// SPDX-License-Identifier: GPL-2.0-only
/*
* nf_nat_pptp.c
*
* NAT support for PPTP (Point to Point Tunneling Protocol).
* PPTP is a protocol for creating virtual private networks.
* It is a specification defined by Microsoft and some vendors
* working with Microsoft. PPTP is built on top of a modified
* version of the Internet Generic Routing Encapsulation Protocol.
* GRE is defined in RFC 1701 and RFC 1702. Documentation of
* PPTP can be found in RFC 2637
*
* (C) 2000-2005 by Harald Welte <[email protected]>
*
* Development of this code funded by Astaro AG (http://www.astaro.com/)
*
* (C) 2006-2012 Patrick McHardy <[email protected]>
*
* TODO: - NAT to a unique tuple, not to TCP source port
* (needs netfilter tuple reservation)
*/
#include <linux/module.h>
#include <linux/tcp.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_helper.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_conntrack_zones.h>
#include <linux/netfilter/nf_conntrack_proto_gre.h>
#include <linux/netfilter/nf_conntrack_pptp.h>
#define NF_NAT_PPTP_VERSION "3.0"
#define REQ_CID(req, off) (*(__be16 *)((char *)(req) + (off)))
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <[email protected]>");
MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
MODULE_ALIAS_NF_NAT_HELPER("pptp");
static void pptp_nat_expected(struct nf_conn *ct,
struct nf_conntrack_expect *exp)
{
struct net *net = nf_ct_net(ct);
const struct nf_conn *master = ct->master;
struct nf_conntrack_expect *other_exp;
struct nf_conntrack_tuple t = {};
const struct nf_ct_pptp_master *ct_pptp_info;
const struct nf_nat_pptp *nat_pptp_info;
struct nf_nat_range2 range;
struct nf_conn_nat *nat;
nat = nf_ct_nat_ext_add(ct);
if (WARN_ON_ONCE(!nat))
return;
nat_pptp_info = &nat->help.nat_pptp_info;
ct_pptp_info = nfct_help_data(master);
/* And here goes the grand finale of corrosion... */
if (exp->dir == IP_CT_DIR_ORIGINAL) {
pr_debug("we are PNS->PAC\n");
/* therefore, build tuple for PAC->PNS */
t.src.l3num = AF_INET;
t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
t.src.u.gre.key = ct_pptp_info->pac_call_id;
t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
t.dst.u.gre.key = ct_pptp_info->pns_call_id;
t.dst.protonum = IPPROTO_GRE;
} else {
pr_debug("we are PAC->PNS\n");
/* build tuple for PNS->PAC */
t.src.l3num = AF_INET;
t.src.u3.ip = master->tuplehash[!exp->dir].tuple.src.u3.ip;
t.src.u.gre.key = nat_pptp_info->pns_call_id;
t.dst.u3.ip = master->tuplehash[!exp->dir].tuple.dst.u3.ip;
t.dst.u.gre.key = nat_pptp_info->pac_call_id;
t.dst.protonum = IPPROTO_GRE;
}
pr_debug("trying to unexpect other dir: ");
nf_ct_dump_tuple_ip(&t);
other_exp = nf_ct_expect_find_get(net, nf_ct_zone(ct), &t);
if (other_exp) {
nf_ct_unexpect_related(other_exp);
nf_ct_expect_put(other_exp);
pr_debug("success\n");
} else {
pr_debug("not found!\n");
}
/* This must be a fresh one. */
BUG_ON(ct->status & IPS_NAT_DONE_MASK);
/* Change src to where master sends to */
range.flags = NF_NAT_RANGE_MAP_IPS;
range.min_addr = range.max_addr
= ct->master->tuplehash[!exp->dir].tuple.dst.u3;
if (exp->dir == IP_CT_DIR_ORIGINAL) {
range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
range.min_proto = range.max_proto = exp->saved_proto;
}
nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
/* For DST manip, map port here to where it's expected. */
range.flags = NF_NAT_RANGE_MAP_IPS;
range.min_addr = range.max_addr
= ct->master->tuplehash[!exp->dir].tuple.src.u3;
if (exp->dir == IP_CT_DIR_REPLY) {
range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
range.min_proto = range.max_proto = exp->saved_proto;
}
nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
}
/* outbound packets == from PNS to PAC */
static int
pptp_outbound_pkt(struct sk_buff *skb,
struct nf_conn *ct,
enum ip_conntrack_info ctinfo,
unsigned int protoff,
struct PptpControlHeader *ctlh,
union pptp_ctrl_union *pptpReq)
{
struct nf_ct_pptp_master *ct_pptp_info;
struct nf_conn_nat *nat = nfct_nat(ct);
struct nf_nat_pptp *nat_pptp_info;
u_int16_t msg;
__be16 new_callid;
unsigned int cid_off;
if (WARN_ON_ONCE(!nat))
return NF_DROP;
nat_pptp_info = &nat->help.nat_pptp_info;
ct_pptp_info = nfct_help_data(ct);
new_callid = ct_pptp_info->pns_call_id;
switch (msg = ntohs(ctlh->messageType)) {
case PPTP_OUT_CALL_REQUEST:
cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
/* FIXME: ideally we would want to reserve a call ID
* here. current netfilter NAT core is not able to do
* this :( For now we use TCP source port. This breaks
