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         /* Some users found 32 chars limit to be too low: */
  41         USERNAME_SIZE = 64,
  42         TTYNAME_SIZE = 32,
  43 };
  44
  45 struct globals {
  46         struct termios tty_attrs;
  47 } FIX_ALIASING;
  48 #define G (*(struct globals*)&bb_common_bufsiz1)
  49 #define INIT_G() do { } while (0)
  50
  51
  52 #if ENABLE_FEATURE_NOLOGIN
  53 static void die_if_nologin(void)
  54 {
  55         FILE *fp;
  56         int c;
  57         int empty = 1;
  58
  59         fp = fopen_for_read("/etc/nologin");
  60         if (!fp) /* assuming it does not exist */
  61                 return;
  62
  63         while ((c = getc(fp)) != EOF) {
  64                 if (c == '\n')
  65                         bb_putchar('\r');
  66                 bb_putchar(c);
  67                 empty = 0;
  68         }
  69         if (empty)
  70                 puts("\r\nSystem closed for routine maintenance\r");
  71
  72         fclose(fp);
  73         fflush_all();
  74         /* Users say that they do need this prior to exit: */
  75         tcdrain(STDOUT_FILENO);
  76         exit(EXIT_FAILURE);
  77 }
  78 #else
  79 # define die_if_nologin() ((void)0)
  80 #endif
  81
  82 #if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
  83 static int check_securetty(const char *short_tty)
  84 {
  85         char *buf = (char*)"/etc/securetty"; /* any non-NULL is ok */
  86         parser_t *parser = config_open2("/etc/securetty", fopen_for_read);
  87         while (config_read(parser, &buf, 1, 1, "# \t", PARSE_NORMAL)) {
  88                 if (strcmp(buf, short_tty) == 0)
  89                         break;
  90                 buf = NULL;
  91         }
  92         config_close(parser);
  93         /* buf != NULL here if config file was not found, empty
  94          * or line was found which equals short_tty */
  95         return buf != NULL;
  96 }
  97 #else
  98 static ALWAYS_INLINE int check_securetty(const char *short_tty UNUSED_PARAM) { return 1; }
  99 #endif
 100
 101 #if ENABLE_SELINUX
 102 static void initselinux(char *username, char *full_tty,
 103                                                 security_context_t *user_sid)
 104 {
 105         security_context_t old_tty_sid, new_tty_sid;
 106
 107         if (!is_selinux_enabled())
 108                 return;
 109
 110         if (get_default_context(username, NULL, user_sid)) {
 111                 bb_error_msg_and_die("can't get SID for %s", username);
 112         }
 113         if (getfilecon(full_tty, &old_tty_sid) < 0) {
 114                 bb_perror_msg_and_die("getfilecon(%s) failed", full_tty);
 115         }
 116         if (security_compute_relabel(*user_sid, old_tty_sid,
 117                                 SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
 118                 bb_perror_msg_and_die("security_change_sid(%s) failed", full_tty);
 119         }
 120         if (setfilecon(full_tty, new_tty_sid) != 0) {
 121                 bb_perror_msg_and_die("chsid(%s, %s) failed", full_tty, new_tty_sid);
 122         }
 123 }
 124 #endif
 125
 126 #if ENABLE_LOGIN_SCRIPTS
 127 static void run_login_script(struct passwd *pw, char *full_tty)
 128 {
 129         char *t_argv[2];
 130
 131         t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
 132         if (t_argv[0]) {
 133                 t_argv[1] = NULL;
