telnet/telnetd/state.c

/*
 * Copyright (c) 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/* based on @(#)state.c	8.1 (Berkeley) 6/4/93 */

#include <autoconf.h>

#include "telnetd.h"
#if	defined(AUTHENTICATION)
#include <libtelnet/auth.h>
#endif
#if defined(ENCRYPTION)
#include <libtelnet/encrypt.h>
#endif

unsigned char	doopt[] = { IAC, DO, '%', 'c', 0 };
unsigned char	dont[] = { IAC, DONT, '%', 'c', 0 };
unsigned char	will[] = { IAC, WILL, '%', 'c', 0 };
unsigned char	wont[] = { IAC, WONT, '%', 'c', 0 };
int	not42 = 1;

static int envvarok (char *);

/*
 * Buffer for sub-options, and macros
 * for suboptions buffer manipulations
 */
unsigned char subbuffer[TELNET_BUFSIZE], *subpointer= subbuffer, *subend= subbuffer;

#define	SB_CLEAR()	subpointer = subbuffer
#define	SB_TERM()	{ subend = subpointer; SB_CLEAR(); }
#define	SB_ACCUM(c)	if (subpointer < (subbuffer+sizeof subbuffer)) { \
				*subpointer++ = (c); \
			}
#define	SB_GET()	((*subpointer++)&0xff)
#define	SB_EOF()	(subpointer >= subend)
#define	SB_LEN()	(subend - subpointer)

#ifdef	ENV_HACK
unsigned char *subsave;
#define SB_SAVE()	subsave = subpointer;
#define	SB_RESTORE()	subpointer = subsave;
#endif


/*
 * State for recv fsm
 */
#define	TS_DATA		0	/* base state */
#define	TS_IAC		1	/* look for double IAC's */
#define	TS_CR		2	/* CR-LF ->'s CR */
#define	TS_SB		3	/* throw away begin's... */
#define	TS_SE		4	/* ...end's (suboption negotiation) */
#define	TS_WILL		5	/* will option negotiation */
#define	TS_WONT		6	/* wont " */
#define	TS_DO		7	/* do " */
#define	TS_DONT		8	/* dont " */

static void sb_auth_complete()
{
  if (!auth_negotiated) {
    static char *error =
      "An environment option was sent before authentication negotiation completed.\r\nThis may create a security hazard. Connection dropped.\r\n";
    netputs(error);
    netflush();
    exit(1);
  }
}

	void
telrcv()
{
	register int c;
	static int state = TS_DATA;
#if	defined(CRAY2) && defined(UNICOS5)
	char *opfrontp = pfrontp;
#endif

	while (ncc > 0) {
		if ((&ptyobuf[BUFSIZ] - pfrontp) < 1)
			break;
		c = *netip++ & 0377, ncc--;
#ifdef	ENCRYPTION
		if (decrypt_input)
			c = (*decrypt_input)(c);
#endif	/* ENCRYPTION */
		switch (state) {

		case TS_CR:
			state = TS_DATA;
			/* Strip off \n or \0 after a \r */
			if ((c == 0) || (c == '\n')) {
				break;
			}
			/* FALL THROUGH */

		case TS_DATA:
			if (c == IAC) {
				state = TS_IAC;
				break;
			}
			/*
			 * We now map \r\n ==> \r for pragmatic reasons.
			 * Many client implementations send \r\n when
			 * the user hits the CarriageReturn key.
			 *
			 * We USED to map \r\n ==> \n, since \r\n says
			 * that we want to be in column 1 of the next
			 * printable line, and \n is the standard
			 * unix way of saying that (\r is only good
			 * if CRMOD is set, which it normally is).
			 */
			if ((c == '\r') && his_state_is_wont(TELOPT_BINARY)) {
				int nc = *netip;
#ifdef	ENCRYPTION
				if (decrypt_input)
					nc = (*decrypt_input)(nc & 0xff);
#endif	/* ENCRYPTION */
#ifdef	LINEMODE
				/*
				 * If we are operating in linemode,
				 * convert to local end-of-line.
				 */
				if (linemode && (ncc > 0) && (('\n' == nc) ||
					 ((0 == nc) && tty_iscrnl())) ) {
					netip++; ncc--;
					c = '\n';
				} else
#endif
				{
#ifdef	ENCRYPTION
					if (decrypt_input)
						(void)(*decrypt_input)(-1);
#endif	/* ENCRYPTION */
					state = TS_CR;
				}
			}
			*pfrontp++ = c;
			break;

		case TS_IAC:
gotiac:			switch (c) {

			/*
			 * Send the process on the pty side an
			 * interrupt.  Do this with a NULL or
			 * interrupt char; depending on the tty mode.
			 */
			case IP:
				DIAG(TD_OPTIONS,
					printoption("td: recv IAC", c));
				interrupt();
				break;

			case BREAK:
				DIAG(TD_OPTIONS,
					printoption("td: recv IAC", c));
				sendbrk();
				break;

			/*
			 * Are You There?
			 */
			case AYT:
				DIAG(TD_OPTIONS,
					printoption("td: recv IAC", c));
				recv_ayt();
				break;

			/*
			 * Abort Output
			 */
			case AO:
			    {
				DIAG(TD_OPTIONS,
					printoption("td: recv IAC", c));
				ptyflush();	/* half-hearted */
				init_termbuf();

				if (slctab[SLC_AO].sptr &&
				    *slctab[SLC_AO].sptr != (cc_t)(_POSIX_VDISABLE)) {
				    *pfrontp++ =
					(unsigned char)*slctab[SLC_AO].sptr;
				}

				netclear();	/* clear buffer back */
				netprintf_urg("%c%c", IAC, DM);
				DIAG(TD_OPTIONS,
					printoption("td: send IAC", DM));
				break;
			    }

