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0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  * Connection tracking support for PPTP (Point to Point Tunneling Protocol).
0004  * PPTP is a protocol for creating virtual private networks.
0005  * It is a specification defined by Microsoft and some vendors
0006  * working with Microsoft.  PPTP is built on top of a modified
0007  * version of the Internet Generic Routing Encapsulation Protocol.
0008  * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
0009  * PPTP can be found in RFC 2637
0010  *
0011  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
0012  *
0013  * Development of this code funded by Astaro AG (http://www.astaro.com/)
0014  *
0015  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
0016  *
0017  * Limitations:
0018  *   - We blindly assume that control connections are always
0019  *     established in PNS->PAC direction.  This is a violation
0020  *     of RFC 2637
0021  *   - We can only support one single call within each session
0022  * TODO:
0023  *   - testing of incoming PPTP calls
0024  */
0025 
0026 #include <linux/module.h>
0027 #include <linux/skbuff.h>
0028 #include <linux/in.h>
0029 #include <linux/tcp.h>
0030 
0031 #include <net/netfilter/nf_conntrack.h>
0032 #include <net/netfilter/nf_conntrack_core.h>
0033 #include <net/netfilter/nf_conntrack_helper.h>
0034 #include <net/netfilter/nf_conntrack_zones.h>
0035 #include <linux/netfilter/nf_conntrack_proto_gre.h>
0036 #include <linux/netfilter/nf_conntrack_pptp.h>
0037 
0038 #define NF_CT_PPTP_VERSION "3.1"
0039 
0040 MODULE_LICENSE("GPL");
0041 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
0042 MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
0043 MODULE_ALIAS("ip_conntrack_pptp");
0044 MODULE_ALIAS_NFCT_HELPER("pptp");
0045 
0046 static DEFINE_SPINLOCK(nf_pptp_lock);
0047 
0048 const struct nf_nat_pptp_hook __rcu *nf_nat_pptp_hook;
0049 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook);
0050 
0051 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
0052 /* PptpControlMessageType names */
0053 static const char *const pptp_msg_name_array[PPTP_MSG_MAX + 1] = {
0054     [0]             = "UNKNOWN_MESSAGE",
0055     [PPTP_START_SESSION_REQUEST]    = "START_SESSION_REQUEST",
0056     [PPTP_START_SESSION_REPLY]  = "START_SESSION_REPLY",
0057     [PPTP_STOP_SESSION_REQUEST] = "STOP_SESSION_REQUEST",
0058     [PPTP_STOP_SESSION_REPLY]   = "STOP_SESSION_REPLY",
0059     [PPTP_ECHO_REQUEST]     = "ECHO_REQUEST",
0060     [PPTP_ECHO_REPLY]       = "ECHO_REPLY",
0061     [PPTP_OUT_CALL_REQUEST]     = "OUT_CALL_REQUEST",
0062     [PPTP_OUT_CALL_REPLY]       = "OUT_CALL_REPLY",
0063     [PPTP_IN_CALL_REQUEST]      = "IN_CALL_REQUEST",
0064     [PPTP_IN_CALL_REPLY]        = "IN_CALL_REPLY",
0065     [PPTP_IN_CALL_CONNECT]      = "IN_CALL_CONNECT",
0066     [PPTP_CALL_CLEAR_REQUEST]   = "CALL_CLEAR_REQUEST",
0067     [PPTP_CALL_DISCONNECT_NOTIFY]   = "CALL_DISCONNECT_NOTIFY",
0068     [PPTP_WAN_ERROR_NOTIFY]     = "WAN_ERROR_NOTIFY",
0069     [PPTP_SET_LINK_INFO]        = "SET_LINK_INFO"
0070 };
0071 
0072 const char *pptp_msg_name(u_int16_t msg)
0073 {
0074     if (msg > PPTP_MSG_MAX)
0075         return pptp_msg_name_array[0];
0076 
0077     return pptp_msg_name_array[msg];
0078 }
0079 EXPORT_SYMBOL(pptp_msg_name);
0080 #endif
0081 
0082 #define SECS *HZ
0083 #define MINS * 60 SECS
0084 #define HOURS * 60 MINS
0085 
0086 #define PPTP_GRE_TIMEOUT        (10 MINS)
0087 #define PPTP_GRE_STREAM_TIMEOUT     (5 HOURS)
0088 
0089 static void pptp_expectfn(struct nf_conn *ct,
0090              struct nf_conntrack_expect *exp)
0091 {
0092     const struct nf_nat_pptp_hook *hook;
0093     struct net *net = nf_ct_net(ct);
0094     pr_debug("increasing timeouts\n");
0095 
0096     /* increase timeout of GRE data channel conntrack entry */
