net/ipv4/netfilter/ip_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/netfilter.h>
  30 #include <linux/ip.h>
  31 #include <linux/in.h>
  32 #include <linux/list.h>
  33 #include <linux/seq_file.h>
  34 #include <linux/interrupt.h>
  35
  36 static DEFINE_RWLOCK(ip_ct_gre_lock);
  37 #define ASSERT_READ_LOCK(x)
  38 #define ASSERT_WRITE_LOCK(x)
  39
  40 #include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
  41 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  42 #include <linux/netfilter_ipv4/ip_conntrack_core.h>
  43
  44 #include <linux/netfilter_ipv4/ip_conntrack_proto_gre.h>
  45 #include <linux/netfilter_ipv4/ip_conntrack_pptp.h>
  46
  47 MODULE_LICENSE("GPL");
  48 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  49 MODULE_DESCRIPTION("netfilter connection tracking protocol helper for GRE");
  50
  51 /* shamelessly stolen from ip_conntrack_proto_udp.c */
  52 #define GRE_TIMEOUT             (30*HZ)
  53 #define GRE_STREAM_TIMEOUT      (180*HZ)
  54
  55 #if 0
  56 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, __FUNCTION__, ## args)
  57 #define DUMP_TUPLE_GRE(x) printk("%u.%u.%u.%u:0x%x -> %u.%u.%u.%u:0x%x\n", \
  58                         NIPQUAD((x)->src.ip), ntohs((x)->src.u.gre.key), \
  59                         NIPQUAD((x)->dst.ip), ntohs((x)->dst.u.gre.key))
  60 #else
  61 #define DEBUGP(x, args...)
  62 #define DUMP_TUPLE_GRE(x)
  63 #endif
  64
  65 /* GRE KEYMAP HANDLING FUNCTIONS */
  66 static LIST_HEAD(gre_keymap_list);
  67
  68 static inline int gre_key_cmpfn(const struct ip_ct_gre_keymap *km,
  69                                 const struct ip_conntrack_tuple *t)
  70 {
  71         return ((km->tuple.src.ip == t->src.ip) &&
  72                 (km->tuple.dst.ip == t->dst.ip) &&
  73                 (km->tuple.dst.protonum == t->dst.protonum) &&
  74                 (km->tuple.dst.u.all == t->dst.u.all));
  75 }
  76
  77 /* look up the source key for a given tuple */
  78 static __be16 gre_keymap_lookup(struct ip_conntrack_tuple *t)
  79 {
  80         struct ip_ct_gre_keymap *km;
  81         __be16 key = 0;
  82
  83         read_lock_bh(&ip_ct_gre_lock);
  84         list_for_each_entry(km, &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(&ip_ct_gre_lock);
  91
  92         DEBUGP("lookup src key 0x%x up key for ", key);
  93         DUMP_TUPLE_GRE(t);
  94
  95         return key;
  96 }
  97
  98 /* add a single keymap entry, associate with specified master ct */
  99 int
 100 ip_ct_gre_keymap_add(struct ip_conntrack *ct,
 101                      struct ip_conntrack_tuple *t, int reply)
 102 {
 103         struct ip_ct_gre_keymap **exist_km, *km;
 104
 105         if (!ct->helper || strcmp(ct->helper->name, "pptp")) {
 106                 DEBUGP("refusing to add GRE keymap to non-pptp session\n");
 107                 return -1;
 108         }
 109
 110         if (!reply)
 111                 exist_km = &ct->help.ct_pptp_info.keymap_orig;
 112         else
 113                 exist_km = &ct->help.ct_pptp_info.keymap_reply;
 114
 115         if (*exist_km) {
 116                 /* check whether it's a retransmission */
 117                 list_for_each_entry(km, &gre_keymap_list, list) {
 118                         if (gre_key_cmpfn(km, t) && km == *exist_km)
 119                                 return 0;
 120                 }
 121                 DEBUGP("trying to override keymap_%s for ct %p\n",
 122                         reply? "reply":"orig", ct);
 123                 return -EEXIST;
 124         }
 125
 126         km = kmalloc(sizeof(*km), GFP_ATOMIC);
 127         if (!km)
 128                 return -ENOMEM;
 129
 130         memcpy(&km->tuple, t, sizeof(*t));
 131         *exist_km = km;
 132
 133         DEBUGP("adding new entry %p: ", km);
 134         DUMP_TUPLE_GRE(&km->tuple);
 135
 136         write_lock_bh(&ip_ct_gre_lock);
 137         list_add_tail(&km->list, &gre_keymap_list);
 138         write_unlock_bh(&ip_ct_gre_lock);
 139
 140         return 0;
 141 }
 142
 143 /* destroy the keymap entries associated with specified master ct */
 144 void ip_ct_gre_keymap_destroy(struct ip_conntrack *ct)
 145 {
 146         DEBUGP("entering for ct %p\n", ct);
 147
 148         if (!ct->helper || strcmp(ct->helper->name, "pptp")) {
 149                 DEBUGP("refusing to destroy GRE keymap to non-pptp session\n");
 150                 return;
 151         }
 152
 153         write_lock_bh(&ip_ct_gre_lock);
 154         if (ct->help.ct_pptp_info.keymap_orig) {
 155                 DEBUGP("removing %p from list\n",
 156                         ct->help.ct_pptp_info.keymap_orig);
 157                 list_del(&ct->help.ct_pptp_info.keymap_orig->list);
 158                 kfree(ct->help.ct_pptp_info.keymap_orig);
 159                 ct->help.ct_pptp_info.keymap_orig = NULL;
 160         }
 161         if (ct->help.ct_pptp_info.keymap_reply) {
 162                 DEBUGP("removing %p from list\n",
 163                         ct->help.ct_pptp_info.keymap_reply);
 164                 list_del(&ct->help.ct_pptp_info.keymap_reply->list);
 165                 kfree(ct->help.ct_pptp_info.keymap_reply);
 166                 ct->help.ct_pptp_info.keymap_reply = NULL;
 167         }
 168         write_unlock_bh(&ip_ct_gre_lock);
 169 }
 170
 171
 172 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
 173
 174 /* invert gre part of tuple */
 175 static int gre_invert_tuple(struct ip_conntrack_tuple *tuple,
 176                             const struct ip_conntrack_tuple *orig)
 177 {
 178         tuple->dst.u.gre.key = orig->src.u.gre.key;
 179         tuple->src.u.gre.key = orig->dst.u.gre.key;
 180
 181         return 1;
 182 }
 183
 184 /* gre hdr info to tuple */
 185 static int gre_pkt_to_tuple(const struct sk_buff *skb,
 186                            unsigned int dataoff,
 187                            struct ip_conntrack_tuple *tuple)
 188 {
 189         struct gre_hdr_pptp _pgrehdr, *pgrehdr;
 190         __be16 srckey;
 191         struct gre_hdr _grehdr, *grehdr;
 192
 193         /* first only delinearize old RFC1701 GRE header */
 194         grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
 195         if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
 196                 /* try to behave like "ip_conntrack_proto_generic" */
 197                 tuple->src.u.all = 0;
 198                 tuple->dst.u.all = 0;
 199                 return 1;
 200         }
 201
 202         /* PPTP header is variable length, only need up to the call_id field */
 203         pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
 204         if (!pgrehdr)
 205                 return 1;
 206
 207         if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
 208                 DEBUGP("GRE_VERSION_PPTP but unknown proto\n");
 209                 return 0;
 210         }
 211
 212         tuple->dst.u.gre.key = pgrehdr->call_id;
 213         srckey = gre_keymap_lookup(tuple);
 214         tuple->src.u.gre.key = srckey;
 215
 216         return 1;
 217 }
 218
 219 /* print gre part of tuple */
 220 static int gre_print_tuple(struct seq_file *s,
 221                            const struct ip_conntrack_tuple *tuple)
 222 {
 223         return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
 224                           ntohs(tuple->src.u.gre.key),
 225                           ntohs(tuple->dst.u.gre.key));
 226 }
 227
 228 /* print private data for conntrack */
 229 static int gre_print_conntrack(struct seq_file *s,
 230                                const struct ip_conntrack *ct)
 231 {
 232         return seq_printf(s, "timeout=%u, stream_timeout=%u ",
 233                           (ct->proto.gre.timeout / HZ),
 234                           (ct->proto.gre.stream_timeout / HZ));
 235 }
 236
 237 /* Returns verdict for packet, and may modify conntrack */
 238 static int gre_packet(struct ip_conntrack *ct,
 239                       const struct sk_buff *skb,
 240                       enum ip_conntrack_info conntrackinfo)
 241 {
 242         /* If we've seen traffic both ways, this is a GRE connection.
