1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * nf_nat_pptp.c
4 *
5 * NAT support for PPTP (Point to Point Tunneling Protocol).
6 * PPTP is a protocol for creating virtual private networks.
7 * It is a specification defined by Microsoft and some vendors
8 * working with Microsoft. PPTP is built on top of a modified
9 * version of the Internet Generic Routing Encapsulation Protocol.
10 * GRE is defined in RFC 1701 and RFC 1702. Documentation of
11 * PPTP can be found in RFC 2637
12 *
13 * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
14 *
15 * Development of this code funded by Astaro AG (http://www.astaro.com/)
16 *
17 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
18 *
19 * TODO: - NAT to a unique tuple, not to TCP source port
20 * (needs netfilter tuple reservation)
21 */
22
23#include <linux/module.h>
24#include <linux/tcp.h>
25
26#include <net/netfilter/nf_nat.h>
27#include <net/netfilter/nf_nat_helper.h>
28#include <net/netfilter/nf_conntrack_helper.h>
29#include <net/netfilter/nf_conntrack_expect.h>
30#include <net/netfilter/nf_conntrack_zones.h>
31#include <linux/netfilter/nf_conntrack_proto_gre.h>
32#include <linux/netfilter/nf_conntrack_pptp.h>
33
34#define NF_NAT_PPTP_VERSION "3.0"
35
36#define REQ_CID(req, off) (*(__be16 *)((char *)(req) + (off)))
37
38MODULE_LICENSE("GPL");
39MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
40MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
41MODULE_ALIAS_NF_NAT_HELPER("pptp");
42
43static void pptp_nat_expected(struct nf_conn *ct,
44 struct nf_conntrack_expect *exp)
45{
46 struct net *net = nf_ct_net(ct);
47 const struct nf_conn *master = ct->master;
48 struct nf_conntrack_expect *other_exp;
49 struct nf_conntrack_tuple t = {};
50 const struct nf_ct_pptp_master *ct_pptp_info;
51 const struct nf_nat_pptp *nat_pptp_info;
52 struct nf_nat_range2 range;
53 struct nf_conn_nat *nat;
54
55 nat = nf_ct_nat_ext_add(ct);
56 if (WARN_ON_ONCE(!nat))
57 return;
58
59 nat_pptp_info = &nat->help.nat_pptp_info;
60 ct_pptp_info = nfct_help_data(ct: master);
61
62 /* And here goes the grand finale of corrosion... */
63 if (exp->dir == IP_CT_DIR_ORIGINAL) {
64 pr_debug("we are PNS->PAC\n");
65 /* therefore, build tuple for PAC->PNS */
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 = ct_pptp_info->pac_call_id;
69 t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
70 t.dst.u.gre.key = ct_pptp_info->pns_call_id;
71 t.dst.protonum = IPPROTO_GRE;
72 } else {
73 pr_debug("we are PAC->PNS\n");
74 /* build tuple for PNS->PAC */
75 t.src.l3num = AF_INET;
76 t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
77 t.src.u.gre.key = nat_pptp_info->pns_call_id;
78 t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
79 t.dst.u.gre.key = nat_pptp_info->pac_call_id;
80 t.dst.protonum = IPPROTO_GRE;
81 }
82
83 pr_debug("trying to unexpect other dir: ");
84 nf_ct_dump_tuple_ip(t: &t);
85 other_exp = nf_ct_expect_find_get(net, zone: nf_ct_zone(ct), tuple: &t);
86 if (other_exp) {
87 nf_ct_unexpect_related(exp: other_exp);
88 nf_ct_expect_put(exp: other_exp);
89 pr_debug("success\n");
90 } else {
91 pr_debug("not found!\n");
92 }
93
94 /* This must be a fresh one. */
95 BUG_ON(ct->status & IPS_NAT_DONE_MASK);
96
97 /* Change src to where master sends to */
98 range.flags = NF_NAT_RANGE_MAP_IPS;
99 range.min_addr = range.max_addr
100 = ct->master->tuplehash[!exp->dir].tuple.dst.u3;
101 if (exp->dir == IP_CT_DIR_ORIGINAL) {
102 range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