			/*
			 * Erase Character and
			 * Erase Line
			 */
			case EC:
			case EL:
			    {
				cc_t ch;

				DIAG(TD_OPTIONS,
					printoption("td: recv IAC", c));
				ptyflush();	/* half-hearted */
				init_termbuf();
				if (c == EC)
					ch = *slctab[SLC_EC].sptr;
				else
					ch = *slctab[SLC_EL].sptr;
				if (ch != (cc_t)(_POSIX_VDISABLE))
					*pfrontp++ = (unsigned char)ch;
				break;
			    }

			/*
			 * Check for urgent data...
			 */
			case DM:
				DIAG(TD_OPTIONS,
					printoption("td: recv IAC", c));
				SYNCHing = stilloob(net);
				settimer(gotDM);
				break;


			/*
			 * Begin option subnegotiation...
			 */
			case SB:
				state = TS_SB;
				SB_CLEAR();
				continue;

			case WILL:
				state = TS_WILL;
				continue;

			case WONT:
				state = TS_WONT;
				continue;

			case DO:
				state = TS_DO;
				continue;

			case DONT:
				state = TS_DONT;
				continue;
			case EOR:
				if (his_state_is_will(TELOPT_EOR))
					doeof();
				break;

			/*
			 * Handle RFC 10xx Telnet linemode option additions
			 * to command stream (EOF, SUSP, ABORT).
			 */
			case xEOF:
				doeof();
				break;

			case SUSP:
				sendsusp();
				break;

			case ABORT:
				sendbrk();
				break;

			case IAC:
				*pfrontp++ = c;
				break;
			}
			state = TS_DATA;
			break;

		case TS_SB:
			if (c == IAC) {
				state = TS_SE;
			} else {
				SB_ACCUM(c);
			}
			break;

		case TS_SE:
			if (c != SE) {
				if (c != IAC) {
					/*
					 * bad form of suboption negotiation.
					 * handle it in such a way as to avoid
					 * damage to local state.  Parse
					 * suboption buffer found so far,
					 * then treat remaining stream as
					 * another command sequence.
					 */

					/* for DIAGNOSTICS */
					SB_ACCUM(IAC);
					SB_ACCUM(c);
					subpointer -= 2;

					SB_TERM();
					suboption();
					state = TS_IAC;
					goto gotiac;
				}
				SB_ACCUM(c);
				state = TS_SB;
			} else {
				/* for DIAGNOSTICS */
				SB_ACCUM(IAC);
				SB_ACCUM(SE);
				subpointer -= 2;

				SB_TERM();
				suboption();	/* handle sub-option */
				state = TS_DATA;
			}
			break;

		case TS_WILL:
			willoption(c);
			state = TS_DATA;
			continue;

		case TS_WONT:
			wontoption(c);
			state = TS_DATA;
			continue;

		case TS_DO:
			dooption(c);
			state = TS_DATA;
			continue;

		case TS_DONT:
			dontoption(c);
			state = TS_DATA;
			continue;

		default:
			syslog(LOG_ERR, "telnetd: panic state=%d", state);
			printf("telnetd: panic state=%d\n", state);
			exit(1);
		}
	}
#if	defined(CRAY2) && defined(UNICOS5)
	if (!linemode) {
		char	xptyobuf[BUFSIZ+NETSLOP];
		char	xbuf2[BUFSIZ];
		register char *cp;
		int n = pfrontp - opfrontp, oc;
		memcpy(xptyobuf, opfrontp, n);
		pfrontp = opfrontp;
		pfrontp += term_input(xptyobuf, pfrontp, n, BUFSIZ+NETSLOP,
					xbuf2, &oc, BUFSIZ);
		for (cp = xbuf2; oc > 0; --oc) {
			if (*cp == IAC)
				netprintf("%c%c", *cp++, IAC);
			else
				netprintf("%c", *cp++);
		}
	}
#endif	/* defined(CRAY2) && defined(UNICOS5) */
}  /* end of telrcv */

/*
 * The will/wont/do/dont state machines are based on Dave Borman's
 * Telnet option processing state machine.
 *
 * These correspond to the following states:
 *	my_state = the last negotiated state
 *	want_state = what I want the state to go to
 *	want_resp = how many requests I have sent
 * All state defaults are negative, and resp defaults to 0.
 *
 * When initiating a request to change state to new_state:
 *
 * if ((want_resp == 0 && new_state == my_state) || want_state == new_state) {
 *	do nothing;
 * } else {
 *	want_state = new_state;
 *	send new_state;
 *	want_resp++;
 * }
 *
 * When receiving new_state:
 *
 * if (want_resp) {
 *	want_resp--;
 *	if (want_resp && (new_state == my_state))
 *		want_resp--;
 * }
 * if ((want_resp == 0) && (new_state != want_state)) {
 *	if (ok_to_switch_to new_state)
 *		want_state = new_state;
 *	else
 *		want_resp++;
 *	send want_state;
 * }
 * my_state = new_state;
 *
 * Note that new_state is implied in these functions by the function itself.
 * will and do imply positive new_state, wont and dont imply negative.
 *
 * Finally, there is one catch.  If we send a negative response to a
 * positive request, my_state will be the positive while want_state will
 * remain negative.  my_state will revert to negative when the negative
 * acknowlegment arrives from the peer.  Thus, my_state generally tells
 * us not only the last negotiated state, but also tells us what the peer
 * wants to be doing as well.  It is important to understand this difference
 * as we may wish to be processing data streams based on our desired state
 * (want_state) or based on what the peer thinks the state is (my_state).
 *
 * This all works fine because if the peer sends a positive request, the data
 * that we receive prior to negative acknowlegment will probably be affected
 * by the positive state, and we can process it as such (if we can; if we
 * can't then it really doesn't matter).  If it is that important, then the
 * peer probably should be buffering until this option state negotiation
 * is complete.
 *
 */
	void
send_do(option, init)
	int option, init;
{
	if (init) {
		if ((do_dont_resp[option] == 0 && his_state_is_will(option)) ||
		    his_want_state_is_will(option))
			return;
		/*
		 * Special case for TELOPT_TM:  We send a DO, but pretend
		 * that we sent a DONT, so that we can send more DOs if
		 * we want to.
		 */
		if (option == TELOPT_TM)
			set_his_want_state_wont(option);
		else
			set_his_want_state_will(option);
		do_dont_resp[option]++;
	}
	netprintf((char *)doopt, option);

