release/src/router/busybox/loginutils/login.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   4  */
   5
   6 //usage:#define login_trivial_usage
   7 //usage:       "[-p] [-h HOST] [[-f] USER]"
   8 //usage:#define login_full_usage "\n\n"
   9 //usage:       "Begin a new session on the system\n"
  10 //usage:     "\n        -f      Don't authenticate (user already authenticated)"
  11 //usage:     "\n        -h      Name of the remote host"
  12 //usage:     "\n        -p      Preserve environment"
  13
  14 #include "libbb.h"
  15 #include <syslog.h>
  16 #include <sys/resource.h>
  17
  18 #if ENABLE_SELINUX
  19 # include <selinux/selinux.h>  /* for is_selinux_enabled()  */
  20 # include <selinux/get_context_list.h> /* for get_default_context() */
  21 # include <selinux/flask.h> /* for security class definitions  */
  22 #endif
  23
  24 #if ENABLE_PAM
  25 /* PAM may include <locale.h>. We may need to undefine bbox's stub define: */
  26 # undef setlocale
  27 /* For some obscure reason, PAM is not in pam/xxx, but in security/xxx.
  28  * Apparently they like to confuse people. */
  29 # include <security/pam_appl.h>
  30 # include <security/pam_misc.h>
  31 static const struct pam_conv conv = {
  32         misc_conv,
  33         NULL
  34 };
  35 #endif
  36
  37 enum {
  38         TIMEOUT = 60,
  39         EMPTY_USERNAME_COUNT = 10,
  40         USERNAME_SIZE = 32,
  41         TTYNAME_SIZE = 32,
  42 };
  43
  44 struct globals {
  45         struct termios tty_attrs;
  46 } FIX_ALIASING;
  47 #define G (*(struct globals*)&bb_common_bufsiz1)
  48 #define INIT_G() do { } while (0)
  49
  50
  51 #if ENABLE_FEATURE_NOLOGIN
  52 static void die_if_nologin(void)
  53 {
  54         FILE *fp;
  55         int c;
  56         int empty = 1;
  57
  58         fp = fopen_for_read("/etc/nologin");
  59         if (!fp) /* assuming it does not exist */
  60                 return;
  61
  62         while ((c = getc(fp)) != EOF) {
  63                 if (c == '\n')
  64                         bb_putchar('\r');
  65                 bb_putchar(c);
  66                 empty = 0;
  67         }
  68         if (empty)
  69                 puts("\r\nSystem closed for routine maintenance\r");
  70
  71         fclose(fp);
  72         fflush_all();
  73         /* Users say that they do need this prior to exit: */
  74         tcdrain(STDOUT_FILENO);
  75         exit(EXIT_FAILURE);
  76 }
  77 #else
  78 # define die_if_nologin() ((void)0)
  79 #endif
  80
  81 #if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
  82 static int check_securetty(const char *short_tty)
  83 {
  84         char *buf = (char*)"/etc/securetty"; /* any non-NULL is ok */
  85         parser_t *parser = config_open2("/etc/securetty", fopen_for_read);
  86         while (config_read(parser, &buf, 1, 1, "# \t", PARSE_NORMAL)) {
  87                 if (strcmp(buf, short_tty) == 0)
  88                         break;
  89                 buf = NULL;
  90         }
  91         config_close(parser);
  92         /* buf != NULL here if config file was not found, empty
  93          * or line was found which equals short_tty */
  94         return buf != NULL;
  95 }
  96 #else
  97 static ALWAYS_INLINE int check_securetty(const char *short_tty UNUSED_PARAM) { return 1; }
  98 #endif
  99
 100 #if ENABLE_SELINUX
 101 static void initselinux(char *username, char *full_tty,
 102                                                 security_context_t *user_sid)
 103 {
 104         security_context_t old_tty_sid, new_tty_sid;
 105
 106         if (!is_selinux_enabled())
 107                 return;
 108
 109         if (get_default_context(username, NULL, user_sid)) {
 110                 bb_error_msg_and_die("can't get SID for %s", username);
 111         }
 112         if (getfilecon(full_tty, &old_tty_sid) < 0) {
