blob: 24ffbde86e8c92e93d023776a313c21c24d58278
| 1 | /* vi: set sw=4 ts=4: */ |
| 2 | /* |
| 3 | * Mini su implementation for busybox |
| 4 | * |
| 5 | * Licensed under GPLv2 or later, see file LICENSE in this source tree. |
| 6 | */ |
| 7 | //config:config SU |
| 8 | //config: bool "su" |
| 9 | //config: default y |
| 10 | //config: select FEATURE_SYSLOG |
| 11 | //config: help |
| 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: |
| 15 | //config: Note that Busybox binary must be setuid root for this applet to |
| 16 | //config: work properly. |
| 17 | //config: |
| 18 | //config:config FEATURE_SU_SYSLOG |
| 19 | //config: bool "Enable su to write to syslog" |
| 20 | //config: default y |
| 21 | //config: depends on SU |
| 22 | //config: |
| 23 | //config:config FEATURE_SU_CHECKS_SHELLS |
| 24 | //config: bool "Enable su to check user's shell to be listed in /etc/shells" |
| 25 | //config: depends on SU |
| 26 | //config: default y |
| 27 | |
| 28 | //applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */ |
| 29 | //applet:IF_SU(APPLET(su, BB_DIR_BIN, BB_SUID_REQUIRE)) |
| 30 | |
| 31 | //kbuild:lib-$(CONFIG_SU) += su.o |
| 32 | |
| 33 | //usage:#define su_trivial_usage |
| 34 | //usage: "[-lmp] [-] [-s SH] [USER [SCRIPT ARGS / -c 'CMD' ARG0 ARGS]]" |
| 35 | //usage:#define su_full_usage "\n\n" |
| 36 | //usage: "Run shell under USER (by default, root)\n" |
| 37 | //usage: "\n -,-l Clear environment, go to home dir, run shell as login shell" |
| 38 | //usage: "\n -p,-m Do not set new $HOME, $SHELL, $USER, $LOGNAME" |
| 39 | //usage: "\n -c CMD Command to pass to 'sh -c'" |
| 40 | //usage: "\n -s SH Shell to use instead of user's default" |
| 41 | |
| 42 | #include "libbb.h" |
| 43 | #include <syslog.h> |
| 44 | |
| 45 | #if ENABLE_FEATURE_SU_CHECKS_SHELLS |
| 46 | /* Return 1 if SHELL is a restricted shell (one not returned by |
| 47 | * getusershell), else 0, meaning it is a standard shell. */ |
| 48 | static int restricted_shell(const char *shell) |
| 49 | { |
| 50 | char *line; |
| 51 | int result = 1; |
| 52 | |
| 53 | /*setusershell(); - getusershell does it itself*/ |
| 54 | while ((line = getusershell()) != NULL) { |
| 55 | if (/* *line != '#' && */ strcmp(line, shell) == 0) { |
| 56 | result = 0; |
| 57 | break; |
| 58 | } |
| 59 | } |
| 60 | if (ENABLE_FEATURE_CLEAN_UP) |
| 61 | endusershell(); |
| 62 | return result; |
| 63 | } |
| 64 | #endif |
| 65 | |
| 66 | #define SU_OPT_mp (3) |
| 67 | #define SU_OPT_l (4) |
| 68 | |
| 69 | int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
| 70 | int su_main(int argc UNUSED_PARAM, char **argv) |
| 71 | { |
| 72 | unsigned flags; |
| 73 | char *opt_shell = NULL; |
| 74 | char *opt_command = NULL; |
| 75 | const char *opt_username = "root"; |
| 76 | struct passwd *pw; |
| 77 | uid_t cur_uid = getuid(); |
| 78 | const char *tty; |
| 79 | #if ENABLE_FEATURE_UTMP |
| 80 | char user_buf[64]; |
| 81 | #endif |
| 82 | const char *old_user; |
| 83 | |
| 84 | /* Note: we don't use "'+': stop at first non-option" idiom here. |
| 85 | * For su, "SCRIPT ARGS" or "-c CMD ARGS" do not stop option parsing: |
| 86 | * ARGS starting with dash will be treated as su options, |
| 87 | * not passed to shell. (Tested on util-linux 2.28). |
| 88 | */ |
| 89 | flags = getopt32(argv, "mplc:s:", &opt_command, &opt_shell); |
| 90 | argv += optind; |
| 91 | |
| 92 | if (argv[0] && LONE_DASH(argv[0])) { |
| 93 | flags |= SU_OPT_l; |
| 94 | argv++; |
| 95 | } |
| 96 | |
| 97 | /* get user if specified */ |
| 98 | if (argv[0]) { |
| 99 | opt_username = argv[0]; |
| 100 | argv++; |
