login-utils/chsh.c

   1 /*
   2  *   chsh.c -- change your login shell
   3  *   (c) 1994 by salvatore valente <svalente@athena.mit.edu>
   4  *   (c) 2012 by Cody Maloney <cmaloney@theoreticalchaos.com>
   5  *
   6  *   this program is free software.  you can redistribute it and
   7  *   modify it under the terms of the gnu general public license.
   8  *   there is no warranty.
   9  *
  10  *   $Author: aebr $
  11  *   $Revision: 1.19 $
  12  *   $Date: 1998/06/11 22:30:14 $
  13  *
  14  * Updated Thu Oct 12 09:33:15 1995 by faith@cs.unc.edu with security
  15  *   patches from Zefram <A.Main@dcs.warwick.ac.uk>
  16  *
  17  * Updated Mon Jul  1 18:46:22 1996 by janl@math.uio.no with security
  18  *   suggestion from Zefram.  Disallowing users with shells not in /etc/shells
  19  *   from changing their shell.
  20  *
  21  *   1999-02-22 Arkadiusz Miśkiewicz <misiek@pld.ORG.PL>
  22  *   - added Native Language Support
  23  */
  24
  25 #include <ctype.h>
  26 #include <errno.h>
  27 #include <getopt.h>
  28 #include <pwd.h>
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include <string.h>
  32 #include <sys/types.h>
  33 #include <unistd.h>
  34
  35 #include "c.h"
  36 #include "env.h"
  37 #include "closestream.h"
  38 #include "islocal.h"
  39 #include "nls.h"
  40 #include "pathnames.h"
  41 #include "pwdutils.h"
  42 #include "setpwnam.h"
  43 #include "strutils.h"
  44 #include "xalloc.h"
  45
  46 #include "ch-common.h"
  47 #include "shells.h"
  48
  49 #ifdef HAVE_LIBSELINUX
  50 # include <selinux/selinux.h>
  51 # include "selinux-utils.h"
  52 #endif
  53
  54 #ifdef HAVE_LIBUSER
  55 # include <libuser/user.h>
  56 # include "libuser.h"
  57 #elif CHFN_CHSH_PASSWORD
  58 # include "auth.h"
  59 #endif
  60
  61 struct sinfo {
  62         char *username;
  63         char *shell;
  64 };
  65
  66 static void __attribute__((__noreturn__)) usage(void)
  67 {
  68         FILE *fp = stdout;
  69         fputs(USAGE_HEADER, fp);
  70         fprintf(fp, _(" %s [options] [<username>]\n"), program_invocation_short_name);
  71
  72         fputs(USAGE_SEPARATOR, fp);
  73         fputs(_("Change your login shell.\n"), fp);
  74
  75         fputs(USAGE_OPTIONS, fp);
  76         fputs(_(" -s, --shell <shell>  specify login shell\n"), fp);
  77         fputs(_(" -l, --list-shells    print list of shells and exit\n"), fp);
  78
  79         fputs(USAGE_SEPARATOR, fp);
  80         fprintf(fp, USAGE_HELP_OPTIONS(22));
  81
  82         fprintf(fp, USAGE_MAN_TAIL("chsh(1)"));
  83         exit(EXIT_SUCCESS);
  84 }
  85
  86 /*
  87  *  parse_argv () --
  88  *      parse the command line arguments, and fill in "pinfo" with any
  89  *      information from the command line.
  90  */
  91 static void parse_argv(int argc, char **argv, struct sinfo *pinfo)
  92 {
  93         static const struct option long_options[] = {
  94                 {"shell",       required_argument, NULL, 's'},
  95                 {"list-shells", no_argument,       NULL, 'l'},
  96                 {"help",        no_argument,       NULL, 'h'},
  97                 {"version",     no_argument,       NULL, 'V'},
  98                 {NULL, 0, NULL, 0},
  99         };
 100         int c;
 101
 102         while ((c = getopt_long(argc, argv, "s:lhuvV", long_options, NULL)) != -1) {
 103                 switch (c) {
 104                 case 'v': /* deprecated */
 105                 case 'V':
 106                         print_version(EXIT_SUCCESS);
 107                 case 'u': /* deprecated */
 108                 case 'h':
 109                         usage();
 110                 case 'l':
 111                         print_shells(stdout, "%s\n");
 112                         exit(EXIT_SUCCESS);
 113                 case 's':
 114                         pinfo->shell = optarg;
 115                         break;
 116                 default:
 117                         errtryhelp(EXIT_FAILURE);
 118                 }
 119         }
 120         /* done parsing arguments.  check for a username. */
 121         if (optind < argc) {
 122                 if (optind + 1 < argc) {
 123                         errx(EXIT_FAILURE, _("cannot handle multiple usernames"));
 124                 }
 125                 pinfo->username = argv[optind];
 126         }
 127 }
 128
 129 /*
 130  *  ask_new_shell () --
 131  *      ask the user for a shell and return it.
 132  */
 133 static char *ask_new_shell(char *question, char *oldshell)
 134 {
 135         int len;
 136         char *ans = NULL;
 137         size_t dummy = 0;
 138
 139         if (!oldshell)
 140                 oldshell = "";
 141         printf("%s [%s]:", question, oldshell);
 142
 143         putchar(' ');
 144         fflush(stdout);
 145
 146         if (getline(&ans, &dummy, stdin) < 0)
 147                 return NULL;
 148
 149         /* remove the newline at the end of ans. */
 150         ltrim_whitespace((unsigned char *) ans);
 151         len = rtrim_whitespace((unsigned char *) ans);
 152         if (len == 0)
 153                 return NULL;
 154         return ans;
 155 }
 156
 157 /*
 158  *  check_shell () -- if the shell is completely invalid, print
 159  *      an error and exit.
