void cgtimer_sub(cgtimer_t *a, cgtimer_t *b, cgtimer_t *res)
{
	res->tv_sec = a->tv_sec - b->tv_sec;
	res->tv_nsec = a->tv_nsec - b->tv_nsec;
	if (res->tv_nsec < 0) {
		res->tv_nsec += 1000000000;
		res->tv_sec--;
	}
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.