ip_pptp_pxy.c

/*
 * Copyright (C) 2012 by Darren Reed.
 *
 * Simple PPTP transparent proxy for in-kernel use.  For use with the NAT
 * code.
 *
 * $Id$
 *
 */
#define	IPF_PPTP_PROXY



/*
 * PPTP proxy
 */
typedef struct pptp_side {
	u_32_t		pptps_nexthdr;
	u_32_t		pptps_next;
	int		pptps_state;
	int		pptps_gothdr;
	int		pptps_len;
	int		pptps_bytes;
	char		*pptps_wptr;
	char		pptps_buffer[512];
} pptp_side_t;

typedef struct pptp_pxy {
	nat_t		*pptp_nat;
	struct ipstate	*pptp_state;
	u_short		pptp_call[2];
	pptp_side_t	pptp_side[2];
	ipnat_t		*pptp_rule;
} pptp_pxy_t;

typedef	struct pptp_hdr {
	u_short		pptph_len;
	u_short		pptph_type;
	u_32_t		pptph_cookie;
} pptp_hdr_t;

#define	PPTP_MSGTYPE_CTL	1
#define	PPTP_MTCTL_STARTREQ	1
#define	PPTP_MTCTL_STARTREP	2
#define	PPTP_MTCTL_STOPREQ	3
#define	PPTP_MTCTL_STOPREP	4
#define	PPTP_MTCTL_ECHOREQ	5
#define	PPTP_MTCTL_ECHOREP	6
#define	PPTP_MTCTL_OUTREQ	7
#define	PPTP_MTCTL_OUTREP	8
#define	PPTP_MTCTL_INREQ	9
#define	PPTP_MTCTL_INREP	10
#define	PPTP_MTCTL_INCONNECT	11
#define	PPTP_MTCTL_CLEAR	12
#define	PPTP_MTCTL_DISCONNECT	13
#define	PPTP_MTCTL_WANERROR	14
#define	PPTP_MTCTL_LINKINFO	15


void ipf_p_pptp_main_load __P((void));
void ipf_p_pptp_main_unload __P((void));
int ipf_p_pptp_new __P((void *, fr_info_t *, ap_session_t *, nat_t *));
void ipf_p_pptp_del __P((ipf_main_softc_t *, ap_session_t *));
int ipf_p_pptp_inout __P((void *, fr_info_t *, ap_session_t *, nat_t *));
void ipf_p_pptp_donatstate __P((fr_info_t *, nat_t *, pptp_pxy_t *));
int ipf_p_pptp_message __P((fr_info_t *, nat_t *, pptp_pxy_t *, pptp_side_t *));
int ipf_p_pptp_nextmessage __P((fr_info_t *, nat_t *, pptp_pxy_t *, int));
int ipf_p_pptp_mctl __P((fr_info_t *, nat_t *, pptp_pxy_t *, pptp_side_t *));

static	frentry_t	pptpfr;

static	int	pptp_proxy_init = 0;
static	int	ipf_p_pptp_debug = 0;
static	int	ipf_p_pptp_gretimeout = IPF_TTLVAL(120);	/* 2 minutes */


/*
 * PPTP application proxy initialization.
 */
void
ipf_p_pptp_main_load()
{
	bzero((char *)&pptpfr, sizeof(pptpfr));
	pptpfr.fr_ref = 1;
	pptpfr.fr_age[0] = ipf_p_pptp_gretimeout;
	pptpfr.fr_age[1] = ipf_p_pptp_gretimeout;
	pptpfr.fr_flags = FR_OUTQUE|FR_PASS|FR_QUICK|FR_KEEPSTATE;
	MUTEX_INIT(&pptpfr.fr_lock, "PPTP proxy rule lock");
	pptp_proxy_init = 1;
}


void
ipf_p_pptp_main_unload()
{
	if (pptp_proxy_init == 1) {
		MUTEX_DESTROY(&pptpfr.fr_lock);
		pptp_proxy_init = 0;
	}
}


