xref: /csrg-svn/libexec/telnetd/telnetd.c (revision 27185)

/*
 * Copyright (c) 1983 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 */

#ifndef lint
char copyright[] =
"@(#) Copyright (c) 1983 Regents of the University of California.\n\
 All rights reserved.\n";
#endif not lint

#ifndef lint
static char sccsid[] = "@(#)telnetd.c	5.9 (Berkeley) 04/19/86";
#endif not lint

/*
 * Stripped-down telnet server.
 */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/time.h>

#include <netinet/in.h>

#include <arpa/telnet.h>

#include <stdio.h>
#include <signal.h>
#include <errno.h>
#include <sgtty.h>
#include <netdb.h>
#include <syslog.h>

#define	BELL	'\07'
#define BANNER	"\r\n\r\n4.3 BSD UNIX (%s)\r\n\r\r\n\r%s"

char	hisopts[256];
char	myopts[256];

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

/*
 * I/O data buffers, pointers, and counters.
 */
char	ptyibuf[BUFSIZ], *ptyip = ptyibuf;
char	ptyobuf[BUFSIZ], *pfrontp = ptyobuf, *pbackp = ptyobuf;
char	netibuf[BUFSIZ], *netip = netibuf;
char	netobuf[BUFSIZ], *nfrontp = netobuf, *nbackp = netobuf;
char	*neturg = 0;		/* one past last bye of urgent data */
int	pcc, ncc;

int	pty, net;
int	inter;
extern	char **environ;
extern	int errno;
char	*line;
int	SYNCHing = 0;		/* we are in TELNET SYNCH mode */
/*
 * The following are some clocks used to decide how to interpret
 * the relationship between various variables.
 */

struct {
    int
	system,			/* what the current time is */
	echotoggle,		/* last time user entered echo character */
	modenegotiated,		/* last time operating mode negotiated */
	didnetreceive,		/* last time we read data from network */
	gotDM;			/* when did we last see a data mark */
} clocks;

#define	settimer(x)	clocks.x = clocks.system++

main(argc, argv)
	char *argv[];
{
	struct sockaddr_in from;
	int on = 1, fromlen;

#if	defined(DEBUG)
	{
	    int s, ns, foo;
	    struct servent *sp;
	    static struct sockaddr_in sin = { AF_INET };

	    sp = getservbyname("telnet", "tcp");
	    if (sp == 0) {
		    fprintf(stderr, "telnetd: tcp/telnet: unknown service\n");
		    exit(1);
	    }
	    sin.sin_port = sp->s_port;
	    argc--, argv++;
	    if (argc > 0) {
		    sin.sin_port = atoi(*argv);
		    sin.sin_port = htons((u_short)sin.sin_port);
	    }

	    s = socket(AF_INET, SOCK_STREAM, 0);
	    if (s < 0) {
		    perror("telnetd: socket");;
		    exit(1);
	    }
	    if (bind(s, &sin, sizeof sin) < 0) {
		perror("bind");
		exit(1);
	    }
	    if (listen(s, 1) < 0) {
		perror("listen");
		exit(1);
	    }
	    foo = sizeof sin;
	    ns = accept(s, &sin, &foo);
	    if (ns < 0) {
		perror("accept");
		exit(1);
	    }
	    dup2(ns, 0);
	    close(s);
	}
#endif	/* defined(DEBUG) */
	openlog("telnetd", LOG_PID | LOG_ODELAY, LOG_DAEMON);
	fromlen = sizeof (from);
	if (getpeername(0, &from, &fromlen) < 0) {
		fprintf(stderr, "%s: ", argv[0]);
		perror("getpeername");
		_exit(1);
	}
	if (setsockopt(0, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof (on)) < 0) {
		syslog(LOG_WARNING, "setsockopt (SO_KEEPALIVE): %m");
	}
	doit(0, &from);
}

char	*envinit[] = { "TERM=network", 0 };
int	cleanup();

