e1385a0990796f333b3ba5f903b8f3900235a1c1
[linux-2.6.git] / 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 static void pptp_nat_expected(struct nf_conn *ct,
41                               struct nf_conntrack_expect *exp)
42 {
43         struct nf_conn *master = ct->master;
44         struct nf_conntrack_expect *other_exp;
45         struct nf_conntrack_tuple t;
46         struct nf_ct_pptp_master *ct_pptp_info;
47         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(&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         /* hook doesn't matter, but it has to do source manip */
97         nf_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
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         /* hook doesn't matter, but it has to do destination manip */
108         nf_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
109 }
110
111 /* outbound packets == from PNS to PAC */
112 static int
113 pptp_outbound_pkt(struct sk_buff *skb,
114                   struct nf_conn *ct,
115                   enum ip_conntrack_info ctinfo,
116                   struct PptpControlHeader *ctlh,
117                   union pptp_ctrl_union *pptpReq)
118
119 {
120         struct nf_ct_pptp_master *ct_pptp_info;
121         struct nf_nat_pptp *nat_pptp_info;
122         u_int16_t msg;
123         __be16 new_callid;
124         unsigned int cid_off;
125
126         ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
127         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
128
129         new_callid = ct_pptp_info->pns_call_id;
130
131         switch (msg = ntohs(ctlh->messageType)) {
132         case PPTP_OUT_CALL_REQUEST:
133                 cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
134                 /* FIXME: ideally we would want to reserve a call ID
135                  * here.  current netfilter NAT core is not able to do
136                  * this :( For now we use TCP source port. This breaks
137                  * multiple calls within one control session */
138
139                 /* save original call ID in nat_info */
140                 nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
141
142                 /* don't use tcph->source since we are at a DSTmanip
143                  * hook (e.g. PREROUTING) and pkt is not mangled yet */
144                 new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
145
146                 /* save new call ID in ct info */
147                 ct_pptp_info->pns_call_id = new_callid;
148                 break;
149         case PPTP_IN_CALL_REPLY:
150                 cid_off = offsetof(union pptp_ctrl_union, icack.callID);
151                 break;
152         case PPTP_CALL_CLEAR_REQUEST:
153                 cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
154                 break;
155         default:
156                 pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
157                          msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] :
158                                                pptp_msg_name[0]);
159                 /* fall through */
160         case PPTP_SET_LINK_INFO:
161                 /* only need to NAT in case PAC is behind NAT box */
162         case PPTP_START_SESSION_REQUEST:
163         case PPTP_START_SESSION_REPLY:
164         case PPTP_STOP_SESSION_REQUEST:
165         case PPTP_STOP_SESSION_REPLY:
166         case PPTP_ECHO_REQUEST:
167         case PPTP_ECHO_REPLY:
168                 /* no need to alter packet */
169                 return NF_ACCEPT;
170         }
171
172         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
173          * down to here */
174         pr_debug("altering call id from 0x%04x to 0x%04x\n",
175                  ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
176
177         /* mangle packet */
178         if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
179                                      cid_off + sizeof(struct pptp_pkt_hdr) +
180                                      sizeof(struct PptpControlHeader),
181                                      sizeof(new_callid), (char *)&new_callid,
182                                      sizeof(new_callid)) == 0)
183                 return NF_DROP;
184         return NF_ACCEPT;
185 }
186
187 static void
188 pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
189              struct nf_conntrack_expect *expect_reply)
190 {
191         struct nf_conn *ct = expect_orig->master;
192         struct nf_ct_pptp_master *ct_pptp_info;
193         struct nf_nat_pptp *nat_pptp_info;
194
195         ct_pptp_info  = &nfct_help(ct)->help.ct_pptp_info;
196         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
197
