login-utils/su.c

   1 /* su for GNU.  Run a shell with substitute user and group IDs.
   2    Copyright (C) 92, 93, 94, 95, 96, 1997 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 #include "system.h"
  79
  80 #if defined(HAVE_SYSLOG_H) && defined(HAVE_SYSLOG)
  81 #include <syslog.h>
  82 #else /* !HAVE_SYSLOG_H */
  83 #ifdef SYSLOG_SUCCESS
  84 #undef SYSLOG_SUCCESS
  85 #endif
  86 #ifdef SYSLOG_FAILURE
  87 #undef SYSLOG_FAILURE
  88 #endif
  89 #ifdef SYSLOG_NON_ROOT
  90 #undef SYSLOG_NON_ROOT
  91 #endif
  92 #endif /* !HAVE_SYSLOG_H */
  93
  94 #ifdef _POSIX_VERSION
  95 #include <limits.h>
  96 #else /* not _POSIX_VERSION */
  97 struct passwd *getpwuid ();
  98 struct group *getgrgid ();
  99 uid_t getuid ();
 100 #include <sys/param.h>
 101 #endif /* not _POSIX_VERSION */
 102
 103 #ifndef HAVE_ENDGRENT
 104 # define endgrent() ((void) 0)
 105 #endif
 106
 107 #ifndef HAVE_ENDPWENT
 108 # define endpwent() ((void) 0)
 109 #endif
 110
 111 #ifdef HAVE_SHADOW_H
 112 #include <shadow.h>
 113 #endif
 114
 115 #include "error.h"
 116
 117 #ifdef HAVE_PATHS_H
 118 #include <paths.h>
 119 #endif
 120
 121 /* The default PATH for simulated logins to non-superuser accounts.  */
 122 #ifdef _PATH_DEFPATH
 123 #define DEFAULT_LOGIN_PATH _PATH_DEFPATH
 124 #else
 125 #define DEFAULT_LOGIN_PATH ":/usr/ucb:/bin:/usr/bin"
 126 #endif
 127
 128 /* The default PATH for simulated logins to superuser accounts.  */
 129 #ifdef _PATH_DEFPATH_ROOT
 130 #define DEFAULT_ROOT_LOGIN_PATH _PATH_DEFPATH_ROOT
 131 #else
 132 #define DEFAULT_ROOT_LOGIN_PATH "/usr/ucb:/bin:/usr/bin:/etc"
 133 #endif
 134
 135 /* The shell to run if none is given in the user's passwd entry.  */
 136 #define DEFAULT_SHELL "/bin/sh"
 137
 138 /* The user to become if none is specified.  */
 139 #define DEFAULT_USER "root"
 140
 141 char *crypt ();
 142 char *getpass ();
 143 char *getusershell ();
 144 void endusershell ();
 145 void setusershell ();
 146
 147 char *basename ();
 148 char *xmalloc ();
 149 char *xrealloc ();
 150 char *xstrdup ();
 151
 152 extern char **environ;
 153
 154 /* The name this program was run with.  */
 155 char *program_name;
 156
 157 /* If nonzero, display usage information and exit.  */
 158 static int show_help;
 159
 160 /* If nonzero, print the version on standard output and exit.  */
 161 static int show_version;
 162
 163 /* If nonzero, pass the `-f' option to the subshell.  */
 164 static int fast_startup;
 165
 166 /* If nonzero, simulate a login instead of just starting a shell.  */
 167 static int simulate_login;
 168
 169 /* If nonzero, change some environment vars to indicate the user su'd to.  */
 170 static int change_environment;
 171
 172 static struct option const longopts[] =
 173 {
 174   {"command", required_argument, 0, 'c'},
 175   {"fast", no_argument, &fast_startup, 1},
 176   {"help", no_argument, &show_help, 1},
 177   {"login", no_argument, &simulate_login, 1},
 178   {"preserve-environment", no_argument, &change_environment, 0},
 179   {"shell", required_argument, 0, 's'},
 180   {"version", no_argument, &show_version, 1},
 181   {0, 0, 0, 0}
 182 };
 183
 184 /* Add VAL to the environment, checking for out of memory errors.  */
 185
 186 static void
 187 xputenv (const char *val)
 188 {
 189   if (putenv (val))
 190     error (1, 0, _("virtual memory exhausted"));
 191 }
 192
 193 /* Return a newly-allocated string whose contents concatenate
 194    those of S1, S2, S3.  */
 195
 196 static char *
 197 concat (const char *s1, const char *s2, const char *s3)
 198 {
 199   int len1 = strlen (s1), len2 = strlen (s2), len3 = strlen (s3);
 200   char *result = (char *) xmalloc (len1 + len2 + len3 + 1);
 201
 202   strcpy (result, s1);
 203   strcpy (result + len1, s2);
 204   strcpy (result + len1 + len2, s3);
