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 tarball for details.
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
33 #include <arpa/telnet.h>
35 /* Structure that describes a session */
37 struct tsession *next;
38 int sockfd_read, sockfd_write, ptyfd;
41 /* two circular buffers */
42 /*char *buf1, *buf2;*/
43 /*#define TS_BUF1 ts->buf1*/
44 /*#define TS_BUF2 TS_BUF2*/
45 #define TS_BUF1 ((unsigned char*)(ts + 1))
46 #define TS_BUF2 (((unsigned char*)(ts + 1)) + BUFSIZE)
47 int rdidx1, wridx1, size1;
48 int rdidx2, wridx2, size2;
51 /* Two buffers are directly after tsession in malloced memory.
52 * Make whole thing fit in 4k */
53 enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
58 static struct tsession *sessions;
59 static const char *loginpath = "/bin/login";
60 static const char *issuefile = "/etc/issue.net";
64 Remove all IAC's from buf1 (received IACs are ignored and must be removed
65 so as to not be interpreted by the terminal). Make an uninterrupted
66 string of characters fit for the terminal. Do this by packing
67 all characters meant for the terminal sequentially towards the end of buf.
69 Return a pointer to the beginning of the characters meant for the terminal.
70 and make *num_totty the number of characters that should be sent to
73 Note - If an IAC (3 byte quantity) starts before (bf + len) but extends
74 past (bf + len) then that IAC will be left unprocessed and *processed
75 will be less than len.
77 CR-LF ->'s CR mapping is also done here, for convenience.
79 NB: may fail to remove iacs which wrap around buffer!
81 static unsigned char *
82 remove_iacs(struct tsession *ts, int *pnum_totty)
84 unsigned char *ptr0 = TS_BUF1 + ts->wridx1;
85 unsigned char *ptr = ptr0;
86 unsigned char *totty = ptr;
87 unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
96 /* We map \r\n ==> \r for pragmatic reasons.
97 * Many client implementations send \r\n when
98 * the user hits the CarriageReturn key.
100 if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
107 if (ptr[1] == NOP) { /* Ignore? (putty keepalive, etc.) */
111 if (ptr[1] == IAC) { /* Literal IAC? (emacs M-DEL) */
118 * TELOPT_NAWS support!
120 if ((ptr+2) >= end) {
121 /* only the beginning of the IAC is in the
122 buffer we were asked to process, we can't
123 process this char. */
127 * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
129 if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
132 break; /* incomplete, can't process */
133 ws.ws_col = (ptr[3] << 8) | ptr[4];
134 ws.ws_row = (ptr[5] << 8) | ptr[6];
135 ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
139 /* skip 3-byte IAC non-SB cmd */
141 fprintf(stderr, "Ignoring IAC %s,%s\n",
142 TELCMD(ptr[1]), TELOPT(ptr[2]));
147 num_totty = totty - ptr0;
148 *pnum_totty = num_totty;
149 /* the difference between ptr and totty is number of iacs
150 we removed from the stream. Adjust buf1 accordingly. */
151 if ((ptr - totty) == 0) /* 99.999% of cases */
153 ts->wridx1 += ptr - totty;
154 ts->size1 -= ptr - totty;
155 /* move chars meant for the terminal towards the end of the buffer */
156 return memmove(ptr - num_totty, ptr0, num_totty);
160 * Converting single 0xff into double on output
162 static size_t iac_safe_write(int fd, const char *buf, size_t count)
165 size_t wr, rc, total;
171 if (*buf == (char)0xff) {
172 rc = safe_write(fd, "\xff\xff", 2);
180 /* count != 0, *buf != 0xff */
181 oxff = memchr(buf, 0xff, count);
185 rc = safe_write(fd, buf, wr);
192 /* here: rc - result of last short write */
193 if ((ssize_t)rc < 0) { /* error? */
201 static struct tsession *
203 USE_FEATURE_TELNETD_STANDALONE(int sock)
204 SKIP_FEATURE_TELNETD_STANDALONE(void)
206 const char *login_argv[2];
207 struct termios termbuf;
209 char tty_name[GETPTY_BUFSIZE];
210 struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
212 /*ts->buf1 = (char *)(ts + 1);*/
213 /*ts->buf2 = ts->buf1 + BUFSIZE;*/
215 /* Got a new connection, set up a tty. */
216 fd = xgetpty(tty_name);
221 #if ENABLE_FEATURE_TELNETD_STANDALONE
222 ts->sockfd_read = sock;
223 /* SO_KEEPALIVE by popular demand */
224 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
226 if (!sock) { /* We are called with fd 0 - we are in inetd mode */
227 sock++; /* so use fd 1 for output */
230 ts->sockfd_write = sock;
234 /* SO_KEEPALIVE by popular demand */
235 setsockopt(0, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
236 /* ts->sockfd_read = 0; - done by xzalloc */
237 ts->sockfd_write = 1;
241 /* Make the telnet client understand we will echo characters so it
242 * should not do it locally. We don't tell the client to run linemode,
