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* ip_nat_pptp.c - Version 3.0
*
* NAT support for PPTP (Point to Point Tunneling Protocol).
* PPTP is a 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 <laforge@gnumonks.org>
*
* Development of this code funded by Astaro AG (http://www.astaro.com/)
*
* TODO: - NAT to a unique tuple, not to TCP source port
* (needs netfilter tuple reservation)
*
* Changes:
* 2002-02-10 - Version 1.3
* - Use ip_nat_mangle_tcp_packet() because of cloned skb's
* in local connections (Philip Craig <philipc@snapgear.com>)
* - add checks for magicCookie and pptp version
* - make argument list of pptp_{out,in}bound_packet() shorter
* - move to C99 style initializers
* - print version number at module loadtime
* 2003-09-22 - Version 1.5
* - use SNATed tcp sourceport as callid, since we get called before
* TCP header is mangled (Philip Craig <philipc@snapgear.com>)
* 2004-10-22 - Version 2.0
* - kernel 2.6.x version
* 2005-06-10 - Version 3.0
* - kernel >= 2.6.11 version,
* funded by Oxcoda NetBox Blue (http://www.netboxblue.com/)
*
*/
#include <linux/config.h>
#include <linux/module.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <net/tcp.h>
#include <linux/netfilter_ipv4/ip_nat.h>
#include <linux/netfilter_ipv4/ip_nat_rule.h>
#include <linux/netfilter_ipv4/ip_nat_helper.h>
#include <linux/netfilter_ipv4/ip_nat_pptp.h>
#include <linux/netfilter_ipv4/ip_conntrack_core.h>
#include <linux/netfilter_ipv4/ip_conntrack_helper.h>
#include <linux/netfilter_ipv4/ip_conntrack_proto_gre.h>
#include <linux/netfilter_ipv4/ip_conntrack_pptp.h>
#define IP_NAT_PPTP_VERSION "3.0"
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
#if 0
extern const char *pptp_msg_name[];
#define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, \
__FUNCTION__, ## args)
#else
#define DEBUGP(format, args...)
#endif
static void pptp_nat_expected(struct ip_conntrack *ct,
struct ip_conntrack_expect *exp)
{
struct ip_conntrack *master = ct->master;
struct ip_conntrack_expect *other_exp;
struct ip_conntrack_tuple t;
struct ip_ct_pptp_master *ct_pptp_info;
struct ip_nat_pptp *nat_pptp_info;
struct ip_nat_range range;
ct_pptp_info = &master->help.ct_pptp_info;
nat_pptp_info = &master->nat.help.nat_pptp_info;
/* And here goes the grand finale of corrosion... */
if (exp->dir == IP_CT_DIR_ORIGINAL) {
DEBUGP("we are PNS->PAC\n");
/* therefore, build tuple for PAC->PNS */
t.src.ip = master->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip;
t.src.u.gre.key = htons(master->help.ct_pptp_info.pac_call_id);
t.dst.ip = master->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip;
t.dst.u.gre.key = htons(master->help.ct_pptp_info.pns_call_id);
t.dst.protonum = IPPROTO_GRE;
} else {
DEBUGP("we are PAC->PNS\n");
/* build tuple for PNS->PAC */
t.src.ip = master->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip;
t.src.u.gre.key =
htons(master->nat.help.nat_pptp_info.pns_call_id);
t.dst.ip = master->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip;
t.dst.u.gre.key =
htons(master->nat.help.nat_pptp_info.pac_call_id);
t.dst.protonum = IPPROTO_GRE;
}
DEBUGP("trying to unexpect other dir: ");
DUMP_TUPLE(&t);
other_exp = ip_conntrack_expect_find(&t);
if (other_exp) {
ip_conntrack_unexpect_related(other_exp);
ip_conntrack_expect_put(other_exp);
DEBUGP("success\n");
} else {
DEBUGP("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 = IP_NAT_RANGE_MAP_IPS;
range.min_ip = range.max_ip
