release/src-rt-6.x.4708/linux/linux-2.6.36/net/ipv4/netfilter/nf_nat_pptp.c

   1 /*
   2  * nf_nat_pptp.c
   3  *
   4  * NAT support for PPTP (Point to Point Tunneling Protocol).
   5  * PPTP is a a protocol for creating virtual private networks.
   6  * It is a specification defined by Microsoft and some vendors
   7  * working with Microsoft.  PPTP is built on top of a modified
   8  * version of the Internet Generic Routing Encapsulation Protocol.
   9  * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
  10  * PPTP can be found in RFC 2637
  11  *
  12  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
  13  *
  14  * Development of this code funded by Astaro AG (http://www.astaro.com/)
  15  *
  16  * TODO: - NAT to a unique tuple, not to TCP source port
  17  *         (needs netfilter tuple reservation)
  18  */
  19
  20 #include <linux/module.h>
  21 #include <linux/tcp.h>
  22
  23 #include <net/netfilter/nf_nat.h>
  24 #include <net/netfilter/nf_nat_helper.h>
  25 #include <net/netfilter/nf_nat_rule.h>
  26 #include <net/netfilter/nf_conntrack_helper.h>
  27 #include <net/netfilter/nf_conntrack_expect.h>
  28 #include <net/netfilter/nf_conntrack_zones.h>
  29 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  30 #include <linux/netfilter/nf_conntrack_pptp.h>
  31
  32 #define NF_NAT_PPTP_VERSION "3.0"
  33
  34 #define REQ_CID(req, off)               (*(__be16 *)((char *)(req) + (off)))
  35
  36 MODULE_LICENSE("GPL");
  37 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  38 MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
  39 MODULE_ALIAS("ip_nat_pptp");
  40
  41 static void pptp_nat_expected(struct nf_conn *ct,
  42                               struct nf_conntrack_expect *exp)
  43 {
  44         struct net *net = nf_ct_net(ct);
  45         const struct nf_conn *master = ct->master;
  46         struct nf_conntrack_expect *other_exp;
  47         struct nf_conntrack_tuple t;
  48         const struct nf_ct_pptp_master *ct_pptp_info;
  49         const struct nf_nat_pptp *nat_pptp_info;
  50         struct nf_nat_range range;
  51
  52         ct_pptp_info = &nfct_help(master)->help.ct_pptp_info;
  53         nat_pptp_info = &nfct_nat(master)->help.nat_pptp_info;
  54
  55         /* And here goes the grand finale of corrosion... */
  56         if (exp->dir == IP_CT_DIR_ORIGINAL) {
  57                 pr_debug("we are PNS->PAC\n");
  58                 /* therefore, build tuple for PAC->PNS */
  59                 t.src.l3num = AF_INET;
  60                 t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  61                 t.src.u.gre.key = ct_pptp_info->pac_call_id;
  62                 t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  63                 t.dst.u.gre.key = ct_pptp_info->pns_call_id;
  64                 t.dst.protonum = IPPROTO_GRE;
  65         } else {
  66                 pr_debug("we are PAC->PNS\n");
  67                 /* build tuple for PNS->PAC */
  68                 t.src.l3num = AF_INET;
  69                 t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  70                 t.src.u.gre.key = nat_pptp_info->pns_call_id;
  71                 t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  72                 t.dst.u.gre.key = nat_pptp_info->pac_call_id;
  73                 t.dst.protonum = IPPROTO_GRE;
  74         }
  75
  76         pr_debug("trying to unexpect other dir: ");
  77         nf_ct_dump_tuple_ip(&t);
  78         other_exp = nf_ct_expect_find_get(net, nf_ct_zone(ct), &t);
  79         if (other_exp) {
  80                 nf_ct_unexpect_related(other_exp);
  81                 nf_ct_expect_put(other_exp);
  82                 pr_debug("success\n");
  83         } else {
  84                 pr_debug("not found!\n");
  85         }
  86
  87         /* This must be a fresh one. */
  88         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
  89
  90         /* Change src to where master sends to */
  91         range.flags = IP_NAT_RANGE_MAP_IPS;
  92         range.min_ip = range.max_ip
  93                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  94         if (exp->dir == IP_CT_DIR_ORIGINAL) {
  95                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
  96                 range.min = range.max = exp->saved_proto;
  97         }
  98         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_SRC);
  99
 100         /* For DST manip, map port here to where it's expected. */
