net/ipv4/netfilter/nf_nat_pptp.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * nf_nat_pptp.c
   4  *
   5  * NAT support for PPTP (Point to Point Tunneling Protocol).
   6  * PPTP is a a protocol for creating virtual private networks.
   7  * It is a specification defined by Microsoft and some vendors
   8  * working with Microsoft.  PPTP is built on top of a modified
   9  * version of the Internet Generic Routing Encapsulation Protocol.
  10  * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
  11  * PPTP can be found in RFC 2637
  12  *
  13  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
  14  *
  15  * Development of this code funded by Astaro AG (http://www.astaro.com/)
  16  *
  17  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  18  *
  19  * TODO: - NAT to a unique tuple, not to TCP source port
  20  *         (needs netfilter tuple reservation)
  21  */
  22
  23 #include <linux/module.h>
  24 #include <linux/tcp.h>
  25
  26 #include <net/netfilter/nf_nat.h>
  27 #include <net/netfilter/nf_nat_helper.h>
  28 #include <net/netfilter/nf_conntrack_helper.h>
  29 #include <net/netfilter/nf_conntrack_expect.h>
  30 #include <net/netfilter/nf_conntrack_zones.h>
  31 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  32 #include <linux/netfilter/nf_conntrack_pptp.h>
  33
  34 #define NF_NAT_PPTP_VERSION "3.0"
  35
  36 #define REQ_CID(req, off)               (*(__be16 *)((char *)(req) + (off)))
  37
  38 MODULE_LICENSE("GPL");
  39 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  40 MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
  41 MODULE_ALIAS_NF_NAT_HELPER("pptp");
  42
  43 static void pptp_nat_expected(struct nf_conn *ct,
  44                               struct nf_conntrack_expect *exp)
  45 {
  46         struct net *net = nf_ct_net(ct);
  47         const struct nf_conn *master = ct->master;
  48         struct nf_conntrack_expect *other_exp;
  49         struct nf_conntrack_tuple t = {};
  50         const struct nf_ct_pptp_master *ct_pptp_info;
  51         const struct nf_nat_pptp *nat_pptp_info;
  52         struct nf_nat_range2 range;
  53         struct nf_conn_nat *nat;
  54
  55         nat = nf_ct_nat_ext_add(ct);
  56         if (WARN_ON_ONCE(!nat))
  57                 return;
  58
  59         nat_pptp_info = &nat->help.nat_pptp_info;
  60         ct_pptp_info = nfct_help_data(master);
  61
  62         /* And here goes the grand finale of corrosion... */
  63         if (exp->dir == IP_CT_DIR_ORIGINAL) {
  64                 pr_debug("we are PNS->PAC\n");
  65                 /* therefore, build tuple for PAC->PNS */
  66                 t.src.l3num = AF_INET;
  67                 t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  68                 t.src.u.gre.key = ct_pptp_info->pac_call_id;
  69                 t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  70                 t.dst.u.gre.key = ct_pptp_info->pns_call_id;
  71                 t.dst.protonum = IPPROTO_GRE;
  72         } else {
  73                 pr_debug("we are PAC->PNS\n");
  74                 /* build tuple for PNS->PAC */
  75                 t.src.l3num = AF_INET;
  76                 t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
  77                 t.src.u.gre.key = nat_pptp_info->pns_call_id;
  78                 t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
  79                 t.dst.u.gre.key = nat_pptp_info->pac_call_id;
  80                 t.dst.protonum = IPPROTO_GRE;
  81         }
  82
  83         pr_debug("trying to unexpect other dir: ");
  84         nf_ct_dump_tuple_ip(&t);
  85         other_exp = nf_ct_expect_find_get(net, nf_ct_zone(ct), &t);
  86         if (other_exp) {
  87                 nf_ct_unexpect_related(other_exp);
  88                 nf_ct_expect_put(other_exp);
  89                 pr_debug("success\n");
  90         } else {
  91                 pr_debug("not found!\n");
  92         }
  93
  94         /* This must be a fresh one. */
  95         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
  96
  97         /* Change src to where master sends to */
  98         range.flags = NF_NAT_RANGE_MAP_IPS;
  99         range.min_addr = range.max_addr
 100                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3;
 101         if (exp->dir == IP_CT_DIR_ORIGINAL) {
 102                 range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
 103                 range.min_proto = range.max_proto = exp->saved_proto;
 104         }
 105         nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
 106
 107         /* For DST manip, map port here to where it's expected. */