103 range.min_proto = range.max_proto = exp->saved_proto;
104 }
105 nf_nat_setup_info(ct, range: &range, maniptype: NF_NAT_MANIP_SRC);
106
107 /* For DST manip, map port here to where it's expected. */
108 range.flags = NF_NAT_RANGE_MAP_IPS;
109 range.min_addr = range.max_addr
110 = ct->master->tuplehash[!exp->dir].tuple.src.u3;
111 if (exp->dir == IP_CT_DIR_REPLY) {
112 range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
113 range.min_proto = range.max_proto = exp->saved_proto;
114 }
115 nf_nat_setup_info(ct, range: &range, maniptype: NF_NAT_MANIP_DST);
116}
117
118/* outbound packets == from PNS to PAC */
119static int
120pptp_outbound_pkt(struct sk_buff *skb,
121 struct nf_conn *ct,
122 enum ip_conntrack_info ctinfo,
123 unsigned int protoff,
124 struct PptpControlHeader *ctlh,
125 union pptp_ctrl_union *pptpReq)
126
127{
128 struct nf_ct_pptp_master *ct_pptp_info;
129 struct nf_conn_nat *nat = nfct_nat(ct);
130 struct nf_nat_pptp *nat_pptp_info;
131 u_int16_t msg;
132 __be16 new_callid;
133 unsigned int cid_off;
134
135 if (WARN_ON_ONCE(!nat))
136 return NF_DROP;
137
138 nat_pptp_info = &nat->help.nat_pptp_info;
139 ct_pptp_info = nfct_help_data(ct);
140
141 new_callid = ct_pptp_info->pns_call_id;
142
143 switch (msg = ntohs(ctlh->messageType)) {
144 case PPTP_OUT_CALL_REQUEST:
145 cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
146 /* FIXME: ideally we would want to reserve a call ID
147 * here. current netfilter NAT core is not able to do
148 * this :( For now we use TCP source port. This breaks
149 * multiple calls within one control session */
150
151 /* save original call ID in nat_info */
152 nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
153
154 /* don't use tcph->source since we are at a DSTmanip
155 * hook (e.g. PREROUTING) and pkt is not mangled yet */
156 new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
157
158 /* save new call ID in ct info */
159 ct_pptp_info->pns_call_id = new_callid;
160 break;
161 case PPTP_IN_CALL_REPLY:
162 cid_off = offsetof(union pptp_ctrl_union, icack.callID);
163 break;
164 case PPTP_CALL_CLEAR_REQUEST:
165 cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
166 break;
167 default:
168 pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
169 pptp_msg_name(msg));
170 fallthrough;
171 case PPTP_SET_LINK_INFO:
172 /* only need to NAT in case PAC is behind NAT box */
173 case PPTP_START_SESSION_REQUEST:
174 case PPTP_START_SESSION_REPLY:
175 case PPTP_STOP_SESSION_REQUEST:
176 case PPTP_STOP_SESSION_REPLY:
177 case PPTP_ECHO_REQUEST:
178 case PPTP_ECHO_REPLY:
179 /* no need to alter packet */
180 return NF_ACCEPT;
181 }
182
183 /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
184 * down to here */
185 pr_debug("altering call id from 0x%04x to 0x%04x\n",
186 ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
187
188 /* mangle packet */
189 if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
190 match_offset: cid_off + sizeof(struct pptp_pkt_hdr) +
191 sizeof(struct PptpControlHeader),
192 match_len: sizeof(new_callid), rep_buffer: (char *)&new_callid,
193 rep_len: sizeof(new_callid)))
194 return NF_DROP;
195 return NF_ACCEPT;
196}
197
198static void
199pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
200 struct nf_conntrack_expect *expect_reply)
201{
202 const struct nf_conn *ct = expect_orig->master;
203 struct nf_conn_nat *nat = nfct_nat(ct);
204 struct nf_ct_pptp_master *ct_pptp_info;
205 struct nf_nat_pptp *nat_pptp_info;
206
207 if (WARN_ON_ONCE(!nat))
208 return;
209
210 nat_pptp_info = &nat->help.nat_pptp_info;