 134                 xsetenv("LOGIN_TTY", full_tty);
 135                 xsetenv("LOGIN_USER", pw->pw_name);
 136                 xsetenv("LOGIN_UID", utoa(pw->pw_uid));
 137                 xsetenv("LOGIN_GID", utoa(pw->pw_gid));
 138                 xsetenv("LOGIN_SHELL", pw->pw_shell);
 139                 spawn_and_wait(t_argv); /* NOMMU-friendly */
 140                 unsetenv("LOGIN_TTY");
 141                 unsetenv("LOGIN_USER");
 142                 unsetenv("LOGIN_UID");
 143                 unsetenv("LOGIN_GID");
 144                 unsetenv("LOGIN_SHELL");
 145         }
 146 }
 147 #else
 148 void run_login_script(struct passwd *pw, char *full_tty);
 149 #endif
 150
 151 #if ENABLE_LOGIN_SESSION_AS_CHILD && ENABLE_PAM
 152 static void login_pam_end(pam_handle_t *pamh)
 153 {
 154         int pamret;
 155
 156         pamret = pam_setcred(pamh, PAM_DELETE_CRED);
 157         if (pamret != PAM_SUCCESS) {
 158                 bb_error_msg("pam_%s failed: %s (%d)", "setcred",
 159                         pam_strerror(pamh, pamret), pamret);
 160         }
 161         pamret = pam_close_session(pamh, 0);
 162         if (pamret != PAM_SUCCESS) {
 163                 bb_error_msg("pam_%s failed: %s (%d)", "close_session",
 164                         pam_strerror(pamh, pamret), pamret);
 165         }
 166         pamret = pam_end(pamh, pamret);
 167         if (pamret != PAM_SUCCESS) {
 168                 bb_error_msg("pam_%s failed: %s (%d)", "end",
 169                         pam_strerror(pamh, pamret), pamret);
 170         }
 171 }
 172 #endif /* ENABLE_PAM */
 173
 174 static void get_username_or_die(char *buf, int size_buf)
 175 {
 176         int c, cntdown;
 177
 178         cntdown = EMPTY_USERNAME_COUNT;
 179  prompt:
 180         print_login_prompt();
 181         /* skip whitespace */
 182         do {
 183                 c = getchar();
 184                 if (c == EOF)
 185                         exit(EXIT_FAILURE);
 186                 if (c == '\n') {
 187                         if (!--cntdown)
 188                                 exit(EXIT_FAILURE);
 189                         goto prompt;
 190                 }
 191         } while (isspace(c)); /* maybe isblank? */
 192
 193         *buf++ = c;
 194         if (!fgets(buf, size_buf-2, stdin))
 195                 exit(EXIT_FAILURE);
 196         if (!strchr(buf, '\n'))
 197                 exit(EXIT_FAILURE);
 198         while ((unsigned char)*buf > ' ')
 199                 buf++;
 200         *buf = '\0';
 201 }
 202
 203 static void motd(void)
 204 {
 205         int fd;
 206
 207         fd = open(bb_path_motd_file, O_RDONLY);
 208         if (fd >= 0) {
 209                 fflush_all();
 210                 bb_copyfd_eof(fd, STDOUT_FILENO);
 211                 close(fd);
 212         }
 213 }
 214
 215 static void alarm_handler(int sig UNUSED_PARAM)
 216 {
 217         /* This is the escape hatch! Poor serial line users and the like
 218          * arrive here when their connection is broken.
 219          * We don't want to block here */
 220         ndelay_on(STDOUT_FILENO);
 221         /* Test for correct attr restoring:
 222          * run "getty 0 -" from a shell, enter bogus username, stop at
 223          * password prompt, let it time out. Without the tcsetattr below,
 224          * when you are back at shell prompt, echo will be still off.
