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  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  17  *
  18  * TODO: - NAT to a unique tuple, not to TCP source port
  19  *         (needs netfilter tuple reservation)
  20  */
  21
  22 #include <linux/module.h>
  23 #include <linux/tcp.h>
  24
  25 #include <net/netfilter/nf_nat.h>
  26 #include <net/netfilter/nf_nat_helper.h>
  27 #include <net/netfilter/nf_conntrack_helper.h>
  28 #include <net/netfilter/nf_conntrack_expect.h>
  29 #include <net/netfilter/nf_conntrack_zones.h>
  30 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  31 #include <linux/netfilter/nf_conntrack_pptp.h>
  32
  33 #define NF_NAT_PPTP_VERSION "3.0"
  34
  35 #define REQ_CID(req, off)               (*(__be16 *)((char *)(req) + (off)))
  36
  37 MODULE_LICENSE("GPL");
  38 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  39 MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
  40 MODULE_ALIAS("ip_nat_pptp");
  41
  42 static void pptp_nat_expected(struct nf_conn *ct,
  43                               struct nf_conntrack_expect *exp)
  44 {
  45         struct net *net = nf_ct_net(ct);
  46         const struct nf_conn *master = ct->master;
  47         struct nf_conntrack_expect *other_exp;
  48         struct nf_conntrack_tuple t = {};
  49         const struct nf_ct_pptp_master *ct_pptp_info;
  50         const struct nf_nat_pptp *nat_pptp_info;
  51         struct nf_nat_range2 range;
  52         struct nf_conn_nat *nat;
  53
  54         nat = nf_ct_nat_ext_add(ct);
  55         if (WARN_ON_ONCE(!nat))
  56                 return;
  57
  58         nat_pptp_info = &nat->help.nat_pptp_info;
  59         ct_pptp_info = nfct_help_data(master);
  60
  61         /* And here goes the grand finale of corrosion... */
  62         if (exp->dir == IP_CT_DIR_ORIGINAL) {
  63                 pr_debug("we are PNS->PAC\n");
  64                 /* therefore, build tuple for PAC->PNS */
  65                 t.src.l3num = AF_INET;
  66                 t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  67                 t.src.u.gre.key = ct_pptp_info->pac_call_id;
  68                 t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  69                 t.dst.u.gre.key = ct_pptp_info->pns_call_id;
  70                 t.dst.protonum = IPPROTO_GRE;
  71         } else {
  72                 pr_debug("we are PAC->PNS\n");
  73                 /* build tuple for PNS->PAC */
  74                 t.src.l3num = AF_INET;
  75                 t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  76                 t.src.u.gre.key = nat_pptp_info->pns_call_id;
  77                 t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  78                 t.dst.u.gre.key = nat_pptp_info->pac_call_id;
  79                 t.dst.protonum = IPPROTO_GRE;
  80         }
  81
  82         pr_debug("trying to unexpect other dir: ");
  83         nf_ct_dump_tuple_ip(&t);
  84         other_exp = nf_ct_expect_find_get(net, nf_ct_zone(ct), &t);
  85         if (other_exp) {
  86                 nf_ct_unexpect_related(other_exp);
  87                 nf_ct_expect_put(other_exp);
  88                 pr_debug("success\n");
  89         } else {
  90                 pr_debug("not found!\n");
  91         }
  92
  93         /* This must be a fresh one. */
  94         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
  95
  96         /* Change src to where master sends to */
  97         range.flags = NF_NAT_RANGE_MAP_IPS;
  98         range.min_addr = range.max_addr
  99                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3;
 100         if (exp->dir == IP_CT_DIR_ORIGINAL) {
 101                 range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
 102                 range.min_proto = range.max_proto = exp->saved_proto;
 103         }
 104         nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
 105
 106         /* For DST manip, map port here to where it's expected. */
 107         range.flags = NF_NAT_RANGE_MAP_IPS;
 108         range.min_addr = range.max_addr
 109                 = ct->master->tuplehash[!exp->dir].tuple.src.u3;
 110         if (exp->dir == IP_CT_DIR_REPLY) {
 111                 range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
 112                 range.min_proto = range.max_proto = exp->saved_proto;
 113         }
 114         nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
 115 }
 116
