/* $NetBSD: ipf.c,v 1.4 2018/12/13 13:11:28 sborrill Exp $ */

/*
 * ipf.c - NAT lookup code for IP Filter.
 *
 * This software is in the public domain.
 * Written by Peter Postma <peter@NetBSD.org>
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: ipf.c,v 1.4 2018/12/13 13:11:28 sborrill Exp $");

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/fcntl.h>

#include <net/if.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ipl.h>
#include <netinet/ip_compat.h>
#include <netinet/ip_fil.h>
#include <netinet/ip_nat.h>

#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>

#include "identd.h"

int
ipf_natlookup(const struct sockaddr_storage *ss,
    struct sockaddr_storage *nat_addr, in_port_t *nat_lport)
{
        natlookup_t nl;
        ipfobj_t obj;
        int dev;

        (void)memset(&obj, 0, sizeof(obj));
        (void)memset(&nl, 0, sizeof(nl));

        /* Build the ipf object description structure. */
        obj.ipfo_rev = IPFILTER_VERSION;
        obj.ipfo_size = sizeof(nl);
        obj.ipfo_ptr = &nl;
        obj.ipfo_type = IPFOBJ_NATLOOKUP;

        /* Build the ipf natlook structure. */
        switch (ss[0].ss_family) {
        case AF_INET:
                (void)memcpy(&nl.nl_realip, &csatosin(&ss[0])->sin_addr,
                    sizeof(struct in_addr));
                (void)memcpy(&nl.nl_outip, &csatosin(&ss[1])->sin_addr,
                    sizeof(struct in_addr));
                nl.nl_realport = ntohs(csatosin(&ss[0])->sin_port);
                nl.nl_outport = ntohs(csatosin(&ss[1])->sin_port);
                nl.nl_flags = IPN_TCP | IPN_IN;
                nl.nl_v = 4; /* IPv4 */
                break;
        case AF_INET6:
                /* XXX IP Filter doesn't support IPv6 NAT yet. */
        default:
                maybe_syslog(LOG_ERR, "Unsupported protocol for NAT lookup "
                    "(no. %d)", ss[0].ss_family);
                return 0;
        }

        /* Open the NAT device and do the lookup. */
        if ((dev = open(IPNAT_NAME, O_RDONLY)) == -1) {
                maybe_syslog(LOG_ERR, "Cannot open %s: %m", IPNAT_NAME);
                return 0;
        }
        if (ioctl(dev, SIOCGNATL, &obj) == -1) {
                maybe_syslog(LOG_ERR, "NAT lookup failure: %m");
                (void)close(dev);
                return 0;
        }
        (void)close(dev);

        /*
         * Put the originating address into nat_addr and fill
         * the port with the ident port, 113.
         */
        switch (ss[0].ss_family) {
        case AF_INET:
                (void)memcpy(&satosin(nat_addr)->sin_addr, &nl.nl_inip,
                    sizeof(struct in_addr));
                satosin(nat_addr)->sin_port = htons(113);
                satosin(nat_addr)->sin_len = sizeof(struct sockaddr_in);
                satosin(nat_addr)->sin_family = AF_INET;
                break;
        case AF_INET6:
                break;
        }
        /* Put the originating port into nat_lport. */
        *nat_lport = nl.nl_inport;

        return 1;
}