mktime_z (timezone_t tz, struct tm *tm)
{
  if (!tz)
    return timegm (tm);
  else
    {
      timezone_t old_tz = set_tz (tz);
      if (old_tz)
        {
          time_t t = mktime (tm);
#if HAVE_TM_ZONE || HAVE_TZNAME
          time_t badtime = -1;
          struct tm tm_1;
          if ((t != badtime
               || (localtime_r (&t, &tm_1) && equal_tm (tm, &tm_1)))
              && !save_abbr (tz, tm))
            t = badtime;
#endif
          if (revert_tz (old_tz))
            return t;
        }
      return -1;
    }
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.