net/netfilter/nf_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/list.h>
  30 #include <linux/seq_file.h>
  31 #include <linux/in.h>
  32 #include <linux/skbuff.h>
  33
  34 #include <net/netfilter/nf_conntrack_l4proto.h>
  35 #include <net/netfilter/nf_conntrack_helper.h>
  36 #include <net/netfilter/nf_conntrack_core.h>
  37 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  38 #include <linux/netfilter/nf_conntrack_pptp.h>
  39
  40 #define GRE_TIMEOUT             (30 * HZ)
  41 #define GRE_STREAM_TIMEOUT      (180 * HZ)
  42
  43 #if 0
  44 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, __FUNCTION__, ## args)
  45 #else
  46 #define DEBUGP(x, args...)
  47 #endif
  48
  49 static DEFINE_RWLOCK(nf_ct_gre_lock);
  50 static LIST_HEAD(gre_keymap_list);
  51
  52 void nf_ct_gre_keymap_flush(void)
  53 {
  54         struct list_head *pos, *n;
  55
  56         write_lock_bh(&nf_ct_gre_lock);
  57         list_for_each_safe(pos, n, &gre_keymap_list) {
  58                 list_del(pos);
  59                 kfree(pos);
  60         }
  61         write_unlock_bh(&nf_ct_gre_lock);
  62 }
  63 EXPORT_SYMBOL(nf_ct_gre_keymap_flush);
  64
  65 static inline int gre_key_cmpfn(const struct nf_ct_gre_keymap *km,
  66                                 const struct nf_conntrack_tuple *t)
  67 {
  68         return km->tuple.src.l3num == t->src.l3num &&
  69                !memcmp(&km->tuple.src.u3, &t->src.u3, sizeof(t->src.u3)) &&
  70                !memcmp(&km->tuple.dst.u3, &t->dst.u3, sizeof(t->dst.u3)) &&
  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 nf_conntrack_tuple *t)
  77 {
  78         struct nf_ct_gre_keymap *km;
  79         __be16 key = 0;
  80
  81         read_lock_bh(&nf_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(&nf_ct_gre_lock);
  89
  90         DEBUGP("lookup src key 0x%x for ", key);
  91         NF_CT_DUMP_TUPLE(t);
  92
  93         return key;
  94 }
  95
  96 /* add a single keymap entry, associate with specified master ct */
  97 int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
  98                          struct nf_conntrack_tuple *t)
  99 {
 100         struct nf_conn_help *help = nfct_help(ct);
 101         struct nf_ct_gre_keymap **kmp, *km;
 102
 103         kmp = &help->help.ct_pptp_info.keymap[dir];
 104         if (*kmp) {
 105                 /* check whether it's a retransmission */
 106                 list_for_each_entry(km, &gre_keymap_list, list) {
 107                         if (gre_key_cmpfn(km, t) && km == *kmp)
 108                                 return 0;
 109                 }
 110                 DEBUGP("trying to override keymap_%s for ct %p\n",
 111                         dir == IP_CT_DIR_REPLY ? "reply" : "orig", ct);
 112                 return -EEXIST;
 113         }
 114
 115         km = kmalloc(sizeof(*km), GFP_ATOMIC);
 116         if (!km)
 117                 return -ENOMEM;
 118         memcpy(&km->tuple, t, sizeof(*t));
 119         *kmp = km;
 120
 121         DEBUGP("adding new entry %p: ", km);
 122         NF_CT_DUMP_TUPLE(&km->tuple);
 123
 124         write_lock_bh(&nf_ct_gre_lock);
 125         list_add_tail(&km->list, &gre_keymap_list);
 126         write_unlock_bh(&nf_ct_gre_lock);
 127
 128         return 0;
 129 }
 130 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_add);
 131
 132 /* destroy the keymap entries associated with specified master ct */
 133 void nf_ct_gre_keymap_destroy(struct nf_conn *ct)
 134 {
 135         struct nf_conn_help *help = nfct_help(ct);
 136         enum ip_conntrack_dir dir;
 137
 138         DEBUGP("entering for ct %p\n", ct);
 139
 140         write_lock_bh(&nf_ct_gre_lock);
 141         for (dir = IP_CT_DIR_ORIGINAL; dir < IP_CT_DIR_MAX; dir++) {
 142                 if (help->help.ct_pptp_info.keymap[dir]) {
 143                         DEBUGP("removing %p from list\n",
 144                                 help->help.ct_pptp_info.keymap[dir]);
 145                         list_del(&help->help.ct_pptp_info.keymap[dir]->list);
 146                         kfree(help->help.ct_pptp_info.keymap[dir]);
 147                         help->help.ct_pptp_info.keymap[dir] = NULL;
 148                 }
 149         }
 150         write_unlock_bh(&nf_ct_gre_lock);
 151 }
 152 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);
 153
 154 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
 155
 156 /* invert gre part of tuple */
 157 static int gre_invert_tuple(struct nf_conntrack_tuple *tuple,
 158                             const struct nf_conntrack_tuple *orig)
 159 {
 160         tuple->dst.u.gre.key = orig->src.u.gre.key;
 161         tuple->src.u.gre.key = orig->dst.u.gre.key;
 162         return 1;
 163 }
 164
 165 /* gre hdr info to tuple */
 166 static int gre_pkt_to_tuple(const struct sk_buff *skb,
 167                            unsigned int dataoff,
 168                            struct nf_conntrack_tuple *tuple)
 169 {
 170         struct gre_hdr_pptp _pgrehdr, *pgrehdr;
 171         __be16 srckey;
 172         struct gre_hdr _grehdr, *grehdr;
