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 "setpwnam.h"
  42 #include "strutils.h"
  43 #include "xalloc.h"
  44
  45 #include "ch-common.h"
  46
  47 #ifdef HAVE_LIBSELINUX
  48 # include <selinux/selinux.h>
  49 # include "selinux_utils.h"
  50 #endif
  51
  52
  53 #ifdef HAVE_LIBUSER
  54 # include <libuser/user.h>
  55 # include "libuser.h"
  56 #elif CHFN_CHSH_PASSWORD
  57 # include "auth.h"
  58 #endif
  59
  60 #ifdef HAVE_LIBREADLINE
  61 # define _FUNCTION_DEF
  62 # include <readline/readline.h>
  63 #endif
  64
  65 struct sinfo {
  66         char *username;
  67         char *shell;
  68 };
  69
  70 static void __attribute__((__noreturn__)) usage(void)
  71 {
  72         FILE *fp = stdout;
  73         fputs(USAGE_HEADER, fp);
  74         fprintf(fp, _(" %s [options] [<username>]\n"), program_invocation_short_name);
  75
  76         fputs(USAGE_SEPARATOR, fp);
  77         fputs(_("Change your login shell.\n"), fp);
  78
  79         fputs(USAGE_OPTIONS, fp);
  80         fputs(_(" -s, --shell <shell>  specify login shell\n"), fp);
  81         fputs(_(" -l, --list-shells    print list of shells and exit\n"), fp);
  82         fputs(USAGE_SEPARATOR, fp);
  83         printf( " -u, --help           %s\n", USAGE_OPTSTR_HELP);
  84         printf( " -v, --version        %s\n", USAGE_OPTSTR_VERSION);
  85         printf(USAGE_MAN_TAIL("chsh(1)"));
  86         exit(EXIT_SUCCESS);
  87 }
  88
  89 /*
  90  *  is_known_shell() -- if the given shell appears in /etc/shells,
  91  *      return true.  if not, return false.
  92  */
  93 static int is_known_shell(const char *shell_name)
  94 {
  95         char *s, ret = 0;
  96
  97         if (!shell_name)
  98                 return 0;
  99
 100         setusershell();
 101         while ((s = getusershell())) {
 102                 if (strcmp(shell_name, s) == 0) {
 103                         ret = 1;
 104                         break;
 105                 }
 106         }
 107         endusershell();
 108         return ret;
 109 }
 110
 111 /*
 112  *  print_shells () -- /etc/shells is outputted to stdout.
 113  */
 114 static void print_shells(void)
 115 {
 116         char *s;
 117
 118         while ((s = getusershell()))
 119                 printf("%s\n", s);
 120         endusershell();
 121 }
 122
 123 #ifdef HAVE_LIBREADLINE
 124 static char *shell_name_generator(const char *text, int state)
 125 {
 126         static size_t len;
 127         char *s;
 128
 129         if (!state) {
 130                 setusershell();
 131                 len = strlen(text);
 132         }
 133
 134         while ((s = getusershell())) {
 135                 if (strncmp(s, text, len) == 0)
 136                         return xstrdup(s);
 137         }
 138         return NULL;
 139 }
 140
 141 static char **shell_name_completion(const char *text,
 142                                     int start __attribute__((__unused__)),
 143                                     int end __attribute__((__unused__)))
 144 {
 145         rl_attempted_completion_over = 1;
 146         return rl_completion_matches(text, shell_name_generator);
 147 }
 148 #endif
 149
 150 /*
 151  *  parse_argv () --
 152  *      parse the command line arguments, and fill in "pinfo" with any
 153  *      information from the command line.