 117 /* outbound packets == from PNS to PAC */
 118 static int
 119 pptp_outbound_pkt(struct sk_buff *skb,
 120                   struct nf_conn *ct,
 121                   enum ip_conntrack_info ctinfo,
 122                   unsigned int protoff,
 123                   struct PptpControlHeader *ctlh,
 124                   union pptp_ctrl_union *pptpReq)
 125
 126 {
 127         struct nf_ct_pptp_master *ct_pptp_info;
 128         struct nf_conn_nat *nat = nfct_nat(ct);
 129         struct nf_nat_pptp *nat_pptp_info;
 130         u_int16_t msg;
 131         __be16 new_callid;
 132         unsigned int cid_off;
 133
 134         if (WARN_ON_ONCE(!nat))
 135                 return NF_DROP;
 136
 137         nat_pptp_info = &nat->help.nat_pptp_info;
 138         ct_pptp_info = nfct_help_data(ct);
 139
 140         new_callid = ct_pptp_info->pns_call_id;
 141
 142         switch (msg = ntohs(ctlh->messageType)) {
 143         case PPTP_OUT_CALL_REQUEST:
 144                 cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
 145                 /* FIXME: ideally we would want to reserve a call ID
 146                  * here.  current netfilter NAT core is not able to do
 147                  * this :( For now we use TCP source port. This breaks
 148                  * multiple calls within one control session */
 149
 150                 /* save original call ID in nat_info */
 151                 nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 152
 153                 /* don't use tcph->source since we are at a DSTmanip
 154                  * hook (e.g. PREROUTING) and pkt is not mangled yet */
 155                 new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 156
 157                 /* save new call ID in ct info */
 158                 ct_pptp_info->pns_call_id = new_callid;
 159                 break;
 160         case PPTP_IN_CALL_REPLY:
 161                 cid_off = offsetof(union pptp_ctrl_union, icack.callID);
 162                 break;
 163         case PPTP_CALL_CLEAR_REQUEST:
 164                 cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
 165                 break;
 166         default:
 167                 pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
 168                          pptp_msg_name(msg));
 169                 /* fall through */
 170         case PPTP_SET_LINK_INFO:
 171                 /* only need to NAT in case PAC is behind NAT box */
 172         case PPTP_START_SESSION_REQUEST:
 173         case PPTP_START_SESSION_REPLY:
 174         case PPTP_STOP_SESSION_REQUEST:
 175         case PPTP_STOP_SESSION_REPLY:
 176         case PPTP_ECHO_REQUEST:
 177         case PPTP_ECHO_REPLY:
 178                 /* no need to alter packet */
 179                 return NF_ACCEPT;
 180         }
 181
 182         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 183          * down to here */
 184         pr_debug("altering call id from 0x%04x to 0x%04x\n",
 185                  ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
 186
 187         /* mangle packet */
 188         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
 189                                       cid_off + sizeof(struct pptp_pkt_hdr) +
 190                                       sizeof(struct PptpControlHeader),
 191                                       sizeof(new_callid), (char *)&new_callid,
 192                                       sizeof(new_callid)))
 193                 return NF_DROP;
 194         return NF_ACCEPT;
 195 }
 196
 197 static void
 198 pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
 199              struct nf_conntrack_expect *expect_reply)
 200 {
 201         const struct nf_conn *ct = expect_orig->master;
 202         struct nf_conn_nat *nat = nfct_nat(ct);
 203         struct nf_ct_pptp_master *ct_pptp_info;
 204         struct nf_nat_pptp *nat_pptp_info;
 205
 206         if (WARN_ON_ONCE(!nat))
 207                 return;
 208
 209         nat_pptp_info = &nat->help.nat_pptp_info;
 210         ct_pptp_info = nfct_help_data(ct);
 211
 212         /* save original PAC call ID in nat_info */
 213         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 214
 215         /* alter expectation for PNS->PAC direction */
 216         expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
 217         expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
 218         expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
