1 /* vi: set sw=4 ts=4: */
4 * Bjorn Wesen, Axis Communications AB (bjornw@axis.com)
6 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
8 * ---------------------------------------------------------------------------
9 * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN
10 ****************************************************************************
12 * The telnetd manpage says it all:
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.
20 * Vladimir Oleynik <dzo@simtreas.ru> 2001
21 * Set process group corrections, initial busybox port
24 //usage:#define telnetd_trivial_usage
26 //usage:#define telnetd_full_usage "\n\n"
27 //usage: "Handle incoming telnet connections"
28 //usage: IF_NOT_FEATURE_TELNETD_STANDALONE(" via inetd") "\n"
29 //usage: "\n -l LOGIN Exec LOGIN on connect"
30 //usage: "\n -f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue"
31 //usage: "\n -K Close connection as soon as login exits"
32 //usage: "\n (normally wait until all programs close slave pty)"
33 //usage: IF_FEATURE_TELNETD_STANDALONE(
34 //usage: "\n -p PORT Port to listen on"
35 //usage: "\n -b ADDR[:PORT] Address to bind to"
36 //usage: "\n -F Run in foreground"
37 //usage: "\n -i Inetd mode"
38 //usage: IF_FEATURE_TELNETD_INETD_WAIT(
39 //usage: "\n -w SEC Inetd 'wait' mode, linger time SEC"
40 //usage: "\n -S Log to syslog (implied by -i or without -F and -w)"
47 #include "common_bufsiz.h"
54 #include <arpa/telnet.h>
58 struct tsession *next;
64 /* two circular buffers */
65 /*char *buf1, *buf2;*/
66 /*#define TS_BUF1(ts) ts->buf1*/
67 /*#define TS_BUF2(ts) TS_BUF2(ts)*/
68 #define TS_BUF1(ts) ((unsigned char*)(ts + 1))
69 #define TS_BUF2(ts) (((unsigned char*)(ts + 1)) + BUFSIZE)
70 int rdidx1, wridx1, size1;
71 int rdidx2, wridx2, size2;
74 /* Two buffers are directly after tsession in malloced memory.
75 * Make whole thing fit in 4k */
76 enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
81 struct tsession *sessions;
82 const char *loginpath;
83 const char *issuefile;
86 #define G (*(struct globals*)bb_common_bufsiz1)
87 #define INIT_G() do { \
88 setup_common_bufsiz(); \
89 G.loginpath = "/bin/login"; \
90 G.issuefile = "/etc/issue.net"; \
94 /* Write some buf1 data to pty, processing IAC's.
95 * Update wridx1 and size1. Return < 0 on error.
96 * Buggy if IAC is present but incomplete: skips them.
99 safe_write_to_pty_decode_iac(struct tsession *ts)
104 unsigned char *found;
106 buf = TS_BUF1(ts) + ts->wridx1;
107 wr = MIN(BUFSIZE - ts->wridx1, ts->size1);
108 found = memchr(buf, IAC, wr);
110 /* There is a "prefix" of non-IAC chars.
111 * Write only them, and return.
116 /* We map \r\n ==> \r for pragmatic reasons:
117 * many client implementations send \r\n when
118 * the user hits the CarriageReturn key.
119 * See RFC 1123 3.3.1 Telnet End-of-Line Convention.
122 found = memchr(buf, '\r', wr);
124 rc = found - buf + 1;
125 rc = safe_write(ts->ptyfd, buf, rc);
128 if (rc < wr /* don't look past available data */
129 && buf[rc-1] == '\r' /* need this: imagine that write was _short_ */
130 && (buf[rc] == '\n' || buf[rc] == '\0')
134 goto update_and_return;
137 /* buf starts with IAC char. Process that sequence.
138 * Example: we get this from our own (bbox) telnet client:
139 * read(5, "\377\374\1""\377\373\37""\377\372\37\0\262\0@\377\360""\377\375\1""\377\375\3"):
140 * IAC WONT ECHO, IAC WILL NAWS, IAC SB NAWS <cols> <rows> IAC SE, IAC DO SGA
143 /* BUG: only the single IAC byte is in the buffer, we just eat IAC */
145 goto update_and_return;
148 /* 2-byte commands (240..250 and 255):
149 * IAC IAC (255) Literal 255. Supported.
