src/su.c

   1 /* su for GNU.  Run a shell with substitute user and group IDs.
   2    Copyright (C) 1992-2002 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 2, or (at your option)
   7    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, write to the Free Software Foundation,
  16    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 /* Run a shell with the real and effective UID and GID and groups
  19    of USER, default `root'.
  20
  21    The shell run is taken from USER's password entry, /bin/sh if
  22    none is specified there.  If the account has a password, su
  23    prompts for a password unless run by a user with real UID 0.
  24
  25    Does not change the current directory.
  26    Sets `HOME' and `SHELL' from the password entry for USER, and if
  27    USER is not root, sets `USER' and `LOGNAME' to USER.
  28    The subshell is not a login shell.
  29
  30    If one or more ARGs are given, they are passed as additional
  31    arguments to the subshell.
  32
  33    Does not handle /bin/sh or other shells specially
  34    (setting argv[0] to "-su", passing -c only to certain shells, etc.).
  35    I don't see the point in doing that, and it's ugly.
  36
  37    This program intentionally does not support a "wheel group" that
  38    restricts who can su to UID 0 accounts.  RMS considers that to
  39    be fascist.
  40
  41    Options:
  42    -, -l, --login       Make the subshell a login shell.
  43                         Unset all environment variables except
  44                         TERM, HOME and SHELL (set as above), and USER
  45                         and LOGNAME (set unconditionally as above), and
  46                         set PATH to a default value.
  47                         Change to USER's home directory.
  48                         Prepend "-" to the shell's name.
  49    -c, --commmand=COMMAND
  50                         Pass COMMAND to the subshell with a -c option
  51                         instead of starting an interactive shell.
  52    -f, --fast           Pass the -f option to the subshell.
  53    -m, -p, --preserve-environment
  54                         Do not change HOME, USER, LOGNAME, SHELL.
  55                         Run $SHELL instead of USER's shell from /etc/passwd
  56                         unless not the superuser and USER's shell is
  57                         restricted.
  58                         Overridden by --login and --shell.
  59    -s, --shell=shell    Run SHELL instead of USER's shell from /etc/passwd
  60                         unless not the superuser and USER's shell is
  61                         restricted.
  62
  63    Compile-time options:
  64    -DSYSLOG_SUCCESS     Log successful su's (by default, to root) with syslog.
  65    -DSYSLOG_FAILURE     Log failed su's (by default, to root) with syslog.
  66
  67    -DSYSLOG_NON_ROOT    Log all su's, not just those to root (UID 0).
  68    Never logs attempted su's to nonexistent accounts.
  69
  70    Written by David MacKenzie <djm@gnu.ai.mit.edu>.  */
  71
  72 #include <config.h>
  73 #include <stdio.h>
  74 #include <getopt.h>
  75 #include <sys/types.h>
  76 #include <pwd.h>
  77 #include <grp.h>
  78
  79 /* Hide any system prototype for getusershell.
