net/ipv4/netfilter/nf_nat_standalone.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8 #include <linux/types.h>
   9 #include <linux/icmp.h>
  10 #include <linux/gfp.h>
  11 #include <linux/ip.h>
  12 #include <linux/netfilter.h>
  13 #include <linux/netfilter_ipv4.h>
  14 #include <linux/module.h>
  15 #include <linux/skbuff.h>
  16 #include <linux/proc_fs.h>
  17 #include <net/ip.h>
  18 #include <net/checksum.h>
  19 #include <linux/spinlock.h>
  20
  21 #include <net/netfilter/nf_conntrack.h>
  22 #include <net/netfilter/nf_conntrack_core.h>
  23 #include <net/netfilter/nf_conntrack_extend.h>
  24 #include <net/netfilter/nf_nat.h>
  25 #include <net/netfilter/nf_nat_rule.h>
  26 #include <net/netfilter/nf_nat_protocol.h>
  27 #include <net/netfilter/nf_nat_core.h>
  28 #include <net/netfilter/nf_nat_helper.h>
  29 #include <linux/netfilter_ipv4/ip_tables.h>
  30
  31 #ifdef CONFIG_XFRM
  32 static void nat_decode_session(struct sk_buff *skb, struct flowi *fl)
  33 {
  34         const struct nf_conn *ct;
  35         const struct nf_conntrack_tuple *t;
  36         enum ip_conntrack_info ctinfo;
  37         enum ip_conntrack_dir dir;
  38         unsigned long statusbit;
  39
  40         ct = nf_ct_get(skb, &ctinfo);
  41         if (ct == NULL)
  42                 return;
  43         dir = CTINFO2DIR(ctinfo);
  44         t = &ct->tuplehash[dir].tuple;
  45
  46         if (dir == IP_CT_DIR_ORIGINAL)
  47                 statusbit = IPS_DST_NAT;
  48         else
  49                 statusbit = IPS_SRC_NAT;
  50
  51         if (ct->status & statusbit) {
  52                 fl->fl4_dst = t->dst.u3.ip;
  53                 if (t->dst.protonum == IPPROTO_TCP ||
  54                     t->dst.protonum == IPPROTO_UDP ||
  55                     t->dst.protonum == IPPROTO_UDPLITE ||
  56                     t->dst.protonum == IPPROTO_DCCP ||
  57                     t->dst.protonum == IPPROTO_SCTP)
  58                         fl->fl_ip_dport = t->dst.u.tcp.port;
  59         }
  60
  61         statusbit ^= IPS_NAT_MASK;
  62
  63         if (ct->status & statusbit) {
  64                 fl->fl4_src = t->src.u3.ip;
  65                 if (t->dst.protonum == IPPROTO_TCP ||
  66                     t->dst.protonum == IPPROTO_UDP ||
  67                     t->dst.protonum == IPPROTO_UDPLITE ||
  68                     t->dst.protonum == IPPROTO_DCCP ||
  69                     t->dst.protonum == IPPROTO_SCTP)
  70                         fl->fl_ip_sport = t->src.u.tcp.port;
  71         }
  72 }
  73 #endif
  74
  75 static unsigned int
  76 nf_nat_fn(unsigned int hooknum,
  77           struct sk_buff *skb,
  78           const struct net_device *in,
  79           const struct net_device *out,
  80           int (*okfn)(struct sk_buff *))
  81 {
  82         struct nf_conn *ct;
  83         enum ip_conntrack_info ctinfo;
  84         struct nf_conn_nat *nat;
  85         /* maniptype == SRC for postrouting. */
  86         enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);
  87
  88         /* We never see fragments: conntrack defrags on pre-routing
  89            and local-out, and nf_nat_out protects post-routing. */
  90         NF_CT_ASSERT(!(ip_hdr(skb)->frag_off & htons(IP_MF | IP_OFFSET)));
  91
  92         ct = nf_ct_get(skb, &ctinfo);
  93         /* Can't track?  It's not due to stress, or conntrack would
  94            have dropped it.  Hence it's the user's responsibilty to
  95            packet filter it out, or implement conntrack/NAT for that
  96            protocol. 8) --RR */
  97         if (!ct)
  98                 return NF_ACCEPT;
  99
 100         /* Don't try to NAT if this packet is not conntracked */
 101         if (ct == &nf_conntrack_untracked)
 102                 return NF_ACCEPT;
 103
 104         nat = nfct_nat(ct);
 105         if (!nat) {
 106                 /* NAT module was loaded late. */
 107                 if (nf_ct_is_confirmed(ct))
 108                         return NF_ACCEPT;
 109                 nat = nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC);
 110                 if (nat == NULL) {
 111                         pr_debug("failed to add NAT extension\n");
 112                         return NF_ACCEPT;
