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 "busybox.h"
   7 #include <utmp.h>
   8 #include <sys/resource.h>
   9 #include <syslog.h>
  10
  11 #ifdef CONFIG_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 #include <errno.h>
  16 #endif
  17
  18 /* import from utmp.c
  19  * XXX: FIXME: provide empty bodies if ENABLE_FEATURE_UTMP == 0
  20  */
  21 static struct utmp utent;
  22 static void read_or_build_utent(int);
  23 static void write_utent(const char *);
  24
  25 enum {
  26         TIMEOUT = 60,
  27         EMPTY_USERNAME_COUNT = 10,
  28         USERNAME_SIZE = 32,
  29         TTYNAME_SIZE = 32,
  30 };
  31
  32 static void die_if_nologin_and_non_root(int amroot);
  33
  34 #if ENABLE_FEATURE_SECURETTY
  35 static int check_securetty(void);
  36 #else
  37 static inline int check_securetty(void) { return 1; }
  38 #endif
  39
  40 static void get_username_or_die(char *buf, int size_buf);
  41 static void motd(void);
  42
  43 static void nonblock(int fd)
  44 {
  45         fcntl(fd, F_SETFL, O_NONBLOCK | fcntl(fd, F_GETFL));
  46 }
  47
  48 static void alarm_handler(int sig ATTRIBUTE_UNUSED)
  49 {
  50         /* This is the escape hatch!  Poor serial line users and the like
  51          * arrive here when their connection is broken.
  52          * We don't want to block here */
  53         nonblock(1);
  54         nonblock(2);
  55         bb_info_msg("\r\nLogin timed out after %d seconds\r", TIMEOUT);
  56         exit(EXIT_SUCCESS);
  57 }
  58
  59
  60 static char full_tty[TTYNAME_SIZE];
  61 static char* short_tty = full_tty;
  62
  63
  64 int login_main(int argc, char **argv)
  65 {
  66         char fromhost[512];
  67         char username[USERNAME_SIZE];
  68         const char *tmp;
  69         int amroot;
  70         int flag;
  71         int count = 0;
  72         struct passwd *pw;
  73         int opt_preserve = 0;
  74         int opt_fflag = 0;
  75         char *opt_host = 0;
  76 #ifdef CONFIG_SELINUX
  77         security_context_t user_sid = NULL;
  78 #endif
  79
  80         username[0] = '\0';
  81         amroot = (getuid() == 0);
  82         signal(SIGALRM, alarm_handler);
  83         alarm(TIMEOUT);
  84
  85         while ((flag = getopt(argc, argv, "f:h:p")) != EOF) {
  86                 switch (flag) {
  87                 case 'p':
  88                         opt_preserve = 1;
  89                         break;
  90                 case 'f':
  91                         /*
  92                          * username must be a separate token
  93                          * (-f root, *NOT* -froot). --marekm
  94                          */
  95                         if (optarg != argv[optind-1])
  96                                 bb_show_usage();
  97
  98                         if (!amroot)    /* Auth bypass only if real UID is zero */
  99                                 bb_error_msg_and_die("-f is for root only");
 100
 101                         safe_strncpy(username, optarg, sizeof(username));
 102                         opt_fflag = 1;
 103                         break;
 104                 case 'h':
 105                         opt_host = optarg;
 106                         break;
 107                 default:
 108                         bb_show_usage();
 109                 }
 110         }
 111         if (optind < argc)             /* user from command line (getty) */
 112                 safe_strncpy(username, argv[optind], sizeof(username));
 113
 114         /* Let's find out and memorize our tty */
 115         if (!isatty(0) || !isatty(1) || !isatty(2))
 116                 return EXIT_FAILURE;            /* Must be a terminal */
 117         safe_strncpy(full_tty, "UNKNOWN", sizeof(full_tty));
 118         tmp = ttyname(0);
 119         if (tmp) {
 120                 safe_strncpy(full_tty, tmp, sizeof(full_tty));
 121                 if (strncmp(full_tty, "/dev/", 5) == 0)
 122                         short_tty = full_tty + 5;
 123         }
 124
 125         if (ENABLE_FEATURE_UTMP) {
 126                 read_or_build_utent(!amroot);
 127                 if (amroot)
 128                         memset(utent.ut_host, 0, sizeof(utent.ut_host));
 129         }
 130
 131         if (opt_host) {
 132                 if (ENABLE_FEATURE_UTMP)
 133                         safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));
 134                 snprintf(fromhost, sizeof(fromhost)-1, " on `%.100s' from "
 135                                         "`%.200s'", short_tty, opt_host);
 136         }
 137         else
 138                 snprintf(fromhost, sizeof(fromhost)-1, " on `%.100s'", short_tty);
 139
 140         bb_setpgrp;
 141
 142         openlog(bb_applet_name, LOG_PID | LOG_CONS | LOG_NOWAIT, LOG_AUTH);
 143
 144         while (1) {
 145                 if (!username[0])
 146                         get_username_or_die(username, sizeof(username));
 147
 148                 pw = getpwnam(username);
 149                 if (!pw) {
 150                         safe_strncpy(username, "UNKNOWN", sizeof(username));
 151                         goto auth_failed;