 160  */
 161 static void check_shell(const char *shell)
 162 {
 163         if (*shell != '/')
 164                 errx(EXIT_FAILURE, _("shell must be a full path name"));
 165         if (access(shell, F_OK) < 0)
 166                 errx(EXIT_FAILURE, _("\"%s\" does not exist"), shell);
 167         if (access(shell, X_OK) < 0)
 168                 errx(EXIT_FAILURE, _("\"%s\" is not executable"), shell);
 169         if (illegal_passwd_chars(shell))
 170                 errx(EXIT_FAILURE, _("%s: has illegal characters"), shell);
 171         if (!is_known_shell(shell)) {
 172 #ifdef ONLY_LISTED_SHELLS
 173                 if (!getuid())
 174                         warnx(_("Warning: \"%s\" is not listed in %s."), shell,
 175                               _PATH_SHELLS);
 176                 else
 177                         errx(EXIT_FAILURE,
 178                              _("\"%s\" is not listed in %s.\n"
 179                                "Use %s -l to see list."), shell, _PATH_SHELLS,
 180                              program_invocation_short_name);
 181 #else
 182                 warnx(_("\"%s\" is not listed in %s.\n"
 183                         "Use %s -l to see list."), shell, _PATH_SHELLS,
 184                        program_invocation_short_name);
 185 #endif
 186         }
 187 }
 188
 189 int main(int argc, char **argv)
 190 {
 191         char *oldshell, *pwbuf;
 192         int nullshell = 0;
 193         const uid_t uid = getuid();
 194         struct sinfo info = { NULL };
 195         struct passwd *pw;
 196
 197         sanitize_env();
 198         setlocale(LC_ALL, "");
 199         bindtextdomain(PACKAGE, LOCALEDIR);
 200         textdomain(PACKAGE);
 201         close_stdout_atexit();
 202
 203         parse_argv(argc, argv, &info);
 204         if (!info.username) {
 205                 pw = xgetpwuid(uid, &pwbuf);
 206                 if (!pw)
 207                         errx(EXIT_FAILURE, _("you (user %d) don't exist."),
 208                              uid);
 209         } else {
 210                 pw = xgetpwnam(info.username, &pwbuf);
 211                 if (!pw)
 212                         errx(EXIT_FAILURE, _("user \"%s\" does not exist."),
 213                              info.username);
 214         }
 215
 216 #ifndef HAVE_LIBUSER
 217         if (!(is_local(pw->pw_name)))
 218                 errx(EXIT_FAILURE, _("can only change local entries"));
 219 #endif
 220
 221 #ifdef HAVE_LIBSELINUX
 222         if (is_selinux_enabled() > 0) {
 223                 char *user_cxt = NULL;
 224
 225                 if (uid == 0 && !ul_selinux_has_access("passwd", "chsh", &user_cxt))
 226                         errx(EXIT_FAILURE,
 227                              _("%s is not authorized to change the shell of %s"),
 228                              user_cxt ? : _("Unknown user context"),
 229                              pw->pw_name);
 230
 231                 if (ul_setfscreatecon_from_file(_PATH_PASSWD) != 0)
 232                         errx(EXIT_FAILURE,
 233                              _("can't set default context for %s"), _PATH_PASSWD);
 234         }
 235 #endif
 236
 237         oldshell = pw->pw_shell;
 238         if (oldshell == NULL || *oldshell == '\0') {
 239                 oldshell = _PATH_BSHELL;        /* default */
 240                 nullshell = 1;
 241         }
 242
 243         /* reality check */
 244 #ifdef HAVE_LIBUSER
 245         /* If we're setuid and not really root, disallow the password change. */
 246         if (is_privileged_execution() && uid != pw->pw_uid) {
 247 #else
 248         if (uid != 0 && uid != pw->pw_uid) {
 249 #endif
 250                 errno = EACCES;
 251                 err(EXIT_FAILURE,
 252                     _("running UID doesn't match UID of user we're "
 253                       "altering, shell change denied"));
 254         }
 255         if (uid != 0 && !is_known_shell(oldshell)) {
 256                 errno = EACCES;
 257                 err(EXIT_FAILURE, _("your shell is not in %s, "
 258                                     "shell change denied"), _PATH_SHELLS);
 259         }
 260
 261         printf(_("Changing shell for %s.\n"), pw->pw_name);
 262
 263 #if !defined(HAVE_LIBUSER) && defined(CHFN_CHSH_PASSWORD)
 264         if (!auth_pam("chsh", uid, pw->pw_name)) {
 265                 return EXIT_FAILURE;
 266         }
 267 #endif
 268         if (!info.shell) {
 269                 info.shell = ask_new_shell(_("New shell"), oldshell);
 270                 if (!info.shell)
 271                         return EXIT_SUCCESS;
 272         }
 273
 274         check_shell(info.shell);
 275
 276         if (!nullshell && strcmp(oldshell, info.shell) == 0)
 277                 errx(EXIT_SUCCESS, _("Shell not changed."));
 278
 279 #ifdef HAVE_LIBUSER
 280         if (set_value_libuser("chsh", pw->pw_name, uid,
 281             LU_LOGINSHELL, info.shell) < 0)
 282                 errx(EXIT_FAILURE, _("Shell *NOT* changed.  Try again later."));
 283 #else
 284         pw->pw_shell = info.shell;
 285         if (setpwnam(pw, ".chsh") < 0)
 286                 err(EXIT_FAILURE, _("setpwnam failed\n"
 287                         "Shell *NOT* changed.  Try again later."));
 288 #endif
 289
 290         printf(_("Shell changed.\n"));
 291         return EXIT_SUCCESS;
 292 }