 101         range.flags = IP_NAT_RANGE_MAP_IPS;
 102         range.min_ip = range.max_ip
 103                 = ct->master->tuplehash[!exp->dir].tuple.src.u3.ip;
 104         if (exp->dir == IP_CT_DIR_REPLY) {
 105                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 106                 range.min = range.max = exp->saved_proto;
 107         }
 108         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_DST);
 109 }
 110
 111 /* outbound packets == from PNS to PAC */
 112 static int
 113 pptp_outbound_pkt(struct sk_buff *skb,
 114                   struct nf_conn *ct,
 115                   enum ip_conntrack_info ctinfo,
 116                   struct PptpControlHeader *ctlh,
 117                   union pptp_ctrl_union *pptpReq)
 118
 119 {
 120         struct nf_ct_pptp_master *ct_pptp_info;
 121         struct nf_nat_pptp *nat_pptp_info;
 122         u_int16_t msg;
 123         __be16 new_callid;
 124         unsigned int cid_off;
 125
 126         ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
 127         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 128
 129         new_callid = ct_pptp_info->pns_call_id;
 130
 131         switch (msg = ntohs(ctlh->messageType)) {
 132         case PPTP_OUT_CALL_REQUEST:
 133                 cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
 134
 135                 /* save original call ID in nat_info */
 136                 nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 137
 138                 /* don't use tcph->source since we are at a DSTmanip
 139                  * hook (e.g. PREROUTING) and pkt is not mangled yet */
 140                 new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 141
 142                 /* save new call ID in ct info */
 143                 ct_pptp_info->pns_call_id = new_callid;
 144                 break;
 145         case PPTP_IN_CALL_REPLY:
 146                 cid_off = offsetof(union pptp_ctrl_union, icack.callID);
 147                 break;
 148         case PPTP_CALL_CLEAR_REQUEST:
 149                 cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
 150                 break;
 151         default:
 152                 pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
 153                          msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] :
 154                                                pptp_msg_name[0]);
 155                 /* fall through */
 156         case PPTP_SET_LINK_INFO:
 157                 /* only need to NAT in case PAC is behind NAT box */
 158         case PPTP_START_SESSION_REQUEST:
 159         case PPTP_START_SESSION_REPLY:
 160         case PPTP_STOP_SESSION_REQUEST:
 161         case PPTP_STOP_SESSION_REPLY:
 162         case PPTP_ECHO_REQUEST:
 163         case PPTP_ECHO_REPLY:
 164                 /* no need to alter packet */
 165                 return NF_ACCEPT;
 166         }
 167
 168         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 169          * down to here */
 170         pr_debug("altering call id from 0x%04x to 0x%04x\n",
 171                  ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
 172
 173         /* mangle packet */
 174         if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
 175                                      cid_off + sizeof(struct pptp_pkt_hdr) +
 176                                      sizeof(struct PptpControlHeader),
 177                                      sizeof(new_callid), (char *)&new_callid,
 178                                      sizeof(new_callid)) == 0)
 179                 return NF_DROP;
 180         return NF_ACCEPT;
 181 }
 182
 183 static void
 184 pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
 185              struct nf_conntrack_expect *expect_reply)
 186 {
 187         const struct nf_conn *ct = expect_orig->master;
 188         struct nf_ct_pptp_master *ct_pptp_info;
 189         struct nf_nat_pptp *nat_pptp_info;
 190
 191         ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
 192         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 193
 194         /* save original PAC call ID in nat_info */
 195         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 196
 197         /* alter expectation for PNS->PAC direction */
 198         expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
 199         expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
 200         expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