 108         range.flags = NF_NAT_RANGE_MAP_IPS;
 109         range.min_addr = range.max_addr
 110                 = ct->master->tuplehash[!exp->dir].tuple.src.u3;
 111         if (exp->dir == IP_CT_DIR_REPLY) {
 112                 range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
 113                 range.min_proto = range.max_proto = exp->saved_proto;
 114         }
 115         nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
 116 }
 117
 118 /* outbound packets == from PNS to PAC */
 119 static int
 120 pptp_outbound_pkt(struct sk_buff *skb,
 121                   struct nf_conn *ct,
 122                   enum ip_conntrack_info ctinfo,
 123                   unsigned int protoff,
 124                   struct PptpControlHeader *ctlh,
 125                   union pptp_ctrl_union *pptpReq)
 126
 127 {
 128         struct nf_ct_pptp_master *ct_pptp_info;
 129         struct nf_conn_nat *nat = nfct_nat(ct);
 130         struct nf_nat_pptp *nat_pptp_info;
 131         u_int16_t msg;
 132         __be16 new_callid;
 133         unsigned int cid_off;
 134
 135         if (WARN_ON_ONCE(!nat))
 136                 return NF_DROP;
 137
 138         nat_pptp_info = &nat->help.nat_pptp_info;
 139         ct_pptp_info = nfct_help_data(ct);
 140
 141         new_callid = ct_pptp_info->pns_call_id;
 142
 143         switch (msg = ntohs(ctlh->messageType)) {
 144         case PPTP_OUT_CALL_REQUEST:
 145                 cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
 146                 /* FIXME: ideally we would want to reserve a call ID
 147                  * here.  current netfilter NAT core is not able to do
 148                  * this :( For now we use TCP source port. This breaks
 149                  * multiple calls within one control session */
 150
 151                 /* save original call ID in nat_info */
 152                 nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 153
 154                 /* don't use tcph->source since we are at a DSTmanip
 155                  * hook (e.g. PREROUTING) and pkt is not mangled yet */
 156                 new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 157
 158                 /* save new call ID in ct info */
 159                 ct_pptp_info->pns_call_id = new_callid;
 160                 break;
 161         case PPTP_IN_CALL_REPLY:
 162                 cid_off = offsetof(union pptp_ctrl_union, icack.callID);
 163                 break;
 164         case PPTP_CALL_CLEAR_REQUEST:
 165                 cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
 166                 break;
 167         default:
 168                 pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
 169                          pptp_msg_name(msg));
 170                 /* fall through */
 171         case PPTP_SET_LINK_INFO:
 172                 /* only need to NAT in case PAC is behind NAT box */
 173         case PPTP_START_SESSION_REQUEST:
 174         case PPTP_START_SESSION_REPLY:
 175         case PPTP_STOP_SESSION_REQUEST:
 176         case PPTP_STOP_SESSION_REPLY:
 177         case PPTP_ECHO_REQUEST:
 178         case PPTP_ECHO_REPLY:
 179                 /* no need to alter packet */
 180                 return NF_ACCEPT;
 181         }
 182
 183         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 184          * down to here */
 185         pr_debug("altering call id from 0x%04x to 0x%04x\n",
 186                  ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
 187
 188         /* mangle packet */
 189         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
 190                                       cid_off + sizeof(struct pptp_pkt_hdr) +
 191                                       sizeof(struct PptpControlHeader),
 192                                       sizeof(new_callid), (char *)&new_callid,
 193                                       sizeof(new_callid)))
 194                 return NF_DROP;
 195         return NF_ACCEPT;
 196 }
 197
 198 static void
 199 pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
 200              struct nf_conntrack_expect *expect_reply)
 201 {
 202         const struct nf_conn *ct = expect_orig->master;
 203         struct nf_conn_nat *nat = nfct_nat(ct);
 204         struct nf_ct_pptp_master *ct_pptp_info;
 205         struct nf_nat_pptp *nat_pptp_info;
 206
 207         if (WARN_ON_ONCE(!nat))
 208                 return;
 209
 210         nat_pptp_info = &nat->help.nat_pptp_info;
 211         ct_pptp_info = nfct_help_data(ct);
 212
 213         /* save original PAC call ID in nat_info */
 214         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 215