 152                 }
 153
 154                 if (pw->pw_passwd[0] == '!' || pw->pw_passwd[0] == '*')
 155                         goto auth_failed;
 156
 157                 if (opt_fflag)
 158                         break; /* -f USER: success without asking passwd */
 159
 160                 if (pw->pw_uid == 0 && !check_securetty())
 161                         goto auth_failed;
 162
 163                 /* Don't check the password if password entry is empty (!) */
 164                 if (!pw->pw_passwd[0])
 165                         break;
 166
 167                 /* authorization takes place here */
 168                 if (correct_password(pw))
 169                         break;
 170
 171 auth_failed:
 172                 opt_fflag = 0;
 173                 bb_do_delay(FAIL_DELAY);
 174                 puts("Login incorrect");
 175                 if (++count == 3) {
 176                         syslog(LOG_WARNING, "invalid password for `%s'%s",
 177                                                 username, fromhost);
 178                         return EXIT_FAILURE;
 179                 }
 180                 username[0] = '\0';
 181         }
 182
 183         alarm(0);
 184         die_if_nologin_and_non_root(pw->pw_uid == 0);
 185
 186         if (ENABLE_FEATURE_UTMP)
 187                 write_utent(username);
 188
 189 #ifdef CONFIG_SELINUX
 190         if (is_selinux_enabled()) {
 191                 security_context_t old_tty_sid, new_tty_sid;
 192
 193                 if (get_default_context(username, NULL, &user_sid)) {
 194                         bb_error_msg_and_die("unable to get SID for %s",
 195                                         username);
 196                 }
 197                 if (getfilecon(full_tty, &old_tty_sid) < 0) {
 198                         bb_perror_msg_and_die("getfilecon(%.100s) failed",
 199                                         full_tty);
 200                 }
 201                 if (security_compute_relabel(user_sid, old_tty_sid,
 202                                         SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
 203                         bb_perror_msg_and_die("security_change_sid(%.100s) failed",
 204                                         full_tty);
 205                 }
 206                 if (setfilecon(full_tty, new_tty_sid) != 0) {
 207                         bb_perror_msg_and_die("chsid(%.100s, %s) failed",
 208                                         full_tty, new_tty_sid);
 209                 }
 210         }
 211 #endif
 212         /* Try these, but don't complain if they fail.
 213          * _f_chown is safe wrt race t=ttyname(0);...;chown(t); */
 214         fchown(0, pw->pw_uid, pw->pw_gid);
 215         fchmod(0, 0600);
 216
 217         if (ENABLE_LOGIN_SCRIPTS) {
 218                 char *script = getenv("LOGIN_PRE_SUID_SCRIPT");
 219                 if (script) {
 220                         char *t_argv[2] = { script, NULL };
 221                         switch (fork()) {
 222                         case -1: break;
 223                         case 0: /* child */
 224                                 xchdir("/");
 225                                 setenv("LOGIN_TTY", full_tty, 1);
 226                                 setenv("LOGIN_USER", pw->pw_name, 1);
 227                                 setenv("LOGIN_UID", utoa(pw->pw_uid), 1);
 228                                 setenv("LOGIN_GID", utoa(pw->pw_gid), 1);
 229                                 setenv("LOGIN_SHELL", pw->pw_shell, 1);
 230                                 execvp(script, t_argv);
 231                                 exit(1);
 232                         default: /* parent */
 233                                 wait(NULL);
 234                         }
 235                 }
 236         }
 237
 238         change_identity(pw);
 239         tmp = pw->pw_shell;
 240         if (!tmp || !*tmp)
 241                 tmp = DEFAULT_SHELL;
 242         setup_environment(tmp, 1, !opt_preserve, pw);
 243
 244         motd();
 245         signal(SIGALRM, SIG_DFL);       /* default alarm signal */
 246
 247         if (pw->pw_uid == 0)
 248                 syslog(LOG_INFO, "root login%s", fromhost);
 249 #ifdef CONFIG_SELINUX
 250         /* well, a simple setexeccon() here would do the job as well,
 251          * but let's play the game for now */
 252         set_current_security_context(user_sid);
 253 #endif
 254         run_shell(tmp, 1, 0, 0);        /* exec the shell finally. */
 255
 256         return EXIT_FAILURE;
 257 }
 258
 259
 260 static void get_username_or_die(char *buf, int size_buf)
 261 {
 262         int c, cntdown;
 263         cntdown = EMPTY_USERNAME_COUNT;
 264 prompt:
 265         /* skip whitespace */
 266         print_login_prompt();
 267         do {
 268                 c = getchar();
 269                 if (c == EOF) exit(1);
 270                 if (c == '\n') {
 271                         if (!--cntdown) exit(1);
 272                         goto prompt;
 273                 }
 274         } while (isspace(c));
 275
 276         *buf++ = c;