0097     ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
0098     ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
0099 
0100     /* Can you see how rusty this code is, compared with the pre-2.6.11
0101      * one? That's what happened to my shiny newnat of 2002 ;( -HW */
0102 
0103     hook = rcu_dereference(nf_nat_pptp_hook);
0104     if (hook && ct->master->status & IPS_NAT_MASK)
0105         hook->expectfn(ct, exp);
0106     else {
0107         struct nf_conntrack_tuple inv_t;
0108         struct nf_conntrack_expect *exp_other;
0109 
0110         /* obviously this tuple inversion only works until you do NAT */
0111         nf_ct_invert_tuple(&inv_t, &exp->tuple);
0112         pr_debug("trying to unexpect other dir: ");
0113         nf_ct_dump_tuple(&inv_t);
0114 
0115         exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
0116         if (exp_other) {
0117             /* delete other expectation.  */
0118             pr_debug("found\n");
0119             nf_ct_unexpect_related(exp_other);
0120             nf_ct_expect_put(exp_other);
0121         } else {
0122             pr_debug("not found\n");
0123         }
0124     }
0125 }
0126 
0127 static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
0128                   const struct nf_conntrack_tuple *t)
0129 {
0130     const struct nf_conntrack_tuple_hash *h;
0131     const struct nf_conntrack_zone *zone;
0132     struct nf_conntrack_expect *exp;
0133     struct nf_conn *sibling;
0134 
0135     pr_debug("trying to timeout ct or exp for tuple ");
0136     nf_ct_dump_tuple(t);
0137 
0138     zone = nf_ct_zone(ct);
0139     h = nf_conntrack_find_get(net, zone, t);
0140     if (h)  {
0141         sibling = nf_ct_tuplehash_to_ctrack(h);
0142         pr_debug("setting timeout of conntrack %p to 0\n", sibling);
0143         sibling->proto.gre.timeout    = 0;
0144         sibling->proto.gre.stream_timeout = 0;
0145         nf_ct_kill(sibling);
0146         nf_ct_put(sibling);
0147         return 1;
0148     } else {
0149         exp = nf_ct_expect_find_get(net, zone, t);
0150         if (exp) {
0151             pr_debug("unexpect_related of expect %p\n", exp);
0152             nf_ct_unexpect_related(exp);
0153             nf_ct_expect_put(exp);
0154             return 1;
0155         }
0156     }
0157     return 0;
0158 }
0159 
0160 /* timeout GRE data connections */
0161 static void pptp_destroy_siblings(struct nf_conn *ct)
0162 {
0163     struct net *net = nf_ct_net(ct);
0164     const struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
0165     struct nf_conntrack_tuple t;
0166 
0167     nf_ct_gre_keymap_destroy(ct);
0168 
0169     /* try original (pns->pac) tuple */
0170     memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
0171     t.dst.protonum = IPPROTO_GRE;
0172     t.src.u.gre.key = ct_pptp_info->pns_call_id;
0173     t.dst.u.gre.key = ct_pptp_info->pac_call_id;
0174     if (!destroy_sibling_or_exp(net, ct, &t))
0175         pr_debug("failed to timeout original pns->pac ct/exp\n");
0176 
0177     /* try reply (pac->pns) tuple */
0178     memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
0179     t.dst.protonum = IPPROTO_GRE;
0180     t.src.u.gre.key = ct_pptp_info->pac_call_id;
0181     t.dst.u.gre.key = ct_pptp_info->pns_call_id;
0182     if (!destroy_sibling_or_exp(net, ct, &t))
0183         pr_debug("failed to timeout reply pac->pns ct/exp\n");
0184 }
0185 
0186 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
0187 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
0188 {
0189     struct nf_conntrack_expect *exp_orig, *exp_reply;
0190     const struct nf_nat_pptp_hook *hook;
0191     enum ip_conntrack_dir dir;
0192     int ret = 1;
0193 
0194     exp_orig = nf_ct_expect_alloc(ct);
0195     if (exp_orig == NULL)
0196         goto out;
0197 
0198     exp_reply = nf_ct_expect_alloc(ct);
0199     if (exp_reply == NULL)