/*
 * Setup for a new PPTP proxy.
 *
 * NOTE: The printf's are broken up with %s in them to prevent them being
 * optimised into puts statements on FreeBSD (this doesn't exist in the kernel)
 */
int
ipf_p_pptp_new(arg, fin, aps, nat)
	void *arg;
	fr_info_t *fin;
	ap_session_t *aps;
	nat_t *nat;
{
	pptp_pxy_t *pptp;
	ipnat_t *ipn;
	ipnat_t *np;
	int size;
	ip_t *ip;

	if (fin->fin_v != 4)
		return -1;

	ip = fin->fin_ip;
	np = nat->nat_ptr;
	size = np->in_size;

	if (ipf_nat_outlookup(fin, 0, IPPROTO_GRE, nat->nat_osrcip,
			  ip->ip_dst) != NULL) {
		if (ipf_p_pptp_debug > 0)
			printf("ipf_p_pptp_new: GRE session already exists\n");
		return -1;
	}

	KMALLOC(pptp, pptp_pxy_t *);
	if (pptp == NULL) {
		if (ipf_p_pptp_debug > 0)
			printf("ipf_p_pptp_new: malloc for aps_data failed\n");
		return -1;
	}
	KMALLOCS(ipn, ipnat_t *, size);
	if (ipn == NULL) {
		KFREE(pptp);
		return -1;
	}

	aps->aps_data = pptp;
	aps->aps_psiz = sizeof(*pptp);
	bzero((char *)pptp, sizeof(*pptp));
	bzero((char *)ipn, size);
	pptp->pptp_rule = ipn;

	/*
	 * Create NAT rule against which the tunnel/transport mapping is
	 * created.  This is required because the current NAT rule does not
	 * describe GRE but TCP instead.
	 */
	ipn->in_size = size;
	ipn->in_ifps[0] = fin->fin_ifp;
	ipn->in_apr = NULL;
	ipn->in_use = 1;
	ipn->in_hits = 1;
	ipn->in_ippip = 1;
	ipn->in_snip = ntohl(nat->nat_nsrcaddr);
	ipn->in_nsrcaddr = fin->fin_saddr;
	ipn->in_dnip = ntohl(nat->nat_ndstaddr);
	ipn->in_ndstaddr = nat->nat_ndstaddr;
	ipn->in_redir = np->in_redir;
	ipn->in_osrcaddr = nat->nat_osrcaddr;
	ipn->in_odstaddr = nat->nat_odstaddr;
	ipn->in_osrcmsk = 0xffffffff;
	ipn->in_nsrcmsk = 0xffffffff;
	ipn->in_odstmsk = 0xffffffff;
	ipn->in_ndstmsk = 0xffffffff;
	ipn->in_flags = (np->in_flags | IPN_PROXYRULE);
	MUTEX_INIT(&ipn->in_lock, "pptp proxy NAT rule");

	ipn->in_namelen = np->in_namelen;
	bcopy(np->in_names, ipn->in_ifnames, ipn->in_namelen);
	ipn->in_ifnames[0] = np->in_ifnames[0];
	ipn->in_ifnames[1] = np->in_ifnames[1];

	ipn->in_pr[0] = IPPROTO_GRE;
	ipn->in_pr[1] = IPPROTO_GRE;

	pptp->pptp_side[0].pptps_wptr = pptp->pptp_side[0].pptps_buffer;
	pptp->pptp_side[1].pptps_wptr = pptp->pptp_side[1].pptps_buffer;
	return 0;
}


void
ipf_p_pptp_donatstate(fin, nat, pptp)
	fr_info_t *fin;
	nat_t *nat;
	pptp_pxy_t *pptp;
{
	ipf_main_softc_t *softc = fin->fin_main_soft;
	fr_info_t fi;
	grehdr_t gre;
	nat_t *nat2;
	u_char p;
	ip_t *ip;

	ip = fin->fin_ip;
	p = ip->ip_p;

	nat2 = pptp->pptp_nat;
	if ((nat2 == NULL) || (pptp->pptp_state == NULL)) {
		bcopy((char *)fin, (char *)&fi, sizeof(fi));
		bzero((char *)&gre, sizeof(gre));
		fi.fin_fi.fi_p = IPPROTO_GRE;
		fi.fin_fr = &pptpfr;
		if ((nat->nat_dir == NAT_OUTBOUND && fin->fin_out) ||
		    (nat->nat_dir == NAT_INBOUND && !fin->fin_out)) {
			fi.fin_data[0] = pptp->pptp_call[0];
			fi.fin_data[1] = pptp->pptp_call[1];
		} else {
			fi.fin_data[0] = pptp->pptp_call[1];
			fi.fin_data[1] = pptp->pptp_call[0];
		}
		ip = fin->fin_ip;
		ip->ip_p = IPPROTO_GRE;
		fi.fin_flx &= ~(FI_TCPUDP|FI_STATE|FI_FRAG);
		fi.fin_flx |= FI_IGNORE;
		fi.fin_dp = &gre;
		gre.gr_flags = htons(1 << 13);

		fi.fin_fi.fi_saddr = nat->nat_osrcaddr;
		fi.fin_fi.fi_daddr = nat->nat_odstaddr;
	}

