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   1 /*
   2  * Stateless NAT actions
   3  *
   4  * Copyright (c) 2007 Herbert Xu <herbert@gondor.apana.org.au>
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License as published by the Free
   8  * Software Foundation; either version 2 of the License, or (at your option)
   9  * any later version.
  10  */
  11
  12 #include <linux/errno.h>
  13 #include <linux/init.h>
  14 #include <linux/kernel.h>
  15 #include <linux/module.h>
  16 #include <linux/netfilter.h>
  17 #include <linux/rtnetlink.h>
  18 #include <linux/skbuff.h>
  19 #include <linux/slab.h>
  20 #include <linux/spinlock.h>
  21 #include <linux/string.h>
  22 #include <linux/tc_act/tc_nat.h>
  23 #include <net/act_api.h>
  24 #include <net/icmp.h>
  25 #include <net/ip.h>
  26 #include <net/netlink.h>
  27 #include <net/tc_act/tc_nat.h>
  28 #include <net/tcp.h>
  29 #include <net/udp.h>
  30
  31
  32 #define NAT_TAB_MASK    15
  33 static struct tcf_common *tcf_nat_ht[NAT_TAB_MASK + 1];
  34 static u32 nat_idx_gen;
  35 static DEFINE_RWLOCK(nat_lock);
  36
  37 static struct tcf_hashinfo nat_hash_info = {
  38         .htab   =       tcf_nat_ht,
  39         .hmask  =       NAT_TAB_MASK,
  40         .lock   =       &nat_lock,
  41 };
  42
  43 static int tcf_nat_init(struct rtattr *rta, struct rtattr *est,
  44                         struct tc_action *a, int ovr, int bind)
  45 {
  46         struct rtattr *tb[TCA_NAT_MAX];
  47         struct tc_nat *parm;
  48         int ret = 0;
  49         struct tcf_nat *p;
  50         struct tcf_common *pc;
  51
  52         if (rta == NULL || rtattr_parse_nested(tb, TCA_NAT_MAX, rta) < 0)
  53                 return -EINVAL;
  54
  55         if (tb[TCA_NAT_PARMS - 1] == NULL ||
  56             RTA_PAYLOAD(tb[TCA_NAT_PARMS - 1]) < sizeof(*parm))
  57                 return -EINVAL;
  58         parm = RTA_DATA(tb[TCA_NAT_PARMS - 1]);
  59
  60         pc = tcf_hash_check(parm->index, a, bind, &nat_hash_info);
  61         if (!pc) {
  62                 pc = tcf_hash_create(parm->index, est, a, sizeof(*p), bind,
  63                                      &nat_idx_gen, &nat_hash_info);
  64                 if (unlikely(!pc))
  65                         return -ENOMEM;
  66                 p = to_tcf_nat(pc);
  67                 ret = ACT_P_CREATED;
  68         } else {
  69                 p = to_tcf_nat(pc);
  70                 if (!ovr) {
  71                         tcf_hash_release(pc, bind, &nat_hash_info);
  72                         return -EEXIST;
  73                 }
  74         }
  75
  76         spin_lock_bh(&p->tcf_lock);
  77         p->old_addr = parm->old_addr;
  78         p->new_addr = parm->new_addr;
  79         p->mask = parm->mask;
  80         p->flags = parm->flags;
  81
  82         p->tcf_action = parm->action;
  83         spin_unlock_bh(&p->tcf_lock);
  84
  85         if (ret == ACT_P_CREATED)
  86                 tcf_hash_insert(pc, &nat_hash_info);
  87
  88         return ret;
  89 }
  90
  91 static int tcf_nat_cleanup(struct tc_action *a, int bind)
  92 {
  93         struct tcf_nat *p = a->priv;
  94
  95         return tcf_hash_release(&p->common, bind, &nat_hash_info);
  96 }
  97
  98 static int tcf_nat(struct sk_buff *skb, struct tc_action *a,
  99                    struct tcf_result *res)
 100 {
 101         struct tcf_nat *p = a->priv;
 102         struct iphdr *iph;
 103         __be32 old_addr;
 104         __be32 new_addr;
 105         __be32 mask;
 106         __be32 addr;
 107         int egress;
 108         int action;
 109         int ihl;
 110
 111         spin_lock(&p->tcf_lock);
 112
 113         p->tcf_tm.lastuse = jiffies;
