Incorrect classification in GTP

[nhnghia]

The 3 fields, sequence number (2 octets), n-pdu number (1 octet) and extension header (1 octet), are present if at least one of 3 bit fields, S, NP, E is present.

So the classification is incorrect:

int gtp_classify_next_proto(ipacket_t * ipacket, unsigned index) {

	int offset = get_packet_offset_at_index(ipacket, index);
	struct gtp_header_generic *gtp = (struct gtp_header_generic*)& ipacket->data[offset];
	int gtp_offset = sizeof (struct gtp_header_generic);
	if(gtp->sequence_number == 1){
		gtp_offset += 4;
	}
	if(gtp->ndpu_number == 1){
		gtp_offset += 2;
	}
	if(gtp->extension_header == 1){
		gtp_offset += 2;	
	}
	if (gtp->message_type == 0xff) {
		classified_proto_t retval;
		retval.proto_id = PROTO_IP;
		retval.offset = gtp_offset;
		retval.status = Classified;
		return set_classified_proto(ipacket, index + 1, retval);
	}
	return 0;
}