nf_conntrack_pptp.c

linux 内核源代码

/*
 * Connection tracking 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 <[e-mail]>
 *
 * Development of this code funded by Astaro AG (http://www.astaro.com/)
 *
 * Limitations:
 * 	 - We blindly assume that control connections are always
 * 	   established in PNS->PAC direction.  This is a violation
 * 	   of RFFC2673
 * 	 - 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 <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 <[e-mail]>");
MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
MODULE_ALIAS("ip_conntrack_pptp");

static DEFINE_SPINLOCK(nf_pptp_lock);

int
(*nf_nat_pptp_hook_outbound)(struct sk_buff *skb,
			     struct nf_conn *ct, enum ip_conntrack_info ctinfo,
			     struct PptpControlHeader *ctlh,
			     union pptp_ctrl_union *pptpReq) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_outbound);

int
(*nf_nat_pptp_hook_inbound)(struct sk_buff *skb,
			    struct nf_conn *ct, enum ip_conntrack_info ctinfo,
			    struct PptpControlHeader *ctlh,
			    union pptp_ctrl_union *pptpReq) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_inbound);

void
(*nf_nat_pptp_hook_exp_gre)(struct nf_conntrack_expect *expect_orig,
			    struct nf_conntrack_expect *expect_reply)
			    __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_exp_gre);

void
(*nf_nat_pptp_hook_expectfn)(struct nf_conn *ct,
			     struct nf_conntrack_expect *exp) __read_mostly;
EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);

#ifdef DEBUG
/* PptpControlMessageType names */
const char *pptp_msg_name[] = {
	"UNKNOWN_MESSAGE",
	"START_SESSION_REQUEST",
	"START_SESSION_REPLY",
	"STOP_SESSION_REQUEST",
	"STOP_SESSION_REPLY",
	"ECHO_REQUEST",
	"ECHO_REPLY",
	"OUT_CALL_REQUEST",
	"OUT_CALL_REPLY",
	"IN_CALL_REQUEST",
	"IN_CALL_REPLY",
	"IN_CALL_CONNECT",
	"CALL_CLEAR_REQUEST",
	"CALL_DISCONNECT_NOTIFY",
	"WAN_ERROR_NOTIFY",
	"SET_LINK_INFO"
};
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)
{
	typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
	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 */

	rcu_read_lock();
	nf_nat_pptp_expectfn = rcu_dereference(nf_nat_pptp_hook_expectfn);
	if (nf_nat_pptp_expectfn && ct->master->status & IPS_NAT_MASK)
		nf_nat_pptp_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_tuplepr(&inv_t, &exp->tuple);
		pr_debug("trying to unexpect other dir: ");
		NF_CT_DUMP_TUPLE(&inv_t);

		exp_other = nf_ct_expect_find_get(&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");
		}
	}
	rcu_read_unlock();
}

static int destroy_sibling_or_exp(const struct nf_conntrack_tuple *t)
{
	struct nf_conntrack_tuple_hash *h;
	struct nf_conntrack_expect *exp;
	struct nf_conn *sibling;

	pr_debug("trying to timeout ct or exp for tuple ");
	NF_CT_DUMP_TUPLE(t);

	h = nf_conntrack_find_get(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;
		if (del_timer(&sibling->timeout))
			sibling->timeout.function((unsigned long)sibling);
		nf_ct_put(sibling);
		return 1;
	} else {
		exp = nf_ct_expect_find_get(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 nf_conn_help *help = nfct_help(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 = help->help.ct_pptp_info.pns_call_id;
	t.dst.u.gre.key = help->help.ct_pptp_info.pac_call_id;
	if (!destroy_sibling_or_exp(&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 = help->help.ct_pptp_info.pac_call_id;
	t.dst.u.gre.key = help->help.ct_pptp_info.pns_call_id;
	if (!destroy_sibling_or_exp(&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;
	enum ip_conntrack_dir dir;
	int ret = 1;
	typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;

	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, ct->tuplehash[dir].tuple.src.l3num,
			  &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, ct->tuplehash[dir].tuple.src.l3num,
			  &ct->tuplehash[dir].tuple.src.u3,
			  &ct->tuplehash[dir].tuple.dst.u3,
			  IPPROTO_GRE, &callid, &peer_callid);
	exp_reply->expectfn = pptp_expectfn;

	nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
	if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
		nf_nat_pptp_exp_gre(exp_orig, exp_reply);
	if (nf_ct_expect_related(exp_orig) != 0)
		goto out_put_both;
	if (nf_ct_expect_related(exp_reply) != 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 inline int
pptp_inbound_pkt(struct sk_buff *skb,
		 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(ct)->help.ct_pptp_info;
	u_int16_t msg;
	__be16 cid = 0, pcid = 0;
	typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;

	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;