networking/telnetd.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Simple telnet server
   4  * Bjorn Wesen, Axis Communications AB (bjornw@axis.com)
   5  *
   6  * Licensed under GPL, see file LICENSE in this tarball for details.
   7  *
   8  * ---------------------------------------------------------------------------
   9  * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN
  10  ****************************************************************************
  11  *
  12  * The telnetd manpage says it all:
  13  *
  14  *   Telnetd operates by allocating a pseudo-terminal device (see pty(4))  for
  15  *   a client, then creating a login process which has the slave side of the
  16  *   pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates the
  17  *   master side of the pseudo-terminal, implementing the telnet protocol and
  18  *   passing characters between the remote client and the login process.
  19  *
  20  * Vladimir Oleynik <dzo@simtreas.ru> 2001
  21  *     Set process group corrections, initial busybox port
  22  */
  23
  24 /*#define DEBUG 1 */
  25
  26 #include <sys/time.h>
  27 #include <sys/socket.h>
  28 #include <sys/wait.h>
  29 #include <sys/ioctl.h>
  30 #include <string.h>
  31 #include <stdlib.h>
  32 #include <unistd.h>
  33 #include <errno.h>
  34 #include <netinet/in.h>
  35 #include <arpa/inet.h>
  36 #include <fcntl.h>
  37 #include <stdio.h>
  38 #include <signal.h>
  39 #include <termios.h>
  40 #ifdef DEBUG
  41 #define TELCMDS
  42 #define TELOPTS
  43 #endif
  44 #include <arpa/telnet.h>
  45 #include <ctype.h>
  46 #include <sys/syslog.h>
  47
  48 #include "busybox.h"
  49
  50 #define BUFSIZE 4000
  51
  52 #ifdef CONFIG_FEATURE_IPV6
  53 #define SOCKET_TYPE     AF_INET6
  54 typedef struct sockaddr_in6 sockaddr_type;
  55 #else
  56 #define SOCKET_TYPE     AF_INET
  57 typedef struct sockaddr_in sockaddr_type;
  58 #endif
  59
  60
  61 #ifdef CONFIG_LOGIN
  62 static const char *loginpath = "/bin/login";
  63 #else
  64 static const char *loginpath;
  65 #endif
  66 static const char *issuefile = "/etc/issue.net";
  67
  68 /* shell name and arguments */
  69
  70 static const char *argv_init[] = {NULL, NULL};
  71
  72 /* structure that describes a session */
  73
  74 struct tsession {
  75 #ifdef CONFIG_FEATURE_TELNETD_INETD
  76         int sockfd_read, sockfd_write, ptyfd;
  77 #else /* CONFIG_FEATURE_TELNETD_INETD */
  78         struct tsession *next;
  79         int sockfd, ptyfd;
  80 #endif /* CONFIG_FEATURE_TELNETD_INETD */
  81         int shell_pid;
  82         /* two circular buffers */
  83         char *buf1, *buf2;
  84         int rdidx1, wridx1, size1;
  85         int rdidx2, wridx2, size2;
  86 };
  87
  88 /*
  89
  90    This is how the buffers are used. The arrows indicate the movement
  91    of data.
  92
  93    +-------+     wridx1++     +------+     rdidx1++     +----------+
  94    |       | <--------------  | buf1 | <--------------  |          |
  95    |       |     size1--      +------+     size1++      |          |
  96    |  pty  |                                        |  socket  |
  97    |       |     rdidx2++     +------+     wridx2++     |          |
  98    |       |  --------------> | buf2 |  --------------> |          |
  99    +-------+     size2++      +------+     size2--      +----------+
 100
 101    Each session has got two buffers.
 102
 103 */
 104
 105 static int maxfd;
 106
 107 static struct tsession *sessions;
 108
 109
 110 /*
 111
 112    Remove all IAC's from the buffer pointed to by bf (recieved IACs are ignored
 113    and must be removed so as to not be interpreted by the terminal).  Make an
 114    uninterrupted string of characters fit for the terminal.  Do this by packing
 115    all characters meant for the terminal sequentially towards the end of bf.
 116
 117    Return a pointer to the beginning of the characters meant for the terminal.
 118    and make *num_totty the number of characters that should be sent to
 119    the terminal.