150 * IAC NOP (241) NOP. Supported.
151 * IAC BRK (243) Break. Like serial line break. TODO via tcsendbreak()?
152 * IAC AYT (246) Are you there. Send back evidence that AYT was seen. TODO (send NOP back)?
153 * Implemented only as part of NAWS:
154 * IAC SB (250) Subnegotiation of an option follows.
155 * IAC SE (240) End of subnegotiation.
156 * These don't look useful:
157 * IAC DM (242) Data mark. What is this?
158 * IAC IP (244) Suspend, interrupt or abort the process. (Ancient cousin of ^C).
159 * IAC AO (245) Abort output. "You can continue running, but do not send me the output".
160 * IAC EC (247) Erase character. The receiver should delete the last received char.
161 * IAC EL (248) Erase line. The receiver should delete everything up tp last newline.
162 * IAC GA (249) Go ahead. For half-duplex lines: "now you talk".
164 if (buf[1] == IAC) { /* Literal 255 (emacs M-DEL) */
165 rc = safe_write(ts->ptyfd, buf, 1);
169 goto update_and_return;
171 if (buf[1] == NOP) { /* NOP (241). Ignore (putty keepalive, etc) */
173 goto update_and_return;
177 /* BUG: only 2 bytes of the IAC is in the buffer, we just eat them */
179 goto update_and_return;
182 /* TELOPT_NAWS support */
183 /* IAC SB, TELOPT_NAWS, 4-byte, IAC SE */
184 if (buf[1] == SB && buf[2] == TELOPT_NAWS) {
187 /* BUG: incomplete, can't process */
189 goto update_and_return;
191 memset(&ws, 0, sizeof(ws));
192 ws.ws_col = (buf[3] << 8) | buf[4];
193 ws.ws_row = (buf[5] << 8) | buf[6];
194 ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
196 goto update_and_return;
199 /* Skip 3-byte cmds (assume they are WILL/WONT/DO/DONT 251..254 codes) */
201 fprintf(stderr, "Ignoring IAC %s,%s\n",
202 TELCMD(buf[1]), TELOPT(buf[2]));
208 if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
212 * Hack. We cannot process IACs which wrap around buffer's end.
213 * Since properly fixing it requires writing bigger code,
214 * we rely instead on this code making it virtually impossible
215 * to have wrapped IAC (people don't type at 2k/second).
216 * It also allows for bigger reads in common case.
218 if (ts->size1 == 0) { /* very typical */
219 //bb_error_msg("zero size1");
225 if (wr != 0 && wr < ts->rdidx1) {
226 /* Buffer is not wrapped yet.
227 * We can easily move it to the beginning.
229 //bb_error_msg("moved %d", wr);
230 memmove(TS_BUF1(ts), TS_BUF1(ts) + wr, ts->size1);
238 * Converting single IAC into double on output
240 static size_t safe_write_double_iac(int fd, const char *buf, size_t count)
243 size_t wr, rc, total;
249 if (*buf == (char)IAC) {
250 static const char IACIAC[] ALIGN1 = { IAC, IAC };
251 rc = safe_write(fd, IACIAC, 2);
252 /* BUG: if partial write was only 1 byte long, we end up emitting just one IAC */
260 /* count != 0, *buf != IAC */
261 IACptr = memchr(buf, IAC, count);
265 rc = safe_write(fd, buf, wr);
272 /* here: rc - result of last short write */
273 if ((ssize_t)rc < 0) { /* error? */
281 /* Must match getopt32 string */
283 OPT_WATCHCHILD = (1 << 2), /* -K */
284 OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
285 OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p PORT */
286 OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
287 OPT_SYSLOG = (1 << 7) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -S */
288 OPT_WAIT = (1 << 8) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -w SEC */
291 static struct tsession *
293 IF_FEATURE_TELNETD_STANDALONE(int sock)
294 IF_NOT_FEATURE_TELNETD_STANDALONE(void)
