builtins.c revision 63045 
1/*-
2 * Copyright (c) 1983, 1991, 1993, 1994
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD: head/usr.sbin/inetd/builtins.c 63045 2000-07-12 20:49:06Z dwmalone $
27 *
28 */
29
30#include <sys/filio.h>
31#include <sys/ioccom.h>
32#include <sys/param.h>
33#include <sys/stat.h>
34#include <sys/socket.h>
35#include <sys/sysctl.h>
36#include <sys/ucred.h>
37#include <sys/uio.h>
38#include <sys/utsname.h>
39
40#include <ctype.h>
41#include <err.h>
42#include <errno.h>
43#include <limits.h>
44#include <pwd.h>
45#include <signal.h>
46#include <stdlib.h>
47#include <string.h>
48#include <sysexits.h>
49#include <syslog.h>
50#include <unistd.h>
51
52#include "inetd.h"
53
54extern int	 debug;
55extern struct servtab *servtab;
56
57char ring[128];
58char *endring;
59
60int check_loop __P((struct sockaddr *, struct servtab *sep));
61void inetd_setproctitle __P((char *, int));
62
63struct biltin biltins[] = {
64	/* Echo received data */
65	{ "echo",	SOCK_STREAM,	1, -1,	echo_stream },
66	{ "echo",	SOCK_DGRAM,	0, 1,	echo_dg },
67
68	/* Internet /dev/null */
69	{ "discard",	SOCK_STREAM,	1, -1,	discard_stream },
70	{ "discard",	SOCK_DGRAM,	0, 1,	discard_dg },
71
72	/* Return 32 bit time since 1970 */
73	{ "time",	SOCK_STREAM,	0, -1,	machtime_stream },
74	{ "time",	SOCK_DGRAM,	0, 1,	machtime_dg },
75
76	/* Return human-readable time */
77	{ "daytime",	SOCK_STREAM,	0, -1,	daytime_stream },
78	{ "daytime",	SOCK_DGRAM,	0, 1,	daytime_dg },
79
80	/* Familiar character generator */
81	{ "chargen",	SOCK_STREAM,	1, -1,	chargen_stream },
82	{ "chargen",	SOCK_DGRAM,	0, 1,	chargen_dg },
83
84	{ "tcpmux",	SOCK_STREAM,	1, -1,	(void (*)())tcpmux },
85
86	{ "auth",	SOCK_STREAM,	1, -1,	ident_stream },
87
88	{ NULL }
89};
90
91/*
92 * RFC864 Character Generator Protocol. Generates character data without
93 * any regard for input.
94 */
95
96void
97initring()
98{
99	int i;
100
101	endring = ring;
102
103	for (i = 0; i <= 128; ++i)
104		if (isprint(i))
105			*endring++ = i;
106}
107
108/* ARGSUSED */
109void
110chargen_dg(s, sep)		/* Character generator */
111	int s;
112	struct servtab *sep;
113{
114	struct sockaddr_storage ss;
115	static char *rs;
116	int len;
117	socklen_t size;
118	char text[LINESIZ+2];
119
120	if (endring == 0) {
121		initring();
122		rs = ring;
123	}
124
125	size = sizeof(ss);
126	if (recvfrom(s, text, sizeof(text), 0,
127		     (struct sockaddr *)&ss, &size) < 0)
128		return;
129
130	if (check_loop((struct sockaddr *)&ss, sep))
131		return;
132
133	if ((len = endring - rs) >= LINESIZ)
134		memmove(text, rs, LINESIZ);
135	else {
136		memmove(text, rs, len);
137		memmove(text + len, ring, LINESIZ - len);
138	}
139	if (++rs == endring)
140		rs = ring;
141	text[LINESIZ] = '\r';
142	text[LINESIZ + 1] = '\n';
143	(void) sendto(s, text, sizeof(text), 0, (struct sockaddr *)&ss, size);
144}
145
146/* ARGSUSED */
147void
148chargen_stream(s, sep)		/* Character generator */
149	int s;
150	struct servtab *sep;
151{
152	int len;
153	char *rs, text[LINESIZ+2];
154
155	inetd_setproctitle(sep->se_service, s);
156
157	if (!endring) {
158		initring();
159		rs = ring;
160	}
161
162	text[LINESIZ] = '\r';
163	text[LINESIZ + 1] = '\n';
164	for (rs = ring;;) {
165		if ((len = endring - rs) >= LINESIZ)
166			memmove(text, rs, LINESIZ);
167		else {
168			memmove(text, rs, len);
169			memmove(text + len, ring, LINESIZ - len);
170		}
171		if (++rs == endring)
172			rs = ring;
173		if (write(s, text, sizeof(text)) != sizeof(text))
174			break;
175	}
176	exit(0);
177}
178
179/*
180 * RFC867 Daytime Protocol. Sends the current date and time as an ascii
181 * character string without any regard for input.
