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Denote multiple arguments with 'arg ...' not 'args'

A few programs used the plural in their synopsis which doesn't read as
clear as the obvious triple-dot notation.

mdoc(7) .Ar defaults to "file ..." if no arguments are given and consistent
use of 'arg ...' matches that behaviour.

Cleanup a few markups of the same argument so the text keeps reading
naturally;  omit unhelpful parts like 'if optional arguments are given,
they are passed along' for tools like time(1) and timeout(1) that obviously
execute commands with whatever arguments where given -- just like doas(1)
which doesn't mention arguments in its DESCRIPTION in the first place.

For expr(1) the difference between 'expressions' and 'expression ...' is
crucial, as arguments must be passed as individual words.

Feedback millert jmc schwarze deraadt
OK jmc

/*	$OpenBSD: su.c,v 1.89 2022/12/22 19:53:23 kn 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. 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/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>
#include <limits.h>
#include <utmp.h>
#include <stdarg.h>
#include <bsd_auth.h>

char   *getloginname(void);
char   *ontty(void);
int	chshell(const char *);
int	verify_user(char *, struct passwd *, char *, login_cap_t *,
	    auth_session_t *);
void	usage(void);
void	auth_err(auth_session_t *, int, const char *, ...);
void	auth_errx(auth_session_t *, int, const char *, ...);

int
main(int argc, char **argv)
{
	int asme = 0, asthem = 0, ch, fastlogin = 0, emlogin = 0, prio;
	int altshell = 0, homeless = 0;
	char *user, *shell = NULL, *avshell, *username, **np;
	char *class = NULL, *style = NULL, *p;
	enum { UNSET, YES, NO } iscsh = UNSET;
	char avshellbuf[PATH_MAX];
	extern char **environ;
	auth_session_t *as;
	struct passwd *pwd;
	login_cap_t *lc;
	uid_t ruid;
	u_int flags;

	if (pledge("stdio unveil rpath getpw proc exec id", NULL) == -1)
		err(1, "pledge");

	while ((ch = getopt(argc, argv, "a:c:fKLlms:-")) != -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 'L':
			emlogin = 1;
			break;
		case 'l':
		case '-':
			asme = 0;
			asthem = 1;
			break;
		case 'm':
			asme = 1;
			asthem = 0;
			break;
		case 's':
			altshell = 1;
			shell = optarg;
			break;
		default:
			usage();
		}
	argv += optind;

	errno = 0;
	prio = getpriority(PRIO_PROCESS, 0);
	if (errno)
		prio = 0;
	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 (ruid && class)
		auth_errx(as, 1, "only the superuser may specify a login class");

	if (ruid && altshell)
		auth_errx(as, 1, "only the superuser may specify a login shell");

	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, NULL);
	if (asme && !altshell) {
		if (pwd->pw_shell && *pwd->pw_shell) {
			if ((shell = strdup(pwd->pw_shell)) == NULL)
				auth_err(as, 1, NULL);
		} else {
			shell = _PATH_BSHELL;
			iscsh = NO;
		}
	}

	if (unveil(_PATH_LOGIN_CONF, "r") == -1)
		err(1, "unveil %s", _PATH_LOGIN_CONF);
	if (unveil(_PATH_LOGIN_CONF ".db", "r") == -1)
		err(1, "unveil %s.db", _PATH_LOGIN_CONF);
	if (unveil(_PATH_LOGIN_CONF_D, "r") == -1)
		err(1, "unveil %s", _PATH_LOGIN_CONF_D);
	if (unveil(_PATH_AUTHPROGDIR, "x") == -1)
		err(1, "unveil %s", _PATH_AUTHPROGDIR);
	if (unveil(_PATH_SHELLS, "r") == -1)
		err(1, "unveil %s", _PATH_SHELLS);
	if (unveil(_PATH_DEVDB, "r") == -1)
		err(1, "unveil %s", _PATH_DEVDB);
	if (unveil(_PATH_NOLOGIN, "r") == -1)
		err(1, "unveil %s", _PATH_NOLOGIN);

	for (;;) {
		char *pw_class = class;

