net/ipv4/netfilter/iptable_nat.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   3  * (C) 2011 Patrick McHardy <kaber@trash.net>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License version 2 as
   7  * published by the Free Software Foundation.
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/netfilter.h>
  12 #include <linux/netfilter_ipv4.h>
  13 #include <linux/netfilter_ipv4/ip_tables.h>
  14 #include <linux/ip.h>
  15 #include <net/ip.h>
  16
  17 #include <net/netfilter/nf_nat.h>
  18 #include <net/netfilter/nf_nat_core.h>
  19 #include <net/netfilter/nf_nat_l3proto.h>
  20
  21 static const struct xt_table nf_nat_ipv4_table = {
  22         .name           = "nat",
  23         .valid_hooks    = (1 << NF_INET_PRE_ROUTING) |
  24                           (1 << NF_INET_POST_ROUTING) |
  25                           (1 << NF_INET_LOCAL_OUT) |
  26                           (1 << NF_INET_LOCAL_IN),
  27         .me             = THIS_MODULE,
  28         .af             = NFPROTO_IPV4,
  29 };
  30
  31 static unsigned int alloc_null_binding(struct nf_conn *ct, unsigned int hooknum)
  32 {
  33         /* Force range to this IP; let proto decide mapping for
  34          * per-proto parts (hence not IP_NAT_RANGE_PROTO_SPECIFIED).
  35          */
  36         struct nf_nat_range range;
  37
  38         range.flags = 0;
  39         pr_debug("Allocating NULL binding for %p (%pI4)\n", ct,
  40                  HOOK2MANIP(hooknum) == NF_NAT_MANIP_SRC ?
  41                  &ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip :
  42                  &ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip);
  43
  44         return nf_nat_setup_info(ct, &range, HOOK2MANIP(hooknum));
  45 }
  46
  47 static unsigned int nf_nat_rule_find(struct sk_buff *skb, unsigned int hooknum,
  48                                      const struct net_device *in,
  49                                      const struct net_device *out,
  50                                      struct nf_conn *ct)
  51 {
  52         struct net *net = nf_ct_net(ct);
  53         unsigned int ret;
  54
  55         ret = ipt_do_table(skb, hooknum, in, out, net->ipv4.nat_table);
  56         if (ret == NF_ACCEPT) {
  57                 if (!nf_nat_initialized(ct, HOOK2MANIP(hooknum)))
  58                         ret = alloc_null_binding(ct, hooknum);
  59         }
  60         return ret;
  61 }
  62
  63 static unsigned int
  64 nf_nat_ipv4_fn(unsigned int hooknum,
  65                struct sk_buff *skb,
  66                const struct net_device *in,
  67                const struct net_device *out,
  68                int (*okfn)(struct sk_buff *))
  69 {
  70         struct nf_conn *ct;
  71         enum ip_conntrack_info ctinfo;
  72         struct nf_conn_nat *nat;
  73         /* maniptype == SRC for postrouting. */
  74         enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);
  75
  76         /* We never see fragments: conntrack defrags on pre-routing
  77          * and local-out, and nf_nat_out protects post-routing.
  78          */
  79         NF_CT_ASSERT(!ip_is_fragment(ip_hdr(skb)));
  80
  81         ct = nf_ct_get(skb, &ctinfo);
  82         /* Can't track?  It's not due to stress, or conntrack would
  83          * have dropped it.  Hence it's the user's responsibilty to
  84          * packet filter it out, or implement conntrack/NAT for that
  85          * protocol. 8) --RR
  86          */
  87         if (!ct)
  88                 return NF_ACCEPT;
  89
  90         /* Don't try to NAT if this packet is not conntracked */
  91         if (nf_ct_is_untracked(ct))
  92                 return NF_ACCEPT;
  93
  94         nat = nfct_nat(ct);
  95         if (!nat) {
  96                 /* NAT module was loaded late. */
  97                 if (nf_ct_is_confirmed(ct))
  98                         return NF_ACCEPT;
  99                 nat = nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC);
 100                 if (nat == NULL) {
 101                         pr_debug("failed to add NAT extension\n");
 102                         return NF_ACCEPT;
 103                 }
 104         }
 105
 106         switch (ctinfo) {
 107         case IP_CT_RELATED:
 108         case IP_CT_RELATED_REPLY:
 109                 if (ip_hdr(skb)->protocol == IPPROTO_ICMP) {
 110                         if (!nf_nat_icmp_reply_translation(skb, ct, ctinfo,
 111                                                            hooknum))
 112                                 return NF_DROP;
 113                         else
 114                                 return NF_ACCEPT;
 115                 }
 116                 /* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
 117         case IP_CT_NEW:
 118                 /* Seen it before?  This can happen for loopback, retrans,
 119                  * or local packets.
