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 tarball for details.
   4  */
   5
   6 #include "libbb.h"
   7 #include <syslog.h>
   8 #include <utmp.h>
   9 #include <sys/resource.h>
  10
  11 #if ENABLE_SELINUX
  12 #include <selinux/selinux.h>  /* for is_selinux_enabled()  */
  13 #include <selinux/get_context_list.h> /* for get_default_context() */
  14 #include <selinux/flask.h> /* for security class definitions  */
  15 #endif
  16
  17 #if ENABLE_PAM
  18 /* PAM may include <locale.h>. We may need to undefine bbox's stub define: */
  19 #undef setlocale
  20 /* For some obscure reason, PAM is not in pam/xxx, but in security/xxx.
  21  * Apparently they like to confuse people. */
  22 #include <security/pam_appl.h>
  23 #include <security/pam_misc.h>
  24 static const struct pam_conv conv = {
  25         misc_conv,
  26         NULL
  27 };
  28 #endif
  29
  30 enum {
  31         TIMEOUT = 60,
  32         EMPTY_USERNAME_COUNT = 10,
  33         USERNAME_SIZE = 32,
  34         TTYNAME_SIZE = 32,
  35 };
  36
  37 static char* short_tty;
  38
  39 #if ENABLE_FEATURE_UTMP
  40 /* vv  Taken from tinylogin utmp.c  vv */
  41 /*
  42  * read_or_build_utent - see if utmp file is correct for this process
  43  *
  44  *      System V is very picky about the contents of the utmp file
  45  *      and requires that a slot for the current process exist.
  46  *      The utmp file is scanned for an entry with the same process
  47  *      ID.  If no entry exists the process exits with a message.
  48  *
  49  *      The "picky" flag is for network and other logins that may
  50  *      use special flags.  It allows the pid checks to be overridden.
  51  *      This means that getty should never invoke login with any
  52  *      command line flags.
  53  */
  54
  55 static void read_or_build_utent(struct utmp *utptr, int run_by_root)
  56 {
  57         struct utmp *ut;
  58         pid_t pid = getpid();
  59
  60         setutent();
  61
  62         /* First, try to find a valid utmp entry for this process.  */
  63         /* If there is one, just use it.  */
  64         while ((ut = getutent()) != NULL)
  65                 if (ut->ut_pid == pid && ut->ut_line[0] && ut->ut_id[0]
  66                  && (ut->ut_type == LOGIN_PROCESS || ut->ut_type == USER_PROCESS)
  67                 ) {
  68                         *utptr = *ut; /* struct copy */
  69                         if (run_by_root) /* why only for root? */
  70                                 memset(utptr->ut_host, 0, sizeof(utptr->ut_host));
  71                         return;
  72                 }
  73
  74 // Why? Do we require non-root to exec login from another
  75 // former login process (e.g. login shell)? Some login's have
  76 // login shells as children, so it won't work...
  77 //      if (!run_by_root)
  78 //              bb_error_msg_and_die("no utmp entry found");
  79
  80         /* Otherwise create a new one.  */
  81         memset(utptr, 0, sizeof(*utptr));
  82         utptr->ut_type = LOGIN_PROCESS;
  83         utptr->ut_pid = pid;
  84         strncpy(utptr->ut_line, short_tty, sizeof(utptr->ut_line));
  85         /* This one is only 4 chars wide. Try to fit something
  86          * remotely meaningful by skipping "tty"... */
  87         strncpy(utptr->ut_id, short_tty + 3, sizeof(utptr->ut_id));
  88         strncpy(utptr->ut_user, "LOGIN", sizeof(utptr->ut_user));
  89         utptr->ut_tv.tv_sec = time(NULL);
  90 }
  91
  92 /*
  93  * write_utent - put a USER_PROCESS entry in the utmp file
  94  *
  95  *      write_utent changes the type of the current utmp entry to
  96  *      USER_PROCESS.  the wtmp file will be updated as well.
