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