 154  */
 155 static void parse_argv(int argc, char **argv, struct sinfo *pinfo)
 156 {
 157         static const struct option long_options[] = {
 158                 {"shell",       required_argument, NULL, 's'},
 159                 {"list-shells", no_argument,       NULL, 'l'},
 160                 {"help",        no_argument,       NULL, 'h'},
 161                 {"version",     no_argument,       NULL, 'v'},
 162                 {NULL, 0, NULL, 0},
 163         };
 164         int c;
 165
 166         while ((c = getopt_long(argc, argv, "s:lhuv", long_options, NULL)) != -1) {
 167                 switch (c) {
 168                 case 'v':
 169                         print_version(EXIT_SUCCESS);
 170                 case 'u': /* deprecated */
 171                 case 'h':
 172                         usage();
 173                 case 'l':
 174                         print_shells();
 175                         exit(EXIT_SUCCESS);
 176                 case 's':
 177                         pinfo->shell = optarg;
 178                         break;
 179                 default:
 180                         errtryhelp(EXIT_FAILURE);
 181                 }
 182         }
 183         /* done parsing arguments.  check for a username. */
 184         if (optind < argc) {
 185                 if (optind + 1 < argc) {
 186                         errx(EXIT_FAILURE, _("cannot handle multiple usernames"));
 187                 }
 188                 pinfo->username = argv[optind];
 189         }
 190 }
 191
 192 /*
 193  *  ask_new_shell () --
 194  *      ask the user for a shell and return it.
 195  */
 196 static char *ask_new_shell(char *question, char *oldshell)
 197 {
 198         int len;
 199         char *ans = NULL;
 200 #ifdef HAVE_LIBREADLINE
 201         rl_attempted_completion_function = shell_name_completion;
 202 #else
 203         size_t dummy = 0;
 204 #endif
 205         if (!oldshell)
 206                 oldshell = "";
 207         printf("%s [%s]\n", question, oldshell);
 208 #ifdef HAVE_LIBREADLINE
 209         if ((ans = readline("> ")) == NULL)
 210 #else
 211         if (getline(&ans, &dummy, stdin) < 0)
 212 #endif
 213                 return NULL;
 214         /* remove the newline at the end of ans. */
 215         ltrim_whitespace((unsigned char *) ans);
 216         len = rtrim_whitespace((unsigned char *) ans);
 217         if (len == 0)
 218                 return NULL;
 219         return ans;
 220 }
 221
 222 /*
 223  *  check_shell () -- if the shell is completely invalid, print
 224  *      an error and exit.
 225  */
 226 static void check_shell(const char *shell)
 227 {
 228         if (*shell != '/')
 229                 errx(EXIT_FAILURE, _("shell must be a full path name"));
 230         if (access(shell, F_OK) < 0)
 231                 errx(EXIT_FAILURE, _("\"%s\" does not exist"), shell);
 232         if (access(shell, X_OK) < 0)
 233                 errx(EXIT_FAILURE, _("\"%s\" is not executable"), shell);
 234         if (illegal_passwd_chars(shell))
 235                 errx(EXIT_FAILURE, _("%s: has illegal characters"), shell);
 236         if (!is_known_shell(shell)) {
 237 #ifdef ONLY_LISTED_SHELLS
 238                 if (!getuid())
 239                         warnx(_("Warning: \"%s\" is not listed in %s."), shell,
 240                               _PATH_SHELLS);
 241                 else
 242                         errx(EXIT_FAILURE,
 243                              _("\"%s\" is not listed in %s.\n"
 244                                "Use %s -l to see list."), shell, _PATH_SHELLS,
 245                              program_invocation_short_name);
 246 #else
 247                 warnx(_("\"%s\" is not listed in %s.\n"
 248                         "Use %s -l to see list."), shell, _PATH_SHELLS,
 249                        program_invocation_short_name);
 250 #endif
 251         }
 252 }
 253
 254 int main(int argc, char **argv)
 255 {
 256         char *oldshell;
 257         int nullshell = 0;
 258         const uid_t uid = getuid();
 259         struct sinfo info = { NULL };
 260         struct passwd *pw;
 261
 262         sanitize_env();
