1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * Mini su implementation for busybox
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4 | *
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5 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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6 | */
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7 | //config:config SU
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8 | //config: bool "su"
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9 | //config: default y
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10 | //config: select FEATURE_SYSLOG
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11 | //config: help
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12 | //config: su is used to become another user during a login session.
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13 | //config: Invoked without a username, su defaults to becoming the super user.
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14 | //config:
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15 | //config: Note that Busybox binary must be setuid root for this applet to
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16 | //config: work properly.
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17 | //config:
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18 | //config:config FEATURE_SU_SYSLOG
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19 | //config: bool "Enable su to write to syslog"
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20 | //config: default y
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21 | //config: depends on SU
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22 | //config:
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23 | //config:config FEATURE_SU_CHECKS_SHELLS
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24 | //config: bool "Enable su to check user's shell to be listed in /etc/shells"
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25 | //config: depends on SU
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26 | //config: default y
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27 |
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28 | //applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */
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29 | //applet:IF_SU(APPLET(su, BB_DIR_BIN, BB_SUID_REQUIRE))
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30 |
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31 | //kbuild:lib-$(CONFIG_SU) += su.o
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32 |
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33 | //usage:#define su_trivial_usage
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34 | //usage: "[OPTIONS] [-] [USER]"
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35 | //usage:#define su_full_usage "\n\n"
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36 | //usage: "Run shell under USER (by default, root)\n"
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37 | //usage: "\n -,-l Clear environment, run shell as login shell"
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38 | //usage: "\n -p,-m Do not set new $HOME, $SHELL, $USER, $LOGNAME"
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39 | //usage: "\n -c CMD Command to pass to 'sh -c'"
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40 | //usage: "\n -s SH Shell to use instead of user's default"
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41 |
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42 | #include "libbb.h"
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43 | #include <syslog.h>
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44 |
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45 | #if ENABLE_FEATURE_SU_CHECKS_SHELLS
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46 | /* Return 1 if SHELL is a restricted shell (one not returned by
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47 | * getusershell), else 0, meaning it is a standard shell. */
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48 | static int restricted_shell(const char *shell)
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49 | {
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50 | char *line;
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51 | int result = 1;
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52 |
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53 | /*setusershell(); - getusershell does it itself*/
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54 | while ((line = getusershell()) != NULL) {
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55 | if (/* *line != '#' && */ strcmp(line, shell) == 0) {
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56 | result = 0;
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57 | break;
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58 | }
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59 | }
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60 | if (ENABLE_FEATURE_CLEAN_UP)
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61 | endusershell();
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62 | return result;
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63 | }
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64 | #endif
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65 |
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66 | #define SU_OPT_mp (3)
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67 | #define SU_OPT_l (4)
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68 |
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69 | int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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70 | int su_main(int argc UNUSED_PARAM, char **argv)
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71 | {
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72 | unsigned flags;
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73 | char *opt_shell = NULL;
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74 | char *opt_command = NULL;
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75 | const char *opt_username = "root";
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76 | struct passwd *pw;
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77 | uid_t cur_uid = getuid();
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78 | const char *tty;
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79 | #if ENABLE_FEATURE_UTMP
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80 | char user_buf[64];
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81 | #endif
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82 | const char *old_user;
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83 |
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84 | flags = getopt32(argv, "mplc:s:", &opt_command, &opt_shell);
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85 | //argc -= optind;
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86 | argv += optind;
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87 |
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88 | if (argv[0] && LONE_DASH(argv[0])) {
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89 | flags |= SU_OPT_l;
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90 | argv++;
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91 | }
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92 |
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93 | /* get user if specified */
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94 | if (argv[0]) {
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95 | opt_username = argv[0];
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96 | argv++;
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97 | }
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98 |
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99 | if (ENABLE_FEATURE_SU_SYSLOG) {
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100 | /* The utmp entry (via getlogin) is probably the best way to
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101 | * identify the user, especially if someone su's from a su-shell.
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102 | * But getlogin can fail -- usually due to lack of utmp entry.
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103 | * in this case resort to getpwuid. */
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104 | #if ENABLE_FEATURE_UTMP
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105 | old_user = user_buf;
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106 | if (getlogin_r(user_buf, sizeof(user_buf)) != 0)
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107 | #endif
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108 | {
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109 | pw = getpwuid(cur_uid);
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110 | old_user = pw ? xstrdup(pw->pw_name) : "";
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111 | }
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112 | tty = xmalloc_ttyname(2);
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113 | if (!tty) {
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114 | tty = "none";
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115 | }
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116 | openlog(applet_name, 0, LOG_AUTH);
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117 | }
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118 |
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119 | pw = xgetpwnam(opt_username);
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120 |
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121 | if (cur_uid == 0 || ask_and_check_password(pw) > 0) {
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122 | if (ENABLE_FEATURE_SU_SYSLOG)
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123 | syslog(LOG_NOTICE, "%c %s %s:%s",
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124 | '+', tty, old_user, opt_username);
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125 | } else {
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126 | if (ENABLE_FEATURE_SU_SYSLOG)
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127 | syslog(LOG_NOTICE, "%c %s %s:%s",
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128 | '-', tty, old_user, opt_username);
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129 | bb_do_delay(LOGIN_FAIL_DELAY);
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130 | bb_error_msg_and_die("incorrect password");
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131 | }
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132 |
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133 | if (ENABLE_FEATURE_CLEAN_UP && ENABLE_FEATURE_SU_SYSLOG) {
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134 | closelog();
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135 | }
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136 |
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137 | if (!opt_shell && (flags & SU_OPT_mp)) {
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138 | /* -s SHELL is not given, but "preserve env" opt is */
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139 | opt_shell = getenv("SHELL");
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140 | }
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141 |
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142 | #if ENABLE_FEATURE_SU_CHECKS_SHELLS
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143 | if (opt_shell && cur_uid != 0 && pw->pw_shell && restricted_shell(pw->pw_shell)) {
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144 | /* The user being su'd to has a nonstandard shell, and so is
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145 | * probably a uucp account or has restricted access. Don't
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146 | * compromise the account by allowing access with a standard
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147 | * shell. */
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148 | bb_error_msg("using restricted shell");
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149 | opt_shell = NULL; /* ignore -s PROG */
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150 | }
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151 | /* else: user can run whatever he wants via "su -s PROG USER".
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152 | * This is safe since PROG is run under user's uid/gid. */
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153 | #endif
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154 | if (!opt_shell)
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155 | opt_shell = pw->pw_shell;
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156 |
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157 | change_identity(pw);
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158 | setup_environment(opt_shell,
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159 | ((flags & SU_OPT_l) / SU_OPT_l * SETUP_ENV_CLEARENV)
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160 | + (!(flags & SU_OPT_mp) * SETUP_ENV_CHANGEENV)
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161 | + (!(flags & SU_OPT_l) * SETUP_ENV_NO_CHDIR),
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162 | pw);
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163 | IF_SELINUX(set_current_security_context(NULL);)
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164 |
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165 | /* Never returns */
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166 | run_shell(opt_shell, flags & SU_OPT_l, opt_command, (const char**)argv);
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167 |
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168 | /* return EXIT_FAILURE; - not reached */
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169 | }
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