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
32 #include <arpa/telnet.h>
33 #include <sys/syslog.h>
36 /* Structure that describes a session */
38 struct tsession *next;
39 int sockfd_read, sockfd_write, ptyfd;
42 /* two circular buffers */
43 /*char *buf1, *buf2;*/
44 /*#define TS_BUF1 ts->buf1*/
45 /*#define TS_BUF2 TS_BUF2*/
46 #define TS_BUF1 ((unsigned char*)(ts + 1))
47 #define TS_BUF2 (((unsigned char*)(ts + 1)) + BUFSIZE)
48 int rdidx1, wridx1, size1;
49 int rdidx2, wridx2, size2;
52 /* Two buffers are directly after tsession in malloced memory.
53 * Make whole thing fit in 4k */
54 enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
59 static struct tsession *sessions;
61 static const char *loginpath = "/bin/login";
63 static const char *loginpath = DEFAULT_SHELL;
65 static const char *issuefile = "/etc/issue.net";
69 Remove all IAC's from buf1 (received IACs are ignored and must be removed
70 so as to not be interpreted by the terminal). Make an uninterrupted
71 string of characters fit for the terminal. Do this by packing
72 all characters meant for the terminal sequentially towards the end of buf.
74 Return a pointer to the beginning of the characters meant for the terminal.
75 and make *num_totty the number of characters that should be sent to
78 Note - If an IAC (3 byte quantity) starts before (bf + len) but extends
79 past (bf + len) then that IAC will be left unprocessed and *processed
80 will be less than len.
82 FIXME - if we mean to send 0xFF to the terminal then it will be escaped,
83 what is the escape character? We aren't handling that situation here.
85 CR-LF ->'s CR mapping is also done here, for convenience.
87 NB: may fail to remove iacs which wrap around buffer!
89 static unsigned char *
90 remove_iacs(struct tsession *ts, int *pnum_totty)
92 unsigned char *ptr0 = TS_BUF1 + ts->wridx1;
93 unsigned char *ptr = ptr0;
94 unsigned char *totty = ptr;
95 unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
104 /* We now map \r\n ==> \r for pragmatic reasons.
105 * Many client implementations send \r\n when
106 * the user hits the CarriageReturn key.
108 if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
112 * TELOPT_NAWS support!
114 if ((ptr+2) >= end) {
115 /* only the beginning of the IAC is in the
116 buffer we were asked to process, we can't
117 process this char. */
122 * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
124 else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
128 break; /* incomplete, can't process */
129 ws.ws_col = (ptr[3] << 8) | ptr[4];
130 ws.ws_row = (ptr[5] << 8) | ptr[6];
131 ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
134 /* skip 3-byte IAC non-SB cmd */
136 fprintf(stderr, "Ignoring IAC %s,%s\n",
137 TELCMD(ptr[1]), TELOPT(ptr[2]));
144 num_totty = totty - ptr0;
145 *pnum_totty = num_totty;
146 /* the difference between ptr and totty is number of iacs
147 we removed from the stream. Adjust buf1 accordingly. */
148 if ((ptr - totty) == 0) /* 99.999% of cases */
150 ts->wridx1 += ptr - totty;
151 ts->size1 -= ptr - totty;
152 /* move chars meant for the terminal towards the end of the buffer */
153 return memmove(ptr - num_totty, ptr0, num_totty);
158 getpty(char *line, int size)
161 #if ENABLE_FEATURE_DEVPTS
162 p = open("/dev/ptmx", O_RDWR);
169 bb_perror_msg("ptsname error (is /dev/pts mounted?)");
172 safe_strncpy(line, name, size);
180 strcpy(line, "/dev/ptyXX");
182 for (i = 0; i < 16; i++) {
183 line[8] = "pqrstuvwxyzabcde"[i];
185 if (stat(line, &stb) < 0) {
188 for (j = 0; j < 16; j++) {
189 line[9] = j < 10 ? j + '0' : j - 10 + 'a';
191 fprintf(stderr, "Trying to open device: %s\n", line);
192 p = open(line, O_RDWR | O_NOCTTY);
199 #endif /* FEATURE_DEVPTS */
204 static struct tsession *
206 USE_FEATURE_TELNETD_STANDALONE(int sock)
207 SKIP_FEATURE_TELNETD_STANDALONE(void)
209 const char *login_argv[2];
210 struct termios termbuf;
213 struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
215 /*ts->buf1 = (char *)(ts + 1);*/
216 /*ts->buf2 = ts->buf1 + BUFSIZE;*/
218 /* Got a new connection, set up a tty. */
219 fd = getpty(tty_name, 32);
221 bb_error_msg("can't create pty");
228 #if ENABLE_FEATURE_TELNETD_STANDALONE
229 ts->sockfd_read = sock;
