src/su.c

   1 /* su for GNU.  Run a shell with substitute user and group IDs.
   2    Copyright (C) 1992-2006, 2008 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  16
  17 /* Run a shell with the real and effective UID and GID and groups
  18    of USER, default `root'.
  19
  20    The shell run is taken from USER's password entry, /bin/sh if
  21    none is specified there.  If the account has a password, su
  22    prompts for a password unless run by a user with real UID 0.
  23
  24    Does not change the current directory.
  25    Sets `HOME' and `SHELL' from the password entry for USER, and if
  26    USER is not root, sets `USER' and `LOGNAME' to USER.
  27    The subshell is not a login shell.
  28
  29    If one or more ARGs are given, they are passed as additional
  30    arguments to the subshell.
  31
  32    Does not handle /bin/sh or other shells specially
  33    (setting argv[0] to "-su", passing -c only to certain shells, etc.).
  34    I don't see the point in doing that, and it's ugly.
  35
  36    This program intentionally does not support a "wheel group" that
  37    restricts who can su to UID 0 accounts.  RMS considers that to
  38    be fascist.
  39
  40    Compile-time options:
  41    -DSYSLOG_SUCCESS     Log successful su's (by default, to root) with syslog.
  42    -DSYSLOG_FAILURE     Log failed su's (by default, to root) with syslog.
  43
  44    -DSYSLOG_NON_ROOT    Log all su's, not just those to root (UID 0).
  45    Never logs attempted su's to nonexistent accounts.
  46
  47    Written by David MacKenzie <djm@gnu.ai.mit.edu>.  */
  48
  49 #include <config.h>
  50 #include <stdio.h>
  51 #include <getopt.h>
  52 #include <sys/types.h>
  53 #include <pwd.h>
  54 #include <grp.h>
  55
  56 /* Hide any system prototype for getusershell.
  57    This is necessary because some Cray systems have a conflicting
  58    prototype (returning `int') in <unistd.h>.  */
  59 #define getusershell _getusershell_sys_proto_
  60
  61 #include "system.h"
  62 #include "getpass.h"
  63
  64 #undef getusershell
  65
  66 #if HAVE_SYSLOG_H && HAVE_SYSLOG
  67 # include <syslog.h>
  68 #else
  69 # undef SYSLOG_SUCCESS
  70 # undef SYSLOG_FAILURE
  71 # undef SYSLOG_NON_ROOT
  72 #endif
  73
  74 #if HAVE_SYS_PARAM_H
  75 # include <sys/param.h>
  76 #endif
  77
  78 #ifndef HAVE_ENDGRENT
  79 # define endgrent() ((void) 0)
  80 #endif
  81
  82 #ifndef HAVE_ENDPWENT
  83 # define endpwent() ((void) 0)
  84 #endif
  85
  86 #if HAVE_SHADOW_H
  87 # include <shadow.h>
  88 #endif
  89
  90 #include "error.h"
  91
  92 /* The official name of this program (e.g., no `g' prefix).  */
  93 #define PROGRAM_NAME "su"
  94
  95 #define AUTHORS proper_name ("David MacKenzie")
  96
  97 #if HAVE_PATHS_H
  98 # include <paths.h>
  99 #endif
 100
 101 /* The default PATH for simulated logins to non-superuser accounts.  */
 102 #ifdef _PATH_DEFPATH
 103 # define DEFAULT_LOGIN_PATH _PATH_DEFPATH
 104 #else
 105 # define DEFAULT_LOGIN_PATH ":/usr/ucb:/bin:/usr/bin"
 106 #endif
 107
 108 /* The default PATH for simulated logins to superuser accounts.  */
 109 #ifdef _PATH_DEFPATH_ROOT
 110 # define DEFAULT_ROOT_LOGIN_PATH _PATH_DEFPATH_ROOT
 111 #else
 112 # define DEFAULT_ROOT_LOGIN_PATH "/usr/ucb:/bin:/usr/bin:/etc"
 113 #endif
 114
 115 /* The shell to run if none is given in the user's passwd entry.  */
 116 #define DEFAULT_SHELL "/bin/sh"
 117
 118 /* The user to become if none is specified.  */
 119 #define DEFAULT_USER "root"
 120
 121 char *crypt (char const *key, char const *salt);
 122 char *getusershell (void);
 123 void endusershell (void);
 124 void setusershell (void);
 125
 126 extern char **environ;
 127
 128 static void run_shell (char const *, char const *, char **, size_t)
 129      ATTRIBUTE_NORETURN;
 130
 131 /* If true, pass the `-f' option to the subshell.  */
 132 static bool fast_startup;
 133
 134 /* If true, simulate a login instead of just starting a shell.  */
 135 static bool simulate_login;
 136
 137 /* If true, change some environment vars to indicate the user su'd to.  */
