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 //config:config LOGIN
   6 //config:       bool "login (25 kb)"
   7 //config:       default y
   8 //config:       select FEATURE_SYSLOG
   9 //config:       help
  10 //config:       login is used when signing onto a system.
  11 //config:
  12 //config:       Note that busybox binary must be setuid root for this applet to
  13 //config:       work properly.
  14 //config:
  15 //config:config LOGIN_SESSION_AS_CHILD
  16 //config:       bool "Run logged in session in a child process"
  17 //config:       default y if PAM
  18 //config:       depends on LOGIN
  19 //config:       help
  20 //config:       Run the logged in session in a child process.  This allows
  21 //config:       login to clean up things such as utmp entries or PAM sessions
  22 //config:       when the login session is complete.  If you use PAM, you
  23 //config:       almost always would want this to be set to Y, else PAM session
  24 //config:       will not be cleaned up.
  25 //config:
  26 //config:config LOGIN_SCRIPTS
  27 //config:       bool "Support login scripts"
  28 //config:       depends on LOGIN
  29 //config:       default y
  30 //config:       help
  31 //config:       Enable this if you want login to execute $LOGIN_PRE_SUID_SCRIPT
  32 //config:       just prior to switching from root to logged-in user.
  33 //config:
  34 //config:config FEATURE_NOLOGIN
  35 //config:       bool "Support /etc/nologin"
  36 //config:       default y
  37 //config:       depends on LOGIN
  38 //config:       help
  39 //config:       The file /etc/nologin is used by (some versions of) login(1).
  40 //config:       If it exists, non-root logins are prohibited.
  41 //config:
  42 //config:config FEATURE_SECURETTY
  43 //config:       bool "Support /etc/securetty"
  44 //config:       default y
  45 //config:       depends on LOGIN
  46 //config:       help
  47 //config:       The file /etc/securetty is used by (some versions of) login(1).
  48 //config:       The file contains the device names of tty lines (one per line,
  49 //config:       without leading /dev/) on which root is allowed to login.
  50
  51 //applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */
  52 //applet:IF_LOGIN(APPLET(login, BB_DIR_BIN, BB_SUID_REQUIRE))
  53
  54 //kbuild:lib-$(CONFIG_LOGIN) += login.o
  55
  56 //usage:#define login_trivial_usage
  57 //usage:       "[-p] [-h HOST] [[-f] USER]"
  58 //usage:#define login_full_usage "\n\n"
  59 //usage:       "Begin a new session on the system\n"
  60 //usage:     "\n        -f      Don't authenticate (user already authenticated)"
  61 //usage:     "\n        -h HOST Host user came from (for network logins)"
  62 //usage:     "\n        -p      Preserve environment"
  63 //usage:     "\n"
  64 //usage:     "\n$LOGIN_TIMEOUT          Seconds (default 60, 0 - disable)"
  65 //usage:        IF_LOGIN_SCRIPTS(
  66 //usage:     "\n$LOGIN_PRE_SUID_SCRIPT  Execute before user ID change"
  67 //usage:        )
  68
  69 #include "libbb.h"
  70 #include "common_bufsiz.h"
  71 #include <syslog.h>
  72
  73 #if ENABLE_SELINUX
  74 # include <selinux/selinux.h>  /* for is_selinux_enabled()  */
  75 # include <selinux/get_context_list.h> /* for get_default_context() */
  76 # /* from deprecated <selinux/flask.h>: */
  77 # undef  SECCLASS_CHR_FILE
  78 # define SECCLASS_CHR_FILE 10
  79 #endif
  80
  81 #if ENABLE_PAM
  82 /* PAM may include <locale.h>. We may need to undefine bbox's stub define: */
  83 # undef setlocale
  84 /* For some obscure reason, PAM is not in pam/xxx, but in security/xxx.
  85  * Apparently they like to confuse people. */
  86 # include <security/pam_appl.h>
  87 # include <security/pam_misc.h>
  88
  89 # if 0
  90 /* This supposedly can be used to avoid double password prompt,
  91  * if used instead of standard misc_conv():
  92  *
  93  * "When we want to authenticate first with local method and then with tacacs for example,
  94  *  the password is asked for local method and if not good is asked a second time for tacacs.