 120
 121    Note - If an IAC (3 byte quantity) starts before (bf + len) but extends
 122    past (bf + len) then that IAC will be left unprocessed and *processed will be
 123    less than len.
 124
 125    FIXME - if we mean to send 0xFF to the terminal then it will be escaped,
 126    what is the escape character?  We aren't handling that situation here.
 127
 128    CR-LF ->'s CR mapping is also done here, for convenience
 129
 130   */
 131 static char *
 132 remove_iacs(struct tsession *ts, int *pnum_totty) {
 133         unsigned char *ptr0 = (unsigned char *)ts->buf1 + ts->wridx1;
 134         unsigned char *ptr = ptr0;
 135         unsigned char *totty = ptr;
 136         unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
 137         int processed;
 138         int num_totty;
 139
 140         while (ptr < end) {
 141                 if (*ptr != IAC) {
 142                         int c = *ptr;
 143                         *totty++ = *ptr++;
 144                         /* We now map \r\n ==> \r for pragmatic reasons.
 145                          * Many client implementations send \r\n when
 146                          * the user hits the CarriageReturn key.
 147                          */
 148                         if (c == '\r' && (*ptr == '\n' || *ptr == 0) && ptr < end)
 149                                 ptr++;
 150                 }
 151                 else {
 152                         /*
 153                          * TELOPT_NAWS support!
 154                          */
 155                         if ((ptr+2) >= end) {
 156                                 /* only the beginning of the IAC is in the
 157                                 buffer we were asked to process, we can't
 158                                 process this char. */
 159                                 break;
 160                         }
 161
 162                         /*
 163                          * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
 164                          */
 165                         else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
 166                                 struct winsize ws;
 167                                 if ((ptr+8) >= end)
 168                                         break;  /* incomplete, can't process */
 169                                 ws.ws_col = (ptr[3] << 8) | ptr[4];
 170                                 ws.ws_row = (ptr[5] << 8) | ptr[6];
 171                                 (void) ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
 172                                 ptr += 9;
 173                         }
 174                         else {
 175                                 /* skip 3-byte IAC non-SB cmd */
 176 #ifdef DEBUG
 177                                 fprintf(stderr, "Ignoring IAC %s,%s\n",
 178                                         TELCMD(*(ptr+1)), TELOPT(*(ptr+2)));
 179 #endif
 180                                 ptr += 3;
 181                         }
 182                 }
 183         }
 184
 185         processed = ptr - ptr0;
 186         num_totty = totty - ptr0;
 187         /* the difference between processed and num_to tty
 188            is all the iacs we removed from the stream.
 189            Adjust buf1 accordingly. */
 190         ts->wridx1 += processed - num_totty;
 191         ts->size1 -= processed - num_totty;
 192         *pnum_totty = num_totty;
 193         /* move the chars meant for the terminal towards the end of the
 194         buffer. */
 195         return memmove(ptr - num_totty, ptr0, num_totty);
 196 }
 197
 198
 199 static int
 200 getpty(char *line)
 201 {
 202         int p;
 203 #ifdef CONFIG_FEATURE_DEVPTS
 204         p = open("/dev/ptmx", 2);
 205         if (p > 0) {
 206                 grantpt(p);
 207                 unlockpt(p);
 208                 strcpy(line, ptsname(p));
 209                 return(p);