  97  */
  98 static void write_utent(struct utmp *utptr, const char *username)
  99 {
 100         utptr->ut_type = USER_PROCESS;
 101         strncpy(utptr->ut_user, username, sizeof(utptr->ut_user));
 102         utptr->ut_tv.tv_sec = time(NULL);
 103         /* other fields already filled in by read_or_build_utent above */
 104         setutent();
 105         pututline(utptr);
 106         endutent();
 107 #if ENABLE_FEATURE_WTMP
 108         if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
 109                 close(creat(bb_path_wtmp_file, 0664));
 110         }
 111         updwtmp(bb_path_wtmp_file, utptr);
 112 #endif
 113 }
 114 #else /* !ENABLE_FEATURE_UTMP */
 115 #define read_or_build_utent(utptr, run_by_root) ((void)0)
 116 #define write_utent(utptr, username) ((void)0)
 117 #endif /* !ENABLE_FEATURE_UTMP */
 118
 119 #if ENABLE_FEATURE_NOLOGIN
 120 static void die_if_nologin(void)
 121 {
 122         FILE *fp;
 123         int c;
 124         int empty = 1;
 125
 126         fp = fopen_for_read("/etc/nologin");
 127         if (!fp) /* assuming it does not exist */
 128                 return;
 129
 130         while ((c = getc(fp)) != EOF) {
 131                 if (c == '\n')
 132                         bb_putchar('\r');
 133                 bb_putchar(c);
 134                 empty = 0;
 135         }
 136         if (empty)
 137                 puts("\r\nSystem closed for routine maintenance\r");
 138
 139         fclose(fp);
 140         fflush(NULL);
 141         /* Users say that they do need this prior to exit: */
 142         tcdrain(STDOUT_FILENO);
 143         exit(EXIT_FAILURE);
 144 }
 145 #else
 146 static ALWAYS_INLINE void die_if_nologin(void) {}
 147 #endif
 148
 149 #if ENABLE_FEATURE_SECURETTY && !ENABLE_PAM
 150 static int check_securetty(void)
 151 {
 152         char *buf = (char*)"/etc/securetty"; /* any non-NULL is ok */
 153         parser_t *parser = config_open2("/etc/securetty", fopen_for_read);
 154         while (config_read(parser, &buf, 1, 1, "# \t", PARSE_NORMAL)) {
 155                 if (strcmp(buf, short_tty) == 0)
 156                         break;
 157                 buf = NULL;
 158         }
 159         config_close(parser);
 160         /* buf != NULL here if config file was not found, empty
 161          * or line was found which equals short_tty */
 162         return buf != NULL;
 163 }
 164 #else
 165 static ALWAYS_INLINE int check_securetty(void) { return 1; }
 166 #endif
 167
 168 #if ENABLE_SELINUX
 169 static void initselinux(char *username, char *full_tty,
 170                                                 security_context_t *user_sid)
 171 {
 172         security_context_t old_tty_sid, new_tty_sid;
 173
 174         if (!is_selinux_enabled())
 175                 return;
 176
 177         if (get_default_context(username, NULL, user_sid)) {
 178                 bb_error_msg_and_die("cannot get SID for %s", username);
 179         }
 180         if (getfilecon(full_tty, &old_tty_sid) < 0) {
 181                 bb_perror_msg_and_die("getfilecon(%s) failed", full_tty);
 182         }
 183         if (security_compute_relabel(*user_sid, old_tty_sid,
 184                                 SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
 185                 bb_perror_msg_and_die("security_change_sid(%s) failed", full_tty);
 186         }
 187         if (setfilecon(full_tty, new_tty_sid) != 0) {
 188                 bb_perror_msg_and_die("chsid(%s, %s) failed", full_tty, new_tty_sid);
 189         }
 190 }
 191 #endif
 192
 193 #if ENABLE_LOGIN_SCRIPTS
 194 static void run_login_script(struct passwd *pw, char *full_tty)
 195 {
 196         char *t_argv[2];
 197
 198         t_argv[0] = getenv("LOGIN_PRE_SUID_SCRIPT");
 199         if (t_argv[0]) {
 200                 t_argv[1] = NULL;