296 #if !ENABLE_FEATURE_TELNETD_STANDALONE
299 const char *login_argv[2];
300 struct termios termbuf;
302 char tty_name[GETPTY_BUFSIZE];
303 struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
305 /*ts->buf1 = (char *)(ts + 1);*/
306 /*ts->buf2 = ts->buf1 + BUFSIZE;*/
308 /* Got a new connection, set up a tty */
309 fd = xgetpty(tty_name);
314 close_on_exec_on(fd);
316 /* SO_KEEPALIVE by popular demand */
317 setsockopt_keepalive(sock);
318 #if ENABLE_FEATURE_TELNETD_STANDALONE
319 ts->sockfd_read = sock;
321 if (sock == 0) { /* We are called with fd 0 - we are in inetd mode */
322 sock++; /* so use fd 1 for output */
325 ts->sockfd_write = sock;
329 /* ts->sockfd_read = 0; - done by xzalloc */
330 ts->sockfd_write = 1;
335 /* Make the telnet client understand we will echo characters so it
336 * should not do it locally. We don't tell the client to run linemode,
337 * because we want to handle line editing and tab completion and other
338 * stuff that requires char-by-char support. */
340 static const char iacs_to_send[] ALIGN1 = {
341 IAC, DO, TELOPT_ECHO,
342 IAC, DO, TELOPT_NAWS,
343 /* This requires telnetd.ctrlSQ.patch (incomplete) */
344 /*IAC, DO, TELOPT_LFLOW,*/
345 IAC, WILL, TELOPT_ECHO,
346 IAC, WILL, TELOPT_SGA
348 /* This confuses safe_write_double_iac(), it will try to duplicate
350 //memcpy(TS_BUF2(ts), iacs_to_send, sizeof(iacs_to_send));
351 //ts->rdidx2 = sizeof(iacs_to_send);
352 //ts->size2 = sizeof(iacs_to_send);
353 /* So just stuff it into TCP stream! (no error check...) */
354 #if ENABLE_FEATURE_TELNETD_STANDALONE
355 safe_write(sock, iacs_to_send, sizeof(iacs_to_send));
357 safe_write(1, iacs_to_send, sizeof(iacs_to_send));
359 /*ts->rdidx2 = 0; - xzalloc did it */
364 pid = vfork(); /* NOMMU-friendly */
368 /* sock will be closed by caller */
369 bb_perror_msg("vfork");
379 /* Careful - we are after vfork! */
381 /* Restore default signal handling ASAP */
382 bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
386 if (ENABLE_FEATURE_UTMP) {
387 len_and_sockaddr *lsa = get_peer_lsa(sock);
388 char *hostname = NULL;
390 hostname = xmalloc_sockaddr2dotted(&lsa->u.sa);
393 write_new_utmp(pid, LOGIN_PROCESS, tty_name, /*username:*/ "LOGIN", hostname);
397 /* Make new session and process group */
400 /* Open the child's side of the tty */
401 /* NB: setsid() disconnects from any previous ctty's. Therefore
402 * we must open child's side of the tty AFTER setsid! */
404 xopen(tty_name, O_RDWR); /* becomes our ctty */
407 tcsetpgrp(0, pid); /* switch this tty's process group to us */
409 /* The pseudo-terminal allocated to the client is configured to operate
410 * in cooked mode, and with XTABS CRMOD enabled (see tty(4)) */
411 tcgetattr(0, &termbuf);
412 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
413 termbuf.c_oflag |= ONLCR | XTABS;
414 termbuf.c_iflag |= ICRNL;
415 termbuf.c_iflag &= ~IXOFF;
416 /*termbuf.c_lflag &= ~ICANON;*/
417 tcsetattr_stdin_TCSANOW(&termbuf);
419 /* Uses FILE-based I/O to stdout, but does fflush_all(),
420 * so should be safe with vfork.
421 * I fear, though, that some users will have ridiculously big
422 * issue files, and they may block writing to fd 1,
423 * (parent is supposed to read it, but parent waits
424 * for vforked child to exec!) */
425 print_login_issue(G.issuefile, tty_name);
427 /* Exec shell / login / whatever */
428 login_argv[0] = G.loginpath;
429 login_argv[1] = NULL;
430 /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
431 * exec external program.
