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/listhelp.h>
  41 #include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
  42 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  43 #include <linux/netfilter_ipv4/ip_conntrack_core.h>
  44
  45 #include <linux/netfilter_ipv4/ip_conntrack_proto_gre.h>
  46 #include <linux/netfilter_ipv4/ip_conntrack_pptp.h>
  47
  48 MODULE_LICENSE("GPL");
  49 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  50 MODULE_DESCRIPTION("netfilter connection tracking protocol helper for GRE");
  51
  52 /* shamelessly stolen from ip_conntrack_proto_udp.c */
  53 #define GRE_TIMEOUT             (30*HZ)
  54 #define GRE_STREAM_TIMEOUT      (180*HZ)
  55
  56 #if 0
  57 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, __FUNCTION__, ## args)
  58 #define DUMP_TUPLE_GRE(x) printk("%u.%u.%u.%u:0x%x -> %u.%u.%u.%u:0x%x\n", \
  59                         NIPQUAD((x)->src.ip), ntohs((x)->src.u.gre.key), \
  60                         NIPQUAD((x)->dst.ip), ntohs((x)->dst.u.gre.key))
  61 #else
  62 #define DEBUGP(x, args...)
  63 #define DUMP_TUPLE_GRE(x)
  64 #endif
  65
  66 /* GRE KEYMAP HANDLING FUNCTIONS */
  67 static LIST_HEAD(gre_keymap_list);
  68
  69 static inline int gre_key_cmpfn(const struct ip_ct_gre_keymap *km,
  70                                 const struct ip_conntrack_tuple *t)
  71 {
  72         return ((km->tuple.src.ip == t->src.ip) &&
  73                 (km->tuple.dst.ip == t->dst.ip) &&
  74                 (km->tuple.dst.protonum == t->dst.protonum) &&
  75                 (km->tuple.dst.u.all == t->dst.u.all));
  76 }
  77
  78 /* look up the source key for a given tuple */
  79 static __be16 gre_keymap_lookup(struct ip_conntrack_tuple *t)
  80 {
  81         struct ip_ct_gre_keymap *km;
  82         __be16 key = 0;
  83
  84         read_lock_bh(&ip_ct_gre_lock);
  85         km = LIST_FIND(&gre_keymap_list, gre_key_cmpfn,
  86                         struct ip_ct_gre_keymap *, t);
  87         if (km)
  88                 key = km->tuple.src.u.gre.key;
  89         read_unlock_bh(&ip_ct_gre_lock);
  90
  91         DEBUGP("lookup src key 0x%x up key for ", key);
  92         DUMP_TUPLE_GRE(t);
  93
  94         return key;
  95 }
  96
  97 /* add a single keymap entry, associate with specified master ct */
  98 int
  99 ip_ct_gre_keymap_add(struct ip_conntrack *ct,
 100                      struct ip_conntrack_tuple *t, int reply)
 101 {
 102         struct ip_ct_gre_keymap **exist_km, *km, *old;
 103
 104         if (!ct->helper || strcmp(ct->helper->name, "pptp")) {
 105                 DEBUGP("refusing to add GRE keymap to non-pptp session\n");
 106                 return -1;
 107         }
 108
 109         if (!reply)
 110                 exist_km = &ct->help.ct_pptp_info.keymap_orig;
 111         else
 112                 exist_km = &ct->help.ct_pptp_info.keymap_reply;
 113
 114         if (*exist_km) {
 115                 /* check whether it's a retransmission */
 116                 old = LIST_FIND(&gre_keymap_list, gre_key_cmpfn,
 117                                 struct ip_ct_gre_keymap *, t);
 118                 if (old == *exist_km) {
 119                         DEBUGP("retransmission\n");
 120                         return 0;
 121                 }
 122
 123                 DEBUGP("trying to override keymap_%s for ct %p\n",
 124                         reply? "reply":"orig", ct);
 125                 return -EEXIST;
 126         }
 127
 128         km = kmalloc(sizeof(*km), GFP_ATOMIC);
 129         if (!km)
 130                 return -ENOMEM;
 131
 132         memcpy(&km->tuple, t, sizeof(*t));
 133         *exist_km = km;
 134
 135         DEBUGP("adding new entry %p: ", km);
 136         DUMP_TUPLE_GRE(&km->tuple);
 137
 138         write_lock_bh(&ip_ct_gre_lock);
 139         list_append(&gre_keymap_list, km);
 140         write_unlock_bh(&ip_ct_gre_lock);
 141
 142         return 0;
 143 }
 144
 145 /* destroy the keymap entries associated with specified master ct */