 114         old_addr = p->old_addr;
 115         new_addr = p->new_addr;
 116         mask = p->mask;
 117         egress = p->flags & TCA_NAT_FLAG_EGRESS;
 118         action = p->tcf_action;
 119
 120         p->tcf_bstats.bytes += skb->len;
 121         p->tcf_bstats.packets++;
 122
 123         spin_unlock(&p->tcf_lock);
 124
 125         if (unlikely(action == TC_ACT_SHOT))
 126                 goto drop;
 127
 128         if (!pskb_may_pull(skb, sizeof(*iph)))
 129                 goto drop;
 130
 131         iph = ip_hdr(skb);
 132
 133         if (egress)
 134                 addr = iph->saddr;
 135         else
 136                 addr = iph->daddr;
 137
 138         if (!((old_addr ^ addr) & mask)) {
 139                 if (skb_cloned(skb) &&
 140                     !skb_clone_writable(skb, sizeof(*iph)) &&
 141                     pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 142                         goto drop;
 143
 144                 new_addr &= mask;
 145                 new_addr |= addr & ~mask;
 146
 147                 /* Rewrite IP header */
 148                 iph = ip_hdr(skb);
 149                 if (egress)
 150                         iph->saddr = new_addr;
 151                 else
 152                         iph->daddr = new_addr;
 153
 154                 nf_csum_replace4(&iph->check, addr, new_addr);
 155         }
 156
 157         ihl = iph->ihl * 4;
 158
 159         /* It would be nice to share code with stateful NAT. */
 160         switch (iph->frag_off & htons(IP_OFFSET) ? 0 : iph->protocol) {
 161         case IPPROTO_TCP:
 162         {
 163                 struct tcphdr *tcph;
 164
 165                 if (!pskb_may_pull(skb, ihl + sizeof(*tcph)) ||
 166                     (skb_cloned(skb) &&
 167                      !skb_clone_writable(skb, ihl + sizeof(*tcph)) &&
 168                      pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
 169                         goto drop;
 170
 171                 tcph = (void *)(skb_network_header(skb) + ihl);
 172                 nf_proto_csum_replace4(&tcph->check, skb, addr, new_addr, 1);
 173                 break;
 174         }
 175         case IPPROTO_UDP:
 176         {
 177                 struct udphdr *udph;
 178
 179                 if (!pskb_may_pull(skb, ihl + sizeof(*udph)) ||
 180                     (skb_cloned(skb) &&
 181                      !skb_clone_writable(skb, ihl + sizeof(*udph)) &&
 182                      pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
 183                         goto drop;
 184
 185                 udph = (void *)(skb_network_header(skb) + ihl);
 186                 if (udph->check || skb->ip_summed == CHECKSUM_PARTIAL) {
 187                         nf_proto_csum_replace4(&udph->check, skb, addr,
 188                                                new_addr, 1);
 189                         if (!udph->check)
 190                                 udph->check = CSUM_MANGLED_0;
 191                 }
 192                 break;
 193         }
 194         case IPPROTO_ICMP:
 195         {
 196                 struct icmphdr *icmph;
 197
 198                 if (!pskb_may_pull(skb, ihl + sizeof(*icmph) + sizeof(*iph)))
 199                         goto drop;
 200
 201                 icmph = (void *)(skb_network_header(skb) + ihl);
 202
 203                 if ((icmph->type != ICMP_DEST_UNREACH) &&
 204                     (icmph->type != ICMP_TIME_EXCEEDED) &&
 205                     (icmph->type != ICMP_PARAMETERPROB))
 206                         break;
 207
 208                 iph = (void *)(icmph + 1);
 209                 if (egress)
 210                         addr = iph->daddr;
 211                 else
