static int rose_create_facilities(unsigned char *buffer, struct rose_sock *rose)
{
	unsigned char *p = buffer + 1;
	char *callsign;
	char buf[11];
	int len, nb;

	/* National Facilities */
	if (rose->rand != 0 || rose->source_ndigis == 1 || rose->dest_ndigis == 1) {
		*p++ = 0x00;
		*p++ = FAC_NATIONAL;

		if (rose->rand != 0) {
			*p++ = FAC_NATIONAL_RAND;
			*p++ = (rose->rand >> 8) & 0xFF;
			*p++ = (rose->rand >> 0) & 0xFF;
		}

		/* Sent before older facilities */
		if ((rose->source_ndigis > 0) || (rose->dest_ndigis > 0)) {
			int maxdigi = 0;
			*p++ = FAC_NATIONAL_DIGIS;
			*p++ = AX25_ADDR_LEN * (rose->source_ndigis + rose->dest_ndigis);
			for (nb = 0 ; nb < rose->source_ndigis ; nb++) {
				if (++maxdigi >= ROSE_MAX_DIGIS)
					break;
				memcpy(p, &rose->source_digis[nb], AX25_ADDR_LEN);
				p[6] |= AX25_HBIT;
				p += AX25_ADDR_LEN;
			}
			for (nb = 0 ; nb < rose->dest_ndigis ; nb++) {
				if (++maxdigi >= ROSE_MAX_DIGIS)
					break;
				memcpy(p, &rose->dest_digis[nb], AX25_ADDR_LEN);
				p[6] &= ~AX25_HBIT;
				p += AX25_ADDR_LEN;
			}
		}

		/* For compatibility */
		if (rose->source_ndigis > 0) {
			*p++ = FAC_NATIONAL_SRC_DIGI;
			*p++ = AX25_ADDR_LEN;
			memcpy(p, &rose->source_digis[0], AX25_ADDR_LEN);
			p   += AX25_ADDR_LEN;
		}

		/* For compatibility */
		if (rose->dest_ndigis > 0) {
			*p++ = FAC_NATIONAL_DEST_DIGI;
			*p++ = AX25_ADDR_LEN;
			memcpy(p, &rose->dest_digis[0], AX25_ADDR_LEN);
			p   += AX25_ADDR_LEN;
		}
	}

	*p++ = 0x00;
	*p++ = FAC_CCITT;

	*p++ = FAC_CCITT_DEST_NSAP;

	callsign = ax2asc(buf, &rose->dest_call);

	*p++ = strlen(callsign) + 10;
	*p++ = (strlen(callsign) + 9) * 2;		/* ??? */

	*p++ = 0x47; *p++ = 0x00; *p++ = 0x11;
	*p++ = ROSE_ADDR_LEN * 2;
	memcpy(p, &rose->dest_addr, ROSE_ADDR_LEN);
	p   += ROSE_ADDR_LEN;

	memcpy(p, callsign, strlen(callsign));
	p   += strlen(callsign);

	*p++ = FAC_CCITT_SRC_NSAP;

	callsign = ax2asc(buf, &rose->source_call);

	*p++ = strlen(callsign) + 10;
	*p++ = (strlen(callsign) + 9) * 2;		/* ??? */

	*p++ = 0x47; *p++ = 0x00; *p++ = 0x11;
	*p++ = ROSE_ADDR_LEN * 2;
	memcpy(p, &rose->source_addr, ROSE_ADDR_LEN);
	p   += ROSE_ADDR_LEN;

	memcpy(p, callsign, strlen(callsign));
	p   += strlen(callsign);

	len       = p - buffer;
	buffer[0] = len - 1;

	return len;
}

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.