243 * because we want to handle line editing and tab completion and other
244 * stuff that requires char-by-char support. */
246 static const char iacs_to_send[] ALIGN1 = {
247 IAC, DO, TELOPT_ECHO,
248 IAC, DO, TELOPT_NAWS,
249 IAC, DO, TELOPT_LFLOW,
250 IAC, WILL, TELOPT_ECHO,
251 IAC, WILL, TELOPT_SGA
253 /* This confuses iac_safe_write(), it will try to duplicate
255 //memcpy(TS_BUF2, iacs_to_send, sizeof(iacs_to_send));
256 //ts->rdidx2 = sizeof(iacs_to_send);
257 //ts->size2 = sizeof(iacs_to_send);
258 /* So just stuff it into TCP buffer! */
259 safe_write(sock, iacs_to_send, sizeof(iacs_to_send));
260 /*ts->rdidx2 = 0; - xzalloc did it! */
264 fflush(NULL); /* flush all streams */
265 pid = vfork(); /* NOMMU-friendly */
269 /* sock will be closed by caller */
270 bb_perror_msg("vfork");
280 /* Careful - we are after vfork! */
282 /* make new session and process group */
285 /* Restore default signal handling */
286 bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
288 /* open the child's side of the tty. */
289 /* NB: setsid() disconnects from any previous ctty's. Therefore
290 * we must open child's side of the tty AFTER setsid! */
292 xopen(tty_name, O_RDWR); /* becomes our ctty */
295 tcsetpgrp(0, getpid()); /* switch this tty's process group to us */
297 /* The pseudo-terminal allocated to the client is configured to operate in
298 * cooked mode, and with XTABS CRMOD enabled (see tty(4)). */
299 tcgetattr(0, &termbuf);
300 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
301 termbuf.c_oflag |= ONLCR | XTABS;
302 termbuf.c_iflag |= ICRNL;
303 termbuf.c_iflag &= ~IXOFF;
304 /*termbuf.c_lflag &= ~ICANON;*/
305 tcsetattr_stdin_TCSANOW(&termbuf);
307 /* Uses FILE-based I/O to stdout, but does fflush(stdout),
308 * so should be safe with vfork.
309 * I fear, though, that some users will have ridiculously big
310 * issue files, and they may block writing to fd 1,
311 * (parent is supposed to read it, but parent waits
312 * for vforked child to exec!) */
313 print_login_issue(issuefile, tty_name);
315 /* Exec shell / login / whatever */
316 login_argv[0] = loginpath;
317 login_argv[1] = NULL;
318 /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
319 * exec external program */
320 BB_EXECVP(loginpath, (char **)login_argv);
321 /* _exit is safer with vfork, and we shouldn't send message
322 * to remote clients anyway */
323 _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", loginpath);*/
326 /* Must match getopt32 string */
328 OPT_WATCHCHILD = (1 << 2), /* -K */
329 OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
330 OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p */
331 OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
334 #if ENABLE_FEATURE_TELNETD_STANDALONE
337 free_session(struct tsession *ts)
339 struct tsession *t = sessions;
341 if (option_mask32 & OPT_INETD)
344 /* Unlink this telnet session from the session list */
348 while (t->next != ts)
354 /* It was said that "normal" telnetd just closes ptyfd,
355 * doesn't send SIGKILL. When we close ptyfd,
356 * kernel sends SIGHUP to processes having slave side opened. */
357 kill(ts->shell_pid, SIGKILL);
358 wait4(ts->shell_pid, NULL, 0, NULL);
361 close(ts->sockfd_read);
362 /* We do not need to close(ts->sockfd_write), it's the same
363 * as sockfd_read unless we are in inetd mode. But in inetd mode
364 * we do not reach this */
367 /* Scan all sessions and find new maxfd */
371 if (maxfd < ts->ptyfd)
373 if (maxfd < ts->sockfd_read)
374 maxfd = ts->sockfd_read;
376 /* Again, sockfd_write == sockfd_read here */
377 if (maxfd < ts->sockfd_write)
378 maxfd = ts->sockfd_write;
384 #else /* !FEATURE_TELNETD_STANDALONE */
386 /* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
387 #define free_session(ts) return 0
391 static void handle_sigchld(int sig UNUSED_PARAM)
396 /* Looping: more than one child may have exited */
398 pid = wait_any_nohang(NULL);
403 if (ts->shell_pid == pid) {
412 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
413 int telnetd_main(int argc UNUSED_PARAM, char **argv)
415 fd_set rdfdset, wrfdset;
419 #if ENABLE_FEATURE_TELNETD_STANDALONE
420 #define IS_INETD (opt & OPT_INETD)
421 int master_fd = master_fd; /* be happy, gcc */
422 unsigned portnbr = 23;
423 char *opt_bindaddr = NULL;
432 /* Even if !STANDALONE, we accept (and ignore) -i, thus people
433 * don't need to guess whether it's ok to pass -i to us */
434 opt = getopt32(argv, "f:l:Ki" USE_FEATURE_TELNETD_STANDALONE("p:b:F"),
435 &issuefile, &loginpath
436 USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
437 if (!IS_INETD /*&& !re_execed*/) {
438 /* inform that we start in standalone mode?
