/* vi: set sw=4 ts=4: */
/*
- * Mini su implementation for busybox
+ * Mini su implementation for busybox
*
- * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
+//config:config SU
+//config: bool "su (19 kb)"
+//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. */
+ * 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)
- return 0;
+ if (/* *line != '#' && */ strcmp(line, shell) == 0) {
+ result = 0;
+ break;
+ }
}
- endusershell();
- return 1;
+ if (ENABLE_FEATURE_CLEAN_UP)
+ endusershell();
+ return result;
}
#endif
#define SU_OPT_mp (3)
-#define SU_OPT_l (4)
+#define SU_OPT_l (4)
int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int su_main(int argc UNUSED_PARAM, char **argv)
struct passwd *pw;
uid_t cur_uid = getuid();
const char *tty;
- char *old_user;
-
+#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);
- //argc -= optind;
argv += optind;
if (argv[0] && LONE_DASH(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.
+ /* 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. */
- const char *user;
#if ENABLE_FEATURE_UTMP
- char user_buf[64];
- user = user_buf;
+ old_user = user_buf;
if (getlogin_r(user_buf, sizeof(user_buf)) != 0)
#endif
{
pw = getpwuid(cur_uid);
- user = pw ? pw->pw_name : "";
- }
- old_user = xstrdup(user);
- tty = xmalloc_ttyname(2);
- if (!tty) {
- tty = "none";
+ old_user = pw ? xstrdup(pw->pw_name) : "";
}
openlog(applet_name, 0, LOG_AUTH);
}
pw = xgetpwnam(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)) {
+ 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();
- free(old_user);
}
- if (!opt_shell && (flags & SU_OPT_mp))
+ 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 && restricted_shell(pw->pw_shell)) {
+ 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. */
+ * 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;
+ 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_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, opt_command, (const char**)argv);
+ run_shell(opt_shell, flags & SU_OPT_l, (const char**)argv);
/* return EXIT_FAILURE; - not reached */
}
projects / oweals / busybox.git / blobdiff