 146 void ip_ct_gre_keymap_destroy(struct ip_conntrack *ct)
 147 {
 148         DEBUGP("entering for ct %p\n", ct);
 149
 150         if (!ct->helper || strcmp(ct->helper->name, "pptp")) {
 151                 DEBUGP("refusing to destroy GRE keymap to non-pptp session\n");
 152                 return;
 153         }
 154
 155         write_lock_bh(&ip_ct_gre_lock);
 156         if (ct->help.ct_pptp_info.keymap_orig) {
 157                 DEBUGP("removing %p from list\n",
 158                         ct->help.ct_pptp_info.keymap_orig);
 159                 list_del(&ct->help.ct_pptp_info.keymap_orig->list);
 160                 kfree(ct->help.ct_pptp_info.keymap_orig);
 161                 ct->help.ct_pptp_info.keymap_orig = NULL;
 162         }
 163         if (ct->help.ct_pptp_info.keymap_reply) {
 164                 DEBUGP("removing %p from list\n",
 165                         ct->help.ct_pptp_info.keymap_reply);
 166                 list_del(&ct->help.ct_pptp_info.keymap_reply->list);
 167                 kfree(ct->help.ct_pptp_info.keymap_reply);
 168                 ct->help.ct_pptp_info.keymap_reply = NULL;
 169         }
 170         write_unlock_bh(&ip_ct_gre_lock);
 171 }
 172
 173
 174 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
 175
 176 /* invert gre part of tuple */
 177 static int gre_invert_tuple(struct ip_conntrack_tuple *tuple,
 178                             const struct ip_conntrack_tuple *orig)
 179 {
 180         tuple->dst.u.gre.key = orig->src.u.gre.key;
 181         tuple->src.u.gre.key = orig->dst.u.gre.key;
 182
 183         return 1;
 184 }
 185
 186 /* gre hdr info to tuple */
 187 static int gre_pkt_to_tuple(const struct sk_buff *skb,
 188                            unsigned int dataoff,
 189                            struct ip_conntrack_tuple *tuple)
 190 {
 191         struct gre_hdr_pptp _pgrehdr, *pgrehdr;
 192         __be16 srckey;
 193         struct gre_hdr _grehdr, *grehdr;
 194
 195         /* first only delinearize old RFC1701 GRE header */
 196         grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
 197         if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
 198                 /* try to behave like "ip_conntrack_proto_generic" */
 199                 tuple->src.u.all = 0;
 200                 tuple->dst.u.all = 0;
 201                 return 1;
 202         }
 203
 204         /* PPTP header is variable length, only need up to the call_id field */
 205         pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
 206         if (!pgrehdr)
 207                 return 1;
 208
 209         if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
 210                 DEBUGP("GRE_VERSION_PPTP but unknown proto\n");
 211                 return 0;
 212         }
 213
 214         tuple->dst.u.gre.key = pgrehdr->call_id;
 215         srckey = gre_keymap_lookup(tuple);
 216         tuple->src.u.gre.key = srckey;
 217
 218         return 1;
 219 }
 220
 221 /* print gre part of tuple */
 222 static int gre_print_tuple(struct seq_file *s,
 223                            const struct ip_conntrack_tuple *tuple)
 224 {
 225         return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
 226                           ntohs(tuple->src.u.gre.key),
 227                           ntohs(tuple->dst.u.gre.key));
 228 }
 229
 230 /* print private data for conntrack */
 231 static int gre_print_conntrack(struct seq_file *s,
 232                                const struct ip_conntrack *ct)
 233 {
 234         return seq_printf(s, "timeout=%u, stream_timeout=%u ",
 235                           (ct->proto.gre.timeout / HZ),
 236                           (ct->proto.gre.stream_timeout / HZ));
 237 }
 238
 239 /* Returns verdict for packet, and may modify conntrack */
 240 static int gre_packet(struct ip_conntrack *ct,
 241                       const struct sk_buff *skb,
 242                       enum ip_conntrack_info conntrackinfo)
 243 {
 244         /* If we've seen traffic both ways, this is a GRE connection.
