nf_nat_amanda.c

Go to the documentation of this file.

/* Amanda extension for TCP NAT alteration.
 * (C) 2002 by Brian J. Murrell <[email protected]>
 * based on a copy of HW's ip_nat_irc.c as well as other modules
 *
 * 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.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/udp.h>

#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_nat_helper.h>
#include <linux/netfilter/nf_conntrack_amanda.h>

MODULE_AUTHOR("Brian J. Murrell <[email protected]>");
MODULE_DESCRIPTION("Amanda NAT helper");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ip_nat_amanda");

static unsigned int help(struct sk_buff *skb,
             enum ip_conntrack_info ctinfo,
             unsigned int protoff,
             unsigned int matchoff,
             unsigned int matchlen,
             struct nf_conntrack_expect *exp)
{
    char buffer[sizeof("65535")];
    u_int16_t port;
    unsigned int ret;

    /* Connection comes from client. */
    exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
    exp->dir = IP_CT_DIR_ORIGINAL;

    /* When you see the packet, we need to NAT it the same as the
     * this one (ie. same IP: it will be TCP and master is UDP). */
    exp->expectfn = nf_nat_follow_master;

    /* Try to get same port: if not, try to change it. */
    for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
        int res;

        exp->tuple.dst.u.tcp.port = htons(port);
        res = nf_ct_expect_related(exp);
        if (res == 0)
            break;
        else if (res != -EBUSY) {
            port = 0;
            break;
        }
    }

    if (port == 0)
        return NF_DROP;

    sprintf(buffer, "%u", port);
    ret = nf_nat_mangle_udp_packet(skb, exp->master, ctinfo,
                       protoff, matchoff, matchlen,
                       buffer, strlen(buffer));
    if (ret != NF_ACCEPT)
        nf_ct_unexpect_related(exp);
    return ret;
}

static void __exit nf_nat_amanda_fini(void)
{
    RCU_INIT_POINTER(nf_nat_amanda_hook, NULL);
    synchronize_rcu();
}

static int __init nf_nat_amanda_init(void)
{
    BUG_ON(nf_nat_amanda_hook != NULL);
    RCU_INIT_POINTER(nf_nat_amanda_hook, help);
    return 0;
}

module_init(nf_nat_amanda_init);
module_exit(nf_nat_amanda_fini);