 173
 174         /* first only delinearize old RFC1701 GRE header */
 175         grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
 176         if (!grehdr || grehdr->version != GRE_VERSION_PPTP) {
 177                 /* try to behave like "nf_conntrack_proto_generic" */
 178                 tuple->src.u.all = 0;
 179                 tuple->dst.u.all = 0;
 180                 return 1;
 181         }
 182
 183         /* PPTP header is variable length, only need up to the call_id field */
 184         pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
 185         if (!pgrehdr)
 186                 return 1;
 187
 188         if (ntohs(grehdr->protocol) != GRE_PROTOCOL_PPTP) {
 189                 DEBUGP("GRE_VERSION_PPTP but unknown proto\n");
 190                 return 0;
 191         }
 192
 193         tuple->dst.u.gre.key = pgrehdr->call_id;
 194         srckey = gre_keymap_lookup(tuple);
 195         tuple->src.u.gre.key = srckey;
 196
 197         return 1;
 198 }
 199
 200 /* print gre part of tuple */
 201 static int gre_print_tuple(struct seq_file *s,
 202                            const struct nf_conntrack_tuple *tuple)
 203 {
 204         return seq_printf(s, "srckey=0x%x dstkey=0x%x ",
 205                           ntohs(tuple->src.u.gre.key),
 206                           ntohs(tuple->dst.u.gre.key));
 207 }
 208
 209 /* print private data for conntrack */
 210 static int gre_print_conntrack(struct seq_file *s,
 211                                const struct nf_conn *ct)
 212 {
 213         return seq_printf(s, "timeout=%u, stream_timeout=%u ",
 214                           (ct->proto.gre.timeout / HZ),
 215                           (ct->proto.gre.stream_timeout / HZ));
 216 }
 217
 218 /* Returns verdict for packet, and may modify conntrack */
 219 static int gre_packet(struct nf_conn *ct,
 220                       const struct sk_buff *skb,
 221                       unsigned int dataoff,
 222                       enum ip_conntrack_info ctinfo,
 223                       int pf,
 224                       unsigned int hooknum)
 225 {
 226         /* If we've seen traffic both ways, this is a GRE connection.
 227          * Extend timeout. */
 228         if (ct->status & IPS_SEEN_REPLY) {
 229                 nf_ct_refresh_acct(ct, ctinfo, skb,
 230                                    ct->proto.gre.stream_timeout);
 231                 /* Also, more likely to be important, and not a probe. */
 232                 set_bit(IPS_ASSURED_BIT, &ct->status);
 233                 nf_conntrack_event_cache(IPCT_STATUS, skb);
 234         } else
 235                 nf_ct_refresh_acct(ct, ctinfo, skb,
 236                                    ct->proto.gre.timeout);
 237
 238         return NF_ACCEPT;
 239 }
 240
 241 /* Called when a new connection for this protocol found. */
 242 static int gre_new(struct nf_conn *ct, const struct sk_buff *skb,
 243                    unsigned int dataoff)
 244 {
 245         DEBUGP(": ");
 246         NF_CT_DUMP_TUPLE(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
 247
 248         /* initialize to sane value.  Ideally a conntrack helper
 249          * (e.g. in case of pptp) is increasing them */
 250         ct->proto.gre.stream_timeout = GRE_STREAM_TIMEOUT;
 251         ct->proto.gre.timeout = GRE_TIMEOUT;
 252
 253         return 1;
 254 }
 255
 256 /* Called when a conntrack entry has already been removed from the hashes
 257  * and is about to be deleted from memory */
 258 static void gre_destroy(struct nf_conn *ct)
 259 {
 260         struct nf_conn *master = ct->master;
 261         DEBUGP(" entering\n");
 262
 263         if (!master)
 264                 DEBUGP("no master !?!\n");
 265         else
 266                 nf_ct_gre_keymap_destroy(master);
 267 }
 268
 269 /* protocol helper struct */
 270 static struct nf_conntrack_l4proto nf_conntrack_l4proto_gre4 = {
 271         .l3proto         = AF_INET,
 272         .l4proto         = IPPROTO_GRE,
 273         .name            = "gre",
 274         .pkt_to_tuple    = gre_pkt_to_tuple,
 275         .invert_tuple    = gre_invert_tuple,
 276         .print_tuple     = gre_print_tuple,
 277         .print_conntrack = gre_print_conntrack,
 278         .packet          = gre_packet,
 279         .new             = gre_new,
 280         .destroy         = gre_destroy,
 281         .me              = THIS_MODULE,
 282 #if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
 283         .tuple_to_nfattr = nf_ct_port_tuple_to_nfattr,
 284         .nfattr_to_tuple = nf_ct_port_nfattr_to_tuple,
 285 #endif
 286 };
 287
 288 static int __init nf_ct_proto_gre_init(void)
 289 {
 290         return nf_conntrack_l4proto_register(&nf_conntrack_l4proto_gre4);
 291 }
 292
 293 static void nf_ct_proto_gre_fini(void)
 294 {
 295         nf_conntrack_l4proto_unregister(&nf_conntrack_l4proto_gre4);
 296         nf_ct_gre_keymap_flush();
 297 }
 298
 299 module_init(nf_ct_proto_gre_init);
 300 module_exit(nf_ct_proto_gre_fini);
 301
 302 MODULE_LICENSE("GPL");