 120                  */
 121                 if (!nf_nat_initialized(ct, maniptype)) {
 122                         unsigned int ret;
 123
 124                         ret = nf_nat_rule_find(skb, hooknum, in, out, ct);
 125                         if (ret != NF_ACCEPT)
 126                                 return ret;
 127                 } else
 128                         pr_debug("Already setup manip %s for ct %p\n",
 129                                  maniptype == NF_NAT_MANIP_SRC ? "SRC" : "DST",
 130                                  ct);
 131                 break;
 132
 133         default:
 134                 /* ESTABLISHED */
 135                 NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED ||
 136                              ctinfo == IP_CT_ESTABLISHED_REPLY);
 137         }
 138
 139         return nf_nat_packet(ct, ctinfo, hooknum, skb);
 140 }
 141
 142 static unsigned int
 143 nf_nat_ipv4_in(unsigned int hooknum,
 144                struct sk_buff *skb,
 145                const struct net_device *in,
 146                const struct net_device *out,
 147                int (*okfn)(struct sk_buff *))
 148 {
 149         unsigned int ret;
 150         __be32 daddr = ip_hdr(skb)->daddr;
 151
 152         ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
 153         if (ret != NF_DROP && ret != NF_STOLEN &&
 154             daddr != ip_hdr(skb)->daddr)
 155                 skb_dst_drop(skb);
 156
 157         return ret;
 158 }
 159
 160 static unsigned int
 161 nf_nat_ipv4_out(unsigned int hooknum,
 162                 struct sk_buff *skb,
 163                 const struct net_device *in,
 164                 const struct net_device *out,
 165                 int (*okfn)(struct sk_buff *))
 166 {
 167 #ifdef CONFIG_XFRM
 168         const struct nf_conn *ct;
 169         enum ip_conntrack_info ctinfo;
 170 #endif
 171         unsigned int ret;
 172
 173         /* root is playing with raw sockets. */
 174         if (skb->len < sizeof(struct iphdr) ||
 175             ip_hdrlen(skb) < sizeof(struct iphdr))
 176                 return NF_ACCEPT;
 177
 178         ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
 179 #ifdef CONFIG_XFRM
 180         if (ret != NF_DROP && ret != NF_STOLEN &&
 181             !(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
 182             (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
 183                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 184
 185                 if ((ct->tuplehash[dir].tuple.src.u3.ip !=
 186                      ct->tuplehash[!dir].tuple.dst.u3.ip) ||
 187                     (ct->tuplehash[dir].tuple.src.u.all !=
 188                      ct->tuplehash[!dir].tuple.dst.u.all))
 189                         if (nf_xfrm_me_harder(skb, AF_INET) < 0)
 190                                 ret = NF_DROP;
 191         }
 192 #endif
 193         return ret;
 194 }
 195
 196 static unsigned int
 197 nf_nat_ipv4_local_fn(unsigned int hooknum,
 198                      struct sk_buff *skb,
 199                      const struct net_device *in,
 200                      const struct net_device *out,
 201                      int (*okfn)(struct sk_buff *))
 202 {
 203         const struct nf_conn *ct;
 204         enum ip_conntrack_info ctinfo;
 205         unsigned int ret;
 206
 207         /* root is playing with raw sockets. */
 208         if (skb->len < sizeof(struct iphdr) ||
 209             ip_hdrlen(skb) < sizeof(struct iphdr))
 210                 return NF_ACCEPT;
 211
 212         ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
 213         if (ret != NF_DROP && ret != NF_STOLEN &&
 214             (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
 215                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 216
