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rcsid[] and sccsid[] and copyright[] are essentially unmaintained (and
unmaintainable).  these days, people use source.  these id's do not provide
any benefit, and do hurt the small install media
(the 33,000 line diff is essentially mechanical)
ok with the idea millert, ok dms

/*	$OpenBSD: rsh.c,v 1.40 2009/10/27 23:59:43 deraadt Exp $	*/

/*-
 * Copyright (c) 1983, 1990 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. 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.
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/file.h>

#include <netinet/in.h>

#include <err.h>
#include <errno.h>
#include <netdb.h>
#include <poll.h>
#include <pwd.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "pathnames.h"

__dead void usage(void);
void sendsig(int);
char *copyargs(char **argv);
void talk(int, sigset_t *, int, int);

/*
 * rsh - remote shell
 */
int rfd2;

int
main(int argc, char *argv[])
{
	struct passwd *pw;
	struct servent *sp;
	sigset_t mask, omask;
	int argoff = 0, asrsh = 0, ch, dflag = 0, nflag = 0, one = 1, rem;
	char *args, *host = NULL, *user = NULL;
	pid_t pid = 0;
	extern char *__progname;
	uid_t uid;

	/* if called as something other than "rsh", use it as the host name */
	if (strcmp(__progname, "rsh") != 0)
		host = __progname;
	else
		asrsh = 1;

	/* handle "rsh host flags" */
	if (!host && argc > 2 && argv[1][0] != '-') {
		host = argv[1];
		argoff = 1;
	}

	while ((ch = getopt(argc - argoff, argv + argoff, "8KLdel:nw")) != -1)
		switch(ch) {
		case '8':	/* -8KLew are ignored to allow rlogin aliases */
		case 'K':
		case 'L':
		case 'e':
		case 'w':
			break;
		case 'd':
			dflag = 1;
			break;
		case 'l':
			user = optarg;
			break;
		case 'n':
			nflag = 1;
			break;
		default:
			usage();
		}
	optind += argoff;

	uid = getuid();

	/* if haven't gotten a host yet, do so */
	if (!host && !(host = argv[optind++]))
		usage();

	/* if no command, login to remote host via ssh. */
	if (!argv[optind]) {
		if (setresuid(uid, uid, uid) == -1)
			err(1, "setresuid");
		if (asrsh)
			*argv = "ssh";
		execv(_PATH_SSH, argv);
		errx(1, "can't exec %s", _PATH_SSH);
	}

	argc -= optind;
	argv += optind;

	if (geteuid() != 0)
		errx(1, "must be setuid root");
	if ((pw = getpwuid(uid)) == NULL)
		errx(1, "unknown user ID %u", uid);
	if (user == NULL)
		user = pw->pw_name;

	args = copyargs(argv);

	if ((sp = getservbyname("shell", "tcp")) == NULL)
		errx(1, "shell/tcp: unknown service");

	(void)unsetenv("RSH");		/* no tricks with rcmd(3) */

	rem = rcmd_af(&host, sp->s_port, pw->pw_name, user, args, &rfd2,
	    PF_UNSPEC);
	if (rem < 0)
		exit(1);
	if (rfd2 < 0)
		errx(1, "can't establish stderr");

	if (setresuid(uid, uid, uid) == -1)
		err(1, "setresuid");

	if (dflag) {
		if (setsockopt(rem, SOL_SOCKET, SO_DEBUG, &one,
		    sizeof(one)) < 0)
			warn("setsockopt");
		if (setsockopt(rfd2, SOL_SOCKET, SO_DEBUG, &one,
		    sizeof(one)) < 0)
			warn("setsockopt");
	}
	sigemptyset(&mask);
	sigaddset(&mask, SIGINT);
	sigaddset(&mask, SIGQUIT);
	sigaddset(&mask, SIGTERM);
	sigprocmask(SIG_BLOCK, &mask, &omask);
	if (signal(SIGINT, SIG_IGN) != SIG_IGN)
		(void)signal(SIGINT, sendsig);
	if (signal(SIGQUIT, SIG_IGN) != SIG_IGN)
		(void)signal(SIGQUIT, sendsig);
	if (signal(SIGTERM, SIG_IGN) != SIG_IGN)
		(void)signal(SIGTERM, sendsig);