231 if (!sock) /* We are called with fd 0 - we are in inetd mode */
233 ts->sockfd_write = sock;
238 /* ts->sockfd_read = 0; - done by xzalloc */
239 ts->sockfd_write = 1;
243 /* Make the telnet client understand we will echo characters so it
244 * should not do it locally. We don't tell the client to run linemode,
245 * because we want to handle line editing and tab completion and other
246 * stuff that requires char-by-char support. */
248 static const char iacs_to_send[] ALIGN1 = {
249 IAC, DO, TELOPT_ECHO,
250 IAC, DO, TELOPT_NAWS,
251 IAC, DO, TELOPT_LFLOW,
252 IAC, WILL, TELOPT_ECHO,
253 IAC, WILL, TELOPT_SGA
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);
260 fflush(NULL); /* flush all streams */
261 pid = vfork(); /* NOMMU-friendly */
265 /* sock_r and sock_w will be closed by caller */
266 bb_perror_msg("vfork");
276 /* Careful - we are after vfork! */
278 /* make new session and process group */
281 /* open the child's side of the tty. */
282 /* NB: setsid() disconnects from any previous ctty's. Therefore
283 * we must open child's side of the tty AFTER setsid! */
284 fd = xopen(tty_name, O_RDWR); /* becomes our ctty */
288 while (fd > 2) close(fd--);
289 tcsetpgrp(0, getpid()); /* switch this tty's process group to us */
291 /* The pseudo-terminal allocated to the client is configured to operate in
292 * cooked mode, and with XTABS CRMOD enabled (see tty(4)). */
293 tcgetattr(0, &termbuf);
294 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
295 termbuf.c_oflag |= ONLCR | XTABS;
296 termbuf.c_iflag |= ICRNL;
297 termbuf.c_iflag &= ~IXOFF;
298 /*termbuf.c_lflag &= ~ICANON;*/
299 tcsetattr(0, TCSANOW, &termbuf);
301 /* Uses FILE-based I/O to stdout, but does fflush(stdout),
302 * so should be safe with vfork.
303 * I fear, though, that some users will have ridiculously big
304 * issue files, and they may block writing to fd 1. */
305 print_login_issue(issuefile, NULL);
307 /* Exec shell / login / whatever */
308 login_argv[0] = loginpath;
309 login_argv[1] = NULL;
310 execvp(loginpath, (char **)login_argv);
311 /* Safer with vfork, and we shouldn't send message
312 * to remote clients anyway */
313 _exit(1); /*bb_perror_msg_and_die("execv %s", loginpath);*/
316 #if ENABLE_FEATURE_TELNETD_STANDALONE
319 free_session(struct tsession *ts)
321 struct tsession *t = sessions;
323 /* Unlink this telnet session from the session list */
327 while (t->next != ts)
333 /* It was said that "normal" telnetd just closes ptyfd,
334 * doesn't send SIGKILL. When we close ptyfd,
335 * kernel sends SIGHUP to processes having slave side opened. */
336 kill(ts->shell_pid, SIGKILL);
337 wait4(ts->shell_pid, NULL, 0, NULL);
340 close(ts->sockfd_read);
341 /* We do not need to close(ts->sockfd_write), it's the same
342 * as sockfd_read unless we are in inetd mode. But in inetd mode
343 * we do not free_session(), ever */
346 /* Scan all sessions and find new maxfd */
350 if (maxfd < ts->ptyfd)
352 if (maxfd < ts->sockfd_read)
353 maxfd = ts->sockfd_read;
355 /* Again, sockfd_write == sockfd_read here */
356 if (maxfd < ts->sockfd_write)
357 maxfd = ts->sockfd_write;
363 #else /* !FEATURE_TELNETD_STANDALONE */
365 /* Never actually called */
366 void free_session(struct tsession *ts);
370 static void handle_sigchld(int sig)
375 pid = waitpid(-1, &sig, WNOHANG);
379 if (ts->shell_pid == pid) {
389 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
390 int telnetd_main(int argc, char **argv)
392 fd_set rdfdset, wrfdset;
396 #if ENABLE_FEATURE_TELNETD_STANDALONE
397 #define IS_INETD (opt & OPT_INETD)
398 int master_fd = master_fd; /* be happy, gcc */
399 unsigned portnbr = 23;
400 char *opt_bindaddr = NULL;
410 OPT_WATCHCHILD = (1 << 2), /* -K */
411 OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
412 OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p */
413 OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
416 /* Even if !STANDALONE, we accept (and ignore) -i, thus people
417 * don't need to guess whether it's ok to pass -i to us */
418 opt = getopt32(argv, "f:l:Ki" USE_FEATURE_TELNETD_STANDALONE("p:b:F"),
419 &issuefile, &loginpath
420 USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
421 if (!IS_INETD /*&& !re_execed*/) {
422 /* inform that we start in standalone mode?
