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 };
  73
  74 /* The work comes in here from netfilter.c. */
  75 static unsigned int
  76 ipt_pre_routing_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         return ipt_do_table(skb, hook, in, out,
  83                             dev_net(in)->ipv4.iptable_mangle);
  84 }
  85
  86 static unsigned int
  87 ipt_post_routing_hook(unsigned int hook,
  88                       struct sk_buff *skb,
  89                       const struct net_device *in,
  90                       const struct net_device *out,
  91                       int (*okfn)(struct sk_buff *))
  92 {
  93         return ipt_do_table(skb, hook, in, out,
  94                             dev_net(out)->ipv4.iptable_mangle);
  95 }
  96
  97 static unsigned int
  98 ipt_local_in_hook(unsigned int hook,
  99                   struct sk_buff *skb,
 100                   const struct net_device *in,
 101                   const struct net_device *out,
 102                   int (*okfn)(struct sk_buff *))
 103 {
 104         return ipt_do_table(skb, hook, in, out,
 105                             dev_net(in)->ipv4.iptable_mangle);
 106 }
 107
 108 static unsigned int
 109 ipt_forward_hook(unsigned int hook,
 110          struct sk_buff *skb,
 111          const struct net_device *in,
 112          const struct net_device *out,
 113          int (*okfn)(struct sk_buff *))
 114 {
 115         return ipt_do_table(skb, hook, in, out,
 116                             dev_net(in)->ipv4.iptable_mangle);
 117 }
 118
 119 static unsigned int
 120 ipt_local_hook(unsigned int hook,
 121                    struct sk_buff *skb,
 122                    const struct net_device *in,
 123                    const struct net_device *out,
 124                    int (*okfn)(struct sk_buff *))
 125 {
 126         unsigned int ret;
 127         const struct iphdr *iph;
 128         u_int8_t tos;
 129         __be32 saddr, daddr;
 130         u_int32_t mark;
 131
 132         /* root is playing with raw sockets. */
 133         if (skb->len < sizeof(struct iphdr) ||
 134             ip_hdrlen(skb) < sizeof(struct iphdr))
 135                 return NF_ACCEPT;
 136
 137         /* Save things which could affect route */
 138         mark = skb->mark;
 139         iph = ip_hdr(skb);
 140         saddr = iph->saddr;
 141         daddr = iph->daddr;
 142         tos = iph->tos;
 143
 144         ret = ipt_do_table(skb, hook, in, out,
 145                            dev_net(out)->ipv4.iptable_mangle);
 146         /* Reroute for ANY change. */
 147         if (ret != NF_DROP && ret != NF_STOLEN && ret != NF_QUEUE) {
 148                 iph = ip_hdr(skb);
 149
 150                 if (iph->saddr != saddr ||
 151                     iph->daddr != daddr ||
 152                     skb->mark != mark ||
 153                     iph->tos != tos)
 154                         if (ip_route_me_harder(skb, RTN_UNSPEC))
 155                                 ret = NF_DROP;
 156         }
 157
 158         return ret;
 159 }
 160
 161 static struct nf_hook_ops ipt_ops[] __read_mostly = {
 162         {
 163                 .hook           = ipt_pre_routing_hook,
 164                 .owner          = THIS_MODULE,
 165                 .pf             = NFPROTO_IPV4,
 166                 .hooknum        = NF_INET_PRE_ROUTING,
 167                 .priority       = NF_IP_PRI_MANGLE,
 168         },
 169         {
 170                 .hook           = ipt_local_in_hook,
 171                 .owner          = THIS_MODULE,
 172                 .pf             = NFPROTO_IPV4,
 173                 .hooknum        = NF_INET_LOCAL_IN,
 174                 .priority       = NF_IP_PRI_MANGLE,
 175         },
 176         {
 177                 .hook           = ipt_forward_hook,
 178                 .owner          = THIS_MODULE,
 179                 .pf             = NFPROTO_IPV4,
 180                 .hooknum        = NF_INET_FORWARD,
 181                 .priority       = NF_IP_PRI_MANGLE,
 182         },
 183         {
 184                 .hook           = ipt_local_hook,
 185                 .owner          = THIS_MODULE,
 186                 .pf             = NFPROTO_IPV4,
 187                 .hooknum        = NF_INET_LOCAL_OUT,
 188                 .priority       = NF_IP_PRI_MANGLE,
 189         },
 190         {
 191                 .hook           = ipt_post_routing_hook,
 192                 .owner          = THIS_MODULE,
 193                 .pf             = NFPROTO_IPV4,
 194                 .hooknum        = NF_INET_POST_ROUTING,
 195                 .priority       = NF_IP_PRI_MANGLE,
 196         },
 197 };
 198
 199 static int __net_init iptable_mangle_net_init(struct net *net)
 200 {
 201         /* Register table */
 202         net->ipv4.iptable_mangle =
 203                 ipt_register_table(net, &packet_mangler, &initial_table.repl);
 204         if (IS_ERR(net->ipv4.iptable_mangle))
 205                 return PTR_ERR(net->ipv4.iptable_mangle);
 206         return 0;
 207 }
 208
 209 static void __net_exit iptable_mangle_net_exit(struct net *net)
 210 {
 211         ipt_unregister_table(net, net->ipv4.iptable_mangle);
 212 }
 213
 214 static struct pernet_operations iptable_mangle_net_ops = {
 215         .init = iptable_mangle_net_init,
 216         .exit = iptable_mangle_net_exit,
 217 };
 218
 219 static int __init iptable_mangle_init(void)
 220 {
 221         int ret;
 222
 223         ret = register_pernet_subsys(&iptable_mangle_net_ops);
 224         if (ret < 0)
 225                 return ret;
 226
 227         /* Register hooks */
 228         ret = nf_register_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 229         if (ret < 0)
 230                 goto cleanup_table;
 231
 232         return ret;
 233
 234  cleanup_table:
 235         unregister_pernet_subsys(&iptable_mangle_net_ops);
 236         return ret;
 237 }
 238
 239 static void __exit iptable_mangle_fini(void)
 240 {
 241         nf_unregister_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 242         unregister_pernet_subsys(&iptable_mangle_net_ops);
 243 }
 244
 245 module_init(iptable_mangle_init);
 246 module_exit(iptable_mangle_fini);