net/netfilter/nf_conntrack_proto_gre.c

   1 /*
   2  * ip_conntrack_proto_gre.c - Version 3.0
   3  *
   4  * Connection tracking protocol helper module for GRE.
   5  *
   6  * GRE is a generic encapsulation protocol, which is generally not very
   7  * suited for NAT, as it has no protocol-specific part as port numbers.
   8  *
   9  * It has an optional key field, which may help us distinguishing two
  10  * connections between the same two hosts.
  11  *
  12  * GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
  13  *
  14  * PPTP is built on top of a modified version of GRE, and has a mandatory
  15  * field called "CallID", which serves us for the same purpose as the key
  16  * field in plain GRE.
  17  *
  18  * Documentation about PPTP can be found in RFC 2637
  19  *
  20  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
  21  *
  22  * Development of this code funded by Astaro AG (http://www.astaro.com/)
  23  *
  24  */
  25
  26 #include <linux/module.h>
  27 #include <linux/types.h>
  28 #include <linux/timer.h>
  29 #include <linux/list.h>
  30 #include <linux/seq_file.h>
  31 #include <linux/in.h>
  32 #include <linux/netdevice.h>
  33 #include <linux/skbuff.h>
  34 #include <net/dst.h>
  35 #include <net/net_namespace.h>
  36 #include <net/netns/generic.h>
  37 #include <net/netfilter/nf_conntrack_l4proto.h>
  38 #include <net/netfilter/nf_conntrack_helper.h>
  39 #include <net/netfilter/nf_conntrack_core.h>
  40 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  41 #include <linux/netfilter/nf_conntrack_pptp.h>
  42
  43 #define GRE_TIMEOUT             (30 * HZ)
  44 #define GRE_STREAM_TIMEOUT      (180 * HZ)
  45
  46 static int proto_gre_net_id;
  47 struct netns_proto_gre {
  48         rwlock_t                keymap_lock;
  49         struct list_head        keymap_list;
  50 };
  51
  52 void nf_ct_gre_keymap_flush(struct net *net)
  53 {
  54         struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
  55         struct nf_ct_gre_keymap *km, *tmp;
  56
  57         write_lock_bh(&net_gre->keymap_lock);
  58         list_for_each_entry_safe(km, tmp, &net_gre->keymap_list, list) {
  59                 list_del(&km->list);
  60                 kfree(km);
  61         }
  62         write_unlock_bh(&net_gre->keymap_lock);
  63 }
  64 EXPORT_SYMBOL(nf_ct_gre_keymap_flush);
  65
  66 static inline int gre_key_cmpfn(const struct nf_ct_gre_keymap *km,
  67                                 const struct nf_conntrack_tuple *t)
  68 {
  69         return km->tuple.src.l3num == t->src.l3num &&
  70                !memcmp(&km->tuple.src.u3, &t->src.u3, sizeof(t->src.u3)) &&
  71                !memcmp(&km->tuple.dst.u3, &t->dst.u3, sizeof(t->dst.u3)) &&
  72                km->tuple.dst.protonum == t->dst.protonum &&
  73                km->tuple.dst.u.all == t->dst.u.all;
  74 }
  75
  76 /* look up the source key for a given tuple */
  77 static __be16 gre_keymap_lookup(struct net *net, struct nf_conntrack_tuple *t)
  78 {
  79         struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
  80         struct nf_ct_gre_keymap *km;
  81         __be16 key = 0;
  82
  83         read_lock_bh(&net_gre->keymap_lock);
  84         list_for_each_entry(km, &net_gre->keymap_list, list) {
  85                 if (gre_key_cmpfn(km, t)) {
  86                         key = km->tuple.src.u.gre.key;
  87                         break;
  88                 }
  89         }
  90         read_unlock_bh(&net_gre->keymap_lock);
  91
  92         pr_debug("lookup src key 0x%x for ", key);
  93         nf_ct_dump_tuple(t);
  94
  95         return key;
  96 }
  97
  98 /* add a single keymap entry, associate with specified master ct */
  99 int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
 100                          struct nf_conntrack_tuple *t)
 101 {
 102         struct net *net = nf_ct_net(ct);
 103         struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
 104         struct nf_conn_help *help = nfct_help(ct);
 105         struct nf_ct_gre_keymap **kmp, *km;
 106
 107         kmp = &help->help.ct_pptp_info.keymap[dir];
 108         if (*kmp) {
 109                 /* check whether it's a retransmission */
 110                 read_lock_bh(&net_gre->keymap_lock);
 111                 list_for_each_entry(km, &net_gre->keymap_list, list) {
 112                         if (gre_key_cmpfn(km, t) && km == *kmp) {
 113                                 read_unlock_bh(&net_gre->keymap_lock);
 114                                 return 0;
 115                         }
 116                 }
 117                 read_unlock_bh(&net_gre->keymap_lock);
 118                 pr_debug("trying to override keymap_%s for ct %p\n",
 119                          dir == IP_CT_DIR_REPLY ? "reply" : "orig", ct);
