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_IP_PRE_ROUTING) | \
  25                             (1 << NF_IP_LOCAL_IN) | \
  26                             (1 << NF_IP_FORWARD) | \
  27                             (1 << NF_IP_LOCAL_OUT) | \
  28                             (1 << NF_IP_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 __initdata
  37 = { { "mangle", MANGLE_VALID_HOOKS, 6,
  38       sizeof(struct ipt_standard) * 5 + sizeof(struct ipt_error),
  39       { [NF_IP_PRE_ROUTING]     = 0,
  40         [NF_IP_LOCAL_IN]        = sizeof(struct ipt_standard),
  41         [NF_IP_FORWARD]         = sizeof(struct ipt_standard) * 2,
  42         [NF_IP_LOCAL_OUT]       = sizeof(struct ipt_standard) * 3,
  43         [NF_IP_POST_ROUTING]    = sizeof(struct ipt_standard) * 4 },
  44       { [NF_IP_PRE_ROUTING]     = 0,
  45         [NF_IP_LOCAL_IN]        = sizeof(struct ipt_standard),
  46         [NF_IP_FORWARD]         = sizeof(struct ipt_standard) * 2,
  47         [NF_IP_LOCAL_OUT]       = sizeof(struct ipt_standard) * 3,
  48         [NF_IP_POST_ROUTING]    = sizeof(struct ipt_standard) * 4 },
  49       0, NULL, { } },
  50     {
  51             /* PRE_ROUTING */
  52             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  53                 0,
  54                 sizeof(struct ipt_entry),
  55                 sizeof(struct ipt_standard),
  56                 0, { 0, 0 }, { } },
  57               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  58                 -NF_ACCEPT - 1 } },
  59             /* LOCAL_IN */
  60             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  61                 0,
  62                 sizeof(struct ipt_entry),
  63                 sizeof(struct ipt_standard),
  64                 0, { 0, 0 }, { } },
  65               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  66                 -NF_ACCEPT - 1 } },
  67             /* FORWARD */
  68             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  69                 0,
  70                 sizeof(struct ipt_entry),
  71                 sizeof(struct ipt_standard),
  72                 0, { 0, 0 }, { } },
  73               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  74                 -NF_ACCEPT - 1 } },
  75             /* LOCAL_OUT */
  76             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  77                 0,
  78                 sizeof(struct ipt_entry),
  79                 sizeof(struct ipt_standard),
  80                 0, { 0, 0 }, { } },
  81               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  82                 -NF_ACCEPT - 1 } },
  83             /* POST_ROUTING */
  84             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  85                 0,
  86                 sizeof(struct ipt_entry),
  87                 sizeof(struct ipt_standard),
  88                 0, { 0, 0 }, { } },
  89               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  90                 -NF_ACCEPT - 1 } },
  91     },
  92     /* ERROR */
  93     { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  94         0,
  95         sizeof(struct ipt_entry),
  96         sizeof(struct ipt_error),
  97         0, { 0, 0 }, { } },
  98       { { { { IPT_ALIGN(sizeof(struct ipt_error_target)), IPT_ERROR_TARGET } },
  99           { } },
 100         "ERROR"
 101       }
 102     }
 103 };
 104
 105 static struct xt_table packet_mangler = {
 106         .name           = "mangle",
 107         .valid_hooks    = MANGLE_VALID_HOOKS,
 108         .lock           = RW_LOCK_UNLOCKED,
 109         .me             = THIS_MODULE,
 110         .af             = AF_INET,
 111 };
 112
 113 /* The work comes in here from netfilter.c. */
 114 static unsigned int
 115 ipt_route_hook(unsigned int hook,
 116          struct sk_buff **pskb,
 117          const struct net_device *in,
 118          const struct net_device *out,
 119          int (*okfn)(struct sk_buff *))
 120 {
 121         return ipt_do_table(pskb, hook, in, out, &packet_mangler);