 201                 xsetenv("LOGIN_TTY", full_tty);
 202                 xsetenv("LOGIN_USER", pw->pw_name);
 203                 xsetenv("LOGIN_UID", utoa(pw->pw_uid));
 204                 xsetenv("LOGIN_GID", utoa(pw->pw_gid));
 205                 xsetenv("LOGIN_SHELL", pw->pw_shell);
 206                 spawn_and_wait(t_argv); /* NOMMU-friendly */
 207                 unsetenv("LOGIN_TTY");
 208                 unsetenv("LOGIN_USER");
 209                 unsetenv("LOGIN_UID");
 210                 unsetenv("LOGIN_GID");
 211                 unsetenv("LOGIN_SHELL");
 212         }
 213 }
 214 #else
 215 void run_login_script(struct passwd *pw, char *full_tty);
 216 #endif
 217
 218 static void get_username_or_die(char *buf, int size_buf)
 219 {
 220         int c, cntdown;
 221
 222         cntdown = EMPTY_USERNAME_COUNT;
 223  prompt:
 224         print_login_prompt();
 225         /* skip whitespace */
 226         do {
 227                 c = getchar();
 228                 if (c == EOF) exit(EXIT_FAILURE);
 229                 if (c == '\n') {
 230                         if (!--cntdown) exit(EXIT_FAILURE);
 231                         goto prompt;
 232                 }
 233         } while (isspace(c));
 234
 235         *buf++ = c;
 236         if (!fgets(buf, size_buf-2, stdin))
 237                 exit(EXIT_FAILURE);
 238         if (!strchr(buf, '\n'))
 239                 exit(EXIT_FAILURE);
 240         while (isgraph(*buf)) buf++;
 241         *buf = '\0';
 242 }
 243
 244 static void motd(void)
 245 {
 246         int fd;
 247
 248         fd = open(bb_path_motd_file, O_RDONLY);
 249         if (fd >= 0) {
 250                 fflush(stdout);
 251                 bb_copyfd_eof(fd, STDOUT_FILENO);
 252                 close(fd);
 253         }
 254 }
 255
 256 static void alarm_handler(int sig UNUSED_PARAM)
 257 {
 258         /* This is the escape hatch!  Poor serial line users and the like
 259          * arrive here when their connection is broken.
 260          * We don't want to block here */
 261         ndelay_on(1);
 262         printf("\r\nLogin timed out after %d seconds\r\n", TIMEOUT);
 263         fflush(stdout);
 264         /* unix API is brain damaged regarding O_NONBLOCK,
 265          * we should undo it, or else we can affect other processes */
 266         ndelay_off(1);
 267         _exit(EXIT_SUCCESS);
 268 }
 269
 270 int login_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 271 int login_main(int argc UNUSED_PARAM, char **argv)
 272 {
 273         enum {
 274                 LOGIN_OPT_f = (1<<0),
 275                 LOGIN_OPT_h = (1<<1),
 276                 LOGIN_OPT_p = (1<<2),
 277         };
 278         char *fromhost;
 279         char username[USERNAME_SIZE];
 280         const char *tmp;
 281         int run_by_root;
 282         unsigned opt;
 283         int count = 0;
 284         struct passwd *pw;
 285         char *opt_host = opt_host; /* for compiler */
 286         char *opt_user = opt_user; /* for compiler */
 287         char *full_tty;
 288         USE_SELINUX(security_context_t user_sid = NULL;)
 289         USE_FEATURE_UTMP(struct utmp utent;)
 290 #if ENABLE_PAM
 291         int pamret;
 292         pam_handle_t *pamh;
 293         const char *pamuser;
 294         const char *failed_msg;
 295         struct passwd pwdstruct;
 296         char pwdbuf[256];
 297 #endif
 298
 299         username[0] = '\0';
 300         signal(SIGALRM, alarm_handler);
 301         alarm(TIMEOUT);
 302
 303         /* More of suid paranoia if called by non-root: */
 304         /* Clear dangerous stuff, set PATH */
 305         run_by_root = !sanitize_env_if_suid();
 306
 307         /* Mandatory paranoia for suid applet:
 308          * ensure that fd# 0,1,2 are opened (at least to /dev/null)
 309          * and any extra open fd's are closed.
