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 <net/sock.h>
  16 #include <net/route.h>
  17 #include <linux/ip.h>
  18 #include <net/ip.h>
  19
  20 MODULE_LICENSE("GPL");
  21 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  22 MODULE_DESCRIPTION("iptables mangle table");
  23
  24 #define MANGLE_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
  25                             (1 << NF_INET_LOCAL_IN) | \
  26                             (1 << NF_INET_FORWARD) | \
  27                             (1 << NF_INET_LOCAL_OUT) | \
  28                             (1 << NF_INET_POST_ROUTING))
  29
  30 /* Ouch - five different hooks? Maybe this should be a config option..... -- BC */
  31 static const struct
  32 {
  33         struct ipt_replace repl;
  34         struct ipt_standard entries[5];
  35         struct ipt_error term;
  36 } initial_table __net_initdata = {
  37         .repl = {
  38                 .name = "mangle",
  39                 .valid_hooks = MANGLE_VALID_HOOKS,
  40                 .num_entries = 6,
  41                 .size = sizeof(struct ipt_standard) * 5 + sizeof(struct ipt_error),
  42                 .hook_entry = {
  43                         [NF_INET_PRE_ROUTING]   = 0,
  44                         [NF_INET_LOCAL_IN]      = sizeof(struct ipt_standard),
  45                         [NF_INET_FORWARD]       = sizeof(struct ipt_standard) * 2,
  46                         [NF_INET_LOCAL_OUT]     = sizeof(struct ipt_standard) * 3,
  47                         [NF_INET_POST_ROUTING]  = sizeof(struct ipt_standard) * 4,
  48                 },
  49                 .underflow = {
  50                         [NF_INET_PRE_ROUTING]   = 0,
  51                         [NF_INET_LOCAL_IN]      = sizeof(struct ipt_standard),
  52                         [NF_INET_FORWARD]       = sizeof(struct ipt_standard) * 2,
  53                         [NF_INET_LOCAL_OUT]     = sizeof(struct ipt_standard) * 3,
  54                         [NF_INET_POST_ROUTING]  = sizeof(struct ipt_standard) * 4,
  55                 },
  56         },
  57         .entries = {
  58                 IPT_STANDARD_INIT(NF_ACCEPT),   /* PRE_ROUTING */
  59                 IPT_STANDARD_INIT(NF_ACCEPT),   /* LOCAL_IN */
  60                 IPT_STANDARD_INIT(NF_ACCEPT),   /* FORWARD */
  61                 IPT_STANDARD_INIT(NF_ACCEPT),   /* LOCAL_OUT */
  62                 IPT_STANDARD_INIT(NF_ACCEPT),   /* POST_ROUTING */
  63         },
  64         .term = IPT_ERROR_INIT,                 /* ERROR */
  65 };
  66
  67 static const struct xt_table packet_mangler = {
  68         .name           = "mangle",
  69         .valid_hooks    = MANGLE_VALID_HOOKS,
  70         .me             = THIS_MODULE,
  71         .af             = NFPROTO_IPV4,
  72         .priority       = NF_IP_PRI_MANGLE,
  73 };
  74
  75 static unsigned int
  76 ipt_local_hook(unsigned int hook,
  77                    struct sk_buff *skb,
  78                    const struct net_device *in,
  79                    const struct net_device *out,
  80                    int (*okfn)(struct sk_buff *))
  81 {
  82         unsigned int ret;
  83         const struct iphdr *iph;
  84         u_int8_t tos;
  85         __be32 saddr, daddr;
  86         u_int32_t mark;
  87
  88         /* root is playing with raw sockets. */
  89         if (skb->len < sizeof(struct iphdr) ||
  90             ip_hdrlen(skb) < sizeof(struct iphdr))
  91                 return NF_ACCEPT;
  92
  93         /* Save things which could affect route */
  94         mark = skb->mark;
  95         iph = ip_hdr(skb);
  96         saddr = iph->saddr;
  97         daddr = iph->daddr;
  98         tos = iph->tos;
  99
 100         ret = ipt_do_table(skb, hook, in, out,
 101                            dev_net(out)->ipv4.iptable_mangle);
 102         /* Reroute for ANY change. */
 103         if (ret != NF_DROP && ret != NF_STOLEN && ret != NF_QUEUE) {
 104                 iph = ip_hdr(skb);
 105
 106                 if (iph->saddr != saddr ||
 107                     iph->daddr != daddr ||
 108                     skb->mark != mark ||
 109                     iph->tos != tos)
 110                         if (ip_route_me_harder(skb, RTN_UNSPEC))
 111                                 ret = NF_DROP;
 112         }
 113
 114         return ret;
 115 }
 116
 117 /* The work comes in here from netfilter.c. */
 118 static unsigned int
 119 iptable_mangle_hook(unsigned int hook,
 120                      struct sk_buff *skb,
 121                      const struct net_device *in,
 122                      const struct net_device *out,
 123                      int (*okfn)(struct sk_buff *))
 124 {
 125         if (hook == NF_INET_LOCAL_OUT)
 126                 return ipt_local_hook(hook, skb, in, out, okfn);
 127
 128         /* PREROUTING/INPUT/FORWARD: */
 129         return ipt_do_table(skb, hook, in, out,
 130                             dev_net(in)->ipv4.iptable_mangle);
 131 }
 132
 133 static struct nf_hook_ops *mangle_ops __read_mostly;
 134
 135 static int __net_init iptable_mangle_net_init(struct net *net)
 136 {
 137         /* Register table */
 138         net->ipv4.iptable_mangle =
 139                 ipt_register_table(net, &packet_mangler, &initial_table.repl);
 140         if (IS_ERR(net->ipv4.iptable_mangle))
 141                 return PTR_ERR(net->ipv4.iptable_mangle);
 142         return 0;
 143 }
 144
 145 static void __net_exit iptable_mangle_net_exit(struct net *net)
 146 {
 147         ipt_unregister_table(net, net->ipv4.iptable_mangle);
 148 }
 149
 150 static struct pernet_operations iptable_mangle_net_ops = {
 151         .init = iptable_mangle_net_init,
 152         .exit = iptable_mangle_net_exit,
 153 };
 154
 155 static int __init iptable_mangle_init(void)
 156 {
 157         int ret;
 158
 159         ret = register_pernet_subsys(&iptable_mangle_net_ops);
 160         if (ret < 0)
 161                 return ret;
 162
 163         /* Register hooks */
 164         mangle_ops = xt_hook_link(&packet_mangler, iptable_mangle_hook);
 165         if (IS_ERR(mangle_ops)) {
 166                 ret = PTR_ERR(mangle_ops);
 167                 goto cleanup_table;
 168         }
 169
 170         return ret;
 171
 172  cleanup_table:
 173         unregister_pernet_subsys(&iptable_mangle_net_ops);
 174         return ret;
 175 }
 176
 177 static void __exit iptable_mangle_fini(void)
 178 {
 179         xt_hook_unlink(&packet_mangler, mangle_ops);
 180         unregister_pernet_subsys(&iptable_mangle_net_ops);
 181 }
 182
 183 module_init(iptable_mangle_init);
 184 module_exit(iptable_mangle_fini);