src/su.c

   1 /* su for GNU.  Run a shell with substitute user and group IDs.
   2    Copyright (C) 1992-2006, 2008-2011 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 #include "system.h"
  57 #include "getpass.h"
  58
  59 #if HAVE_SYSLOG_H && HAVE_SYSLOG
  60 # include <syslog.h>
  61 #else
  62 # undef SYSLOG_SUCCESS
  63 # undef SYSLOG_FAILURE
  64 # undef SYSLOG_NON_ROOT
  65 #endif
  66
  67 #if HAVE_SYS_PARAM_H
  68 # include <sys/param.h>
  69 #endif
  70
  71 #ifndef HAVE_ENDGRENT
  72 # define endgrent() ((void) 0)
  73 #endif
  74
  75 #ifndef HAVE_ENDPWENT
  76 # define endpwent() ((void) 0)
  77 #endif
  78
  79 #if HAVE_SHADOW_H
  80 # include <shadow.h>
  81 #endif
  82
  83 #include "error.h"
  84
  85 /* The official name of this program (e.g., no `g' prefix).  */
  86 #define PROGRAM_NAME "su"
  87
  88 #define AUTHORS proper_name ("David MacKenzie")
  89
  90 #if HAVE_PATHS_H
  91 # include <paths.h>
  92 #endif
  93
  94 /* The default PATH for simulated logins to non-superuser accounts.  */
  95 #ifdef _PATH_DEFPATH
  96 # define DEFAULT_LOGIN_PATH _PATH_DEFPATH
  97 #else
  98 # define DEFAULT_LOGIN_PATH ":/usr/ucb:/bin:/usr/bin"
  99 #endif
 100
 101 /* The default PATH for simulated logins to superuser accounts.  */
 102 #ifdef _PATH_DEFPATH_ROOT
 103 # define DEFAULT_ROOT_LOGIN_PATH _PATH_DEFPATH_ROOT
 104 #else
 105 # define DEFAULT_ROOT_LOGIN_PATH "/usr/ucb:/bin:/usr/bin:/etc"
 106 #endif
 107
 108 /* The shell to run if none is given in the user's passwd entry.  */
 109 #define DEFAULT_SHELL "/bin/sh"
 110
 111 /* The user to become if none is specified.  */
 112 #define DEFAULT_USER "root"
 113
 114 char *crypt (char const *key, char const *salt);
 115
 116 static void run_shell (char const *, char const *, char **, size_t)
 117      ATTRIBUTE_NORETURN;
 118
 119 /* If true, pass the `-f' option to the subshell.  */
 120 static bool fast_startup;
 121
 122 /* If true, simulate a login instead of just starting a shell.  */
 123 static bool simulate_login;
 124
 125 /* If true, change some environment vars to indicate the user su'd to.  */
 126 static bool change_environment;
 127
 128 static struct option const longopts[] =
 129 {
 130   {"command", required_argument, NULL, 'c'},
 131   {"fast", no_argument, NULL, 'f'},
 132   {"login", no_argument, NULL, 'l'},
 133   {"preserve-environment", no_argument, NULL, 'p'},
 134   {"shell", required_argument, NULL, 's'},
 135   {GETOPT_HELP_OPTION_DECL},
 136   {GETOPT_VERSION_OPTION_DECL},
 137   {NULL, 0, NULL, 0}
 138 };
 139
 140 /* Add NAME=VAL to the environment, checking for out of memory errors.  */
 141
 142 static void
 143 xsetenv (char const *name, char const *val)
 144 {
 145   size_t namelen = strlen (name);
 146   size_t vallen = strlen (val);
 147   char *string = xmalloc (namelen + 1 + vallen + 1);
 148   strcpy (string, name);
 149   string[namelen] = '=';
 150   strcpy (string + namelen + 1, val);
 151   if (putenv (string) != 0)
 152     xalloc_die ();
 153 }
 154
 155 #if defined SYSLOG_SUCCESS || defined SYSLOG_FAILURE
 156 /* Log the fact that someone has run su to the user given by PW;
 157    if SUCCESSFUL is true, they gave the correct password, etc.  */
 158
 159 static void
 160 log_su (struct passwd const *pw, bool successful)
 161 {
 162   const char *new_user, *old_user, *tty;
 163
 164 # ifndef SYSLOG_NON_ROOT
 165   if (pw->pw_uid)
 166     return;
 167 # endif
 168   new_user = pw->pw_name;
 169   /* The utmp entry (via getlogin) is probably the best way to identify
 170      the user, especially if someone su's from a su-shell.  */
 171   old_user = getlogin ();
 172   if (!old_user)
 173     {
 174       /* getlogin can fail -- usually due to lack of utmp entry.