	DIAG(TD_OPTIONS, printoption("td: send do", option));
}

#ifdef	AUTHENTICATION
extern void auth_request();
#endif
#ifdef	LINEMODE
static void doclientstat(void);
#endif
#ifdef	ENCRYPTION
extern void encrypt_send_support();
#endif	/* ENCRYPTION */

	void
willoption(option)
	int option;
{
	int changeok = 0;
	void (*func)() = 0;

	/*
	 * process input from peer.
	 */

	DIAG(TD_OPTIONS, printoption("td: recv will", option));

	if (do_dont_resp[option]) {
		do_dont_resp[option]--;
		if (do_dont_resp[option] && his_state_is_will(option))
			do_dont_resp[option]--;
	}
	if (do_dont_resp[option] == 0) {
	    if (his_want_state_is_wont(option)) {
		switch (option) {

		case TELOPT_BINARY:
			init_termbuf();
			tty_binaryin(1);
			set_termbuf();
			changeok++;
			break;

		case TELOPT_ECHO:
			/*
			 * See comments below for more info.
			 */
			not42 = 0;	/* looks like a 4.2 system */
			break;

		case TELOPT_TM:
#if	defined(LINEMODE) && defined(KLUDGELINEMODE)
			/*
			 * This telnetd implementation does not really
			 * support timing marks, it just uses them to
			 * support the kludge linemode stuff.  If we
			 * receive a will or wont TM in response to our
			 * do TM request that may have been sent to
			 * determine kludge linemode support, process
			 * it, otherwise TM should get a negative
			 * response back.
			 */
			/*
			 * Handle the linemode kludge stuff.
			 * If we are not currently supporting any
			 * linemode at all, then we assume that this
			 * is the client telling us to use kludge
			 * linemode in response to our query.  Set the
			 * linemode type that is to be supported, note
			 * that the client wishes to use linemode, and
			 * eat the will TM as though it never arrived.
			 */
			if (lmodetype < KLUDGE_LINEMODE) {
				lmodetype = KLUDGE_LINEMODE;
				clientstat(TELOPT_LINEMODE, WILL, 0);
				send_wont(TELOPT_SGA, 1);
			} else if (lmodetype == NO_AUTOKLUDGE) {
				lmodetype = KLUDGE_OK;
			}
#endif	/* defined(LINEMODE) && defined(KLUDGELINEMODE) */
			/*
			 * We never respond to a WILL TM, and
			 * we leave the state WONT.
			 */
			return;

		case TELOPT_LFLOW:
			/*
			 * If we are going to support flow control
			 * option, then don't worry peer that we can't
			 * change the flow control characters.
			 */
			slctab[SLC_XON].defset.flag &= ~SLC_LEVELBITS;
			slctab[SLC_XON].defset.flag |= SLC_DEFAULT;
			slctab[SLC_XOFF].defset.flag &= ~SLC_LEVELBITS;
			slctab[SLC_XOFF].defset.flag |= SLC_DEFAULT;
		case TELOPT_TTYPE:
		case TELOPT_SGA:
		case TELOPT_NAWS:
		case TELOPT_TSPEED:
		case TELOPT_XDISPLOC:
		case TELOPT_NEW_ENVIRON:
		case TELOPT_OLD_ENVIRON:
			changeok++;
			break;

#ifdef	LINEMODE
		case TELOPT_LINEMODE:
# ifdef	KLUDGELINEMODE
			/*
			 * Note client's desire to use linemode.
			 */
			lmodetype = REAL_LINEMODE;
# endif	/* KLUDGELINEMODE */
			func = doclientstat;
			changeok++;
			break;
#endif	/* LINEMODE */

#ifdef	AUTHENTICATION
		case TELOPT_AUTHENTICATION:
			func = auth_request;
			changeok++;
			break;
#endif

#ifdef	ENCRYPTION
		case TELOPT_ENCRYPT:
			func = encrypt_send_support;
			changeok++;
			break;
#endif	/* ENCRYPTION */

		default:
			break;
		}
		if (changeok) {
			set_his_want_state_will(option);
			send_do(option, 0);
		} else {
			do_dont_resp[option]++;
			send_dont(option, 0);
		}
	    } else {
		/*
		 * Option processing that should happen when
		 * we receive conformation of a change in
		 * state that we had requested.
		 */
		switch (option) {
		case TELOPT_ECHO:
			not42 = 0;	/* looks like a 4.2 system */
			/*
			 * Egads, he responded "WILL ECHO".  Turn
			 * it off right now!
			 */
			send_dont(option, 1);
			/*
			 * "WILL ECHO".  Kludge upon kludge!
			 * A 4.2 client is now echoing user input at
			 * the tty.  This is probably undesireable and
			 * it should be stopped.  The client will
			 * respond WONT TM to the DO TM that we send to
			 * check for kludge linemode.  When the WONT TM
			 * arrives, linemode will be turned off and a
			 * change propogated to the pty.  This change
			 * will cause us to process the new pty state
			 * in localstat(), which will notice that
			 * linemode is off and send a WILL ECHO
			 * so that we are properly in character mode and
			 * all is well.
			 */
			break;
#ifdef	LINEMODE
		case TELOPT_LINEMODE:
# ifdef	KLUDGELINEMODE
			/*
			 * Note client's desire to use linemode.
			 */
			lmodetype = REAL_LINEMODE;
# endif	/* KLUDGELINEMODE */
			func = doclientstat;
			break;
#endif	/* LINEMODE */