 212                         addr = iph->saddr;
 213
 214                 if ((old_addr ^ addr) & mask)
 215                         break;
 216
 217                 if (skb_cloned(skb) &&
 218                     !skb_clone_writable(skb,
 219                                         ihl + sizeof(*icmph) + sizeof(*iph)) &&
 220                     pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
 221                         goto drop;
 222
 223                 icmph = (void *)(skb_network_header(skb) + ihl);
 224                 iph = (void *)(icmph + 1);
 225
 226                 new_addr &= mask;
 227                 new_addr |= addr & ~mask;
 228
 229                 /* XXX Fix up the inner checksums. */
 230                 if (egress)
 231                         iph->daddr = new_addr;
 232                 else
 233                         iph->saddr = new_addr;
 234
 235                 nf_proto_csum_replace4(&icmph->checksum, skb, addr, new_addr,
 236                                        1);
 237                 break;
 238         }
 239         default:
 240                 break;
 241         }
 242
 243         return action;
 244
 245 drop:
 246         spin_lock(&p->tcf_lock);
 247         p->tcf_qstats.drops++;
 248         spin_unlock(&p->tcf_lock);
 249         return TC_ACT_SHOT;
 250 }
 251
 252 static int tcf_nat_dump(struct sk_buff *skb, struct tc_action *a,
 253                         int bind, int ref)
 254 {
 255         unsigned char *b = skb_tail_pointer(skb);
 256         struct tcf_nat *p = a->priv;
 257         struct tc_nat *opt;
 258         struct tcf_t t;
 259         int s;
 260
 261         s = sizeof(*opt);
 262
 263         /* netlink spinlocks held above us - must use ATOMIC */
 264         opt = kzalloc(s, GFP_ATOMIC);
 265         if (unlikely(!opt))
 266                 return -ENOBUFS;
 267
 268         opt->old_addr = p->old_addr;
 269         opt->new_addr = p->new_addr;
 270         opt->mask = p->mask;
 271         opt->flags = p->flags;
 272
 273         opt->index = p->tcf_index;
 274         opt->action = p->tcf_action;
 275         opt->refcnt = p->tcf_refcnt - ref;
 276         opt->bindcnt = p->tcf_bindcnt - bind;
 277
 278         RTA_PUT(skb, TCA_NAT_PARMS, s, opt);
 279         t.install = jiffies_to_clock_t(jiffies - p->tcf_tm.install);
 280         t.lastuse = jiffies_to_clock_t(jiffies - p->tcf_tm.lastuse);
 281         t.expires = jiffies_to_clock_t(p->tcf_tm.expires);
 282         RTA_PUT(skb, TCA_NAT_TM, sizeof(t), &t);
 283
 284         kfree(opt);
 285
 286         return skb->len;
 287
 288 rtattr_failure:
 289         nlmsg_trim(skb, b);
 290         kfree(opt);
 291         return -1;
 292 }
 293
 294 static struct tc_action_ops act_nat_ops = {
 295         .kind           =       "nat",
 296         .hinfo          =       &nat_hash_info,
 297         .type           =       TCA_ACT_NAT,
 298         .capab          =       TCA_CAP_NONE,
 299         .owner          =       THIS_MODULE,
 300         .act            =       tcf_nat,
 301         .dump           =       tcf_nat_dump,
 302         .cleanup        =       tcf_nat_cleanup,
 303         .lookup         =       tcf_hash_search,
 304         .init           =       tcf_nat_init,
 305         .walk           =       tcf_generic_walker
 306 };
 307
 308 MODULE_DESCRIPTION("Stateless NAT actions");
 309 MODULE_LICENSE("GPL");
 310
 311 static int __init nat_init_module(void)
 312 {
 313         return tcf_register_action(&act_nat_ops);
 314 }
 315
 316 static void __exit nat_cleanup_module(void)
 317 {
 318         tcf_unregister_action(&act_nat_ops);
 319 }
 320
 321 module_init(nat_init_module);
 322 module_exit(nat_cleanup_module);