  95  *  So if we want to authenticate a user with tacacs, and the user exists localy, the password is
  96  *  asked two times before authentication is accepted."
  97  *
  98  * However, code looks shaky. For example, why misc_conv() return value is ignored?
  99  * Are msg[i] and resp[i] indexes handled correctly?
 100  */
 101 static char *passwd = NULL;
 102 static int my_conv(int num_msg, const struct pam_message **msg,
 103                 struct pam_response **resp, void *data)
 104 {
 105         int i;
 106         for (i = 0; i < num_msg; i++) {
 107                 switch (msg[i]->msg_style) {
 108                 case PAM_PROMPT_ECHO_OFF:
 109                         if (passwd == NULL) {
 110                                 misc_conv(num_msg, msg, resp, data);
 111                                 passwd = xstrdup(resp[i]->resp);
 112                                 return PAM_SUCCESS;
 113                         }
 114
 115                         resp[0] = xzalloc(sizeof(struct pam_response));
 116                         resp[0]->resp = passwd;
 117                         passwd = NULL;
 118                         resp[0]->resp_retcode = PAM_SUCCESS;
 119                         resp[1] = NULL;
 120                         return PAM_SUCCESS;
 121
 122                 default:
 123                         break;
 124                 }
 125         }
 126
 127         return PAM_SUCCESS;
 128 }
 129 # endif
 130
 131 static const struct pam_conv conv = {
 132         misc_conv,
 133         NULL
 134 };
 135 #endif
 136
 137 enum {
 138         EMPTY_USERNAME_COUNT = 10,
 139         /* Some users found 32 chars limit to be too low: */
 140         USERNAME_SIZE = 64,
 141         TTYNAME_SIZE = 32,
 142 };
 143
 144 struct globals {
 145         struct termios tty_attrs;
 146         int timeout;
 147 } FIX_ALIASING;
 148 #define G (*(struct globals*)bb_common_bufsiz1)
 149 #define INIT_G() do { setup_common_bufsiz(); } while (0)
 150
 151
 152 #if ENABLE_FEATURE_NOLOGIN
 153 static void die_if_nologin(void)
 154 {
 155         FILE *fp;
 156         int c;
 157         int empty = 1;
 158
 159         fp = fopen_for_read("/etc/nologin");
 160         if (!fp) /* assuming it does not exist */
 161                 return;
 162
 163         while ((c = getc(fp)) != EOF) {
 164                 if (c == '\n')
 165                         bb_putchar('\r');
 166                 bb_putchar(c);
 167                 empty = 0;
 168         }
 169         if (empty)
 170                 puts("\r\nSystem closed for routine maintenance\r");
 171
 172         fclose(fp);
 173         fflush_all();
 174         /* Users say that they do need this prior to exit: */
 175         tcdrain(STDOUT_FILENO);
 176         exit_FAILURE();
 177 }
 178 #else
 179 # define die_if_nologin() ((void)0)
 180 #endif
 181
 182 #if ENABLE_SELINUX
 183 static void initselinux(char *username, char *full_tty,
 184                                                 security_context_t *user_sid)
 185 {
 186         security_context_t old_tty_sid, new_tty_sid;
 187
 188         if (!is_selinux_enabled())
 189                 return;
 190
 191         if (get_default_context(username, NULL, user_sid)) {
 192                 bb_error_msg_and_die("can't get SID for %s", username);
 193         }
 194         if (getfilecon(full_tty, &old_tty_sid) < 0) {
 195                 bb_perror_msg_and_die("getfilecon(%s) failed", full_tty);
 196         }
 197         if (security_compute_relabel(*user_sid, old_tty_sid,
 198                                 SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
 199                 bb_perror_msg_and_die("security_change_sid(%s) failed", full_tty);
 200         }
 201         if (setfilecon(full_tty, new_tty_sid) != 0) {