#ifdef	AUTHENTICATION
		case TELOPT_AUTHENTICATION:
			func = auth_request;
			break;
#endif

#ifdef	ENCRYPTION
		case TELOPT_ENCRYPT:
			func = encrypt_send_support;
			break;
#endif	/* ENCRYPTION */
		case TELOPT_LFLOW:
			func = flowstat;
			break;
		}
	    }
	}
	set_his_state_will(option);
	if (func)
		(*func)();
}  /* end of willoption */

	void
send_dont(option, init)
	int option, init;
{
	if (init) {
		if ((do_dont_resp[option] == 0 && his_state_is_wont(option)) ||
		    his_want_state_is_wont(option))
			return;
		set_his_want_state_wont(option);
		do_dont_resp[option]++;
	}
	netprintf((char *)dont, option);

	DIAG(TD_OPTIONS, printoption("td: send dont", option));
}

	void
wontoption(option)
	int option;
{
	/*
	 * Process client input.
	 */

	DIAG(TD_OPTIONS, printoption("td: recv wont", option));

	if (do_dont_resp[option]) {
		do_dont_resp[option]--;
		if (do_dont_resp[option] && his_state_is_wont(option))
			do_dont_resp[option]--;
	}
	if (do_dont_resp[option] == 0) {
	    if (his_want_state_is_will(option)) {
		/* it is always ok to change to negative state */
		switch (option) {
		case TELOPT_ECHO:
			not42 = 1; /* doesn't seem to be a 4.2 system */
			break;

		case TELOPT_BINARY:
			init_termbuf();
			tty_binaryin(0);
			set_termbuf();
			break;

#ifdef	LINEMODE
		case TELOPT_LINEMODE:
# ifdef	KLUDGELINEMODE
			/*
			 * If real linemode is supported, then client is
			 * asking to turn linemode off.
			 */
			if (lmodetype != REAL_LINEMODE)
				break;
			lmodetype = KLUDGE_LINEMODE;
# endif	/* KLUDGELINEMODE */
			clientstat(TELOPT_LINEMODE, WONT, 0);
			break;
#endif	/* LINEMODE */

		case TELOPT_TM:
			/*
			 * If we get a WONT TM, and had sent a DO TM,
			 * don't respond with a DONT TM, just leave it
			 * as is.  Short circut the state machine to
			 * achive this.
			 */
			set_his_want_state_wont(TELOPT_TM);
			return;

		case TELOPT_LFLOW:
			/*
			 * If we are not going to support flow control
			 * option, then let peer know that we can't
			 * change the flow control characters.
			 */
			slctab[SLC_XON].defset.flag &= ~SLC_LEVELBITS;
			slctab[SLC_XON].defset.flag |= SLC_CANTCHANGE;
			slctab[SLC_XOFF].defset.flag &= ~SLC_LEVELBITS;
			slctab[SLC_XOFF].defset.flag |= SLC_CANTCHANGE;
			break;

#if	defined(AUTHENTICATION)
		case TELOPT_AUTHENTICATION:
			auth_finished(0, AUTH_REJECT);
			break;
#endif

		/*
		 * For options that we might spin waiting for
		 * sub-negotiation, if the client turns off the
		 * option rather than responding to the request,
		 * we have to treat it here as if we got a response
		 * to the sub-negotiation, (by updating the timers)
		 * so that we'll break out of the loop.
		 */
		case TELOPT_TTYPE:
			settimer(ttypesubopt);
			break;

		case TELOPT_TSPEED:
			settimer(tspeedsubopt);
			break;

		case TELOPT_XDISPLOC:
			settimer(xdisplocsubopt);
			break;

		case TELOPT_OLD_ENVIRON:
			settimer(oenvironsubopt);
			break;

		case TELOPT_NEW_ENVIRON:
			settimer(environsubopt);
			break;

		default:
			break;
		}
		set_his_want_state_wont(option);
		if (his_state_is_will(option))
			send_dont(option, 0);
	    } else {
		switch (option) {
		case TELOPT_TM:
#if	defined(LINEMODE) && defined(KLUDGELINEMODE)
			if (lmodetype < NO_AUTOKLUDGE) {
				lmodetype = NO_LINEMODE;
				clientstat(TELOPT_LINEMODE, WONT, 0);
				send_will(TELOPT_SGA, 1);
				send_will(TELOPT_ECHO, 1);
			}
#endif	/* defined(LINEMODE) && defined(KLUDGELINEMODE) */
			break;

#if	defined(AUTHENTICATION)
		case TELOPT_AUTHENTICATION:
			auth_finished(0, AUTH_REJECT);
			break;
#endif
		default:
			break;
		}
	    }
	}
	set_his_state_wont(option);

}  /* end of wontoption */

	void
send_will(option, init)
	int option, init;
{
	if (init) {
		if ((will_wont_resp[option] == 0 && my_state_is_will(option))||
		    my_want_state_is_will(option))
			return;
		set_my_want_state_will(option);
		will_wont_resp[option]++;
	}
	netprintf((char *)will, option);

	DIAG(TD_OPTIONS, printoption("td: send will", option));
}

#if	!defined(LINEMODE) || !defined(KLUDGELINEMODE)
/*
 * When we get a DONT SGA, we will try once to turn it
 * back on.  If the other side responds DONT SGA, we
 * leave it at that.  This is so that when we talk to
 * clients that understand KLUDGELINEMODE but not LINEMODE,
 * we'll keep them in char-at-a-time mode.
 */
int turn_on_sga = 0;
#endif

	void
dooption(option)
	int option;
{
	int changeok = 0;