= ct->master->tuplehash[!exp->dir].tuple.dst.ip;
if (exp->dir == IP_CT_DIR_ORIGINAL) {
range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
range.min = range.max = exp->saved_proto;
}
/* hook doesn't matter, but it has to do source manip */
ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
/* For DST manip, map port here to where it's expected. */
range.flags = IP_NAT_RANGE_MAP_IPS;
range.min_ip = range.max_ip
= ct->master->tuplehash[!exp->dir].tuple.src.ip;
if (exp->dir == IP_CT_DIR_REPLY) {
range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
range.min = range.max = exp->saved_proto;
}
/* hook doesn't matter, but it has to do destination manip */
ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
}
/* outbound packets == from PNS to PAC */
static int
pptp_outbound_pkt(struct sk_buff **pskb,
struct ip_conntrack *ct,
enum ip_conntrack_info ctinfo,
struct PptpControlHeader *ctlh,
union pptp_ctrl_union *pptpReq)
{
struct ip_ct_pptp_master *ct_pptp_info = &ct->help.ct_pptp_info;
struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
u_int16_t msg, new_callid;
unsigned int cid_off;
new_callid = htons(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 = ntohs(new_callid);
break;
case PPTP_IN_CALL_REPLY:
cid_off = offsetof(union pptp_ctrl_union, icreq.callID);
break;
case PPTP_CALL_CLEAR_REQUEST:
cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
break;
default:
DEBUGP("unknown outbound packet 0x%04x:%s\n", msg,
(msg <= PPTP_MSG_MAX)?
pptp_msg_name[msg]:pptp_msg_name[0]);
/* fall through */
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 */
DEBUGP("altering call id from 0x%04x to 0x%04x\n",
ntohs(*(u_int16_t *)pptpReq + cid_off), ntohs(new_callid));
/* mangle packet */
if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
cid_off + sizeof(struct pptp_pkt_hdr) +
sizeof(struct PptpControlHeader),
sizeof(new_callid), (char *)&new_callid,
sizeof(new_callid)) == 0)
return NF_DROP;
return NF_ACCEPT;
}
static int
pptp_exp_gre(struct ip_conntrack_expect *expect_orig,
struct ip_conntrack_expect *expect_reply)
{
struct ip_ct_pptp_master *ct_pptp_info =
&expect_orig->master->help.ct_pptp_info;
struct ip_nat_pptp *nat_pptp_info =
&expect_orig->master->nat.help.nat_pptp_info;
struct ip_conntrack *ct = expect_orig->master;
struct ip_conntrack_tuple inv_t;
struct ip_conntrack_tuple *orig_t, *reply_t;
/* save original PAC call ID in nat_info */
nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
/* alter expectation */
orig_t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
reply_t = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
/* alter expectation for PNS->PAC direction */
invert_tuplepr(&inv_t, &expect_orig->tuple);
expect_orig->saved_proto.gre.key = htons(ct_pptp_info->pns_call_id);
expect_orig->tuple.src.u.gre.key = htons(nat_pptp_info->pns_call_id);
expect_orig->tuple.dst.u.gre.key = htons(ct_pptp_info->pac_call_id);
expect_orig->dir = IP_CT_DIR_ORIGINAL;
inv_t.src.ip = reply_t->src.ip;
inv_t.dst.ip = reply_t->dst.ip;
inv_t.src.u.gre.key = htons(nat_pptp_info->pac_call_id);
inv_t.dst.u.gre.key = htons(ct_pptp_info->pns_call_id);
if (!ip_conntrack_expect_related(expect_orig)) {
DEBUGP("successfully registered expect\n");
} else {
DEBUGP("can't expect_related(expect_orig)\n");
return 1;
}
/* alter expectation for PAC->PNS direction */
invert_tuplepr(&inv_t, &expect_reply->tuple);
expect_reply->saved_proto.gre.key = htons(nat_pptp_info->pns_call_id);
