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/config.h>
  27 #include <linux/module.h>
  28 #include <linux/types.h>
  29 #include <linux/timer.h>
  30 #include <linux/netfilter.h>
  31 #include <linux/ip.h>
  32 #include <linux/in.h>
  33 #include <linux/list.h>
  34
  35 static DEFINE_RWLOCK(ip_ct_gre_lock);
  36 #define ASSERT_READ_LOCK(x)
  37 #define ASSERT_WRITE_LOCK(x)
  38
  39 #include <linux/netfilter_ipv4/listhelp.h>
  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 u_int32_t gre_keymap_lookup(struct ip_conntrack_tuple *t)
  79 {
  80         struct ip_ct_gre_keymap *km;
  81         u_int32_t key = 0;
  82
  83         read_lock_bh(&ip_ct_gre_lock);
  84         km = LIST_FIND(&gre_keymap_list, gre_key_cmpfn,
  85                         struct ip_ct_gre_keymap *, t);
  86         if (km)
  87                 key = km->tuple.src.u.gre.key;
  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, *old;
 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                 old = LIST_FIND(&gre_keymap_list, gre_key_cmpfn,
 116                                 struct ip_ct_gre_keymap *, t);
 117                 if (old == *exist_km) {
 118                         DEBUGP("retransmission\n");
 119                         return 0;
 120                 }
 121
 122                 DEBUGP("trying to override keymap_%s for ct %p\n",
 123                         reply? "reply":"orig", ct);
 124                 return -EEXIST;
 125         }
 126
 127         km = kmalloc(sizeof(*km), GFP_ATOMIC);
 128         if (!km)
 129                 return -ENOMEM;
 130
 131         memcpy(&km->tuple, t, sizeof(*t));
 132         *exist_km = km;
 133
 134         DEBUGP("adding new entry %p: ", km);
 135         DUMP_TUPLE_GRE(&km->tuple);
 136
 137         write_lock_bh(&ip_ct_gre_lock);
 138         list_append(&gre_keymap_list, km);
 139         write_unlock_bh(&ip_ct_gre_lock);
 140
 141         return 0;
 142 }
 143
 144 /* destroy the keymap entries associated with specified master ct */
 145 void ip_ct_gre_keymap_destroy(struct ip_conntrack *ct)
 146 {
 147         DEBUGP("entering for ct %p\n", ct);
 148
 149         if (!ct->helper || strcmp(ct->helper->name, "pptp")) {
 150                 DEBUGP("refusing to destroy GRE keymap to non-pptp session\n");
 151                 return;
 152         }
 153
 154         write_lock_bh(&ip_ct_gre_lock);
 155         if (ct->help.ct_pptp_info.keymap_orig) {
 156                 DEBUGP("removing %p from list\n",
 157                         ct->help.ct_pptp_info.keymap_orig);
 158                 list_del(&ct->help.ct_pptp_info.keymap_orig->list);
 159                 kfree(ct->help.ct_pptp_info.keymap_orig);
 160                 ct->help.ct_pptp_info.keymap_orig = NULL;
 161         }
 162         if (ct->help.ct_pptp_info.keymap_reply) {
 163                 DEBUGP("removing %p from list\n",
 164                         ct->help.ct_pptp_info.keymap_reply);
 165                 list_del(&ct->help.ct_pptp_info.keymap_reply->list);
 166                 kfree(ct->help.ct_pptp_info.keymap_reply);
 167                 ct->help.ct_pptp_info.keymap_reply = NULL;
 168         }
 169         write_unlock_bh(&ip_ct_gre_lock);
 170 }
 171
 172
 173 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
 174
 175 /* invert gre part of tuple */
 176 static int gre_invert_tuple(struct ip_conntrack_tuple *tuple,
 177                             const struct ip_conntrack_tuple *orig)
 178 {
 179         tuple->dst.u.gre.key = orig->src.u.gre.key;
 180         tuple->src.u.gre.key = orig->dst.u.gre.key;
 181
 182         return 1;
 183 }
 184
 185 /* gre hdr info to tuple */
 186 static int gre_pkt_to_tuple(const struct sk_buff *skb,
 187                            unsigned int dataoff,
 188                            struct ip_conntrack_tuple *tuple)
 189 {
 190         struct gre_hdr_pptp _pgrehdr, *pgrehdr;
 191         u_int32_t srckey;
 192         struct gre_hdr _grehdr, *grehdr;
 193
 194         /* first only delinearize old RFC1701 GRE header */
 195         grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
 196         if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
 197                 /* try to behave like "ip_conntrack_proto_generic" */
 198                 tuple->src.u.all = 0;
 199                 tuple->dst.u.all = 0;
 200                 return 1;
 201         }
 202
 203         /* PPTP header is variable length, only need up to the call_id field */
 204         pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
 205         if (!pgrehdr)
 206                 return 1;
 207
 208         if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
 209                 DEBUGP("GRE_VERSION_PPTP but unknown proto\n");
 210                 return 0;
 211         }
 212
 213         tuple->dst.u.gre.key = pgrehdr->call_id;
 214         srckey = gre_keymap_lookup(tuple);
 215         tuple->src.u.gre.key = srckey;
 216
 217         return 1;
 218 }
 219
 220 /* print gre part of tuple */
 221 static int gre_print_tuple(struct seq_file *s,
 222                            const struct ip_conntrack_tuple *tuple)
 223 {
 224         return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
 225                           ntohs(tuple->src.u.gre.key),
 226                           ntohs(tuple->dst.u.gre.key));
 227 }
 228
 229 /* print private data for conntrack */
 230 static int gre_print_conntrack(struct seq_file *s,
 231                                const struct ip_conntrack *ct)
 232 {
 233         return seq_printf(s, "timeout=%u, stream_timeout=%u ",
 234                           (ct->proto.gre.timeout / HZ),
 235                           (ct->proto.gre.stream_timeout / HZ));
 236 }
 237
 238 /* Returns verdict for packet, and may modify conntrack */
 239 static int gre_packet(struct ip_conntrack *ct,
 240                       const struct sk_buff *skb,
 241                       enum ip_conntrack_info conntrackinfo)
 242 {
 243         /* If we've seen traffic both ways, this is a GRE connection.
 244          * Extend timeout. */
 245         if (ct->status & IPS_SEEN_REPLY) {
 246                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 247                                    ct->proto.gre.stream_timeout);
 248                 /* Also, more likely to be important, and not a probe. */
 249                 set_bit(IPS_ASSURED_BIT, &ct->status);
 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 void __exit ip_ct_proto_gre_fini(void)
 311 {
 312         struct list_head *pos, *n;
 313
 314         /* delete all keymap entries */
 315         write_lock_bh(&ip_ct_gre_lock);
 316         list_for_each_safe(pos, n, &gre_keymap_list) {
 317                 DEBUGP("deleting keymap %p at module unload time\n", pos);
 318                 list_del(pos);
 319                 kfree(pos);
 320         }
 321         write_unlock_bh(&ip_ct_gre_lock);
 322
 323         ip_conntrack_protocol_unregister(&gre);
 324 }
 325
 326 EXPORT_SYMBOL(ip_ct_gre_keymap_add);
 327 EXPORT_SYMBOL(ip_ct_gre_keymap_destroy);