	/*
	 * Update NAT timeout/create NAT if missing.
	 */
	if (nat2 != NULL)
		ipf_queueback(softc->ipf_ticks, &nat2->nat_tqe);
	else {
#ifdef USE_MUTEXES
		ipf_nat_softc_t *softn = softc->ipf_nat_soft;
#endif

		MUTEX_ENTER(&softn->ipf_nat_new);
		nat2 = ipf_nat_add(&fi, pptp->pptp_rule, &pptp->pptp_nat,
				   NAT_SLAVE, nat->nat_dir);
		MUTEX_EXIT(&softn->ipf_nat_new);
		if (nat2 != NULL) {
			(void) ipf_nat_proto(&fi, nat2, 0);
			MUTEX_ENTER(&nat2->nat_lock);
			ipf_nat_update(&fi, nat2);
			MUTEX_EXIT(&nat2->nat_lock);
		}
	}

	READ_ENTER(&softc->ipf_state);
	if (pptp->pptp_state != NULL) {
		ipf_queueback(softc->ipf_ticks, &pptp->pptp_state->is_sti);
		RWLOCK_EXIT(&softc->ipf_state);
	} else {
		RWLOCK_EXIT(&softc->ipf_state);
		if (nat2 != NULL) {
			if (nat->nat_dir == NAT_INBOUND)
				fi.fin_fi.fi_daddr = nat2->nat_ndstaddr;
			else
				fi.fin_fi.fi_saddr = nat2->nat_osrcaddr;
		}
		fi.fin_ifp = NULL;
		(void) ipf_state_add(softc, &fi, &pptp->pptp_state, 0);
	}
	ip->ip_p = p;
	return;
}


/*
 * Try and build up the next PPTP message in the TCP stream and if we can
 * build it up completely (fits in our buffer) then pass it off to the message
 * parsing function.
 */
int
ipf_p_pptp_nextmessage(fin, nat, pptp, rev)
	fr_info_t *fin;
	nat_t *nat;
	pptp_pxy_t *pptp;
	int rev;
{
	static const char *funcname = "ipf_p_pptp_nextmessage";
	pptp_side_t *pptps;
	u_32_t start, end;
	pptp_hdr_t *hdr;
	tcphdr_t *tcp;
	int dlen, off;
	u_short len;
	char *msg;

	tcp = fin->fin_dp;
	dlen = fin->fin_dlen - (TCP_OFF(tcp) << 2);
	start = ntohl(tcp->th_seq);
	pptps = &pptp->pptp_side[rev];
	off = (char *)tcp - (char *)fin->fin_ip + (TCP_OFF(tcp) << 2) +
	      fin->fin_ipoff;

	if (dlen <= 0)
		return 0;
	/*
	 * If the complete data packet is before what we expect to see
	 * "next", just ignore it as the chances are we've already seen it.
	 * The next if statement following this one really just causes packets
	 * ahead of what we've seen to be dropped, implying that something in
	 * the middle went missing and we want to see that first.
	 */
	end = start + dlen;
	if (pptps->pptps_next > end && pptps->pptps_next > start)
		return 0;

	if (pptps->pptps_next != start) {
		if (ipf_p_pptp_debug > 5)
			printf("%s: next (%x) != start (%x)\n", funcname,
				pptps->pptps_next, start);
		return -1;
	}

	msg = (char *)fin->fin_dp + (TCP_OFF(tcp) << 2);