 205   result[len1 + len2 + len3] = 0;
 206
 207   return result;
 208 }
 209
 210 /* Return the number of elements in ARR, a null-terminated array.  */
 211
 212 static int
 213 elements (char **arr)
 214 {
 215   int n = 0;
 216
 217   for (n = 0; *arr; ++arr)
 218     ++n;
 219   return n;
 220 }
 221
 222 #if defined (SYSLOG_SUCCESS) || defined (SYSLOG_FAILURE)
 223 /* Log the fact that someone has run su to the user given by PW;
 224    if SUCCESSFUL is nonzero, they gave the correct password, etc.  */
 225
 226 static void
 227 log_su (const struct passwd *pw, int successful)
 228 {
 229   const char *new_user, *old_user, *tty;
 230
 231 #ifndef SYSLOG_NON_ROOT
 232   if (pw->pw_uid)
 233     return;
 234 #endif
 235   new_user = pw->pw_name;
 236   /* The utmp entry (via getlogin) is probably the best way to identify
 237      the user, especially if someone su's from a su-shell.  */
 238   old_user = getlogin ();
 239   if (old_user == NULL)
 240     {
 241       /* getlogin can fail -- usually due to lack of utmp entry.
 242          Resort to getpwuid.  */
 243       struct passwd *pwd = getpwuid (getuid ());
 244       old_user = (pwd ? pwd->pw_name : "");
 245     }
 246   tty = ttyname (2);
 247   if (tty == NULL)
 248     tty = "none";
 249   /* 4.2BSD openlog doesn't have the third parameter.  */
 250   openlog (basename (program_name), 0
 251 #ifdef LOG_AUTH
 252            , LOG_AUTH
 253 #endif
 254            );
 255   syslog (LOG_NOTICE,
 256 #ifdef SYSLOG_NON_ROOT
 257           "%s(to %s) %s on %s",
 258 #else
 259           "%s%s on %s",
 260 #endif
 261           successful ? "" : "FAILED SU ",
 262 #ifdef SYSLOG_NON_ROOT
 263           new_user,
 264 #endif
 265           old_user, tty);
 266   closelog ();
 267 }
 268 #endif
 269
 270 /* Ask the user for a password.
 271    Return 1 if the user gives the correct password for entry PW,
 272    0 if not.  Return 1 without asking for a password if run by UID 0
 273    or if PW has an empty password.  */
 274
 275 static int
 276 correct_password (const struct passwd *pw)
 277 {
 278   char *unencrypted, *encrypted, *correct;
 279 #ifdef HAVE_SHADOW_H
 280   /* Shadow passwd stuff for SVR3 and maybe other systems.  */
 281   struct spwd *sp = getspnam (pw->pw_name);
 282
 283   endspent ();
 284   if (sp)
 285     correct = sp->sp_pwdp;
 286   else
 287 #endif
 288   correct = pw->pw_passwd;
 289
 290   if (getuid () == 0 || correct == 0 || correct[0] == '\0')
 291     return 1;
 292
 293   unencrypted = getpass (_("Password:"));
 294   if (unencrypted == NULL)
 295     {
 296       error (0, 0, _("getpass: cannot open /dev/tty"));
 297       return 0;
 298     }
 299   encrypted = crypt (unencrypted, correct);
 300   memset (unencrypted, 0, strlen (unencrypted));
 301   return strcmp (encrypted, correct) == 0;
 302 }
 303
 304 /* Update `environ' for the new shell based on PW, with SHELL being
 305    the value for the SHELL environment variable.  */
 306
 307 static void
 308 modify_environment (const struct passwd *pw, const char *shell)
 309 {
 310   char *term;
 311
 312   if (simulate_login)
 313     {
 314       /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
 315          Unset all other environment variables.  */
 316       term = getenv ("TERM");
 317       environ = (char **) xmalloc (2 * sizeof (char *));
 318       environ[0] = 0;
 319       if (term)
 320         xputenv (concat ("TERM", "=", term));
 321       xputenv (concat ("HOME", "=", pw->pw_dir));
 322       xputenv (concat ("SHELL", "=", shell));
 323       xputenv (concat ("USER", "=", pw->pw_name));
 324       xputenv (concat ("LOGNAME", "=", pw->pw_name));
 325       xputenv (concat ("PATH", "=", (pw->pw_uid
 326                                      ? DEFAULT_LOGIN_PATH
