// SPDX-License-Identifier: GPL-2.0-only
/*
* Connection tracking 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]>
*
* Limitations:
* - We blindly assume that control connections are always
* established in PNS->PAC direction. This is a violation
* of RFC 2637
* - We can only support one single call within each session
* TODO:
* - testing of incoming PPTP calls
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/in.h>
#include <linux/tcp.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_conntrack_helper.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_CT_PPTP_VERSION "3.1"
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <[email protected]>");
MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
MODULE_ALIAS("ip_conntrack_pptp");
MODULE_ALIAS_NFCT_HELPER("pptp");
static DEFINE_SPINLOCK(nf_pptp_lock);
const struct nf_nat_pptp_hook __rcu *nf_nat_pptp_hook;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook);
#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
/* PptpControlMessageType names */
static const char *const pptp_msg_name_array[PPTP_MSG_MAX + 1] = {
[0] = "UNKNOWN_MESSAGE",
[PPTP_START_SESSION_REQUEST] = "START_SESSION_REQUEST",
[PPTP_START_SESSION_REPLY] = "START_SESSION_REPLY",
[PPTP_STOP_SESSION_REQUEST] = "STOP_SESSION_REQUEST",
[PPTP_STOP_SESSION_REPLY] = "STOP_SESSION_REPLY",
[PPTP_ECHO_REQUEST] = "ECHO_REQUEST",
[PPTP_ECHO_REPLY] = "ECHO_REPLY",
[PPTP_OUT_CALL_REQUEST] = "OUT_CALL_REQUEST",
[PPTP_OUT_CALL_REPLY] = "OUT_CALL_REPLY",
[PPTP_IN_CALL_REQUEST] = "IN_CALL_REQUEST",
[PPTP_IN_CALL_REPLY] = "IN_CALL_REPLY",
[PPTP_IN_CALL_CONNECT] = "IN_CALL_CONNECT",
[PPTP_CALL_CLEAR_REQUEST] = "CALL_CLEAR_REQUEST",
[PPTP_CALL_DISCONNECT_NOTIFY] = "CALL_DISCONNECT_NOTIFY",
[PPTP_WAN_ERROR_NOTIFY] = "WAN_ERROR_NOTIFY",
[PPTP_SET_LINK_INFO] = "SET_LINK_INFO"
};
const char *pptp_msg_name(u_int16_t msg)
{
if (msg > PPTP_MSG_MAX)
return pptp_msg_name_array[0];
return pptp_msg_name_array[msg];
}
EXPORT_SYMBOL(pptp_msg_name);
#endif
#define SECS *HZ
#define MINS * 60 SECS
#define HOURS * 60 MINS
#define PPTP_GRE_TIMEOUT (10 MINS)
#define PPTP_GRE_STREAM_TIMEOUT (5 HOURS)
static void pptp_expectfn(struct nf_conn *ct,
struct nf_conntrack_expect *exp)
{
const struct nf_nat_pptp_hook *hook;
struct net *net = nf_ct_net(ct);
pr_debug("increasing timeouts\n");
/* increase timeout of GRE data channel conntrack entry */
ct->proto.gre.timeout = PPTP_GRE_TIMEOUT;
ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
/* Can you see how rusty this code is, compared with the pre-2.6.11
* one? That's what happened to my shiny newnat of 2002 ;( -HW */
hook = rcu_dereference(nf_nat_pptp_hook);
if (hook && ct->master->status & IPS_NAT_MASK)
hook->expectfn(ct, exp);
else {
struct nf_conntrack_tuple inv_t;
struct nf_conntrack_expect *exp_other;
/* obviously this tuple inversion only works until you do NAT */
nf_ct_invert_tuple(&inv_t, &exp->tuple);
pr_debug("trying to unexpect other dir: ");
nf_ct_dump_tuple(&inv_t);
exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
if (exp_other) {
/* delete other expectation. */
pr_debug("found\n");
nf_ct_unexpect_related(exp_other);
nf_ct_expect_put(exp_other);
} else {
pr_debug("not found\n");
}
}
}
static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
