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