 327                                      : DEFAULT_ROOT_LOGIN_PATH)));
 328     }
 329   else
 330     {
 331       /* Set HOME, SHELL, and if not becoming a super-user,
 332          USER and LOGNAME.  */
 333       if (change_environment)
 334         {
 335           xputenv (concat ("HOME", "=", pw->pw_dir));
 336           xputenv (concat ("SHELL", "=", shell));
 337           if (pw->pw_uid)
 338             {
 339               xputenv (concat ("USER", "=", pw->pw_name));
 340               xputenv (concat ("LOGNAME", "=", pw->pw_name));
 341             }
 342         }
 343     }
 344 }
 345
 346 /* Become the user and group(s) specified by PW.  */
 347
 348 static void
 349 change_identity (const struct passwd *pw)
 350 {
 351 #ifdef HAVE_INITGROUPS
 352   errno = 0;
 353   if (initgroups (pw->pw_name, pw->pw_gid) == -1)
 354     error (1, errno, _("cannot set groups"));
 355   endgrent ();
 356 #endif
 357   if (setgid (pw->pw_gid))
 358     error (1, errno, _("cannot set group id"));
 359   if (setuid (pw->pw_uid))
 360     error (1, errno, _("cannot set user id"));
 361 }
 362
 363 /* Run SHELL, or DEFAULT_SHELL if SHELL is empty.
 364    If COMMAND is nonzero, pass it to the shell with the -c option.
 365    If ADDITIONAL_ARGS is nonzero, pass it to the shell as more
 366    arguments.  */
 367
 368 static void
 369 run_shell (const char *shell, const char *command, char **additional_args)
 370 {
 371   const char **args;
 372   int argno = 1;
 373
 374   if (additional_args)
 375     args = (const char **) xmalloc (sizeof (char *)
 376                                     * (10 + elements (additional_args)));
 377   else
 378     args = (const char **) xmalloc (sizeof (char *) * 10);
 379   if (simulate_login)
 380     {
 381       char *arg0;
 382       char *shell_basename;
 383
 384       shell_basename = basename (shell);
 385       arg0 = xmalloc (strlen (shell_basename) + 2);
 386       arg0[0] = '-';
 387       strcpy (arg0 + 1, shell_basename);
 388       args[0] = arg0;
 389     }
 390   else
 391     args[0] = basename (shell);
 392   if (fast_startup)
 393     args[argno++] = "-f";
 394   if (command)
 395     {
 396       args[argno++] = "-c";
 397       args[argno++] = command;
 398     }
 399   if (additional_args)
 400     for (; *additional_args; ++additional_args)
 401       args[argno++] = *additional_args;
 402   args[argno] = NULL;
 403   execv (shell, (char **) args);
 404   error (1, errno, _("cannot run %s"), shell);
 405 }
 406
 407 /* Return 1 if SHELL is a restricted shell (one not returned by
 408    getusershell), else 0, meaning it is a standard shell.  */
 409
 410 static int
 411 restricted_shell (const char *shell)
 412 {
 413   char *line;
 414
 415   setusershell ();
 416   while ((line = getusershell ()) != NULL)
 417     {
 418       if (*line != '#' && strcmp (line, shell) == 0)
 419         {
 420           endusershell ();
 421           return 0;
 422         }
 423     }
 424   endusershell ();
 425   return 1;
 426 }
 427
 428 static void
 429 usage (int status)
 430 {
 431   if (status != 0)
 432     fprintf (stderr, _("Try `%s --help' for more information.\n"),
 433              program_name);
 434   else
 435     {
 436       printf (_("Usage: %s [OPTION]... [-] [USER [ARG]...]\n"), program_name);
 437       printf (_("\
 438 Change the effective user id and group id to that of USER.\n\
 439 \n\
 440   -, -l, --login               make the shell a login shell\n\
 441   -c, --commmand=COMMAND       pass a single COMMAND to the shell with -c\n\
 442   -f, --fast                   pass -f to the shell (for csh or tcsh)\n\
 443   -m, --preserve-environment   do not reset environment variables\n\
 444   -p                           same as -m\n\