 243          * Extend timeout. */
 244         if (ct->status & IPS_SEEN_REPLY) {
 245                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 246                                    ct->proto.gre.stream_timeout);
 247                 /* Also, more likely to be important, and not a probe. */
 248                 set_bit(IPS_ASSURED_BIT, &ct->status);
 249                 ip_conntrack_event_cache(IPCT_STATUS, skb);
 250         } else
 251                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 252                                    ct->proto.gre.timeout);
 253
 254         return NF_ACCEPT;
 255 }
 256
 257 /* Called when a new connection for this protocol found. */
 258 static int gre_new(struct ip_conntrack *ct,
 259                    const struct sk_buff *skb)
 260 {
 261         DEBUGP(": ");
 262         DUMP_TUPLE_GRE(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 263
 264         /* initialize to sane value.  Ideally a conntrack helper
 265          * (e.g. in case of pptp) is increasing them */
 266         ct->proto.gre.stream_timeout = GRE_STREAM_TIMEOUT;
 267         ct->proto.gre.timeout = GRE_TIMEOUT;
 268
 269         return 1;
 270 }
 271
 272 /* Called when a conntrack entry has already been removed from the hashes
 273  * and is about to be deleted from memory */
 274 static void gre_destroy(struct ip_conntrack *ct)
 275 {
 276         struct ip_conntrack *master = ct->master;
 277         DEBUGP(" entering\n");
 278
 279         if (!master)
 280                 DEBUGP("no master !?!\n");
 281         else
 282                 ip_ct_gre_keymap_destroy(master);
 283 }
 284
 285 /* protocol helper struct */
 286 static struct ip_conntrack_protocol gre = {
 287         .proto           = IPPROTO_GRE,
 288         .name            = "gre",
 289         .pkt_to_tuple    = gre_pkt_to_tuple,
 290         .invert_tuple    = gre_invert_tuple,
 291         .print_tuple     = gre_print_tuple,
 292         .print_conntrack = gre_print_conntrack,
 293         .packet          = gre_packet,
 294         .new             = gre_new,
 295         .destroy         = gre_destroy,
 296         .me              = THIS_MODULE,
 297 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 298     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 299         .tuple_to_nfattr = ip_ct_port_tuple_to_nfattr,
 300         .nfattr_to_tuple = ip_ct_port_nfattr_to_tuple,
 301 #endif
 302 };
 303
 304 /* ip_conntrack_proto_gre initialization */
 305 int __init ip_ct_proto_gre_init(void)
 306 {
 307         return ip_conntrack_protocol_register(&gre);
 308 }
 309
 310 /* This cannot be __exit, as it is invoked from ip_conntrack_helper_pptp.c's
 311  * init() code on errors.
 312  */
 313 void ip_ct_proto_gre_fini(void)
 314 {
 315         struct list_head *pos, *n;
 316
 317         /* delete all keymap entries */
 318         write_lock_bh(&ip_ct_gre_lock);
 319         list_for_each_safe(pos, n, &gre_keymap_list) {
 320                 DEBUGP("deleting keymap %p at module unload time\n", pos);
 321                 list_del(pos);
 322                 kfree(pos);
 323         }
 324         write_unlock_bh(&ip_ct_gre_lock);
 325
 326         ip_conntrack_protocol_unregister(&gre);
 327 }
 328
 329 EXPORT_SYMBOL(ip_ct_gre_keymap_add);
 330 EXPORT_SYMBOL(ip_ct_gre_keymap_destroy);