expect_reply->tuple.src.u.gre.key = htons(nat_pptp_info->pac_call_id);
expect_reply->tuple.dst.u.gre.key = htons(ct_pptp_info->pns_call_id);
expect_reply->dir = IP_CT_DIR_REPLY;
inv_t.src.ip = orig_t->src.ip;
inv_t.dst.ip = orig_t->dst.ip;
inv_t.src.u.gre.key = htons(nat_pptp_info->pns_call_id);
inv_t.dst.u.gre.key = htons(ct_pptp_info->pac_call_id);
if (!ip_conntrack_expect_related(expect_reply)) {
DEBUGP("successfully registered expect\n");
} else {
DEBUGP("can't expect_related(expect_reply)\n");
ip_conntrack_unexpect_related(expect_orig);
return 1;
}
if (ip_ct_gre_keymap_add(ct, &expect_reply->tuple, 0) < 0) {
DEBUGP("can't register original keymap\n");
ip_conntrack_unexpect_related(expect_orig);
ip_conntrack_unexpect_related(expect_reply);
return 1;
}
if (ip_ct_gre_keymap_add(ct, &inv_t, 1) < 0) {
DEBUGP("can't register reply keymap\n");
ip_conntrack_unexpect_related(expect_orig);
ip_conntrack_unexpect_related(expect_reply);
ip_ct_gre_keymap_destroy(ct);
return 1;
}
return 0;
}
/* inbound packets == from PAC to PNS */
static int
pptp_inbound_pkt(struct sk_buff **pskb,
struct ip_conntrack *ct,
enum ip_conntrack_info ctinfo,
struct PptpControlHeader *ctlh,
union pptp_ctrl_union *pptpReq)
{
struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
u_int16_t msg, new_cid = 0, new_pcid;
unsigned int pcid_off, cid_off = 0;
new_pcid = htons(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);
cid_off = offsetof(union pptp_ctrl_union, ocack.callID);
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:
DEBUGP("unknown inbound packet %s\n", (msg <= PPTP_MSG_MAX)?
pptp_msg_name[msg]:pptp_msg_name[0]);
/* fall through */
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 */
DEBUGP("altering peer call id from 0x%04x to 0x%04x\n",
ntohs(*(u_int16_t *)pptpReq + pcid_off), ntohs(new_pcid));
if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
pcid_off + sizeof(struct pptp_pkt_hdr) +
sizeof(struct PptpControlHeader),
sizeof(new_pcid), (char *)&new_pcid,
sizeof(new_pcid)) == 0)
return NF_DROP;
if (new_cid) {
DEBUGP("altering call id from 0x%04x to 0x%04x\n",
ntohs(*(u_int16_t *)pptpReq + cid_off), ntohs(new_cid));
if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
cid_off + sizeof(struct pptp_pkt_hdr) +
sizeof(struct PptpControlHeader),
sizeof(new_cid), (char *)&new_cid,
sizeof(new_cid)) == 0)
return NF_DROP;
}
return NF_ACCEPT;
}
extern int __init ip_nat_proto_gre_init(void);
extern void __exit ip_nat_proto_gre_fini(void);
static int __init init(void)
{
int ret;
DEBUGP("%s: registering NAT helper\n", __FILE__);
ret = ip_nat_proto_gre_init();
if (ret < 0)
return ret;
BUG_ON(ip_nat_pptp_hook_outbound);
ip_nat_pptp_hook_outbound = &pptp_outbound_pkt;
BUG_ON(ip_nat_pptp_hook_inbound);
ip_nat_pptp_hook_inbound = &pptp_inbound_pkt;
BUG_ON(ip_nat_pptp_hook_exp_gre);
ip_nat_pptp_hook_exp_gre = &pptp_exp_gre;
BUG_ON(ip_nat_pptp_hook_expectfn);
ip_nat_pptp_hook_expectfn = &pptp_nat_expected;
printk("ip_nat_pptp version %s loaded\n", IP_NAT_PPTP_VERSION);
return 0;
}
static void __exit fini(void)
{
DEBUGP("cleanup_module\n" );
ip_nat_pptp_hook_expectfn = NULL;
ip_nat_pptp_hook_exp_gre = NULL;
ip_nat_pptp_hook_inbound = NULL;
ip_nat_pptp_hook_outbound = NULL;
ip_nat_proto_gre_fini();
/* Make sure noone calls it, meanwhile */
synchronize_net();
printk("ip_nat_pptp version %s unloaded\n", IP_NAT_PPTP_VERSION);
}
module_init(init);
module_exit(fini);
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