  80    This is necessary because some Cray systems have a conflicting
  81    prototype (returning `int') in <unistd.h>.  */
  82 #define getusershell _getusershell_sys_proto_
  83
  84 #include "system.h"
  85 #include "closeout.h"
  86 #include "dirname.h"
  87
  88 #undef getusershell
  89
  90 #if HAVE_SYSLOG_H && HAVE_SYSLOG
  91 # include <syslog.h>
  92 #else
  93 # undef SYSLOG_SUCCESS
  94 # undef SYSLOG_FAILURE
  95 # undef SYSLOG_NON_ROOT
  96 #endif
  97
  98 #if HAVE_SYS_PARAM_H
  99 # include <sys/param.h>
 100 #endif
 101
 102 #ifndef HAVE_ENDGRENT
 103 # define endgrent() ((void) 0)
 104 #endif
 105
 106 #ifndef HAVE_ENDPWENT
 107 # define endpwent() ((void) 0)
 108 #endif
 109
 110 #if HAVE_SHADOW_H
 111 # include <shadow.h>
 112 #endif
 113
 114 #include "error.h"
 115
 116 /* The official name of this program (e.g., no `g' prefix).  */
 117 #define PROGRAM_NAME "su"
 118
 119 #define AUTHORS "David MacKenzie"
 120
 121 #if HAVE_PATHS_H
 122 # include <paths.h>
 123 #endif
 124
 125 /* The default PATH for simulated logins to non-superuser accounts.  */
 126 #ifdef _PATH_DEFPATH
 127 # define DEFAULT_LOGIN_PATH _PATH_DEFPATH
 128 #else
 129 # define DEFAULT_LOGIN_PATH ":/usr/ucb:/bin:/usr/bin"
 130 #endif
 131
 132 /* The default PATH for simulated logins to superuser accounts.  */
 133 #ifdef _PATH_DEFPATH_ROOT
 134 # define DEFAULT_ROOT_LOGIN_PATH _PATH_DEFPATH_ROOT
 135 #else
 136 # define DEFAULT_ROOT_LOGIN_PATH "/usr/ucb:/bin:/usr/bin:/etc"
 137 #endif
 138
 139 /* The shell to run if none is given in the user's passwd entry.  */
 140 #define DEFAULT_SHELL "/bin/sh"
 141
 142 /* The user to become if none is specified.  */
 143 #define DEFAULT_USER "root"
 144
 145 char *crypt ();
 146 char *getpass ();
 147 char *getusershell ();
 148 void endusershell ();
 149 void setusershell ();
 150
 151 extern char **environ;
 152
 153 static void run_shell (const char *, const char *, char **)
 154      ATTRIBUTE_NORETURN;
 155
 156 /* The name this program was run with.  */
 157 char *program_name;
 158
 159 /* If nonzero, pass the `-f' option to the subshell.  */
 160 static int fast_startup;
 161
 162 /* If nonzero, simulate a login instead of just starting a shell.  */
 163 static int simulate_login;
 164
 165 /* If nonzero, change some environment vars to indicate the user su'd to.  */
 166 static int change_environment;
 167
 168 static struct option const longopts[] =
 169 {
 170   {"command", required_argument, 0, 'c'},
 171   {"fast", no_argument, NULL, 'f'},
 172   {"login", no_argument, NULL, 'l'},
 173   {"preserve-environment", no_argument, &change_environment, 0},
 174   {"shell", required_argument, 0, 's'},
 175   {GETOPT_HELP_OPTION_DECL},
 176   {GETOPT_VERSION_OPTION_DECL},
 177   {0, 0, 0, 0}
 178 };
 179
 180 /* Add VAL to the environment, checking for out of memory errors.  */
 181
 182 static void
 183 xputenv (char *val)
 184 {
 185   if (putenv (val))
 186     xalloc_die ();
 187 }
 188
 189 /* Return a newly-allocated string whose contents concatenate
 190    those of S1, S2, S3.  */
 191
 192 static char *
 193 concat (const char *s1, const char *s2, const char *s3)
 194 {
 195   int len1 = strlen (s1), len2 = strlen (s2), len3 = strlen (s3);
 196   char *result = (char *) xmalloc (len1 + len2 + len3 + 1);
 197
 198   strcpy (result, s1);
 199   strcpy (result + len1, s2);
 200   strcpy (result + len1 + len2, s3);
 201   result[len1 + len2 + len3] = 0;
 202
 203   return result;
 204 }
 205
 206 /* Return the number of elements in ARR, a null-terminated array.  */
 207
 208 static int
 209 elements (char **arr)
 210 {
 211   int n = 0;
 212
 213   for (n = 0; *arr; ++arr)
 214     ++n;
 215   return n;
 216 }
 217
 218 #if defined (SYSLOG_SUCCESS) || defined (SYSLOG_FAILURE)
 219 /* Log the fact that someone has run su to the user given by PW;
 220    if SUCCESSFUL is nonzero, they gave the correct password, etc.  */
 221
 222 static void
 223 log_su (const struct passwd *pw, int successful)
 224 {
 225   const char *new_user, *old_user, *tty;
 226
 227 # ifndef SYSLOG_NON_ROOT
 228   if (pw->pw_uid)
 229     return;
 230 # endif
 231   new_user = pw->pw_name;
 232   /* The utmp entry (via getlogin) is probably the best way to identify
 233      the user, especially if someone su's from a su-shell.  */
 234   old_user = getlogin ();
 235   if (old_user == NULL)
 236     {
 237       /* getlogin can fail -- usually due to lack of utmp entry.