 120                 return -EEXIST;
 121         }
 122
 123         km = kmalloc(sizeof(*km), GFP_ATOMIC);
 124         if (!km)
 125                 return -ENOMEM;
 126         memcpy(&km->tuple, t, sizeof(*t));
 127         *kmp = km;
 128
 129         pr_debug("adding new entry %p: ", km);
 130         nf_ct_dump_tuple(&km->tuple);
 131
 132         write_lock_bh(&net_gre->keymap_lock);
 133         list_add_tail(&km->list, &net_gre->keymap_list);
 134         write_unlock_bh(&net_gre->keymap_lock);
 135
 136         return 0;
 137 }
 138 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_add);
 139
 140 /* destroy the keymap entries associated with specified master ct */
 141 void nf_ct_gre_keymap_destroy(struct nf_conn *ct)
 142 {
 143         struct net *net = nf_ct_net(ct);
 144         struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
 145         struct nf_conn_help *help = nfct_help(ct);
 146         enum ip_conntrack_dir dir;
 147
 148         pr_debug("entering for ct %p\n", ct);
 149
 150         write_lock_bh(&net_gre->keymap_lock);
 151         for (dir = IP_CT_DIR_ORIGINAL; dir < IP_CT_DIR_MAX; dir++) {
 152                 if (help->help.ct_pptp_info.keymap[dir]) {
 153                         pr_debug("removing %p from list\n",
 154                                  help->help.ct_pptp_info.keymap[dir]);
 155                         list_del(&help->help.ct_pptp_info.keymap[dir]->list);
 156                         kfree(help->help.ct_pptp_info.keymap[dir]);
 157                         help->help.ct_pptp_info.keymap[dir] = NULL;
 158                 }
 159         }
 160         write_unlock_bh(&net_gre->keymap_lock);
 161 }
 162 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);
 163
 164 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
 165
 166 /* invert gre part of tuple */
 167 static bool gre_invert_tuple(struct nf_conntrack_tuple *tuple,
 168                              const struct nf_conntrack_tuple *orig)
 169 {
 170         tuple->dst.u.gre.key = orig->src.u.gre.key;
 171         tuple->src.u.gre.key = orig->dst.u.gre.key;
 172         return true;
 173 }
 174
 175 /* gre hdr info to tuple */
 176 static bool gre_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
 177                              struct nf_conntrack_tuple *tuple)
 178 {
 179         struct net *net = dev_net(skb->dev ? skb->dev : skb->dst->dev);
 180         const struct gre_hdr_pptp *pgrehdr;
 181         struct gre_hdr_pptp _pgrehdr;
 182         __be16 srckey;
 183         const struct gre_hdr *grehdr;
 184         struct gre_hdr _grehdr;
 185
 186         /* first only delinearize old RFC1701 GRE header */
 187         grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
 188         if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
 189                 /* try to behave like "nf_conntrack_proto_generic" */
 190                 tuple->src.u.all = 0;
 191                 tuple->dst.u.all = 0;
 192                 return true;
 193         }
 194
 195         /* PPTP header is variable length, only need up to the call_id field */
 196         pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
 197         if (!pgrehdr)
 198                 return true;
 199
 200         if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
 201                 pr_debug("GRE_VERSION_PPTP but unknown proto\n");
 202                 return false;
 203         }
 204
 205         tuple->dst.u.gre.key = pgrehdr->call_id;
 206         srckey = gre_keymap_lookup(net, tuple);
 207         tuple->src.u.gre.key = srckey;
 208
 209         return true;
 210 }
 211
 212 /* print gre part of tuple */
 213 static int gre_print_tuple(struct seq_file *s,
 214                            const struct nf_conntrack_tuple *tuple)
 215 {
 216         return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
 217                           ntohs(tuple->src.u.gre.key),
 218                           ntohs(tuple->dst.u.gre.key));
 219 }
 220
 221 /* print private data for conntrack */
 222 static int gre_print_conntrack(struct seq_file *s,
 223                                const struct nf_conn *ct)
 224 {
 225         return seq_printf(s, "timeout=%u, stream_timeout=%u ",
 226                           (ct->proto.gre.timeout / HZ),
 227                           (ct->proto.gre.stream_timeout / HZ));
 228 }
 229
 230 /* Returns verdict for packet, and may modify conntrack */
 231 static int gre_packet(struct nf_conn *ct,
 232                       const struct sk_buff *skb,
 233                       unsigned int dataoff,
 234                       enum ip_conntrack_info ctinfo,
 235                       u_int8_t pf,
 236                       unsigned int hooknum)
 237 {
 238         /* If we've seen traffic both ways, this is a GRE connection.
