iptable_mangle.c

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/*
 * This is the 1999 rewrite of IP Firewalling, aiming for kernel 2.3.x.
 *
 * Copyright (C) 1999 Paul `Rusty' Russell & Michael J. Neuling
 * Copyright (C) 2000-2004 Netfilter Core Team <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/module.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <net/route.h>
#include <linux/ip.h>
#include <net/ip.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Netfilter Core Team <[email protected]>");
MODULE_DESCRIPTION("iptables mangle table");

#define MANGLE_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
                (1 << NF_INET_LOCAL_IN) | \
                (1 << NF_INET_FORWARD) | \
                (1 << NF_INET_LOCAL_OUT) | \
                (1 << NF_INET_POST_ROUTING))

static const struct xt_table packet_mangler = {
    .name       = "mangle",
    .valid_hooks    = MANGLE_VALID_HOOKS,
    .me     = THIS_MODULE,
    .af     = NFPROTO_IPV4,
    .priority   = NF_IP_PRI_MANGLE,
};

static unsigned int
ipt_mangle_out(struct sk_buff *skb, const struct net_device *out)
{
    unsigned int ret;
    const struct iphdr *iph;
    u_int8_t tos;
    __be32 saddr, daddr;
    u_int32_t mark;

    /* root is playing with raw sockets. */
    if (skb->len < sizeof(struct iphdr) ||
        ip_hdrlen(skb) < sizeof(struct iphdr))
        return NF_ACCEPT;

    /* Save things which could affect route */
    mark = skb->mark;
    iph = ip_hdr(skb);
    saddr = iph->saddr;
    daddr = iph->daddr;
    tos = iph->tos;

    ret = ipt_do_table(skb, NF_INET_LOCAL_OUT, NULL, out,
               dev_net(out)->ipv4.iptable_mangle);
    /* Reroute for ANY change. */
    if (ret != NF_DROP && ret != NF_STOLEN) {
        iph = ip_hdr(skb);

        if (iph->saddr != saddr ||
            iph->daddr != daddr ||
            skb->mark != mark ||
            iph->tos != tos)
            if (ip_route_me_harder(skb, RTN_UNSPEC))
                ret = NF_DROP;
    }

    return ret;
}

/* The work comes in here from netfilter.c. */
static unsigned int
iptable_mangle_hook(unsigned int hook,
             struct sk_buff *skb,
             const struct net_device *in,
             const struct net_device *out,
             int (*okfn)(struct sk_buff *))
{
    if (hook == NF_INET_LOCAL_OUT)
        return ipt_mangle_out(skb, out);
    if (hook == NF_INET_POST_ROUTING)
        return ipt_do_table(skb, hook, in, out,
                    dev_net(out)->ipv4.iptable_mangle);
    /* PREROUTING/INPUT/FORWARD: */
    return ipt_do_table(skb, hook, in, out,
                dev_net(in)->ipv4.iptable_mangle);
}

static struct nf_hook_ops *mangle_ops __read_mostly;

static int __net_init iptable_mangle_net_init(struct net *net)
{
    struct ipt_replace *repl;

    repl = ipt_alloc_initial_table(&packet_mangler);
    if (repl == NULL)
        return -ENOMEM;
    net->ipv4.iptable_mangle =
        ipt_register_table(net, &packet_mangler, repl);
    kfree(repl);
    return PTR_RET(net->ipv4.iptable_mangle);
}

static void __net_exit iptable_mangle_net_exit(struct net *net)
{
    ipt_unregister_table(net, net->ipv4.iptable_mangle);
}

static struct pernet_operations iptable_mangle_net_ops = {
    .init = iptable_mangle_net_init,
    .exit = iptable_mangle_net_exit,
};

static int __init iptable_mangle_init(void)
{
    int ret;

    ret = register_pernet_subsys(&iptable_mangle_net_ops);
    if (ret < 0)
        return ret;

    /* Register hooks */
    mangle_ops = xt_hook_link(&packet_mangler, iptable_mangle_hook);
    if (IS_ERR(mangle_ops)) {
        ret = PTR_ERR(mangle_ops);
        unregister_pernet_subsys(&iptable_mangle_net_ops);
    }

    return ret;
}

static void __exit iptable_mangle_fini(void)
{
    xt_hook_unlink(&packet_mangler, mangle_ops);
    unregister_pernet_subsys(&iptable_mangle_net_ops);
}

module_init(iptable_mangle_init);
module_exit(iptable_mangle_fini);