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chsh.c

/*
 * Copyright 1989 - 1994, Julianne Frances Haugh
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of Julianne F. Haugh nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY JULIE HAUGH AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL JULIE HAUGH OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <config.h>

#include "rcsid.h"
RCSID (PKG_VER "$Id: chsh.c 6 2005-03-20 15:34:28Z bubulle $")
#include <sys/types.h>
#include <stdio.h>
#include <fcntl.h>
#include <signal.h>
#include "prototypes.h"
#include "defines.h"
#include <pwd.h>
#include "pwio.h"
#include "getdef.h"
#include "pwauth.h"
#ifdef HAVE_SHADOW_H
#include <shadow.h>
#endif
#ifdef USE_PAM
#include "pam_defs.h"
#endif
#ifndef SHELLS_FILE
#define SHELLS_FILE "/etc/shells"
#endif
/* global variables */
static char *Prog;            /* Program name */
static int amroot;            /* Real UID is root */
static char loginsh[BUFSIZ];  /* Name of new login shell */

/* external identifiers */

#ifdef      NDBM
extern int pw_dbm_mode;
#endif

/* local function prototypes */
static void usage (void);
static void new_fields (void);
static int restricted_shell (const char *);

/*
 * usage - print command line syntax and exit
 */

static void usage (void)
{
      fprintf (stderr, _("Usage: %s [-s shell] [name]\n"), Prog);
      exit (1);
}

/*
 * new_fields - change the user's login shell information interactively
 *
 * prompt the user for the login shell and change it according to the
 * response, or leave it alone if nothing was entered.
 */

static void new_fields (void)
{
      printf (_
            ("Enter the new value, or press return for the default\n"));
      change_field (loginsh, sizeof loginsh, _("Login Shell"));
}

/*
 * restricted_shell - return true if the named shell begins with 'r' or 'R'
 *
 * If the first letter of the filename is 'r' or 'R', the shell is
 * considered to be restricted.
 */

static int restricted_shell (const char *sh)
{
#if 0
      char *cp = Basename ((char *) sh);

      return *cp == 'r' || *cp == 'R';
#else
      /*
       * Shells not listed in /etc/shells are considered to be restricted.
       * Changed this to avoid confusion with "rc" (the plan9 shell - not
       * restricted despite the name starting with 'r').  --marekm
       */
      return !check_shell (sh);
#endif
}


/*
 * chsh - this command controls changes to the user's shell
 *
 *    The only supported option is -s which permits the the login shell to
 *    be set from the command line.
 */

int main (int argc, char **argv)
{
      char *user;       /* User name                         */
      int flag;         /* Current command line flag         */
      int sflg = 0;           /* -s - set shell from command line  */
      const struct passwd *pw;      /* Password entry from /etc/passwd   */
      struct passwd pwent;    /* New password entry                */

      sanitize_env ();

      setlocale (LC_ALL, "");
      bindtextdomain (PACKAGE, LOCALEDIR);
      textdomain (PACKAGE);

      /*
       * This command behaves different for root and non-root users.
       */

      amroot = getuid () == 0;
#ifdef      NDBM
      pw_dbm_mode = O_RDWR;
#endif

      /*
       * Get the program name. The program name is used as a prefix to
       * most error messages.
       */

      Prog = Basename (argv[0]);

      OPENLOG ("chsh");

      /*
       * There is only one option, but use getopt() anyway to
       * keep things consistent.
       */

      while ((flag = getopt (argc, argv, "s:")) != EOF) {
            switch (flag) {
            case 's':
                  sflg++;
                  STRFCPY (loginsh, optarg);
                  break;
            default:
                  usage ();
            }
      }

      /*
       * There should be only one remaining argument at most and it should
       * be the user's name.
       */

      if (argc > optind + 1)
            usage ();

      /*
       * Get the name of the user to check. It is either the command line
       * name, or the name getlogin() returns.
       */

      if (optind < argc) {
            user = argv[optind];
            pw = getpwnam (user);
            if (!pw) {
                  fprintf (stderr,
                         _("%s: Unknown user %s\n"), Prog, user);
                  exit (1);
            }
      } else {
            pw = get_my_pwent ();
            if (!pw) {
                  fprintf (stderr,
                         _
                         ("%s: Cannot determine your user name.\n"),
                         Prog);
                  exit (1);
            }
            user = xstrdup (pw->pw_name);
      }

#ifdef      USE_NIS
      /*
       * Now we make sure this is a LOCAL password entry for this user ...
       */

      if (__ispwNIS ()) {
            char *nis_domain;
            char *nis_master;

            fprintf (stderr,
                   _("%s: cannot change user `%s' on NIS client.\n"),
                   Prog, user);

            if (!yp_get_default_domain (&nis_domain) &&
                !yp_master (nis_domain, "passwd.byname",
                        &nis_master)) {
                  fprintf (stderr,
                         _
                         ("%s: `%s' is the NIS master for this client.\n"),
                         Prog, nis_master);
            }
            exit (1);
      }
#endif

