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Instead of trying to do clever and figure out a root instance for Kerberos,
send tell the auth program who the invoking user is, and rely on it to handle
root instances for Kerberos.

This makes the code much cleaner and simpler.

ok millertt@

/*	$OpenBSD: su.c,v 1.40 2001/06/25 21:29:31 hin Exp $	*/

/*
 * Copyright (c) 1988 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.
 */

#ifndef lint
char copyright[] =
"@(#) Copyright (c) 1988 The Regents of the University of California.\n\
 All rights reserved.\n";
#endif /* not lint */

#ifndef lint
/*static char sccsid[] = "from: @(#)su.c	5.26 (Berkeley) 7/6/91";*/
static char rcsid[] = "$OpenBSD: su.c,v 1.40 2001/06/25 21:29:31 hin Exp $";
#endif /* not lint */

#include <sys/param.h>
#include <sys/time.h>
#include <sys/resource.h>

#include <err.h>
#include <errno.h>
#include <grp.h>
#include <login_cap.h>
#include <paths.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#ifdef __STDC__
#include <stdarg.h>
#else
#include <varargs.h>
#endif
#include <bsd_auth.h>

char   *ontty __P((void));
int	chshell __P((char *));
void	usage __P((void));
void	auth_err __P((auth_session_t *, int, const char *, ...));
void	auth_errx __P((auth_session_t *, int, const char *, ...));

int
main(argc, argv)
	int argc;
	char **argv;
{
	extern char **environ;
	enum { UNSET, YES, NO } iscsh;
	struct passwd *pwd;
	struct group *gr;
	uid_t ruid;
	login_cap_t *lc;
	auth_session_t *as;
	int asme, asthem, authok, ch, fastlogin, prio;
	char *class, *style, *p, **g;
	char *user, *shell, *avshell, *username, **np, *fullname;
	char shellbuf[MAXPATHLEN], avshellbuf[MAXPATHLEN];

	iscsh = UNSET;
	class = shell = style = NULL;
	asme = asthem = fastlogin = 0;
	while ((ch = getopt(argc, argv, "-a:c:fKlm")) != -1)
		switch(ch) {
		case 'a':
			if (style)
				usage();
			style = optarg;
			break;
		case 'c':
			if (class)
				usage();
			class = optarg;
			break;
		case 'f':
			fastlogin = 1;
			break;
		case 'K':
			if (style)
				usage();
			style = "passwd";
			break;
		case '-':
		case 'l':
			asme = 0;
			asthem = 1;
			break;
		case 'm':
			asme = 1;
			asthem = 0;
			break;
		case '?':
		default:
			usage();
		}
	argv += optind;

	errno = 0;
	prio = getpriority(PRIO_PROCESS, 0);
	if (errno)
		prio = 0;
	(void)setpriority(PRIO_PROCESS, 0, -2);
	openlog("su", LOG_CONS, 0);

	if ((as = auth_open()) == NULL) {
		syslog(LOG_ERR, "auth_open: %m");
		err(1, "unable to initialize BSD authentication");
	}
	auth_setoption(as, "login", "yes");

	/* get current login name and shell */
	ruid = getuid();
	username = getlogin();

	if(username != NULL)
		auth_setoption(as, "invokinguser", username);

	if (username == NULL || (pwd = getpwnam(username)) == NULL ||
	    pwd->pw_uid != ruid)
		pwd = getpwuid(ruid);
	if (pwd == NULL)
		auth_errx(as, 1, "who are you?");
	if ((username = strdup(pwd->pw_name)) == NULL)
		auth_err(as, 1, "can't allocate memory");
	if (asme) {
		if (pwd->pw_shell && *pwd->pw_shell) {
			strlcpy(shellbuf, pwd->pw_shell, sizeof(shellbuf));
			shell = shellbuf;
		} else {
			shell = _PATH_BSHELL;
			iscsh = NO;
		}
	}

	/* get target login information, default to root */
	user = *argv ? *argv : "root";
	np = *argv ? argv : argv - 1;

	if ((pwd = getpwnam(user)) == NULL)
		auth_errx(as, 1, "unknown login %s", user);
	if ((user = strdup(pwd->pw_name)) == NULL)
		auth_err(as, 1, "can't allocate memory");

	/* If the user specified a login class and we are root, use it */
	if (ruid && class)
		auth_errx(as, 1, "only the superuser may specify a login class");
	if (class)
		pwd->pw_class = class;
	if ((lc = login_getclass(pwd->pw_class)) == NULL)
		auth_errx(as, 1, "no such login class: %s",
		    class ? class : LOGIN_DEFCLASS);

	if (ruid) {
		/*
		 * If we are trying to become root and the default style
		 * is being used, don't bother to look it up (we might be
		 * be su'ing up to fix /etc/login.conf)
		 */
		if ((pwd->pw_uid || !style || strcmp(style, LOGIN_DEFSTYLE)) &&
		    (style = login_getstyle(lc, style, "auth-su")) == NULL)
			auth_errx(as, 1, "invalid authentication type");
		fullname = user;
		/*
		 * Let the authentication program know whether they are
		 * in group wheel or not (if trying to become super user)
		 */
		if (pwd->pw_uid == 0 && (gr = getgrgid((gid_t)0))
		    && gr->gr_mem && *(gr->gr_mem)) {
			for (g = gr->gr_mem; *g; ++g) {
				if (strcmp(username, *g) == 0) {
					auth_setoption(as, "wheel", "yes");
					break;
				}
			}
			if (!*g)
				auth_setoption(as, "wheel", "no");
		}