	/*
	 * Process client input.
	 */

	DIAG(TD_OPTIONS, printoption("td: recv do", option));

	if (will_wont_resp[option]) {
		will_wont_resp[option]--;
		if (will_wont_resp[option] && my_state_is_will(option))
			will_wont_resp[option]--;
	}
	if ((will_wont_resp[option] == 0) && (my_want_state_is_wont(option))) {
		switch (option) {
		case TELOPT_ECHO:
#ifdef	LINEMODE
# ifdef	KLUDGELINEMODE
			if (lmodetype == NO_LINEMODE)
# else
			if (his_state_is_wont(TELOPT_LINEMODE))
# endif
#endif
			{
				init_termbuf();
				tty_setecho(1);
				set_termbuf();
			}
			changeok++;
			break;

		case TELOPT_BINARY:
			init_termbuf();
			tty_binaryout(1);
			set_termbuf();
			changeok++;
			break;

		case TELOPT_SGA:
#if	defined(LINEMODE) && defined(KLUDGELINEMODE)
			/*
			 * If kludge linemode is in use, then we must
			 * process an incoming do SGA for linemode
			 * purposes.
			 */
			if (lmodetype == KLUDGE_LINEMODE) {
				/*
				 * Receipt of "do SGA" in kludge
				 * linemode is the peer asking us to
				 * turn off linemode.  Make note of
				 * the request.
				 */
				clientstat(TELOPT_LINEMODE, WONT, 0);
				/*
				 * If linemode did not get turned off
				 * then don't tell peer that we did.
				 * Breaking here forces a wont SGA to
				 * be returned.
				 */
				if (linemode)
					break;
			}
#else
			turn_on_sga = 0;
#endif	/* defined(LINEMODE) && defined(KLUDGELINEMODE) */
			changeok++;
			break;

		case TELOPT_STATUS:
			changeok++;
			break;

		case TELOPT_TM:
			/*
			 * Special case for TM.  We send a WILL, but
			 * pretend we sent a WONT.
			 */
			send_will(option, 0);
			set_my_want_state_wont(option);
			set_my_state_wont(option);
			return;

		case TELOPT_LOGOUT:
			/*
			 * When we get a LOGOUT option, respond
			 * with a WILL LOGOUT, make sure that
			 * it gets written out to the network,
			 * and then just go away...
			 */
			set_my_want_state_will(TELOPT_LOGOUT);
			send_will(TELOPT_LOGOUT, 0);
			set_my_state_will(TELOPT_LOGOUT);
			(void)netflush();
			(void)signal(SIGCHLD, SIG_DFL);
			cleanup(0);
			/* NOT REACHED */
			break;

#ifdef	ENCRYPTION
		case TELOPT_ENCRYPT:
			changeok++;
			break;
#endif	/* ENCRYPTION */
		case TELOPT_LINEMODE:
		case TELOPT_TTYPE:
		case TELOPT_NAWS:
		case TELOPT_TSPEED:
		case TELOPT_LFLOW:
		case TELOPT_XDISPLOC:
#ifdef	TELOPT_ENVIRON
		case TELOPT_NEW_ENVIRON:
#endif
		case TELOPT_OLD_ENVIRON:
		default:
			break;
		}
		if (changeok) {
			set_my_want_state_will(option);
			send_will(option, 0);
		} else {
			will_wont_resp[option]++;
			send_wont(option, 0);
		}
	}
	set_my_state_will(option);

}  /* end of dooption */

	void
send_wont(option, init)
	int option, init;
{
	if (init) {
		if ((will_wont_resp[option] == 0 && my_state_is_wont(option)) ||
		    my_want_state_is_wont(option))
			return;
		set_my_want_state_wont(option);
		will_wont_resp[option]++;
	}
	netprintf((char *)wont, option);

	DIAG(TD_OPTIONS, printoption("td: send wont", option));
}

	void
dontoption(option)
	int option;
{
	/*
	 * Process client input.
	 */


	DIAG(TD_OPTIONS, printoption("td: recv dont", option));

	if (will_wont_resp[option]) {
		will_wont_resp[option]--;
		if (will_wont_resp[option] && my_state_is_wont(option))
			will_wont_resp[option]--;
	}
	if ((will_wont_resp[option] == 0) && (my_want_state_is_will(option))) {
		switch (option) {
		case TELOPT_BINARY:
			init_termbuf();
			tty_binaryout(0);
			set_termbuf();
			break;

		case TELOPT_ECHO:	/* we should stop echoing */
#ifdef	LINEMODE
# ifdef	KLUDGELINEMODE
			if ((lmodetype != REAL_LINEMODE) &&
			    (lmodetype != KLUDGE_LINEMODE))
# else
			if (his_state_is_wont(TELOPT_LINEMODE))
# endif
#endif
			{
				init_termbuf();
				tty_setecho(0);
				set_termbuf();
			}
			break;

		case TELOPT_SGA:
#if	defined(LINEMODE) && defined(KLUDGELINEMODE)
			/*
			 * If kludge linemode is in use, then we
			 * must process an incoming do SGA for
			 * linemode purposes.
			 */
			if ((lmodetype == KLUDGE_LINEMODE) ||
			    (lmodetype == KLUDGE_OK)) {
				/*
				 * The client is asking us to turn
				 * linemode on.
				 */
				lmodetype = KLUDGE_LINEMODE;
				clientstat(TELOPT_LINEMODE, WILL, 0);
				/*
				 * If we did not turn line mode on,
				 * then what do we say?  Will SGA?
				 * This violates design of telnet.
				 * Gross.  Very Gross.
				 */
			}
			break;
#else
			set_my_want_state_wont(option);
			if (my_state_is_will(option))
				send_wont(option, 0);
			set_my_state_wont(option);
			if (turn_on_sga ^= 1)
				send_will(option, 1);
			return;
#endif	/* defined(LINEMODE) && defined(KLUDGELINEMODE) */

		default:
			break;
		}

		set_my_want_state_wont(option);
		if (my_state_is_will(option))
			send_wont(option, 0);
	}
	set_my_state_wont(option);

