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 <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 #if 0
  41 extern const char *pptp_msg_name[];
  42 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, \
  43                                        __FUNCTION__, ## args)
  44 #else
  45 #define DEBUGP(format, args...)
  46 #endif
  47
  48 static void pptp_nat_expected(struct nf_conn *ct,
  49                               struct nf_conntrack_expect *exp)
  50 {
  51         struct nf_conn *master = ct->master;
  52         struct nf_conntrack_expect *other_exp;
  53         struct nf_conntrack_tuple t;
  54         struct nf_ct_pptp_master *ct_pptp_info;
  55         struct nf_nat_pptp *nat_pptp_info;
  56         struct ip_nat_range range;
  57
  58         ct_pptp_info = &nfct_help(master)->help.ct_pptp_info;
  59         nat_pptp_info = &nfct_nat(master)->help.nat_pptp_info;
  60
  61         /* And here goes the grand finale of corrosion... */
  62         if (exp->dir == IP_CT_DIR_ORIGINAL) {
  63                 DEBUGP("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                 DEBUGP("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         DEBUGP("trying to unexpect other dir: ");
  83         NF_CT_DUMP_TUPLE(&t);
  84         other_exp = nf_conntrack_expect_find_get(&t);
  85         if (other_exp) {
  86                 nf_conntrack_unexpect_related(other_exp);
  87                 nf_conntrack_expect_put(other_exp);
  88                 DEBUGP("success\n");
  89         } else {
  90                 DEBUGP("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 = IP_NAT_RANGE_MAP_IPS;
  98         range.min_ip = range.max_ip
  99                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
 100         if (exp->dir == IP_CT_DIR_ORIGINAL) {
 101                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 102                 range.min = range.max = exp->saved_proto;
 103         }
 104         /* hook doesn't matter, but it has to do source manip */
 105         nf_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
 106
 107         /* For DST manip, map port here to where it's expected. */
 108         range.flags = IP_NAT_RANGE_MAP_IPS;
 109         range.min_ip = range.max_ip
 110                 = ct->master->tuplehash[!exp->dir].tuple.src.u3.ip;
 111         if (exp->dir == IP_CT_DIR_REPLY) {
 112                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 113                 range.min = range.max = exp->saved_proto;
 114         }
 115         /* hook doesn't matter, but it has to do destination manip */
 116         nf_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
 117 }
 118
 119 /* outbound packets == from PNS to PAC */
 120 static int
 121 pptp_outbound_pkt(struct sk_buff **pskb,
 122                   struct nf_conn *ct,
 123                   enum ip_conntrack_info ctinfo,
 124                   struct PptpControlHeader *ctlh,
 125                   union pptp_ctrl_union *pptpReq)
 126
 127 {
 128         struct nf_ct_pptp_master *ct_pptp_info;
 129         struct nf_nat_pptp *nat_pptp_info;
 130         u_int16_t msg;
 131         __be16 new_callid;
 132         unsigned int cid_off;
 133
 134         ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
 135         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 136
 137         new_callid = ct_pptp_info->pns_call_id;
 138
 139         switch (msg = ntohs(ctlh->messageType)) {
 140         case PPTP_OUT_CALL_REQUEST:
 141                 cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
 142                 /* FIXME: ideally we would want to reserve a call ID
 143                  * here.  current netfilter NAT core is not able to do
 144                  * this :( For now we use TCP source port. This breaks
 145                  * multiple calls within one control session */
 146
 147                 /* save original call ID in nat_info */
 148                 nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 149
 150                 /* don't use tcph->source since we are at a DSTmanip
 151                  * hook (e.g. PREROUTING) and pkt is not mangled yet */
 152                 new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 153
 154                 /* save new call ID in ct info */
 155                 ct_pptp_info->pns_call_id = new_callid;
 156                 break;
 157         case PPTP_IN_CALL_REPLY:
 158                 cid_off = offsetof(union pptp_ctrl_union, icack.callID);
 159                 break;
 160         case PPTP_CALL_CLEAR_REQUEST:
 161                 cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
 162                 break;
 163         default:
 164                 DEBUGP("unknown outbound packet 0x%04x:%s\n", msg,
 165                       (msg <= PPTP_MSG_MAX)?