 210         }
 211 #else
 212         struct stat stb;
 213         int i;
 214         int j;
 215
 216         strcpy(line, "/dev/ptyXX");
 217
 218         for (i = 0; i < 16; i++) {
 219                 line[8] = "pqrstuvwxyzabcde"[i];
 220                 line[9] = '0';
 221                 if (stat(line, &stb) < 0) {
 222                         continue;
 223                 }
 224                 for (j = 0; j < 16; j++) {
 225                         line[9] = j < 10 ? j + '0' : j - 10 + 'a';
 226                         if ((p = open(line, O_RDWR | O_NOCTTY)) >= 0) {
 227                                 line[5] = 't';
 228                                 return p;
 229                         }
 230                 }
 231         }
 232 #endif /* CONFIG_FEATURE_DEVPTS */
 233         return -1;
 234 }
 235
 236
 237 static void
 238 send_iac(struct tsession *ts, unsigned char command, int option)
 239 {
 240         /* We rely on that there is space in the buffer for now.  */
 241         char *b = ts->buf2 + ts->rdidx2;
 242         *b++ = IAC;
 243         *b++ = command;
 244         *b++ = option;
 245         ts->rdidx2 += 3;
 246         ts->size2 += 3;
 247 }
 248
 249
 250 static struct tsession *
 251 #ifdef CONFIG_FEATURE_TELNETD_INETD
 252 make_new_session(void)
 253 #else /* CONFIG_FEATURE_TELNETD_INETD */
 254 make_new_session(int sockfd)
 255 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 256 {
 257         struct termios termbuf;
 258         int pty, pid;
 259         char tty_name[32];
 260         struct tsession *ts = malloc(sizeof(struct tsession) + BUFSIZE * 2);
 261
 262         ts->buf1 = (char *)(&ts[1]);
 263         ts->buf2 = ts->buf1 + BUFSIZE;
 264
 265 #ifdef CONFIG_FEATURE_TELNETD_INETD
 266         ts->sockfd_read = 0;
 267         ts->sockfd_write = 1;
 268 #else /* CONFIG_FEATURE_TELNETD_INETD */
 269         ts->sockfd = sockfd;
 270 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 271
 272         ts->rdidx1 = ts->wridx1 = ts->size1 = 0;
 273         ts->rdidx2 = ts->wridx2 = ts->size2 = 0;
 274
 275         /* Got a new connection, set up a tty and spawn a shell.  */
 276
 277         pty = getpty(tty_name);
 278
 279         if (pty < 0) {
 280                 syslog(LOG_ERR, "All network ports in use!");
 281                 return 0;
 282         }
 283
 284         if (pty > maxfd)
 285                 maxfd = pty;
 286
 287         ts->ptyfd = pty;
 288
 289         /* Make the telnet client understand we will echo characters so it
 290          * should not do it locally. We don't tell the client to run linemode,
 291          * because we want to handle line editing and tab completion and other
 292          * stuff that requires char-by-char support.
 293          */
 294
 295         send_iac(ts, DO, TELOPT_ECHO);
 296         send_iac(ts, DO, TELOPT_NAWS);
 297         send_iac(ts, DO, TELOPT_LFLOW);
 298         send_iac(ts, WILL, TELOPT_ECHO);
 299         send_iac(ts, WILL, TELOPT_SGA);
 300
 301
 302         if ((pid = fork()) < 0) {
 303                 syslog(LOG_ERR, "Can`t forking");
 304         }
 305         if (pid == 0) {
 306                 /* In child, open the child's side of the tty.  */
 307                 int i;
 308
 309                 for(i = 0; i <= maxfd; i++)
 310                         close(i);
 311                 /* make new process group */
 312                 setsid();
 313
 314                 if (open(tty_name, O_RDWR /*| O_NOCTTY*/) < 0) {
 315                         syslog(LOG_ERR, "Could not open tty");
 316                         exit(1);
 317                         }
 318                 dup(0);
 319                 dup(0);
 320
 321                 tcsetpgrp(0, getpid());
 322
 323                 /* The pseudo-terminal allocated to the client is configured to operate in
 324                  * cooked mode, and with XTABS CRMOD enabled (see tty(4)).