	while (dlen > 0) {
		off += pptps->pptps_bytes;
		if (pptps->pptps_gothdr == 0) {
			/*
			 * PPTP has an 8 byte header that inclues the cookie.
			 * The start of every message should include one and
			 * it should match 1a2b3c4d.  Byte order is ignored,
			 * deliberately, when printing out the error.
			 */
			len = MIN(8 - pptps->pptps_bytes, dlen);
			COPYDATA(fin->fin_m, off, len, pptps->pptps_wptr);
			pptps->pptps_bytes += len;
			pptps->pptps_wptr += len;
			hdr = (pptp_hdr_t *)pptps->pptps_buffer;
			if (pptps->pptps_bytes == 8) {
				pptps->pptps_next += 8;
				if (ntohl(hdr->pptph_cookie) != 0x1a2b3c4d) {
					if (ipf_p_pptp_debug > 1)
						printf("%s: bad cookie (%x)\n",
						       funcname,
						       hdr->pptph_cookie);
					return -1;
				}
			}
			dlen -= len;
			msg += len;
			off += len;

			pptps->pptps_gothdr = 1;
			len = ntohs(hdr->pptph_len);
			pptps->pptps_len = len;
			pptps->pptps_nexthdr += len;

			/*
			 * If a message is too big for the buffer, just set
			 * the fields for the next message to come along.
			 * The messages defined in RFC 2637 will not exceed
			 * 512 bytes (in total length) so this is likely a
			 * bad data packet, anyway.
			 */
			if (len > sizeof(pptps->pptps_buffer)) {
				if (ipf_p_pptp_debug > 3)
					printf("%s: message too big (%d)\n",
					       funcname, len);
				pptps->pptps_next = pptps->pptps_nexthdr;
				pptps->pptps_wptr = pptps->pptps_buffer;
				pptps->pptps_gothdr = 0;
				pptps->pptps_bytes = 0;
				pptps->pptps_len = 0;
				break;
			}
		}

		len = MIN(pptps->pptps_len - pptps->pptps_bytes, dlen);
		COPYDATA(fin->fin_m, off, len, pptps->pptps_wptr);
		pptps->pptps_bytes += len;
		pptps->pptps_wptr += len;
		pptps->pptps_next += len;

		if (pptps->pptps_len > pptps->pptps_bytes)
			break;

		ipf_p_pptp_message(fin, nat, pptp, pptps);
		pptps->pptps_wptr = pptps->pptps_buffer;
		pptps->pptps_gothdr = 0;
		pptps->pptps_bytes = 0;
		pptps->pptps_len = 0;

		start += len;
		msg += len;
		dlen -= len;
	}

	return 0;
}


/*
 * handle a complete PPTP message
 */
int
ipf_p_pptp_message(fin, nat, pptp, pptps)
	fr_info_t *fin;
	nat_t *nat;
	pptp_pxy_t *pptp;
	pptp_side_t *pptps;
{
	pptp_hdr_t *hdr = (pptp_hdr_t *)pptps->pptps_buffer;

	switch (ntohs(hdr->pptph_type))
	{
	case PPTP_MSGTYPE_CTL :
		ipf_p_pptp_mctl(fin, nat, pptp, pptps);
		break;

	default :
		break;
	}
	return 0;
}


/*
 * handle a complete PPTP control message
 */
int
ipf_p_pptp_mctl(fin, nat, pptp, pptps)
	fr_info_t *fin;
	nat_t *nat;
	pptp_pxy_t *pptp;
	pptp_side_t *pptps;
{
	u_short *buffer = (u_short *)(pptps->pptps_buffer);
	pptp_side_t *pptpo;

	if (pptps == &pptp->pptp_side[0])
		pptpo = &pptp->pptp_side[1];
	else
		pptpo = &pptp->pptp_side[0];

