nf-queue.c

/* This example is placed in the public domain. */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <arpa/inet.h>

#include <libmnl/libmnl.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nfnetlink.h>
#include <linux/netfilter/nfnetlink_queue.h>

static int parse_attr_cb(const struct nlattr *attr, void *data)
{
        const struct nlattr **tb = data;
        int type = mnl_attr_get_type(attr);

        /* skip unsupported attribute in user-space */
        if (mnl_attr_type_valid(attr, NFQA_MAX) < 0)
                return MNL_CB_OK;

        switch(type) {
        case NFQA_MARK:
        case NFQA_IFINDEX_INDEV:
        case NFQA_IFINDEX_OUTDEV:
        case NFQA_IFINDEX_PHYSINDEV:
        case NFQA_IFINDEX_PHYSOUTDEV:
                if (mnl_attr_validate(attr, MNL_TYPE_U32) < 0) {
                        perror("mnl_attr_validate");
                        return MNL_CB_ERROR;
                }
                break;
        case NFQA_TIMESTAMP:
                if (mnl_attr_validate2(attr, MNL_TYPE_UNSPEC,
                    sizeof(struct nfqnl_msg_packet_timestamp)) < 0) {
                        perror("mnl_attr_validate2");
                        return MNL_CB_ERROR;
                }
                break;
        case NFQA_HWADDR:
                if (mnl_attr_validate2(attr, MNL_TYPE_UNSPEC,
                    sizeof(struct nfqnl_msg_packet_hw)) < 0) {
                        perror("mnl_attr_validate2");
                        return MNL_CB_ERROR;
                }
                break;
        case NFQA_PAYLOAD:
                break;
        }
        tb[type] = attr;
        return MNL_CB_OK;
}

static int queue_cb(const struct nlmsghdr *nlh, void *data)
{
        struct nlattr *tb[NFQA_MAX+1] = {};
        struct nfqnl_msg_packet_hdr *ph = NULL;
        uint32_t id = 0;

        mnl_attr_parse(nlh, sizeof(struct nfgenmsg), parse_attr_cb, tb);
        if (tb[NFQA_PACKET_HDR]) {
                ph = mnl_attr_get_payload(tb[NFQA_PACKET_HDR]);
                id = ntohl(ph->packet_id);

                printf("packet received (id=%u hw=0x%04x hook=%u)\n",
                       id, ntohs(ph->hw_protocol), ph->hook);
        }

        return MNL_CB_OK + id;
}

static struct nlmsghdr *
nfq_build_cfg_pf_request(char *buf, uint8_t command)
{
        struct nlmsghdr *nlh = mnl_nlmsg_put_header(buf);
        nlh->nlmsg_type = (NFNL_SUBSYS_QUEUE << 8) | NFQNL_MSG_CONFIG;
        nlh->nlmsg_flags = NLM_F_REQUEST;

        struct nfgenmsg *nfg = mnl_nlmsg_put_extra_header(nlh, sizeof(*nfg));
        nfg->nfgen_family = AF_UNSPEC;
        nfg->version = NFNETLINK_V0;

        struct nfqnl_msg_config_cmd cmd = {
                .command = command,
                .pf = htons(AF_INET),
        };
        mnl_attr_put(nlh, NFQA_CFG_CMD, sizeof(cmd), &cmd);

        return nlh;
}

static struct nlmsghdr *
nfq_build_cfg_request(char *buf, uint8_t command, int queue_num)
{
        struct nlmsghdr *nlh = mnl_nlmsg_put_header(buf);
        nlh->nlmsg_type = (NFNL_SUBSYS_QUEUE << 8) | NFQNL_MSG_CONFIG;
        nlh->nlmsg_flags = NLM_F_REQUEST;

        struct nfgenmsg *nfg = mnl_nlmsg_put_extra_header(nlh, sizeof(*nfg));
        nfg->nfgen_family = AF_UNSPEC;
        nfg->version = NFNETLINK_V0;
        nfg->res_id = htons(queue_num);

        struct nfqnl_msg_config_cmd cmd = {
                .command = command,
                .pf = htons(AF_INET),
        };
        mnl_attr_put(nlh, NFQA_CFG_CMD, sizeof(cmd), &cmd);

