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  * Extended to all five netfilter hooks by Brad Chapman & Harald Welte
  12  */
  13 #include <linux/module.h>
  14 #include <linux/netfilter_ipv4/ip_tables.h>
  15 #include <linux/netdevice.h>
  16 #include <linux/skbuff.h>
  17 #include <net/sock.h>
  18 #include <net/route.h>
  19 #include <linux/ip.h>
  20
  21 MODULE_LICENSE("GPL");
  22 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  23 MODULE_DESCRIPTION("iptables mangle table");
  24
  25 #define MANGLE_VALID_HOOKS ((1 << NF_IP_PRE_ROUTING) | \
  26                             (1 << NF_IP_LOCAL_IN) | \
  27                             (1 << NF_IP_FORWARD) | \
  28                             (1 << NF_IP_LOCAL_OUT) | \
  29                             (1 << NF_IP_POST_ROUTING))
  30
  31 /* Ouch - five different hooks? Maybe this should be a config option..... -- BC */
  32 static struct
  33 {
  34         struct ipt_replace repl;
  35         struct ipt_standard entries[5];
  36         struct ipt_error term;
  37 } initial_table __initdata
  38 = { { "mangle", MANGLE_VALID_HOOKS, 6,
  39       sizeof(struct ipt_standard) * 5 + sizeof(struct ipt_error),
  40       { [NF_IP_PRE_ROUTING]     = 0,
  41         [NF_IP_LOCAL_IN]        = sizeof(struct ipt_standard),
  42         [NF_IP_FORWARD]         = sizeof(struct ipt_standard) * 2,
  43         [NF_IP_LOCAL_OUT]       = sizeof(struct ipt_standard) * 3,
  44         [NF_IP_POST_ROUTING]    = sizeof(struct ipt_standard) * 4 },
  45       { [NF_IP_PRE_ROUTING]     = 0,
  46         [NF_IP_LOCAL_IN]        = sizeof(struct ipt_standard),
  47         [NF_IP_FORWARD]         = sizeof(struct ipt_standard) * 2,
  48         [NF_IP_LOCAL_OUT]       = sizeof(struct ipt_standard) * 3,
  49         [NF_IP_POST_ROUTING]    = sizeof(struct ipt_standard) * 4 },
  50       0, NULL, { } },
  51     {
  52             /* PRE_ROUTING */
  53             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  54                 0,
  55                 sizeof(struct ipt_entry),
  56                 sizeof(struct ipt_standard),
  57                 0, { 0, 0 }, { } },
  58               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  59                 -NF_ACCEPT - 1 } },
  60             /* LOCAL_IN */
  61             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  62                 0,
  63                 sizeof(struct ipt_entry),
  64                 sizeof(struct ipt_standard),
  65                 0, { 0, 0 }, { } },
  66               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  67                 -NF_ACCEPT - 1 } },
  68             /* FORWARD */
  69             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  70                 0,
  71                 sizeof(struct ipt_entry),
  72                 sizeof(struct ipt_standard),
  73                 0, { 0, 0 }, { } },
  74               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  75                 -NF_ACCEPT - 1 } },
  76             /* LOCAL_OUT */
  77             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  78                 0,
  79                 sizeof(struct ipt_entry),
  80                 sizeof(struct ipt_standard),
  81                 0, { 0, 0 }, { } },
  82               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  83                 -NF_ACCEPT - 1 } },
  84             /* POST_ROUTING */
  85             { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  86                 0,
  87                 sizeof(struct ipt_entry),
  88                 sizeof(struct ipt_standard),
  89                 0, { 0, 0 }, { } },
  90               { { { { IPT_ALIGN(sizeof(struct ipt_standard_target)), "" } }, { } },
  91                 -NF_ACCEPT - 1 } },
  92     },
  93     /* ERROR */
  94     { { { { 0 }, { 0 }, { 0 }, { 0 }, "", "", { 0 }, { 0 }, 0, 0, 0 },
  95         0,
  96         sizeof(struct ipt_entry),
  97         sizeof(struct ipt_error),
  98         0, { 0, 0 }, { } },
  99       { { { { IPT_ALIGN(sizeof(struct ipt_error_target)), IPT_ERROR_TARGET } },
 100           { } },
 101         "ERROR"
 102       }
 103     }
 104 };
 105
