net/ipv4/netfilter/iptable_mangle.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 #include <linux/module.h>
  12 #include <linux/netfilter_ipv4/ip_tables.h>
  13 #include <linux/netdevice.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/slab.h>
  16 #include <net/sock.h>
  17 #include <net/route.h>
  18 #include <linux/ip.h>
  19 #include <net/ip.h>
  20
  21 MODULE_LICENSE("GPL");
  22 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  23 MODULE_DESCRIPTION("iptables mangle table");
  24
  25 #define MANGLE_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
  26                             (1 << NF_INET_LOCAL_IN) | \
  27                             (1 << NF_INET_FORWARD) | \
  28                             (1 << NF_INET_LOCAL_OUT) | \
  29                             (1 << NF_INET_POST_ROUTING))
  30
  31 static int __net_init iptable_mangle_table_init(struct net *net);
  32
  33 static const struct xt_table packet_mangler = {
  34         .name           = "mangle",
  35         .valid_hooks    = MANGLE_VALID_HOOKS,
  36         .me             = THIS_MODULE,
  37         .af             = NFPROTO_IPV4,
  38         .priority       = NF_IP_PRI_MANGLE,
  39         .table_init     = iptable_mangle_table_init,
  40 };
  41
  42 static unsigned int
  43 ipt_mangle_out(struct sk_buff *skb, const struct nf_hook_state *state)
  44 {
  45         unsigned int ret;
  46         const struct iphdr *iph;
  47         u_int8_t tos;
  48         __be32 saddr, daddr;
  49         u_int32_t mark;
  50         int err;
  51
  52         /* root is playing with raw sockets. */
  53         if (skb->len < sizeof(struct iphdr) ||
  54             ip_hdrlen(skb) < sizeof(struct iphdr))
  55                 return NF_ACCEPT;
  56
  57         /* Save things which could affect route */
  58         mark = skb->mark;
  59         iph = ip_hdr(skb);
  60         saddr = iph->saddr;
  61         daddr = iph->daddr;
  62         tos = iph->tos;
  63
  64         ret = ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
  65         /* Reroute for ANY change. */
  66         if (ret != NF_DROP && ret != NF_STOLEN) {
  67                 iph = ip_hdr(skb);
  68
  69                 if (iph->saddr != saddr ||
  70                     iph->daddr != daddr ||
  71                     skb->mark != mark ||
  72                     iph->tos != tos) {
  73                         err = ip_route_me_harder(state->net, skb, RTN_UNSPEC);
  74                         if (err < 0)
  75                                 ret = NF_DROP_ERR(err);
  76                 }
  77         }
  78
  79         return ret;
  80 }
  81
  82 /* The work comes in here from netfilter.c. */
  83 static unsigned int
  84 iptable_mangle_hook(void *priv,
  85                      struct sk_buff *skb,
  86                      const struct nf_hook_state *state)
  87 {
  88         if (state->hook == NF_INET_LOCAL_OUT)
  89                 return ipt_mangle_out(skb, state);
  90         return ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
  91 }
  92
  93 static struct nf_hook_ops *mangle_ops __read_mostly;
  94 static int __net_init iptable_mangle_table_init(struct net *net)
  95 {
  96         struct ipt_replace *repl;
  97         int ret;
  98
  99         if (net->ipv4.iptable_mangle)
 100                 return 0;
 101
 102         repl = ipt_alloc_initial_table(&packet_mangler);
 103         if (repl == NULL)
 104                 return -ENOMEM;
 105         ret = ipt_register_table(net, &packet_mangler, repl, mangle_ops,
 106                                  &net->ipv4.iptable_mangle);
 107         kfree(repl);
 108         return ret;
 109 }
 110
 111 static void __net_exit iptable_mangle_net_exit(struct net *net)
 112 {
 113         if (!net->ipv4.iptable_mangle)
 114                 return;
 115         ipt_unregister_table(net, net->ipv4.iptable_mangle, mangle_ops);
 116         net->ipv4.iptable_mangle = NULL;
 117 }
 118
 119 static struct pernet_operations iptable_mangle_net_ops = {
 120         .exit = iptable_mangle_net_exit,
 121 };
 122
 123 static int __init iptable_mangle_init(void)
 124 {
 125         int ret;
 126
 127         mangle_ops = xt_hook_ops_alloc(&packet_mangler, iptable_mangle_hook);
 128         if (IS_ERR(mangle_ops)) {
 129                 ret = PTR_ERR(mangle_ops);
 130                 return ret;
 131         }
 132
 133         ret = register_pernet_subsys(&iptable_mangle_net_ops);
 134         if (ret < 0) {
 135                 kfree(mangle_ops);
 136                 return ret;
 137         }
 138
 139         ret = iptable_mangle_table_init(&init_net);
 140         if (ret) {
 141                 unregister_pernet_subsys(&iptable_mangle_net_ops);
 142                 kfree(mangle_ops);
 143         }
 144
 145         return ret;
 146 }
 147
 148 static void __exit iptable_mangle_fini(void)
 149 {
 150         unregister_pernet_subsys(&iptable_mangle_net_ops);
 151         kfree(mangle_ops);
 152 }
 153
 154 module_init(iptable_mangle_init);
 155 module_exit(iptable_mangle_fini);