 325                  */
 326
 327                 tcgetattr(0, &termbuf);
 328                 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
 329                 termbuf.c_oflag |= ONLCR|XTABS;
 330                 termbuf.c_iflag |= ICRNL;
 331                 termbuf.c_iflag &= ~IXOFF;
 332                 /*termbuf.c_lflag &= ~ICANON;*/
 333                 tcsetattr(0, TCSANOW, &termbuf);
 334
 335                 print_login_issue(issuefile, NULL);
 336
 337                 /* exec shell, with correct argv and env */
 338                 execv(loginpath, (char *const *)argv_init);
 339
 340                 /* NOT REACHED */
 341                 syslog(LOG_ERR, "execv error");
 342                 exit(1);
 343         }
 344
 345         ts->shell_pid = pid;
 346
 347         return ts;
 348 }
 349
 350 #ifndef CONFIG_FEATURE_TELNETD_INETD
 351 static void
 352 free_session(struct tsession *ts)
 353 {
 354         struct tsession *t = sessions;
 355
 356         /* Unlink this telnet session from the session list.  */
 357         if(t == ts)
 358                 sessions = ts->next;
 359         else {
 360                 while(t->next != ts)
 361                         t = t->next;
 362                 t->next = ts->next;
 363         }
 364
 365         kill(ts->shell_pid, SIGKILL);
 366
 367         wait4(ts->shell_pid, NULL, 0, NULL);
 368
 369         close(ts->ptyfd);
 370         close(ts->sockfd);
 371
 372         if(ts->ptyfd == maxfd || ts->sockfd == maxfd)
 373                 maxfd--;
 374         if(ts->ptyfd == maxfd || ts->sockfd == maxfd)
 375                 maxfd--;
 376
 377         free(ts);
 378 }
 379 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 380
 381 int
 382 telnetd_main(int argc, char **argv)
 383 {
 384 #ifndef CONFIG_FEATURE_TELNETD_INETD
 385         sockaddr_type sa;
 386         int master_fd;
 387 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 388         fd_set rdfdset, wrfdset;
 389         int selret;
 390 #ifndef CONFIG_FEATURE_TELNETD_INETD
 391         int on = 1;
 392         int portnbr = 23;
 393         struct in_addr bind_addr = { .s_addr = 0x0 };
 394 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 395         int c;
 396         static const char options[] =
 397 #ifdef CONFIG_FEATURE_TELNETD_INETD
 398                 "f:l:";
 399 #else /* CONFIG_EATURE_TELNETD_INETD */
 400                 "f:l:p:b:";
 401 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 402         int maxlen, w, r;
 403
 404 #ifndef CONFIG_LOGIN
 405         loginpath = DEFAULT_SHELL;
 406 #endif
 407
 408         for (;;) {
 409                 c = getopt( argc, argv, options);
 410                 if (c == EOF) break;
 411                 switch (c) {
 412                         case 'f':
 413                                 issuefile = optarg;
 414                                 break;
 415                         case 'l':
 416                                 loginpath = optarg;
 417                                 break;
 418 #ifndef CONFIG_FEATURE_TELNETD_INETD
 419                         case 'p':
 420                                 portnbr = atoi(optarg);
 421                                 break;
 422                         case 'b':
 423                                 if (inet_aton(optarg, &bind_addr) == 0)
 424                                         bb_show_usage();
 425                                 break;
 426 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 427                         default:
 428                                 bb_show_usage();
 429                 }
 430         }
 431
 432         if (access(loginpath, X_OK) < 0) {
 433                 bb_error_msg_and_die ("'%s' unavailable.", loginpath);
 434         }
 435
 436         argv_init[0] = loginpath;
 437
 438         openlog(bb_applet_name, 0, LOG_USER);
 439
 440 #ifdef CONFIG_FEATURE_TELNETD_INETD
 441         maxfd = 1;
 442         sessions = make_new_session();
 443 #else /* CONFIG_EATURE_TELNETD_INETD */
 444         sessions = 0;
 445
 446         /* Grab a TCP socket.  */
 447
 448         master_fd = bb_xsocket(SOCKET_TYPE, SOCK_STREAM, 0);
 449         (void)setsockopt(master_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
 450
 451         /* Set it to listen to specified port.  */
 452
 453         memset((void *)&sa, 0, sizeof(sa));
 454 #ifdef CONFIG_FEATURE_IPV6
 455         sa.sin6_family = AF_INET6;
 456         sa.sin6_port = htons(portnbr);
 457         /* sa.sin6_addr = bind_addr6; */
 458 #else
 459         sa.sin_family = AF_INET;
 460         sa.sin_port = htons(portnbr);
 461         sa.sin_addr = bind_addr;
 462 #endif
 463
 464         bb_xbind(master_fd, (struct sockaddr *) &sa, sizeof(sa));
 465         bb_xlisten(master_fd, 1);
 466         bb_xdaemon(0, 0);
 467
 468         maxfd = master_fd;
 469 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 470
 471         do {
 472                 struct tsession *ts;
 473
 474                 FD_ZERO(&rdfdset);
 475                 FD_ZERO(&wrfdset);
 476
 477                 /* select on the master socket, all telnet sockets and their
 478                  * ptys if there is room in their respective session buffers.