 113                 bb_perror_msg_and_die("getfilecon(%s) failed", full_tty);
 114         }
 115         if (security_compute_relabel(*user_sid, old_tty_sid,
 116                                 SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
 117                 bb_perror_msg_and_die("security_change_sid(%s) failed", full_tty);
 118         }
 119         if (setfilecon(full_tty, new_tty_sid) != 0) {
 120                 bb_perror_msg_and_die("chsid(%s, %s) failed", full_tty, new_tty_sid);
 121         }
 122 }
 123 #endif
 124
 125 #if ENABLE_LOGIN_SCRIPTS
 126 static void run_login_script(struct passwd *pw, char *full_tty)
 127 {
 128         char *t_argv[2];
 129
 130         t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
 131         if (t_argv[0]) {
 132                 t_argv[1] = NULL;
 133                 xsetenv("LOGIN_TTY", full_tty);
 134                 xsetenv("LOGIN_USER", pw->pw_name);
 135                 xsetenv("LOGIN_UID", utoa(pw->pw_uid));
 136                 xsetenv("LOGIN_GID", utoa(pw->pw_gid));
 137                 xsetenv("LOGIN_SHELL", pw->pw_shell);
 138                 spawn_and_wait(t_argv); /* NOMMU-friendly */
 139                 unsetenv("LOGIN_TTY");
 140                 unsetenv("LOGIN_USER");
 141                 unsetenv("LOGIN_UID");
 142                 unsetenv("LOGIN_GID");
 143                 unsetenv("LOGIN_SHELL");
 144         }
 145 }
 146 #else
 147 void run_login_script(struct passwd *pw, char *full_tty);
 148 #endif
 149
 150 #if ENABLE_LOGIN_SESSION_AS_CHILD && ENABLE_PAM
 151 static void login_pam_end(pam_handle_t *pamh)
 152 {
 153         int pamret;
 154
 155         pamret = pam_setcred(pamh, PAM_DELETE_CRED);
 156         if (pamret != PAM_SUCCESS) {
 157                 bb_error_msg("pam_%s failed: %s (%d)", "setcred",
 158                         pam_strerror(pamh, pamret), pamret);
 159         }
 160         pamret = pam_close_session(pamh, 0);
 161         if (pamret != PAM_SUCCESS) {
 162                 bb_error_msg("pam_%s failed: %s (%d)", "close_session",
 163                         pam_strerror(pamh, pamret), pamret);
 164         }
 165         pamret = pam_end(pamh, pamret);
 166         if (pamret != PAM_SUCCESS) {
 167                 bb_error_msg("pam_%s failed: %s (%d)", "end",
 168                         pam_strerror(pamh, pamret), pamret);
 169         }
 170 }
 171 #endif /* ENABLE_PAM */
 172
 173 static void get_username_or_die(char *buf, int size_buf)
 174 {
 175         int c, cntdown;
 176
 177         cntdown = EMPTY_USERNAME_COUNT;
 178  prompt:
 179         print_login_prompt();
 180         /* skip whitespace */
 181         do {
 182                 c = getchar();
 183                 if (c == EOF)
 184                         exit(EXIT_FAILURE);
 185                 if (c == '\n') {
 186                         if (!--cntdown)
 187                                 exit(EXIT_FAILURE);
 188                         goto prompt;
 189                 }
 190         } while (isspace(c)); /* maybe isblank? */
 191
 192         *buf++ = c;
 193         if (!fgets(buf, size_buf-2, stdin))
 194                 exit(EXIT_FAILURE);
 195         if (!strchr(buf, '\n'))
 196                 exit(EXIT_FAILURE);
 197         while ((unsigned char)*buf > ' ')
 198                 buf++;
 199         *buf = '\0';
 200 }
 201
 202 static void motd(void)
 203 {
 204         int fd;
 205
 206         fd = open(bb_path_motd_file, O_RDONLY);
 207         if (fd >= 0) {
 208                 fflush_all();
 209                 bb_copyfd_eof(fd, STDOUT_FILENO);
 210                 close(fd);
 211         }
 212 }
 213
 214 static void alarm_handler(int sig UNUSED_PARAM)
 215 {
 216         /* This is the escape hatch! Poor serial line users and the like
 217          * arrive here when their connection is broken.