 201         expect_orig->dir = IP_CT_DIR_ORIGINAL;
 202
 203         /* alter expectation for PAC->PNS direction */
 204         expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
 205         expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
 206         expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
 207         expect_reply->dir = IP_CT_DIR_REPLY;
 208 }
 209
 210 /* inbound packets == from PAC to PNS */
 211 static int
 212 pptp_inbound_pkt(struct sk_buff *skb,
 213                  struct nf_conn *ct,
 214                  enum ip_conntrack_info ctinfo,
 215                  struct PptpControlHeader *ctlh,
 216                  union pptp_ctrl_union *pptpReq)
 217 {
 218         const struct nf_nat_pptp *nat_pptp_info;
 219         u_int16_t msg;
 220         __be16 new_pcid;
 221         unsigned int pcid_off;
 222
 223         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 224         new_pcid = nat_pptp_info->pns_call_id;
 225
 226         switch (msg = ntohs(ctlh->messageType)) {
 227         case PPTP_OUT_CALL_REPLY:
 228                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 229                 break;
 230         case PPTP_IN_CALL_CONNECT:
 231                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 232                 break;
 233         case PPTP_IN_CALL_REQUEST:
 234                 /* only need to nat in case PAC is behind NAT box */
 235                 return NF_ACCEPT;
 236         case PPTP_WAN_ERROR_NOTIFY:
 237                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 238                 break;
 239         case PPTP_CALL_DISCONNECT_NOTIFY:
 240                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 241                 break;
 242         case PPTP_SET_LINK_INFO:
 243                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 244                 break;
 245         default:
 246                 pr_debug("unknown inbound packet %s\n",
 247                          msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] :
 248                                                pptp_msg_name[0]);
 249                 /* fall through */
 250         case PPTP_START_SESSION_REQUEST:
 251         case PPTP_START_SESSION_REPLY:
 252         case PPTP_STOP_SESSION_REQUEST:
 253         case PPTP_STOP_SESSION_REPLY:
 254         case PPTP_ECHO_REQUEST:
 255         case PPTP_ECHO_REPLY:
 256                 /* no need to alter packet */
 257                 return NF_ACCEPT;
 258         }
 259
 260         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 261          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 262
 263         /* mangle packet */
 264         pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
 265                  ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
 266
 267         if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
 268                                      pcid_off + sizeof(struct pptp_pkt_hdr) +
 269                                      sizeof(struct PptpControlHeader),
 270                                      sizeof(new_pcid), (char *)&new_pcid,
 271                                      sizeof(new_pcid)) == 0)
 272                 return NF_DROP;
 273         return NF_ACCEPT;
 274 }
 275
 276 static int __init nf_nat_helper_pptp_init(void)
 277 {
 278         nf_nat_need_gre();
 279
 280         BUG_ON(nf_nat_pptp_hook_outbound != NULL);
 281         rcu_assign_pointer(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
 282
 283         BUG_ON(nf_nat_pptp_hook_inbound != NULL);
 284         rcu_assign_pointer(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
 285
 286         BUG_ON(nf_nat_pptp_hook_exp_gre != NULL);
 287         rcu_assign_pointer(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
 288
 289         BUG_ON(nf_nat_pptp_hook_expectfn != NULL);
 290         rcu_assign_pointer(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
 291         return 0;
 292 }
 293
 294 static void __exit nf_nat_helper_pptp_fini(void)
 295 {
 296         rcu_assign_pointer(nf_nat_pptp_hook_expectfn, NULL);
 297         rcu_assign_pointer(nf_nat_pptp_hook_exp_gre, NULL);
 298         rcu_assign_pointer(nf_nat_pptp_hook_inbound, NULL);
 299         rcu_assign_pointer(nf_nat_pptp_hook_outbound, NULL);
 300         synchronize_rcu();
 301 }
 302
 303 module_init(nf_nat_helper_pptp_init);
 304 module_exit(nf_nat_helper_pptp_fini);