iptable_filter.c

Go to the documentation of this file.

/*
 * 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/moduleparam.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/slab.h>
#include <net/ip.h>

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

#define FILTER_VALID_HOOKS ((1 << NF_INET_LOCAL_IN) | \
                (1 << NF_INET_FORWARD) | \
                (1 << NF_INET_LOCAL_OUT))

static const struct xt_table packet_filter = {
    .name       = "filter",
    .valid_hooks    = FILTER_VALID_HOOKS,
    .me     = THIS_MODULE,
    .af     = NFPROTO_IPV4,
    .priority   = NF_IP_PRI_FILTER,
};

static unsigned int
iptable_filter_hook(unsigned int hook, struct sk_buff *skb,
            const struct net_device *in, const struct net_device *out,
            int (*okfn)(struct sk_buff *))
{
    const struct net *net;

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

    net = dev_net((in != NULL) ? in : out);
    return ipt_do_table(skb, hook, in, out, net->ipv4.iptable_filter);
}

static struct nf_hook_ops *filter_ops __read_mostly;

/* Default to forward because I got too much mail already. */
static bool forward = true;
module_param(forward, bool, 0000);

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

    repl = ipt_alloc_initial_table(&packet_filter);
    if (repl == NULL)
        return -ENOMEM;
    /* Entry 1 is the FORWARD hook */
    ((struct ipt_standard *)repl->entries)[1].target.verdict =
        forward ? -NF_ACCEPT - 1 : -NF_DROP - 1;

    net->ipv4.iptable_filter =
        ipt_register_table(net, &packet_filter, repl);
    kfree(repl);
    return PTR_RET(net->ipv4.iptable_filter);
}

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

static struct pernet_operations iptable_filter_net_ops = {
    .init = iptable_filter_net_init,
    .exit = iptable_filter_net_exit,
};

static int __init iptable_filter_init(void)
{
    int ret;

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

    /* Register hooks */
    filter_ops = xt_hook_link(&packet_filter, iptable_filter_hook);
    if (IS_ERR(filter_ops)) {
        ret = PTR_ERR(filter_ops);
        unregister_pernet_subsys(&iptable_filter_net_ops);
    }

    return ret;
}

static void __exit iptable_filter_fini(void)
{
    xt_hook_unlink(&packet_filter, filter_ops);
    unregister_pernet_subsys(&iptable_filter_net_ops);
}

module_init(iptable_filter_init);
module_exit(iptable_filter_fini);