 238          Resort to getpwuid.  */
 239       struct passwd *pwd = getpwuid (getuid ());
 240       old_user = (pwd ? pwd->pw_name : "");
 241     }
 242   tty = ttyname (2);
 243   if (tty == NULL)
 244     tty = "none";
 245   /* 4.2BSD openlog doesn't have the third parameter.  */
 246   openlog (base_name (program_name), 0
 247 # ifdef LOG_AUTH
 248            , LOG_AUTH
 249 # endif
 250            );
 251   syslog (LOG_NOTICE,
 252 # ifdef SYSLOG_NON_ROOT
 253           "%s(to %s) %s on %s",
 254 # else
 255           "%s%s on %s",
 256 # endif
 257           successful ? "" : "FAILED SU ",
 258 # ifdef SYSLOG_NON_ROOT
 259           new_user,
 260 # endif
 261           old_user, tty);
 262   closelog ();
 263 }
 264 #endif
 265
 266 /* Ask the user for a password.
 267    Return 1 if the user gives the correct password for entry PW,
 268    0 if not.  Return 1 without asking for a password if run by UID 0
 269    or if PW has an empty password.  */
 270
 271 static int
 272 correct_password (const struct passwd *pw)
 273 {
 274   char *unencrypted, *encrypted, *correct;
 275 #if HAVE_GETSPNAM && HAVE_STRUCT_SPWD_SP_PWDP
 276   /* Shadow passwd stuff for SVR3 and maybe other systems.  */
 277   struct spwd *sp = getspnam (pw->pw_name);
 278
 279   endspent ();
 280   if (sp)
 281     correct = sp->sp_pwdp;
 282   else
 283 #endif
 284     correct = pw->pw_passwd;
 285
 286   if (getuid () == 0 || correct == 0 || correct[0] == '\0')
 287     return 1;
 288
 289   unencrypted = getpass (_("Password:"));
 290   if (unencrypted == NULL)
 291     {
 292       error (0, 0, _("getpass: cannot open /dev/tty"));
 293       return 0;
 294     }
 295   encrypted = crypt (unencrypted, correct);
 296   memset (unencrypted, 0, strlen (unencrypted));
 297   return strcmp (encrypted, correct) == 0;
 298 }
 299
 300 /* Update `environ' for the new shell based on PW, with SHELL being
 301    the value for the SHELL environment variable.  */
 302
 303 static void
 304 modify_environment (const struct passwd *pw, const char *shell)
 305 {
 306   char *term;
 307
 308   if (simulate_login)
 309     {
 310       /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
 311          Unset all other environment variables.  */
 312       term = getenv ("TERM");
 313       environ = (char **) xmalloc (2 * sizeof (char *));
 314       environ[0] = 0;
 315       if (term)
 316         xputenv (concat ("TERM", "=", term));
 317       xputenv (concat ("HOME", "=", pw->pw_dir));
 318       xputenv (concat ("SHELL", "=", shell));
 319       xputenv (concat ("USER", "=", pw->pw_name));
 320       xputenv (concat ("LOGNAME", "=", pw->pw_name));
 321       xputenv (concat ("PATH", "=", (pw->pw_uid
 322                                      ? DEFAULT_LOGIN_PATH
 323                                      : DEFAULT_ROOT_LOGIN_PATH)));
 324     }
 325   else
 326     {
 327       /* Set HOME, SHELL, and if not becoming a super-user,
 328          USER and LOGNAME.  */
 329       if (change_environment)
 330         {
 331           xputenv (concat ("HOME", "=", pw->pw_dir));
 332           xputenv (concat ("SHELL", "=", shell));
 333           if (pw->pw_uid)
 334             {
 335               xputenv (concat ("USER", "=", pw->pw_name));
 336               xputenv (concat ("LOGNAME", "=", pw->pw_name));
 337             }
 338         }
 339     }
 340 }
 341
 342 /* Become the user and group(s) specified by PW.  */
 343
 344 static void
 345 change_identity (const struct passwd *pw)
 346 {
 347 #ifdef HAVE_INITGROUPS
 348   errno = 0;
 349   if (initgroups (pw->pw_name, pw->pw_gid) == -1)
 350     error (EXIT_FAILURE, errno, _("cannot set groups"));
 351   endgrent ();
 352 #endif
 353   if (setgid (pw->pw_gid))
 354     error (EXIT_FAILURE, errno, _("cannot set group id"));
 355   if (setuid (pw->pw_uid))
 356     error (EXIT_FAILURE, errno, _("cannot set user id"));
 357 }
 358
 359 /* Run SHELL, or DEFAULT_SHELL if SHELL is empty.