 445   -s, --shell=SHELL            run SHELL if /etc/shells allows it\n\
 446       --help                   display this help and exit\n\
 447       --version                output version information and exit\n\
 448 \n\
 449 A mere - implies -l.   If USER not given, assume root.\n\
 450 "));
 451       puts (_("\nReport bugs to <sh-utils-bugs@gnu.ai.mit.edu>."));
 452     }
 453   exit (status);
 454 }
 455
 456 int
 457 main (int argc, char **argv)
 458 {
 459   int optc;
 460   const char *new_user = DEFAULT_USER;
 461   char *command = 0;
 462   char **additional_args = 0;
 463   char *shell = 0;
 464   struct passwd *pw;
 465   struct passwd pw_copy;
 466
 467   program_name = argv[0];
 468   setlocale (LC_ALL, "");
 469   bindtextdomain (PACKAGE, LOCALEDIR);
 470   textdomain (PACKAGE);
 471
 472   fast_startup = 0;
 473   simulate_login = 0;
 474   change_environment = 1;
 475
 476   while ((optc = getopt_long (argc, argv, "c:flmps:", longopts, NULL)) != -1)
 477     {
 478       switch (optc)
 479         {
 480         case 0:
 481           break;
 482
 483         case 'c':
 484           command = optarg;
 485           break;
 486
 487         case 'f':
 488           fast_startup = 1;
 489           break;
 490
 491         case 'l':
 492           simulate_login = 1;
 493           break;
 494
 495         case 'm':
 496         case 'p':
 497           change_environment = 0;
 498           break;
 499
 500         case 's':
 501           shell = optarg;
 502           break;
 503
 504         default:
 505           usage (1);
 506         }
 507     }
 508
 509   if (show_version)
 510     {
 511       printf ("su (%s) %s\n", GNU_PACKAGE, VERSION);
 512       exit (0);
 513     }
 514
 515   if (show_help)
 516     usage (0);
 517
 518   if (optind < argc && !strcmp (argv[optind], "-"))
 519     {
 520       simulate_login = 1;
 521       ++optind;
 522     }
 523   if (optind < argc)
 524     new_user = argv[optind++];
 525   if (optind < argc)
 526     additional_args = argv + optind;
 527
 528   pw = getpwnam (new_user);
 529   if (pw == 0)
 530     error (1, 0, _("user %s does not exist"), new_user);
 531   endpwent ();
 532
 533   /* Make a copy of the password information and point pw at the local
 534      copy instead.  Otherwise, some systems (e.g. Linux) would clobber
 535      the static data through the getlogin call from log_su.  */
 536   pw_copy = *pw;
 537   pw = &pw_copy;
 538   pw->pw_name = xstrdup (pw->pw_name);
 539   pw->pw_dir = xstrdup (pw->pw_dir);
 540   pw->pw_shell = xstrdup (pw->pw_shell);
 541
 542   if (!correct_password (pw))
 543     {
 544 #ifdef SYSLOG_FAILURE
 545       log_su (pw, 0);
 546 #endif
 547       error (1, 0, _("incorrect password"));
 548     }
 549 #ifdef SYSLOG_SUCCESS
 550   else
 551     {
 552       log_su (pw, 1);
 553     }
 554 #endif
 555
 556   if (pw->pw_shell == 0 || pw->pw_shell[0] == 0)
 557     pw->pw_shell = (char *) DEFAULT_SHELL;
 558   if (shell == 0 && change_environment == 0)
 559     shell = getenv ("SHELL");
 560   if (shell != 0 && getuid () && restricted_shell (pw->pw_shell))
 561     {
 562       /* The user being su'd to has a nonstandard shell, and so is
 563          probably a uucp account or has restricted access.  Don't
 564          compromise the account by allowing access with a standard
 565          shell.  */
 566       error (0, 0, _("using restricted shell %s"), pw->pw_shell);
 567       shell = 0;
 568     }
 569   if (shell == 0)
 570     {
 571       shell = xstrdup (pw->pw_shell);
 572     }
 573   modify_environment (pw, shell);
 574
 575   change_identity (pw);
 576   if (simulate_login && chdir (pw->pw_dir))
 577     error (0, errno, _("warning: cannot change directory to %s"), pw->pw_dir);
 578
 579   run_shell (shell, command, additional_args);
 580 }