter('pre_get_posts',  'restrict_media');
function restrict_media($arg) {
  global $user_ID;
  if ( current_user_can('editor') ) { // Disable this to apply on all roles
    if ($arg->query['post_type'] == 'attachment' && is_admin()) {
      $arg->query['author'] = $user_ID;
      $arg->query_vars['author'] = $user_ID;
    }
  }
  return $arg;
}