 175          Resort to getpwuid.  */
 176       struct passwd *pwd = getpwuid (getuid ());
 177       old_user = (pwd ? pwd->pw_name : "");
 178     }
 179   tty = ttyname (STDERR_FILENO);
 180   if (!tty)
 181     tty = "none";
 182   /* 4.2BSD openlog doesn't have the third parameter.  */
 183   openlog (last_component (program_name), 0
 184 # ifdef LOG_AUTH
 185            , LOG_AUTH
 186 # endif
 187            );
 188   syslog (LOG_NOTICE,
 189 # ifdef SYSLOG_NON_ROOT
 190           "%s(to %s) %s on %s",
 191 # else
 192           "%s%s on %s",
 193 # endif
 194           successful ? "" : "FAILED SU ",
 195 # ifdef SYSLOG_NON_ROOT
 196           new_user,
 197 # endif
 198           old_user, tty);
 199   closelog ();
 200 }
 201 #endif
 202
 203 /* Ask the user for a password.
 204    Return true if the user gives the correct password for entry PW,
 205    false if not.  Return true without asking for a password if run by UID 0
 206    or if PW has an empty password.  */
 207
 208 static bool
 209 correct_password (const struct passwd *pw)
 210 {
 211   char *unencrypted, *encrypted, *correct;
 212 #if HAVE_GETSPNAM && HAVE_STRUCT_SPWD_SP_PWDP
 213   /* Shadow passwd stuff for SVR3 and maybe other systems.  */
 214   struct spwd *sp = getspnam (pw->pw_name);
 215
 216   endspent ();
 217   if (sp)
 218     correct = sp->sp_pwdp;
 219   else
 220 #endif
 221     correct = pw->pw_passwd;
 222
 223   if (getuid () == 0 || !correct || correct[0] == '\0')
 224     return true;
 225
 226   unencrypted = getpass (_("Password:"));
 227   if (!unencrypted)
 228     {
 229       error (0, 0, _("getpass: cannot open /dev/tty"));
 230       return false;
 231     }
 232   encrypted = crypt (unencrypted, correct);
 233   memset (unencrypted, 0, strlen (unencrypted));
 234   return STREQ (encrypted, correct);
 235 }
 236
 237 /* Update `environ' for the new shell based on PW, with SHELL being
 238    the value for the SHELL environment variable.  */
 239
 240 static void
 241 modify_environment (const struct passwd *pw, const char *shell)
 242 {
 243   if (simulate_login)
 244     {
 245       /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
 246          Unset all other environment variables.  */
 247       char const *term = getenv ("TERM");
 248       if (term)
 249         term = xstrdup (term);
 250       environ = xmalloc ((6 + !!term) * sizeof (char *));
 251       environ[0] = NULL;
 252       if (term)
 253         xsetenv ("TERM", term);
 254       xsetenv ("HOME", pw->pw_dir);
 255       xsetenv ("SHELL", shell);
 256       xsetenv ("USER", pw->pw_name);
 257       xsetenv ("LOGNAME", pw->pw_name);
 258       xsetenv ("PATH", (pw->pw_uid
 259                         ? DEFAULT_LOGIN_PATH
 260                         : DEFAULT_ROOT_LOGIN_PATH));
 261     }
 262   else
 263     {
 264       /* Set HOME, SHELL, and if not becoming a super-user,
 265          USER and LOGNAME.  */
 266       if (change_environment)
 267         {
 268           xsetenv ("HOME", pw->pw_dir);
 269           xsetenv ("SHELL", shell);
 270           if (pw->pw_uid)
 271             {
 272               xsetenv ("USER", pw->pw_name);
 273               xsetenv ("LOGNAME", pw->pw_name);
 274             }
 275         }
 276     }
 277 }
 278
 279 /* Become the user and group(s) specified by PW.  */
 280
 281 static void
 282 change_identity (const struct passwd *pw)
 283 {
 284 #ifdef HAVE_INITGROUPS
 285   errno = 0;
 286   if (initgroups (pw->pw_name, pw->pw_gid) == -1)
 287     error (EXIT_CANCELED, errno, _("cannot set groups"));
 288   endgrent ();
 289 #endif
 290   if (setgid (pw->pw_gid))
 291     error (EXIT_CANCELED, errno, _("cannot set group id"));
 292   if (setuid (pw->pw_uid))
 293     error (EXIT_CANCELED, errno, _("cannot set user id"));
 294 }
 295
 296 /* Run SHELL, or DEFAULT_SHELL if SHELL is empty.