 202                 bb_perror_msg_and_die("chsid(%s, %s) failed", full_tty, new_tty_sid);
 203         }
 204 }
 205 #endif
 206
 207 #if ENABLE_LOGIN_SCRIPTS
 208 static void run_login_script(struct passwd *pw, char *full_tty)
 209 {
 210         char *t_argv[2];
 211
 212         t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
 213         if (t_argv[0]) {
 214                 t_argv[1] = NULL;
 215                 xsetenv("LOGIN_TTY", full_tty);
 216                 xsetenv("LOGIN_USER", pw->pw_name);
 217                 xsetenv("LOGIN_UID", utoa(pw->pw_uid));
 218                 xsetenv("LOGIN_GID", utoa(pw->pw_gid));
 219                 xsetenv("LOGIN_SHELL", pw->pw_shell);
 220                 spawn_and_wait(t_argv); /* NOMMU-friendly */
 221                 unsetenv("LOGIN_TTY");
 222                 unsetenv("LOGIN_USER");
 223                 unsetenv("LOGIN_UID");
 224                 unsetenv("LOGIN_GID");
 225                 unsetenv("LOGIN_SHELL");
 226         }
 227 }
 228 #else
 229 void run_login_script(struct passwd *pw, char *full_tty);
 230 #endif
 231
 232 #if ENABLE_LOGIN_SESSION_AS_CHILD && ENABLE_PAM
 233 static void login_pam_end(pam_handle_t *pamh)
 234 {
 235         int pamret;
 236
 237         pamret = pam_setcred(pamh, PAM_DELETE_CRED);
 238         if (pamret != PAM_SUCCESS) {
 239                 bb_error_msg("pam_%s failed: %s (%d)", "setcred",
 240                         pam_strerror(pamh, pamret), pamret);
 241         }
 242         pamret = pam_close_session(pamh, 0);
 243         if (pamret != PAM_SUCCESS) {
 244                 bb_error_msg("pam_%s failed: %s (%d)", "close_session",
 245                         pam_strerror(pamh, pamret), pamret);
 246         }
 247         pamret = pam_end(pamh, pamret);
 248         if (pamret != PAM_SUCCESS) {
 249                 bb_error_msg("pam_%s failed: %s (%d)", "end",
 250                         pam_strerror(pamh, pamret), pamret);
 251         }
 252 }
 253 #else
 254 # define login_pam_end(pamh) ((void)0)
 255 #endif
 256
 257 static void get_username_or_die(char *buf, int size_buf)
 258 {
 259         int c, cntdown;
 260
 261         cntdown = EMPTY_USERNAME_COUNT;
 262  prompt:
 263         print_login_prompt();
 264         /* skip whitespace */
 265         do {
 266                 c = getchar();
 267                 if (c == EOF)
 268                         exit_FAILURE();
 269                 if (c == '\n') {
 270                         if (!--cntdown)
 271                                 exit_FAILURE();
 272                         goto prompt;
 273                 }
 274         } while (isspace(c)); /* maybe isblank? */
 275
 276         *buf++ = c;
 277         if (!fgets(buf, size_buf-2, stdin))
 278                 exit_FAILURE();
 279         if (!strchr(buf, '\n'))
 280                 exit_FAILURE();
 281         while ((unsigned char)*buf > ' ')
 282                 buf++;
 283         *buf = '\0';
 284 }
 285
 286 static void motd(void)
 287 {
 288         int fd;
 289
 290         fd = open(bb_path_motd_file, O_RDONLY);
 291         if (fd >= 0) {
 292                 fflush_all();
 293                 bb_copyfd_eof(fd, STDOUT_FILENO);
 294                 close(fd);
 295         }
 296 }
 297
 298 static void alarm_handler(int sig UNUSED_PARAM)
 299 {
 300         /* This is the escape hatch! Poor serial line users and the like
 301          * arrive here when their connection is broken.
 302          * We don't want to block here */
 303         ndelay_on(STDOUT_FILENO);
 304         /* Test for correct attr restoring:
 305          * run "getty 0 -" from a shell, enter bogus username, stop at
 306          * password prompt, let it time out. Without the tcsetattr below,
 307          * when you are back at shell prompt, echo will be still off.