 310          * (The name of the function is misleading. Not daemonizing here.) */
 311         bb_daemonize_or_rexec(DAEMON_ONLY_SANITIZE | DAEMON_CLOSE_EXTRA_FDS, NULL);
 312
 313         opt = getopt32(argv, "f:h:p", &opt_user, &opt_host);
 314         if (opt & LOGIN_OPT_f) {
 315                 if (!run_by_root)
 316                         bb_error_msg_and_die("-f is for root only");
 317                 safe_strncpy(username, opt_user, sizeof(username));
 318         }
 319         argv += optind;
 320         if (argv[0]) /* user from command line (getty) */
 321                 safe_strncpy(username, argv[0], sizeof(username));
 322
 323         /* Let's find out and memorize our tty */
 324         if (!isatty(STDIN_FILENO) || !isatty(STDOUT_FILENO) || !isatty(STDERR_FILENO))
 325                 return EXIT_FAILURE;            /* Must be a terminal */
 326         full_tty = xmalloc_ttyname(STDIN_FILENO);
 327         if (!full_tty)
 328                 full_tty = xstrdup("UNKNOWN");
 329         short_tty = full_tty;
 330         if (strncmp(full_tty, "/dev/", 5) == 0)
 331                 short_tty += 5;
 332
 333         read_or_build_utent(&utent, run_by_root);
 334
 335         if (opt & LOGIN_OPT_h) {
 336                 USE_FEATURE_UTMP(safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));)
 337                 fromhost = xasprintf(" on '%s' from '%s'", short_tty, opt_host);
 338         } else {
 339                 fromhost = xasprintf(" on '%s'", short_tty);
 340         }
 341
 342         /* Was breaking "login <username>" from shell command line: */
 343         /*bb_setpgrp();*/
 344
 345         openlog(applet_name, LOG_PID | LOG_CONS, LOG_AUTH);
 346
 347         while (1) {
 348                 /* flush away any type-ahead (as getty does) */
 349                 ioctl(0, TCFLSH, TCIFLUSH);
 350
 351                 if (!username[0])
 352                         get_username_or_die(username, sizeof(username));
 353
 354 #if ENABLE_PAM
 355                 pamret = pam_start("login", username, &conv, &pamh);
 356                 if (pamret != PAM_SUCCESS) {
 357                         failed_msg = "start";
 358                         goto pam_auth_failed;
 359                 }
 360                 /* set TTY (so things like securetty work) */
 361                 pamret = pam_set_item(pamh, PAM_TTY, short_tty);
 362                 if (pamret != PAM_SUCCESS) {
 363                         failed_msg = "set_item(TTY)";
 364                         goto pam_auth_failed;
 365                 }
 366                 pamret = pam_authenticate(pamh, 0);
 367                 if (pamret != PAM_SUCCESS) {
 368                         failed_msg = "authenticate";
 369                         goto pam_auth_failed;
 370                         /* TODO: or just "goto auth_failed"
 371                          * since user seems to enter wrong password
 372                          * (in this case pamret == 7)
 373                          */
 374                 }
 375                 /* check that the account is healthy */
 376                 pamret = pam_acct_mgmt(pamh, 0);
 377                 if (pamret != PAM_SUCCESS) {
 378                         failed_msg = "acct_mgmt";
 379                         goto pam_auth_failed;
 380                 }
 381                 /* read user back */
 382                 pamuser = NULL;
 383                 /* gcc: "dereferencing type-punned pointer breaks aliasing rules..."