		/* get target user, default to root unless in -L mode */
		if (*argv) {
			user = *argv;
		} else if (emlogin) {
			if ((user = getloginname()) == NULL) {
				auth_close(as);
				exit(1);
			}
		} else {
			user = "root";
		}
		/* style may be specified as part of the username */
		if ((p = strchr(user, ':')) != NULL) {
			*p++ = '\0';
			style = p;	/* XXX overrides -a flag */
		}

		/*
		 * Clean and setup our current authentication session.
		 * Note that options *are* not cleared.
		 */
		auth_clean(as);
		if (auth_setitem(as, AUTHV_INTERACTIVE, "True") != 0 ||
		    auth_setitem(as, AUTHV_NAME, user) != 0)
			auth_err(as, 1, NULL);
		if ((user = auth_getitem(as, AUTHV_NAME)) == NULL)
			auth_errx(as, 1, "internal error");
		if (auth_setpwd(as, NULL) || (pwd = auth_getpwd(as)) == NULL) {
			if (emlogin)
				pwd = NULL;
			else
				auth_errx(as, 1, "unknown login %s", user);
		}

		/* If the user specified a login class, use it */
		if (pw_class == NULL && pwd != NULL)
			pw_class = pwd->pw_class;
		if ((lc = login_getclass(pw_class)) == NULL)
			auth_errx(as, 1, "no such login class: %s",
			    pw_class ? pw_class : LOGIN_DEFCLASS);

		if ((ruid == 0 && !emlogin) ||
		    verify_user(username, pwd, style, lc, as) == 0)
			break;
		syslog(LOG_AUTH|LOG_WARNING, "BAD SU %s to %s%s",
		    username, user, ontty());
		if (!emlogin) {
			fprintf(stderr, "Sorry\n");
			auth_close(as);
			exit(1);
		}
		fprintf(stderr, "Login incorrect\n");
	}
	if (pwd == NULL)
		auth_errx(as, 1, "internal error");

	if (pledge("stdio unveil rpath getpw exec id", NULL) == -1)
		err(1, "pledge");

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

	if (unveil(shell, "x") == -1)
		err(1, "unveil %s", shell);
	if (unveil(pwd->pw_dir, "r") == -1)
		err(1, "unveil %s", pwd->pw_dir);

	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");

			setegid(pwd->pw_gid);
			seteuid(pwd->pw_uid);

			homeless = chdir(pwd->pw_dir);
			if (homeless == -1) {
				if (login_getcapbool(lc, "requirehome", 0)) {
					auth_err(as, 1, "%s", pwd->pw_dir);
				} else {
					if (unveil("/", "r") == -1)
						err(1, "unveil /");
					printf("No home directory %s!\n", pwd->pw_dir);
					printf("Logging in with home = \"/\".\n");
					if (chdir("/") == -1)
						auth_err(as, 1, "/");
				}
			}
			setegid(0);	/* XXX use a saved gid instead? */
			seteuid(0);
		} 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", homeless ? "/" : pwd->pw_dir, 1) == -1 ||
		    setenv("SHELL", shell, 1) == -1)
			auth_err(as, 1, "unable to set environment");
	} else if (altshell) {
		if (setenv("SHELL", shell, 1) == -1)
			auth_err(as, 1, "unable to set environment");
	}
	if (pledge("stdio rpath getpw exec id", NULL) == -1)
		err(1, "pledge");

	np = *argv ? argv : argv - 1;