 308          */
 309         tcsetattr_stdin_TCSANOW(&G.tty_attrs);
 310         printf("\r\nLogin timed out after %u seconds\r\n", G.timeout);
 311         fflush_all();
 312         /* unix API is brain damaged regarding O_NONBLOCK,
 313          * we should undo it, or else we can affect other processes */
 314         ndelay_off(STDOUT_FILENO);
 315         _exit_SUCCESS();
 316 }
 317
 318 int login_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 319 int login_main(int argc UNUSED_PARAM, char **argv)
 320 {
 321         enum {
 322                 LOGIN_OPT_f = (1<<0),
 323                 LOGIN_OPT_h = (1<<1),
 324                 LOGIN_OPT_p = (1<<2),
 325         };
 326         char *fromhost;
 327         char username[USERNAME_SIZE];
 328         int run_by_root;
 329         unsigned opt;
 330         int count = 0;
 331         struct passwd *pw;
 332         char *opt_host = NULL;
 333         char *opt_user = opt_user; /* for compiler */
 334         char *full_tty;
 335         char *short_tty;
 336         IF_SELINUX(security_context_t user_sid = NULL;)
 337 #if ENABLE_PAM
 338         int pamret;
 339         pam_handle_t *pamh;
 340         const char *pamuser;
 341         const char *failed_msg;
 342         struct passwd pwdstruct;
 343         char pwdbuf[256];
 344         char **pamenv;
 345 #endif
 346 #if ENABLE_LOGIN_SESSION_AS_CHILD
 347         pid_t child_pid;
 348 #endif
 349         IF_FEATURE_UTMP(pid_t my_pid;)
 350
 351         INIT_G();
 352
 353         G.timeout = xatoi_positive(getenv("LOGIN_TIMEOUT") ? : "60");
 354
 355         /* More of suid paranoia if called by non-root: */
 356         /* Clear dangerous stuff, set PATH */
 357         run_by_root = !sanitize_env_if_suid();
 358
 359         /* Mandatory paranoia for suid applet:
 360          * ensure that fd# 0,1,2 are opened (at least to /dev/null)
 361          * and any extra open fd's are closed.
 362          */
 363         bb_daemon_helper(DAEMON_CLOSE_EXTRA_FDS);
 364
 365         username[0] = '\0';
 366         opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
 367         if (opt & LOGIN_OPT_f) {
 368                 if (!run_by_root)
 369                         bb_simple_error_msg_and_die("-f is for root only");
 370                 safe_strncpy(username, opt_user, sizeof(username));
 371         }
 372         argv += optind;
 373         if (argv[0]) /* user from command line (getty) */
 374                 safe_strncpy(username, argv[0], sizeof(username));
 375
 376         /* Save tty attributes - and by doing it, check that it's indeed a tty */
 377         if (tcgetattr(STDIN_FILENO, &G.tty_attrs) < 0
 378          || !isatty(STDOUT_FILENO)
 379          /*|| !isatty(STDERR_FILENO) - no, guess some people might want to redirect this */
 380         ) {
 381                 return EXIT_FAILURE;  /* Must be a terminal */
 382         }
 383
 384         /* We install timeout handler only _after_ we saved G.tty_attrs */
 385         signal(SIGALRM, alarm_handler);
 386         alarm(G.timeout);
 387
 388         /* Find out and memorize our tty name */
 389         full_tty = xmalloc_ttyname(STDIN_FILENO);
 390         if (!full_tty)
 391                 full_tty = xstrdup("UNKNOWN");
 392         short_tty = skip_dev_pfx(full_tty);
 393
 394         if (opt_host) {
 395                 fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
 396         } else {
 397                 fromhost = xasprintf(" on '%s'", short_tty);
 398         }
 399
 400         /* Was breaking "login <username>" from shell command line: */
 401         /*bb_setpgrp();*/
 402
 403         openlog(applet_name, LOG_PID | LOG_CONS, LOG_AUTH);
 404
 405         while (1) {
 406                 /* flush away any type-ahead (as getty does) */
 407                 tcflush(0, TCIFLUSH);
 408
 409                 if (!username[0])
 410                         get_username_or_die(username, sizeof(username));
 411
 412 #if ENABLE_PAM
 413                 pamret = pam_start("login", username, &conv, &pamh);
 414                 if (pamret != PAM_SUCCESS) {
 415                         failed_msg = "start";
 416                         goto pam_auth_failed;
 417                 }
 418                 /* set TTY (so things like securetty work) */
 419                 pamret = pam_set_item(pamh, PAM_TTY, short_tty);
 420                 if (pamret != PAM_SUCCESS) {
 421                         failed_msg = "set_item(TTY)";
 422                         goto pam_auth_failed;