const struct nf_conntrack_tuple *t)
{
const struct nf_conntrack_tuple_hash *h;
const struct nf_conntrack_zone *zone;
struct nf_conntrack_expect *exp;
struct nf_conn *sibling;
pr_debug("trying to timeout ct or exp for tuple ");
nf_ct_dump_tuple(t);
zone = nf_ct_zone(ct);
h = nf_conntrack_find_get(net, zone, t);
if (h) {
sibling = nf_ct_tuplehash_to_ctrack(h);
pr_debug("setting timeout of conntrack %p to 0\n", sibling);
sibling->proto.gre.timeout = 0;
sibling->proto.gre.stream_timeout = 0;
nf_ct_kill(sibling);
nf_ct_put(sibling);
return 1;
} else {
exp = nf_ct_expect_find_get(net, zone, t);
if (exp) {
pr_debug("unexpect_related of expect %p\n", exp);
nf_ct_unexpect_related(exp);
nf_ct_expect_put(exp);
return 1;
}
}
return 0;
}
/* timeout GRE data connections */
static void pptp_destroy_siblings(struct nf_conn *ct)
{
struct net *net = nf_ct_net(ct);
const struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
struct nf_conntrack_tuple t;
nf_ct_gre_keymap_destroy(ct);
/* try original (pns->pac) tuple */
memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
t.dst.protonum = IPPROTO_GRE;
t.src.u.gre.key = ct_pptp_info->pns_call_id;
t.dst.u.gre.key = ct_pptp_info->pac_call_id;
if (!destroy_sibling_or_exp(net, ct, &t))
pr_debug("failed to timeout original pns->pac ct/exp\n");
/* try reply (pac->pns) tuple */
memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
t.dst.protonum = IPPROTO_GRE;
t.src.u.gre.key = ct_pptp_info->pac_call_id;
t.dst.u.gre.key = ct_pptp_info->pns_call_id;
if (!destroy_sibling_or_exp(net, ct, &t))
pr_debug("failed to timeout reply pac->pns ct/exp\n");
}
/* expect GRE connections (PNS->PAC and PAC->PNS direction) */
static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
{
struct nf_conntrack_expect *exp_orig, *exp_reply;
const struct nf_nat_pptp_hook *hook;
enum ip_conntrack_dir dir;
int ret = 1;
exp_orig = nf_ct_expect_alloc(ct);
if (exp_orig == NULL)
goto out;
exp_reply = nf_ct_expect_alloc(ct);
if (exp_reply == NULL)
goto out_put_orig;
/* original direction, PNS->PAC */
dir = IP_CT_DIR_ORIGINAL;
nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
nf_ct_l3num(ct),
&ct->tuplehash[dir].tuple.src.u3,
&ct->tuplehash[dir].tuple.dst.u3,
IPPROTO_GRE, &peer_callid, &callid);
exp_orig->expectfn = pptp_expectfn;
/* reply direction, PAC->PNS */
dir = IP_CT_DIR_REPLY;
nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
nf_ct_l3num(ct),
&ct->tuplehash[dir].tuple.src.u3,
&ct->tuplehash[dir].tuple.dst.u3,
IPPROTO_GRE, &callid, &peer_callid);
exp_reply->expectfn = pptp_expectfn;
hook = rcu_dereference(nf_nat_pptp_hook);
if (hook && ct->status & IPS_NAT_MASK)
hook->exp_gre(exp_orig, exp_reply);
if (nf_ct_expect_related(exp_orig, 0) != 0)
goto out_put_both;
if (nf_ct_expect_related(exp_reply, 0) != 0)
goto out_unexpect_orig;
/* Add GRE keymap entries */
if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
goto out_unexpect_both;
if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
nf_ct_gre_keymap_destroy(ct);
goto out_unexpect_both;
}
ret = 0;
out_put_both:
nf_ct_expect_put(exp_reply);
out_put_orig:
nf_ct_expect_put(exp_orig);
out:
return ret;
out_unexpect_both:
nf_ct_unexpect_related(exp_reply);
out_unexpect_orig:
nf_ct_unexpect_related(exp_orig);
goto out_put_both;
}
static int
pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