}  /* end of dontoption */

#ifdef	ENV_HACK
int env_ovar = -1;
int env_ovalue = -1;
#else	/* ENV_HACK */
# define env_ovar OLD_ENV_VAR
# define env_ovalue OLD_ENV_VALUE
#endif	/* ENV_HACK */

/*
 * suboption()
 *
 *	Look at the sub-option buffer, and try to be helpful to the other
 * side.
 *
 *	Currently we recognize:
 *
 *	Terminal type is
 *	Linemode
 *	Window size
 *	Terminal speed
 */
	void
suboption()
{
    register int subchar;

    DIAG(TD_OPTIONS, {netflush(); printsub('<', subpointer, SB_LEN()+2);});

    subchar = SB_GET();
    switch (subchar) {
    case TELOPT_TSPEED: {
	register int xspeed, rspeed;

	if (his_state_is_wont(TELOPT_TSPEED))	/* Ignore if option disabled */
		break;

	sb_auth_complete();

	settimer(tspeedsubopt);

	if (SB_EOF() || SB_GET() != TELQUAL_IS)
		return;

	xspeed = atoi((char *)subpointer);

	while (SB_GET() != ',' && !SB_EOF());
	if (SB_EOF())
		return;

	rspeed = atoi((char *)subpointer);
	clientstat(TELOPT_TSPEED, xspeed, rspeed);

	break;

    }  /* end of case TELOPT_TSPEED */

    case TELOPT_TTYPE: {		/* Yaaaay! */
	char *tt;

	if (his_state_is_wont(TELOPT_TTYPE))	/* Ignore if option disabled */
		break;
	sb_auth_complete();
	settimer(ttypesubopt);

	if (SB_EOF() || SB_GET() != TELQUAL_IS) {
	    return;		/* ??? XXX but, this is the most robust */
	}

	tt = terminaltype;

	while ((tt < (terminaltype + sizeof(terminaltype) - 1)) && !SB_EOF()) {
	    register int c;

	    c = SB_GET();
	    if (isupper(c)) {
		c = tolower(c);
	    }
	    *tt++ = c;    /* accumulate name */
	}
	*tt = 0;
	break;
    }  /* end of case TELOPT_TTYPE */

    case TELOPT_NAWS: {
	register int xwinsize, ywinsize;

	if (his_state_is_wont(TELOPT_NAWS))	/* Ignore if option disabled */
		break;

	if (SB_EOF())
		return;
	xwinsize = SB_GET() << 8;
	if (SB_EOF())
		return;
	xwinsize |= SB_GET();
	if (SB_EOF())
		return;
	ywinsize = SB_GET() << 8;
	if (SB_EOF())
		return;
	ywinsize |= SB_GET();
	clientstat(TELOPT_NAWS, xwinsize, ywinsize);

	break;

    }  /* end of case TELOPT_NAWS */

#ifdef	LINEMODE
    case TELOPT_LINEMODE: {
	register int request;

	if (his_state_is_wont(TELOPT_LINEMODE))	/* Ignore if option disabled */
		break;
	/*
	 * Process linemode suboptions.
	 */
	if (SB_EOF())
	    break;		/* garbage was sent */
	request = SB_GET();	/* get will/wont */

	if (SB_EOF())
	    break;		/* another garbage check */

	if (request == LM_SLC) {  /* SLC is not preceeded by WILL or WONT */
		/*
		 * Process suboption buffer of slc's
		 */
		start_slc(1);
		do_opt_slc(subpointer, subend - subpointer);
		(void) end_slc(0);
		break;
	} else if (request == LM_MODE) {
		if (SB_EOF())
		    return;
		useeditmode = SB_GET();  /* get mode flag */
		clientstat(LM_MODE, 0, 0);
		break;
	}

	if (SB_EOF())
	    break;
	switch (SB_GET()) {  /* what suboption? */
	case LM_FORWARDMASK:
		/*
		 * According to spec, only server can send request for
		 * forwardmask, and client can only return a positive response.
		 * So don't worry about it.
		 */

	default:
		break;
	}
	break;
    }  /* end of case TELOPT_LINEMODE */
#endif
    case TELOPT_STATUS: {
	int mode;

	if (SB_EOF())
	    break;
	mode = SB_GET();
	switch (mode) {
	case TELQUAL_SEND:
	    if (my_state_is_will(TELOPT_STATUS))
		send_status();
	    break;

	case TELQUAL_IS:
	    break;

	default:
	    break;
	}
	break;
    }  /* end of case TELOPT_STATUS */

    case TELOPT_XDISPLOC: {
	if (SB_EOF() || SB_GET() != TELQUAL_IS)
		return;
	sb_auth_complete();
	settimer(xdisplocsubopt);
	subpointer[SB_LEN()] = '\0';
	(void)setenv("DISPLAY", (char *)subpointer, 1);
	break;
    }  /* end of case TELOPT_XDISPLOC */

#ifdef	TELOPT_NEW_ENVIRON
    case TELOPT_NEW_ENVIRON:
#endif
    case TELOPT_OLD_ENVIRON: {
	register int c;
	register char *cp, *varp, *valp;

	if (SB_EOF())
		return;
	sb_auth_complete();
	c = SB_GET();
	if (c == TELQUAL_IS) {
		if (subchar == TELOPT_OLD_ENVIRON)
			settimer(oenvironsubopt);
		else
			settimer(environsubopt);
	} else if (c != TELQUAL_INFO) {
		return;
	}