* multiple calls within one control session */
/* save original call ID in nat_info */
nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
/* don't use tcph->source since we are at a DSTmanip
* hook (e.g. PREROUTING) and pkt is not mangled yet */
new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
/* save new call ID in ct info */
ct_pptp_info->pns_call_id = new_callid;
break;
case PPTP_IN_CALL_REPLY:
cid_off = offsetof(union pptp_ctrl_union, icack.callID);
break;
case PPTP_CALL_CLEAR_REQUEST:
cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
break;
default:
pr_debug("unknown outbound packet 0x%04x:%s\n", msg,
pptp_msg_name(msg));
fallthrough;
case PPTP_SET_LINK_INFO:
/* only need to NAT in case PAC is behind NAT box */
case PPTP_START_SESSION_REQUEST:
case PPTP_START_SESSION_REPLY:
case PPTP_STOP_SESSION_REQUEST:
case PPTP_STOP_SESSION_REPLY:
case PPTP_ECHO_REQUEST:
case PPTP_ECHO_REPLY:
/* no need to alter packet */
return NF_ACCEPT;
}
/* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
* down to here */
pr_debug("altering call id from 0x%04x to 0x%04x\n",
ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
/* mangle packet */
if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
cid_off + sizeof(struct pptp_pkt_hdr) +
sizeof(struct PptpControlHeader),
sizeof(new_callid), (char *)&new_callid,
sizeof(new_callid)))
return NF_DROP;
return NF_ACCEPT;
}
static void
pptp_exp_gre(struct nf_conntrack_expect *expect_orig,
struct nf_conntrack_expect *expect_reply)
{
const struct nf_conn *ct = expect_orig->master;
struct nf_conn_nat *nat = nfct_nat(ct);
struct nf_ct_pptp_master *ct_pptp_info;
struct nf_nat_pptp *nat_pptp_info;
if (WARN_ON_ONCE(!nat))
return;
nat_pptp_info = &nat->help.nat_pptp_info;
ct_pptp_info = nfct_help_data(ct);
/* save original PAC call ID in nat_info */
nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
/* alter expectation for PNS->PAC direction */
expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
expect_orig->dir = IP_CT_DIR_ORIGINAL;
/* alter expectation for PAC->PNS direction */
expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
expect_reply->dir = IP_CT_DIR_REPLY;
}
/* inbound packets == from PAC to PNS */
static int
pptp_inbound_pkt(struct sk_buff *skb,
struct nf_conn *ct,
enum ip_conntrack_info ctinfo,
unsigned int protoff,
struct PptpControlHeader *ctlh,
union pptp_ctrl_union *pptpReq)
{
const struct nf_nat_pptp *nat_pptp_info;
struct nf_conn_nat *nat = nfct_nat(ct);
u_int16_t msg;
__be16 new_pcid;
unsigned int pcid_off;
if (WARN_ON_ONCE(!nat))
return NF_DROP;
nat_pptp_info = &nat->help.nat_pptp_info;
new_pcid = nat_pptp_info->pns_call_id;
switch (msg = ntohs(ctlh->messageType)) {
case PPTP_OUT_CALL_REPLY:
pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
break;
case PPTP_IN_CALL_CONNECT:
pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
break;
case PPTP_IN_CALL_REQUEST:
/* only need to nat in case PAC is behind NAT box */
return NF_ACCEPT;
case PPTP_WAN_ERROR_NOTIFY:
pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
break;
case PPTP_CALL_DISCONNECT_NOTIFY:
pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
break;
case PPTP_SET_LINK_INFO:
pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
break;
default:
pr_debug("unknown inbound packet %s\n", pptp_msg_name(msg));
fallthrough;
case PPTP_START_SESSION_REQUEST:
case PPTP_START_SESSION_REPLY:
case PPTP_STOP_SESSION_REQUEST:
case PPTP_STOP_SESSION_REPLY:
case PPTP_ECHO_REQUEST:
case PPTP_ECHO_REPLY:
/* no need to alter packet */
return NF_ACCEPT;
}
/* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
* WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
/* mangle packet */
pr_debug("altering peer call id from 0x%04x to 0x%04x\n",
ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff,
pcid_off + sizeof(struct pptp_pkt_hdr) +
sizeof(struct PptpControlHeader),
sizeof(new_pcid), (char *)&new_pcid,
sizeof(new_pcid)))
return NF_DROP;
return NF_ACCEPT;
}
static const struct nf_nat_pptp_hook pptp_hooks = {
.outbound = pptp_outbound_pkt,
.inbound = pptp_inbound_pkt,
.exp_gre = pptp_exp_gre,
.expectfn = pptp_nat_expected,
};
static int __init nf_nat_helper_pptp_init(void)
{
WARN_ON(nf_nat_pptp_hook != NULL);
RCU_INIT_POINTER(nf_nat_pptp_hook, &pptp_hooks);
return 0;
}
static void __exit nf_nat_helper_pptp_fini(void)
{
RCU_INIT_POINTER(nf_nat_pptp_hook, NULL);
synchronize_rcu();
}
module_init(nf_nat_helper_pptp_init);
module_exit(nf_nat_helper_pptp_fini);
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