198         /* save original PAC call ID in nat_info */
199         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
200
201         /* alter expectation for PNS->PAC direction */
202         expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
203         expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
204         expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
205         expect_orig->dir = IP_CT_DIR_ORIGINAL;
206
207         /* alter expectation for PAC->PNS direction */
208         expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
209         expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
210         expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
211         expect_reply->dir = IP_CT_DIR_REPLY;
212 }
213
214 /* inbound packets == from PAC to PNS */
215 static int
216 pptp_inbound_pkt(struct sk_buff *skb,
217                  struct nf_conn *ct,
218                  enum ip_conntrack_info ctinfo,
219                  struct PptpControlHeader *ctlh,
220                  union pptp_ctrl_union *pptpReq)
221 {
222         struct nf_nat_pptp *nat_pptp_info;
223         u_int16_t msg;
224         __be16 new_pcid;
225         unsigned int pcid_off;
226
227         nat_pptp_info = &nfct_nat(ct)->help.nat_pptp_info;
228         new_pcid = nat_pptp_info->pns_call_id;
229
230         switch (msg = ntohs(ctlh->messageType)) {
231         case PPTP_OUT_CALL_REPLY:
232                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
233                 break;
234         case PPTP_IN_CALL_CONNECT:
235                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
236                 break;
237         case PPTP_IN_CALL_REQUEST:
238                 /* only need to nat in case PAC is behind NAT box */
239                 return NF_ACCEPT;
240         case PPTP_WAN_ERROR_NOTIFY:
241                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
242                 break;
243         case PPTP_CALL_DISCONNECT_NOTIFY:
244                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
245                 break;
246         case PPTP_SET_LINK_INFO:
247                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
248                 break;
249         default:
250                 pr_debug("unknown inbound packet %s\n",
251                          msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] :
252                                                pptp_msg_name[0]);
253                 /* fall through */
254         case PPTP_START_SESSION_REQUEST:
255         case PPTP_START_SESSION_REPLY:
256         case PPTP_STOP_SESSION_REQUEST:
257         case PPTP_STOP_SESSION_REPLY:
258         case PPTP_ECHO_REQUEST:
259         case PPTP_ECHO_REPLY:
260                 /* no need to alter packet */
261                 return NF_ACCEPT;
262         }
263
264         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
265          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
266
267         /* mangle packet */
268         pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
269                  ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
270
271         if (nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
272                                      pcid_off + sizeof(struct pptp_pkt_hdr) +
273                                      sizeof(struct PptpControlHeader),
274                                      sizeof(new_pcid), (char *)&new_pcid,
275                                      sizeof(new_pcid)) == 0)
276                 return NF_DROP;
277         return NF_ACCEPT;
278 }
279
280 static int __init nf_nat_helper_pptp_init(void)
281 {
282         nf_nat_need_gre();
283
284         BUG_ON(rcu_dereference(nf_nat_pptp_hook_outbound));
285         rcu_assign_pointer(nf_nat_pptp_hook_outbound, pptp_outbound_pkt);
286
287         BUG_ON(rcu_dereference(nf_nat_pptp_hook_inbound));
288         rcu_assign_pointer(nf_nat_pptp_hook_inbound, pptp_inbound_pkt);
289
290         BUG_ON(rcu_dereference(nf_nat_pptp_hook_exp_gre));
291         rcu_assign_pointer(nf_nat_pptp_hook_exp_gre, pptp_exp_gre);
292
293         BUG_ON(rcu_dereference(nf_nat_pptp_hook_expectfn));
294         rcu_assign_pointer(nf_nat_pptp_hook_expectfn, pptp_nat_expected);
295         return 0;
296 }
297
298 static void __exit nf_nat_helper_pptp_fini(void)
299 {
300         rcu_assign_pointer(nf_nat_pptp_hook_expectfn, NULL);
301         rcu_assign_pointer(nf_nat_pptp_hook_exp_gre, NULL);
302         rcu_assign_pointer(nf_nat_pptp_hook_inbound, NULL);
303         rcu_assign_pointer(nf_nat_pptp_hook_outbound, NULL);
304         synchronize_rcu();
305 }
306
307 module_init(nf_nat_helper_pptp_init);
308 module_exit(nf_nat_helper_pptp_fini);