 225          */
 226         tcsetattr_stdin_TCSANOW(&G.tty_attrs);
 227         printf("\r\nLogin timed out after %u seconds\r\n", TIMEOUT);
 228         fflush_all();
 229         /* unix API is brain damaged regarding O_NONBLOCK,
 230          * we should undo it, or else we can affect other processes */
 231         ndelay_off(STDOUT_FILENO);
 232         _exit(EXIT_SUCCESS);
 233 }
 234
 235 int login_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 236 int login_main(int argc UNUSED_PARAM, char **argv)
 237 {
 238         enum {
 239                 LOGIN_OPT_f = (1<<0),
 240                 LOGIN_OPT_h = (1<<1),
 241                 LOGIN_OPT_p = (1<<2),
 242         };
 243         char *fromhost;
 244         char username[USERNAME_SIZE];
 245         int run_by_root;
 246         unsigned opt;
 247         int count = 0;
 248         struct passwd *pw;
 249         char *opt_host = NULL;
 250         char *opt_user = opt_user; /* for compiler */
 251         char *full_tty;
 252         char *short_tty;
 253         IF_SELINUX(security_context_t user_sid = NULL;)
 254 #if ENABLE_PAM
 255         int pamret;
 256         pam_handle_t *pamh;
 257         const char *pamuser;
 258         const char *failed_msg;
 259         struct passwd pwdstruct;
 260         char pwdbuf[256];
 261         char **pamenv;
 262 #endif
 263 #if ENABLE_LOGIN_SESSION_AS_CHILD
 264         pid_t child_pid;
 265 #endif
 266
 267         INIT_G();
 268
 269         /* More of suid paranoia if called by non-root: */
 270         /* Clear dangerous stuff, set PATH */
 271         run_by_root = !sanitize_env_if_suid();
 272
 273         /* Mandatory paranoia for suid applet:
 274          * ensure that fd# 0,1,2 are opened (at least to /dev/null)
 275          * and any extra open fd's are closed.
 276          * (The name of the function is misleading. Not daemonizing here.) */
 277         bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);
 278
 279         username[0] = '\0';
 280         opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
 281         if (opt & LOGIN_OPT_f) {
 282                 if (!run_by_root)
 283                         bb_error_msg_and_die("-f is for root only");
 284                 safe_strncpy(username, opt_user, sizeof(username));
 285         }
 286         argv += optind;
 287         if (argv[0]) /* user from command line (getty) */
 288                 safe_strncpy(username, argv[0], sizeof(username));
 289
 290         /* Save tty attributes - and by doing it, check that it's indeed a tty */
 291         if (tcgetattr(STDIN_FILENO, &G.tty_attrs) < 0
 292          || !isatty(STDOUT_FILENO)
 293          /*|| !isatty(STDERR_FILENO) - no, guess some people might want to redirect this */
 294         ) {
 295                 return EXIT_FAILURE;  /* Must be a terminal */
 296         }
 297
 298         /* We install timeout handler only _after_ we saved G.tty_attrs */
 299         signal(SIGALRM, alarm_handler);
 300         alarm(TIMEOUT);
 301
 302         /* Find out and memorize our tty name */
 303         full_tty = xmalloc_ttyname(STDIN_FILENO);
 304         if (!full_tty)
 305                 full_tty = xstrdup("UNKNOWN");
 306         short_tty = skip_dev_pfx(full_tty);
 307
 308         if (opt_host) {
 309                 fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
 310         } else {
 311                 fromhost = xasprintf(" on '%s'", short_tty);
 312         }
 313
 314         /* Was breaking "login <username>" from shell command line: */
 315         /*bb_setpgrp();*/
 316
 317         openlog(applet_name, LOG_PID | LOG_CONS, LOG_AUTH);
 318
 319         while (1) {
 320                 /* flush away any type-ahead (as getty does) */
 321                 tcflush(0, TCIFLUSH);
 322
 323                 if (!username[0])
 324                         get_username_or_die(username, sizeof(username));
 325
 326 #if ENABLE_PAM
 327                 pamret = pam_start("login", username, &conv, &pamh);
 328                 if (pamret != PAM_SUCCESS) {
 329                         failed_msg = "start";
 330                         goto pam_auth_failed;
 331                 }
 332                 /* set TTY (so things like securetty work) */
 333                 pamret = pam_set_item(pamh, PAM_TTY, short_tty);
 334                 if (pamret != PAM_SUCCESS) {
 335                         failed_msg = "set_item(TTY)";
 336                         goto pam_auth_failed;
 337                 }
 338                 /* set RHOST */
 339                 if (opt_host) {
 340                         pamret = pam_set_item(pamh, PAM_RHOST, opt_host);
 341                         if (pamret != PAM_SUCCESS) {
 342                                 failed_msg = "set_item(RHOST)";
 343                                 goto pam_auth_failed;
 344                         }
 345                 }
 346                 if (!(opt & LOGIN_OPT_f)) {
 347                         pamret = pam_authenticate(pamh, 0);
 348                         if (pamret != PAM_SUCCESS) {
 349                                 failed_msg = "authenticate";
 350                                 goto pam_auth_failed;
 351                                 /* TODO: or just "goto auth_failed"
 352                                  * since user seems to enter wrong password
 353                                  * (in this case pamret == 7)
 354                                  */
 355                         }
 356                 }
 357                 /* check that the account is healthy */
 358                 pamret = pam_acct_mgmt(pamh, 0);
 359                 if (pamret != PAM_SUCCESS) {
 360                         failed_msg = "acct_mgmt";
 361                         goto pam_auth_failed;
 362                 }
 363                 /* read user back */
 364                 pamuser = NULL;
 365                 /* gcc: "dereferencing type-punned pointer breaks aliasing rules..."
