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 #include <linux/seq_file.h>
  35 #include <linux/interrupt.h>
  36
  37 static DEFINE_RWLOCK(ip_ct_gre_lock);
  38 #define ASSERT_READ_LOCK(x)
  39 #define ASSERT_WRITE_LOCK(x)
  40
  41 #include <linux/netfilter_ipv4/listhelp.h>
  42 #include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
  43 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  44 #include <linux/netfilter_ipv4/ip_conntrack_core.h>
  45
  46 #include <linux/netfilter_ipv4/ip_conntrack_proto_gre.h>
  47 #include <linux/netfilter_ipv4/ip_conntrack_pptp.h>
  48
  49 MODULE_LICENSE("GPL");
  50 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  51 MODULE_DESCRIPTION("netfilter connection tracking protocol helper for GRE");
  52
  53 /* shamelessly stolen from ip_conntrack_proto_udp.c */
  54 #define GRE_TIMEOUT             (30*HZ)
  55 #define GRE_STREAM_TIMEOUT      (180*HZ)
  56
  57 #if 0
  58 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, __FUNCTION__, ## args)
  59 #define DUMP_TUPLE_GRE(x) printk("%u.%u.%u.%u:0x%x -> %u.%u.%u.%u:0x%x\n", \
  60                         NIPQUAD((x)->src.ip), ntohs((x)->src.u.gre.key), \
  61                         NIPQUAD((x)->dst.ip), ntohs((x)->dst.u.gre.key))
  62 #else
  63 #define DEBUGP(x, args...)
  64 #define DUMP_TUPLE_GRE(x)
  65 #endif
  66
  67 /* GRE KEYMAP HANDLING FUNCTIONS */
  68 static LIST_HEAD(gre_keymap_list);
  69
  70 static inline int gre_key_cmpfn(const struct ip_ct_gre_keymap *km,
  71                                 const struct ip_conntrack_tuple *t)
  72 {
  73         return ((km->tuple.src.ip == t->src.ip) &&
  74                 (km->tuple.dst.ip == t->dst.ip) &&
  75                 (km->tuple.dst.protonum == t->dst.protonum) &&
  76                 (km->tuple.dst.u.all == t->dst.u.all));
  77 }
  78
  79 /* look up the source key for a given tuple */
  80 static u_int32_t gre_keymap_lookup(struct ip_conntrack_tuple *t)
  81 {
  82         struct ip_ct_gre_keymap *km;
  83         u_int32_t key = 0;
  84
  85         read_lock_bh(&ip_ct_gre_lock);
  86         km = LIST_FIND(&gre_keymap_list, gre_key_cmpfn,
  87                         struct ip_ct_gre_keymap *, t);
  88         if (km)
  89                 key = km->tuple.src.u.gre.key;
  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, *old;
 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                 old = LIST_FIND(&gre_keymap_list, gre_key_cmpfn,
 118                                 struct ip_ct_gre_keymap *, t);
 119                 if (old == *exist_km) {
 120                         DEBUGP("retransmission\n");
 121                         return 0;
 122                 }
 123
 124                 DEBUGP("trying to override keymap_%s for ct %p\n",
 125                         reply? "reply":"orig", ct);
 126                 return -EEXIST;
 127         }
 128
 129         km = kmalloc(sizeof(*km), GFP_ATOMIC);
 130         if (!km)
 131                 return -ENOMEM;
 132
 133         memcpy(&km->tuple, t, sizeof(*t));
 134         *exist_km = km;
 135
 136         DEBUGP("adding new entry %p: ", km);
 137         DUMP_TUPLE_GRE(&km->tuple);
 138
 139         write_lock_bh(&ip_ct_gre_lock);
 140         list_append(&gre_keymap_list, km);
 141         write_unlock_bh(&ip_ct_gre_lock);
 142
 143         return 0;
 144 }
 145
 146 /* destroy the keymap entries associated with specified master ct */
 147 void ip_ct_gre_keymap_destroy(struct ip_conntrack *ct)
 148 {
 149         DEBUGP("entering for ct %p\n", ct);
 150
 151         if (!ct->helper || strcmp(ct->helper->name, "pptp")) {
 152                 DEBUGP("refusing to destroy GRE keymap to non-pptp session\n");
 153                 return;
 154         }
 155
 156         write_lock_bh(&ip_ct_gre_lock);
 157         if (ct->help.ct_pptp_info.keymap_orig) {
 158                 DEBUGP("removing %p from list\n",
 159                         ct->help.ct_pptp_info.keymap_orig);
 160                 list_del(&ct->help.ct_pptp_info.keymap_orig->list);
 161                 kfree(ct->help.ct_pptp_info.keymap_orig);
 162                 ct->help.ct_pptp_info.keymap_orig = NULL;
 163         }
 164         if (ct->help.ct_pptp_info.keymap_reply) {
 165                 DEBUGP("removing %p from list\n",
 166                         ct->help.ct_pptp_info.keymap_reply);
 167                 list_del(&ct->help.ct_pptp_info.keymap_reply->list);
 168                 kfree(ct->help.ct_pptp_info.keymap_reply);
 169                 ct->help.ct_pptp_info.keymap_reply = NULL;
 170         }
 171         write_unlock_bh(&ip_ct_gre_lock);
 172 }
 173
 174
 175 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
 176
 177 /* invert gre part of tuple */
 178 static int gre_invert_tuple(struct ip_conntrack_tuple *tuple,
 179                             const struct ip_conntrack_tuple *orig)
 180 {
 181         tuple->dst.u.gre.key = orig->src.u.gre.key;
 182         tuple->src.u.gre.key = orig->dst.u.gre.key;
 183
 184         return 1;
 185 }
 186
 187 /* gre hdr info to tuple */
 188 static int gre_pkt_to_tuple(const struct sk_buff *skb,
 189                            unsigned int dataoff,
 190                            struct ip_conntrack_tuple *tuple)
 191 {
 192         struct gre_hdr_pptp _pgrehdr, *pgrehdr;
 193         u_int32_t srckey;
 194         struct gre_hdr _grehdr, *grehdr;
 195