 218          * We don't want to block here */
 219         ndelay_on(STDOUT_FILENO);
 220         /* Test for correct attr restoring:
 221          * run "getty 0 -" from a shell, enter bogus username, stop at
 222          * password prompt, let it time out. Without the tcsetattr below,
 223          * when you are back at shell prompt, echo will be still off.
 224          */
 225         tcsetattr_stdin_TCSANOW(&G.tty_attrs);
 226         printf("\r\nLogin timed out after %u seconds\r\n", TIMEOUT);
 227         fflush_all();
 228         /* unix API is brain damaged regarding O_NONBLOCK,
 229          * we should undo it, or else we can affect other processes */
 230         ndelay_off(STDOUT_FILENO);
 231         _exit(EXIT_SUCCESS);
 232 }
 233
 234 int login_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 235 int login_main(int argc UNUSED_PARAM, char **argv)
 236 {
 237         enum {
 238                 LOGIN_OPT_f = (1<<0),
 239                 LOGIN_OPT_h = (1<<1),
 240                 LOGIN_OPT_p = (1<<2),
 241         };
 242         char *fromhost;
 243         char username[USERNAME_SIZE];
 244         int run_by_root;
 245         unsigned opt;
 246         int count = 0;
 247         struct passwd *pw;
 248         char *opt_host = NULL;
 249         char *opt_user = opt_user; /* for compiler */
 250         char *full_tty;
 251         char *short_tty;
 252         IF_SELINUX(security_context_t user_sid = NULL;)
 253 #if ENABLE_PAM
 254         int pamret;
 255         pam_handle_t *pamh;
 256         const char *pamuser;
 257         const char *failed_msg;
 258         struct passwd pwdstruct;
 259         char pwdbuf[256];
 260         char **pamenv;
 261 #endif
 262 #if ENABLE_LOGIN_SESSION_AS_CHILD
 263         pid_t child_pid;
 264 #endif
 265
 266         INIT_G();
 267
 268         /* More of suid paranoia if called by non-root: */
 269         /* Clear dangerous stuff, set PATH */
 270         run_by_root = !sanitize_env_if_suid();
 271
 272         /* Mandatory paranoia for suid applet:
 273          * ensure that fd# 0,1,2 are opened (at least to /dev/null)
 274          * and any extra open fd's are closed.
 275          * (The name of the function is misleading. Not daemonizing here.) */
 276         bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);
 277
 278         username[0] = '\0';
 279         opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
 280         if (opt & LOGIN_OPT_f) {
 281                 if (!run_by_root)
 282                         bb_error_msg_and_die("-f is for root only");
 283                 safe_strncpy(username, opt_user, sizeof(username));
 284         }
 285         argv += optind;
 286         if (argv[0]) /* user from command line (getty) */
 287                 safe_strncpy(username, argv[0], sizeof(username));
 288
 289         /* Save tty attributes - and by doing it, check that it's indeed a tty */
 290         if (tcgetattr(STDIN_FILENO, &G.tty_attrs) < 0
 291          || !isatty(STDOUT_FILENO)
 292          /*|| !isatty(STDERR_FILENO) - no, guess some people might want to redirect this */
 293         ) {
 294                 return EXIT_FAILURE;  /* Must be a terminal */
 295         }
 296
 297         /* We install timeout handler only _after_ we saved G.tty_attrs */
 298         signal(SIGALRM, alarm_handler);
 299         alarm(TIMEOUT);
 300
 301         /* Find out and memorize our tty name */
 302         full_tty = xmalloc_ttyname(STDIN_FILENO);
 303         if (!full_tty)
 304                 full_tty = xstrdup("UNKNOWN");
 305         short_tty = skip_dev_pfx(full_tty);
 306
 307         if (opt_host) {
 308                 fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
 309         } else {
 310                 fromhost = xasprintf(" on '%s'", short_tty);
 311         }
 312
 313         /* Was breaking "login <username>" from shell command line: */
 314         /*bb_setpgrp();*/
 315
 316         openlog(applet_name, LOG_PID | LOG_CONS, LOG_AUTH);
 317
 318         while (1) {
 319                 /* flush away any type-ahead (as getty does) */
 320                 tcflush(0, TCIFLUSH);
 321
 322                 if (!username[0])
 323                         get_username_or_die(username, sizeof(username));
 324
 325 #if ENABLE_PAM
 326                 pamret = pam_start("login", username, &conv, &pamh);
 327                 if (pamret != PAM_SUCCESS) {
 328                         failed_msg = "start";
 329                         goto pam_auth_failed;
 330                 }