 423                 }
 424                 /* set RHOST */
 425                 if (opt_host) {
 426                         pamret = pam_set_item(pamh, PAM_RHOST, opt_host);
 427                         if (pamret != PAM_SUCCESS) {
 428                                 failed_msg = "set_item(RHOST)";
 429                                 goto pam_auth_failed;
 430                         }
 431                 }
 432                 if (!(opt & LOGIN_OPT_f)) {
 433                         pamret = pam_authenticate(pamh, 0);
 434                         if (pamret != PAM_SUCCESS) {
 435                                 failed_msg = "authenticate";
 436                                 goto pam_auth_failed;
 437                                 /* TODO: or just "goto auth_failed"
 438                                  * since user seems to enter wrong password
 439                                  * (in this case pamret == 7)
 440                                  */
 441                         }
 442                 }
 443                 /* check that the account is healthy */
 444                 pamret = pam_acct_mgmt(pamh, 0);
 445                 if (pamret == PAM_NEW_AUTHTOK_REQD) {
 446                         pamret = pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK);
 447                 }
 448                 if (pamret != PAM_SUCCESS) {
 449                         failed_msg = "acct_mgmt";
 450                         goto pam_auth_failed;
 451                 }
 452                 /* read user back */
 453                 pamuser = NULL;
 454                 /* gcc: "dereferencing type-punned pointer breaks aliasing rules..."
 455                  * thus we cast to (void*) */
 456                 if (pam_get_item(pamh, PAM_USER, (void*)&pamuser) != PAM_SUCCESS) {
 457                         failed_msg = "get_item(USER)";
 458                         goto pam_auth_failed;
 459                 }
 460                 if (!pamuser || !pamuser[0])
 461                         goto auth_failed;
 462                 safe_strncpy(username, pamuser, sizeof(username));
 463                 /* Don't use "pw = getpwnam(username);",
 464                  * PAM is said to be capable of destroying static storage
 465                  * used by getpwnam(). We are using safe(r) function */
 466                 pw = NULL;
 467                 getpwnam_r(username, &pwdstruct, pwdbuf, sizeof(pwdbuf), &pw);
 468                 if (!pw)
 469                         goto auth_failed;
 470                 pamret = pam_open_session(pamh, 0);
 471                 if (pamret != PAM_SUCCESS) {
 472                         failed_msg = "open_session";
 473                         goto pam_auth_failed;
 474                 }
 475                 pamret = pam_setcred(pamh, PAM_ESTABLISH_CRED);
 476                 if (pamret != PAM_SUCCESS) {
 477                         failed_msg = "setcred";
 478                         goto pam_auth_failed;
 479                 }
 480                 break; /* success, continue login process */
 481
 482  pam_auth_failed:
 483                 /* syslog, because we don't want potential attacker
 484                  * to know _why_ login failed */
 485                 syslog(LOG_WARNING, "pam_%s call failed: %s (%d)", failed_msg,
 486                                         pam_strerror(pamh, pamret), pamret);
 487                 login_pam_end(pamh);
 488                 safe_strncpy(username, "UNKNOWN", sizeof(username));
 489 #else /* not PAM */
 490                 pw = getpwnam(username);
 491                 if (!pw) {
 492                         strcpy(username, "UNKNOWN");
 493                         goto fake_it;
 494                 }
 495
 496                 if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
 497                         goto auth_failed;
 498
 499                 if (opt & LOGIN_OPT_f)
 500                         break; /* -f USER: success without asking passwd */
 501
 502                 if (pw->pw_uid == 0 && !is_tty_secure(short_tty))
 503                         goto auth_failed;
 504
 505                 /* Don't check the password if password entry is empty (!) */
 506                 if (!pw->pw_passwd[0])
 507                         break;
 508  fake_it:
 509                 /* Password reading and authorization takes place here.
 510                  * Note that reads (in no-echo mode) trash tty attributes.
 511                  * If we get interrupted by SIGALRM, we need to restore attrs.
