Adding an invalid rule to nftables that makes nft segfault

nft-rule-add.c

/*
 * (C) 2012 by Pablo Neira Ayuso <pablo@netfilter.org>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This software has been sponsored by Sophos Astaro <http://www.sophos.com>
 */

#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 struct nftnl_rule *setup_rule()
{
    struct nftnl_rule *rule;
    struct nftnl_expr *payload_expr, *cmp_expr;
    uint8_t mac[6] = {0, 0, 0, 0, 0, 0};

    rule = nftnl_rule_alloc();
    nftnl_rule_set(rule, NFTNL_RULE_TABLE, "my_table");
    nftnl_rule_set(rule, NFTNL_RULE_CHAIN, "my_chain");
    nftnl_rule_set_u32(rule, NFTNL_RULE_FAMILY, NFPROTO_INET);


    payload_expr = nftnl_expr_alloc("payload");
    nftnl_expr_set_u32(payload_expr, NFTNL_EXPR_PAYLOAD_BASE, NFT_PAYLOAD_LL_HEADER);
    nftnl_expr_set_u32(payload_expr, NFTNL_EXPR_PAYLOAD_DREG, NFT_REG_1);
    nftnl_expr_set_u32(payload_expr, NFTNL_EXPR_PAYLOAD_OFFSET, 0);
    nftnl_expr_set_u32(payload_expr, NFTNL_EXPR_PAYLOAD_LEN, 6);
    nftnl_rule_add_expr(rule, payload_expr);

    cmp_expr = nftnl_expr_alloc("cmp");
    nftnl_expr_set_u32(cmp_expr, NFTNL_EXPR_CMP_SREG, NFT_REG_1);
    nftnl_expr_set_u32(cmp_expr, NFTNL_EXPR_CMP_OP, NFT_CMP_EQ);
    nftnl_expr_set(cmp_expr, NFTNL_EXPR_CMP_DATA, &mac, 6);
    nftnl_rule_add_expr(rule, cmp_expr);

	return rule;
}

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

    r = setup_rule();

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

	batching = nftnl_batch_is_supported();
	if (batching < 0) {
		perror("cannot talk to nfnetlink");
		exit(EXIT_FAILURE);
	}

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

	if (batching) {
		nftnl_batch_begin(mnl_nlmsg_batch_current(batch), seq++);
		mnl_nlmsg_batch_next(batch);
	}

	nlh = nftnl_rule_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);

	if (batching) {
		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;
}