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                 return NF_ACCEPT;
 137
 138         /* Save things which could affect route */
 139         mark = skb->mark;
 140         iph = ip_hdr(skb);
 141         saddr = iph->saddr;
 142         daddr = iph->daddr;
 143         tos = iph->tos;
 144
 145         ret = ipt_do_table(skb, hook, in, out,
 146                            dev_net(out)->ipv4.iptable_mangle);
 147         /* Reroute for ANY change. */
 148         if (ret != NF_DROP && ret != NF_STOLEN && ret != NF_QUEUE) {
 149                 iph = ip_hdr(skb);
 150
 151                 if (iph->saddr != saddr ||
 152                     iph->daddr != daddr ||
 153                     skb->mark != mark ||
 154                     iph->tos != tos)
 155                         if (ip_route_me_harder(skb, RTN_UNSPEC))
 156                                 ret = NF_DROP;
 157         }
 158
 159         return ret;
 160 }
 161
 162 static struct nf_hook_ops ipt_ops[] __read_mostly = {
 163         {
 164                 .hook           = ipt_pre_routing_hook,
 165                 .owner          = THIS_MODULE,
 166                 .pf             = PF_INET,
 167                 .hooknum        = NF_INET_PRE_ROUTING,
 168                 .priority       = NF_IP_PRI_MANGLE,
 169         },
 170         {
 171                 .hook           = ipt_local_in_hook,
 172                 .owner          = THIS_MODULE,
 173                 .pf             = PF_INET,
 174                 .hooknum        = NF_INET_LOCAL_IN,
 175                 .priority       = NF_IP_PRI_MANGLE,
 176         },
 177         {
 178                 .hook           = ipt_forward_hook,
 179                 .owner          = THIS_MODULE,
 180                 .pf             = PF_INET,
 181                 .hooknum        = NF_INET_FORWARD,
 182                 .priority       = NF_IP_PRI_MANGLE,
 183         },
 184         {
 185                 .hook           = ipt_local_hook,
 186                 .owner          = THIS_MODULE,
 187                 .pf             = PF_INET,
 188                 .hooknum        = NF_INET_LOCAL_OUT,
 189                 .priority       = NF_IP_PRI_MANGLE,
 190         },
 191         {
 192                 .hook           = ipt_post_routing_hook,
 193                 .owner          = THIS_MODULE,
 194                 .pf             = PF_INET,
 195                 .hooknum        = NF_INET_POST_ROUTING,
 196                 .priority       = NF_IP_PRI_MANGLE,
 197         },
 198 };
 199
 200 static int __net_init iptable_mangle_net_init(struct net *net)
 201 {
 202         /* Register table */
 203         net->ipv4.iptable_mangle =
 204                 ipt_register_table(net, &packet_mangler, &initial_table.repl);
 205         if (IS_ERR(net->ipv4.iptable_mangle))
 206                 return PTR_ERR(net->ipv4.iptable_mangle);
 207         return 0;
 208 }
 209
 210 static void __net_exit iptable_mangle_net_exit(struct net *net)
 211 {
 212         ipt_unregister_table(net->ipv4.iptable_mangle);
 213 }
 214
 215 static struct pernet_operations iptable_mangle_net_ops = {
 216         .init = iptable_mangle_net_init,
 217         .exit = iptable_mangle_net_exit,
 218 };
 219
 220 static int __init iptable_mangle_init(void)
 221 {
 222         int ret;
 223
 224         ret = register_pernet_subsys(&iptable_mangle_net_ops);
 225         if (ret < 0)
 226                 return ret;
 227
 228         /* Register hooks */
 229         ret = nf_register_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 230         if (ret < 0)
 231                 goto cleanup_table;
 232
 233         return ret;
 234
 235  cleanup_table:
 236         unregister_pernet_subsys(&iptable_mangle_net_ops);
 237         return ret;
 238 }
 239
 240 static void __exit iptable_mangle_fini(void)
 241 {
 242         nf_unregister_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 243         unregister_pernet_subsys(&iptable_mangle_net_ops);
 244 }
 245
 246 module_init(iptable_mangle_init);
 247 module_exit(iptable_mangle_fini);