 512                  */
 513                 if (ask_and_check_password(pw) > 0)
 514                         break;
 515 #endif /* ENABLE_PAM */
 516  auth_failed:
 517                 opt &= ~LOGIN_OPT_f;
 518                 pause_after_failed_login();
 519                 /* TODO: doesn't sound like correct English phrase to me */
 520                 puts("Login incorrect");
 521                 syslog(LOG_WARNING, "invalid password for '%s'%s",
 522                                         username, fromhost);
 523                 if (++count == 3) {
 524                         if (ENABLE_FEATURE_CLEAN_UP)
 525                                 free(fromhost);
 526                         return EXIT_FAILURE;
 527                 }
 528                 username[0] = '\0';
 529         } /* while (1) */
 530
 531         alarm(0);
 532         /* We can ignore /etc/nologin if we are logging in as root,
 533          * it doesn't matter whether we are run by root or not */
 534         if (pw->pw_uid != 0)
 535                 die_if_nologin();
 536
 537         IF_FEATURE_UTMP(my_pid = getpid();)
 538         update_utmp(my_pid, USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
 539
 540 #if ENABLE_LOGIN_SESSION_AS_CHILD
 541         child_pid = vfork();
 542         if (child_pid != 0) {
 543                 if (child_pid < 0)
 544                         bb_simple_perror_msg("vfork");
 545                 else {
 546                         wait_for_exitstatus(child_pid);
 547                 }
 548                 update_utmp_DEAD_PROCESS(my_pid);
 549                 login_pam_end(pamh);
 550                 return 0;
 551         }
 552 #endif
 553
 554         IF_SELINUX(initselinux(username, full_tty, &user_sid);)
 555
 556         /* Try these, but don't complain if they fail.
 557          * _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
 558         fchown(0, pw->pw_uid, pw->pw_gid);
 559         fchmod(0, 0600);
 560
 561         /* We trust environment only if we run by root */
 562         if (ENABLE_LOGIN_SCRIPTS && run_by_root)
 563                 run_login_script(pw, full_tty);
 564
 565         change_identity(pw);
 566         setup_environment(pw->pw_shell,
 567                         (!(opt & LOGIN_OPT_p) * SETUP_ENV_CLEARENV)
 568                                 + SETUP_ENV_CHANGEENV
 569                                 + SETUP_ENV_CHDIR,
 570                         pw);
 571
 572 #if ENABLE_PAM
 573         /* Modules such as pam_env will setup the PAM environment,
 574          * which should be copied into the new environment. */
 575         pamenv = pam_getenvlist(pamh);
 576         if (pamenv) while (*pamenv) {
 577                 putenv(*pamenv);
 578                 pamenv++;
 579         }
 580 #endif
 581
 582         if (access(".hushlogin", F_OK) != 0)
 583                 motd();
 584
 585         if (pw->pw_uid == 0)
 586                 syslog(LOG_INFO, "root login%s", fromhost);
 587
 588         if (ENABLE_FEATURE_CLEAN_UP)
 589                 free(fromhost);
 590
 591         /* well, a simple setexeccon() here would do the job as well,
 592          * but let's play the game for now */
 593         IF_SELINUX(set_current_security_context(user_sid);)
 594
 595         // util-linux login also does:
 596         // /* start new session */
 597         // setsid();
 598         // /* TIOCSCTTY: steal tty from other process group */
 599         // if (ioctl(0, TIOCSCTTY, 1)) error_msg...
 600         // BBox login used to do this (see above):
 601         // bb_setpgrp();
 602         // If this stuff is really needed, add it and explain why!
 603
 604         /* Set signals to defaults */
 605         /* Non-ignored signals revert to SIG_DFL on exec anyway */
 606         /*signal(SIGALRM, SIG_DFL);*/
 607
 608         /* Is this correct? This way user can ctrl-c out of /etc/profile,
 609          * potentially creating security breach (tested with bash 3.0).
 610          * But without this, bash 3.0 will not enable ctrl-c either.
 611          * Maybe bash is buggy?
 612          * Need to find out what standards say about /bin/login -
 613          * should we leave SIGINT etc enabled or disabled?
 614          * Also note: sulogin does not do it! Why?
 615          */
 616         signal(SIGINT, SIG_DFL);
 617
 618         /* Exec login shell with no additional parameters */
 619         exec_login_shell(pw->pw_shell);
 620
 621         /* return EXIT_FAILURE; - not reached */
 622 }