X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;f=loginutils%2Fsu.c;h=d04b85fb13767521c655efe4dd4f46ebad70af43;hb=0af5265180877f4e8fbf8f1d9f2999b3fd2205d3;hp=de8c18d25e40ef1b26247078e9e756c7bed5909f;hpb=4e12b1a2a9e68685dff61acaee1e1f6c377d978c;p=oweals%2Fbusybox.git diff --git a/loginutils/su.c b/loginutils/su.c index de8c18d25..d04b85fb1 100644 --- a/loginutils/su.c +++ b/loginutils/su.c @@ -1,15 +1,69 @@ /* 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" +//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 + +//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 +#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) +#define SU_OPT_l (4) int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; int su_main(int argc UNUSED_PARAM, char **argv) @@ -21,10 +75,17 @@ 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; + /* 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])) { @@ -39,24 +100,28 @@ int su_main(int argc UNUSED_PARAM, char **argv) } 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. */ - old_user = xstrdup(USE_FEATURE_UTMP(getlogin() ? : ) (pw = getpwuid(cur_uid)) ? pw->pw_name : ""); - tty = xmalloc_ttyname(2) ? : "none"; + /* 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) : ""; + } + tty = xmalloc_ttyname(2); + if (!tty) { + tty = "none"; + } 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)) { + if (cur_uid == 0 || ask_and_check_password(pw) > 0) { if (ENABLE_FEATURE_SU_SYSLOG) syslog(LOG_NOTICE, "%c %s %s:%s", '+', tty, old_user, opt_username); @@ -64,37 +129,65 @@ int su_main(int argc UNUSED_PARAM, char **argv) 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 && 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 params: shell, clear_env, change_env, pw */ - setup_environment(opt_shell, flags & SU_OPT_l, !(flags & SU_OPT_mp), pw); - USE_SELINUX(set_current_security_context(NULL);) + 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 + * 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 */ }