conntrack_create_nat.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <arpa/inet.h>

#include <libnetfilter_conntrack/libnetfilter_conntrack.h>
#include <libnetfilter_conntrack/libnetfilter_conntrack_tcp.h>

int main(void)
{
        int ret;
        struct nfct_handle *h;
        struct nf_conntrack *ct;

        ct = nfct_new();
        if (!ct) {
                perror("nfct_new");
                return 0;
        }

        nfct_set_attr_u8(ct, ATTR_L3PROTO, AF_INET);
        nfct_set_attr_u32(ct, ATTR_IPV4_SRC, inet_addr("1.1.1.1"));
        nfct_set_attr_u32(ct, ATTR_IPV4_DST, inet_addr("2.2.2.2"));
        
        nfct_set_attr_u8(ct, ATTR_L4PROTO, IPPROTO_TCP);
        nfct_set_attr_u16(ct, ATTR_PORT_SRC, htons(20));
        nfct_set_attr_u16(ct, ATTR_PORT_DST, htons(10));

        nfct_setobjopt(ct, NFCT_SOPT_SETUP_REPLY);

        nfct_set_attr_u8(ct, ATTR_TCP_STATE, TCP_CONNTRACK_SYN_SENT);
        nfct_set_attr_u32(ct, ATTR_TIMEOUT, 100);

        nfct_set_attr_u32(ct, ATTR_SNAT_IPV4, inet_addr("8.8.8.8"));

        h = nfct_open(CONNTRACK, 0);
        if (!h) {
                perror("nfct_open");
                return -1;
        }

        ret = nfct_query(h, NFCT_Q_CREATE, ct);

        printf("TEST: create conntrack ");
        if (ret == -1)
                printf("(%d)(%s)\n", ret, strerror(errno));
        else
                printf("(OK)\n");

        nfct_close(h);

        ret == -1 ? exit(EXIT_FAILURE) : exit(EXIT_SUCCESS);
}