      /*
       * Non-privileged users are only allowed to change the shell if the
       * UID of the user matches the current real UID.
       */

      if (!amroot && pw->pw_uid != getuid ()) {
            SYSLOG ((LOG_WARN, "can't change shell for `%s'", user));
            closelog ();
            fprintf (stderr,
                   _("You may not change the shell for %s.\n"),
                   user);
            exit (1);
      }

      /*
       * Non-privileged users are only allowed to change the shell if it
       * is not a restricted one.
       */

      if (!amroot && restricted_shell (pw->pw_shell)) {
            SYSLOG ((LOG_WARN, "can't change shell for `%s'", user));
            closelog ();
            fprintf (stderr,
                   _("You may not change the shell for %s.\n"),
                   user);
            exit (1);
      }

      /*
         * Non-privileged users are optionally authenticated (must enter
         * the password of the user whose information is being changed)
         * before any changes can be made. Idea from util-linux
         * chfn/chsh.  --marekm
       */

      if (!amroot && getdef_bool ("CHFN_AUTH"))
            passwd_check (pw->pw_name, pw->pw_passwd, "chsh");

      /*
       * Now get the login shell. Either get it from the password
       * file, or use the value from the command line.
       */

      if (!sflg)
            STRFCPY (loginsh, pw->pw_shell);

      /*
       * If the login shell was not set on the command line, let the user
       * interactively change it.
       */

      if (!sflg) {
            printf (_("Changing the login shell for %s\n"), user);
            new_fields ();
      }

      /*
       * Check all of the fields for valid information. The shell
       * field may not contain any illegal characters. Non-privileged
       * users are restricted to using the shells in /etc/shells.
       * The shell must be executable by the user.
       */

      if (valid_field (loginsh, ":,=")) {
            fprintf (stderr, _("%s: Invalid entry: %s\n"), Prog,
                   loginsh);
            closelog ();
            exit (1);
      }
      if (!amroot
          && (!check_shell (loginsh) || access (loginsh, X_OK) != 0)) {
            fprintf (stderr, _("%s is an invalid shell.\n"), loginsh);
            closelog ();
            exit (1);
      }

      /*
       * Before going any further, raise the ulimit to prevent
       * colliding into a lowered ulimit, and set the real UID
       * to root to protect against unexpected signals. Any
       * keyboard signals are set to be ignored.
       */

      if (setuid (0)) {
            SYSLOG ((LOG_ERR, "can't setuid(0)"));
            closelog ();
            fprintf (stderr, _("Cannot change ID to root.\n"));
            exit (1);
      }
      pwd_init ();

      /*
       * The passwd entry is now ready to be committed back to
       * the password file. Get a lock on the file and open it.
       */

      if (!pw_lock ()) {
            SYSLOG ((LOG_WARN, "can't lock /etc/passwd"));
            closelog ();
            fprintf (stderr,
                   _
                   ("Cannot lock the password file; try again later.\n"));
            exit (1);
      }
      if (!pw_open (O_RDWR)) {
            SYSLOG ((LOG_ERR, "can't open /etc/passwd"));
            closelog ();
            fprintf (stderr, _("Cannot open the password file.\n"));
            pw_unlock ();
            exit (1);
      }

      /*
       * Get the entry to update using pw_locate() - we want the real
       * one from /etc/passwd, not the one from getpwnam() which could
       * contain the shadow password if (despite the warnings) someone
       * enables AUTOSHADOW (or SHADOW_COMPAT in libc).  --marekm
       */
      pw = pw_locate (user);
      if (!pw) {
            pw_unlock ();
            fprintf (stderr,
                   _("%s: %s not found in /etc/passwd\n"), Prog,
                   user);
            exit (1);
      }

      /*
       * Make a copy of the entry, then change the shell field. The other
       * fields remain unchanged.
       */
      pwent = *pw;
      pwent.pw_shell = loginsh;

      /*
       * Update the passwd file entry. If there is a DBM file, update
       * that entry as well.
       */

      if (!pw_update (&pwent)) {
            SYSLOG ((LOG_ERR, "error updating passwd entry"));
            closelog ();
            fprintf (stderr,
                   _("Error updating the password entry.\n"));
            pw_unlock ();
            exit (1);
      }
#ifdef NDBM
      if (pw_dbm_present () && !pw_dbm_update (&pwent)) {
            SYSLOG ((LOG_ERR, "error updating DBM passwd entry"));
            closelog ();
            fprintf (stderr,
                   _("Error updating the DBM password entry.\n"));
            pw_unlock ();
            exit (1);
      }
      endpwent ();
#endif

      /*
       * Changes have all been made, so commit them and unlock the file.
       */

      if (!pw_close ()) {
            SYSLOG ((LOG_ERR, "can't rewrite /etc/passwd"));
            closelog ();
            fprintf (stderr,
                   _("Cannot commit password file changes.\n"));
            pw_unlock ();
            exit (1);
      }
      if (!pw_unlock ()) {
            SYSLOG ((LOG_ERR, "can't unlock /etc/passwd"));
            closelog ();
            fprintf (stderr, _("Cannot unlock the password file.\n"));
            exit (1);
      }
      SYSLOG ((LOG_INFO, "changed user `%s' shell to `%s'", user,
             loginsh));
      closelog ();
      exit (0);
}

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