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 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 struct xt_table packet_mangler = {
  68         .name           = "mangle",
  69         .valid_hooks    = MANGLE_VALID_HOOKS,
  70         .lock           = __RW_LOCK_UNLOCKED(packet_mangler.lock),
  71         .me             = THIS_MODULE,
  72         .af             = AF_INET,
  73 };
  74
  75 /* The work comes in here from netfilter.c. */
  76 static unsigned int
  77 ipt_pre_routing_hook(unsigned int hook,
  78                      struct sk_buff *skb,
  79                      const struct net_device *in,
  80                      const struct net_device *out,
  81                      int (*okfn)(struct sk_buff *))
  82 {
  83         return ipt_do_table(skb, hook, in, out,
  84                             dev_net(in)->ipv4.iptable_mangle);
  85 }
  86
  87 static unsigned int
  88 ipt_post_routing_hook(unsigned int hook,
  89                       struct sk_buff *skb,
  90                       const struct net_device *in,
  91                       const struct net_device *out,
  92                       int (*okfn)(struct sk_buff *))
  93 {
  94         return ipt_do_table(skb, hook, in, out,
  95                             dev_net(out)->ipv4.iptable_mangle);
  96 }
  97
  98 static unsigned int
  99 ipt_local_in_hook(unsigned int hook,
 100                   struct sk_buff *skb,
 101                   const struct net_device *in,
 102                   const struct net_device *out,
 103                   int (*okfn)(struct sk_buff *))
 104 {
 105         return ipt_do_table(skb, hook, in, out,
 106                             dev_net(in)->ipv4.iptable_mangle);
 107 }
 108
 109 static unsigned int
 110 ipt_forward_hook(unsigned int hook,
 111          struct sk_buff *skb,
 112          const struct net_device *in,
 113          const struct net_device *out,
 114          int (*okfn)(struct sk_buff *))
 115 {
 116         return ipt_do_table(skb, hook, in, out,
 117                             dev_net(in)->ipv4.iptable_mangle);
 118 }
 119
 120 static unsigned int
 121 ipt_local_hook(unsigned int hook,
 122                    struct sk_buff *skb,
 123                    const struct net_device *in,
 124                    const struct net_device *out,
 125                    int (*okfn)(struct sk_buff *))
 126 {
 127         unsigned int ret;
 128         const struct iphdr *iph;
 129         u_int8_t tos;
 130         __be32 saddr, daddr;
 131         u_int32_t mark;
 132
 133         /* root is playing with raw sockets. */
 134         if (skb->len < sizeof(struct iphdr)
 135             || ip_hdrlen(skb) < sizeof(struct iphdr)) {
 136                 if (net_ratelimit())
 137                         printk("iptable_mangle: ignoring short SOCK_RAW "
 138                                "packet.\n");
 139                 return NF_ACCEPT;
 140         }
 141
 142         /* Save things which could affect route */
 143         mark = skb->mark;
 144         iph = ip_hdr(skb);
 145         saddr = iph->saddr;
 146         daddr = iph->daddr;
 147         tos = iph->tos;
 148
 149         ret = ipt_do_table(skb, hook, in, out,
 150                            dev_net(out)->ipv4.iptable_mangle);
 151         /* Reroute for ANY change. */
 152         if (ret != NF_DROP && ret != NF_STOLEN && ret != NF_QUEUE) {
 153                 iph = ip_hdr(skb);
 154
 155                 if (iph->saddr != saddr ||
 156                     iph->daddr != daddr ||
 157                     skb->mark != mark ||
 158                     iph->tos != tos)
 159                         if (ip_route_me_harder(skb, RTN_UNSPEC))
 160                                 ret = NF_DROP;
 161         }
 162
 163         return ret;
 164 }
 165
 166 static struct nf_hook_ops ipt_ops[] __read_mostly = {
 167         {
 168                 .hook           = ipt_pre_routing_hook,
 169                 .owner          = THIS_MODULE,
 170                 .pf             = PF_INET,
 171                 .hooknum        = NF_INET_PRE_ROUTING,
 172                 .priority       = NF_IP_PRI_MANGLE,
 173         },
 174         {
 175                 .hook           = ipt_local_in_hook,
 176                 .owner          = THIS_MODULE,
 177                 .pf             = PF_INET,
 178                 .hooknum        = NF_INET_LOCAL_IN,
 179                 .priority       = NF_IP_PRI_MANGLE,
 180         },
 181         {
 182                 .hook           = ipt_forward_hook,
 183                 .owner          = THIS_MODULE,
 184                 .pf             = PF_INET,
 185                 .hooknum        = NF_INET_FORWARD,
 186                 .priority       = NF_IP_PRI_MANGLE,
 187         },
 188         {
 189                 .hook           = ipt_local_hook,
 190                 .owner          = THIS_MODULE,
 191                 .pf             = PF_INET,
 192                 .hooknum        = NF_INET_LOCAL_OUT,
 193                 .priority       = NF_IP_PRI_MANGLE,
 194         },
 195         {
 196                 .hook           = ipt_post_routing_hook,
 197                 .owner          = THIS_MODULE,
 198                 .pf             = PF_INET,
 199                 .hooknum        = NF_INET_POST_ROUTING,
 200                 .priority       = NF_IP_PRI_MANGLE,
 201         },
 202 };
 203
 204 static int __net_init iptable_mangle_net_init(struct net *net)
 205 {
 206         /* Register table */
 207         net->ipv4.iptable_mangle =
 208                 ipt_register_table(net, &packet_mangler, &initial_table.repl);
 209         if (IS_ERR(net->ipv4.iptable_mangle))
 210                 return PTR_ERR(net->ipv4.iptable_mangle);
 211         return 0;
 212 }
 213
 214 static void __net_exit iptable_mangle_net_exit(struct net *net)
 215 {
 216         ipt_unregister_table(net->ipv4.iptable_mangle);
 217 }
 218
 219 static struct pernet_operations iptable_mangle_net_ops = {
 220         .init = iptable_mangle_net_init,
 221         .exit = iptable_mangle_net_exit,
 222 };
 223
 224 static int __init iptable_mangle_init(void)
 225 {
 226         int ret;
 227
 228         ret = register_pernet_subsys(&iptable_mangle_net_ops);
 229         if (ret < 0)
 230                 return ret;
 231
 232         /* Register hooks */
 233         ret = nf_register_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 234         if (ret < 0)
 235                 goto cleanup_table;
 236
 237         return ret;
 238
 239  cleanup_table:
 240         unregister_pernet_subsys(&iptable_mangle_net_ops);
 241         return ret;
 242 }
 243
 244 static void __exit iptable_mangle_fini(void)
 245 {
 246         nf_unregister_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 247         unregister_pernet_subsys(&iptable_mangle_net_ops);
 248 }
 249
 250 module_init(iptable_mangle_init);
 251 module_exit(iptable_mangle_fini);