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 static int __net_init iptable_filter_table_init(struct net *net);
  27
  28 static const struct xt_table packet_filter = {
  29         .name           = "filter",
  30         .valid_hooks    = FILTER_VALID_HOOKS,
  31         .me             = THIS_MODULE,
  32         .af             = NFPROTO_IPV4,
  33         .priority       = NF_IP_PRI_FILTER,
  34         .table_init     = iptable_filter_table_init,
  35 };
  36
  37 static unsigned int
  38 iptable_filter_hook(void *priv, struct sk_buff *skb,
  39                     const struct nf_hook_state *state)
  40 {
  41         if (state->hook == NF_INET_LOCAL_OUT &&
  42             (skb->len < sizeof(struct iphdr) ||
  43              ip_hdrlen(skb) < sizeof(struct iphdr)))
  44                 /* root is playing with raw sockets. */
  45                 return NF_ACCEPT;
  46
  47         return ipt_do_table(skb, state, state->net->ipv4.iptable_filter);
  48 }
  49
  50 static struct nf_hook_ops *filter_ops __read_mostly;
  51
  52 /* Default to forward because I got too much mail already. */
  53 static bool forward __read_mostly = true;
  54 module_param(forward, bool, 0000);
  55
  56 static int __net_init iptable_filter_table_init(struct net *net)
  57 {
  58         struct ipt_replace *repl;
  59         int err;
  60
  61         if (net->ipv4.iptable_filter)
  62                 return 0;
  63
  64         repl = ipt_alloc_initial_table(&packet_filter);
  65         if (repl == NULL)
  66                 return -ENOMEM;
  67         /* Entry 1 is the FORWARD hook */
  68         ((struct ipt_standard *)repl->entries)[1].target.verdict =
  69                 forward ? -NF_ACCEPT - 1 : -NF_DROP - 1;
  70
  71         err = ipt_register_table(net, &packet_filter, repl, filter_ops,
  72                                  &net->ipv4.iptable_filter);
  73         kfree(repl);
  74         return err;
  75 }
  76
  77 static int __net_init iptable_filter_net_init(struct net *net)
  78 {
  79         if (net == &init_net || !forward)
  80                 return iptable_filter_table_init(net);
  81
  82         return 0;
  83 }
  84
  85 static void __net_exit iptable_filter_net_exit(struct net *net)
  86 {
  87         if (!net->ipv4.iptable_filter)
  88                 return;
  89         ipt_unregister_table(net, net->ipv4.iptable_filter, filter_ops);
  90         net->ipv4.iptable_filter = NULL;
  91 }
  92
  93 static struct pernet_operations iptable_filter_net_ops = {
  94         .init = iptable_filter_net_init,
  95         .exit = iptable_filter_net_exit,
  96 };
  97
  98 static int __init iptable_filter_init(void)
  99 {
 100         int ret;
 101
 102         filter_ops = xt_hook_ops_alloc(&packet_filter, iptable_filter_hook);
 103         if (IS_ERR(filter_ops))
 104                 return PTR_ERR(filter_ops);
 105
 106         ret = register_pernet_subsys(&iptable_filter_net_ops);
 107         if (ret < 0)
 108                 kfree(filter_ops);
 109
 110         return ret;
 111 }
 112
 113 static void __exit iptable_filter_fini(void)
 114 {
 115         unregister_pernet_subsys(&iptable_filter_net_ops);
 116         kfree(filter_ops);
 117 }
 118
 119 module_init(iptable_filter_init);
 120 module_exit(iptable_filter_fini);