 331                 /* set TTY (so things like securetty work) */
 332                 pamret = pam_set_item(pamh, PAM_TTY, short_tty);
 333                 if (pamret != PAM_SUCCESS) {
 334                         failed_msg = "set_item(TTY)";
 335                         goto pam_auth_failed;
 336                 }
 337                 /* set RHOST */
 338                 if (opt_host) {
 339                         pamret = pam_set_item(pamh, PAM_RHOST, opt_host);
 340                         if (pamret != PAM_SUCCESS) {
 341                                 failed_msg = "set_item(RHOST)";
 342                                 goto pam_auth_failed;
 343                         }
 344                 }
 345                 if (!(opt & LOGIN_OPT_f)) {
 346                         pamret = pam_authenticate(pamh, 0);
 347                         if (pamret != PAM_SUCCESS) {
 348                                 failed_msg = "authenticate";
 349                                 goto pam_auth_failed;
 350                                 /* TODO: or just "goto auth_failed"
 351                                  * since user seems to enter wrong password
 352                                  * (in this case pamret == 7)
 353                                  */
 354                         }
 355                 }
 356                 /* check that the account is healthy */
 357                 pamret = pam_acct_mgmt(pamh, 0);
 358                 if (pamret != PAM_SUCCESS) {
 359                         failed_msg = "acct_mgmt";
 360                         goto pam_auth_failed;
 361                 }
 362                 /* read user back */
 363                 pamuser = NULL;
 364                 /* gcc: "dereferencing type-punned pointer breaks aliasing rules..."
 365                  * thus we cast to (void*) */
 366                 if (pam_get_item(pamh, PAM_USER, (void*)&pamuser) != PAM_SUCCESS) {
 367                         failed_msg = "get_item(USER)";
 368                         goto pam_auth_failed;
 369                 }
 370                 if (!pamuser || !pamuser[0])
 371                         goto auth_failed;
 372                 safe_strncpy(username, pamuser, sizeof(username));
 373                 /* Don't use "pw = getpwnam(username);",
 374                  * PAM is said to be capable of destroying static storage
 375                  * used by getpwnam(). We are using safe(r) function */
 376                 pw = NULL;
 377                 getpwnam_r(username, &pwdstruct, pwdbuf, sizeof(pwdbuf), &pw);
 378                 if (!pw)
 379                         goto auth_failed;
 380                 pamret = pam_open_session(pamh, 0);
 381                 if (pamret != PAM_SUCCESS) {
 382                         failed_msg = "open_session";
 383                         goto pam_auth_failed;
 384                 }
 385                 pamret = pam_setcred(pamh, PAM_ESTABLISH_CRED);
 386                 if (pamret != PAM_SUCCESS) {
 387                         failed_msg = "setcred";
 388                         goto pam_auth_failed;
 389                 }
 390                 break; /* success, continue login process */
 391
 392  pam_auth_failed:
 393                 /* syslog, because we don't want potential attacker
 394                  * to know _why_ login failed */
 395                 syslog(LOG_WARNING, "pam_%s call failed: %s (%d)", failed_msg,
 396                                         pam_strerror(pamh, pamret), pamret);
 397                 safe_strncpy(username, "UNKNOWN", sizeof(username));
 398 #else /* not PAM */
 399                 pw = getpwnam(username);
 400                 if (!pw) {
 401                         strcpy(username, "UNKNOWN");
 402                         goto fake_it;
 403                 }
 404
 405                 if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
 406                         goto auth_failed;
 407
 408                 if (opt & LOGIN_OPT_f)
 409                         break; /* -f USER: success without asking passwd */
 410
 411                 if (pw->pw_uid == 0 && !check_securetty(short_tty))
 412                         goto auth_failed;
 413
 414                 /* Don't check the password if password entry is empty (!) */
 415                 if (!pw->pw_passwd[0])
 416                         break;
 417  fake_it:
 418                 /* Password reading and authorization takes place here.
 419                  * Note that reads (in no-echo mode) trash tty attributes.
 420                  * If we get interrupted by SIGALRM, we need to restore attrs.