#ifdef	TELOPT_NEW_ENVIRON
	if (subchar == TELOPT_NEW_ENVIRON) {
	    while (!SB_EOF()) {
		c = SB_GET();
		if ((c == NEW_ENV_VAR) || (c == ENV_USERVAR))
			break;
	    }
	} else
#endif
	{
#ifdef	ENV_HACK
	    /*
	     * We only want to do this if we haven't already decided
	     * whether or not the other side has its VALUE and VAR
	     * reversed.
	     */
	    if (env_ovar < 0) {
		register int last = -1;		/* invalid value */
		int empty = 0;
		int got_var = 0, got_value = 0, got_uservar = 0;

		/*
		 * The other side might have its VALUE and VAR values
		 * reversed.  To be interoperable, we need to determine
		 * which way it is.  If the first recognized character
		 * is a VAR or VALUE, then that will tell us what
		 * type of client it is.  If the fist recognized
		 * character is a USERVAR, then we continue scanning
		 * the suboption looking for two consecutive
		 * VAR or VALUE fields.  We should not get two
		 * consecutive VALUE fields, so finding two
		 * consecutive VALUE or VAR fields will tell us
		 * what the client is.
		 */
		SB_SAVE();
		while (!SB_EOF()) {
			c = SB_GET();
			switch(c) {
			case OLD_ENV_VAR:
				if (last < 0 || last == OLD_ENV_VAR
				    || (empty && (last == OLD_ENV_VALUE)))
					goto env_ovar_ok;
				got_var++;
				last = OLD_ENV_VAR;
				break;
			case OLD_ENV_VALUE:
				if (last < 0 || last == OLD_ENV_VALUE
				    || (empty && (last == OLD_ENV_VAR)))
					goto env_ovar_wrong;
				got_value++;
				last = OLD_ENV_VALUE;
				break;
			case ENV_USERVAR:
				/* count strings of USERVAR as one */
				if (last != ENV_USERVAR)
					got_uservar++;
				if (empty) {
					if (last == OLD_ENV_VALUE)
						goto env_ovar_ok;
					if (last == OLD_ENV_VAR)
						goto env_ovar_wrong;
				}
				last = ENV_USERVAR;
				break;
			case ENV_ESC:
				if (!SB_EOF())
					c = SB_GET();
				/* FALL THROUGH */
			default:
				empty = 0;
				continue;
			}
			empty = 1;
		}
		if (empty) {
			if (last == OLD_ENV_VALUE)
				goto env_ovar_ok;
			if (last == OLD_ENV_VAR)
				goto env_ovar_wrong;
		}
		/*
		 * Ok, the first thing was a USERVAR, and there
		 * are not two consecutive VAR or VALUE commands,
		 * and none of the VAR or VALUE commands are empty.
		 * If the client has sent us a well-formed option,
		 * then the number of VALUEs received should always
		 * be less than or equal to the number of VARs and
		 * USERVARs received.
		 *
		 * If we got exactly as many VALUEs as VARs and
		 * USERVARs, the client has the same definitions.
		 *
		 * If we got exactly as many VARs as VALUEs and
		 * USERVARS, the client has reversed definitions.
		 */
		if (got_uservar + got_var == got_value) {
	    env_ovar_ok:
			env_ovar = OLD_ENV_VAR;
			env_ovalue = OLD_ENV_VALUE;
		} else if (got_uservar + got_value == got_var) {
	    env_ovar_wrong:
			env_ovar = OLD_ENV_VALUE;
			env_ovalue = OLD_ENV_VAR;
			DIAG(TD_OPTIONS,
			     netputs("ENVIRON VALUE and VAR are reversed!\r\n"));
		}
	    }
	    SB_RESTORE();
#endif

	    while (!SB_EOF()) {
		c = SB_GET();
		if ((c == env_ovar) || (c == ENV_USERVAR))
			break;
	    }
	}

	if (SB_EOF())
		return;

	cp = varp = (char *)subpointer;
	valp = 0;

	while (!SB_EOF()) {
		c = SB_GET();
		if (subchar == TELOPT_OLD_ENVIRON) {
			if (c == env_ovar)
				c = NEW_ENV_VAR;
			else if (c == env_ovalue)
				c = NEW_ENV_VALUE;
		}
		switch (c) {

		case NEW_ENV_VALUE:
			*cp = '\0';
			cp = valp = (char *)subpointer;
			break;

		case NEW_ENV_VAR:
		case ENV_USERVAR:
			*cp = '\0';
			if (envvarok(varp)) {
				if (valp)
					(void)setenv(varp, valp, 1);
				else
					unsetenv(varp);
			}
			cp = varp = (char *)subpointer;
			valp = 0;
			break;

		case ENV_ESC:
			if (SB_EOF())
				break;
			c = SB_GET();
			/* FALL THROUGH */
		default:
			*cp++ = c;
			break;
		}
	}
	*cp = '\0';
	if (envvarok(varp)) {
		if (valp)
			(void)setenv(varp, valp, 1);
		else
			unsetenv(varp);
	}
	break;
    }  /* end of case TELOPT_NEW_ENVIRON */
#if	defined(AUTHENTICATION)
    case TELOPT_AUTHENTICATION:
	if (SB_EOF())
		break;
	switch(SB_GET()) {
	case TELQUAL_SEND:
	case TELQUAL_REPLY:
		/*
		 * These are sent by us and cannot be sent by
		 * the client.
		 */
		break;
	case TELQUAL_IS:
		if (!auth_negotiated)
			auth_is(subpointer, SB_LEN());
		break;
	case TELQUAL_NAME:
		if (!auth_negotiated)
			auth_name(subpointer, SB_LEN());
		break;
	}
	break;
#endif
#ifdef	ENCRYPTION
    case TELOPT_ENCRYPT:
	if (SB_EOF())
		break;
	switch(SB_GET()) {
	case ENCRYPT_SUPPORT:
		encrypt_support(subpointer, SB_LEN());
		break;
	case ENCRYPT_IS:
		encrypt_is(subpointer, SB_LEN());
		break;
	case ENCRYPT_REPLY:
		encrypt_reply(subpointer, SB_LEN());
		break;
	case ENCRYPT_START:
		encrypt_start(subpointer, SB_LEN());
		break;
	case ENCRYPT_END:
		encrypt_end();
		break;
	case ENCRYPT_REQSTART:
		encrypt_request_start(subpointer, SB_LEN());
		break;
	case ENCRYPT_REQEND:
		/*
		 * We can always send an REQEND so that we cannot
		 * get stuck encrypting.  We should only get this
		 * if we have been able to get in the correct mode
		 * anyhow.
		 */
		encrypt_request_end();
		break;
	case ENCRYPT_ENC_KEYID:
		encrypt_enc_keyid(subpointer, SB_LEN());
		break;
	case ENCRYPT_DEC_KEYID:
		encrypt_dec_keyid(subpointer, SB_LEN());
		break;
	default:
		break;
	}
	break;
#endif	/* ENCRYPTION */