 263         setlocale(LC_ALL, "");
 264         bindtextdomain(PACKAGE, LOCALEDIR);
 265         textdomain(PACKAGE);
 266         close_stdout_atexit();
 267
 268         parse_argv(argc, argv, &info);
 269         if (!info.username) {
 270                 pw = getpwuid(uid);
 271                 if (!pw)
 272                         errx(EXIT_FAILURE, _("you (user %d) don't exist."),
 273                              uid);
 274         } else {
 275                 pw = getpwnam(info.username);
 276                 if (!pw)
 277                         errx(EXIT_FAILURE, _("user \"%s\" does not exist."),
 278                              info.username);
 279         }
 280
 281 #ifndef HAVE_LIBUSER
 282         if (!(is_local(pw->pw_name)))
 283                 errx(EXIT_FAILURE, _("can only change local entries"));
 284 #endif
 285
 286 #ifdef HAVE_LIBSELINUX
 287         if (is_selinux_enabled() > 0) {
 288                 if (uid == 0) {
 289                         access_vector_t av = get_access_vector("passwd", "chsh");
 290
 291                         if (selinux_check_passwd_access(av) != 0) {
 292                                 security_context_t user_context;
 293                                 if (getprevcon(&user_context) < 0)
 294                                         user_context =
 295                                             (security_context_t) NULL;
 296
 297                                 errx(EXIT_FAILURE,
 298                                      _("%s is not authorized to change the shell of %s"),
 299                                      user_context ? : _("Unknown user context"),
 300                                      pw->pw_name);
 301                         }
 302                 }
 303                 if (setupDefaultContext(_PATH_PASSWD) != 0)
 304                         errx(EXIT_FAILURE,
 305                              _("can't set default context for %s"), _PATH_PASSWD);
 306         }
 307 #endif
 308
 309         oldshell = pw->pw_shell;
 310         if (oldshell == NULL || *oldshell == '\0') {
 311                 oldshell = _PATH_BSHELL;        /* default */
 312                 nullshell = 1;
 313         }
 314
 315         /* reality check */
 316 #ifdef HAVE_LIBUSER
 317         /* If we're setuid and not really root, disallow the password change. */
 318         if (geteuid() != getuid() && uid != pw->pw_uid) {
 319 #else
 320         if (uid != 0 && uid != pw->pw_uid) {
 321 #endif
 322                 errno = EACCES;
 323                 err(EXIT_FAILURE,
 324                     _("running UID doesn't match UID of user we're "
 325                       "altering, shell change denied"));
 326         }
 327         if (uid != 0 && !is_known_shell(oldshell)) {
 328                 errno = EACCES;
 329                 err(EXIT_FAILURE, _("your shell is not in %s, "
 330                                     "shell change denied"), _PATH_SHELLS);
 331         }
 332
 333         printf(_("Changing shell for %s.\n"), pw->pw_name);
 334
 335 #if !defined(HAVE_LIBUSER) && defined(CHFN_CHSH_PASSWORD)
 336         if (!auth_pam("chsh", uid, pw->pw_name)) {
 337                 return EXIT_FAILURE;
 338         }
 339 #endif
 340         if (!info.shell) {
 341                 info.shell = ask_new_shell(_("New shell"), oldshell);
 342                 if (!info.shell)
 343                         return EXIT_SUCCESS;
 344         }
 345
 346         check_shell(info.shell);
 347
 348         if (!nullshell && strcmp(oldshell, info.shell) == 0)
 349                 errx(EXIT_SUCCESS, _("Shell not changed."));
 350
 351 #ifdef HAVE_LIBUSER
 352         if (set_value_libuser("chsh", pw->pw_name, uid,
 353             LU_LOGINSHELL, info.shell) < 0)
 354                 errx(EXIT_FAILURE, _("Shell *NOT* changed.  Try again later."));
 355 #else
 356         pw->pw_shell = info.shell;
 357         if (setpwnam(pw, ".chsh") < 0)
 358                 err(EXIT_FAILURE, _("setpwnam failed\n"
 359                         "Shell *NOT* changed.  Try again later."));
 360 #endif
 361
 362         printf(_("Shell changed.\n"));
 363         return EXIT_SUCCESS;
 364 }