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   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/skbuff.h>
  33
  34 #include <net/netfilter/nf_conntrack_l4proto.h>
  35 #include <net/netfilter/nf_conntrack_helper.h>
  36 #include <net/netfilter/nf_conntrack_core.h>
  37 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  38 #include <linux/netfilter/nf_conntrack_pptp.h>
  39
  40 #define GRE_TIMEOUT             (30 * HZ)
  41 #define GRE_STREAM_TIMEOUT      (180 * HZ)
  42
  43 static DEFINE_RWLOCK(nf_ct_gre_lock);
  44 static LIST_HEAD(gre_keymap_list);
  45
  46 void nf_ct_gre_keymap_flush(void)
  47 {
  48         struct nf_ct_gre_keymap *km, *tmp;
  49
  50         write_lock_bh(&nf_ct_gre_lock);
  51         list_for_each_entry_safe(km, tmp, &gre_keymap_list, list) {
  52                 list_del(&km->list);
  53                 kfree(km);
  54         }
  55         write_unlock_bh(&nf_ct_gre_lock);
  56 }
  57 EXPORT_SYMBOL(nf_ct_gre_keymap_flush);
  58
  59 static inline int gre_key_cmpfn(const struct nf_ct_gre_keymap *km,
  60                                 const struct nf_conntrack_tuple *t)
  61 {
  62         return km->tuple.src.l3num == t->src.l3num &&
  63                !memcmp(&km->tuple.src.u3, &t->src.u3, sizeof(t->src.u3)) &&
  64                !memcmp(&km->tuple.dst.u3, &t->dst.u3, sizeof(t->dst.u3)) &&
  65                km->tuple.dst.protonum == t->dst.protonum &&
  66                km->tuple.dst.u.all == t->dst.u.all;
  67 }
  68
  69 /* look up the source key for a given tuple */
  70 static __be16 gre_keymap_lookup(struct nf_conntrack_tuple *t)
  71 {
  72         struct nf_ct_gre_keymap *km;
  73         __be16 key = 0;
  74
  75         read_lock_bh(&nf_ct_gre_lock);
  76         list_for_each_entry(km, &gre_keymap_list, list) {
  77                 if (gre_key_cmpfn(km, t)) {
  78                         key = km->tuple.src.u.gre.key;
  79                         break;
  80                 }
  81         }
  82         read_unlock_bh(&nf_ct_gre_lock);
  83
  84         pr_debug("lookup src key 0x%x for ", key);
  85         nf_ct_dump_tuple(t);
  86
  87         return key;
  88 }
  89
  90 /* add a single keymap entry, associate with specified master ct */
  91 int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
  92                          struct nf_conntrack_tuple *t)
  93 {
  94         struct nf_conn_help *help = nfct_help(ct);
  95         struct nf_ct_gre_keymap **kmp, *km;
  96
  97         kmp = &help->help.ct_pptp_info.keymap[dir];
  98         if (*kmp) {
  99                 /* check whether it's a retransmission */
 100                 read_lock_bh(&nf_ct_gre_lock);
 101                 list_for_each_entry(km, &gre_keymap_list, list) {
 102                         if (gre_key_cmpfn(km, t) && km == *kmp) {
 103                                 read_unlock_bh(&nf_ct_gre_lock);
 104                                 return 0;
 105                         }
 106                 }
 107                 read_unlock_bh(&nf_ct_gre_lock);
 108                 pr_debug("trying to override keymap_%s for ct %p\n",
 109                          dir == IP_CT_DIR_REPLY ? "reply" : "orig", ct);
 110                 return -EEXIST;
 111         }
 112
 113         km = kmalloc(sizeof(*km), GFP_ATOMIC);
 114         if (!km)
 115                 return -ENOMEM;
 116         memcpy(&km->tuple, t, sizeof(*t));
 117         *kmp = km;
 118
 119         pr_debug("adding new entry %p: ", km);
 120         nf_ct_dump_tuple(&km->tuple);
 121
 122         write_lock_bh(&nf_ct_gre_lock);
 123         list_add_tail(&km->list, &gre_keymap_list);
 124         write_unlock_bh(&nf_ct_gre_lock);
 125
 126         return 0;
 127 }
 128 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_add);
 129
 130 /* destroy the keymap entries associated with specified master ct */
 131 void nf_ct_gre_keymap_destroy(struct nf_conn *ct)
 132 {
 133         struct nf_conn_help *help = nfct_help(ct);
 134         enum ip_conntrack_dir dir;
 135
 136         pr_debug("entering for ct %p\n", ct);
 137
 138         write_lock_bh(&nf_ct_gre_lock);
 139         for (dir = IP_CT_DIR_ORIGINAL; dir < IP_CT_DIR_MAX; dir++) {
 140                 if (help->help.ct_pptp_info.keymap[dir]) {
 141                         pr_debug("removing %p from list\n",
 142                                  help->help.ct_pptp_info.keymap[dir]);
 143                         list_del(&help->help.ct_pptp_info.keymap[dir]->list);
 144                         kfree(help->help.ct_pptp_info.keymap[dir]);
 145                         help->help.ct_pptp_info.keymap[dir] = NULL;
 146                 }
 147         }
 148         write_unlock_bh(&nf_ct_gre_lock);
 149 }
 150 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);
 151
 152 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
 153
 154 /* invert gre part of tuple */
 155 static bool gre_invert_tuple(struct nf_conntrack_tuple *tuple,
 156                              const struct nf_conntrack_tuple *orig)
 157 {
 158         tuple->dst.u.gre.key = orig->src.u.gre.key;
 159         tuple->src.u.gre.key = orig->dst.u.gre.key;
 160         return true;
 161 }
 162
 163 /* gre hdr info to tuple */
 164 static bool gre_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
 165                              struct nf_conntrack_tuple *tuple)