 366                  * thus we cast to (void*) */
 367                 if (pam_get_item(pamh, PAM_USER, (void*)&pamuser) != PAM_SUCCESS) {
 368                         failed_msg = "get_item(USER)";
 369                         goto pam_auth_failed;
 370                 }
 371                 if (!pamuser || !pamuser[0])
 372                         goto auth_failed;
 373                 safe_strncpy(username, pamuser, sizeof(username));
 374                 /* Don't use "pw = getpwnam(username);",
 375                  * PAM is said to be capable of destroying static storage
 376                  * used by getpwnam(). We are using safe(r) function */
 377                 pw = NULL;
 378                 getpwnam_r(username, &pwdstruct, pwdbuf, sizeof(pwdbuf), &pw);
 379                 if (!pw)
 380                         goto auth_failed;
 381                 pamret = pam_open_session(pamh, 0);
 382                 if (pamret != PAM_SUCCESS) {
 383                         failed_msg = "open_session";
 384                         goto pam_auth_failed;
 385                 }
 386                 pamret = pam_setcred(pamh, PAM_ESTABLISH_CRED);
 387                 if (pamret != PAM_SUCCESS) {
 388                         failed_msg = "setcred";
 389                         goto pam_auth_failed;
 390                 }
 391                 break; /* success, continue login process */
 392
 393  pam_auth_failed:
 394                 /* syslog, because we don't want potential attacker
 395                  * to know _why_ login failed */
 396                 syslog(LOG_WARNING, "pam_%s call failed: %s (%d)", failed_msg,
 397                                         pam_strerror(pamh, pamret), pamret);
 398                 safe_strncpy(username, "UNKNOWN", sizeof(username));
 399 #else /* not PAM */
 400                 pw = getpwnam(username);
 401                 if (!pw) {
 402                         strcpy(username, "UNKNOWN");
 403                         goto fake_it;
 404                 }
 405
 406                 if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
 407                         goto auth_failed;
 408
 409                 if (opt & LOGIN_OPT_f)
 410                         break; /* -f USER: success without asking passwd */
 411
 412                 if (pw->pw_uid == 0 && !check_securetty(short_tty))
 413                         goto auth_failed;
 414
 415                 /* Don't check the password if password entry is empty (!) */
 416                 if (!pw->pw_passwd[0])
 417                         break;
 418  fake_it:
 419                 /* Password reading and authorization takes place here.
 420                  * Note that reads (in no-echo mode) trash tty attributes.
 421                  * If we get interrupted by SIGALRM, we need to restore attrs.