 479                  */
 480
 481 #ifndef CONFIG_FEATURE_TELNETD_INETD
 482                 FD_SET(master_fd, &rdfdset);
 483 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 484
 485                 ts = sessions;
 486 #ifndef CONFIG_FEATURE_TELNETD_INETD
 487                 while (ts) {
 488 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 489                         /* buf1 is used from socket to pty
 490                          * buf2 is used from pty to socket
 491                          */
 492                         if (ts->size1 > 0) {
 493                                 FD_SET(ts->ptyfd, &wrfdset);  /* can write to pty */
 494                         }
 495                         if (ts->size1 < BUFSIZE) {
 496 #ifdef CONFIG_FEATURE_TELNETD_INETD
 497                                 FD_SET(ts->sockfd_read, &rdfdset); /* can read from socket */
 498 #else /* CONFIG_FEATURE_TELNETD_INETD */
 499                                 FD_SET(ts->sockfd, &rdfdset); /* can read from socket */
 500 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 501                         }
 502                         if (ts->size2 > 0) {
 503 #ifdef CONFIG_FEATURE_TELNETD_INETD
 504                                 FD_SET(ts->sockfd_write, &wrfdset); /* can write to socket */
 505 #else /* CONFIG_FEATURE_TELNETD_INETD */
 506                                 FD_SET(ts->sockfd, &wrfdset); /* can write to socket */
 507 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 508                         }
 509                         if (ts->size2 < BUFSIZE) {
 510                                 FD_SET(ts->ptyfd, &rdfdset);  /* can read from pty */
 511                         }
 512 #ifndef CONFIG_FEATURE_TELNETD_INETD
 513                         ts = ts->next;
 514                 }
 515 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 516
 517                 selret = select(maxfd + 1, &rdfdset, &wrfdset, 0, 0);
 518
 519                 if (!selret)
 520                         break;
 521
 522 #ifndef CONFIG_FEATURE_TELNETD_INETD
 523                 /* First check for and accept new sessions.  */
 524                 if (FD_ISSET(master_fd, &rdfdset)) {
 525                         int fd, salen;
 526
 527                         salen = sizeof(sa);
 528                         if ((fd = accept(master_fd, (struct sockaddr *)&sa,
 529                                                 &salen)) < 0) {
 530                                 continue;
 531                         } else {
 532                                 /* Create a new session and link it into
 533                                         our active list.  */
 534                                 struct tsession *new_ts = make_new_session(fd);
 535                                 if (new_ts) {
 536                                         new_ts->next = sessions;
 537                                         sessions = new_ts;
 538                                         if (fd > maxfd)
 539                                                 maxfd = fd;
 540                                 } else {
 541                                         close(fd);
 542                                 }
 543                         }
 544                 }
 545
 546                 /* Then check for data tunneling.  */
 547
 548                 ts = sessions;
 549                 while (ts) { /* For all sessions...  */
 550 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 551 #ifndef CONFIG_FEATURE_TELNETD_INETD
 552                         struct tsession *next = ts->next; /* in case we free ts. */
 553 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 554
 555                         if (ts->size1 && FD_ISSET(ts->ptyfd, &wrfdset)) {
 556                                 int num_totty;
 557                                 char *ptr;
 558                                 /* Write to pty from buffer 1.  */
 559
 560                                 ptr = remove_iacs(ts, &num_totty);
 561
 562                                 w = write(ts->ptyfd, ptr, num_totty);
 563                                 if (w < 0) {
 564 #ifdef CONFIG_FEATURE_TELNETD_INETD
 565                                         exit(0);
 566 #else /* CONFIG_FEATURE_TELNETD_INETD */
 567                                         free_session(ts);
 568                                         ts = next;
 569                                         continue;
 570 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 571                                 }
 572                                 ts->wridx1 += w;
 573                                 ts->size1 -= w;
 574                                 if (ts->wridx1 == BUFSIZE)
 575                                         ts->wridx1 = 0;
 576                         }
 577
 578 #ifdef CONFIG_FEATURE_TELNETD_INETD
 579                         if (ts->size2 && FD_ISSET(ts->sockfd_write, &wrfdset)) {
