/* PRETTY PRINT TCP PACKET HEADER */
void print_tcp_load(const uint8_t *packet, unsigned int len) {
unsigned int data_offset = sizeof(eth_hdr) + sizeof(ip_hdr);
unsigned int data_len = len - data_offset;
const uint8_t *data = packet + data_offset;
indent(2);
printf("\nTCP PACKET in HEX (%d bytes)\n", data_len);
nat_tcp_hdr *tcp = get_nat_tcp_hdr(packet, len);
indent(3);
printf("Src Port = %d\n", ntohs(tcp->tcp_sport));
indent(3);
printf("Dst Port = %d\n", ntohs(tcp->tcp_dport));
indent(3);
printf("Seq # = %X\n", ntohl(tcp->tcp_seq));
indent(3);
printf("Acq # = %X\n", ntohl(tcp->tcp_ack));
indent(3);
printf("Unused = %X %X %X %X\n", tcp->unused1[0], tcp->unused1[1], tcp->unused1[2], tcp->unused1[3]);
indent(3);
printf("Sum = %X\n", tcp->tcp_sum);
indent(3);
printf("Unused = %X %X\n", tcp->unused2[0], tcp->unused2[1]);
printf("\n");
int i; for(i=0; i<data_len; i++){ printf("%X ", data[i]); }
printf("\n\n");
}
/*
* Overwrite the ip and port of a packet for nat
*/
void populate_nat_packet(ip_hdr *ip, const uint8_t *packet, unsigned int len, nat_entry *ne, int nat_type) {
nat_tcp_hdr *tcp = NULL;
nat_udp_hdr *udp = NULL;
nat_icmp_hdr *icmp = NULL;
/* rewrite the ip address */
if(nat_type == NAT_EXTERNAL) { ip->ip_src.s_addr = ne->nat_ext.ip.s_addr; }
else if(nat_type == NAT_INTERNAL) { ip->ip_dst.s_addr = ne->nat_int.ip.s_addr; }
switch(ip->ip_p) {
case IP_PROTO_TCP:
tcp = get_nat_tcp_hdr(packet, len);
if(nat_type == NAT_EXTERNAL) { tcp->tcp_sport = ne->nat_ext.port; }
else if(nat_type == NAT_INTERNAL) { tcp->tcp_dport = ne->nat_int.port; }
break;
case IP_PROTO_UDP:
udp = get_nat_udp_hdr(packet, len);
if(nat_type == NAT_EXTERNAL) { udp->udp_sport = ne->nat_ext.port; }
else if(nat_type == NAT_INTERNAL) { udp->udp_dport = ne->nat_int.port; }
break;
case IP_PROTO_ICMP:
icmp = get_nat_icmp_hdr(packet, len);
if( (icmp->icmp_type == ICMP_TYPE_ECHO_REQUEST) || (icmp->icmp_type == ICMP_TYPE_ECHO_REPLY) ) {
/* overwrite the identifier */
if(nat_type == NAT_EXTERNAL) { icmp->icmp_opt1 = ne->nat_ext.port; }
else if(nat_type == NAT_INTERNAL) { icmp->icmp_opt1 = ne->nat_int.port; }
}
else if( (icmp->icmp_type == ICMP_TYPE_TIME_EXCEEDED) || (icmp->icmp_type == ICMP_TYPE_DESTINATION_UNREACHABLE) ) {
/* overwrite the ip and ip sum inside the icmp data */
uint16_t checksum = 0;
ip_hdr *data_ip = get_ip_hdr_from_icmp_data(packet, len);
if(nat_type == NAT_EXTERNAL) {
data_ip->ip_dst.s_addr = ne->nat_ext.ip.s_addr;
checksum = nat_checksum(data_ip->ip_sum, ne->nat_ext.checksum_ip, ne->nat_int.checksum_ip);
}
else if(nat_type == NAT_INTERNAL) {
data_ip->ip_src.s_addr = ne->nat_int.ip.s_addr;
checksum = nat_checksum(data_ip->ip_sum, ne->nat_int.checksum_ip, ne->nat_ext.checksum_ip);
}
bzero(&ip->ip_sum, sizeof(uint16_t));
data_ip->ip_sum = checksum;
if( (data_ip->ip_p == IP_PROTO_TCP) || (data_ip->ip_p == IP_PROTO_UDP) ) {
/* overwrite the port inside the icmp data */
uint16_t *ports = get_nat_port_list_from_icmp_data(packet, len);
if(nat_type == NAT_EXTERNAL) { *(ports+1) = ne->nat_ext.port; }
else if(nat_type == NAT_INTERNAL) { *ports = ne->nat_int.port; }
}
else if( data_ip->ip_p == IP_PROTO_ICMP ) {
nat_icmp_hdr *icmp_data = get_icmp_hdr_from_icmp_data(packet, len);
/* overwrite the id and checksum of the original echo packet */
if( (icmp_data->icmp_type == ICMP_TYPE_ECHO_REQUEST) || (icmp_data->icmp_type == ICMP_TYPE_ECHO_REPLY) ) {
if(nat_type == NAT_EXTERNAL) {
icmp_data->icmp_opt1 = ne->nat_ext.port;
checksum = nat_checksum(icmp_data->icmp_sum, ne->nat_ext.checksum_port, ne->nat_int.checksum_port);
}
else if(nat_type == NAT_INTERNAL) {
icmp_data->icmp_opt1 = ne->nat_int.port;
checksum = nat_checksum(icmp_data->icmp_sum, ne->nat_int.checksum_port, ne->nat_ext.checksum_port);
}
bzero(&icmp_data->icmp_sum, sizeof(uint16_t));
icmp_data->icmp_sum = checksum;
}
}
}
break;
default:
printf("Invalid IP protocol found in the ip header while overwriting the packet with nat entries\n");
break;
}
}
