nfct-mnl-create.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <arpa/inet.h>

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

#include <linux/netfilter/nf_conntrack_tcp.h>

int main(void)
{
        struct mnl_socket *nl;
        struct nlmsghdr *nlh;
        struct nfgenmsg *nfh;
        char buf[MNL_SOCKET_BUFFER_SIZE];
        unsigned int seq, portid;
        struct nf_conntrack *ct;
        int ret;

        nl = mnl_socket_open(NETLINK_NETFILTER);
        if (nl == NULL) {
                perror("mnl_socket_open");
                exit(EXIT_FAILURE);
        }

        if (mnl_socket_bind(nl, 0, MNL_SOCKET_AUTOPID) < 0) {
                perror("mnl_socket_bind");
                exit(EXIT_FAILURE);
        }
        portid = mnl_socket_get_portid(nl);

        nlh = mnl_nlmsg_put_header(buf);
        nlh->nlmsg_type = (NFNL_SUBSYS_CTNETLINK << 8) | IPCTNL_MSG_CT_NEW;
        nlh->nlmsg_flags = NLM_F_REQUEST|NLM_F_CREATE|NLM_F_EXCL|NLM_F_ACK;
        nlh->nlmsg_seq = seq = time(NULL);

        nfh = mnl_nlmsg_put_extra_header(nlh, sizeof(struct nfgenmsg));
        nfh->nfgen_family = AF_INET;
        nfh->version = NFNETLINK_V0;
        nfh->res_id = 0;

        ct = nfct_new();
        if (ct == NULL) {
                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_nlmsg_build(nlh, ct);

        ret = mnl_socket_sendto(nl, nlh, nlh->nlmsg_len);
        if (ret == -1) {
                perror("mnl_socket_recvfrom");
                exit(EXIT_FAILURE);
        }

        ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
        while (ret > 0) {
                ret = mnl_cb_run(buf, ret, seq, portid, NULL, NULL);
                if (ret <= MNL_CB_STOP)
                        break;
                ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
        }
        if (ret == -1) {
                perror("mnl_socket_recvfrom");
                exit(EXIT_FAILURE);
        }

        mnl_socket_close(nl);

        return 0;
}