/*
 * Get a pty, scan input lines.
 */
doit(f, who)
	int f;
	struct sockaddr_in *who;
{
	char *host, *inet_ntoa();
	int i, p, t;
	struct sgttyb b;
	struct hostent *hp;
	char c;

	for (c = 'p'; c <= 's'; c++) {
		struct stat stb;

		line = "/dev/ptyXX";
		line[strlen("/dev/pty")] = c;
		line[strlen("/dev/ptyp")] = '0';
		if (stat(line, &stb) < 0)
			break;
		for (i = 0; i < 16; i++) {
			line[strlen("/dev/ptyp")] = "0123456789abcdef"[i];
			p = open(line, 2);
			if (p > 0)
				goto gotpty;
		}
	}
	fatal(f, "All network ports in use");
	/*NOTREACHED*/
gotpty:
	dup2(f, 0);
	line[strlen("/dev/")] = 't';
	t = open("/dev/tty", O_RDWR);
	if (t >= 0) {
		ioctl(t, TIOCNOTTY, 0);
		close(t);
	}
	t = open(line, O_RDWR);
	if (t < 0)
		fatalperror(f, line, errno);
	ioctl(t, TIOCGETP, &b);
	b.sg_flags = CRMOD|XTABS|ANYP;
	ioctl(t, TIOCSETP, &b);
	ioctl(p, TIOCGETP, &b);
	b.sg_flags &= ~ECHO;
	ioctl(p, TIOCSETP, &b);
	hp = gethostbyaddr(&who->sin_addr, sizeof (struct in_addr),
		who->sin_family);
	if (hp)
		host = hp->h_name;
	else
		host = inet_ntoa(who->sin_addr);
	if ((i = fork()) < 0)
		fatalperror(f, "fork", errno);
	if (i)
		telnet(f, p);
	close(f);
	close(p);
	dup2(t, 0);
	dup2(t, 1);
	dup2(t, 2);
	close(t);
	environ = envinit;
	execl("/bin/login", "login", "-h", host, 0);
	fatalperror(f, "/bin/login", errno);
	/*NOTREACHED*/
}

fatal(f, msg)
	int f;
	char *msg;
{
	char buf[BUFSIZ];

	(void) sprintf(buf, "telnetd: %s.\r\n", msg);
	(void) write(f, buf, strlen(buf));
	exit(1);
}

fatalperror(f, msg, errno)
	int f;
	char *msg;
	int errno;
{
	char buf[BUFSIZ];
	extern char *sys_errlist[];

	(void) sprintf(buf, "%s: %s\r\n", msg, sys_errlist[errno]);
	fatal(f, buf);
}


/*
 * Check a descriptor to see if out of band data exists on it.
 */


stilloob(s)
int	s;		/* socket number */
{
    static struct timeval timeout = { 0 };
    fd_set	excepts;
    int value;

    do {
	FD_ZERO(&excepts);
	FD_SET(s, &excepts);
	value = select(s+1, (fd_set *)0, (fd_set *)0, &excepts, &timeout);
    } while ((value == -1) && (errno = EINTR));

    if (value < 0) {
	fatalperror(pty, "select", errno);
    }
    if (FD_ISSET(s, &excepts)) {
	return 1;
    } else {
	return 0;
    }
}

/*
 * Main loop.  Select from pty and network, and
 * hand data to telnet receiver finite state machine.
 */
telnet(f, p)
{
	int on = 1;
	char hostname[32];

	net = f, pty = p;
	ioctl(f, FIONBIO, &on);
	ioctl(p, FIONBIO, &on);
	signal(SIGTSTP, SIG_IGN);
	signal(SIGCHLD, cleanup);
	setpgrp(0, 0);

	/*
	 * Request to do remote echo and to suppress go ahead.
	 */
	dooption(TELOPT_ECHO);
	dooption(TELOPT_SGA);
	/*
	 * Show banner that getty never gave.
	 */
	gethostname(hostname, sizeof (hostname));
	sprintf(nfrontp, BANNER, hostname, "");
	nfrontp += strlen(nfrontp);
	for (;;) {
		fd_set ibits, obits, xbits;
		register int c;

		if (ncc < 0 && pcc < 0)
			break;

		FD_ZERO(&ibits);
		FD_ZERO(&obits);
		FD_ZERO(&xbits);
		/*
		 * Never look for input if there's still
		 * stuff in the corresponding output buffer
		 */
		if (nfrontp - nbackp || pcc > 0) {
			FD_SET(f, &obits);
		} else {
			FD_SET(p, &ibits);
		}
		if (pfrontp - pbackp || ncc > 0) {
			FD_SET(p, &obits);
		} else {
			FD_SET(f, &ibits);
		}
		if (!SYNCHing) {
			FD_SET(f, &xbits);
		}
		if ((c = select(16, &ibits, &obits, &xbits,
						(struct timeval *)0)) < 1) {
			if (c == -1) {
				if (errno == EINTR) {
					continue;
				}
			}
			sleep(5);
			continue;
		}

		/*
		 * Any urgent data?
		 */
		if (FD_ISSET(net, &xbits)) {
		    SYNCHing = 1;
		}

