nft-rule-add.c

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * (C) 2012 by Pablo Neira Ayuso <pablo@netfilter.org>
 *
 * This software has been sponsored by Sophos Astaro <http://www.sophos.com>
 */

#define _GNU_SOURCE     /* for tcphdr.dest */
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <stddef.h>     /* for offsetof */
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>

#include <linux/netfilter.h>
#include <linux/netfilter/nfnetlink.h>
#include <linux/netfilter/nf_tables.h>

#include <libmnl/libmnl.h>
#include <libnftnl/rule.h>
#include <libnftnl/expr.h>

static void add_payload(struct nftnl_rule *r, uint32_t base, uint32_t dreg,
                        uint32_t offset, uint32_t len)
{
        struct nftnl_expr *e;

        e = nftnl_expr_alloc("payload");
        if (e == NULL) {
                perror("expr payload oom");
                exit(EXIT_FAILURE);
        }

        nftnl_expr_set_u32(e, NFTNL_EXPR_PAYLOAD_BASE, base);
        nftnl_expr_set_u32(e, NFTNL_EXPR_PAYLOAD_DREG, dreg);
        nftnl_expr_set_u32(e, NFTNL_EXPR_PAYLOAD_OFFSET, offset);
        nftnl_expr_set_u32(e, NFTNL_EXPR_PAYLOAD_LEN, len);

        nftnl_rule_add_expr(r, e);
}

static void add_cmp(struct nftnl_rule *r, uint32_t sreg, uint32_t op,
                    const void *data, uint32_t data_len)
{
        struct nftnl_expr *e;

        e = nftnl_expr_alloc("cmp");
        if (e == NULL) {
                perror("expr cmp oom");
                exit(EXIT_FAILURE);
        }

        nftnl_expr_set_u32(e, NFTNL_EXPR_CMP_SREG, sreg);
        nftnl_expr_set_u32(e, NFTNL_EXPR_CMP_OP, op);
        nftnl_expr_set(e, NFTNL_EXPR_CMP_DATA, data, data_len);

        nftnl_rule_add_expr(r, e);
}

static void add_counter(struct nftnl_rule *r)
{
        struct nftnl_expr *e;

        e = nftnl_expr_alloc("counter");
        if (e == NULL) {
                perror("expr counter oom");
                exit(EXIT_FAILURE);
        }

        nftnl_rule_add_expr(r, e);
}

static struct nftnl_rule *setup_rule(uint8_t family, const char *table,
                                   const char *chain, const char *handle)
{
        struct nftnl_rule *r = NULL;
        uint8_t proto;
        uint16_t dport;
        uint64_t handle_num;

        r = nftnl_rule_alloc();
        if (r == NULL) {
                perror("OOM");
                exit(EXIT_FAILURE);
        }

        nftnl_rule_set_str(r, NFTNL_RULE_TABLE, table);
        nftnl_rule_set_str(r, NFTNL_RULE_CHAIN, chain);
        nftnl_rule_set_u32(r, NFTNL_RULE_FAMILY, family);

        if (handle != NULL) {
                handle_num = atoll(handle);
                nftnl_rule_set_u64(r, NFTNL_RULE_POSITION, handle_num);
        }

        proto = IPPROTO_TCP;
        add_payload(r, NFT_PAYLOAD_NETWORK_HEADER, NFT_REG_1,
                    offsetof(struct iphdr, protocol), sizeof(uint8_t));
        add_cmp(r, NFT_REG_1, NFT_CMP_EQ, &proto, sizeof(uint8_t));

        dport = htons(22);
        add_payload(r, NFT_PAYLOAD_TRANSPORT_HEADER, NFT_REG_1,
                    offsetof(struct tcphdr, dest), sizeof(uint16_t));
        add_cmp(r, NFT_REG_1, NFT_CMP_EQ, &dport, sizeof(uint16_t));

        add_counter(r);

        return r;
}

int main(int argc, char *argv[])
{
        struct mnl_socket *nl;
        struct nftnl_rule *r;
        struct nlmsghdr *nlh;
        struct mnl_nlmsg_batch *batch;
        uint8_t family;
        char buf[MNL_SOCKET_BUFFER_SIZE];
        uint32_t seq = time(NULL);
        int ret;

        if (argc < 4 || argc > 5) {
                fprintf(stderr, "Usage: %s <family> <table> <chain>\n", argv[0]);
                exit(EXIT_FAILURE);
        }

        if (strcmp(argv[1], "ip") == 0)
                family = NFPROTO_IPV4;
        else if (strcmp(argv[1], "ip6") == 0)
                family = NFPROTO_IPV6;
        else if (strcmp(argv[1], "inet") == 0)
                family = NFPROTO_INET;
        else {
                fprintf(stderr, "Unknown family: ip, ip6, inet\n");
                exit(EXIT_FAILURE);
        }

        if (argc != 5)
                r = setup_rule(family, argv[2], argv[3], NULL);
        else
                r = setup_rule(family, argv[2], argv[3], argv[4]);

        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);
        }

        batch = mnl_nlmsg_batch_start(buf, sizeof(buf));

        nftnl_batch_begin(mnl_nlmsg_batch_current(batch), seq++);
        mnl_nlmsg_batch_next(batch);

        nlh = nftnl_nlmsg_build_hdr(mnl_nlmsg_batch_current(batch),
                                    NFT_MSG_NEWRULE,
                                    nftnl_rule_get_u32(r, NFTNL_RULE_FAMILY),
                                    NLM_F_APPEND | NLM_F_CREATE | NLM_F_ACK,
                                    seq++);
        nftnl_rule_nlmsg_build_payload(nlh, r);
        nftnl_rule_free(r);
        mnl_nlmsg_batch_next(batch);

        nftnl_batch_end(mnl_nlmsg_batch_current(batch), seq++);
        mnl_nlmsg_batch_next(batch);

        ret = mnl_socket_sendto(nl, mnl_nlmsg_batch_head(batch),
                                mnl_nlmsg_batch_size(batch));
        if (ret == -1) {
                perror("mnl_socket_sendto");
                exit(EXIT_FAILURE);
        }

        mnl_nlmsg_batch_stop(batch);

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

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

        mnl_socket_close(nl);

        return EXIT_SUCCESS;
}