 166                       pptp_msg_name[msg]:pptp_msg_name[0]);
 167                 /* fall through */
 168         case PPTP_SET_LINK_INFO:
 169                 /* only need to NAT in case PAC is behind NAT box */
 170         case PPTP_START_SESSION_REQUEST:
 171         case PPTP_START_SESSION_REPLY:
 172         case PPTP_STOP_SESSION_REQUEST:
 173         case PPTP_STOP_SESSION_REPLY:
 174         case PPTP_ECHO_REQUEST:
 175         case PPTP_ECHO_REPLY:
 176                 /* no need to alter packet */
 177                 return NF_ACCEPT;
 178         }
 179
 180         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 181          * down to here */
 182         DEBUGP("altering call id from 0x%04x to 0x%04x\n",
 183                 ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
 184
 185         /* mangle packet */
 186         if (nf_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 187                                      cid_off + sizeof(struct pptp_pkt_hdr) +
 188                                      sizeof(struct PptpControlHeader),
 189                                      sizeof(new_callid), (char *)&new_callid,
 190                                      sizeof(new_callid)) == 0)
 191                 return NF_DROP;
 192         return NF_ACCEPT;
 193 }
 194
 195 static void
 196 pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
 197              struct nf_conntrack_expect *expect_reply)
 198 {
 199         struct nf_conn *ct = expect_orig->master;
 200         struct nf_ct_pptp_master *ct_pptp_info;
 201         struct nf_nat_pptp *nat_pptp_info;
 202
 203         ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
 204         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 205
 206         /* save original PAC call ID in nat_info */
 207         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 208
 209         /* alter expectation for PNS->PAC direction */
 210         expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
 211         expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
 212         expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
 213         expect_orig->dir = IP_CT_DIR_ORIGINAL;
 214
 215         /* alter expectation for PAC->PNS direction */
 216         expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
 217         expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
 218         expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
 219         expect_reply->dir = IP_CT_DIR_REPLY;
 220 }
 221
 222 /* inbound packets == from PAC to PNS */
 223 static int
 224 pptp_inbound_pkt(struct sk_buff **pskb,
 225                  struct nf_conn *ct,
 226                  enum ip_conntrack_info ctinfo,
 227                  struct PptpControlHeader *ctlh,
 228                  union pptp_ctrl_union *pptpReq)
 229 {
 230         struct nf_nat_pptp *nat_pptp_info;
 231         u_int16_t msg;
 232         __be16 new_pcid;
 233         unsigned int pcid_off;
 234
 235         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
 236         new_pcid = nat_pptp_info->pns_call_id;
 237
 238         switch (msg = ntohs(ctlh->messageType)) {
 239         case PPTP_OUT_CALL_REPLY:
 240                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 241                 break;
 242         case PPTP_IN_CALL_CONNECT:
 243                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 244                 break;
 245         case PPTP_IN_CALL_REQUEST:
 246                 /* only need to nat in case PAC is behind NAT box */
 247                 return NF_ACCEPT;
 248         case PPTP_WAN_ERROR_NOTIFY:
 249                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 250                 break;
 251         case PPTP_CALL_DISCONNECT_NOTIFY:
 252                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 253                 break;
 254         case PPTP_SET_LINK_INFO:
 255                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 256                 break;
 257         default:
 258                 DEBUGP("unknown inbound packet %s\n", (msg <= PPTP_MSG_MAX)?
 259                         pptp_msg_name[msg]:pptp_msg_name[0]);
 260                 /* fall through */
 261         case PPTP_START_SESSION_REQUEST:
 262         case PPTP_START_SESSION_REPLY:
 263         case PPTP_STOP_SESSION_REQUEST:
 264         case PPTP_STOP_SESSION_REPLY:
 265         case PPTP_ECHO_REQUEST:
 266         case PPTP_ECHO_REPLY:
 267                 /* no need to alter packet */
 268                 return NF_ACCEPT;
 269         }
 270
 271         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 272          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 273
 274         /* mangle packet */
 275         DEBUGP("altering peer call id from 0x%04x to 0x%04x\n",
 276                 ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
 277
 278         if (nf_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 279                                      pcid_off + sizeof(struct pptp_pkt_hdr) +
 280                                      sizeof(struct PptpControlHeader),
 281                                      sizeof(new_pcid), (char *)&new_pcid,
 282                                      sizeof(new_pcid)) == 0)
 283                 return NF_DROP;
 284         return NF_ACCEPT;
 285 }
 286
 287 static int __init nf_nat_helper_pptp_init(void)
 288 {
 289         nf_nat_need_gre();
 290
 291         BUG_ON(rcu_dereference(nf_nat_pptp_hook_outbound));
 292         rcu_assign_pointer(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
 293
 294         BUG_ON(rcu_dereference(nf_nat_pptp_hook_inbound));
 295         rcu_assign_pointer(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
 296
 297         BUG_ON(rcu_dereference(nf_nat_pptp_hook_exp_gre));
 298         rcu_assign_pointer(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
 299
 300         BUG_ON(rcu_dereference(nf_nat_pptp_hook_expectfn));
 301         rcu_assign_pointer(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
 302         return 0;
 303 }
 304
 305 static void __exit nf_nat_helper_pptp_fini(void)
 306 {
 307         rcu_assign_pointer(nf_nat_pptp_hook_expectfn, NULL);
 308         rcu_assign_pointer(nf_nat_pptp_hook_exp_gre, NULL);
 309         rcu_assign_pointer(nf_nat_pptp_hook_inbound, NULL);
 310         rcu_assign_pointer(nf_nat_pptp_hook_outbound, NULL);
 311         synchronize_rcu();
 312 }
 313
 314 module_init(nf_nat_helper_pptp_init);
 315 module_exit(nf_nat_helper_pptp_fini);