182 */
183
184/* ARGSUSED */
185void
186daytime_dg(s, sep)		/* Return human-readable time of day */
187	int s;
188	struct servtab *sep;
189{
190	char buffer[256];
191	time_t clock;
192	struct sockaddr_storage ss;
193	socklen_t size;
194
195	clock = time((time_t *) 0);
196
197	size = sizeof(ss);
198	if (recvfrom(s, buffer, sizeof(buffer), 0,
199		     (struct sockaddr *)&ss, &size) < 0)
200		return;
201
202	if (check_loop((struct sockaddr *)&ss, sep))
203		return;
204
205	(void) sprintf(buffer, "%.24s\r\n", ctime(&clock));
206	(void) sendto(s, buffer, strlen(buffer), 0,
207		      (struct sockaddr *)&ss, size);
208}
209
210/* ARGSUSED */
211void
212daytime_stream(s, sep)		/* Return human-readable time of day */
213	int s;
214	struct servtab *sep;
215{
216	char buffer[256];
217	time_t clock;
218
219	clock = time((time_t *) 0);
220
221	(void) sprintf(buffer, "%.24s\r\n", ctime(&clock));
222	(void) send(s, buffer, strlen(buffer), MSG_EOF);
223}
224
225/*
226 * RFC863 Discard Protocol. Any data received is thrown away and no response
227 * is sent.
228 */
229
230/* ARGSUSED */
231void
232discard_dg(s, sep)		/* Discard service -- ignore data */
233	int s;
234	struct servtab *sep;
235{
236	char buffer[BUFSIZE];
237
238	(void) read(s, buffer, sizeof(buffer));
239}
240
241/* ARGSUSED */
242void
243discard_stream(s, sep)		/* Discard service -- ignore data */
244	int s;
245	struct servtab *sep;
246{
247	int ret;
248	char buffer[BUFSIZE];
249
250	inetd_setproctitle(sep->se_service, s);
251	while (1) {
252		while ((ret = read(s, buffer, sizeof(buffer))) > 0)
253			;
254		if (ret == 0 || errno != EINTR)
255			break;
256	}
257	exit(0);
258}
259
260/*
261 * RFC862 Echo Protocol. Any data received is sent back to the sender as
262 * received.
263 */
264
265/* ARGSUSED */
266void
267echo_dg(s, sep)			/* Echo service -- echo data back */
268	int s;
269	struct servtab *sep;
270{
271	char buffer[BUFSIZE];
272	int i;
273	socklen_t size;
274	struct sockaddr_storage ss;
275
276	size = sizeof(ss);
277	if ((i = recvfrom(s, buffer, sizeof(buffer), 0,
278			  (struct sockaddr *)&ss, &size)) < 0)
279		return;
280
281	if (check_loop((struct sockaddr *)&ss, sep))
282		return;
283
284	(void) sendto(s, buffer, i, 0, (struct sockaddr *)&ss, size);
285}
286
287/* ARGSUSED */
288void
289echo_stream(s, sep)		/* Echo service -- echo data back */
290	int s;
291	struct servtab *sep;
292{
293	char buffer[BUFSIZE];
294	int i;
295
296	inetd_setproctitle(sep->se_service, s);
297	while ((i = read(s, buffer, sizeof(buffer))) > 0 &&
298	    write(s, buffer, i) > 0)
299		;
300	exit(0);
301}
302
303/*
304 * RFC1413 Identification Protocol. Given a TCP port number pair, return a
305 * character string which identifies the owner of that connection on the
306 * server's system. Extended to allow for ~/.fakeid support and ~/.noident
307 * support.