        return nlh;
}

static struct nlmsghdr *
nfq_build_cfg_params(char *buf, uint8_t mode, int range, int queue_num)
{
        struct nlmsghdr *nlh = mnl_nlmsg_put_header(buf);
        nlh->nlmsg_type = (NFNL_SUBSYS_QUEUE << 8) | NFQNL_MSG_CONFIG;
        nlh->nlmsg_flags = NLM_F_REQUEST;

        struct nfgenmsg *nfg = mnl_nlmsg_put_extra_header(nlh, sizeof(*nfg));
        nfg->nfgen_family = AF_UNSPEC;
        nfg->version = NFNETLINK_V0;
        nfg->res_id = htons(queue_num);

        struct nfqnl_msg_config_params params = {
                .copy_range = htonl(range),
                .copy_mode = mode,
        };
        mnl_attr_put(nlh, NFQA_CFG_PARAMS, sizeof(params), &params);

        return nlh;
}

static struct nlmsghdr *
nfq_build_verdict(char *buf, int id, int queue_num, int verd)
{
        struct nlmsghdr *nlh;
        struct nfgenmsg *nfg;

        nlh = mnl_nlmsg_put_header(buf);
        nlh->nlmsg_type = (NFNL_SUBSYS_QUEUE << 8) | NFQNL_MSG_VERDICT;
        nlh->nlmsg_flags = NLM_F_REQUEST;
        nfg = mnl_nlmsg_put_extra_header(nlh, sizeof(*nfg));
        nfg->nfgen_family = AF_UNSPEC;
        nfg->version = NFNETLINK_V0;
        nfg->res_id = htons(queue_num);

        struct nfqnl_msg_verdict_hdr vh = {
                .verdict = htonl(verd),
                .id = htonl(id),
        };
        mnl_attr_put(nlh, NFQA_VERDICT_HDR, sizeof(vh), &vh);

        return nlh;
}

int main(int argc, char *argv[])
{
        struct mnl_socket *nl;
        char buf[MNL_SOCKET_BUFFER_SIZE];
        struct nlmsghdr *nlh;
        int ret;
        unsigned int portid, queue_num;

        if (argc != 2) {
                printf("Usage: %s [queue_num]\n", argv[0]);
                exit(EXIT_FAILURE);
        }
        queue_num = atoi(argv[1]);

        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 = nfq_build_cfg_pf_request(buf, NFQNL_CFG_CMD_PF_UNBIND);

        if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
                perror("mnl_socket_sendto");
                exit(EXIT_FAILURE);
        }

        nlh = nfq_build_cfg_pf_request(buf, NFQNL_CFG_CMD_PF_BIND);

        if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
                perror("mnl_socket_sendto");
                exit(EXIT_FAILURE);
        }

        nlh = nfq_build_cfg_request(buf, NFQNL_CFG_CMD_BIND, queue_num);

        if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
                perror("mnl_socket_sendto");
                exit(EXIT_FAILURE);
        }

        nlh = nfq_build_cfg_params(buf, NFQNL_COPY_PACKET, 0xFFFF, queue_num);

        if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
                perror("mnl_socket_sendto");
                exit(EXIT_FAILURE);
        }

        ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
        if (ret == -1) {
                perror("mnl_socket_recvfrom");
                exit(EXIT_FAILURE);
        }
        while (ret > 0) {
                uint32_t id;

                ret = mnl_cb_run(buf, ret, 0, portid, queue_cb, NULL);
                if (ret < 0){
                        perror("mnl_cb_run");
                        exit(EXIT_FAILURE);
                }

                id = ret - MNL_CB_OK;
                nlh = nfq_build_verdict(buf, id, queue_num, NF_ACCEPT);
                if (mnl_socket_sendto(nl, nlh, nlh->nlmsg_len) < 0) {
                        perror("mnl_socket_sendto");
                        exit(EXIT_FAILURE);
                }

                ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
                if (ret == -1) {
                        perror("mnl_socket_recvfrom");
                        exit(EXIT_FAILURE);
                }
        }

        mnl_socket_close(nl);

        return 0;
}