 113                 }
 114         }
 115
 116         switch (ctinfo) {
 117         case IP_CT_RELATED:
 118         case IP_CT_RELATED+IP_CT_IS_REPLY:
 119                 if (ip_hdr(skb)->protocol == IPPROTO_ICMP) {
 120                         if (!nf_nat_icmp_reply_translation(ct, ctinfo,
 121                                                            hooknum, skb))
 122                                 return NF_DROP;
 123                         else
 124                                 return NF_ACCEPT;
 125                 }
 126                 /* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
 127         case IP_CT_NEW:
 128
 129                 /* Seen it before?  This can happen for loopback, retrans,
 130                    or local packets.. */
 131                 if (!nf_nat_initialized(ct, maniptype)) {
 132                         unsigned int ret;
 133
 134                         if (hooknum == NF_INET_LOCAL_IN)
 135                                 /* LOCAL_IN hook doesn't have a chain!  */
 136                                 ret = alloc_null_binding(ct, hooknum);
 137                         else
 138                                 ret = nf_nat_rule_find(skb, hooknum, in, out,
 139                                                        ct);
 140
 141                         if (ret != NF_ACCEPT) {
 142                                 return ret;
 143                         }
 144                 } else
 145                         pr_debug("Already setup manip %s for ct %p\n",
 146                                  maniptype == IP_NAT_MANIP_SRC ? "SRC" : "DST",
 147                                  ct);
 148                 break;
 149
 150         default:
 151                 /* ESTABLISHED */
 152                 NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED ||
 153                              ctinfo == (IP_CT_ESTABLISHED+IP_CT_IS_REPLY));
 154         }
 155
 156         return nf_nat_packet(ct, ctinfo, hooknum, skb);
 157 }
 158
 159 static unsigned int
 160 nf_nat_in(unsigned int hooknum,
 161           struct sk_buff *skb,
 162           const struct net_device *in,
 163           const struct net_device *out,
 164           int (*okfn)(struct sk_buff *))
 165 {
 166         unsigned int ret;
 167         __be32 daddr = ip_hdr(skb)->daddr;
 168
 169         ret = nf_nat_fn(hooknum, skb, in, out, okfn);
 170         if (ret != NF_DROP && ret != NF_STOLEN &&
 171             daddr != ip_hdr(skb)->daddr)
 172                 skb_dst_drop(skb);
 173
 174         return ret;
 175 }
 176
 177 static unsigned int
 178 nf_nat_out(unsigned int hooknum,
 179            struct sk_buff *skb,
 180            const struct net_device *in,
 181            const struct net_device *out,
 182            int (*okfn)(struct sk_buff *))
 183 {
 184 #ifdef CONFIG_XFRM
 185         const struct nf_conn *ct;
 186         enum ip_conntrack_info ctinfo;
 187 #endif
 188         unsigned int ret;
 189
 190         /* root is playing with raw sockets. */
 191         if (skb->len < sizeof(struct iphdr) ||
 192             ip_hdrlen(skb) < sizeof(struct iphdr))
 193                 return NF_ACCEPT;
 194
 195         ret = nf_nat_fn(hooknum, skb, in, out, okfn);
 196 #ifdef CONFIG_XFRM
 197         if (ret != NF_DROP && ret != NF_STOLEN &&
 198             (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
 199                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 200
 201                 if ((ct->tuplehash[dir].tuple.src.u3.ip !=
 202                      ct->tuplehash[!dir].tuple.dst.u3.ip) ||
 203                     (ct->tuplehash[dir].tuple.src.u.all !=
 204                      ct->tuplehash[!dir].tuple.dst.u.all)
 205                    )
 206                         return ip_xfrm_me_harder(skb) == 0 ? ret : NF_DROP;
 207         }
 208 #endif
 209         return ret;
 210 }
 211
 212 static unsigned int
 213 nf_nat_local_fn(unsigned int hooknum,
 214                 struct sk_buff *skb,
 215                 const struct net_device *in,
 216                 const struct net_device *out,
 217                 int (*okfn)(struct sk_buff *))
 218 {
 219         const struct nf_conn *ct;
 220         enum ip_conntrack_info ctinfo;
 221         unsigned int ret;