432 * NB: sock is either 0 or has CLOEXEC set on it.
433 * fd has CLOEXEC set on it too. These two fds will be closed here.
435 BB_EXECVP(G.loginpath, (char **)login_argv);
436 /* _exit is safer with vfork, and we shouldn't send message
437 * to remote clients anyway */
438 _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", G.loginpath);*/
441 #if ENABLE_FEATURE_TELNETD_STANDALONE
444 free_session(struct tsession *ts)
448 if (option_mask32 & OPT_INETD)
451 /* Unlink this telnet session from the session list */
454 G.sessions = ts->next;
456 while (t->next != ts)
462 /* It was said that "normal" telnetd just closes ptyfd,
463 * doesn't send SIGKILL. When we close ptyfd,
464 * kernel sends SIGHUP to processes having slave side opened. */
465 kill(ts->shell_pid, SIGKILL);
466 waitpid(ts->shell_pid, NULL, 0);
469 close(ts->sockfd_read);
470 /* We do not need to close(ts->sockfd_write), it's the same
471 * as sockfd_read unless we are in inetd mode. But in inetd mode
472 * we do not reach this */
475 /* Scan all sessions and find new maxfd */
479 if (G.maxfd < ts->ptyfd)
481 if (G.maxfd < ts->sockfd_read)
482 G.maxfd = ts->sockfd_read;
484 /* Again, sockfd_write == sockfd_read here */
485 if (G.maxfd < ts->sockfd_write)
486 G.maxfd = ts->sockfd_write;
492 #else /* !FEATURE_TELNETD_STANDALONE */
494 /* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
495 #define free_session(ts) return 0
499 static void handle_sigchld(int sig UNUSED_PARAM)
503 int save_errno = errno;
505 /* Looping: more than one child may have exited */
507 pid = wait_any_nohang(NULL);
512 if (ts->shell_pid == pid) {
514 update_utmp_DEAD_PROCESS(pid);
524 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
525 int telnetd_main(int argc UNUSED_PARAM, char **argv)
527 fd_set rdfdset, wrfdset;
531 #if ENABLE_FEATURE_TELNETD_STANDALONE
532 #define IS_INETD (opt & OPT_INETD)
533 int master_fd = master_fd; /* for compiler */
534 int sec_linger = sec_linger;
535 char *opt_bindaddr = NULL;
545 /* -w NUM, and implies -F. -w and -i don't mix */
546 IF_FEATURE_TELNETD_INETD_WAIT(opt_complementary = "wF:i--w:w--i";)
547 /* Even if !STANDALONE, we accept (and ignore) -i, thus people
548 * don't need to guess whether it's ok to pass -i to us */
549 opt = getopt32(argv, "f:l:Ki"
550 IF_FEATURE_TELNETD_STANDALONE("p:b:F")
551 IF_FEATURE_TELNETD_INETD_WAIT("Sw:+"),
552 &G.issuefile, &G.loginpath
553 IF_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr)
554 IF_FEATURE_TELNETD_INETD_WAIT(, &sec_linger)
556 if (!IS_INETD /*&& !re_execed*/) {
557 /* inform that we start in standalone mode?
558 * May be useful when people forget to give -i */
559 /*bb_error_msg("listening for connections");*/
560 if (!(opt & OPT_FOREGROUND)) {
561 /* DAEMON_CHDIR_ROOT was giving inconsistent
562 * behavior with/without -F, -i */
563 bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
566 /* Redirect log to syslog early, if needed */
567 if (IS_INETD || (opt & OPT_SYSLOG) || !(opt & OPT_FOREGROUND)) {
568 openlog(applet_name, LOG_PID, LOG_DAEMON);
569 logmode = LOGMODE_SYSLOG;
571 #if ENABLE_FEATURE_TELNETD_STANDALONE
573 G.sessions = make_new_session(0);
574 if (!G.sessions) /* pty opening or vfork problem, exit */
575 return 1; /* make_new_session printed error message */
578 if (!(opt & OPT_WAIT)) {
579 unsigned portnbr = 23;
581 portnbr = xatou16(opt_portnbr);
582 master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
583 xlisten(master_fd, 1);
585 close_on_exec_on(master_fd);
588 G.sessions = make_new_session();
589 if (!G.sessions) /* pty opening or vfork problem, exit */
590 return 1; /* make_new_session printed error message */
593 /* We don't want to die if just one session is broken */
594 signal(SIGPIPE, SIG_IGN);
596 if (opt & OPT_WATCHCHILD)
597 signal(SIGCHLD, handle_sigchld);
598 else /* prevent dead children from becoming zombies */
599 signal(SIGCHLD, SIG_IGN);