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

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

	setpriority(PRIO_PROCESS, 0, prio);
	if (emlogin) {
		flags = LOGIN_SETALL & ~LOGIN_SETPATH;
		/*
		 * Only call setlogin() if this process is a session leader.
		 * In practice, this means the login name will be set only if
		 * we are exec'd by a shell.  This is important because
		 * otherwise the parent shell's login name would change too.
		 */
		if (getsid(0) != getpid())
			flags &= ~LOGIN_SETLOGIN;
	} else {
		flags = LOGIN_SETRESOURCES|LOGIN_SETGROUP|LOGIN_SETUSER;
		if (!asme)
			flags |= LOGIN_SETRTABLE;
		if (asthem)
			flags |= LOGIN_SETENV|LOGIN_SETPRIORITY|LOGIN_SETUMASK;
	}
	if (setusercontext(lc, pwd, pwd->pw_uid, flags) != 0)
		auth_err(as, 1, "unable to set user context");

	if (pledge("stdio rpath exec", NULL) == -1)
		err(1, "pledge");

	if (pwd->pw_uid && auth_approval(as, lc, pwd->pw_name, "su") == 0)
		auth_errx(as, 1, "approval failure");
	auth_close(as);

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

int
verify_user(char *from, struct passwd *pwd, char *style,
    login_cap_t *lc, auth_session_t *as)
{
	struct group *gr;
	char **g, *cp;
	int authok;

	/*
	 * 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 == NULL || pwd->pw_uid != 0 || style == NULL ||
	    strcmp(style, LOGIN_DEFSTYLE) != 0) &&
	    (style = login_getstyle(lc, style, "auth-su")) == NULL)
		auth_errx(as, 1, "invalid authentication type");

	/*
	 * Let the authentication program know whether they are
	 * in group wheel or not (if trying to become super user)
	 */
	if (pwd != NULL && pwd->pw_uid == 0 && (gr = getgrgid(0)) != NULL &&
	    gr->gr_mem != NULL && *(gr->gr_mem) != NULL) {
		for (g = gr->gr_mem; *g; ++g) {
			if (strcmp(from, *g) == 0) {
				auth_setoption(as, "wheel", "yes");
				break;
			}
		}
		if (!*g)
			auth_setoption(as, "wheel", "no");
	}

	auth_verify(as, style, NULL, lc->lc_class, (char *)NULL);
	authok = auth_getstate(as);
	if ((authok & AUTH_ALLOW) == 0) {
		if ((cp = auth_getvalue(as, "errormsg")) != NULL)
			fprintf(stderr, "%s\n", cp);
		return(1);
	}
	return(0);
}

int
chshell(const char *sh)
{
	char *cp;
	int found = 0;

	setusershell();
	while ((cp = getusershell()) != NULL) {
		if (strcmp(cp, sh) == 0) {
			found = 1;
			break;
		}
	}
	endusershell();
	return (found);
}

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

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

/*
 * Allow for a '.' and 16 characters for any instance as well as
 * space for a ':' and 16 characters defining the authentication type.
 */
#define NBUFSIZ		(UT_NAMESIZE + 1 + 16 + 1 + 16)

char *
getloginname(void)
{
	static char nbuf[NBUFSIZ], *p;
	int ch;

	for (;;) {
		printf("login: ");
		for (p = nbuf; (ch = getchar()) != '\n'; ) {
			if (ch == EOF)
				return (NULL);
			if (p < nbuf + (NBUFSIZ - 1))
				*p++ = ch;
		}
		if (p > nbuf) {
			if (nbuf[0] == '-') {
				fprintf(stderr,
				    "login names may not start with '-'.\n");
			} else {
				*p = '\0';
				break;
			}
		}
	}
	return (nbuf);
}

void
usage(void)
{
	extern char *__progname;

	fprintf(stderr, "usage: %s [-fKLlm] [-a auth-type] [-c login-class] "
	    "[-s login-shell]\n"
	    "%-*s[login [shell-argument ...]]\n", __progname,
	    (int)strlen(__progname) + 8, "");
	exit(1);
}

void
auth_err(auth_session_t *as, int eval, const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vwarn(fmt, ap);
	va_end(ap);
	auth_close(as);
	exit(eval);
}

void
auth_errx(auth_session_t *as, int eval, const char *fmt, ...)
{
	va_list ap;

	va_start(ap, fmt);
	vwarnx(fmt, ap);
	va_end(ap);
	auth_close(as);
	exit(eval);
}