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