 245          * Extend timeout. */
 246         if (ct->status & IPS_SEEN_REPLY) {
 247                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 248                                    ct->proto.gre.stream_timeout);
 249                 /* Also, more likely to be important, and not a probe. */
 250                 set_bit(IPS_ASSURED_BIT, &ct->status);
 251                 ip_conntrack_event_cache(IPCT_STATUS, skb);
 252         } else
 253                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 254                                    ct->proto.gre.timeout);
 255
 256         return NF_ACCEPT;
 257 }
 258
 259 /* Called when a new connection for this protocol found. */
 260 static int gre_new(struct ip_conntrack *ct,
 261                    const struct sk_buff *skb)
 262 {
 263         DEBUGP(": ");
 264         DUMP_TUPLE_GRE(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 265
 266         /* initialize to sane value.  Ideally a conntrack helper
 267          * (e.g. in case of pptp) is increasing them */
 268         ct->proto.gre.stream_timeout = GRE_STREAM_TIMEOUT;
 269         ct->proto.gre.timeout = GRE_TIMEOUT;
 270
 271         return 1;
 272 }
 273
 274 /* Called when a conntrack entry has already been removed from the hashes
 275  * and is about to be deleted from memory */
 276 static void gre_destroy(struct ip_conntrack *ct)
 277 {
 278         struct ip_conntrack *master = ct->master;
 279         DEBUGP(" entering\n");
 280
 281         if (!master)
 282                 DEBUGP("no master !?!\n");
 283         else
 284                 ip_ct_gre_keymap_destroy(master);
 285 }
 286
 287 /* protocol helper struct */
 288 static struct ip_conntrack_protocol gre = {
 289         .proto           = IPPROTO_GRE,
 290         .name            = "gre",
 291         .pkt_to_tuple    = gre_pkt_to_tuple,
 292         .invert_tuple    = gre_invert_tuple,
 293         .print_tuple     = gre_print_tuple,
 294         .print_conntrack = gre_print_conntrack,
 295         .packet          = gre_packet,
 296         .new             = gre_new,
 297         .destroy         = gre_destroy,
 298         .me              = THIS_MODULE,
 299 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 300     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 301         .tuple_to_nfattr = ip_ct_port_tuple_to_nfattr,
 302         .nfattr_to_tuple = ip_ct_port_nfattr_to_tuple,
 303 #endif
 304 };
 305
 306 /* ip_conntrack_proto_gre initialization */
 307 int __init ip_ct_proto_gre_init(void)
 308 {
 309         return ip_conntrack_protocol_register(&gre);
 310 }
 311
 312 /* This cannot be __exit, as it is invoked from ip_conntrack_helper_pptp.c's
 313  * init() code on errors.
 314  */
 315 void ip_ct_proto_gre_fini(void)
 316 {
 317         struct list_head *pos, *n;
 318
 319         /* delete all keymap entries */
 320         write_lock_bh(&ip_ct_gre_lock);
 321         list_for_each_safe(pos, n, &gre_keymap_list) {
 322                 DEBUGP("deleting keymap %p at module unload time\n", pos);
 323                 list_del(pos);
 324                 kfree(pos);
 325         }
 326         write_unlock_bh(&ip_ct_gre_lock);
 327
 328         ip_conntrack_protocol_unregister(&gre);
 329 }
 330
 331 EXPORT_SYMBOL(ip_ct_gre_keymap_add);
 332 EXPORT_SYMBOL(ip_ct_gre_keymap_destroy);