308 */
309
310/* ARGSUSED */
311void
312iderror(lport, fport, s, er)	/* Generic ident_stream error-sending func */
313	int lport, fport, s, er;
314{
315	char *p;
316
317	asprintf(&p, "%d , %d : ERROR : %s\r\n", lport, fport,
318	    er == -1 ? "HIDDEN-USER" : er ? strerror(er) : "UNKNOWN-ERROR");
319	if (p == NULL) {
320		syslog(LOG_ERR, "asprintf: %m");
321		exit(EX_OSERR);
322	}
323	send(s, p, strlen(p), MSG_EOF);
324	free(p);
325
326	exit(0);
327}
328
329/* ARGSUSED */
330void
331ident_stream(s, sep)		/* Ident service (AKA "auth") */
332	int s;
333	struct servtab *sep;
334{
335	struct utsname un;
336	struct stat sb;
337	struct sockaddr_in sin[2];
338#ifdef INET6
339	struct sockaddr_in6 sin6[2];
340#endif
341	struct sockaddr_storage ss[2];
342	struct ucred uc;
343	struct timeval tv = {
344		10,
345		0
346	}, to;
347	struct passwd *pw = NULL;
348	fd_set fdset;
349	char buf[BUFSIZE], *cp = NULL, *p, **av, *osname = NULL, garbage[7], e;
350	char *fallback = NULL;
351	socklen_t socklen;
352	ssize_t ssize;
353	size_t size, bufsiz;
354	int c, fflag = 0, nflag = 0, rflag = 0, argc = 0, usedfallback = 0;
355	int gflag = 0, getcredfail = 0, onreadlen;
356	u_short lport, fport;
357
358	inetd_setproctitle(sep->se_service, s);
359	/*
360	 * Reset getopt() since we are a fork() but not an exec() from
361	 * a parent which used getopt() already.
362	 */
363	optind = 1;
364	optreset = 1;
365	/*
366	 * Take the internal argument vector and count it out to make an
367	 * argument count for getopt. This can be used for any internal
368	 * service to read arguments and use getopt() easily.
369	 */
370	for (av = sep->se_argv; *av; av++)
371		argc++;
372	if (argc) {
373		int sec, usec;
374		size_t i;
375		u_int32_t random;
376
377		while ((c = getopt(argc, sep->se_argv, "d:fgno:rt:")) != -1)
378			switch (c) {
379			case 'd':
380				fallback = optarg;
381				break;
382			case 'f':
383				fflag = 1;
384				break;
385			case 'g':
386				gflag = 1;
387				random = 0;	/* Shush, compiler. */
388				/*
389				 * The number of bits in "random" divided
390				 * by the number of bits needed per iteration
391				 * gives a more optimal way to reload the
392				 * random number only when necessary.
393				 *
394				 * I'm using base-36, so I need at least 6
395				 * bits; round it up to 8 bits to make it
396				 * easier.
397				 */
398				for (i = 0; i < sizeof(garbage) - 1; i++) {
399					const char *const base36 =
400					    "0123456789"
401					    "abcdefghijklmnopqrstuvwxyz";
402					if (i % (sizeof(random) * 8 / 8) == 0)
403						random = arc4random();
404					garbage[i] =
405					    base36[(random & 0xff) % 36];
406					random >>= 8;
407				}
408				garbage[i] = '\0';
409				break;
410			case 'n':
411				nflag = 1;
412				break;
413			case 'o':
414				osname = optarg;
415				break;
416			case 'r':
417				rflag = 1;
418				break;
419			case 't':
420				switch (sscanf(optarg, "%d.%d", &sec, &usec)) {
421				case 2:
422					tv.tv_usec = usec;
423				case 1:
424					tv.tv_sec = sec;
425					break;
426				default:
427					if (debug)
428						warnx("bad -t argument");
429					break;
430				}
431				break;
432			default:
433				break;
434			}
435	}
436	if (osname == NULL) {
437		if (uname(&un) == -1)
438			iderror(0, 0, s, errno);
439		osname = un.sysname;
440	}
441	socklen = sizeof(ss[0]);
442	if (getsockname(s, (struct sockaddr *)&ss[0], &socklen) == -1)
443		iderror(0, 0, s, errno);
444	socklen = sizeof(ss[1]);
445	if (getpeername(s, (struct sockaddr *)&ss[1], &socklen) == -1)
446		iderror(0, 0, s, errno);
447	/*
448	 * We're going to prepare for and execute reception of a
449	 * packet of data from the user. The data is in the format
450	 * "local_port , foreign_port\r\n" (with local being the
451	 * server's port and foreign being the client's.)