	/*
	 * Breakout to handle all the various messages.  Most are just state
	 * transition.
	 */
	switch (ntohs(buffer[4]))
	{
	case PPTP_MTCTL_STARTREQ :
		pptps->pptps_state = PPTP_MTCTL_STARTREQ;
		break;
	case PPTP_MTCTL_STARTREP :
		if (pptpo->pptps_state == PPTP_MTCTL_STARTREQ)
			pptps->pptps_state = PPTP_MTCTL_STARTREP;
		break;
	case PPTP_MTCTL_STOPREQ :
		pptps->pptps_state = PPTP_MTCTL_STOPREQ;
		break;
	case PPTP_MTCTL_STOPREP :
		if (pptpo->pptps_state == PPTP_MTCTL_STOPREQ)
			pptps->pptps_state = PPTP_MTCTL_STOPREP;
		break;
	case PPTP_MTCTL_ECHOREQ :
		pptps->pptps_state = PPTP_MTCTL_ECHOREQ;
		break;
	case PPTP_MTCTL_ECHOREP :
		if (pptpo->pptps_state == PPTP_MTCTL_ECHOREQ)
			pptps->pptps_state = PPTP_MTCTL_ECHOREP;
		break;
	case PPTP_MTCTL_OUTREQ :
		pptps->pptps_state = PPTP_MTCTL_OUTREQ;
		break;
	case PPTP_MTCTL_OUTREP :
		if (pptpo->pptps_state == PPTP_MTCTL_OUTREQ) {
			pptps->pptps_state = PPTP_MTCTL_OUTREP;
			pptp->pptp_call[0] = buffer[7];
			pptp->pptp_call[1] = buffer[6];
			ipf_p_pptp_donatstate(fin, nat, pptp);
		}
		break;
	case PPTP_MTCTL_INREQ :
		pptps->pptps_state = PPTP_MTCTL_INREQ;
		break;
	case PPTP_MTCTL_INREP :
		if (pptpo->pptps_state == PPTP_MTCTL_INREQ) {
			pptps->pptps_state = PPTP_MTCTL_INREP;
			pptp->pptp_call[0] = buffer[7];
			pptp->pptp_call[1] = buffer[6];
			ipf_p_pptp_donatstate(fin, nat, pptp);
		}
		break;
	case PPTP_MTCTL_INCONNECT :
		pptps->pptps_state = PPTP_MTCTL_INCONNECT;
		break;
	case PPTP_MTCTL_CLEAR :
		pptps->pptps_state = PPTP_MTCTL_CLEAR;
		break;
	case PPTP_MTCTL_DISCONNECT :
		pptps->pptps_state = PPTP_MTCTL_DISCONNECT;
		break;
	case PPTP_MTCTL_WANERROR :
		pptps->pptps_state = PPTP_MTCTL_WANERROR;
		break;
	case PPTP_MTCTL_LINKINFO :
		pptps->pptps_state = PPTP_MTCTL_LINKINFO;
		break;
	}

	return 0;
}


/*
 * For outgoing PPTP packets.  refresh timeouts for NAT & state entries, if
 * we can.  If they have disappeared, recreate them.
 */
int
ipf_p_pptp_inout(arg, fin, aps, nat)
	void *arg;
	fr_info_t *fin;
	ap_session_t *aps;
	nat_t *nat;
{
	pptp_pxy_t *pptp;
	tcphdr_t *tcp;
	int rev;

	if ((fin->fin_out == 1) && (nat->nat_dir == NAT_INBOUND))
		rev = 1;
	else if ((fin->fin_out == 0) && (nat->nat_dir == NAT_OUTBOUND))
		rev = 1;
	else
		rev = 0;

	tcp = (tcphdr_t *)fin->fin_dp;
	if ((tcp->th_flags & TH_OPENING) == TH_OPENING) {
		pptp = (pptp_pxy_t *)aps->aps_data;
		pptp->pptp_side[1 - rev].pptps_next = ntohl(tcp->th_ack);
		pptp->pptp_side[1 - rev].pptps_nexthdr = ntohl(tcp->th_ack);
		pptp->pptp_side[rev].pptps_next = ntohl(tcp->th_seq) + 1;
		pptp->pptp_side[rev].pptps_nexthdr = ntohl(tcp->th_seq) + 1;
	}
	return ipf_p_pptp_nextmessage(fin, nat, (pptp_pxy_t *)aps->aps_data,
				     rev);
}


/*
 * clean up after ourselves.
 */
void
ipf_p_pptp_del(softc, aps)
	ipf_main_softc_t *softc;
	ap_session_t *aps;
{
	pptp_pxy_t *pptp;

	pptp = aps->aps_data;

	if (pptp != NULL) {
		/*
		 * Don't bother changing any of the NAT structure details,
		 * *_del() is on a callback from aps_free(), from nat_delete()
		 */

		READ_ENTER(&softc->ipf_state);
		if (pptp->pptp_state != NULL) {
			ipf_state_setpending(softc, pptp->pptp_state);
		}
		RWLOCK_EXIT(&softc->ipf_state);

		if (pptp->pptp_nat != NULL)
			ipf_nat_setpending(softc, pptp->pptp_nat);
		pptp->pptp_rule->in_flags |= IPN_DELETE;
		ipf_nat_rule_deref(softc, &pptp->pptp_rule);
	}
}