| 101 | } |
| 102 | |
| 103 | if (ENABLE_FEATURE_SU_SYSLOG) { |
| 104 | /* The utmp entry (via getlogin) is probably the best way to |
| 105 | * identify the user, especially if someone su's from a su-shell. |
| 106 | * But getlogin can fail -- usually due to lack of utmp entry. |
| 107 | * in this case resort to getpwuid. */ |
| 108 | #if ENABLE_FEATURE_UTMP |
| 109 | old_user = user_buf; |
| 110 | if (getlogin_r(user_buf, sizeof(user_buf)) != 0) |
| 111 | #endif |
| 112 | { |
| 113 | pw = getpwuid(cur_uid); |
| 114 | old_user = pw ? xstrdup(pw->pw_name) : ""; |
| 115 | } |
| 116 | tty = xmalloc_ttyname(2); |
| 117 | if (!tty) { |
| 118 | tty = "none"; |
| 119 | } |
| 120 | openlog(applet_name, 0, LOG_AUTH); |
| 121 | } |
| 122 | |
| 123 | pw = xgetpwnam(opt_username); |
| 124 | |
| 125 | if (cur_uid == 0 || ask_and_check_password(pw) > 0) { |
| 126 | if (ENABLE_FEATURE_SU_SYSLOG) |
| 127 | syslog(LOG_NOTICE, "%c %s %s:%s", |
| 128 | '+', tty, old_user, opt_username); |
| 129 | } else { |
| 130 | if (ENABLE_FEATURE_SU_SYSLOG) |
| 131 | syslog(LOG_NOTICE, "%c %s %s:%s", |
| 132 | '-', tty, old_user, opt_username); |
| 133 | bb_do_delay(LOGIN_FAIL_DELAY); |
| 134 | bb_error_msg_and_die("incorrect password"); |
| 135 | } |
| 136 | |
| 137 | if (ENABLE_FEATURE_CLEAN_UP && ENABLE_FEATURE_SU_SYSLOG) { |
| 138 | closelog(); |
| 139 | } |
| 140 | |
| 141 | if (!opt_shell && (flags & SU_OPT_mp)) { |
| 142 | /* -s SHELL is not given, but "preserve env" opt is */ |
| 143 | opt_shell = getenv("SHELL"); |
| 144 | } |
| 145 | |
| 146 | #if ENABLE_FEATURE_SU_CHECKS_SHELLS |
| 147 | if (opt_shell && cur_uid != 0 && pw->pw_shell && restricted_shell(pw->pw_shell)) { |
| 148 | /* The user being su'd to has a nonstandard shell, and so is |
| 149 | * probably a uucp account or has restricted access. Don't |
| 150 | * compromise the account by allowing access with a standard |
| 151 | * shell. */ |
| 152 | bb_error_msg("using restricted shell"); |
| 153 | opt_shell = NULL; /* ignore -s PROG */ |
| 154 | } |
| 155 | /* else: user can run whatever he wants via "su -s PROG USER". |
| 156 | * This is safe since PROG is run under user's uid/gid. */ |
| 157 | #endif |
| 158 | if (!opt_shell) |
| 159 | opt_shell = pw->pw_shell; |
| 160 | |
| 161 | change_identity(pw); |
| 162 | setup_environment(opt_shell, |
| 163 | ((flags & SU_OPT_l) / SU_OPT_l * SETUP_ENV_CLEARENV) |
| 164 | + (!(flags & SU_OPT_mp) * SETUP_ENV_CHANGEENV) |
| 165 | + (!(flags & SU_OPT_l) * SETUP_ENV_NO_CHDIR), |
| 166 | pw); |
| 167 | IF_SELINUX(set_current_security_context(NULL);) |
| 168 | |
| 169 | if (opt_command) { |
| 170 | *--argv = opt_command; |
| 171 | *--argv = (char*)"-c"; |
| 172 | } |
| 173 | |
| 174 | /* A nasty ioctl exists which can stuff data into input queue: |
| 175 | * #include <sys/ioctl.h> |
| 176 | * int main() { |
| 177 | * const char *msg = "echo $UID\n"; |
| 178 | * while (*msg) ioctl(0, TIOCSTI, *msg++); |
| 179 | * return 0; |
| 180 | * } |
| 181 | * With "su USER -c EXPLOIT" run by root, exploit can make root shell |
| 182 | * read as input and execute arbitrary command. |
| 183 | * It's debatable whether we need to protect against this |
| 184 | * (root may hesitate to run unknown scripts interactively). |
| 185 | * |
| 186 | * Some versions of su run -c CMD in a different session: |
| 187 | * ioctl(TIOCSTI) works only on the controlling tty. |
| 188 | */ |
| 189 | |
| 190 | /* Never returns */ |
| 191 | run_shell(opt_shell, flags & SU_OPT_l, (const char**)argv); |
| 192 | |
| 193 | /* return EXIT_FAILURE; - not reached */ |
| 194 | } |
| 195 |