		/*
		 * Something to read from the network...
		 */
		if (FD_ISSET(net, &ibits)) {
#if	!defined(IOCTL_TO_DO_UNIX_OOB_IN_TCP_WAY)
			/*
			 * In 4.2 (and some early 4.3) systems, the
			 * OOB indication and data handling in the kernel
			 * is such that if two separate TCP Urgent requests
			 * come in, one byte of TCP data will be overlaid.
			 * This is fatal for Telnet, but we try to live
			 * with it.
			 *
			 * In addition, in 4.2 (and...), a special protocol
			 * is needed to pick up the TCP Urgent data in
			 * the correct sequence.
			 *
			 * What we do is:  if we think we are in urgent
			 * mode, we look to see if we are "at the mark".
			 * If we are, we do an OOB receive.  If we run
			 * this twice, we will do the OOB receive twice,
			 * but the second will fail, since the second
			 * time we were "at the mark", but there wasn't
			 * any data there (the kernel doesn't reset
			 * "at the mark" until we do a normal read).
			 * Once we've read the OOB data, we go ahead
			 * and do normal reads.
			 *
			 * There is also another problem, which is that
			 * since the OOB byte we read doesn't put us
			 * out of OOB state, and since that byte is most
			 * likely the TELNET DM (data mark), we would
			 * stay in the TELNET SYNCH (SYNCHing) state.
			 * So, clocks to the rescue.  If we've "just"
			 * received a DM, then we test for the
			 * presence of OOB data when the receive OOB
			 * fails (and AFTER we did the normal mode read
			 * to clear "at the mark").
			 */
		    if (SYNCHing) {
			int atmark;

			ioctl(net, SIOCATMARK, (char *)&atmark);
			if (atmark) {
			    ncc = recv(net, netibuf, sizeof (netibuf), MSG_OOB);
			    if ((ncc == -1) && (errno == EINVAL)) {
				ncc = read(net, netibuf, sizeof (netibuf));
				if (clocks.didnetreceive < clocks.gotDM) {
				    SYNCHing = stilloob(net);
				}
			    }
			} else {
			    ncc = read(net, netibuf, sizeof (netibuf));
			}
		    } else {
			ncc = read(net, netibuf, sizeof (netibuf));
		    }
		    settimer(didnetreceive);
#else	/* !defined(IOCTL_TO_DO_UNIX_OOB_IN_TCP_WAY) */
		    ncc = read(net, netibuf, sizeof (netibuf));
#endif	/* !defined(IOCTL_TO_DO_UNIX_OOB_IN_TCP_WAY) */
		    if (ncc < 0 && errno == EWOULDBLOCK)
			ncc = 0;
		    else {
			if (ncc <= 0) {
			    break;
			}
			netip = netibuf;
		    }
		}

		/*
		 * Something to read from the pty...
		 */
		if (FD_ISSET(p, &ibits)) {
			pcc = read(p, ptyibuf, BUFSIZ);
			if (pcc < 0 && errno == EWOULDBLOCK)
				pcc = 0;
			else {
				if (pcc <= 0)
					break;
				ptyip = ptyibuf;
			}
		}

		while (pcc > 0) {
			if ((&netobuf[BUFSIZ] - nfrontp) < 2)
				break;
			c = *ptyip++ & 0377, pcc--;
			if (c == IAC)
				*nfrontp++ = c;
			*nfrontp++ = c;
			if (c == '\r') {
				if (pcc > 0 && ((*ptyip & 0377) == '\n')) {
					*nfrontp++ = *ptyip++ & 0377;
					pcc--;
				} else
					*nfrontp++ = '\0';
			}
		}
		if (FD_ISSET(f, &obits) && (nfrontp - nbackp) > 0)
			netflush();
		if (ncc > 0)
			telrcv();
		if (FD_ISSET(p, &obits) && (pfrontp - pbackp) > 0)
			ptyflush();
	}
	cleanup();
}

/*
 * 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_BEGINNEG	3	/* throw away begin's... */
#define	TS_ENDNEG	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 " */

telrcv()
{
	register int c;
	static int state = TS_DATA;

	while (ncc > 0) {
		if ((&ptyobuf[BUFSIZ] - pfrontp) < 2)
			return;
		c = *netip++ & 0377, ncc--;
		switch (state) {

		case TS_CR:
			state = TS_DATA;
			if ((c == 0) || (c == '\n')) {
				break;
			}
			/* FALL THROUGH */

		case TS_DATA:
			if (c == IAC) {
				state = TS_IAC;
				break;
			}
			if (inter > 0)
				break;
			/*
			 * We 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 (!myopts[TELOPT_BINARY] && c == '\r') {
				if ((ncc > 0) && ('\n' == *netip)) {
					netip++; ncc--;
					c = '\n';
				} else {
					state = TS_CR;
				}
			}
			*pfrontp++ = c;
			break;

		case TS_IAC:
			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 BREAK:
			case IP:
				interrupt();
				break;