 216         /* alter expectation for PNS->PAC direction */
 217         expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
 218         expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
 219         expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
 220         expect_orig->dir = IP_CT_DIR_ORIGINAL;
 221
 222         /* alter expectation for PAC->PNS direction */
 223         expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
 224         expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
 225         expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
 226         expect_reply->dir = IP_CT_DIR_REPLY;
 227 }
 228
 229 /* inbound packets == from PAC to PNS */
 230 static int
 231 pptp_inbound_pkt(struct sk_buff *skb,
 232                  struct nf_conn *ct,
 233                  enum ip_conntrack_info ctinfo,
 234                  unsigned int protoff,
 235                  struct PptpControlHeader *ctlh,
 236                  union pptp_ctrl_union *pptpReq)
 237 {
 238         const struct nf_nat_pptp *nat_pptp_info;
 239         struct nf_conn_nat *nat = nfct_nat(ct);
 240         u_int16_t msg;
 241         __be16 new_pcid;
 242         unsigned int pcid_off;
 243
 244         if (WARN_ON_ONCE(!nat))
 245                 return NF_DROP;
 246
 247         nat_pptp_info = &nat->help.nat_pptp_info;
 248         new_pcid = nat_pptp_info->pns_call_id;
 249
 250         switch (msg = ntohs(ctlh->messageType)) {
 251         case PPTP_OUT_CALL_REPLY:
 252                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 253                 break;
 254         case PPTP_IN_CALL_CONNECT:
 255                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 256                 break;
 257         case PPTP_IN_CALL_REQUEST:
 258                 /* only need to nat in case PAC is behind NAT box */
 259                 return NF_ACCEPT;
 260         case PPTP_WAN_ERROR_NOTIFY:
 261                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 262                 break;
 263         case PPTP_CALL_DISCONNECT_NOTIFY:
 264                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 265                 break;
 266         case PPTP_SET_LINK_INFO:
 267                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 268                 break;
 269         default:
 270                 pr_debug("unknown inbound packet %s\n", pptp_msg_name(msg));
 271                 /* fall through */
 272         case PPTP_START_SESSION_REQUEST:
 273         case PPTP_START_SESSION_REPLY:
 274         case PPTP_STOP_SESSION_REQUEST:
 275         case PPTP_STOP_SESSION_REPLY:
 276         case PPTP_ECHO_REQUEST:
 277         case PPTP_ECHO_REPLY:
 278                 /* no need to alter packet */
 279                 return NF_ACCEPT;
 280         }
 281
 282         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 283          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 284
 285         /* mangle packet */
 286         pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
 287                  ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
 288
 289         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
 290                                       pcid_off + sizeof(struct pptp_pkt_hdr) +
 291                                       sizeof(struct PptpControlHeader),
 292                                       sizeof(new_pcid), (char *)&new_pcid,
 293                                       sizeof(new_pcid)))
 294                 return NF_DROP;
 295         return NF_ACCEPT;
 296 }
 297
 298 static int __init nf_nat_helper_pptp_init(void)
 299 {
 300         BUG_ON(nf_nat_pptp_hook_outbound != NULL);
 301         RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
 302
 303         BUG_ON(nf_nat_pptp_hook_inbound != NULL);
 304         RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
 305
 306         BUG_ON(nf_nat_pptp_hook_exp_gre != NULL);
 307         RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
 308
 309         BUG_ON(nf_nat_pptp_hook_expectfn != NULL);
 310         RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
 311         return 0;
 312 }
 313
 314 static void __exit nf_nat_helper_pptp_fini(void)
 315 {
 316         RCU_INIT_POINTER(nf_nat_pptp_hook_expectfn, NULL);
 317         RCU_INIT_POINTER(nf_nat_pptp_hook_exp_gre, NULL);
 318         RCU_INIT_POINTER(nf_nat_pptp_hook_inbound, NULL);
 319         RCU_INIT_POINTER(nf_nat_pptp_hook_outbound, NULL);
 320         synchronize_rcu();
 321 }
 322
 323 module_init(nf_nat_helper_pptp_init);
 324 module_exit(nf_nat_helper_pptp_fini);