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         .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_IP_PRE_ROUTING]     = 0,
  44                         [NF_IP_LOCAL_IN]        = sizeof(struct ipt_standard),
  45                         [NF_IP_FORWARD]         = sizeof(struct ipt_standard) * 2,
  46                         [NF_IP_LOCAL_OUT]       = sizeof(struct ipt_standard) * 3,
  47                         [NF_IP_POST_ROUTING]    = sizeof(struct ipt_standard) * 4,
  48                 },
  49                 .underflow = {
  50                         [NF_IP_PRE_ROUTING]     = 0,
  51                         [NF_IP_LOCAL_IN]        = sizeof(struct ipt_standard),
  52                         [NF_IP_FORWARD]         = sizeof(struct ipt_standard) * 2,
  53                         [NF_IP_LOCAL_OUT]       = sizeof(struct ipt_standard) * 3,
  54                         [NF_IP_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,
  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_route_hook(unsigned int hook,
  78          struct sk_buff **pskb,
  79          const struct net_device *in,
  80          const struct net_device *out,
  81          int (*okfn)(struct sk_buff *))
  82 {
  83         return ipt_do_table(pskb, hook, in, out, &packet_mangler);
  84 }
  85
  86 static unsigned int
  87 ipt_local_hook(unsigned int hook,
  88                    struct sk_buff **pskb,
  89                    const struct net_device *in,
  90                    const struct net_device *out,
  91                    int (*okfn)(struct sk_buff *))
  92 {
  93         unsigned int ret;
  94         const struct iphdr *iph;
  95         u_int8_t tos;
  96         __be32 saddr, daddr;
  97         u_int32_t mark;
  98
  99         /* root is playing with raw sockets. */
 100         if ((*pskb)->len < sizeof(struct iphdr)
 101             || ip_hdrlen(*pskb) < sizeof(struct iphdr)) {
 102                 if (net_ratelimit())
 103                         printk("iptable_mangle: ignoring short SOCK_RAW "
 104                                "packet.\n");
 105                 return NF_ACCEPT;
 106         }
 107
 108         /* Save things which could affect route */
 109         mark = (*pskb)->mark;
 110         iph = ip_hdr(*pskb);
 111         saddr = iph->saddr;
 112         daddr = iph->daddr;
 113         tos = iph->tos;
 114
 115         ret = ipt_do_table(pskb, hook, in, out, &packet_mangler);
 116         /* Reroute for ANY change. */
 117         if (ret != NF_DROP && ret != NF_STOLEN && ret != NF_QUEUE) {
 118                 iph = ip_hdr(*pskb);
 119
 120                 if (iph->saddr != saddr ||
 121                     iph->daddr != daddr ||
 122                     (*pskb)->mark != mark ||
 123                     iph->tos != tos)
 124                         if (ip_route_me_harder(pskb, RTN_UNSPEC))
 125                                 ret = NF_DROP;
 126         }
 127
 128         return ret;
 129 }
 130
 131 static struct nf_hook_ops ipt_ops[] = {
 132         {
 133                 .hook           = ipt_route_hook,
 134                 .owner          = THIS_MODULE,
 135                 .pf             = PF_INET,
 136                 .hooknum        = NF_IP_PRE_ROUTING,
 137                 .priority       = NF_IP_PRI_MANGLE,
 138         },
 139         {
 140                 .hook           = ipt_route_hook,
 141                 .owner          = THIS_MODULE,
 142                 .pf             = PF_INET,
 143                 .hooknum        = NF_IP_LOCAL_IN,
 144                 .priority       = NF_IP_PRI_MANGLE,
 145         },
 146         {
 147                 .hook           = ipt_route_hook,
 148                 .owner          = THIS_MODULE,
 149                 .pf             = PF_INET,
 150                 .hooknum        = NF_IP_FORWARD,
 151                 .priority       = NF_IP_PRI_MANGLE,
 152         },
 153         {
 154                 .hook           = ipt_local_hook,
 155                 .owner          = THIS_MODULE,
 156                 .pf             = PF_INET,
 157                 .hooknum        = NF_IP_LOCAL_OUT,
 158                 .priority       = NF_IP_PRI_MANGLE,
 159         },
 160         {
 161                 .hook           = ipt_route_hook,
 162                 .owner          = THIS_MODULE,
 163                 .pf             = PF_INET,
 164                 .hooknum        = NF_IP_POST_ROUTING,
 165                 .priority       = NF_IP_PRI_MANGLE,
 166         },
 167 };
 168
 169 static int __init iptable_mangle_init(void)
 170 {
 171         int ret;
 172
 173         /* Register table */
 174         ret = ipt_register_table(&packet_mangler, &initial_table.repl);
 175         if (ret < 0)
 176                 return ret;
 177
 178         /* Register hooks */
 179         ret = nf_register_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 180         if (ret < 0)
 181                 goto cleanup_table;
 182
 183         return ret;
 184
 185  cleanup_table:
 186         ipt_unregister_table(&packet_mangler);
 187         return ret;
 188 }
 189
 190 static void __exit iptable_mangle_fini(void)
 191 {
 192         nf_unregister_hooks(ipt_ops, ARRAY_SIZE(ipt_ops));
 193         ipt_unregister_table(&packet_mangler);
 194 }
 195
 196 module_init(iptable_mangle_init);
 197 module_exit(iptable_mangle_fini);