busybox/loginutils/su.c

/* vi: set sw=4 ts=4: */
/*
 *  Mini su implementation for busybox
 *
 *  Licensed under the GPL v2, see the file LICENSE in this tarball.
 */

#include "busybox.h"
#include <syslog.h>

int su_main(int argc, char **argv)
{
	unsigned long flags;
	char *opt_shell = 0;
	char *opt_command = 0;
	char *opt_username = "root";
	char **opt_args = 0;
	struct passwd *pw;
	uid_t cur_uid = getuid();
	const char *tty;
	char *old_user;

	flags = bb_getopt_ulflags(argc, argv, "mplc:s:", &opt_command, &opt_shell);
#define SU_OPT_mp (3)
#define SU_OPT_l (4)

	if (optind < argc  && argv[optind][0] == '-' && argv[optind][1] == 0) {
		flags |= SU_OPT_l;
		++optind;
	}

	/* get user if specified */
	if (optind < argc) opt_username = argv [optind++];

	if (optind < argc) opt_args = argv + optind;

	if (ENABLE_SU_SYSLOG) {
		/* The utmp entry (via getlogin) is probably the best way to identify
		the user, especially if someone su's from a su-shell.
		But getlogin can fail -- usually due to lack of utmp entry.
		in this case resort to getpwuid.  */
		old_user = xstrdup(USE_FEATURE_UTMP(getlogin() ? : ) (pw = getpwuid(cur_uid)) ? pw->pw_name : "");
		tty = ttyname(2) ? : "none";
		openlog(bb_applet_name, 0, LOG_AUTH);
	}

	pw = getpwnam(opt_username);
	if (!pw) bb_error_msg_and_die("Unknown id: %s", opt_username);

	/* Make sure pw->pw_shell is non-NULL.  It may be NULL when NEW_USER
	   is a username that is retrieved via NIS (YP), but that doesn't have
	   a default shell listed.  */
	if (!pw->pw_shell || !pw->pw_shell[0]) pw->pw_shell = (char *)DEFAULT_SHELL;

	if ((cur_uid == 0) || correct_password(pw)) {
		if (ENABLE_SU_SYSLOG)
			syslog(LOG_NOTICE, "+ %s %s:%s", tty, old_user, opt_username);
	} else {
		if (ENABLE_SU_SYSLOG)
			syslog(LOG_NOTICE, "- %s %s:%s", tty, old_user, opt_username);
		bb_error_msg_and_die("incorrect password");
	}

	if (ENABLE_FEATURE_CLEAN_UP && ENABLE_SU_SYSLOG) {
		closelog();
		free(old_user);
	}

	if (!opt_shell && (flags & SU_OPT_mp)) opt_shell = getenv("SHELL");

	if (opt_shell && cur_uid && restricted_shell(pw->pw_shell)) {
		/* The user being su'd to has a nonstandard shell, and so is
		   probably a uucp account or has restricted access.  Don't
		   compromise the account by allowing access with a standard
		   shell.  */
		bb_error_msg("using restricted shell");
		opt_shell = 0;
	}

	if (!opt_shell) opt_shell = pw->pw_shell;

	change_identity(pw);
	setup_environment(opt_shell, flags & SU_OPT_l, !(flags & SU_OPT_mp), pw);
	USE_SELINUX(set_current_security_context(NULL);)

	/* Never returns */
	run_shell(opt_shell, flags & SU_OPT_l, opt_command, (const char**)opt_args);

	return EXIT_FAILURE;
}