452	 */
453	gettimeofday(&to, NULL);
454	to.tv_sec += tv.tv_sec;
455	if ((to.tv_usec += tv.tv_usec) >= 1000000) {
456		to.tv_usec -= 1000000;
457		to.tv_sec++;
458	}
459
460	size = 0;
461	bufsiz = sizeof(buf) - 1;
462	FD_ZERO(&fdset);
463 	while (bufsiz > 0 && (size == 0 || buf[size - 1] != '\n')) {
464		gettimeofday(&tv, NULL);
465		tv.tv_sec = to.tv_sec - tv.tv_sec;
466		tv.tv_usec = to.tv_usec - tv.tv_usec;
467		if (tv.tv_usec < 0) {
468			tv.tv_usec += 1000000;
469			tv.tv_sec--;
470		}
471		if (tv.tv_sec < 0)
472			break;
473		FD_SET(s, &fdset);
474		if (select(s + 1, &fdset, NULL, NULL, &tv) == -1)
475			iderror(0, 0, s, errno);
476		if (ioctl(s, FIONREAD, &onreadlen) == -1)
477			iderror(0, 0, s, errno);
478		if (onreadlen > bufsiz)
479			onreadlen = bufsiz;
480		ssize = read(s, &buf[size], (size_t)onreadlen);
481		if (ssize == -1)
482			iderror(0, 0, s, errno);
483		bufsiz -= ssize;
484		size += ssize;
485 	}
486	buf[size] = '\0';
487	/* Read two characters, and check for a delimiting character */
488	if (sscanf(buf, "%hu , %hu%c", &lport, &fport, &e) != 3 || isdigit(e))
489		iderror(0, 0, s, 0);
490	if (gflag) {
491		cp = garbage;
492		goto printit;
493	}
494
495	/*
496	 * If not "real" (-r), send a HIDDEN-USER error for everything.
497	 * If -d is used to set a fallback username, this is used to
498	 * override it, and the fallback is returned instead.
499	 */
500	if (!rflag) {
501		if (fallback == NULL)
502			iderror(lport, fport, s, -1);
503		else {
504			cp = fallback;
505			goto printit;
506		}
507	}
508
509	/*
510	 * We take the input and construct an array of two sockaddr_ins
511	 * which contain the local address information and foreign
512	 * address information, respectively, used to look up the
513	 * credentials for the socket (which are returned by the
514	 * sysctl "net.inet.tcp.getcred" when we call it.) The
515	 * arrays have been filled in above via get{peer,sock}name(),
516	 * so right here we are only setting the ports.
517	 */
518	if (ss[0].ss_family != ss[1].ss_family)
519		iderror(lport, fport, s, errno);
520	size = sizeof(uc);
521	switch (ss[0].ss_family) {
522	case AF_INET:
523		sin[0] = *(struct sockaddr_in *)&ss[0];
524		sin[0].sin_port = htons(lport);
525		sin[1] = *(struct sockaddr_in *)&ss[1];
526		sin[1].sin_port = htons(fport);
527		if (sysctlbyname("net.inet.tcp.getcred", &uc, &size, sin,
528				 sizeof(sin)) == -1)
529			getcredfail = 1;
530		break;
531#ifdef INET6
532	case AF_INET6:
533		sin6[0] = *(struct sockaddr_in6 *)&ss[0];
534		sin6[0].sin6_port = htons(lport);
535		sin6[1] = *(struct sockaddr_in6 *)&ss[1];
536		sin6[1].sin6_port = htons(fport);
537		if (sysctlbyname("net.inet6.tcp6.getcred", &uc, &size, sin6,
538				 sizeof(sin6)) == -1)
539			getcredfail = 1;
540		break;
541#endif
542	default: /* should not reach here */
543		getcredfail = 1;
544		break;
545	}
546	if (getcredfail != 0) {
547		if (fallback == NULL)		/* Use a default, if asked to */
548			iderror(lport, fport, s, errno);
549		usedfallback = 1;
550	} else {
551		/* Look up the pw to get the username */
552		pw = getpwuid(uc.cr_uid);
553	}
554	if (pw == NULL && !usedfallback)		/* No such user... */
555		iderror(lport, fport, s, errno);
556	/*
557	 * If enabled, we check for a file named ".noident" in the user's
558	 * home directory. If found, we return HIDDEN-USER.