 360    If COMMAND is nonzero, pass it to the shell with the -c option.
 361    If ADDITIONAL_ARGS is nonzero, pass it to the shell as more
 362    arguments.  */
 363
 364 static void
 365 run_shell (const char *shell, const char *command, char **additional_args)
 366 {
 367   const char **args;
 368   int argno = 1;
 369
 370   if (additional_args)
 371     args = (const char **) xmalloc (sizeof (char *)
 372                                     * (10 + elements (additional_args)));
 373   else
 374     args = (const char **) xmalloc (sizeof (char *) * 10);
 375   if (simulate_login)
 376     {
 377       char *arg0;
 378       char *shell_basename;
 379
 380       shell_basename = base_name (shell);
 381       arg0 = xmalloc (strlen (shell_basename) + 2);
 382       arg0[0] = '-';
 383       strcpy (arg0 + 1, shell_basename);
 384       args[0] = arg0;
 385     }
 386   else
 387     args[0] = base_name (shell);
 388   if (fast_startup)
 389     args[argno++] = "-f";
 390   if (command)
 391     {
 392       args[argno++] = "-c";
 393       args[argno++] = command;
 394     }
 395   if (additional_args)
 396     for (; *additional_args; ++additional_args)
 397       args[argno++] = *additional_args;
 398   args[argno] = NULL;
 399   execv (shell, (char **) args);
 400
 401   {
 402     int exit_status = (errno == ENOENT ? 127 : 126);
 403     error (0, errno, "%s", shell);
 404     exit (exit_status);
 405   }
 406 }
 407
 408 /* Return 1 if SHELL is a restricted shell (one not returned by
 409    getusershell), else 0, meaning it is a standard shell.  */
 410
 411 static int
 412 restricted_shell (const char *shell)
 413 {
 414   char *line;
 415
 416   setusershell ();
 417   while ((line = getusershell ()) != NULL)
 418     {
 419       if (*line != '#' && strcmp (line, shell) == 0)
 420         {
 421           endusershell ();
 422           return 0;
 423         }
 424     }
 425   endusershell ();
 426   return 1;
 427 }
 428
 429 void
 430 usage (int status)
 431 {
 432   if (status != 0)
 433     fprintf (stderr, _("Try `%s --help' for more information.\n"),
 434              program_name);
 435   else
 436     {
 437       printf (_("Usage: %s [OPTION]... [-] [USER [ARG]...]\n"), program_name);
 438       fputs (_("\
 439 Change the effective user id and group id to that of USER.\n\
 440 \n\
 441   -, -l, --login               make the shell a login shell\n\
 442   -c, --commmand=COMMAND       pass a single COMMAND to the shell with -c\n\
 443   -f, --fast                   pass -f to the shell (for csh or tcsh)\n\
 444   -m, --preserve-environment   do not reset environment variables\n\
 445   -p                           same as -m\n\
 446   -s, --shell=SHELL            run SHELL if /etc/shells allows it\n\
 447 "), stdout);
 448       fputs (HELP_OPTION_DESCRIPTION, stdout);
 449       fputs (VERSION_OPTION_DESCRIPTION, stdout);
 450       fputs (_("\
 451 \n\
 452 A mere - implies -l.   If USER not given, assume root.\n\
 453 "), stdout);
 454       printf (_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
 455       close_stdout ();
 456     }
 457   exit (status);
 458 }
 459
 460 int
 461 main (int argc, char **argv)
 462 {
 463   int optc;
 464   const char *new_user = DEFAULT_USER;
 465   char *command = 0;
 466   char **additional_args = 0;
 467   char *shell = 0;
 468   struct passwd *pw;