 384                  * thus we cast to (void*) */
 385                 if (pam_get_item(pamh, PAM_USER, (void*)&pamuser) != PAM_SUCCESS) {
 386                         failed_msg = "get_item(USER)";
 387                         goto pam_auth_failed;
 388                 }
 389                 if (!pamuser || !pamuser[0])
 390                         goto auth_failed;
 391                 safe_strncpy(username, pamuser, sizeof(username));
 392                 /* Don't use "pw = getpwnam(username);",
 393                  * PAM is said to be capable of destroying static storage
 394                  * used by getpwnam(). We are using safe(r) function */
 395                 pw = NULL;
 396                 getpwnam_r(username, &pwdstruct, pwdbuf, sizeof(pwdbuf), &pw);
 397                 if (!pw)
 398                         goto auth_failed;
 399                 pamret = pam_open_session(pamh, 0);
 400                 if (pamret != PAM_SUCCESS) {
 401                         failed_msg = "open_session";
 402                         goto pam_auth_failed;
 403                 }
 404                 pamret = pam_setcred(pamh, PAM_ESTABLISH_CRED);
 405                 if (pamret != PAM_SUCCESS) {
 406                         failed_msg = "setcred";
 407                         goto pam_auth_failed;
 408                 }
 409                 break; /* success, continue login process */
 410
 411  pam_auth_failed:
 412                 bb_error_msg("pam_%s call failed: %s (%d)", failed_msg,
 413                                         pam_strerror(pamh, pamret), pamret);
 414                 safe_strncpy(username, "UNKNOWN", sizeof(username));
 415 #else /* not PAM */
 416                 pw = getpwnam(username);
 417                 if (!pw) {
 418                         strcpy(username, "UNKNOWN");
 419                         goto fake_it;
 420                 }
 421
 422                 if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
 423                         goto auth_failed;
 424
 425                 if (opt & LOGIN_OPT_f)
 426                         break; /* -f USER: success without asking passwd */
 427
 428                 if (pw->pw_uid == 0 && !check_securetty())
 429                         goto auth_failed;
 430
 431                 /* Don't check the password if password entry is empty (!) */
 432                 if (!pw->pw_passwd[0])
 433                         break;
 434  fake_it:
 435                 /* authorization takes place here */
 436                 if (correct_password(pw))
 437                         break;
 438 #endif /* ENABLE_PAM */
 439  auth_failed:
 440                 opt &= ~LOGIN_OPT_f;
 441                 bb_do_delay(FAIL_DELAY);
 442                 /* TODO: doesn't sound like correct English phrase to me */
 443                 puts("Login incorrect");
 444                 if (++count == 3) {
 445                         syslog(LOG_WARNING, "invalid password for '%s'%s",
 446                                                 username, fromhost);
 447                         return EXIT_FAILURE;
 448                 }
 449                 username[0] = '\0';
 450         } /* while (1) */
 451
 452         alarm(0);
 453         /* We can ignore /etc/nologin if we are logging in as root,
 454          * it doesn't matter whether we are run by root or not */
 455         if (pw->pw_uid != 0)
 456                 die_if_nologin();
 457
 458         write_utent(&utent, username);
 459
 460         USE_SELINUX(initselinux(username, full_tty, &user_sid));
 461
 462         /* Try these, but don't complain if they fail.
 463          * _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
 464         fchown(0, pw->pw_uid, pw->pw_gid);
 465         fchmod(0, 0600);
 466
 467         /* We trust environment only if we run by root */
 468         if (ENABLE_LOGIN_SCRIPTS && run_by_root)
 469                 run_login_script(pw, full_tty);
 470
 471         change_identity(pw);
 472         tmp = pw->pw_shell;
 473         if (!tmp || !*tmp)
 474                 tmp = DEFAULT_SHELL;
 475         /* setup_environment params: shell, clear_env, change_env, pw */
 476         setup_environment(tmp, !(opt & LOGIN_OPT_p), 1, pw);
 477
 478         motd();
 479
 480         if (pw->pw_uid == 0)
 481                 syslog(LOG_INFO, "root login%s", fromhost);
 482
 483         /* well, a simple setexeccon() here would do the job as well,
 484          * but let's play the game for now */
 485         USE_SELINUX(set_current_security_context(user_sid);)
 486
 487         // util-linux login also does:
 488         // /* start new session */
 489         // setsid();
 490         // /* TIOCSCTTY: steal tty from other process group */
 491         // if (ioctl(0, TIOCSCTTY, 1)) error_msg...
 492         // BBox login used to do this (see above):
 493         // bb_setpgrp();
 494         // If this stuff is really needed, add it and explain why!
 495
 496         /* Set signals to defaults */
 497         /* Non-ignored signals revert to SIG_DFL on exec anyway */
 498         /*signal(SIGALRM, SIG_DFL);*/
 499
 500         /* Is this correct? This way user can ctrl-c out of /etc/profile,
 501          * potentially creating security breach (tested with bash 3.0).
 502          * But without this, bash 3.0 will not enable ctrl-c either.
 503          * Maybe bash is buggy?
 504          * Need to find out what standards say about /bin/login -
 505          * should we leave SIGINT etc enabled or disabled? */
 506         signal(SIGINT, SIG_DFL);
 507
 508         /* Exec login shell with no additional parameters */
 509         run_shell(tmp, 1, NULL, NULL);
 510
 511         /* return EXIT_FAILURE; - not reached */
 512 }