559	 */
560	if (nflag && !usedfallback) {
561		if (asprintf(&p, "%s/.noident", pw->pw_dir) == -1)
562			iderror(lport, fport, s, errno);
563		if (lstat(p, &sb) == 0) {
564			free(p);
565			iderror(lport, fport, s, -1);
566		}
567		free(p);
568	}
569	/*
570	 * Here, if enabled, we read a user's ".fakeid" file in their
571	 * home directory. It consists of a line containing the name
572	 * they want.
573	 */
574	if (fflag && !usedfallback) {
575		FILE *fakeid = NULL;
576
577		if (asprintf(&p, "%s/.fakeid", pw->pw_dir) == -1)
578			iderror(lport, fport, s, errno);
579		/*
580		 * Here we set ourself to effectively be the user, so we don't
581		 * open any files we have no permission to open, especially
582		 * symbolic links to sensitive root-owned files or devices.
583		 */
584		seteuid(pw->pw_uid);
585		setegid(pw->pw_gid);
586		/*
587		 * If we were to lstat() here, it would do no good, since it
588		 * would introduce a race condition and could be defeated.
589		 * Therefore, we open the file we have permissions to open
590		 * and if it's not a regular file, we close it and end up
591		 * returning the user's real username.
592		 */
593		fakeid = fopen(p, "r");
594		free(p);
595		if (fakeid != NULL &&
596		    fstat(fileno(fakeid), &sb) != -1 && S_ISREG(sb.st_mode)) {
597			buf[sizeof(buf) - 1] = '\0';
598			if (fgets(buf, sizeof(buf), fakeid) == NULL) {
599				cp = pw->pw_name;
600				fclose(fakeid);
601				goto printit;
602			}
603			fclose(fakeid);
604			/*
605			 * Usually, the file will have the desired identity
606			 * in the form "identity\n", so we use strtok() to
607			 * end the string (which fgets() doesn't do.)
608			 */
609			buf[strcspn(buf, "\r\n")] = '\0';
610			cp = buf;
611			/* Allow for beginning white space... */
612			while (isspace(*cp))
613				cp++;
614			/* ...and ending white space. */
615			cp[strcspn(cp, " \t")] = '\0';
616			/* User names of >16 characters are invalid */
617			if (strlen(cp) > 16)
618				cp[16] = '\0';
619			/*
620			 * If the name is a zero-length string or matches
621			 * the name of another user, it's invalid, so
622			 * we will return their real identity instead.
623			 */
624
625			if (!*cp || getpwnam(cp))
626				cp = getpwuid(uc.cr_uid)->pw_name;
627		} else
628			cp = pw->pw_name;
629	} else if (!usedfallback)
630		cp = pw->pw_name;
631	else
632		cp = fallback;
633printit:
634	/* Finally, we make and send the reply. */
635	if (asprintf(&p, "%d , %d : USERID : %s : %s\r\n", lport, fport, osname,
636	    cp) == -1) {
637		syslog(LOG_ERR, "asprintf: %m");
638		exit(EX_OSERR);
639	}
640	send(s, p, strlen(p), MSG_EOF);
641	free(p);
642
643	exit(0);
644}
645
646/*
647 * RFC738 Time Server.
648 * Return a machine readable date and time, in the form of the
649 * number of seconds since midnight, Jan 1, 1900.  Since gettimeofday
650 * returns the number of seconds since midnight, Jan 1, 1970,
651 * we must add 2208988800 seconds to this figure to make up for
652 * some seventy years Bell Labs was asleep.