0200         goto out_put_orig;
0201 
0202     /* original direction, PNS->PAC */
0203     dir = IP_CT_DIR_ORIGINAL;
0204     nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
0205               nf_ct_l3num(ct),
0206               &ct->tuplehash[dir].tuple.src.u3,
0207               &ct->tuplehash[dir].tuple.dst.u3,
0208               IPPROTO_GRE, &peer_callid, &callid);
0209     exp_orig->expectfn = pptp_expectfn;
0210 
0211     /* reply direction, PAC->PNS */
0212     dir = IP_CT_DIR_REPLY;
0213     nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
0214               nf_ct_l3num(ct),
0215               &ct->tuplehash[dir].tuple.src.u3,
0216               &ct->tuplehash[dir].tuple.dst.u3,
0217               IPPROTO_GRE, &callid, &peer_callid);
0218     exp_reply->expectfn = pptp_expectfn;
0219 
0220     hook = rcu_dereference(nf_nat_pptp_hook);
0221     if (hook && ct->status & IPS_NAT_MASK)
0222         hook->exp_gre(exp_orig, exp_reply);
0223     if (nf_ct_expect_related(exp_orig, 0) != 0)
0224         goto out_put_both;
0225     if (nf_ct_expect_related(exp_reply, 0) != 0)
0226         goto out_unexpect_orig;
0227 
0228     /* Add GRE keymap entries */
0229     if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
0230         goto out_unexpect_both;
0231     if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
0232         nf_ct_gre_keymap_destroy(ct);
0233         goto out_unexpect_both;
0234     }
0235     ret = 0;
0236 
0237 out_put_both:
0238     nf_ct_expect_put(exp_reply);
0239 out_put_orig:
0240     nf_ct_expect_put(exp_orig);
0241 out:
0242     return ret;
0243 
0244 out_unexpect_both:
0245     nf_ct_unexpect_related(exp_reply);
0246 out_unexpect_orig:
0247     nf_ct_unexpect_related(exp_orig);
0248     goto out_put_both;
0249 }
0250 
0251 static int
0252 pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
0253          struct PptpControlHeader *ctlh,
0254          union pptp_ctrl_union *pptpReq,
0255          unsigned int reqlen,
0256          struct nf_conn *ct,
0257          enum ip_conntrack_info ctinfo)
0258 {
0259     struct nf_ct_pptp_master *info = nfct_help_data(ct);
0260     const struct nf_nat_pptp_hook *hook;
0261     u_int16_t msg;
0262     __be16 cid = 0, pcid = 0;
0263 
0264     msg = ntohs(ctlh->messageType);
0265     pr_debug("inbound control message %s\n", pptp_msg_name(msg));
0266 
0267     switch (msg) {
0268     case PPTP_START_SESSION_REPLY:
0269         /* server confirms new control session */
0270         if (info->sstate < PPTP_SESSION_REQUESTED)
0271             goto invalid;
0272         if (pptpReq->srep.resultCode == PPTP_START_OK)
0273             info->sstate = PPTP_SESSION_CONFIRMED;
0274         else
0275             info->sstate = PPTP_SESSION_ERROR;
0276         break;
0277 
0278     case PPTP_STOP_SESSION_REPLY:
0279         /* server confirms end of control session */
0280         if (info->sstate > PPTP_SESSION_STOPREQ)
0281             goto invalid;
0282         if (pptpReq->strep.resultCode == PPTP_STOP_OK)
0283             info->sstate = PPTP_SESSION_NONE;
0284         else
0285             info->sstate = PPTP_SESSION_ERROR;
0286         break;
0287 
0288     case PPTP_OUT_CALL_REPLY:
0289         /* server accepted call, we now expect GRE frames */
0290         if (info->sstate != PPTP_SESSION_CONFIRMED)
0291             goto invalid;
0292         if (info->cstate != PPTP_CALL_OUT_REQ &&
0293             info->cstate != PPTP_CALL_OUT_CONF)
0294             goto invalid;
0295 
0296         cid = pptpReq->ocack.callID;
0297         pcid = pptpReq->ocack.peersCallID;
0298         if (info->pns_call_id != pcid)
0299             goto invalid;
0300         pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name(msg),
0301              ntohs(cid), ntohs(pcid));
0302 
0303         if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