 106 static struct xt_table packet_mangler = {
 107         .name           = "mangle",
 108         .valid_hooks    = MANGLE_VALID_HOOKS,
 109         .lock           = RW_LOCK_UNLOCKED,
 110         .me             = THIS_MODULE,
 111         .af             = AF_INET,
 112 };
 113
 114 /* The work comes in here from netfilter.c. */
 115 static unsigned int
 116 ipt_route_hook(unsigned int hook,
 117          struct sk_buff **pskb,
 118          const struct net_device *in,
 119          const struct net_device *out,
 120          int (*okfn)(struct sk_buff *))
 121 {
 122         return ipt_do_table(pskb, hook, in, out, &packet_mangler);
 123 }
 124
 125 static unsigned int
 126 ipt_local_hook(unsigned int hook,
 127                    struct sk_buff **pskb,
 128                    const struct net_device *in,
 129                    const struct net_device *out,
 130                    int (*okfn)(struct sk_buff *))
 131 {
 132         unsigned int ret;
 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             || (*pskb)->nh.iph->ihl * 4 < 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         saddr = (*pskb)->nh.iph->saddr;
 148         daddr = (*pskb)->nh.iph->daddr;
 149         tos = (*pskb)->nh.iph->tos;
 150
 151         ret = ipt_do_table(pskb, hook, in, out, &packet_mangler);
 152         /* Reroute for ANY change. */
 153         if (ret != NF_DROP && ret != NF_STOLEN && ret != NF_QUEUE
 154             && ((*pskb)->nh.iph->saddr != saddr
 155                 || (*pskb)->nh.iph->daddr != daddr
 156                 || (*pskb)->mark != mark
 157                 || (*pskb)->nh.iph->tos != tos))
 158                 if (ip_route_me_harder(pskb, RTN_UNSPEC))
 159                         ret = NF_DROP;
 160
 161         return ret;
 162 }
 163
 164 static struct nf_hook_ops ipt_ops[] = {
 165         {
 166                 .hook           = ipt_route_hook,
 167                 .owner          = THIS_MODULE,
 168                 .pf             = PF_INET,
 169                 .hooknum        = NF_IP_PRE_ROUTING,
 170                 .priority       = NF_IP_PRI_MANGLE,
 171         },
 172         {
 173                 .hook           = ipt_route_hook,
 174                 .owner          = THIS_MODULE,
 175                 .pf             = PF_INET,
 176                 .hooknum        = NF_IP_LOCAL_IN,
 177                 .priority       = NF_IP_PRI_MANGLE,
 178         },
 179         {
 180                 .hook           = ipt_route_hook,
 181                 .owner          = THIS_MODULE,
 182                 .pf             = PF_INET,
 183                 .hooknum        = NF_IP_FORWARD,
 184                 .priority       = NF_IP_PRI_MANGLE,
 185         },
 186         {
 187                 .hook           = ipt_local_hook,
 188                 .owner          = THIS_MODULE,
 189                 .pf             = PF_INET,
 190                 .hooknum        = NF_IP_LOCAL_OUT,
 191                 .priority       = NF_IP_PRI_MANGLE,
 192         },
 193         {
 194                 .hook           = ipt_route_hook,
 195                 .owner          = THIS_MODULE,
 196                 .pf             = PF_INET,
 197                 .hooknum        = NF_IP_POST_ROUTING,
 198                 .priority       = NF_IP_PRI_MANGLE,
 199         },
 200 };
 201
 202 static int __init iptable_mangle_init(void)
 203 {
 204         int ret;
 205
 206         /* Register table */
 207         ret = ipt_register_table(&packet_mangler, &initial_table.repl);
 208         if (ret < 0)
 209                 return ret;
 210
 211         /* Register hooks */
 212         ret = nf_register_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 213         if (ret < 0)
 214                 goto cleanup_table;
 215
 216         return ret;
 217
 218  cleanup_table:
 219         ipt_unregister_table(&packet_mangler);
 220         return ret;
 221 }
 222
 223 static void __exit iptable_mangle_fini(void)
 224 {
 225         nf_unregister_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 226         ipt_unregister_table(&packet_mangler);
 227 }
 228
 229 module_init(iptable_mangle_init);
 230 module_exit(iptable_mangle_fini);