439 * May be useful when people forget to give -i */
440 /*bb_error_msg("listening for connections");*/
441 if (!(opt & OPT_FOREGROUND)) {
442 /* DAEMON_CHDIR_ROOT was giving inconsistent
443 * behavior with/without -F, -i */
444 bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
447 /* Redirect log to syslog early, if needed */
448 if (IS_INETD || !(opt & OPT_FOREGROUND)) {
449 openlog(applet_name, 0, LOG_USER);
450 logmode = LOGMODE_SYSLOG;
452 USE_FEATURE_TELNETD_STANDALONE(
454 portnbr = xatou16(opt_portnbr);
457 /* Used to check access(loginpath, X_OK) here. Pointless.
458 * exec will do this for us for free later. */
460 #if ENABLE_FEATURE_TELNETD_STANDALONE
462 sessions = make_new_session(0);
463 if (!sessions) /* pty opening or vfork problem, exit */
464 return 1; /* make_new_session prints error message */
466 master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
467 xlisten(master_fd, 1);
470 sessions = make_new_session();
471 if (!sessions) /* pty opening or vfork problem, exit */
472 return 1; /* make_new_session prints error message */
475 /* We don't want to die if just one session is broken */
476 signal(SIGPIPE, SIG_IGN);
478 if (opt & OPT_WATCHCHILD)
479 signal(SIGCHLD, handle_sigchld);
480 else /* prevent dead children from becoming zombies */
481 signal(SIGCHLD, SIG_IGN);
484 This is how the buffers are used. The arrows indicate the movement
486 +-------+ wridx1++ +------+ rdidx1++ +----------+
487 | | <-------------- | buf1 | <-------------- | |
488 | | size1-- +------+ size1++ | |
490 | | rdidx2++ +------+ wridx2++ | |
491 | | --------------> | buf2 | --------------> | |
492 +-------+ size2++ +------+ size2-- +----------+
494 size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
495 size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
497 Each session has got two buffers. Buffers are circular. If sizeN == 0,
498 buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
505 /* Select on the master socket, all telnet sockets and their
506 * ptys if there is room in their session buffers.
507 * NB: scalability problem: we recalculate entire bitmap
508 * before each select. Can be a problem with 500+ connections. */
511 struct tsession *next = ts->next; /* in case we free ts. */
512 if (ts->shell_pid == -1) {
513 /* Child died and we detected that */
516 if (ts->size1 > 0) /* can write to pty */
517 FD_SET(ts->ptyfd, &wrfdset);
518 if (ts->size1 < BUFSIZE) /* can read from socket */
519 FD_SET(ts->sockfd_read, &rdfdset);
520 if (ts->size2 > 0) /* can write to socket */
521 FD_SET(ts->sockfd_write, &wrfdset);
522 if (ts->size2 < BUFSIZE) /* can read from pty */
523 FD_SET(ts->ptyfd, &rdfdset);
528 FD_SET(master_fd, &rdfdset);
529 /* This is needed because free_session() does not
530 * take master_fd into account when it finds new
531 * maxfd among remaining fd's */
532 if (master_fd > maxfd)
536 count = select(maxfd + 1, &rdfdset, &wrfdset, NULL, NULL);
538 goto again; /* EINTR or ENOMEM */
540 #if ENABLE_FEATURE_TELNETD_STANDALONE
541 /* First check for and accept new sessions. */
542 if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
544 struct tsession *new_ts;
546 fd = accept(master_fd, NULL, NULL);
549 /* Create a new session and link it into our active list */
550 new_ts = make_new_session(fd);
552 new_ts->next = sessions;
560 /* Then check for data tunneling. */
562 while (ts) { /* For all sessions... */
563 struct tsession *next = ts->next; /* in case we free ts. */
565 if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
568 /* Write to pty from buffer 1. */
569 ptr = remove_iacs(ts, &num_totty);
570 count = safe_write(ts->ptyfd, ptr, num_totty);
578 if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
582 if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
583 /* Write to socket from buffer 2. */
584 count = MIN(BUFSIZE - ts->wridx2, ts->size2);
585 count = iac_safe_write(ts->sockfd_write, (void*)(TS_BUF2 + ts->wridx2), count);
593 if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
597 /* Should not be needed, but... remove_iacs is actually buggy
598 * (it cannot process iacs which wrap around buffer's end)!
599 * Since properly fixing it requires writing bigger code,
600 * we rely instead on this code making it virtually impossible
601 * to have wrapped iac (people don't type at 2k/second).
602 * It also allows for bigger reads in common case. */
603 if (ts->size1 == 0) {
607 if (ts->size2 == 0) {
612 if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
613 /* Read from socket to buffer 1. */
614 count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
615 count = safe_read(ts->sockfd_read, TS_BUF1 + ts->rdidx1, count);
617 if (count < 0 && errno == EAGAIN)
621 /* Ignore trailing NUL if it is there */
622 if (!TS_BUF1[ts->rdidx1 + count - 1]) {
627 if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
631 if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
632 /* Read from pty to buffer 2. */
633 count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
634 count = safe_read(ts->ptyfd, TS_BUF2 + ts->rdidx2, count);
636 if (count < 0 && errno == EAGAIN)
642 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */