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
  38 #include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
  39 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  40 #include <linux/netfilter_ipv4/ip_conntrack_core.h>
  41
  42 #include <linux/netfilter_ipv4/ip_conntrack_proto_gre.h>
  43 #include <linux/netfilter_ipv4/ip_conntrack_pptp.h>
  44
  45 MODULE_LICENSE("GPL");
  46 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  47 MODULE_DESCRIPTION("netfilter connection tracking protocol helper for GRE");
  48
  49 /* shamelessly stolen from ip_conntrack_proto_udp.c */
  50 #define GRE_TIMEOUT             (30*HZ)
  51 #define GRE_STREAM_TIMEOUT      (180*HZ)
  52
  53 #if 0
  54 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, __FUNCTION__, ## args)
  55 #define DUMP_TUPLE_GRE(x) printk("%u.%u.%u.%u:0x%x -> %u.%u.%u.%u:0x%x\n", \
  56                         NIPQUAD((x)->src.ip), ntohs((x)->src.u.gre.key), \
  57                         NIPQUAD((x)->dst.ip), ntohs((x)->dst.u.gre.key))
  58 #else
  59 #define DEBUGP(x, args...)
  60 #define DUMP_TUPLE_GRE(x)
  61 #endif
  62
  63 /* GRE KEYMAP HANDLING FUNCTIONS */
  64 static LIST_HEAD(gre_keymap_list);
  65
  66 static inline int gre_key_cmpfn(const struct ip_ct_gre_keymap *km,
  67                                 const struct ip_conntrack_tuple *t)
  68 {
  69         return ((km->tuple.src.ip == t->src.ip) &&
  70                 (km->tuple.dst.ip == t->dst.ip) &&
  71                 (km->tuple.dst.protonum == t->dst.protonum) &&
  72                 (km->tuple.dst.u.all == t->dst.u.all));
  73 }
  74
  75 /* look up the source key for a given tuple */
  76 static __be16 gre_keymap_lookup(struct ip_conntrack_tuple *t)
  77 {
  78         struct ip_ct_gre_keymap *km;
  79         __be16 key = 0;
  80
  81         read_lock_bh(&ip_ct_gre_lock);
  82         list_for_each_entry(km, &gre_keymap_list, list) {
  83                 if (gre_key_cmpfn(km, t)) {
  84                         key = km->tuple.src.u.gre.key;
  85                         break;
  86                 }
  87         }
  88         read_unlock_bh(&ip_ct_gre_lock);
  89
  90         DEBUGP("lookup src key 0x%x up key for ", key);
  91         DUMP_TUPLE_GRE(t);
  92
  93         return key;
  94 }
  95
  96 /* add a single keymap entry, associate with specified master ct */
  97 int
  98 ip_ct_gre_keymap_add(struct ip_conntrack *ct,
  99                      struct ip_conntrack_tuple *t, int reply)
 100 {
 101         struct ip_ct_gre_keymap **exist_km, *km;
 102
 103         if (!ct->helper || strcmp(ct->helper->name, "pptp")) {
 104                 DEBUGP("refusing to add GRE keymap to non-pptp session\n");
 105                 return -1;
 106         }
 107
 108         if (!reply)
 109                 exist_km = &ct->help.ct_pptp_info.keymap_orig;
 110         else
 111                 exist_km = &ct->help.ct_pptp_info.keymap_reply;
 112
 113         if (*exist_km) {
 114                 /* check whether it's a retransmission */
 115                 list_for_each_entry(km, &gre_keymap_list, list) {
 116                         if (gre_key_cmpfn(km, t) && km == *exist_km)
 117                                 return 0;
 118                 }
 119                 DEBUGP("trying to override keymap_%s for ct %p\n",
 120                         reply? "reply":"orig", ct);
 121                 return -EEXIST;
 122         }
 123
 124         km = kmalloc(sizeof(*km), GFP_ATOMIC);
 125         if (!km)
 126                 return -ENOMEM;
 127
 128         memcpy(&km->tuple, t, sizeof(*t));
 129         *exist_km = km;
 130
 131         DEBUGP("adding new entry %p: ", km);
 132         DUMP_TUPLE_GRE(&km->tuple);
 133
 134         write_lock_bh(&ip_ct_gre_lock);
 135         list_add_tail(&km->list, &gre_keymap_list);
 136         write_unlock_bh(&ip_ct_gre_lock);
 137
 138         return 0;
 139 }
 140
 141 /* destroy the keymap entries associated with specified master ct */
 142 void ip_ct_gre_keymap_destroy(struct ip_conntrack *ct)
 143 {
 144         DEBUGP("entering for ct %p\n", ct);
 145
 146         if (!ct->helper || strcmp(ct->helper->name, "pptp")) {
 147                 DEBUGP("refusing to destroy GRE keymap to non-pptp session\n");
 148                 return;
 149         }
 150
 151         write_lock_bh(&ip_ct_gre_lock);
 152         if (ct->help.ct_pptp_info.keymap_orig) {
 153                 DEBUGP("removing %p from list\n",
 154                         ct->help.ct_pptp_info.keymap_orig);
 155                 list_del(&ct->help.ct_pptp_info.keymap_orig->list);
 156                 kfree(ct->help.ct_pptp_info.keymap_orig);
 157                 ct->help.ct_pptp_info.keymap_orig = NULL;
 158         }
 159         if (ct->help.ct_pptp_info.keymap_reply) {
 160                 DEBUGP("removing %p from list\n",
 161                         ct->help.ct_pptp_info.keymap_reply);
 162                 list_del(&ct->help.ct_pptp_info.keymap_reply->list);
 163                 kfree(ct->help.ct_pptp_info.keymap_reply);
 164                 ct->help.ct_pptp_info.keymap_reply = NULL;
 165         }
 166         write_unlock_bh(&ip_ct_gre_lock);
 167 }
 168
 169
 170 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
 171
 172 /* invert gre part of tuple */
 173 static int gre_invert_tuple(struct ip_conntrack_tuple *tuple,
 174                             const struct ip_conntrack_tuple *orig)
 175 {
 176         tuple->dst.u.gre.key = orig->src.u.gre.key;
 177         tuple->src.u.gre.key = orig->dst.u.gre.key;
 178
 179         return 1;
 180 }
 181
 182 /* gre hdr info to tuple */
 183 static int gre_pkt_to_tuple(const struct sk_buff *skb,
 184                            unsigned int dataoff,
 185                            struct ip_conntrack_tuple *tuple)
 186 {
 187         struct gre_hdr_pptp _pgrehdr, *pgrehdr;
 188         __be16 srckey;
 189         struct gre_hdr _grehdr, *grehdr;
 190
 191         /* first only delinearize old RFC1701 GRE header */
 192         grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
 193         if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
 194                 /* try to behave like "ip_conntrack_proto_generic" */
 195                 tuple->src.u.all = 0;
 196                 tuple->dst.u.all = 0;
 197                 return 1;
 198         }
 199
 200         /* PPTP header is variable length, only need up to the call_id field */
 201         pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
 202         if (!pgrehdr)
 203                 return 1;
 204
 205         if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
 206                 DEBUGP("GRE_VERSION_PPTP but unknown proto\n");
 207                 return 0;
 208         }
 209
 210         tuple->dst.u.gre.key = pgrehdr->call_id;
 211         srckey = gre_keymap_lookup(tuple);
 212         tuple->src.u.gre.key = srckey;
 213
 214         return 1;
 215 }
 216
 217 /* print gre part of tuple */
 218 static int gre_print_tuple(struct seq_file *s,
 219                            const struct ip_conntrack_tuple *tuple)
 220 {
 221         return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
 222                           ntohs(tuple->src.u.gre.key),
 223                           ntohs(tuple->dst.u.gre.key));
 224 }
 225
 226 /* print private data for conntrack */
 227 static int gre_print_conntrack(struct seq_file *s,
 228                                const struct ip_conntrack *ct)
 229 {
 230         return seq_printf(s, "timeout=%u, stream_timeout=%u ",
 231                           (ct->proto.gre.timeout / HZ),
 232                           (ct->proto.gre.stream_timeout / HZ));
 233 }
 234
 235 /* Returns verdict for packet, and may modify conntrack */
 236 static int gre_packet(struct ip_conntrack *ct,
 237                       const struct sk_buff *skb,
 238                       enum ip_conntrack_info conntrackinfo)
 239 {
 240         /* If we've seen traffic both ways, this is a GRE connection.