 297    If COMMAND is nonzero, pass it to the shell with the -c option.
 298    Pass ADDITIONAL_ARGS to the shell as more arguments; there
 299    are N_ADDITIONAL_ARGS extra arguments.  */
 300
 301 static void
 302 run_shell (char const *shell, char const *command, char **additional_args,
 303            size_t n_additional_args)
 304 {
 305   size_t n_args = 1 + fast_startup + 2 * !!command + n_additional_args + 1;
 306   char const **args = xnmalloc (n_args, sizeof *args);
 307   size_t argno = 1;
 308
 309   if (simulate_login)
 310     {
 311       char *arg0;
 312       char *shell_basename;
 313
 314       shell_basename = last_component (shell);
 315       arg0 = xmalloc (strlen (shell_basename) + 2);
 316       arg0[0] = '-';
 317       strcpy (arg0 + 1, shell_basename);
 318       args[0] = arg0;
 319     }
 320   else
 321     args[0] = last_component (shell);
 322   if (fast_startup)
 323     args[argno++] = "-f";
 324   if (command)
 325     {
 326       args[argno++] = "-c";
 327       args[argno++] = command;
 328     }
 329   memcpy (args + argno, additional_args, n_additional_args * sizeof *args);
 330   args[argno + n_additional_args] = NULL;
 331   execv (shell, (char **) args);
 332
 333   {
 334     int exit_status = (errno == ENOENT ? EXIT_ENOENT : EXIT_CANNOT_INVOKE);
 335     error (0, errno, "%s", shell);
 336     exit (exit_status);
 337   }
 338 }
 339
 340 /* Return true if SHELL is a restricted shell (one not returned by
 341    getusershell), else false, meaning it is a standard shell.  */
 342
 343 static bool
 344 restricted_shell (const char *shell)
 345 {
 346   char *line;
 347
 348   setusershell ();
 349   while ((line = getusershell ()) != NULL)
 350     {
 351       if (*line != '#' && STREQ (line, shell))
 352         {
 353           endusershell ();
 354           return false;
 355         }
 356     }
 357   endusershell ();
 358   return true;
 359 }
 360
 361 void
 362 usage (int status)
 363 {
 364   if (status != EXIT_SUCCESS)
 365     fprintf (stderr, _("Try `%s --help' for more information.\n"),
 366              program_name);
 367   else
 368     {
 369       printf (_("Usage: %s [OPTION]... [-] [USER [ARG]...]\n"), program_name);
 370       fputs (_("\
 371 Change the effective user id and group id to that of USER.\n\
 372 \n\
 373   -, -l, --login               make the shell a login shell\n\
 374   -c, --command=COMMAND        pass a single COMMAND to the shell with -c\n\
 375   -f, --fast                   pass -f to the shell (for csh or tcsh)\n\
 376   -m, --preserve-environment   do not reset environment variables\n\
 377   -p                           same as -m\n\
 378   -s, --shell=SHELL            run SHELL if /etc/shells allows it\n\
 379 "), stdout);
 380       fputs (HELP_OPTION_DESCRIPTION, stdout);
 381       fputs (VERSION_OPTION_DESCRIPTION, stdout);
 382       fputs (_("\
 383 \n\
 384 A mere - implies -l.   If USER not given, assume root.\n\
 385 "), stdout);
 386       emit_ancillary_info ();
 387     }
 388   exit (status);
 389 }
 390
 391 int
 392 main (int argc, char **argv)
 393 {
 394   int optc;
 395   const char *new_user = DEFAULT_USER;
 396   char *command = NULL;
 397   char *shell = NULL;
 398   struct passwd *pw;
 399   struct passwd pw_copy;
 400
 401   initialize_main (&argc, &argv);
 402   set_program_name (argv[0]);
 403   setlocale (LC_ALL, "");
 404   bindtextdomain (PACKAGE, LOCALEDIR);
 405   textdomain (PACKAGE);
 406
 407   initialize_exit_failure (EXIT_CANCELED);
 408   atexit (close_stdout);
 409
 410   fast_startup = false;