			/*
			 * Are You There?
			 */
			case AYT:
				strcpy(nfrontp, "\r\n[Yes]\r\n");
				nfrontp += 9;
				break;

			/*
			 * Abort Output
			 */
			case AO: {
					struct ltchars tmpltc;

					ptyflush();	/* half-hearted */
					ioctl(pty, TIOCGLTC, &tmpltc);
					if (tmpltc.t_flushc != '\377') {
						*pfrontp++ = tmpltc.t_flushc;
					}
					*nfrontp++ = IAC;
					*nfrontp++ = DM;
					neturg = nfrontp;
					break;
				}

			/*
			 * Erase Character and
			 * Erase Line
			 */
			case EC:
			case EL: {
					struct sgttyb b;
					char ch;

					ptyflush();	/* half-hearted */
					ioctl(pty, TIOCGETP, &b);
					ch = (c == EC) ?
						b.sg_erase : b.sg_kill;
					if (ch != '\377') {
						*pfrontp++ = ch;
					}
					break;
				}

			/*
			 * Check for urgent data...
			 */
			case DM:
				SYNCHing = stilloob(net);
				settimer(gotDM);
				break;


			/*
			 * Begin option subnegotiation...
			 */
			case SB:
				state = TS_BEGINNEG;
				continue;

			case WILL:
			case WONT:
			case DO:
			case DONT:
				state = TS_WILL + (c - WILL);
				continue;

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

		case TS_BEGINNEG:
			if (c == IAC)
				state = TS_ENDNEG;
			break;

		case TS_ENDNEG:
			state = c == SE ? TS_DATA : TS_BEGINNEG;
			break;

		case TS_WILL:
			if (!hisopts[c])
				willoption(c);
			state = TS_DATA;
			continue;

		case TS_WONT:
			if (hisopts[c])
				wontoption(c);
			state = TS_DATA;
			continue;

		case TS_DO:
			if (!myopts[c])
				dooption(c);
			state = TS_DATA;
			continue;

		case TS_DONT:
			if (myopts[c]) {
				myopts[c] = 0;
				sprintf(nfrontp, wont, c);
				nfrontp += sizeof (wont) - 2;
			}
			state = TS_DATA;
			continue;

		default:
			printf("telnetd: panic state=%d\n", state);
			exit(1);
		}
	}
}

willoption(option)
	int option;
{
	char *fmt;

	switch (option) {

	case TELOPT_BINARY:
		mode(RAW, 0);
		goto common;

	case TELOPT_ECHO:
		mode(0, ECHO|CRMOD);
		/*FALL THRU*/

	case TELOPT_SGA:
	common:
		hisopts[option] = 1;
		fmt = doopt;
		break;

	case TELOPT_TM:
		fmt = dont;
		break;

	default:
		fmt = dont;
		break;
	}
	sprintf(nfrontp, fmt, option);
	nfrontp += sizeof (dont) - 2;
}

wontoption(option)
	int option;
{
	char *fmt;

	switch (option) {

	case TELOPT_ECHO:
		mode(ECHO|CRMOD, 0);
		goto common;

	case TELOPT_BINARY:
		mode(0, RAW);
		/*FALL THRU*/

	case TELOPT_SGA:
	common:
		hisopts[option] = 0;
		fmt = dont;
		break;

	default:
		fmt = dont;
	}
	sprintf(nfrontp, fmt, option);
	nfrontp += sizeof (doopt) - 2;
}

dooption(option)
	int option;
{
	char *fmt;

	switch (option) {

	case TELOPT_TM:
		fmt = wont;
		break;

	case TELOPT_ECHO:
		mode(ECHO|CRMOD, 0);
		goto common;

	case TELOPT_BINARY:
		mode(RAW, 0);
		/*FALL THRU*/

	case TELOPT_SGA:
	common:
		fmt = will;
		break;

	default:
		fmt = wont;
		break;
	}
	sprintf(nfrontp, fmt, option);
	nfrontp += sizeof (doopt) - 2;
}

mode(on, off)
	int on, off;
{
	struct sgttyb b;

	ptyflush();
	ioctl(pty, TIOCGETP, &b);
	b.sg_flags |= on;
	b.sg_flags &= ~off;
	ioctl(pty, TIOCSETP, &b);
}