		auth_verify(as, style, fullname, lc->lc_class, NULL);
		authok = auth_getstate(as);
		if ((authok & AUTH_ALLOW) == 0) {
			if ((p = auth_getvalue(as, "errormsg")) != NULL)
				fprintf(stderr, "%s\n", p);
			fprintf(stderr, "Sorry\n");
			syslog(LOG_AUTH|LOG_WARNING,
				"BAD SU %s to %s%s", username, user, ontty());
			auth_close(as);
			exit(1);
		}
	}

	if (asme) {
		/* if asme and non-standard target shell, must be root */
		if (!chshell(pwd->pw_shell) && ruid)
			auth_errx(as, 1, "permission denied (shell).");
	} else if (pwd->pw_shell && *pwd->pw_shell) {
		shell = pwd->pw_shell;
		iscsh = UNSET;
	} else {
		shell = _PATH_BSHELL;
		iscsh = NO;
	}

	if ((p = strrchr(shell, '/')))
		avshell = p+1;
	else
		avshell = shell;

	/* if we're forking a csh, we want to slightly muck the args */
	if (iscsh == UNSET)
		iscsh = strcmp(avshell, "csh") ? NO : YES;

	if (!asme) {
		if (asthem) {
			p = getenv("TERM");
			if ((environ = calloc(1, sizeof (char *))) == NULL)
				auth_errx(as, 1, "calloc");
			if (setusercontext(lc, pwd, pwd->pw_uid, LOGIN_SETPATH))
				auth_err(as, 1, "unable to set user context");
			if (p && setenv("TERM", p, 1) == -1)
				auth_err(as, 1, "unable to set environment");

			seteuid(pwd->pw_uid);
			setegid(pwd->pw_gid);
			if (chdir(pwd->pw_dir) < 0)
				auth_err(as, 1, "%s", pwd->pw_dir);
			seteuid(0);
			setegid(0);	/* XXX use a saved gid instead? */
		} else if (pwd->pw_uid == 0) {
			if (setusercontext(lc,
			    pwd, pwd->pw_uid, LOGIN_SETPATH|LOGIN_SETUMASK))
				auth_err(as, 1, "unable to set user context");
		}
		if (asthem || pwd->pw_uid) {
			if (setenv("LOGNAME", pwd->pw_name, 1) == -1 ||
			    setenv("USER", pwd->pw_name, 1) == -1)
				auth_err(as, 1, "unable to set environment");
		}
		if (setenv("HOME", pwd->pw_dir, 1) == -1 ||
		    setenv("SHELL", shell, 1) == -1)
			auth_err(as, 1, "unable to set environment");
	}

	if (iscsh == YES) {
		if (fastlogin)
			*np-- = "-f";
		if (asme)
			*np-- = "-m";
	}

	if (asthem) {
		avshellbuf[0] = '-';
		strlcpy(avshellbuf+1, avshell, sizeof(avshellbuf) - 1);
		avshell = avshellbuf;
	} else if (iscsh == YES) {
		/* csh strips the first character... */
		avshellbuf[0] = '_';
		strlcpy(avshellbuf+1, avshell, sizeof(avshellbuf) - 1);
		avshell = avshellbuf;
	}
			
	*np = avshell;

	if (ruid != 0)
		syslog(LOG_NOTICE|LOG_AUTH, "%s to %s%s",
		    username, user, ontty());

	(void)setpriority(PRIO_PROCESS, 0, prio);
	if (setusercontext(lc, pwd, pwd->pw_uid,
	    (asthem ? (LOGIN_SETPRIORITY | LOGIN_SETUMASK) : 0) |
	    LOGIN_SETRESOURCES | LOGIN_SETGROUP | LOGIN_SETUSER))
		auth_err(as, 1, "unable to set user context");
	if (pwd->pw_uid && auth_approval(as, lc, pwd->pw_name, "su") <= 0)
		auth_err(as, 1, "approval failure");
	auth_close(as);

	execv(shell, np);
	err(1, "%s", shell);
}

int
chshell(sh)
	char *sh;
{
	char *cp;

	while ((cp = getusershell()) != NULL)
		if (strcmp(cp, sh) == 0)
			return (1);
	return (0);
}

char *
ontty()
{
	static char buf[MAXPATHLEN + 4];
	char *p;

	buf[0] = 0;
	if ((p = ttyname(STDERR_FILENO)))
		snprintf(buf, sizeof(buf), " on %s", p);
	return (buf);
}

void
usage()
{
	extern char *__progname;

	fprintf(stderr, "usage: %s [-fKlm] [-a auth-type] %s ", __progname,
	    "[-c login-class] [login [shell arguments]]\n");
	exit(1);
}

void
#ifdef __STDC__
auth_err(auth_session_t *as, int eval, const char *fmt, ...)
#else
auth_err(va_alist)
	va_dcl
#endif
{
	va_list ap;
#ifdef __STDC__
	va_start(ap, fmt);
#else
	auth_session_t *as;
	int eval;
	const char *fmt;

	va_start(ap);
	as = va_arg(ap, auth_session_t *);
	eval = va_arg(ap, int);
	fmt = va_arg(ap, const char *);
#endif
	verr(eval, fmt, ap);
	auth_close(as);
	va_end(ap);
}

void
#ifdef __STDC__
auth_errx(auth_session_t *as, int eval, const char *fmt, ...)
#else
auth_errx(va_alist)
	va_dcl
#endif
{
	va_list ap;
#ifdef __STDC__
	va_start(ap, fmt);
#else
	auth_session_t *as;
	int eval;
	const char *fmt;

	va_start(ap);
	as = va_arg(ap, auth_session_t *);
	eval = va_arg(ap, int);
	fmt = va_arg(ap, const char *);
#endif
	verrx(eval, fmt, ap);
	auth_close(as);
	va_end(ap);
}