 122 }
 123
 124 static unsigned int
 125 ipt_local_hook(unsigned int hook,
 126                    struct sk_buff **pskb,
 127                    const struct net_device *in,
 128                    const struct net_device *out,
 129                    int (*okfn)(struct sk_buff *))
 130 {
 131         unsigned int ret;
 132         const struct iphdr *iph;
 133         u_int8_t tos;
 134         __be32 saddr, daddr;
 135         u_int32_t mark;
 136
 137         /* root is playing with raw sockets. */
 138         if ((*pskb)->len < sizeof(struct iphdr)
 139             || ip_hdrlen(*pskb) < sizeof(struct iphdr)) {
 140                 if (net_ratelimit())
 141                         printk("ipt_hook: happy cracking.\n");
 142                 return NF_ACCEPT;
 143         }
 144
 145         /* Save things which could affect route */
 146         mark = (*pskb)->mark;
 147         iph = ip_hdr(*pskb);
 148         saddr = iph->saddr;
 149         daddr = iph->daddr;
 150         tos = iph->tos;
 151
 152         ret = ipt_do_table(pskb, hook, in, out, &packet_mangler);
 153         /* Reroute for ANY change. */
 154         if (ret != NF_DROP && ret != NF_STOLEN && ret != NF_QUEUE) {
 155                 iph = ip_hdr(*pskb);
 156
 157                 if (iph->saddr != saddr ||
 158                     iph->daddr != daddr ||
 159                     (*pskb)->mark != mark ||
 160                     iph->tos != tos)
 161                         if (ip_route_me_harder(pskb, RTN_UNSPEC))
 162                                 ret = NF_DROP;
 163         }
 164
 165         return ret;
 166 }
 167
 168 static struct nf_hook_ops ipt_ops[] = {
 169         {
 170                 .hook           = ipt_route_hook,
 171                 .owner          = THIS_MODULE,
 172                 .pf             = PF_INET,
 173                 .hooknum        = NF_IP_PRE_ROUTING,
 174                 .priority       = NF_IP_PRI_MANGLE,
 175         },
 176         {
 177                 .hook           = ipt_route_hook,
 178                 .owner          = THIS_MODULE,
 179                 .pf             = PF_INET,
 180                 .hooknum        = NF_IP_LOCAL_IN,
 181                 .priority       = NF_IP_PRI_MANGLE,
 182         },
 183         {
 184                 .hook           = ipt_route_hook,
 185                 .owner          = THIS_MODULE,
 186                 .pf             = PF_INET,
 187                 .hooknum        = NF_IP_FORWARD,
 188                 .priority       = NF_IP_PRI_MANGLE,
 189         },
 190         {
 191                 .hook           = ipt_local_hook,
 192                 .owner          = THIS_MODULE,
 193                 .pf             = PF_INET,
 194                 .hooknum        = NF_IP_LOCAL_OUT,
 195                 .priority       = NF_IP_PRI_MANGLE,
 196         },
 197         {
 198                 .hook           = ipt_route_hook,
 199                 .owner          = THIS_MODULE,
 200                 .pf             = PF_INET,
 201                 .hooknum        = NF_IP_POST_ROUTING,
 202                 .priority       = NF_IP_PRI_MANGLE,
 203         },
 204 };
 205
 206 static int __init iptable_mangle_init(void)
 207 {
 208         int ret;
 209
 210         /* Register table */
 211         ret = ipt_register_table(&packet_mangler, &initial_table.repl);
 212         if (ret < 0)
 213                 return ret;
 214
 215         /* Register hooks */
 216         ret = nf_register_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 217         if (ret < 0)
 218                 goto cleanup_table;
 219
 220         return ret;
 221
 222  cleanup_table:
 223         ipt_unregister_table(&packet_mangler);
 224         return ret;
 225 }
 226
 227 static void __exit iptable_mangle_fini(void)
 228 {
 229         nf_unregister_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 230         ipt_unregister_table(&packet_mangler);
 231 }
 232
 233 module_init(iptable_mangle_init);
 234 module_exit(iptable_mangle_fini);