/*
 * Send interrupt to process on other side of pty.
 * If it is in raw mode, just write NULL;
 * otherwise, write intr char.
 */
interrupt()
{
	struct sgttyb b;
	struct tchars tchars;

	ptyflush();	/* half-hearted */
	ioctl(pty, TIOCGETP, &b);
	if (b.sg_flags & RAW) {
		*pfrontp++ = '\0';
		return;
	}
	*pfrontp++ = ioctl(pty, TIOCGETC, &tchars) < 0 ?
		'\177' : tchars.t_intrc;
}

ptyflush()
{
	int n;

	if ((n = pfrontp - pbackp) > 0)
		n = write(pty, pbackp, n);
	if (n < 0)
		return;
	pbackp += n;
	if (pbackp == pfrontp)
		pbackp = pfrontp = ptyobuf;
}

#if	0
netflush()
{
	int n;

	if ((n = nfrontp - nbackp) > 0)
		n = write(net, nbackp, n);
	if (n < 0) {
		if (errno == EWOULDBLOCK)
			return;
		/* should blow this guy away... */
		return;
	}
	nbackp += n;
	if (nbackp == nfrontp)
		nbackp = nfrontp = netobuf;
}
#else	/* 0 */


/*
 *  netflush
 *		Send as much data as possible to the network,
 *	handling requests for urgent data.
 */


netflush()
{
    int n;

    if ((n = nfrontp - nbackp) > 0) {
	if (!neturg) {
	    n = write(net, nbackp, n);	/* normal write */
	} else {
	    n = neturg - nbackp;
	    /*
	     * In 4.2 (and 4.3) systems, there is some question about
	     * what byte in a sendOOB operation is the "OOB" data.
	     * To make ourselves compatible, we only send ONE byte
	     * out of band, the one WE THINK should be OOB (though
	     * we really have more the TCP philosophy of urgent data
	     * rather than the Unix philosophy of OOB data).
	     */
	    if (n > 1) {
		n = send(net, nbackp, n-1, 0);	/* send URGENT all by itself */
	    } else {
		n = send(net, nbackp, n, MSG_OOB);	/* URGENT data */
	    }
	}
    }
    if (n < 0) {
	if (errno == EWOULDBLOCK)
	    return;
	/* should blow this guy away... */
	return;
    }
    nbackp += n;
    if (nbackp >= neturg) {
	neturg = 0;
    }
    if (nbackp == nfrontp) {
	nbackp = nfrontp = netobuf;
    }
}
#endif	/* 0 */

cleanup()
{

	rmut();
	vhangup();	/* XXX */
	shutdown(net, 2);
	exit(1);
}

#include <utmp.h>

struct	utmp wtmp;
char	wtmpf[]	= "/usr/adm/wtmp";
char	utmpf[] = "/etc/utmp";
#define SCPYN(a, b)	strncpy(a, b, sizeof(a))
#define SCMPN(a, b)	strncmp(a, b, sizeof(a))

rmut()
{
	register f;
	int found = 0;
	struct utmp *u, *utmp;
	int nutmp;
	struct stat statbf;

	f = open(utmpf, O_RDWR);
	if (f >= 0) {
		fstat(f, &statbf);
		utmp = (struct utmp *)malloc(statbf.st_size);
		if (!utmp)
			syslog(LOG_ERR, "utmp malloc failed");
		if (statbf.st_size && utmp) {
			nutmp = read(f, utmp, statbf.st_size);
			nutmp /= sizeof(struct utmp);

			for (u = utmp ; u < &utmp[nutmp] ; u++) {
				if (SCMPN(u->ut_line, line+5) ||
				    u->ut_name[0]==0)
					continue;
				lseek(f, ((long)u)-((long)utmp), L_SET);
				SCPYN(u->ut_name, "");
				SCPYN(u->ut_host, "");
				time(&u->ut_time);
				write(f, (char *)u, sizeof(wtmp));
				found++;
			}
		}
		close(f);
	}
	if (found) {
		f = open(wtmpf, O_WRONLY|O_APPEND);
		if (f >= 0) {
			SCPYN(wtmp.ut_line, line+5);
			SCPYN(wtmp.ut_name, "");
			SCPYN(wtmp.ut_host, "");
			time(&wtmp.ut_time);
			write(f, (char *)&wtmp, sizeof(wtmp));
			close(f);
		}
	}
	chmod(line, 0666);
	chown(line, 0, 0);
	line[strlen("/dev/")] = 'p';
	chmod(line, 0666);
	chown(line, 0, 0);
}