 219         expect_orig->dir = IP_CT_DIR_ORIGINAL;
 220
 221         /* alter expectation for PAC->PNS direction */
 222         expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
 223         expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
 224         expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
 225         expect_reply->dir = IP_CT_DIR_REPLY;
 226 }
 227
 228 /* inbound packets == from PAC to PNS */
 229 static int
 230 pptp_inbound_pkt(struct sk_buff *skb,
 231                  struct nf_conn *ct,
 232                  enum ip_conntrack_info ctinfo,
 233                  unsigned int protoff,
 234                  struct PptpControlHeader *ctlh,
 235                  union pptp_ctrl_union *pptpReq)
 236 {
 237         const struct nf_nat_pptp *nat_pptp_info;
 238         struct nf_conn_nat *nat = nfct_nat(ct);
 239         u_int16_t msg;
 240         __be16 new_pcid;
 241         unsigned int pcid_off;
 242
 243         if (WARN_ON_ONCE(!nat))
 244                 return NF_DROP;
 245
 246         nat_pptp_info = &nat->help.nat_pptp_info;
 247         new_pcid = nat_pptp_info->pns_call_id;
 248
 249         switch (msg = ntohs(ctlh->messageType)) {
 250         case PPTP_OUT_CALL_REPLY:
 251                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 252                 break;
 253         case PPTP_IN_CALL_CONNECT:
 254                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 255                 break;
 256         case PPTP_IN_CALL_REQUEST:
 257                 /* only need to nat in case PAC is behind NAT box */
 258                 return NF_ACCEPT;
 259         case PPTP_WAN_ERROR_NOTIFY:
 260                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 261                 break;
 262         case PPTP_CALL_DISCONNECT_NOTIFY:
 263                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 264                 break;
 265         case PPTP_SET_LINK_INFO:
 266                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 267                 break;
 268         default:
 269                 pr_debug("unknown inbound packet %s\n", pptp_msg_name(msg));
 270                 /* fall through */
 271         case PPTP_START_SESSION_REQUEST:
 272         case PPTP_START_SESSION_REPLY:
 273         case PPTP_STOP_SESSION_REQUEST:
 274         case PPTP_STOP_SESSION_REPLY:
 275         case PPTP_ECHO_REQUEST:
 276         case PPTP_ECHO_REPLY:
 277                 /* no need to alter packet */
 278                 return NF_ACCEPT;
 279         }
 280
 281         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 282          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 283
 284         /* mangle packet */
 285         pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
 286                  ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
 287
 288         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
 289                                       pcid_off + sizeof(struct pptp_pkt_hdr) +
 290                                       sizeof(struct PptpControlHeader),
 291                                       sizeof(new_pcid), (char *)&new_pcid,
 292                                       sizeof(new_pcid)))
 293                 return NF_DROP;
 294         return NF_ACCEPT;
 295 }
 296
 297 static int __init nf_nat_helper_pptp_init(void)
 298 {
 299         nf_nat_need_gre();
 300
 301         BUG_ON(nf_nat_pptp_hook_outbound != NULL);
 302         RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
 303
 304         BUG_ON(nf_nat_pptp_hook_inbound != NULL);
 305         RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
 306
 307         BUG_ON(nf_nat_pptp_hook_exp_gre != NULL);
 308         RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
 309
 310         BUG_ON(nf_nat_pptp_hook_expectfn != NULL);
 311         RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
 312         return 0;
 313 }
 314
 315 static void __exit nf_nat_helper_pptp_fini(void)
 316 {
 317         RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, NULL);
 318         RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, NULL);
 319         RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, NULL);
 320         RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, NULL);
 321         synchronize_rcu();
 322 }
 323
 324 module_init(nf_nat_helper_pptp_init);
 325 module_exit(nf_nat_helper_pptp_fini);