653 */
654
655unsigned long
656machtime()
657{
658	struct timeval tv;
659
660	if (gettimeofday(&tv, (struct timezone *)NULL) < 0) {
661		if (debug)
662			warnx("unable to get time of day");
663		return (0L);
664	}
665#define	OFFSET ((u_long)25567 * 24*60*60)
666	return (htonl((long)(tv.tv_sec + OFFSET)));
667#undef OFFSET
668}
669
670/* ARGSUSED */
671void
672machtime_dg(s, sep)
673	int s;
674	struct servtab *sep;
675{
676	unsigned long result;
677	struct sockaddr_storage ss;
678	socklen_t size;
679
680	size = sizeof(ss);
681	if (recvfrom(s, (char *)&result, sizeof(result), 0,
682		     (struct sockaddr *)&ss, &size) < 0)
683		return;
684
685	if (check_loop((struct sockaddr *)&ss, sep))
686		return;
687
688	result = machtime();
689	(void) sendto(s, (char *) &result, sizeof(result), 0,
690		      (struct sockaddr *)&ss, size);
691}
692
693/* ARGSUSED */
694void
695machtime_stream(s, sep)
696	int s;
697	struct servtab *sep;
698{
699	unsigned long result;
700
701	result = machtime();
702	(void) send(s, (char *) &result, sizeof(result), MSG_EOF);
703}
704
705/*
706 * RFC1078 TCP Port Service Multiplexer (TCPMUX). Service connections to
707 * services based on the service name sent.
708 *
709 *  Based on TCPMUX.C by Mark K. Lottor November 1988
710 *  sri-nic::ps:<mkl>tcpmux.c
711 */
712
713#define MAX_SERV_LEN	(256+2)		/* 2 bytes for \r\n */
714#define strwrite(fd, buf)	(void) write(fd, buf, sizeof(buf)-1)
715
716static int		/* # of characters upto \r,\n or \0 */
717getline(fd, buf, len)
718	int fd;
719	char *buf;
720	int len;
721{
722	int count = 0, n;
723	struct sigaction sa;
724
725	sa.sa_flags = 0;
726	sigemptyset(&sa.sa_mask);
727	sa.sa_handler = SIG_DFL;
728	sigaction(SIGALRM, &sa, (struct sigaction *)0);
729	do {
730		alarm(10);
731		n = read(fd, buf, len-count);
732		alarm(0);
733		if (n == 0)
734			return (count);
735		if (n < 0)
736			return (-1);
737		while (--n >= 0) {
738			if (*buf == '\r' || *buf == '\n' || *buf == '\0')
739				return (count);
740			count++;
741			buf++;
742		}
743	} while (count < len);
744	return (count);
745}
746
747struct servtab *
748tcpmux(s)
749	int s;
750{
751	struct servtab *sep;
752	char service[MAX_SERV_LEN+1];
753	int len;
754
755	/* Get requested service name */
756	if ((len = getline(s, service, MAX_SERV_LEN)) < 0) {
757		strwrite(s, "-Error reading service name\r\n");
758		return (NULL);
759	}
760	service[len] = '\0';
761
762	if (debug)
763		warnx("tcpmux: someone wants %s", service);
764
765	/*
766	 * Help is a required command, and lists available services,
767	 * one per line.
768	 */
769	if (!strcasecmp(service, "help")) {
770		for (sep = servtab; sep; sep = sep->se_next) {
771			if (!ISMUX(sep))
772				continue;
773			(void)write(s,sep->se_service,strlen(sep->se_service));
774			strwrite(s, "\r\n");
775		}
776		return (NULL);
777	}
778
779	/* Try matching a service in inetd.conf with the request */
780	for (sep = servtab; sep; sep = sep->se_next) {
781		if (!ISMUX(sep))
782			continue;
783		if (!strcasecmp(service, sep->se_service)) {
784			if (ISMUXPLUS(sep)) {
785				strwrite(s, "+Go\r\n");
786			}
787			return (sep);
788		}
789	}
790	strwrite(s, "-Service not available\r\n");
791	return (NULL);
792}
793