 580 #else /* CONFIG_FEATURE_TELNETD_INETD */
 581                         if (ts->size2 && FD_ISSET(ts->sockfd, &wrfdset)) {
 582 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 583                                 /* Write to socket from buffer 2.  */
 584                                 maxlen = MIN(BUFSIZE - ts->wridx2, ts->size2);
 585 #ifdef CONFIG_FEATURE_TELNETD_INETD
 586                                 w = write(ts->sockfd_write, ts->buf2 + ts->wridx2, maxlen);
 587                                 if (w < 0)
 588                                         exit(0);
 589 #else /* CONFIG_FEATURE_TELNETD_INETD */
 590                                 w = write(ts->sockfd, ts->buf2 + ts->wridx2, maxlen);
 591                                 if (w < 0) {
 592                                         free_session(ts);
 593                                         ts = next;
 594                                         continue;
 595                                 }
 596 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 597                                 ts->wridx2 += w;
 598                                 ts->size2 -= w;
 599                                 if (ts->wridx2 == BUFSIZE)
 600                                         ts->wridx2 = 0;
 601                         }
 602
 603 #ifdef CONFIG_FEATURE_TELNETD_INETD
 604                         if (ts->size1 < BUFSIZE && FD_ISSET(ts->sockfd_read, &rdfdset)) {
 605 #else /* CONFIG_FEATURE_TELNETD_INETD */
 606                         if (ts->size1 < BUFSIZE && FD_ISSET(ts->sockfd, &rdfdset)) {
 607 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 608                                 /* Read from socket to buffer 1. */
 609                                 maxlen = MIN(BUFSIZE - ts->rdidx1,
 610                                                 BUFSIZE - ts->size1);
 611 #ifdef CONFIG_FEATURE_TELNETD_INETD
 612                                 r = read(ts->sockfd_read, ts->buf1 + ts->rdidx1, maxlen);
 613                                 if (!r || (r < 0 && errno != EINTR))
 614                                         exit(0);
 615 #else /* CONFIG_FEATURE_TELNETD_INETD */
 616                                 r = read(ts->sockfd, ts->buf1 + ts->rdidx1, maxlen);
 617                                 if (!r || (r < 0 && errno != EINTR)) {
 618                                         free_session(ts);
 619                                         ts = next;
 620                                         continue;
 621                                 }
 622 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 623                                 if(!*(ts->buf1 + ts->rdidx1 + r - 1)) {
 624                                         r--;
 625                                         if(!r)
 626                                                 continue;
 627                                 }
 628                                 ts->rdidx1 += r;
 629                                 ts->size1 += r;
 630                                 if (ts->rdidx1 == BUFSIZE)
 631                                         ts->rdidx1 = 0;
 632                         }
 633
 634                         if (ts->size2 < BUFSIZE && FD_ISSET(ts->ptyfd, &rdfdset)) {
 635                                 /* Read from pty to buffer 2.  */
 636                                 maxlen = MIN(BUFSIZE - ts->rdidx2,
 637                                                 BUFSIZE - ts->size2);
 638                                 r = read(ts->ptyfd, ts->buf2 + ts->rdidx2, maxlen);
 639                                 if (!r || (r < 0 && errno != EINTR)) {
 640 #ifdef CONFIG_FEATURE_TELNETD_INETD
 641                                         exit(0);
 642 #else /* CONFIG_FEATURE_TELNETD_INETD */
 643                                         free_session(ts);
 644                                         ts = next;
 645                                         continue;
 646 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 647                                 }
 648                                 ts->rdidx2 += r;
 649                                 ts->size2 += r;
 650                                 if (ts->rdidx2 == BUFSIZE)
 651                                         ts->rdidx2 = 0;
 652                         }
 653
 654                         if (ts->size1 == 0) {
 655                                 ts->rdidx1 = 0;
 656                                 ts->wridx1 = 0;
 657                         }
 658                         if (ts->size2 == 0) {
 659                                 ts->rdidx2 = 0;
 660                                 ts->wridx2 = 0;
 661                         }
 662 #ifndef CONFIG_FEATURE_TELNETD_INETD
 663                         ts = next;
 664                 }
 665 #endif /* CONFIG_FEATURE_TELNETD_INETD */
 666
 667         } while (1);
 668
 669         return 0;
 670 }