0304             info->cstate = PPTP_CALL_OUT_CONF;
0305             info->pac_call_id = cid;
0306             exp_gre(ct, cid, pcid);
0307         } else
0308             info->cstate = PPTP_CALL_NONE;
0309         break;
0310 
0311     case PPTP_IN_CALL_REQUEST:
0312         /* server tells us about incoming call request */
0313         if (info->sstate != PPTP_SESSION_CONFIRMED)
0314             goto invalid;
0315 
0316         cid = pptpReq->icreq.callID;
0317         pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
0318         info->cstate = PPTP_CALL_IN_REQ;
0319         info->pac_call_id = cid;
0320         break;
0321 
0322     case PPTP_IN_CALL_CONNECT:
0323         /* server tells us about incoming call established */
0324         if (info->sstate != PPTP_SESSION_CONFIRMED)
0325             goto invalid;
0326         if (info->cstate != PPTP_CALL_IN_REP &&
0327             info->cstate != PPTP_CALL_IN_CONF)
0328             goto invalid;
0329 
0330         pcid = pptpReq->iccon.peersCallID;
0331         cid = info->pac_call_id;
0332 
0333         if (info->pns_call_id != pcid)
0334             goto invalid;
0335 
0336         pr_debug("%s, PCID=%X\n", pptp_msg_name(msg), ntohs(pcid));
0337         info->cstate = PPTP_CALL_IN_CONF;
0338 
0339         /* we expect a GRE connection from PAC to PNS */
0340         exp_gre(ct, cid, pcid);
0341         break;
0342 
0343     case PPTP_CALL_DISCONNECT_NOTIFY:
0344         /* server confirms disconnect */
0345         cid = pptpReq->disc.callID;
0346         pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
0347         info->cstate = PPTP_CALL_NONE;
0348 
0349         /* untrack this call id, unexpect GRE packets */
0350         pptp_destroy_siblings(ct);
0351         break;
0352 
0353     case PPTP_WAN_ERROR_NOTIFY:
0354     case PPTP_SET_LINK_INFO:
0355     case PPTP_ECHO_REQUEST:
0356     case PPTP_ECHO_REPLY:
0357         /* I don't have to explain these ;) */
0358         break;
0359 
0360     default:
0361         goto invalid;
0362     }
0363 
0364     hook = rcu_dereference(nf_nat_pptp_hook);
0365     if (hook && ct->status & IPS_NAT_MASK)
0366         return hook->inbound(skb, ct, ctinfo, protoff, ctlh, pptpReq);
0367     return NF_ACCEPT;
0368 
0369 invalid:
0370     pr_debug("invalid %s: type=%d cid=%u pcid=%u "
0371          "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
0372          pptp_msg_name(msg),
0373          msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
0374          ntohs(info->pns_call_id), ntohs(info->pac_call_id));
0375     return NF_ACCEPT;
0376 }
0377 
0378 static int
0379 pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
0380           struct PptpControlHeader *ctlh,
0381           union pptp_ctrl_union *pptpReq,
0382           unsigned int reqlen,
0383           struct nf_conn *ct,
0384           enum ip_conntrack_info ctinfo)
0385 {
0386     struct nf_ct_pptp_master *info = nfct_help_data(ct);
0387     const struct nf_nat_pptp_hook *hook;
0388     u_int16_t msg;
0389     __be16 cid = 0, pcid = 0;
0390 
0391     msg = ntohs(ctlh->messageType);
0392     pr_debug("outbound control message %s\n", pptp_msg_name(msg));
0393 
0394     switch (msg) {
0395     case PPTP_START_SESSION_REQUEST:
0396         /* client requests for new control session */
0397         if (info->sstate != PPTP_SESSION_NONE)
0398             goto invalid;
0399         info->sstate = PPTP_SESSION_REQUESTED;
0400         break;
0401 
0402     case PPTP_STOP_SESSION_REQUEST:
0403         /* client requests end of control session */
0404         info->sstate = PPTP_SESSION_STOPREQ;
0405         break;
0406 
0407     case PPTP_OUT_CALL_REQUEST:
0408         /* client initiating connection to server */
0409         if (info->sstate != PPTP_SESSION_CONFIRMED)
0410             goto invalid;
0411         info->cstate = PPTP_CALL_OUT_REQ;
