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 net_device *in, const struct net_device *out,
  38                     int (*okfn)(struct sk_buff *))
  39 {
  40         const struct net *net;
  41
  42         if (ops->hooknum == NF_INET_LOCAL_OUT &&
  43             (skb->len < sizeof(struct iphdr) ||
  44              ip_hdrlen(skb) < sizeof(struct iphdr)))
  45                 /* root is playing with raw sockets. */
  46                 return NF_ACCEPT;
  47
  48         net = dev_net((in != NULL) ? in : out);
  49         return ipt_do_table(skb, ops->hooknum, in, out,
  50                             net->ipv4.iptable_filter);
  51 }
  52
  53 static struct nf_hook_ops *filter_ops __read_mostly;
  54
  55 /* Default to forward because I got too much mail already. */
  56 static bool forward = true;
  57 module_param(forward, bool, 0000);
  58
  59 static int __net_init iptable_filter_net_init(struct net *net)
  60 {
  61         struct ipt_replace *repl;
  62
  63         repl = ipt_alloc_initial_table(&packet_filter);
  64         if (repl == NULL)
  65                 return -ENOMEM;
  66         /* Entry 1 is the FORWARD hook */
  67         ((struct ipt_standard *)repl->entries)[1].target.verdict =
  68                 forward ? -NF_ACCEPT - 1 : -NF_DROP - 1;
  69
  70         net->ipv4.iptable_filter =
  71                 ipt_register_table(net, &packet_filter, repl);
  72         kfree(repl);
  73         return PTR_ERR_OR_ZERO(net->ipv4.iptable_filter);
  74 }
  75
  76 static void __net_exit iptable_filter_net_exit(struct net *net)
  77 {
  78         ipt_unregister_table(net, net->ipv4.iptable_filter);
  79 }
  80
  81 static struct pernet_operations iptable_filter_net_ops = {
  82         .init = iptable_filter_net_init,
  83         .exit = iptable_filter_net_exit,
  84 };
  85
  86 static int __init iptable_filter_init(void)
  87 {
  88         int ret;
  89
  90         ret = register_pernet_subsys(&iptable_filter_net_ops);
  91         if (ret < 0)
  92                 return ret;
  93
  94         /* Register hooks */
  95         filter_ops = xt_hook_link(&packet_filter, iptable_filter_hook);
  96         if (IS_ERR(filter_ops)) {
  97                 ret = PTR_ERR(filter_ops);
  98                 unregister_pernet_subsys(&iptable_filter_net_ops);
  99         }
 100
 101         return ret;
 102 }
 103
 104 static void __exit iptable_filter_fini(void)
 105 {
 106         xt_hook_unlink(&packet_filter, filter_ops);
 107         unregister_pernet_subsys(&iptable_filter_net_ops);
 108 }
 109
 110 module_init(iptable_filter_init);
 111 module_exit(iptable_filter_fini);