net/ipv4/netfilter/iptable_filter.c

   1 /*
   2  * This is the 1999 rewrite of IP Firewalling, aiming for kernel 2.3.x.
   3  *
   4  * Copyright (C) 1999 Paul `Rusty' Russell & Michael J. Neuling
   5  * Copyright (C) 2000-2004 Netfilter Core Team <coreteam@netfilter.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/moduleparam.h>
  15 #include <linux/netfilter_ipv4/ip_tables.h>
  16 #include <linux/slab.h>
  17 #include <net/ip.h>
  18
  19 MODULE_LICENSE("GPL");
  20 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  21 MODULE_DESCRIPTION("iptables filter table");
  22
  23 #define FILTER_VALID_HOOKS ((1 << NF_INET_LOCAL_IN) | \
  24                             (1 << NF_INET_FORWARD) | \
  25                             (1 << NF_INET_LOCAL_OUT))
  26
  27 static const struct xt_table packet_filter = {
  28         .name           = "filter",
  29         .valid_hooks    = FILTER_VALID_HOOKS,
  30         .me             = THIS_MODULE,
  31         .af             = NFPROTO_IPV4,
  32         .priority       = NF_IP_PRI_FILTER,
  33 };
  34
  35 static unsigned int
  36 iptable_filter_hook(const struct nf_hook_ops *ops, struct sk_buff *skb,
  37                     const struct nf_hook_state *state)
  38 {
  39         if (ops->hooknum == NF_INET_LOCAL_OUT &&
  40             (skb->len < sizeof(struct iphdr) ||
  41              ip_hdrlen(skb) < sizeof(struct iphdr)))
  42                 /* root is playing with raw sockets. */
  43                 return NF_ACCEPT;
  44
  45         return ipt_do_table(skb, ops->hooknum, state,
  46                             state->net->ipv4.iptable_filter);
  47 }
  48
  49 static struct nf_hook_ops *filter_ops __read_mostly;
  50
  51 /* Default to forward because I got too much mail already. */
  52 static bool forward = true;
  53 module_param(forward, bool, 0000);
  54
  55 static int __net_init iptable_filter_net_init(struct net *net)
  56 {
  57         struct ipt_replace *repl;
  58
  59         repl = ipt_alloc_initial_table(&packet_filter);
  60         if (repl == NULL)
  61                 return -ENOMEM;
  62         /* Entry 1 is the FORWARD hook */
  63         ((struct ipt_standard *)repl->entries)[1].target.verdict =
  64                 forward ? -NF_ACCEPT - 1 : -NF_DROP - 1;
  65
  66         net->ipv4.iptable_filter =
  67                 ipt_register_table(net, &packet_filter, repl);
  68         kfree(repl);
  69         return PTR_ERR_OR_ZERO(net->ipv4.iptable_filter);
  70 }
  71
  72 static void __net_exit iptable_filter_net_exit(struct net *net)
  73 {
  74         ipt_unregister_table(net, net->ipv4.iptable_filter);
  75 }
  76
  77 static struct pernet_operations iptable_filter_net_ops = {
  78         .init = iptable_filter_net_init,
  79         .exit = iptable_filter_net_exit,
  80 };
  81
  82 static int __init iptable_filter_init(void)
  83 {
  84         int ret;
  85
  86         ret = register_pernet_subsys(&iptable_filter_net_ops);
  87         if (ret < 0)
  88                 return ret;
  89
  90         /* Register hooks */
  91         filter_ops = xt_hook_link(&packet_filter, iptable_filter_hook);
  92         if (IS_ERR(filter_ops)) {
  93                 ret = PTR_ERR(filter_ops);
  94                 unregister_pernet_subsys(&iptable_filter_net_ops);
  95         }
  96
  97         return ret;
  98 }
  99
 100 static void __exit iptable_filter_fini(void)
 101 {
 102         xt_hook_unlink(&packet_filter, filter_ops);
 103         unregister_pernet_subsys(&iptable_filter_net_ops);
 104 }
 105
 106 module_init(iptable_filter_init);
 107 module_exit(iptable_filter_fini);