 222
 223         /* root is playing with raw sockets. */
 224         if (skb->len < sizeof(struct iphdr) ||
 225             ip_hdrlen(skb) < sizeof(struct iphdr))
 226                 return NF_ACCEPT;
 227
 228         ret = nf_nat_fn(hooknum, skb, in, out, okfn);
 229         if (ret != NF_DROP && ret != NF_STOLEN &&
 230             (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
 231                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 232
 233                 if (ct->tuplehash[dir].tuple.dst.u3.ip !=
 234                     ct->tuplehash[!dir].tuple.src.u3.ip) {
 235                         if (ip_route_me_harder(skb, RTN_UNSPEC))
 236                                 ret = NF_DROP;
 237                 }
 238 #ifdef CONFIG_XFRM
 239                 else if (ct->tuplehash[dir].tuple.dst.u.all !=
 240                          ct->tuplehash[!dir].tuple.src.u.all)
 241                         if (ip_xfrm_me_harder(skb))
 242                                 ret = NF_DROP;
 243 #endif
 244         }
 245         return ret;
 246 }
 247
 248 /* We must be after connection tracking and before packet filtering. */
 249
 250 static struct nf_hook_ops nf_nat_ops[] __read_mostly = {
 251         /* Before packet filtering, change destination */
 252         {
 253                 .hook           = nf_nat_in,
 254                 .owner          = THIS_MODULE,
 255                 .pf             = NFPROTO_IPV4,
 256                 .hooknum        = NF_INET_PRE_ROUTING,
 257                 .priority       = NF_IP_PRI_NAT_DST,
 258         },
 259         /* After packet filtering, change source */
 260         {
 261                 .hook           = nf_nat_out,
 262                 .owner          = THIS_MODULE,
 263                 .pf             = NFPROTO_IPV4,
 264                 .hooknum        = NF_INET_POST_ROUTING,
 265                 .priority       = NF_IP_PRI_NAT_SRC,
 266         },
 267         /* Before packet filtering, change destination */
 268         {
 269                 .hook           = nf_nat_local_fn,
 270                 .owner          = THIS_MODULE,
 271                 .pf             = NFPROTO_IPV4,
 272                 .hooknum        = NF_INET_LOCAL_OUT,
 273                 .priority       = NF_IP_PRI_NAT_DST,
 274         },
 275         /* After packet filtering, change source */
 276         {
 277                 .hook           = nf_nat_fn,
 278                 .owner          = THIS_MODULE,
 279                 .pf             = NFPROTO_IPV4,
 280                 .hooknum        = NF_INET_LOCAL_IN,
 281                 .priority       = NF_IP_PRI_NAT_SRC,
 282         },
 283 };
 284
 285 static int __init nf_nat_standalone_init(void)
 286 {
 287         int ret = 0;
 288
 289         need_ipv4_conntrack();
 290
 291 #ifdef CONFIG_XFRM
 292         BUG_ON(ip_nat_decode_session != NULL);
 293         rcu_assign_pointer(ip_nat_decode_session, nat_decode_session);
 294 #endif
 295         ret = nf_nat_rule_init();
 296         if (ret < 0) {
 297                 printk("nf_nat_init: can't setup rules.\n");
 298                 goto cleanup_decode_session;
 299         }
 300         ret = nf_register_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 301         if (ret < 0) {
 302                 printk("nf_nat_init: can't register hooks.\n");
 303                 goto cleanup_rule_init;
 304         }
 305         return ret;
 306
 307  cleanup_rule_init:
 308         nf_nat_rule_cleanup();
 309  cleanup_decode_session:
 310 #ifdef CONFIG_XFRM
 311         rcu_assign_pointer(ip_nat_decode_session, NULL);
 312         synchronize_net();
 313 #endif
 314         return ret;
 315 }
 316
 317 static void __exit nf_nat_standalone_fini(void)
 318 {
 319         nf_unregister_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 320         nf_nat_rule_cleanup();
 321 #ifdef CONFIG_XFRM
 322         rcu_assign_pointer(ip_nat_decode_session, NULL);
 323         synchronize_net();
 324 #endif
 325         /* Conntrack caches are unregistered in nf_conntrack_cleanup */
 326 }
 327
 328 module_init(nf_nat_standalone_init);
 329 module_exit(nf_nat_standalone_fini);
 330
 331 MODULE_LICENSE("GPL");
 332 MODULE_ALIAS("ip_nat");