    default:
	break;
    }  /* end of switch */

}  /* end of suboption */

#ifdef	LINEMODE
static	void
doclientstat()
{
	clientstat(TELOPT_LINEMODE, WILL, 0);
}
#endif

#define	ADD(c)	 *ncp++ = c;
#define	ADD_DATA(c) { *ncp++ = c; if (c == SE) *ncp++ = c; }
	void
send_status()
{
	unsigned char statusbuf[256];
	register unsigned char *ncp;
	register unsigned char i;

	ncp = statusbuf;

	netflush();	/* get rid of anything waiting to go out */

	ADD(IAC);
	ADD(SB);
	ADD(TELOPT_STATUS);
	ADD(TELQUAL_IS);

	/*
	 * We check the want_state rather than the current state,
	 * because if we received a DO/WILL for an option that we
	 * don't support, and the other side didn't send a DONT/WONT
	 * in response to our WONT/DONT, then the "state" will be
	 * WILL/DO, and the "want_state" will be WONT/DONT.  We
	 * need to go by the latter.
	 */
	for (i = 0; i < (unsigned char)NTELOPTS; i++) {
		if (my_want_state_is_will(i)) {
			ADD(WILL);
			ADD_DATA(i);
			if (i == IAC)
				ADD(IAC);
		}
		if (his_want_state_is_will(i)) {
			ADD(DO);
			ADD_DATA(i);
			if (i == IAC)
				ADD(IAC);
		}
	}

	if (his_want_state_is_will(TELOPT_LFLOW)) {
		ADD(SB);
		ADD(TELOPT_LFLOW);
		if (flowmode) {
			ADD(LFLOW_ON);
		} else {
			ADD(LFLOW_OFF);
		}
		ADD(SE);

		if (restartany >= 0) {
			ADD(SB)
			ADD(TELOPT_LFLOW);
			if (restartany) {
				ADD(LFLOW_RESTART_ANY);
			} else {
				ADD(LFLOW_RESTART_XON);
			}
			ADD(SE)
			ADD(SB);
		}
	}

#ifdef	LINEMODE
	if (his_want_state_is_will(TELOPT_LINEMODE)) {
		unsigned char *cp, *cpe;
		int len;

		ADD(SB);
		ADD(TELOPT_LINEMODE);
		ADD(LM_MODE);
		ADD_DATA(editmode);
		if (editmode == IAC)
			ADD(IAC);
		ADD(SE);

		ADD(SB);
		ADD(TELOPT_LINEMODE);
		ADD(LM_SLC);
		start_slc(0);
		send_slc();
		len = end_slc(&cp);
		for (cpe = cp + len; cp < cpe; cp++)
			ADD_DATA(*cp);
		ADD(SE);
	}
#endif	/* LINEMODE */

	ADD(IAC);
	ADD(SE);

	netwrite(statusbuf, (unsigned) (ncp - statusbuf));
	netflush();	/* Send it on its way */

	DIAG(TD_OPTIONS,
		{printsub('>', statusbuf, ncp - statusbuf); netflush();});
}

static int envvarok(varp)
	char *varp;
{
	if (!strchr(varp, '=') &&
	    strcmp(varp, "TERMCAP") && /* to prevent a security hole  */
	    strcmp(varp, "TERMINFO") &&	/* with tgetent */
	    strcmp(varp, "TERMPATH") &&
	    strcmp(varp, "HOME") && /* to prevent the tegetent bug  */
	    strncmp(varp, "LD_", strlen("LD_")) && /* most systems */
	    strncmp(varp, "_RLD_", strlen("_RLD_")) && /* irix */
	    strncmp(varp, "KRB5", strlen("KRB5")) && /* v5 */
	    /* The above is a catch-all for now.  Here are some of the
	       specific ones we must avoid passing, at least until we
	       can prove it can be done safely.  Keep this list around
	       in case someone wants to remove the catch-all.  */
	    strcmp(varp, "KRB5_CONFIG") && /* v5 */
	    strcmp(varp, "KRB5CCNAME") &&  /* v5 */
	    strcmp(varp, "KRB5_KTNAME") && /* v5 */
	    strcmp(varp, "KRBTKFILE") &&   /* v4 */
	    strcmp(varp, "KRB_CONF") &&	   /* cns v4 */
	    strcmp(varp, "KRB_REALMS") &&  /* cns v4 */
	    strcmp(varp, "LIBPATH") &&     /* AIX */
	    strcmp(varp, "RESOLV_HOST_CONF") && /* linux */
	    strcmp(varp, "NLSPATH") && /* locale stuff */
	    strncmp(varp, "LC_", strlen("LC_")) && /* locale stuff */
	    strcmp(varp, "IFS") &&
	    (varp[0] != '-')) {
		return 1;
	} else {
		syslog(LOG_INFO, "Rejected the attempt to modify the environment variable \"%s\"", varp);
		return 0;
	}

}