 217                 if (ct->tuplehash[dir].tuple.dst.u3.ip !=
 218                     ct->tuplehash[!dir].tuple.src.u3.ip) {
 219                         if (ip_route_me_harder(skb, RTN_UNSPEC))
 220                                 ret = NF_DROP;
 221                 }
 222 #ifdef CONFIG_XFRM
 223                 else if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
 224                          ct->tuplehash[dir].tuple.dst.u.all !=
 225                          ct->tuplehash[!dir].tuple.src.u.all)
 226                         if (nf_xfrm_me_harder(skb, AF_INET) < 0)
 227                                 ret = NF_DROP;
 228 #endif
 229         }
 230         return ret;
 231 }
 232
 233 static struct nf_hook_ops nf_nat_ipv4_ops[] __read_mostly = {
 234         /* Before packet filtering, change destination */
 235         {
 236                 .hook           = nf_nat_ipv4_in,
 237                 .owner          = THIS_MODULE,
 238                 .pf             = NFPROTO_IPV4,
 239                 .hooknum        = NF_INET_PRE_ROUTING,
 240                 .priority       = NF_IP_PRI_NAT_DST,
 241         },
 242         /* After packet filtering, change source */
 243         {
 244                 .hook           = nf_nat_ipv4_out,
 245                 .owner          = THIS_MODULE,
 246                 .pf             = NFPROTO_IPV4,
 247                 .hooknum        = NF_INET_POST_ROUTING,
 248                 .priority       = NF_IP_PRI_NAT_SRC,
 249         },
 250         /* Before packet filtering, change destination */
 251         {
 252                 .hook           = nf_nat_ipv4_local_fn,
 253                 .owner          = THIS_MODULE,
 254                 .pf             = NFPROTO_IPV4,
 255                 .hooknum        = NF_INET_LOCAL_OUT,
 256                 .priority       = NF_IP_PRI_NAT_DST,
 257         },
 258         /* After packet filtering, change source */
 259         {
 260                 .hook           = nf_nat_ipv4_fn,
 261                 .owner          = THIS_MODULE,
 262                 .pf             = NFPROTO_IPV4,
 263                 .hooknum        = NF_INET_LOCAL_IN,
 264                 .priority       = NF_IP_PRI_NAT_SRC,
 265         },
 266 };
 267
 268 static int __net_init iptable_nat_net_init(struct net *net)
 269 {
 270         struct ipt_replace *repl;
 271
 272         repl = ipt_alloc_initial_table(&nf_nat_ipv4_table);
 273         if (repl == NULL)
 274                 return -ENOMEM;
 275         net->ipv4.nat_table = ipt_register_table(net, &nf_nat_ipv4_table, repl);
 276         kfree(repl);
 277         if (IS_ERR(net->ipv4.nat_table))
 278                 return PTR_ERR(net->ipv4.nat_table);
 279         return 0;
 280 }
 281
 282 static void __net_exit iptable_nat_net_exit(struct net *net)
 283 {
 284         ipt_unregister_table(net, net->ipv4.nat_table);
 285 }
 286
 287 static struct pernet_operations iptable_nat_net_ops = {
 288         .init   = iptable_nat_net_init,
 289         .exit   = iptable_nat_net_exit,
 290 };
 291
 292 static int __init iptable_nat_init(void)
 293 {
 294         int err;
 295
 296         err = register_pernet_subsys(&iptable_nat_net_ops);
 297         if (err < 0)
 298                 goto err1;
 299
 300         err = nf_register_hooks(nf_nat_ipv4_ops, ARRAY_SIZE(nf_nat_ipv4_ops));
 301         if (err < 0)
 302                 goto err2;
 303         return 0;
 304
 305 err2:
 306         unregister_pernet_subsys(&iptable_nat_net_ops);
 307 err1:
 308         return err;
 309 }
 310
 311 static void __exit iptable_nat_exit(void)
 312 {
 313         nf_unregister_hooks(nf_nat_ipv4_ops, ARRAY_SIZE(nf_nat_ipv4_ops));
 314         unregister_pernet_subsys(&iptable_nat_net_ops);
 315 }
 316
 317 module_init(iptable_nat_init);
 318 module_exit(iptable_nat_exit);
 319
 320 MODULE_LICENSE("GPL");