211 ct_pptp_info = nfct_help_data(ct);
212
213 /* save original PAC call ID in nat_info */
214 nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
215
216 /* alter expectation for PNS->PAC direction */
217 expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
218 expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
219 expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
220 expect_orig->dir = IP_CT_DIR_ORIGINAL;
221
222 /* alter expectation for PAC->PNS direction */
223 expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
224 expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
225 expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
226 expect_reply->dir = IP_CT_DIR_REPLY;
227}
228
229/* inbound packets == from PAC to PNS */
230static int
231pptp_inbound_pkt(struct sk_buff *skb,
232 struct nf_conn *ct,
233 enum ip_conntrack_info ctinfo,
234 unsigned int protoff,
235 struct PptpControlHeader *ctlh,
236 union pptp_ctrl_union *pptpReq)
237{
238 const struct nf_nat_pptp *nat_pptp_info;
239 struct nf_conn_nat *nat = nfct_nat(ct);
240 u_int16_t msg;
241 __be16 new_pcid;
242 unsigned int pcid_off;
243
244 if (WARN_ON_ONCE(!nat))
245 return NF_DROP;
246
247 nat_pptp_info = &nat->help.nat_pptp_info;
248 new_pcid = nat_pptp_info->pns_call_id;
249
250 switch (msg = ntohs(ctlh->messageType)) {
251 case PPTP_OUT_CALL_REPLY:
252 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
253 break;
254 case PPTP_IN_CALL_CONNECT:
255 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
256 break;
257 case PPTP_IN_CALL_REQUEST:
258 /* only need to nat in case PAC is behind NAT box */
259 return NF_ACCEPT;
260 case PPTP_WAN_ERROR_NOTIFY:
261 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
262 break;
263 case PPTP_CALL_DISCONNECT_NOTIFY:
264 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
265 break;
266 case PPTP_SET_LINK_INFO:
267 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
268 break;
269 default:
270 pr_debug("unknown inbound packet %s\n", pptp_msg_name(msg));
271 fallthrough;
272 case PPTP_START_SESSION_REQUEST:
273 case PPTP_START_SESSION_REPLY:
274 case PPTP_STOP_SESSION_REQUEST:
275 case PPTP_STOP_SESSION_REPLY:
276 case PPTP_ECHO_REQUEST:
277 case PPTP_ECHO_REPLY:
278 /* no need to alter packet */
279 return NF_ACCEPT;
280 }
281
282 /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
283 * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
284
285 /* mangle packet */
286 pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
287 ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
288
289 if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
290 match_offset: pcid_off + sizeof(struct pptp_pkt_hdr) +
291 sizeof(struct PptpControlHeader),
292 match_len: sizeof(new_pcid), rep_buffer: (char *)&new_pcid,
293 rep_len: sizeof(new_pcid)))
294 return NF_DROP;
295 return NF_ACCEPT;
296}
297
298static const struct nf_nat_pptp_hook pptp_hooks = {
299 .outbound = pptp_outbound_pkt,
300 .inbound = pptp_inbound_pkt,
301 .exp_gre = pptp_exp_gre,
302 .expectfn = pptp_nat_expected,
303};
304
305static int __init nf_nat_helper_pptp_init(void)
306{
307 WARN_ON(nf_nat_pptp_hook != NULL);
308 RCU_INIT_POINTER(nf_nat_pptp_hook, &pptp_hooks);
309
310 return 0;
311}
312
313static void __exit nf_nat_helper_pptp_fini(void)
314{
315 RCU_INIT_POINTER(nf_nat_pptp_hook, NULL);
316 synchronize_rcu();
317}
318
319module_init(nf_nat_helper_pptp_init);
320module_exit(nf_nat_helper_pptp_fini);
321

source code of linux/net/ipv4/netfilter/nf_nat_pptp.c