 138 static bool change_environment;
 139
 140 static struct option const longopts[] =
 141 {
 142   {"command", required_argument, NULL, 'c'},
 143   {"fast", no_argument, NULL, 'f'},
 144   {"login", no_argument, NULL, 'l'},
 145   {"preserve-environment", no_argument, NULL, 'p'},
 146   {"shell", required_argument, NULL, 's'},
 147   {GETOPT_HELP_OPTION_DECL},
 148   {GETOPT_VERSION_OPTION_DECL},
 149   {NULL, 0, NULL, 0}
 150 };
 151
 152 /* Add NAME=VAL to the environment, checking for out of memory errors.  */
 153
 154 static void
 155 xsetenv (char const *name, char const *val)
 156 {
 157   size_t namelen = strlen (name);
 158   size_t vallen = strlen (val);
 159   char *string = xmalloc (namelen + 1 + vallen + 1);
 160   strcpy (string, name);
 161   string[namelen] = '=';
 162   strcpy (string + namelen + 1, val);
 163   if (putenv (string) != 0)
 164     xalloc_die ();
 165 }
 166
 167 #if defined SYSLOG_SUCCESS || defined SYSLOG_FAILURE
 168 /* Log the fact that someone has run su to the user given by PW;
 169    if SUCCESSFUL is true, they gave the correct password, etc.  */
 170
 171 static void
 172 log_su (struct passwd const *pw, bool successful)
 173 {
 174   const char *new_user, *old_user, *tty;
 175
 176 # ifndef SYSLOG_NON_ROOT
 177   if (pw->pw_uid)
 178     return;
 179 # endif
 180   new_user = pw->pw_name;
 181   /* The utmp entry (via getlogin) is probably the best way to identify
 182      the user, especially if someone su's from a su-shell.  */
 183   old_user = getlogin ();
 184   if (!old_user)
 185     {
 186       /* getlogin can fail -- usually due to lack of utmp entry.
 187          Resort to getpwuid.  */
 188       struct passwd *pwd = getpwuid (getuid ());
 189       old_user = (pwd ? pwd->pw_name : "");
 190     }
 191   tty = ttyname (STDERR_FILENO);
 192   if (!tty)
 193     tty = "none";
 194   /* 4.2BSD openlog doesn't have the third parameter.  */
 195   openlog (last_component (program_name), 0
 196 # ifdef LOG_AUTH
 197            , LOG_AUTH
 198 # endif
 199            );
 200   syslog (LOG_NOTICE,
 201 # ifdef SYSLOG_NON_ROOT
 202           "%s(to %s) %s on %s",
 203 # else
 204           "%s%s on %s",
 205 # endif
 206           successful ? "" : "FAILED SU ",
 207 # ifdef SYSLOG_NON_ROOT
 208           new_user,
 209 # endif
 210           old_user, tty);
 211   closelog ();
 212 }
 213 #endif
 214
 215 /* Ask the user for a password.
 216    Return true if the user gives the correct password for entry PW,
 217    false if not.  Return true without asking for a password if run by UID 0
 218    or if PW has an empty password.  */
 219
 220 static bool
 221 correct_password (const struct passwd *pw)
 222 {
 223   char *unencrypted, *encrypted, *correct;
 224 #if HAVE_GETSPNAM && HAVE_STRUCT_SPWD_SP_PWDP
 225   /* Shadow passwd stuff for SVR3 and maybe other systems.  */
 226   struct spwd *sp = getspnam (pw->pw_name);
 227
 228   endspent ();
 229   if (sp)
 230     correct = sp->sp_pwdp;
 231   else
 232 #endif
 233     correct = pw->pw_passwd;
 234
 235   if (getuid () == 0 || !correct || correct[0] == '\0')
 236     return true;
 237
 238   unencrypted = getpass (_("Password:"));
 239   if (!unencrypted)
 240     {
 241       error (0, 0, _("getpass: cannot open /dev/tty"));
 242       return false;
 243     }
 244   encrypted = crypt (unencrypted, correct);
 245   memset (unencrypted, 0, strlen (unencrypted));
 246   return STREQ (encrypted, correct);
 247 }
 248
 249 /* Update `environ' for the new shell based on PW, with SHELL being
 250    the value for the SHELL environment variable.  */
 251
 252 static void
 253 modify_environment (const struct passwd *pw, const char *shell)
 254 {
 255   if (simulate_login)
 256     {
 257       /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
 258          Unset all other environment variables.  */
 259       char const *term = getenv ("TERM");
 260       if (term)
 261         term = xstrdup (term);
 262       environ = xmalloc ((6 + !!term) * sizeof (char *));
 263       environ[0] = NULL;
 264       if (term)
 265         xsetenv ("TERM", term);
