| /* vi: set sw=4 ts=4: */ |
| /* |
| * Mini su implementation for busybox |
| * |
| * Licensed under GPLv2 or later, see file LICENSE in this source tree. |
| */ |
| //config:config SU |
| //config: bool "su" |
| //config: default y |
| //config: select FEATURE_SYSLOG |
| //config: help |
| //config: su is used to become another user during a login session. |
| //config: Invoked without a username, su defaults to becoming the super user. |
| //config: Note that busybox binary must be setuid root for this applet to |
| //config: work properly. |
| //config: |
| //config:config FEATURE_SU_SYSLOG |
| //config: bool "Log to syslog all attempts to use su" |
| //config: default y |
| //config: depends on SU |
| //config: |
| //config:config FEATURE_SU_CHECKS_SHELLS |
| //config: bool "If user's shell is not in /etc/shells, disallow -s PROG" |
| //config: default y |
| //config: depends on SU |
| //config: |
| //config:config FEATURE_SU_BLANK_PW_NEEDS_SECURE_TTY |
| //config: bool "Allow blank passwords only on TTYs in /etc/securetty" |
| //config: default n |
| //config: depends on SU |
| |
| //applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */ |
| //applet:IF_SU(APPLET(su, BB_DIR_BIN, BB_SUID_REQUIRE)) |
| |
| //kbuild:lib-$(CONFIG_SU) += su.o |
| |
| //usage:#define su_trivial_usage |
| //usage: "[-lmp] [-] [-s SH] [USER [SCRIPT ARGS / -c 'CMD' ARG0 ARGS]]" |
| //usage:#define su_full_usage "\n\n" |
| //usage: "Run shell under USER (by default, root)\n" |
| //usage: "\n -,-l Clear environment, go to home dir, run shell as login shell" |
| //usage: "\n -p,-m Do not set new $HOME, $SHELL, $USER, $LOGNAME" |
| //usage: "\n -c CMD Command to pass to 'sh -c'" |
| //usage: "\n -s SH Shell to use instead of user's default" |
| |
| #include "libbb.h" |
| #include <syslog.h> |
| |
| #if ENABLE_FEATURE_SU_CHECKS_SHELLS |
| /* Return 1 if SHELL is a restricted shell (one not returned by |
| * getusershell), else 0, meaning it is a standard shell. */ |
| static int restricted_shell(const char *shell) |
| { |
| char *line; |
| int result = 1; |
| |
| /*setusershell(); - getusershell does it itself*/ |
| while ((line = getusershell()) != NULL) { |
| if (/* *line != '#' && */ strcmp(line, shell) == 0) { |
| result = 0; |
| break; |
| } |
| } |
| if (ENABLE_FEATURE_CLEAN_UP) |
| endusershell(); |
| return result; |
| } |
| #endif |
| |
| #define SU_OPT_mp (3) |
| #define SU_OPT_l (4) |
| |
| int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
| int su_main(int argc UNUSED_PARAM, char **argv) |
| { |
| unsigned flags; |
| char *opt_shell = NULL; |
| char *opt_command = NULL; |
| const char *opt_username = "root"; |
| struct passwd *pw; |
| uid_t cur_uid = getuid(); |
| const char *tty; |
| #if ENABLE_FEATURE_UTMP |
| char user_buf[64]; |
| #endif |
| const char *old_user; |
| int r; |
| |
| /* Note: we don't use "'+': stop at first non-option" idiom here. |
| * For su, "SCRIPT ARGS" or "-c CMD ARGS" do not stop option parsing: |
| * ARGS starting with dash will be treated as su options, |
| * not passed to shell. (Tested on util-linux 2.28). |
