getgrouplist is a bad function, written by bad people

getgrouplist

static gboolean
user_is_in_admin_group (uid_t user, const char *admin_group)
{
  if (user == G_MAXUINT)
    return FALSE;
  if (admin_group == NULL || *admin_group == '\0')
    admin_group = "wheel";

  struct passwd *pw = getpwuid (user);
  if (pw == NULL)
    return FALSE;

  int n_groups = 10;
  gid_t *groups = g_new0 (gid_t, n_groups);
  while (1)
    {
      int max_n_groups = n_groups;
      int ret = getgrouplist (pw->pw_name, pw->pw_gid, groups, &max_n_groups);

      if (ret >= 0)
        {
          n_groups = max_n_groups;
          break;
        }

      /* some systems fail to update n_groups so we just grow it by approximation */
      if (n_groups == max_n_groups)
        n_groups = 2 * max_n_groups;
      else
        n_groups = max_n_groups;

      groups = g_renew (gid_t, groups, n_groups);
    }

  gboolean retval = FALSE;
  for (int i = 0; i < n_groups; i++)
    {
      struct group *gr = getgrgid (groups[i]);

      if (gr != NULL && strcmp (gr->gr_name, admin_group) == 0)
        {
          retval = TRUE;
          break;
        }
    }

  g_free (groups);

  return retval;
}