struct PptpControlHeader *ctlh,
union pptp_ctrl_union *pptpReq,
unsigned int reqlen,
struct nf_conn *ct,
enum ip_conntrack_info ctinfo)
{
struct nf_ct_pptp_master *info = nfct_help_data(ct);
const struct nf_nat_pptp_hook *hook;
u_int16_t msg;
__be16 cid = 0, pcid = 0;
msg = ntohs(ctlh->messageType);
pr_debug("inbound control message %s\n", pptp_msg_name(msg));
switch (msg) {
case PPTP_START_SESSION_REPLY:
/* server confirms new control session */
if (info->sstate < PPTP_SESSION_REQUESTED)
goto invalid;
if (pptpReq->srep.resultCode == PPTP_START_OK)
info->sstate = PPTP_SESSION_CONFIRMED;
else
info->sstate = PPTP_SESSION_ERROR;
break;
case PPTP_STOP_SESSION_REPLY:
/* server confirms end of control session */
if (info->sstate > PPTP_SESSION_STOPREQ)
goto invalid;
if (pptpReq->strep.resultCode == PPTP_STOP_OK)
info->sstate = PPTP_SESSION_NONE;
else
info->sstate = PPTP_SESSION_ERROR;
break;
case PPTP_OUT_CALL_REPLY:
/* server accepted call, we now expect GRE frames */
if (info->sstate != PPTP_SESSION_CONFIRMED)
goto invalid;
if (info->cstate != PPTP_CALL_OUT_REQ &&
info->cstate != PPTP_CALL_OUT_CONF)
goto invalid;
cid = pptpReq->ocack.callID;
pcid = pptpReq->ocack.peersCallID;
if (info->pns_call_id != pcid)
goto invalid;
pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name(msg),
ntohs(cid), ntohs(pcid));
if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
info->cstate = PPTP_CALL_OUT_CONF;
info->pac_call_id = cid;
exp_gre(ct, cid, pcid);
} else
info->cstate = PPTP_CALL_NONE;
break;
case PPTP_IN_CALL_REQUEST:
/* server tells us about incoming call request */
if (info->sstate != PPTP_SESSION_CONFIRMED)
goto invalid;
cid = pptpReq->icreq.callID;
pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
info->cstate = PPTP_CALL_IN_REQ;
info->pac_call_id = cid;
break;
case PPTP_IN_CALL_CONNECT:
/* server tells us about incoming call established */
if (info->sstate != PPTP_SESSION_CONFIRMED)
goto invalid;
if (info->cstate != PPTP_CALL_IN_REP &&
info->cstate != PPTP_CALL_IN_CONF)
goto invalid;
pcid = pptpReq->iccon.peersCallID;
cid = info->pac_call_id;
if (info->pns_call_id != pcid)
goto invalid;
pr_debug("%s, PCID=%X\n", pptp_msg_name(msg), ntohs(pcid));
info->cstate = PPTP_CALL_IN_CONF;
/* we expect a GRE connection from PAC to PNS */
exp_gre(ct, cid, pcid);
break;
case PPTP_CALL_DISCONNECT_NOTIFY:
/* server confirms disconnect */
cid = pptpReq->disc.callID;
pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
info->cstate = PPTP_CALL_NONE;
/* untrack this call id, unexpect GRE packets */
pptp_destroy_siblings(ct);
break;
case PPTP_WAN_ERROR_NOTIFY:
case PPTP_SET_LINK_INFO:
case PPTP_ECHO_REQUEST:
case PPTP_ECHO_REPLY:
/* I don't have to explain these ;) */
break;
default:
goto invalid;
}
hook = rcu_dereference(nf_nat_pptp_hook);
if (hook && ct->status & IPS_NAT_MASK)
return hook->inbound(skb, ct, ctinfo, protoff, ctlh, pptpReq);
return NF_ACCEPT;
invalid:
pr_debug("invalid %s: type=%d cid=%u pcid=%u "
"cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
pptp_msg_name(msg),
msg, ntohs(cid), ntohs(pcid), info->cstate, info->sstate,
ntohs(info->pns_call_id), ntohs(info->pac_call_id));
return NF_ACCEPT;
}
static int
pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
struct PptpControlHeader *ctlh,