| */ |
| flags = getopt32(argv, "mplc:s:", &opt_command, &opt_shell); |
| argv += optind; |
| |
| if (argv[0] && LONE_DASH(argv[0])) { |
| flags |= SU_OPT_l; |
| argv++; |
| } |
| |
| /* get user if specified */ |
| if (argv[0]) { |
| opt_username = argv[0]; |
| argv++; |
| } |
| |
| tty = xmalloc_ttyname(STDIN_FILENO); |
| if (!tty) |
| tty = "none"; |
| tty = skip_dev_pfx(tty); |
| |
| if (ENABLE_FEATURE_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. */ |
| #if ENABLE_FEATURE_UTMP |
| old_user = user_buf; |
| if (getlogin_r(user_buf, sizeof(user_buf)) != 0) |
| #endif |
| { |
| pw = getpwuid(cur_uid); |
| old_user = pw ? xstrdup(pw->pw_name) : ""; |
| } |
| openlog(applet_name, 0, LOG_AUTH); |
| } |
| |
| pw = xgetpwnam(opt_username); |
| |
| r = 1; |
| if (cur_uid != 0) |
| r = ask_and_check_password(pw); |
| if (r > 0) { |
| if (ENABLE_FEATURE_SU_BLANK_PW_NEEDS_SECURE_TTY |
| && r == CHECKPASS_PW_HAS_EMPTY_PASSWORD |
| && !is_tty_secure(tty) |
| ) { |
| goto fail; |
| } |
| if (ENABLE_FEATURE_SU_SYSLOG) |
| syslog(LOG_NOTICE, "%c %s %s:%s", |
| '+', tty, old_user, opt_username); |
| } else { |
| fail: |
| if (ENABLE_FEATURE_SU_SYSLOG) |
| syslog(LOG_NOTICE, "%c %s %s:%s", |
| '-', tty, old_user, opt_username); |
| bb_do_delay(LOGIN_FAIL_DELAY); |
| bb_error_msg_and_die("incorrect password"); |
| } |
| |
| if (ENABLE_FEATURE_CLEAN_UP && ENABLE_FEATURE_SU_SYSLOG) { |
| closelog(); |
| } |
| |
| if (!opt_shell && (flags & SU_OPT_mp)) { |
| /* -s SHELL is not given, but "preserve env" opt is */ |
| opt_shell = getenv("SHELL"); |
| } |
| |
| #if ENABLE_FEATURE_SU_CHECKS_SHELLS |
| if (opt_shell && cur_uid != 0 && pw->pw_shell && 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 = NULL; /* ignore -s PROG */ |
| } |
| /* else: user can run whatever he wants via "su -s PROG USER". |
| * This is safe since PROG is run under user's uid/gid. */ |
| #endif |
| if (!opt_shell) |
| opt_shell = pw->pw_shell; |
| |
| change_identity(pw); |
| setup_environment(opt_shell, |
| ((flags & SU_OPT_l) / SU_OPT_l * SETUP_ENV_CLEARENV) |
| + (!(flags & SU_OPT_mp) * SETUP_ENV_CHANGEENV) |
| + (!(flags & SU_OPT_l) * SETUP_ENV_NO_CHDIR), |
| pw); |
| IF_SELINUX(set_current_security_context(NULL);) |
| |
| if (opt_command) { |
| *--argv = opt_command; |
| *--argv = (char*)"-c"; |
| } |
| |
| /* A nasty ioctl exists which can stuff data into input queue: |
| * #include <sys/ioctl.h> |
| * int main() { |
| * const char *msg = "echo $UID\n"; |
| * while (*msg) ioctl(0, TIOCSTI, *msg++); |
| * return 0; |
| * } |
| * With "su USER -c EXPLOIT" run by root, exploit can make root shell |
| * read as input and execute arbitrary command. |
| * It's debatable whether we need to protect against this |
| * (root may hesitate to run unknown scripts interactively). |
| * |
| * Some versions of su run -c CMD in a different session: |
| * ioctl(TIOCSTI) works only on the controlling tty. |
| */ |
| |
| /* Never returns */ |
| run_shell(opt_shell, flags & SU_OPT_l, (const char**)argv); |
| |
| /* return EXIT_FAILURE; - not reached */ |
| } |