 266       xsetenv ("HOME", pw->pw_dir);
 267       xsetenv ("SHELL", shell);
 268       xsetenv ("USER", pw->pw_name);
 269       xsetenv ("LOGNAME", pw->pw_name);
 270       xsetenv ("PATH", (pw->pw_uid
 271                         ? DEFAULT_LOGIN_PATH
 272                         : DEFAULT_ROOT_LOGIN_PATH));
 273     }
 274   else
 275     {
 276       /* Set HOME, SHELL, and if not becoming a super-user,
 277          USER and LOGNAME.  */
 278       if (change_environment)
 279         {
 280           xsetenv ("HOME", pw->pw_dir);
 281           xsetenv ("SHELL", shell);
 282           if (pw->pw_uid)
 283             {
 284               xsetenv ("USER", pw->pw_name);
 285               xsetenv ("LOGNAME", pw->pw_name);
 286             }
 287         }
 288     }
 289 }
 290
 291 /* Become the user and group(s) specified by PW.  */
 292
 293 static void
 294 change_identity (const struct passwd *pw)
 295 {
 296 #ifdef HAVE_INITGROUPS
 297   errno = 0;
 298   if (initgroups (pw->pw_name, pw->pw_gid) == -1)
 299     error (EXIT_FAILURE, errno, _("cannot set groups"));
 300   endgrent ();
 301 #endif
 302   if (setgid (pw->pw_gid))
 303     error (EXIT_FAILURE, errno, _("cannot set group id"));
 304   if (setuid (pw->pw_uid))
 305     error (EXIT_FAILURE, errno, _("cannot set user id"));
 306 }
 307
 308 /* Run SHELL, or DEFAULT_SHELL if SHELL is empty.
 309    If COMMAND is nonzero, pass it to the shell with the -c option.
 310    Pass ADDITIONAL_ARGS to the shell as more arguments; there
 311    are N_ADDITIONAL_ARGS extra arguments.  */
 312
 313 static void
 314 run_shell (char const *shell, char const *command, char **additional_args,
 315            size_t n_additional_args)
 316 {
 317   size_t n_args = 1 + fast_startup + 2 * !!command + n_additional_args + 1;
 318   char const **args = xnmalloc (n_args, sizeof *args);
 319   size_t argno = 1;
 320
 321   if (simulate_login)
 322     {
 323       char *arg0;
 324       char *shell_basename;
 325
 326       shell_basename = last_component (shell);
 327       arg0 = xmalloc (strlen (shell_basename) + 2);
 328       arg0[0] = '-';
 329       strcpy (arg0 + 1, shell_basename);
 330       args[0] = arg0;
 331     }
 332   else
 333     args[0] = last_component (shell);
 334   if (fast_startup)
 335     args[argno++] = "-f";
 336   if (command)
 337     {
 338       args[argno++] = "-c";
 339       args[argno++] = command;
 340     }
 341   memcpy (args + argno, additional_args, n_additional_args * sizeof *args);
 342   args[argno + n_additional_args] = NULL;
 343   execv (shell, (char **) args);
 344
 345   {
 346     int exit_status = (errno == ENOENT ? EXIT_ENOENT : EXIT_CANNOT_INVOKE);
 347     error (0, errno, "%s", shell);
 348     exit (exit_status);
 349   }
 350 }
 351
 352 /* Return true if SHELL is a restricted shell (one not returned by
 353    getusershell), else false, meaning it is a standard shell.  */
 354
 355 static bool
 356 restricted_shell (const char *shell)
 357 {
 358   char *line;
 359
 360   setusershell ();
 361   while ((line = getusershell ()) != NULL)
 362     {
 363       if (*line != '#' && STREQ (line, shell))
 364         {
 365           endusershell ();
 366           return false;
 367         }
 368     }
 369   endusershell ();
 370   return true;
 371 }
 372
 373 void
 374 usage (int status)
 375 {
 376   if (status != EXIT_SUCCESS)
 377     fprintf (stderr, _("Try `%s --help' for more information.\n"),
 378              program_name);
 379   else
 380     {
 381       printf (_("Usage: %s [OPTION]... [-] [USER [ARG]...]\n"), program_name);
 382       fputs (_("\
 383 Change the effective user id and group id to that of USER.\n\
 384 \n\
 385   -, -l, --login               make the shell a login shell\n\
 386   -c, --command=COMMAND        pass a single COMMAND to the shell with -c\n\
 387   -f, --fast                   pass -f to the shell (for csh or tcsh)\n\
 388   -m, --preserve-environment   do not reset environment variables\n\
 389   -p                           same as -m\n\
 390   -s, --shell=SHELL            run SHELL if /etc/shells allows it\n\