 277         if (!fgets(buf, size_buf-2, stdin))
 278                 exit(1);
 279         if (!strchr(buf, '\n'))
 280                 exit(1);
 281         while (isgraph(*buf)) buf++;
 282         *buf = '\0';
 283 }
 284
 285
 286 static void die_if_nologin_and_non_root(int amroot)
 287 {
 288         FILE *fp;
 289         int c;
 290
 291         if (access(bb_path_nologin_file, F_OK))
 292                 return;
 293
 294         fp = fopen(bb_path_nologin_file, "r");
 295         if (fp) {
 296                 while ((c = getc(fp)) != EOF)
 297                         putchar((c=='\n') ? '\r' : c);
 298                 fflush(stdout);
 299                 fclose(fp);
 300         } else
 301                 puts("\r\nSystem closed for routine maintenance\r");
 302         if (!amroot)
 303                 exit(1);
 304         puts("\r\n[Disconnect bypassed -- root login allowed.]\r");
 305 }
 306
 307 #if ENABLE_FEATURE_SECURETTY
 308
 309 static int check_securetty(void)
 310 {
 311         FILE *fp;
 312         int i;
 313         char buf[BUFSIZ];
 314
 315         fp = fopen(bb_path_securetty_file, "r");
 316         if (!fp) {
 317                 /* A missing securetty file is not an error. */
 318                 return 1;
 319         }
 320         while (fgets(buf, sizeof(buf)-1, fp)) {
 321                 for(i = strlen(buf)-1; i>=0; --i) {
 322                         if (!isspace(buf[i]))
 323                                 break;
 324                 }
 325                 buf[++i] = '\0';
 326                 if ((buf[0]=='\0') || (buf[0]=='#'))
 327                         continue;
 328                 if (strcmp(buf, short_tty) == 0) {
 329                         fclose(fp);
 330                         return 1;
 331                 }
 332         }
 333         fclose(fp);
 334         return 0;
 335 }
 336
 337 #endif
 338
 339 static void motd(void)
 340 {
 341         FILE *fp;
 342         int c;
 343
 344         fp = fopen(bb_path_motd_file, "r");
 345         if (fp) {
 346                 while ((c = getc(fp)) != EOF)
 347                         putchar(c);
 348                 fclose(fp);
 349         }
 350 }
 351
 352
 353 #if ENABLE_FEATURE_UTMP
 354 /* vv  Taken from tinylogin utmp.c  vv */
 355
 356 /*
 357  * read_or_build_utent - see if utmp file is correct for this process
 358  *
 359  *      System V is very picky about the contents of the utmp file
 360  *      and requires that a slot for the current process exist.
 361  *      The utmp file is scanned for an entry with the same process
 362  *      ID.  If no entry exists the process exits with a message.
 363  *
 364  *      The "picky" flag is for network and other logins that may
 365  *      use special flags.  It allows the pid checks to be overridden.
 366  *      This means that getty should never invoke login with any
 367  *      command line flags.
 368  */
 369
 370 static void read_or_build_utent(int picky)
 371 {
 372         struct utmp *ut;
 373         pid_t pid = getpid();
 374
 375         setutent();
 376
 377         /* First, try to find a valid utmp entry for this process.  */
 378         while ((ut = getutent()))
 379                 if (ut->ut_pid == pid && ut->ut_line[0] && ut->ut_id[0] &&
 380                 (ut->ut_type == LOGIN_PROCESS || ut->ut_type == USER_PROCESS))
 381                         break;
 382
 383         /* If there is one, just use it, otherwise create a new one.  */
 384         if (ut) {
 385                 utent = *ut;
 386         } else {
 387                 if (picky)
 388                         bb_error_msg_and_die("no utmp entry found");
 389
 390                 memset(&utent, 0, sizeof(utent));
 391                 utent.ut_type = LOGIN_PROCESS;
 392                 utent.ut_pid = pid;
 393                 strncpy(utent.ut_line, short_tty, sizeof(utent.ut_line));
 394                 /* This one is only 4 chars wide. Try to fit something
 395                  * remotely meaningful by skipping "tty"... */
 396                 strncpy(utent.ut_id, short_tty + 3, sizeof(utent.ut_id));
 397                 strncpy(utent.ut_user, "LOGIN", sizeof(utent.ut_user));
 398                 utent.ut_time = time(NULL);
 399         }
 400 }
 401
 402 /*
 403  * write_utent - put a USER_PROCESS entry in the utmp file
 404  *
 405  *      write_utent changes the type of the current utmp entry to
 406  *      USER_PROCESS.  the wtmp file will be updated as well.
 407  */
 408
 409 static void write_utent(const char *username)
 410 {
 411         utent.ut_type = USER_PROCESS;
 412         strncpy(utent.ut_user, username, sizeof(utent.ut_user));
 413         utent.ut_time = time(NULL);
 414         /* other fields already filled in by read_or_build_utent above */
 415         setutent();
 416         pututline(&utent);
 417         endutent();
 418 #if ENABLE_FEATURE_WTMP
 419         if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
 420                 close(creat(bb_path_wtmp_file, 0664));
 421         }
 422         updwtmp(bb_path_wtmp_file, &utent);
 423 #endif
 424 }
 425 #endif /* CONFIG_FEATURE_UTMP */