 196         /* first only delinearize old RFC1701 GRE header */
 197         grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
 198         if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
 199                 /* try to behave like "ip_conntrack_proto_generic" */
 200                 tuple->src.u.all = 0;
 201                 tuple->dst.u.all = 0;
 202                 return 1;
 203         }
 204
 205         /* PPTP header is variable length, only need up to the call_id field */
 206         pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
 207         if (!pgrehdr)
 208                 return 1;
 209
 210         if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
 211                 DEBUGP("GRE_VERSION_PPTP but unknown proto\n");
 212                 return 0;
 213         }
 214
 215         tuple->dst.u.gre.key = pgrehdr->call_id;
 216         srckey = gre_keymap_lookup(tuple);
 217         tuple->src.u.gre.key = srckey;
 218
 219         return 1;
 220 }
 221
 222 /* print gre part of tuple */
 223 static int gre_print_tuple(struct seq_file *s,
 224                            const struct ip_conntrack_tuple *tuple)
 225 {
 226         return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
 227                           ntohs(tuple->src.u.gre.key),
 228                           ntohs(tuple->dst.u.gre.key));
 229 }
 230
 231 /* print private data for conntrack */
 232 static int gre_print_conntrack(struct seq_file *s,
 233                                const struct ip_conntrack *ct)
 234 {
 235         return seq_printf(s, "timeout=%u, stream_timeout=%u ",
 236                           (ct->proto.gre.timeout / HZ),
 237                           (ct->proto.gre.stream_timeout / HZ));
 238 }
 239
 240 /* Returns verdict for packet, and may modify conntrack */
 241 static int gre_packet(struct ip_conntrack *ct,
 242                       const struct sk_buff *skb,
 243                       enum ip_conntrack_info conntrackinfo)
 244 {
 245         /* If we've seen traffic both ways, this is a GRE connection.
 246          * Extend timeout. */
 247         if (ct->status & IPS_SEEN_REPLY) {
 248                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 249                                    ct->proto.gre.stream_timeout);
 250                 /* Also, more likely to be important, and not a probe. */
 251                 set_bit(IPS_ASSURED_BIT, &ct->status);
 252                 ip_conntrack_event_cache(IPCT_STATUS, skb);
 253         } else
 254                 ip_ct_refresh_acct(ct, conntrackinfo, skb,
 255                                    ct->proto.gre.timeout);
 256
 257         return NF_ACCEPT;
 258 }
 259
 260 /* Called when a new connection for this protocol found. */
 261 static int gre_new(struct ip_conntrack *ct,
 262                    const struct sk_buff *skb)
 263 {
 264         DEBUGP(": ");
 265         DUMP_TUPLE_GRE(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 266
 267         /* initialize to sane value.  Ideally a conntrack helper
 268          * (e.g. in case of pptp) is increasing them */
 269         ct->proto.gre.stream_timeout = GRE_STREAM_TIMEOUT;
 270         ct->proto.gre.timeout = GRE_TIMEOUT;
 271
 272         return 1;
 273 }
 274
 275 /* Called when a conntrack entry has already been removed from the hashes
 276  * and is about to be deleted from memory */
 277 static void gre_destroy(struct ip_conntrack *ct)
 278 {
 279         struct ip_conntrack *master = ct->master;
 280         DEBUGP(" entering\n");
 281
 282         if (!master)
 283                 DEBUGP("no master !?!\n");
 284         else
 285                 ip_ct_gre_keymap_destroy(master);
 286 }
 287
 288 /* protocol helper struct */
 289 static struct ip_conntrack_protocol gre = {
 290         .proto           = IPPROTO_GRE,
 291         .name            = "gre",
 292         .pkt_to_tuple    = gre_pkt_to_tuple,
 293         .invert_tuple    = gre_invert_tuple,
 294         .print_tuple     = gre_print_tuple,
 295         .print_conntrack = gre_print_conntrack,
 296         .packet          = gre_packet,
 297         .new             = gre_new,
 298         .destroy         = gre_destroy,
 299         .me              = THIS_MODULE,
 300 #if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
 301     defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
 302         .tuple_to_nfattr = ip_ct_port_tuple_to_nfattr,
 303         .nfattr_to_tuple = ip_ct_port_nfattr_to_tuple,
 304 #endif
 305 };
 306
 307 /* ip_conntrack_proto_gre initialization */
 308 int __init ip_ct_proto_gre_init(void)
 309 {
 310         return ip_conntrack_protocol_register(&gre);
 311 }
 312
 313 /* This cannot be __exit, as it is invoked from ip_conntrack_helper_pptp.c's
 314  * init() code on errors.
 315  */
 316 void ip_ct_proto_gre_fini(void)
 317 {
 318         struct list_head *pos, *n;
 319
 320         /* delete all keymap entries */
 321         write_lock_bh(&ip_ct_gre_lock);
 322         list_for_each_safe(pos, n, &gre_keymap_list) {
 323                 DEBUGP("deleting keymap %p at module unload time\n", pos);
 324                 list_del(pos);
 325                 kfree(pos);
 326         }
 327         write_unlock_bh(&ip_ct_gre_lock);
 328
 329         ip_conntrack_protocol_unregister(&gre);
 330 }
 331
 332 EXPORT_SYMBOL(ip_ct_gre_keymap_add);
 333 EXPORT_SYMBOL(ip_ct_gre_keymap_destroy);