 241          * Extend timeout. */
 242         if (ct->status & IPS_SEEN_REPLY) {
 243                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 244                                    ct->proto.gre.stream_timeout);
 245                 /* Also, more likely to be important, and not a probe. */
 246                 set_bit(IPS_ASSURED_BIT, &ct->status);
 247                 ip_conntrack_event_cache(IPCT_STATUS, skb);
 248         } else
 249                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 250                                    ct->proto.gre.timeout);
 251
 252         return NF_ACCEPT;
 253 }
 254
 255 /* Called when a new connection for this protocol found. */
 256 static int gre_new(struct ip_conntrack *ct,
 257                    const struct sk_buff *skb)
 258 {
 259         DEBUGP(": ");
 260         DUMP_TUPLE_GRE(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 261
 262         /* initialize to sane value.  Ideally a conntrack helper
 263          * (e.g. in case of pptp) is increasing them */
 264         ct->proto.gre.stream_timeout = GRE_STREAM_TIMEOUT;
 265         ct->proto.gre.timeout = GRE_TIMEOUT;
 266
 267         return 1;
 268 }
 269
 270 /* Called when a conntrack entry has already been removed from the hashes
 271  * and is about to be deleted from memory */
 272 static void gre_destroy(struct ip_conntrack *ct)
 273 {
 274         struct ip_conntrack *master = ct->master;
 275         DEBUGP(" entering\n");
 276
 277         if (!master)
 278                 DEBUGP("no master !?!\n");
 279         else
 280                 ip_ct_gre_keymap_destroy(master);
 281 }
 282
 283 /* protocol helper struct */
 284 static struct ip_conntrack_protocol gre = {
 285         .proto           = IPPROTO_GRE,
 286         .name            = "gre",
 287         .pkt_to_tuple    = gre_pkt_to_tuple,
 288         .invert_tuple    = gre_invert_tuple,
 289         .print_tuple     = gre_print_tuple,
 290         .print_conntrack = gre_print_conntrack,
 291         .packet          = gre_packet,
 292         .new             = gre_new,
 293         .destroy         = gre_destroy,
 294         .me              = THIS_MODULE,
 295 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 296     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 297         .tuple_to_nfattr = ip_ct_port_tuple_to_nfattr,
 298         .nfattr_to_tuple = ip_ct_port_nfattr_to_tuple,
 299 #endif
 300 };
 301
 302 /* ip_conntrack_proto_gre initialization */
 303 int __init ip_ct_proto_gre_init(void)
 304 {
 305         return ip_conntrack_protocol_register(&gre);
 306 }
 307
 308 /* This cannot be __exit, as it is invoked from ip_conntrack_helper_pptp.c's
 309  * init() code on errors.
 310  */
 311 void ip_ct_proto_gre_fini(void)
 312 {
 313         struct list_head *pos, *n;
 314
 315         /* delete all keymap entries */
 316         write_lock_bh(&ip_ct_gre_lock);
 317         list_for_each_safe(pos, n, &gre_keymap_list) {
 318                 DEBUGP("deleting keymap %p at module unload time\n", pos);
 319                 list_del(pos);
 320                 kfree(pos);
 321         }
 322         write_unlock_bh(&ip_ct_gre_lock);
 323
 324         ip_conntrack_protocol_unregister(&gre);
 325 }
 326
 327 EXPORT_SYMBOL(ip_ct_gre_keymap_add);
 328 EXPORT_SYMBOL(ip_ct_gre_keymap_destroy);