 391 "), stdout);
 392       fputs (HELP_OPTION_DESCRIPTION, stdout);
 393       fputs (VERSION_OPTION_DESCRIPTION, stdout);
 394       fputs (_("\
 395 \n\
 396 A mere - implies -l.   If USER not given, assume root.\n\
 397 "), stdout);
 398       emit_bug_reporting_address ();
 399     }
 400   exit (status);
 401 }
 402
 403 int
 404 main (int argc, char **argv)
 405 {
 406   int optc;
 407   const char *new_user = DEFAULT_USER;
 408   char *command = NULL;
 409   char *shell = NULL;
 410   struct passwd *pw;
 411   struct passwd pw_copy;
 412
 413   initialize_main (&argc, &argv);
 414   set_program_name (argv[0]);
 415   setlocale (LC_ALL, "");
 416   bindtextdomain (PACKAGE, LOCALEDIR);
 417   textdomain (PACKAGE);
 418
 419   initialize_exit_failure (EXIT_FAILURE);
 420   atexit (close_stdout);
 421
 422   fast_startup = false;
 423   simulate_login = false;
 424   change_environment = true;
 425
 426   while ((optc = getopt_long (argc, argv, "c:flmps:", longopts, NULL)) != -1)
 427     {
 428       switch (optc)
 429         {
 430         case 'c':
 431           command = optarg;
 432           break;
 433
 434         case 'f':
 435           fast_startup = true;
 436           break;
 437
 438         case 'l':
 439           simulate_login = true;
 440           break;
 441
 442         case 'm':
 443         case 'p':
 444           change_environment = false;
 445           break;
 446
 447         case 's':
 448           shell = optarg;
 449           break;
 450
 451         case_GETOPT_HELP_CHAR;
 452
 453         case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
 454
 455         default:
 456           usage (EXIT_FAILURE);
 457         }
 458     }
 459
 460   if (optind < argc && STREQ (argv[optind], "-"))
 461     {
 462       simulate_login = true;
 463       ++optind;
 464     }
 465   if (optind < argc)
 466     new_user = argv[optind++];
 467
 468   pw = getpwnam (new_user);
 469   if (! (pw && pw->pw_name && pw->pw_name[0] && pw->pw_dir && pw->pw_dir[0]
 470          && pw->pw_passwd))
 471     error (EXIT_FAILURE, 0, _("user %s does not exist"), new_user);
 472
 473   /* Make a copy of the password information and point pw at the local
 474      copy instead.  Otherwise, some systems (e.g. GNU/Linux) would clobber
 475      the static data through the getlogin call from log_su.
 476      Also, make sure pw->pw_shell is a nonempty string.
 477      It may be NULL when NEW_USER is a username that is retrieved via NIS (YP),
 478      but that doesn't have a default shell listed.  */
 479   pw_copy = *pw;
 480   pw = &pw_copy;
 481   pw->pw_name = xstrdup (pw->pw_name);
 482   pw->pw_passwd = xstrdup (pw->pw_passwd);
 483   pw->pw_dir = xstrdup (pw->pw_dir);
 484   pw->pw_shell = xstrdup (pw->pw_shell && pw->pw_shell[0]
 485                           ? pw->pw_shell
 486                           : DEFAULT_SHELL);
 487   endpwent ();
 488
 489   if (!correct_password (pw))
 490     {
 491 #ifdef SYSLOG_FAILURE
 492       log_su (pw, false);
 493 #endif
 494       error (EXIT_FAILURE, 0, _("incorrect password"));
 495     }
 496 #ifdef SYSLOG_SUCCESS
 497   else
 498     {
 499       log_su (pw, true);
 500     }
 501 #endif
 502
 503   if (!shell && !change_environment)
 504     shell = getenv ("SHELL");
 505   if (shell && getuid () != 0 && restricted_shell (pw->pw_shell))
 506     {
 507       /* The user being su'd to has a nonstandard shell, and so is
 508          probably a uucp account or has restricted access.  Don't
 509          compromise the account by allowing access with a standard
 510          shell.  */
 511       error (0, 0, _("using restricted shell %s"), pw->pw_shell);
 512       shell = NULL;
 513     }
 514   shell = xstrdup (shell ? shell : pw->pw_shell);
 515   modify_environment (pw, shell);
 516
 517   change_identity (pw);
 518   if (simulate_login && chdir (pw->pw_dir) != 0)
 519     error (0, errno, _("warning: cannot change directory to %s"), pw->pw_dir);
 520
 521   run_shell (shell, command, argv + optind, MAX (0, argc - optind));
 522 }