 422                  */
 423                 if (correct_password(pw))
 424                         break;
 425 #endif /* ENABLE_PAM */
 426  auth_failed:
 427                 opt &= ~LOGIN_OPT_f;
 428                 bb_do_delay(LOGIN_FAIL_DELAY);
 429                 /* TODO: doesn't sound like correct English phrase to me */
 430                 puts("Login incorrect");
 431                 if (++count == 3) {
 432                         syslog(LOG_WARNING, "invalid password for '%s'%s",
 433                                                 username, fromhost);
 434
 435                         if (ENABLE_FEATURE_CLEAN_UP)
 436                                 free(fromhost);
 437
 438                         return EXIT_FAILURE;
 439                 }
 440                 username[0] = '\0';
 441         } /* while (1) */
 442
 443         alarm(0);
 444         /* We can ignore /etc/nologin if we are logging in as root,
 445          * it doesn't matter whether we are run by root or not */
 446         if (pw->pw_uid != 0)
 447                 die_if_nologin();
 448
 449 #if ENABLE_LOGIN_SESSION_AS_CHILD
 450         child_pid = vfork();
 451         if (child_pid != 0) {
 452                 if (child_pid < 0)
 453                         bb_perror_msg("vfork");
 454                 else {
 455                         if (safe_waitpid(child_pid, NULL, 0) == -1)
 456                                 bb_perror_msg("waitpid");
 457                         update_utmp(child_pid, DEAD_PROCESS, NULL, NULL, NULL);
 458                 }
 459                 IF_PAM(login_pam_end(pamh);)
 460                 return 0;
 461         }
 462 #endif
 463
 464         IF_SELINUX(initselinux(username, full_tty, &user_sid);)
 465
 466         /* Try these, but don't complain if they fail.
 467          * _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
 468         fchown(0, pw->pw_uid, pw->pw_gid);
 469         fchmod(0, 0600);
 470
 471         update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
 472
 473         /* We trust environment only if we run by root */
 474         if (ENABLE_LOGIN_SCRIPTS && run_by_root)
 475                 run_login_script(pw, full_tty);
 476
 477         change_identity(pw);
 478         setup_environment(pw->pw_shell,
 479                         (!(opt & LOGIN_OPT_p) * SETUP_ENV_CLEARENV) + SETUP_ENV_CHANGEENV,
 480                         pw);
 481
 482 #if ENABLE_PAM
 483         /* Modules such as pam_env will setup the PAM environment,
 484          * which should be copied into the new environment. */
 485         pamenv = pam_getenvlist(pamh);
 486         if (pamenv) while (*pamenv) {
 487                 putenv(*pamenv);
 488                 pamenv++;
 489         }
 490 #endif
 491
 492         motd();
 493
 494         if (pw->pw_uid == 0)
 495                 syslog(LOG_INFO, "root login%s", fromhost);
 496
 497         if (ENABLE_FEATURE_CLEAN_UP)
 498                 free(fromhost);
 499
 500         /* well, a simple setexeccon() here would do the job as well,
 501          * but let's play the game for now */
 502         IF_SELINUX(set_current_security_context(user_sid);)
 503
 504         // util-linux login also does:
 505         // /* start new session */
 506         // setsid();
 507         // /* TIOCSCTTY: steal tty from other process group */
 508         // if (ioctl(0, TIOCSCTTY, 1)) error_msg...
 509         // BBox login used to do this (see above):
 510         // bb_setpgrp();
 511         // If this stuff is really needed, add it and explain why!
 512
 513         /* Set signals to defaults */
 514         /* Non-ignored signals revert to SIG_DFL on exec anyway */
 515         /*signal(SIGALRM, SIG_DFL);*/
 516
 517         /* Is this correct? This way user can ctrl-c out of /etc/profile,
 518          * potentially creating security breach (tested with bash 3.0).
 519          * But without this, bash 3.0 will not enable ctrl-c either.
 520          * Maybe bash is buggy?
 521          * Need to find out what standards say about /bin/login -
 522          * should we leave SIGINT etc enabled or disabled? */
 523         signal(SIGINT, SIG_DFL);
 524
 525         /* Exec login shell with no additional parameters */
 526         run_shell(pw->pw_shell, 1, NULL, NULL);
 527
 528         /* return EXIT_FAILURE; - not reached */
 529 }