 411   simulate_login = false;
 412   change_environment = true;
 413
 414   while ((optc = getopt_long (argc, argv, "c:flmps:", longopts, NULL)) != -1)
 415     {
 416       switch (optc)
 417         {
 418         case 'c':
 419           command = optarg;
 420           break;
 421
 422         case 'f':
 423           fast_startup = true;
 424           break;
 425
 426         case 'l':
 427           simulate_login = true;
 428           break;
 429
 430         case 'm':
 431         case 'p':
 432           change_environment = false;
 433           break;
 434
 435         case 's':
 436           shell = optarg;
 437           break;
 438
 439         case_GETOPT_HELP_CHAR;
 440
 441         case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
 442
 443         default:
 444           usage (EXIT_CANCELED);
 445         }
 446     }
 447
 448   if (optind < argc && STREQ (argv[optind], "-"))
 449     {
 450       simulate_login = true;
 451       ++optind;
 452     }
 453   if (optind < argc)
 454     new_user = argv[optind++];
 455
 456   pw = getpwnam (new_user);
 457   if (! (pw && pw->pw_name && pw->pw_name[0] && pw->pw_dir && pw->pw_dir[0]
 458          && pw->pw_passwd))
 459     error (EXIT_CANCELED, 0, _("user %s does not exist"), new_user);
 460
 461   /* Make a copy of the password information and point pw at the local
 462      copy instead.  Otherwise, some systems (e.g. GNU/Linux) would clobber
 463      the static data through the getlogin call from log_su.
 464      Also, make sure pw->pw_shell is a nonempty string.
 465      It may be NULL when NEW_USER is a username that is retrieved via NIS (YP),
 466      but that doesn't have a default shell listed.  */
 467   pw_copy = *pw;
 468   pw = &pw_copy;
 469   pw->pw_name = xstrdup (pw->pw_name);
 470   pw->pw_passwd = xstrdup (pw->pw_passwd);
 471   pw->pw_dir = xstrdup (pw->pw_dir);
 472   pw->pw_shell = xstrdup (pw->pw_shell && pw->pw_shell[0]
 473                           ? pw->pw_shell
 474                           : DEFAULT_SHELL);
 475   endpwent ();
 476
 477   if (!correct_password (pw))
 478     {
 479 #ifdef SYSLOG_FAILURE
 480       log_su (pw, false);
 481 #endif
 482       error (EXIT_CANCELED, 0, _("incorrect password"));
 483     }
 484 #ifdef SYSLOG_SUCCESS
 485   else
 486     {
 487       log_su (pw, true);
 488     }
 489 #endif
 490
 491   if (!shell && !change_environment)
 492     shell = getenv ("SHELL");
 493   if (shell && getuid () != 0 && restricted_shell (pw->pw_shell))
 494     {
 495       /* The user being su'd to has a nonstandard shell, and so is
 496          probably a uucp account or has restricted access.  Don't
 497          compromise the account by allowing access with a standard
 498          shell.  */
 499       error (0, 0, _("using restricted shell %s"), pw->pw_shell);
 500       shell = NULL;
 501     }
 502   shell = xstrdup (shell ? shell : pw->pw_shell);
 503   modify_environment (pw, shell);
 504
 505   change_identity (pw);
 506   if (simulate_login && chdir (pw->pw_dir) != 0)
 507     error (0, errno, _("warning: cannot change directory to %s"), pw->pw_dir);
 508
 509   /* error() flushes stderr, but does not check for write failure.
 510      Normally, we would catch this via our atexit() hook of
 511      close_stdout, but execv() gets in the way.  If stderr
 512      encountered a write failure, there is no need to try calling
 513      error() again.  */
 514   if (ferror (stderr))
 515     exit (EXIT_CANCELED);
 516
 517   run_shell (shell, command, argv + optind, MAX (0, argc - optind));
 518 }