0412         /* track PNS call id */
0413         cid = pptpReq->ocreq.callID;
0414         pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
0415         info->pns_call_id = cid;
0416         break;
0417 
0418     case PPTP_IN_CALL_REPLY:
0419         /* client answers incoming call */
0420         if (info->cstate != PPTP_CALL_IN_REQ &&
0421             info->cstate != PPTP_CALL_IN_REP)
0422             goto invalid;
0423 
0424         cid = pptpReq->icack.callID;
0425         pcid = pptpReq->icack.peersCallID;
0426         if (info->pac_call_id != pcid)
0427             goto invalid;
0428         pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name(msg),
0429              ntohs(cid), ntohs(pcid));
0430 
0431         if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
0432             /* part two of the three-way handshake */
0433             info->cstate = PPTP_CALL_IN_REP;
0434             info->pns_call_id = cid;
0435         } else
0436             info->cstate = PPTP_CALL_NONE;
0437         break;
0438 
0439     case PPTP_CALL_CLEAR_REQUEST:
0440         /* client requests hangup of call */
0441         if (info->sstate != PPTP_SESSION_CONFIRMED)
0442             goto invalid;
0443         /* FUTURE: iterate over all calls and check if
0444          * call ID is valid.  We don't do this without newnat,
0445          * because we only know about last call */
0446         info->cstate = PPTP_CALL_CLEAR_REQ;
0447         break;
0448 
0449     case PPTP_SET_LINK_INFO:
0450     case PPTP_ECHO_REQUEST:
0451     case PPTP_ECHO_REPLY:
0452         /* I don't have to explain these ;) */
0453         break;
0454 
0455     default:
0456         goto invalid;
0457     }
0458 
0459     hook = rcu_dereference(nf_nat_pptp_hook);
0460     if (hook && ct->status & IPS_NAT_MASK)
0461         return hook->outbound(skb, ct, ctinfo, protoff, ctlh, pptpReq);
0462     return NF_ACCEPT;
0463 
0464 invalid:
0465     pr_debug("invalid %s: type=%d cid=%u pcid=%u "
0466          "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
0467          pptp_msg_name(msg),
0468          msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
0469          ntohs(info->pns_call_id), ntohs(info->pac_call_id));
0470     return NF_ACCEPT;
0471 }
0472 
0473 static const unsigned int pptp_msg_size[] = {
0474     [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
0475     [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
0476     [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
0477     [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
0478     [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
0479     [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
0480     [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
0481     [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
0482     [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
0483     [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
0484     [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
0485     [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
0486     [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
0487 };
0488 
0489 /* track caller id inside control connection, call expect_related */
0490 static int
0491 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
0492             struct nf_conn *ct, enum ip_conntrack_info ctinfo)
0493 
0494 {
0495     int dir = CTINFO2DIR(ctinfo);
0496     const struct nf_ct_pptp_master *info = nfct_help_data(ct);
0497     const struct tcphdr *tcph;
0498     struct tcphdr _tcph;
0499     const struct pptp_pkt_hdr *pptph;
0500     struct pptp_pkt_hdr _pptph;
0501     struct PptpControlHeader _ctlh, *ctlh;
0502     union pptp_ctrl_union _pptpReq, *pptpReq;
0503     unsigned int tcplen = skb->len - protoff;
0504     unsigned int datalen, reqlen, nexthdr_off;