602 This is how the buffers are used. The arrows indicate data flow.
604 +-------+ wridx1++ +------+ rdidx1++ +----------+
605 | | <-------------- | buf1 | <-------------- | |
606 | | size1-- +------+ size1++ | |
608 | | rdidx2++ +------+ wridx2++ | |
609 | | --------------> | buf2 | --------------> | |
610 +-------+ size2++ +------+ size2-- +----------+
612 size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
613 size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
615 Each session has got two buffers. Buffers are circular. If sizeN == 0,
616 buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
623 /* Select on the master socket, all telnet sockets and their
624 * ptys if there is room in their session buffers.
625 * NB: scalability problem: we recalculate entire bitmap
626 * before each select. Can be a problem with 500+ connections. */
629 struct tsession *next = ts->next; /* in case we free ts */
630 if (ts->shell_pid == -1) {
631 /* Child died and we detected that */
634 if (ts->size1 > 0) /* can write to pty */
635 FD_SET(ts->ptyfd, &wrfdset);
636 if (ts->size1 < BUFSIZE) /* can read from socket */
637 FD_SET(ts->sockfd_read, &rdfdset);
638 if (ts->size2 > 0) /* can write to socket */
639 FD_SET(ts->sockfd_write, &wrfdset);
640 if (ts->size2 < BUFSIZE) /* can read from pty */
641 FD_SET(ts->ptyfd, &rdfdset);
646 FD_SET(master_fd, &rdfdset);
647 /* This is needed because free_session() does not
648 * take master_fd into account when it finds new
649 * maxfd among remaining fd's */
650 if (master_fd > G.maxfd)
655 struct timeval *tv_ptr = NULL;
656 #if ENABLE_FEATURE_TELNETD_INETD_WAIT
658 if ((opt & OPT_WAIT) && !G.sessions) {
659 tv.tv_sec = sec_linger;
664 count = select(G.maxfd + 1, &rdfdset, &wrfdset, NULL, tv_ptr);
666 if (count == 0) /* "telnetd -w SEC" timed out */
669 goto again; /* EINTR or ENOMEM */
671 #if ENABLE_FEATURE_TELNETD_STANDALONE
672 /* Check for and accept new sessions */
673 if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
675 struct tsession *new_ts;
677 fd = accept(master_fd, NULL, NULL);
680 close_on_exec_on(fd);
682 /* Create a new session and link it into active list */
683 new_ts = make_new_session(fd);
685 new_ts->next = G.sessions;
693 /* Then check for data tunneling */
695 while (ts) { /* For all sessions... */
696 struct tsession *next = ts->next; /* in case we free ts */
698 if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
699 /* Write to pty from buffer 1 */
700 count = safe_write_to_pty_decode_iac(ts);
708 if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
709 /* Write to socket from buffer 2 */
710 count = MIN(BUFSIZE - ts->wridx2, ts->size2);
711 count = safe_write_double_iac(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count);
718 if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
721 if (ts->size2 == 0) {
728 if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
729 /* Read from socket to buffer 1 */
730 count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
731 count = safe_read(ts->sockfd_read, TS_BUF1(ts) + ts->rdidx1, count);
733 if (count < 0 && errno == EAGAIN)
737 /* Ignore trailing NUL if it is there */
738 if (!TS_BUF1(ts)[ts->rdidx1 + count - 1]) {
743 if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
747 if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
748 /* Read from pty to buffer 2 */
749 count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
750 count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count);
752 if (count < 0 && errno == EAGAIN)
758 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */
765 if (ts->shell_pid > 0)
766 update_utmp_DEAD_PROCESS(ts->shell_pid);