1 /* vi: set sw=4 ts=4: */
3 * Mini su implementation for busybox
5 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
10 //config: select FEATURE_SYSLOG
12 //config: su is used to become another user during a login session.
13 //config: Invoked without a username, su defaults to becoming the super user.
14 //config: Note that busybox binary must be setuid root for this applet to
15 //config: work properly.
17 //config:config FEATURE_SU_SYSLOG
18 //config: bool "Log to syslog all attempts to use su"
20 //config: depends on SU
22 //config:config FEATURE_SU_CHECKS_SHELLS
23 //config: bool "If user's shell is not in /etc/shells, disallow -s PROG"
25 //config: depends on SU
27 //applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */
28 //applet:IF_SU(APPLET(su, BB_DIR_BIN, BB_SUID_REQUIRE))
30 //kbuild:lib-$(CONFIG_SU) += su.o
32 //usage:#define su_trivial_usage
33 //usage: "[-lmp] [-] [-s SH] [USER [SCRIPT ARGS / -c 'CMD' ARG0 ARGS]]"
34 //usage:#define su_full_usage "\n\n"
35 //usage: "Run shell under USER (by default, root)\n"
36 //usage: "\n -,-l Clear environment, go to home dir, run shell as login shell"
37 //usage: "\n -p,-m Do not set new $HOME, $SHELL, $USER, $LOGNAME"
38 //usage: "\n -c CMD Command to pass to 'sh -c'"
39 //usage: "\n -s SH Shell to use instead of user's default"
44 #if ENABLE_FEATURE_SU_CHECKS_SHELLS
45 /* Return 1 if SHELL is a restricted shell (one not returned by
46 * getusershell), else 0, meaning it is a standard shell. */
47 static int restricted_shell(const char *shell)
52 /*setusershell(); - getusershell does it itself*/
53 while ((line = getusershell()) != NULL) {
54 if (/* *line != '#' && */ strcmp(line, shell) == 0) {
59 if (ENABLE_FEATURE_CLEAN_UP)
68 int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
69 int su_main(int argc UNUSED_PARAM, char **argv)
72 char *opt_shell = NULL;
73 char *opt_command = NULL;
74 const char *opt_username = "root";
76 uid_t cur_uid = getuid();
78 #if ENABLE_FEATURE_UTMP
83 /* Note: we don't use "'+': stop at first non-option" idiom here.
84 * For su, "SCRIPT ARGS" or "-c CMD ARGS" do not stop option parsing:
85 * ARGS starting with dash will be treated as su options,
86 * not passed to shell. (Tested on util-linux 2.28).
88 flags = getopt32(argv, "mplc:s:", &opt_command, &opt_shell);
91 if (argv[0] && LONE_DASH(argv[0])) {
96 /* get user if specified */
98 opt_username = argv[0];
102 if (ENABLE_FEATURE_SU_SYSLOG) {
103 /* The utmp entry (via getlogin) is probably the best way to
104 * identify the user, especially if someone su's from a su-shell.
105 * But getlogin can fail -- usually due to lack of utmp entry.
106 * in this case resort to getpwuid. */
107 #if ENABLE_FEATURE_UTMP
109 if (getlogin_r(user_buf, sizeof(user_buf)) != 0)
112 pw = getpwuid(cur_uid);
113 old_user = pw ? xstrdup(pw->pw_name) : "";
115 tty = xmalloc_ttyname(2);
119 openlog(applet_name, 0, LOG_AUTH);
122 pw = xgetpwnam(opt_username);
124 if (cur_uid == 0 || ask_and_check_password(pw) > 0) {
125 if (ENABLE_FEATURE_SU_SYSLOG)
126 syslog(LOG_NOTICE, "%c %s %s:%s",
127 '+', tty, old_user, opt_username);
129 if (ENABLE_FEATURE_SU_SYSLOG)
130 syslog(LOG_NOTICE, "%c %s %s:%s",
131 '-', tty, old_user, opt_username);
132 bb_do_delay(LOGIN_FAIL_DELAY);
133 bb_error_msg_and_die("incorrect password");
136 if (ENABLE_FEATURE_CLEAN_UP && ENABLE_FEATURE_SU_SYSLOG) {
140 if (!opt_shell && (flags & SU_OPT_mp)) {
141 /* -s SHELL is not given, but "preserve env" opt is */
142 opt_shell = getenv("SHELL");
145 #if ENABLE_FEATURE_SU_CHECKS_SHELLS
146 if (opt_shell && cur_uid != 0 && pw->pw_shell && restricted_shell(pw->pw_shell)) {
147 /* The user being su'd to has a nonstandard shell, and so is
148 * probably a uucp account or has restricted access. Don't
149 * compromise the account by allowing access with a standard
151 bb_error_msg("using restricted shell");
152 opt_shell = NULL; /* ignore -s PROG */
154 /* else: user can run whatever he wants via "su -s PROG USER".
155 * This is safe since PROG is run under user's uid/gid. */
158 opt_shell = pw->pw_shell;
161 setup_environment(opt_shell,
162 ((flags & SU_OPT_l) / SU_OPT_l * SETUP_ENV_CLEARENV)
163 + (!(flags & SU_OPT_mp) * SETUP_ENV_CHANGEENV)
164 + (!(flags & SU_OPT_l) * SETUP_ENV_NO_CHDIR),
166 IF_SELINUX(set_current_security_context(NULL);)
169 *--argv = opt_command;
170 *--argv = (char*)"-c";
173 /* A nasty ioctl exists which can stuff data into input queue:
174 * #include <sys/ioctl.h>
176 * const char *msg = "echo $UID\n";
177 * while (*msg) ioctl(0, TIOCSTI, *msg++);
180 * With "su USER -c EXPLOIT" run by root, exploit can make root shell
181 * read as input and execute arbitrary command.
182 * It's debatable whether we need to protect against this
183 * (root may hesitate to run unknown scripts interactively).
185 * Some versions of su run -c CMD in a different session:
186 * ioctl(TIOCSTI) works only on the controlling tty.
190 run_shell(opt_shell, flags & SU_OPT_l, (const char**)argv);
192 /* return EXIT_FAILURE; - not reached */