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