union pptp_ctrl_union *pptpReq,
unsigned int reqlen,
struct nf_conn *ct,
enum ip_conntrack_info ctinfo)
{
struct nf_ct_pptp_master *info = nfct_help_data(ct);
const struct nf_nat_pptp_hook *hook;
u_int16_t msg;
__be16 cid = 0, pcid = 0;
msg = ntohs(ctlh->messageType);
pr_debug("outbound control message %s\n", pptp_msg_name(msg));
switch (msg) {
case PPTP_START_SESSION_REQUEST:
/* client requests for new control session */
if (info->sstate != PPTP_SESSION_NONE)
goto invalid;
info->sstate = PPTP_SESSION_REQUESTED;
break;
case PPTP_STOP_SESSION_REQUEST:
/* client requests end of control session */
info->sstate = PPTP_SESSION_STOPREQ;
break;
case PPTP_OUT_CALL_REQUEST:
/* client initiating connection to server */
if (info->sstate != PPTP_SESSION_CONFIRMED)
goto invalid;
info->cstate = PPTP_CALL_OUT_REQ;
/* track PNS call id */
cid = pptpReq->ocreq.callID;
pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
info->pns_call_id = cid;
break;
case PPTP_IN_CALL_REPLY:
/* client answers incoming call */
if (info->cstate != PPTP_CALL_IN_REQ &&
info->cstate != PPTP_CALL_IN_REP)
goto invalid;
cid = pptpReq->icack.callID;
pcid = pptpReq->icack.peersCallID;
if (info->pac_call_id != pcid)
goto invalid;
pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name(msg),
ntohs(cid), ntohs(pcid));
if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
/* part two of the three-way handshake */
info->cstate = PPTP_CALL_IN_REP;
info->pns_call_id = cid;
} else
info->cstate = PPTP_CALL_NONE;
break;
case PPTP_CALL_CLEAR_REQUEST:
/* client requests hangup of call */
if (info->sstate != PPTP_SESSION_CONFIRMED)
goto invalid;
/* FUTURE: iterate over all calls and check if
* call ID is valid. We don't do this without newnat,
* because we only know about last call */
info->cstate = PPTP_CALL_CLEAR_REQ;
break;
case PPTP_SET_LINK_INFO:
case PPTP_ECHO_REQUEST:
case PPTP_ECHO_REPLY:
/* I don't have to explain these ;) */
break;
default:
goto invalid;
}
hook = rcu_dereference(nf_nat_pptp_hook);
if (hook && ct->status & IPS_NAT_MASK)
return hook->outbound(skb, ct, ctinfo, protoff, ctlh, pptpReq);
return NF_ACCEPT;
invalid:
pr_debug("invalid %s: type=%d cid=%u pcid=%u "
"cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
pptp_msg_name(msg),
msg, ntohs(cid), ntohs(pcid), info->cstate, info->sstate,
ntohs(info->pns_call_id), ntohs(info->pac_call_id));
return NF_ACCEPT;
}
static const unsigned int pptp_msg_size[] = {
[PPTP_START_SESSION_REQUEST] = sizeof(struct PptpStartSessionRequest),
[PPTP_START_SESSION_REPLY] = sizeof(struct PptpStartSessionReply),
[PPTP_STOP_SESSION_REQUEST] = sizeof(struct PptpStopSessionRequest),
[PPTP_STOP_SESSION_REPLY] = sizeof(struct PptpStopSessionReply),
[PPTP_OUT_CALL_REQUEST] = sizeof(struct PptpOutCallRequest),
[PPTP_OUT_CALL_REPLY] = sizeof(struct PptpOutCallReply),
[PPTP_IN_CALL_REQUEST] = sizeof(struct PptpInCallRequest),
[PPTP_IN_CALL_REPLY] = sizeof(struct PptpInCallReply),
[PPTP_IN_CALL_CONNECT] = sizeof(struct PptpInCallConnected),
[PPTP_CALL_CLEAR_REQUEST] = sizeof(struct PptpClearCallRequest),
[PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
[PPTP_WAN_ERROR_NOTIFY] = sizeof(struct PptpWanErrorNotify),
[PPTP_SET_LINK_INFO] = sizeof(struct PptpSetLinkInfo),
};
/* track caller id inside control connection, call expect_related */
static int
conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
struct nf_conn *ct, enum ip_conntrack_info ctinfo)
{
int dir = CTINFO2DIR(ctinfo);
const struct nf_ct_pptp_master *info = nfct_help_data(ct);
const struct tcphdr *tcph;
struct tcphdr _tcph;
const struct pptp_pkt_hdr *pptph;
struct pptp_pkt_hdr _pptph;
struct PptpControlHeader _ctlh, *ctlh;
union pptp_ctrl_union _pptpReq, *pptpReq;
unsigned int tcplen = skb->len - protoff;
unsigned int datalen, reqlen, nexthdr_off;
int oldsstate, oldcstate;
int ret;
u_int16_t msg;
#if IS_ENABLED(CONFIG_NF_NAT)
if (!nf_ct_is_confirmed(ct) && (ct->status & IPS_NAT_MASK)) {
struct nf_conn_nat *nat = nf_ct_ext_find(ct, NF_CT_EXT_NAT);
if (!nat && !nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC))
return NF_DROP;
}
#endif
/* don't do any tracking before tcp handshake complete */
if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
return NF_ACCEPT;
nexthdr_off = protoff;
tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
if (!tcph)
return NF_ACCEPT;
nexthdr_off += tcph->doff * 4;
datalen = tcplen - tcph->doff * 4;
pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
if (!pptph) {
pr_debug("no full PPTP header, can't track\n");
return NF_ACCEPT;
}
nexthdr_off += sizeof(_pptph);
datalen -= sizeof(_pptph);
/* if it's not a control message we can't do anything with it */
if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
pr_debug("not a control packet\n");
return NF_ACCEPT;
}
ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
if (!ctlh)
return NF_ACCEPT;
nexthdr_off += sizeof(_ctlh);
datalen -= sizeof(_ctlh);
reqlen = datalen;
msg = ntohs(ctlh->messageType);
if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
return NF_ACCEPT;
if (reqlen > sizeof(*pptpReq))
reqlen = sizeof(*pptpReq);
pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
if (!pptpReq)
return NF_ACCEPT;
oldsstate = info->sstate;
oldcstate = info->cstate;
spin_lock_bh(&nf_pptp_lock);
/* FIXME: We just blindly assume that the control connection is always
* established from PNS->PAC. However, RFC makes no guarantee */
if (dir == IP_CT_DIR_ORIGINAL)
/* client -> server (PNS -> PAC) */
ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
ctinfo);
else
/* server -> client (PAC -> PNS) */
ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
ctinfo);
pr_debug("sstate: %d->%d, cstate: %d->%d\n",
oldsstate, info->sstate, oldcstate, info->cstate);
spin_unlock_bh(&nf_pptp_lock);
return ret;
}
static const struct nf_conntrack_expect_policy pptp_exp_policy = {
.max_expected = 2,
.timeout = 5 * 60,
};
/* control protocol helper */
static struct nf_conntrack_helper pptp __read_mostly = {
.name = "pptp",
.me = THIS_MODULE,
.tuple.src.l3num = AF_INET,
.tuple.src.u.tcp.port = cpu_to_be16(PPTP_CONTROL_PORT),
.tuple.dst.protonum = IPPROTO_TCP,
.help = conntrack_pptp_help,
.destroy = pptp_destroy_siblings,
.expect_policy = &pptp_exp_policy,
};
static int __init nf_conntrack_pptp_init(void)
{
NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_pptp_master));
return nf_conntrack_helper_register(&pptp);
}
static void __exit nf_conntrack_pptp_fini(void)
{
nf_conntrack_helper_unregister(&pptp);
}
module_init(nf_conntrack_pptp_init);
module_exit(nf_conntrack_pptp_fini);
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