 166 {
 167         const struct gre_hdr_pptp *pgrehdr;
 168         struct gre_hdr_pptp _pgrehdr;
 169         __be16 srckey;
 170         const struct gre_hdr *grehdr;
 171         struct gre_hdr _grehdr;
 172
 173         /* first only delinearize old RFC1701 GRE header */
 174         grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
 175         if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
 176                 /* try to behave like "nf_conntrack_proto_generic" */
 177                 tuple->src.u.all = 0;
 178                 tuple->dst.u.all = 0;
 179                 return true;
 180         }
 181
 182         /* PPTP header is variable length, only need up to the call_id field */
 183         pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
 184         if (!pgrehdr)
 185                 return true;
 186
 187         if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
 188                 pr_debug("GRE_VERSION_PPTP but unknown proto\n");
 189                 return false;
 190         }
 191
 192         tuple->dst.u.gre.key = pgrehdr->call_id;
 193         srckey = gre_keymap_lookup(tuple);
 194         tuple->src.u.gre.key = srckey;
 195
 196         return true;
 197 }
 198
 199 /* print gre part of tuple */
 200 static int gre_print_tuple(struct seq_file *s,
 201                            const struct nf_conntrack_tuple *tuple)
 202 {
 203         return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
 204                           ntohs(tuple->src.u.gre.key),
 205                           ntohs(tuple->dst.u.gre.key));
 206 }
 207
 208 /* print private data for conntrack */
 209 static int gre_print_conntrack(struct seq_file *s,
 210                                const struct nf_conn *ct)
 211 {
 212         return seq_printf(s, "timeout=%u, stream_timeout=%u ",
 213                           (ct->proto.gre.timeout / HZ),
 214                           (ct->proto.gre.stream_timeout / HZ));
 215 }
 216
 217 /* Returns verdict for packet, and may modify conntrack */
 218 static int gre_packet(struct nf_conn *ct,
 219                       const struct sk_buff *skb,
 220                       unsigned int dataoff,
 221                       enum ip_conntrack_info ctinfo,
 222                       u_int8_t pf,
 223                       unsigned int hooknum)
 224 {
 225         /* If we've seen traffic both ways, this is a GRE connection.
 226          * Extend timeout. */
 227         if (ct->status & IPS_SEEN_REPLY) {
 228                 nf_ct_refresh_acct(ct, ctinfo, skb,
 229                                    ct->proto.gre.stream_timeout);
 230                 /* Also, more likely to be important, and not a probe. */
 231                 set_bit(IPS_ASSURED_BIT, &ct->status);
 232                 nf_conntrack_event_cache(IPCT_STATUS, skb);
 233         } else
 234                 nf_ct_refresh_acct(ct, ctinfo, skb,
 235                                    ct->proto.gre.timeout);
 236
 237         return NF_ACCEPT;
 238 }
 239
 240 /* Called when a new connection for this protocol found. */
 241 static bool gre_new(struct nf_conn *ct, const struct sk_buff *skb,
 242                     unsigned int dataoff)
 243 {
 244         pr_debug(": ");
 245         nf_ct_dump_tuple(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 246
 247         /* initialize to sane value.  Ideally a conntrack helper
 248          * (e.g. in case of pptp) is increasing them */
 249         ct->proto.gre.stream_timeout = GRE_STREAM_TIMEOUT;
 250         ct->proto.gre.timeout = GRE_TIMEOUT;
 251
 252         return true;
 253 }
 254
 255 /* Called when a conntrack entry has already been removed from the hashes
 256  * and is about to be deleted from memory */
 257 static void gre_destroy(struct nf_conn *ct)
 258 {
 259         struct nf_conn *master = ct->master;
 260         pr_debug(" entering\n");
 261
 262         if (!master)
 263                 pr_debug("no master !?!\n");
 264         else
 265                 nf_ct_gre_keymap_destroy(master);
 266 }
 267
 268 /* protocol helper struct */
 269 static struct nf_conntrack_l4proto nf_conntrack_l4proto_gre4 __read_mostly = {
 270         .l3proto         = AF_INET,
 271         .l4proto         = IPPROTO_GRE,
 272         .name            = "gre",
 273         .pkt_to_tuple    = gre_pkt_to_tuple,
 274         .invert_tuple    = gre_invert_tuple,
 275         .print_tuple     = gre_print_tuple,
 276         .print_conntrack = gre_print_conntrack,
 277         .packet          = gre_packet,
 278         .new             = gre_new,
 279         .destroy         = gre_destroy,
 280         .me              = THIS_MODULE,
 281 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 282         .tuple_to_nlattr = nf_ct_port_tuple_to_nlattr,
 283         .nlattr_to_tuple = nf_ct_port_nlattr_to_tuple,
 284         .nla_policy      = nf_ct_port_nla_policy,
 285 #endif
 286 };
 287
 288 static int __init nf_ct_proto_gre_init(void)
 289 {
 290         return nf_conntrack_l4proto_register(&nf_conntrack_l4proto_gre4);
 291 }
 292
 293 static void nf_ct_proto_gre_fini(void)
 294 {
 295         nf_conntrack_l4proto_unregister(&nf_conntrack_l4proto_gre4);
 296         nf_ct_gre_keymap_flush();
 297 }
 298
 299 module_init(nf_ct_proto_gre_init);
 300 module_exit(nf_ct_proto_gre_fini);
 301
 302 MODULE_LICENSE("GPL");