423 * May be useful when people forget to give -i */
424 /*bb_error_msg("listening for connections");*/
425 if (!(opt & OPT_FOREGROUND)) {
426 /* DAEMON_CHDIR_ROOT was giving inconsistent
427 * behavior with/without -F, -i */
428 bb_daemonize_or_rexec(0 /*DAEMON_CHDIR_ROOT*/, argv);
431 /* Redirect log to syslog early, if needed */
432 if (IS_INETD || !(opt & OPT_FOREGROUND)) {
433 openlog(applet_name, 0, LOG_USER);
434 logmode = LOGMODE_SYSLOG;
436 USE_FEATURE_TELNETD_STANDALONE(
438 portnbr = xatou16(opt_portnbr);
441 /* Used to check access(loginpath, X_OK) here. Pointless.
442 * exec will do this for us for free later. */
444 #if ENABLE_FEATURE_TELNETD_STANDALONE
446 sessions = make_new_session(0);
447 if (!sessions) /* pty opening or vfork problem, exit */
448 return 1; /* make_new_session prints error message */
450 master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
451 xlisten(master_fd, 1);
454 sessions = make_new_session();
455 if (!sessions) /* pty opening or vfork problem, exit */
456 return 1; /* make_new_session prints error message */
459 /* We don't want to die if just one session is broken */
460 signal(SIGPIPE, SIG_IGN);
462 if (opt & OPT_WATCHCHILD)
463 signal(SIGCHLD, handle_sigchld);
466 This is how the buffers are used. The arrows indicate the movement
468 +-------+ wridx1++ +------+ rdidx1++ +----------+
469 | | <-------------- | buf1 | <-------------- | |
470 | | size1-- +------+ size1++ | |
472 | | rdidx2++ +------+ wridx2++ | |
473 | | --------------> | buf2 | --------------> | |
474 +-------+ size2++ +------+ size2-- +----------+
476 size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
477 size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
479 Each session has got two buffers. Buffers are circular. If sizeN == 0,
480 buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
487 /* Select on the master socket, all telnet sockets and their
488 * ptys if there is room in their session buffers.
489 * NB: scalability problem: we recalculate entire bitmap
490 * before each select. Can be a problem with 500+ connections. */
493 struct tsession *next = ts->next; /* in case we free ts. */
494 if (ts->shell_pid == -1) {
497 if (ts->size1 > 0) /* can write to pty */
498 FD_SET(ts->ptyfd, &wrfdset);
499 if (ts->size1 < BUFSIZE) /* can read from socket */
500 FD_SET(ts->sockfd_read, &rdfdset);
501 if (ts->size2 > 0) /* can write to socket */
502 FD_SET(ts->sockfd_write, &wrfdset);
503 if (ts->size2 < BUFSIZE) /* can read from pty */
504 FD_SET(ts->ptyfd, &rdfdset);
509 FD_SET(master_fd, &rdfdset);
510 /* This is needed because free_session() does not
511 * take into account master_fd when it finds new
512 * maxfd among remaining fd's */
513 if (master_fd > maxfd)
517 count = select(maxfd + 1, &rdfdset, &wrfdset, NULL, NULL);
519 goto again; /* EINTR or ENOMEM */
521 #if ENABLE_FEATURE_TELNETD_STANDALONE
522 /* First check for and accept new sessions. */
523 if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
525 struct tsession *new_ts;
527 fd = accept(master_fd, NULL, NULL);
530 /* Create a new session and link it into our active list */
531 new_ts = make_new_session(fd);
533 new_ts->next = sessions;
541 /* Then check for data tunneling. */
543 while (ts) { /* For all sessions... */
544 struct tsession *next = ts->next; /* in case we free ts. */
546 if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
549 /* Write to pty from buffer 1. */
550 ptr = remove_iacs(ts, &num_totty);
551 count = safe_write(ts->ptyfd, ptr, num_totty);
561 if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
565 if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
566 /* Write to socket from buffer 2. */
567 count = MIN(BUFSIZE - ts->wridx2, ts->size2);
568 count = safe_write(ts->sockfd_write, TS_BUF2 + ts->wridx2, count);
578 if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
582 /* Should not be needed, but... remove_iacs is actually buggy
583 * (it cannot process iacs which wrap around buffer's end)!
584 * Since properly fixing it requires writing bigger code,
585 * we rely instead on this code making it virtually impossible
586 * to have wrapped iac (people don't type at 2k/second).
587 * It also allows for bigger reads in common case. */
588 if (ts->size1 == 0) {
592 if (ts->size2 == 0) {
597 if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
598 /* Read from socket to buffer 1. */
599 count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
600 count = safe_read(ts->sockfd_read, TS_BUF1 + ts->rdidx1, count);
602 if (count < 0 && errno == EAGAIN)
608 /* Ignore trailing NUL if it is there */
609 if (!TS_BUF1[ts->rdidx1 + count - 1]) {
614 if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
618 if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
619 /* Read from pty to buffer 2. */
620 count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
621 count = safe_read(ts->ptyfd, TS_BUF2 + ts->rdidx2, count);
623 if (count < 0 && errno == EAGAIN)
631 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */