#ifdef __linux__
#define _BSD_SOURCE
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/tcp.h>
#include <netinet/udp.h>
#include <arpa/inet.h>
#include "pktlib.h"
#include "pktbuf.h"
#include "nat.h"
struct natentry {
 struct {
 in_addr_t ipaddr;
 int port;
 } global;
 struct {
 in_addr_t ipaddr;
 int port;
 } local;
};
struct nattable { /* NATテーブル */
 int num;
 struct natentry *entries;
};
struct _natif {
 in_addr_t ipaddr;
 struct nattable icmp;
 struct nattable tcp;
 struct nattable udp;
};
static int nattable_init(struct nattable *tbl, int num)
{
 int i;
 tbl->num = num;
 tbl->entries = malloc(sizeof(tbl->entries[0]) * num);
 memset(tbl->entries, 0, sizeof(tbl->entries[0]) * num);
 for (i = 0; i < num; i++) { tbl->entries[i].global.port = 10000 + i;
 }
 return 0;
}
static struct natentry *nattable_get_free_entry(struct nattable *tbl)
{
 int i;
 for (i = 0; i < tbl->num; i++) {
 if (tbl->entries[i].local.port == 0)
 return &tbl->entries[i];
 }
 return NULL;
}
static struct natentry *nattable_add_entry(struct nattable *tbl,
					 in_addr_t global_ipaddr,
					 in_addr_t local_ipaddr,
					 int local_port)
{
 struct natentry *entry;
 entry = nattable_get_free_entry(tbl);
 entry->global.ipaddr = global_ipaddr;
 entry->local.ipaddr = local_ipaddr;
 entry->local.port = local_port;
 return entry;
}
static struct natentry *nattable_search_global(struct nattable *tbl,
					 in_addr_t global_ipaddr,
					 int global_port)
{
 int i;
 for (i = 0; i < tbl->num; i++) {
 if ((tbl->entries[i].global.ipaddr == global_ipaddr) &&
	(tbl->entries[i].global.port == global_port)) {
 return &tbl->entries[i];
 }
 }
 return NULL;
}
static struct natentry *nattable_search_local(struct nattable *tbl,
					 in_addr_t local_ipaddr,
					 int local_port)
{
 int i;
 for (i = 0; i < tbl->num; i++) {
 if ((tbl->entries[i].local.ipaddr == local_ipaddr) &&
	(tbl->entries[i].local.port == local_port)) {
 return &tbl->entries[i];
 }
 }
 return NULL;
}
natif_t natif_create(int entry_num, in_addr_t ipaddr)
{
 natif_t natif;
 natif = malloc(sizeof(*natif));
 memset(natif, 0, sizeof(*natif));
 natif->ipaddr = ipaddr;
 nattable_init(&natif->icmp, entry_num);
 nattable_init(&natif->tcp, entry_num);
 nattable_init(&natif->udp, entry_num);
 return natif;
}
enum {
 NAT_DIRECTION_INCOMING,
 NAT_DIRECTION_OUTGOING,
};
static pktbuf_t nat_icmp(natif_t natif, pktbuf_t pktbuf, struct ip *iphdr, int direction)
{
 char *p;
 struct icmp *icmphdr;
 struct natentry *entry;
 p = pktbuf_get_header(pktbuf);
 if (pktbuf_get_size(pktbuf) < sizeof(*icmphdr)) return pktbuf; icmphdr = (struct icmp *)p; switch (direction) { case NAT_DIRECTION_INCOMING: entry = nattable_search_global(&natif->icmp, ntohl(iphdr->ip_dst.s_addr),
				 ntohs(icmphdr->icmp_id));
 if (entry == NULL)
 return pktbuf;
 iphdr->ip_dst.s_addr = htonl(entry->local.ipaddr);
 icmphdr->icmp_id = htons(entry->local.port);
 break;
 case NAT_DIRECTION_OUTGOING:
 entry = nattable_search_local(&natif->icmp, ntohl(iphdr->ip_src.s_addr),
				 ntohs(icmphdr->icmp_id));
 if (entry == NULL) {
 entry = nattable_add_entry(&natif->icmp, natif->ipaddr,
				 ntohl(iphdr->ip_src.s_addr),
				 ntohs(icmphdr->icmp_id));
 }
 iphdr->ip_src.s_addr = htonl(natif->ipaddr);
 icmphdr->icmp_id = htons(entry->global.port);
 break;
 default:
 break;
 }
 return pktbuf;
}
static pktbuf_t nat_tcp(natif_t natif, pktbuf_t pktbuf, struct ip *iphdr, int direction)
{
 char *p;
 struct tcphdr *tcphdr;
 struct natentry *entry;
 p = pktbuf_get_header(pktbuf);
 if (pktbuf_get_size(pktbuf) < sizeof(*tcphdr)) return pktbuf; tcphdr = (struct tcphdr *)p; switch (direction) { case NAT_DIRECTION_INCOMING: entry = nattable_search_global(&natif->tcp, ntohl(iphdr->ip_dst.s_addr),
				 ntohs(tcphdr->th_dport));
 if (entry == NULL)
 return pktbuf;
 iphdr->ip_dst.s_addr = htonl(entry->local.ipaddr);
 tcphdr->th_dport = htons(entry->local.port);
 break;
 case NAT_DIRECTION_OUTGOING:
 entry = nattable_search_local(&natif->tcp, ntohl(iphdr->ip_src.s_addr),
				 ntohs(tcphdr->th_sport));
 if (entry == NULL) {
 entry = nattable_add_entry(&natif->tcp, natif->ipaddr,
				 ntohl(iphdr->ip_src.s_addr),
				 ntohs(tcphdr->th_sport));
 }
 iphdr->ip_src.s_addr = htonl(natif->ipaddr);
 tcphdr->th_sport = htons(entry->global.port);
 break;
 default:
 break;
 }
 return pktbuf;
}
static pktbuf_t nat_udp(natif_t natif, pktbuf_t pktbuf, struct ip *iphdr, int direction)
{
 char *p;
 struct udphdr *udphdr;
 struct natentry *entry;
 p = pktbuf_get_header(pktbuf);
 if (pktbuf_get_size(pktbuf) < sizeof(*udphdr)) return pktbuf; udphdr = (struct udphdr *)p; switch (direction) { case NAT_DIRECTION_INCOMING: entry = nattable_search_global(&natif->udp, ntohl(iphdr->ip_dst.s_addr),
				 ntohs(udphdr->uh_dport));
 if (entry == NULL)
 return pktbuf;
 iphdr->ip_dst.s_addr = htonl(entry->local.ipaddr);
 udphdr->uh_dport = htons(entry->local.port);
 break;
 case NAT_DIRECTION_OUTGOING:
 entry = nattable_search_local(&natif->udp, ntohl(iphdr->ip_src.s_addr),
				 ntohs(udphdr->uh_sport));
 if (entry == NULL) {
 entry = nattable_add_entry(&natif->udp, natif->ipaddr,
				 ntohl(iphdr->ip_src.s_addr),
				 ntohs(udphdr->uh_sport));
 }
 iphdr->ip_src.s_addr = htonl(natif->ipaddr);
 udphdr->uh_sport = htons(entry->global.port);
 break;
 default:
 break;
 }
 return pktbuf;
}
static pktbuf_t proc_ip(natif_t natif, pktbuf_t pktbuf, int direction)
{
 char *p;
 struct ip *iphdr;
 int hdrsize, paysize;
 p = pktbuf_get_header(pktbuf);
 if (pktbuf_get_size(pktbuf) < sizeof(*iphdr)) return pktbuf; iphdr = (struct ip *)p; hdrsize = iphdr->ip_hl << 2; paysize = ntohs(iphdr->ip_len) - hdrsize;
 if (pktbuf_get_size(pktbuf) < hdrsize) return pktbuf; switch (direction) { case NAT_DIRECTION_INCOMING: if (ntohl(iphdr->ip_dst.s_addr) != natif->ipaddr)
 return pktbuf;
 break;
 case NAT_DIRECTION_OUTGOING:
 if (ntohl(iphdr->ip_src.s_addr) == natif->ipaddr)
 return pktbuf;
 break;
 default:
 break;
 }
 fprintf(stderr, "NAT(before) %-15s", inet_ntoa(iphdr->ip_src));
 fprintf(stderr, " -> %-15s\n", inet_ntoa(iphdr->ip_dst));
 if (pktbuf_get_size(pktbuf) < hdrsize + paysize) return pktbuf; pktbuf_delete_header(pktbuf, hdrsize); switch (iphdr->ip_p) {
 case IPPROTO_ICMP: pktbuf = nat_icmp(natif, pktbuf, iphdr, direction); break;
 case IPPROTO_TCP: pktbuf = nat_tcp( natif, pktbuf, iphdr, direction); break;
 case IPPROTO_UDP: pktbuf = nat_udp( natif, pktbuf, iphdr, direction); break;
 default: break;
 }
 if (pktbuf == NULL)
 return NULL;
 pktbuf_add_header(pktbuf, hdrsize);
 fprintf(stderr, "NAT(after) %-15s", inet_ntoa(iphdr->ip_src));
 fprintf(stderr, " -> %-15s\n", inet_ntoa(iphdr->ip_dst));
 return pktbuf;
}
pktbuf_t natif_packet_incoming(natif_t natif, pktbuf_t pktbuf)
{
 return proc_ip(natif, pktbuf, NAT_DIRECTION_INCOMING);
}
pktbuf_t natif_packet_outgoing(natif_t natif, pktbuf_t pktbuf)
{
 return proc_ip(natif, pktbuf, NAT_DIRECTION_OUTGOING);
}
int natif_add_entry_tcp(natif_t natif, int global_port,
			in_addr_t local_ipaddr, int local_port)
{
 struct natentry *entry;
 entry = nattable_add_entry(&natif->tcp, natif->ipaddr,
			 local_ipaddr, local_port);
 entry->global.port = global_port;
 return 0;
}
int natif_add_entry_udp(natif_t natif, int global_port,
			in_addr_t local_ipaddr, int local_port)
{
 struct natentry *entry;
 entry = nattable_add_entry(&natif->udp, natif->ipaddr,
			 local_ipaddr, local_port);
 entry->global.port = global_port;
 return 0;
}
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