 239          * Extend timeout. */
 240         if (ct->status & IPS_SEEN_REPLY) {
 241                 nf_ct_refresh_acct(ct, ctinfo, skb,
 242                                    ct->proto.gre.stream_timeout);
 243                 /* Also, more likely to be important, and not a probe. */
 244                 set_bit(IPS_ASSURED_BIT, &ct->status);
 245                 nf_conntrack_event_cache(IPCT_STATUS, ct);
 246         } else
 247                 nf_ct_refresh_acct(ct, ctinfo, skb,
 248                                    ct->proto.gre.timeout);
 249
 250         return NF_ACCEPT;
 251 }
 252
 253 /* Called when a new connection for this protocol found. */
 254 static bool gre_new(struct nf_conn *ct, const struct sk_buff *skb,
 255                     unsigned int dataoff)
 256 {
 257         pr_debug(": ");
 258         nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 259
 260         /* initialize to sane value.  Ideally a conntrack helper
 261          * (e.g. in case of pptp) is increasing them */
 262         ct->proto.gre.stream_timeout = GRE_STREAM_TIMEOUT;
 263         ct->proto.gre.timeout = GRE_TIMEOUT;
 264
 265         return true;
 266 }
 267
 268 /* Called when a conntrack entry has already been removed from the hashes
 269  * and is about to be deleted from memory */
 270 static void gre_destroy(struct nf_conn *ct)
 271 {
 272         struct nf_conn *master = ct->master;
 273         pr_debug(" entering\n");
 274
 275         if (!master)
 276                 pr_debug("no master !?!\n");
 277         else
 278                 nf_ct_gre_keymap_destroy(master);
 279 }
 280
 281 /* protocol helper struct */
 282 static struct nf_conntrack_l4proto nf_conntrack_l4proto_gre4 __read_mostly = {
 283         .l3proto         = AF_INET,
 284         .l4proto         = IPPROTO_GRE,
 285         .name            = "gre",
 286         .pkt_to_tuple    = gre_pkt_to_tuple,
 287         .invert_tuple    = gre_invert_tuple,
 288         .print_tuple     = gre_print_tuple,
 289         .print_conntrack = gre_print_conntrack,
 290         .packet          = gre_packet,
 291         .new             = gre_new,
 292         .destroy         = gre_destroy,
 293         .me              = THIS_MODULE,
 294 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 295         .tuple_to_nlattr = nf_ct_port_tuple_to_nlattr,
 296         .nlattr_to_tuple = nf_ct_port_nlattr_to_tuple,
 297         .nla_policy      = nf_ct_port_nla_policy,
 298 #endif
 299 };
 300
 301 static int proto_gre_net_init(struct net *net)
 302 {
 303         struct netns_proto_gre *net_gre;
 304         int rv;
 305
 306         net_gre = kmalloc(sizeof(struct netns_proto_gre), GFP_KERNEL);
 307         if (!net_gre)
 308                 return -ENOMEM;
 309         rwlock_init(&net_gre->keymap_lock);
 310         INIT_LIST_HEAD(&net_gre->keymap_list);
 311
 312         rv = net_assign_generic(net, proto_gre_net_id, net_gre);
 313         if (rv < 0)
 314                 kfree(net_gre);
 315         return rv;
 316 }
 317
 318 static void proto_gre_net_exit(struct net *net)
 319 {
 320         struct netns_proto_gre *net_gre = net_generic(net, proto_gre_net_id);
 321
 322         nf_ct_gre_keymap_flush(net);
 323         kfree(net_gre);
 324 }
 325
 326 static struct pernet_operations proto_gre_net_ops = {
 327         .init = proto_gre_net_init,
 328         .exit = proto_gre_net_exit,
 329 };
 330
 331 static int __init nf_ct_proto_gre_init(void)
 332 {
 333         int rv;
 334
 335         rv = nf_conntrack_l4proto_register(&nf_conntrack_l4proto_gre4);
 336         if (rv < 0)
 337                 return rv;
 338         rv = register_pernet_gen_subsys(&proto_gre_net_id, &proto_gre_net_ops);
 339         if (rv < 0)
 340                 nf_conntrack_l4proto_unregister(&nf_conntrack_l4proto_gre4);
 341         return rv;
 342 }
 343
 344 static void __exit nf_ct_proto_gre_fini(void)
 345 {
 346         nf_conntrack_l4proto_unregister(&nf_conntrack_l4proto_gre4);
 347         unregister_pernet_gen_subsys(proto_gre_net_id, &proto_gre_net_ops);
 348 }
 349
 350 module_init(nf_ct_proto_gre_init);
 351 module_exit(nf_ct_proto_gre_fini);
 352
 353 MODULE_LICENSE("GPL");