 421                  */
 422                 if (correct_password(pw))
 423                         break;
 424 #endif /* ENABLE_PAM */
 425  auth_failed:
 426                 opt &= ~LOGIN_OPT_f;
 427                 bb_do_delay(LOGIN_FAIL_DELAY);
 428                 /* TODO: doesn't sound like correct English phrase to me */
 429                 puts("Login incorrect");
 430                 if (++count == 3) {
 431                         syslog(LOG_WARNING, "invalid password for '%s'%s",
 432                                                 username, fromhost);
 433
 434                         if (ENABLE_FEATURE_CLEAN_UP)
 435                                 free(fromhost);
 436
 437                         return EXIT_FAILURE;
 438                 }
 439                 username[0] = '\0';
 440         } /* while (1) */
 441
 442         alarm(0);
 443         /* We can ignore /etc/nologin if we are logging in as root,
 444          * it doesn't matter whether we are run by root or not */
 445         if (pw->pw_uid != 0)
 446                 die_if_nologin();
 447
 448 #if ENABLE_LOGIN_SESSION_AS_CHILD
 449         child_pid = vfork();
 450         if (child_pid != 0) {
 451                 if (child_pid < 0)
 452                         bb_perror_msg("vfork");
 453                 else {
 454                         if (safe_waitpid(child_pid, NULL, 0) == -1)
 455                                 bb_perror_msg("waitpid");
 456                         update_utmp(child_pid, DEAD_PROCESS, NULL, NULL, NULL);
 457                 }
 458                 IF_PAM(login_pam_end(pamh);)
 459                 return 0;
 460         }
 461 #endif
 462
 463         IF_SELINUX(initselinux(username, full_tty, &user_sid);)
 464
 465         /* Try these, but don't complain if they fail.
 466          * _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
 467         fchown(0, pw->pw_uid, pw->pw_gid);
 468         fchmod(0, 0600);
 469
 470         update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
 471
 472         /* We trust environment only if we run by root */
 473         if (ENABLE_LOGIN_SCRIPTS && run_by_root)
 474                 run_login_script(pw, full_tty);
 475
 476         change_identity(pw);
 477         setup_environment(pw->pw_shell,
 478                         (!(opt & LOGIN_OPT_p) * SETUP_ENV_CLEARENV) + SETUP_ENV_CHANGEENV,
 479                         pw);
 480
 481 #if ENABLE_PAM
 482         /* Modules such as pam_env will setup the PAM environment,
 483          * which should be copied into the new environment. */
 484         pamenv = pam_getenvlist(pamh);
 485         if (pamenv) while (*pamenv) {
 486                 putenv(*pamenv);
 487                 pamenv++;
 488         }
 489 #endif
 490
 491         motd();
 492
 493         if (pw->pw_uid == 0)
 494                 syslog(LOG_INFO, "root login%s", fromhost);
 495
 496         if (ENABLE_FEATURE_CLEAN_UP)
 497                 free(fromhost);
 498
 499         /* well, a simple setexeccon() here would do the job as well,
 500          * but let's play the game for now */
 501         IF_SELINUX(set_current_security_context(user_sid);)
 502
 503         // util-linux login also does:
 504         // /* start new session */
 505         // setsid();
 506         // /* TIOCSCTTY: steal tty from other process group */
 507         // if (ioctl(0, TIOCSCTTY, 1)) error_msg...
 508         // BBox login used to do this (see above):
 509         // bb_setpgrp();
 510         // If this stuff is really needed, add it and explain why!
 511
 512         /* Set signals to defaults */
 513         /* Non-ignored signals revert to SIG_DFL on exec anyway */
 514         /*signal(SIGALRM, SIG_DFL);*/
 515
 516         /* Is this correct? This way user can ctrl-c out of /etc/profile,
 517          * potentially creating security breach (tested with bash 3.0).
 518          * But without this, bash 3.0 will not enable ctrl-c either.
 519          * Maybe bash is buggy?
 520          * Need to find out what standards say about /bin/login -
 521          * should we leave SIGINT etc enabled or disabled? */
 522         signal(SIGINT, SIG_DFL);
 523
 524         /* Exec login shell with no additional parameters */
 525         run_shell(pw->pw_shell, 1, NULL, NULL);
 526
 527         /* return EXIT_FAILURE; - not reached */
 528 }