	if (!nflag) {
		if ((pid = fork()) < 0)
			err(1, "fork");
	}

	(void)ioctl(rfd2, FIONBIO, &one);
	(void)ioctl(rem, FIONBIO, &one);

	talk(nflag, &omask, pid, rem);

	if (!nflag)
		(void)kill(pid, SIGKILL);

	return 0;
}

void
talk(int nflag, sigset_t *omask, pid_t pid, int rem)
{
	int cc, wc;
	char *bp;
	struct pollfd pfd[2];
	char buf[BUFSIZ];

	if (!nflag && pid == 0) {
		(void)close(rfd2);

reread:		errno = 0;
		if ((cc = read(STDIN_FILENO, buf, sizeof buf)) <= 0)
			goto done;
		bp = buf;

		pfd[0].fd = rem;
		pfd[0].events = POLLOUT;
rewrite:
		if (poll(pfd, 1, INFTIM) < 0) {
			if (errno != EINTR)
				err(1, "poll");
			goto rewrite;
		}
		if (pfd[0].revents & (POLLERR|POLLHUP|POLLNVAL))
			err(1, "poll");
		wc = write(rem, bp, cc);
		if (wc < 0) {
			if (errno == EWOULDBLOCK)
				goto rewrite;
			goto done;
		}
		bp += wc;
		cc -= wc;
		if (cc == 0)
			goto reread;
		goto rewrite;
done:
		(void)shutdown(rem, 1);
		exit(0);
	}

	sigprocmask(SIG_SETMASK, omask, NULL);
	pfd[1].fd = rfd2;
	pfd[1].events = POLLIN;
	pfd[0].fd = rem;
	pfd[0].events = POLLIN;
	do {
		if (poll(pfd, 2, INFTIM) < 0) {
			if (errno != EINTR)
				err(1, "poll");
			continue;
		}
		if ((pfd[0].revents & (POLLERR|POLLHUP|POLLNVAL)) ||
		    (pfd[1].revents & (POLLERR|POLLHUP|POLLNVAL)))
			err(1, "poll");
		if (pfd[1].revents & POLLIN) {
			errno = 0;
			cc = read(rfd2, buf, sizeof buf);
			if (cc <= 0) {
				if (errno != EWOULDBLOCK)
					pfd[1].revents = 0;
			} else
				(void)write(STDERR_FILENO, buf, cc);
		}
		if (pfd[0].revents & POLLIN) {
			errno = 0;
			cc = read(rem, buf, sizeof buf);
			if (cc <= 0) {
				if (errno != EWOULDBLOCK)
					pfd[0].revents = 0;
			} else
				(void)write(STDOUT_FILENO, buf, cc);
		}
	} while ((pfd[0].revents & POLLIN) || (pfd[1].revents & POLLIN));
}

void
sendsig(int signo)
{
	int save_errno = errno;

	(void)write(rfd2, &signo, 1);
	errno = save_errno;
}

char *
copyargs(char **argv)
{
	char **ap, *p, *args;
	size_t cc, len;

	cc = 0;
	for (ap = argv; *ap; ++ap)
		cc += strlen(*ap) + 1;
	if ((args = malloc(cc)) == NULL)
		err(1, NULL);
	for (p = args, ap = argv; *ap; ++ap) {
		len = strlcpy(p, *ap, cc);
		if (len >= cc)
			errx(1, "copyargs overflow");
		p += len;
		cc -= len;
		if (ap[1]) {
			*p++ = ' ';
			cc--;
		}
	}
	return(args);
}

__dead void
usage(void)
{
	(void)fprintf(stderr,
	    "usage: rsh [-dn] [-l username] hostname [command]\n");
	exit(1);
}