 469   struct passwd pw_copy;
 470
 471   program_name = argv[0];
 472   setlocale (LC_ALL, "");
 473   bindtextdomain (PACKAGE, LOCALEDIR);
 474   textdomain (PACKAGE);
 475
 476   fast_startup = 0;
 477   simulate_login = 0;
 478   change_environment = 1;
 479
 480   while ((optc = getopt_long (argc, argv, "c:flmps:", longopts, NULL)) != -1)
 481     {
 482       switch (optc)
 483         {
 484         case 0:
 485           break;
 486
 487         case 'c':
 488           command = optarg;
 489           break;
 490
 491         case 'f':
 492           fast_startup = 1;
 493           break;
 494
 495         case 'l':
 496           simulate_login = 1;
 497           break;
 498
 499         case 'm':
 500         case 'p':
 501           change_environment = 0;
 502           break;
 503
 504         case 's':
 505           shell = optarg;
 506           break;
 507
 508         case_GETOPT_HELP_CHAR;
 509
 510         case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
 511
 512         default:
 513           usage (EXIT_FAILURE);
 514         }
 515     }
 516
 517   if (optind < argc && !strcmp (argv[optind], "-"))
 518     {
 519       simulate_login = 1;
 520       ++optind;
 521     }
 522   if (optind < argc)
 523     new_user = argv[optind++];
 524   if (optind < argc)
 525     additional_args = argv + optind;
 526
 527   pw = getpwnam (new_user);
 528   if (pw == 0)
 529     error (EXIT_FAILURE, 0, _("user %s does not exist"), new_user);
 530   endpwent ();
 531
 532   /* Make sure pw->pw_shell is non-NULL.  It may be NULL when NEW_USER
 533      is a username that is retrieved via NIS (YP), but that doesn't have
 534      a default shell listed.  */
 535   if (pw->pw_shell == NULL || pw->pw_shell[0] == '\0')
 536     pw->pw_shell = (char *) DEFAULT_SHELL;
 537
 538   /* Make a copy of the password information and point pw at the local
 539      copy instead.  Otherwise, some systems (e.g. Linux) would clobber
 540      the static data through the getlogin call from log_su.  */
 541   pw_copy = *pw;
 542   pw = &pw_copy;
 543   pw->pw_name = xstrdup (pw->pw_name);
 544   pw->pw_dir = xstrdup (pw->pw_dir);
 545   pw->pw_shell = xstrdup (pw->pw_shell);
 546
 547   if (!correct_password (pw))
 548     {
 549 #ifdef SYSLOG_FAILURE
 550       log_su (pw, 0);
 551 #endif
 552       error (EXIT_FAILURE, 0, _("incorrect password"));
 553     }
 554 #ifdef SYSLOG_SUCCESS
 555   else
 556     {
 557       log_su (pw, 1);
 558     }
 559 #endif
 560
 561   if (shell == 0 && change_environment == 0)
 562     shell = getenv ("SHELL");
 563   if (shell != 0 && getuid () && restricted_shell (pw->pw_shell))
 564     {
 565       /* The user being su'd to has a nonstandard shell, and so is
 566          probably a uucp account or has restricted access.  Don't
 567          compromise the account by allowing access with a standard
 568          shell.  */
 569       error (0, 0, _("using restricted shell %s"), pw->pw_shell);
 570       shell = 0;
 571     }
 572   if (shell == 0)
 573     {
 574       shell = xstrdup (pw->pw_shell);
 575     }
 576   modify_environment (pw, shell);
 577
 578   change_identity (pw);
 579   if (simulate_login && chdir (pw->pw_dir))
 580     error (0, errno, _("warning: cannot change directory to %s"), pw->pw_dir);
 581
 582   run_shell (shell, command, additional_args);
 583 }