0505     int oldsstate, oldcstate;
0506     int ret;
0507     u_int16_t msg;
0508 
0509 #if IS_ENABLED(CONFIG_NF_NAT)
0510     if (!nf_ct_is_confirmed(ct) && (ct->status & IPS_NAT_MASK)) {
0511         struct nf_conn_nat *nat = nf_ct_ext_find(ct, NF_CT_EXT_NAT);
0512 
0513         if (!nat && !nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC))
0514             return NF_DROP;
0515     }
0516 #endif
0517     /* don't do any tracking before tcp handshake complete */
0518     if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
0519         return NF_ACCEPT;
0520 
0521     nexthdr_off = protoff;
0522     tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
0523     if (!tcph)
0524         return NF_ACCEPT;
0525 
0526     nexthdr_off += tcph->doff * 4;
0527     datalen = tcplen - tcph->doff * 4;
0528 
0529     pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
0530     if (!pptph) {
0531         pr_debug("no full PPTP header, can't track\n");
0532         return NF_ACCEPT;
0533     }
0534     nexthdr_off += sizeof(_pptph);
0535     datalen -= sizeof(_pptph);
0536 
0537     /* if it's not a control message we can't do anything with it */
0538     if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
0539         ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
0540         pr_debug("not a control packet\n");
0541         return NF_ACCEPT;
0542     }
0543 
0544     ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
0545     if (!ctlh)
0546         return NF_ACCEPT;
0547     nexthdr_off += sizeof(_ctlh);
0548     datalen -= sizeof(_ctlh);
0549 
0550     reqlen = datalen;
0551     msg = ntohs(ctlh->messageType);
0552     if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
0553         return NF_ACCEPT;
0554     if (reqlen > sizeof(*pptpReq))
0555         reqlen = sizeof(*pptpReq);
0556 
0557     pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
0558     if (!pptpReq)
0559         return NF_ACCEPT;
0560 
0561     oldsstate = info->sstate;
0562     oldcstate = info->cstate;
0563 
0564     spin_lock_bh(&nf_pptp_lock);
0565 
0566     /* FIXME: We just blindly assume that the control connection is always
0567      * established from PNS->PAC.  However, RFC makes no guarantee */
0568     if (dir == IP_CT_DIR_ORIGINAL)
0569         /* client -> server (PNS -> PAC) */
0570         ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
0571                     ctinfo);
0572     else
0573         /* server -> client (PAC -> PNS) */
0574         ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
0575                        ctinfo);
0576     pr_debug("sstate: %d->%d, cstate: %d->%d\n",
0577          oldsstate, info->sstate, oldcstate, info->cstate);
0578     spin_unlock_bh(&nf_pptp_lock);
0579 
0580     return ret;
0581 }
0582 
0583 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
0584     .max_expected   = 2,
0585     .timeout    = 5 * 60,
0586 };
0587 
0588 /* control protocol helper */
0589 static struct nf_conntrack_helper pptp __read_mostly = {
0590     .name           = "pptp",
0591     .me         = THIS_MODULE,
0592     .tuple.src.l3num    = AF_INET,
0593     .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
0594     .tuple.dst.protonum = IPPROTO_TCP,
0595     .help           = conntrack_pptp_help,
0596     .destroy        = pptp_destroy_siblings,
0597     .expect_policy      = &pptp_exp_policy,
0598 };
0599 
0600 static int __init nf_conntrack_pptp_init(void)
0601 {
0602     NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_pptp_master));
0603 
0604     return nf_conntrack_helper_register(&pptp);
0605 }
0606 
0607 static void __exit nf_conntrack_pptp_fini(void)
0608 {
0609     nf_conntrack_helper_unregister(&pptp);
0610 }
0611 
0612 module_init(nf_conntrack_pptp_init);
0613 module_exit(nf_conntrack_pptp_fini);
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