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 */
232 sock++; /* so use fd 1 for output */
235 ts->sockfd_write = sock;
239 /* ts->sockfd_read = 0; - done by xzalloc */
240 ts->sockfd_write = 1;
244 /* Make the telnet client understand we will echo characters so it
245 * should not do it locally. We don't tell the client to run linemode,
246 * because we want to handle line editing and tab completion and other
247 * stuff that requires char-by-char support. */
249 static const char iacs_to_send[] ALIGN1 = {
250 IAC, DO, TELOPT_ECHO,
251 IAC, DO, TELOPT_NAWS,
252 IAC, DO, TELOPT_LFLOW,
253 IAC, WILL, TELOPT_ECHO,
254 IAC, WILL, TELOPT_SGA
256 memcpy(TS_BUF2, iacs_to_send, sizeof(iacs_to_send));
257 ts->rdidx2 = sizeof(iacs_to_send);
258 ts->size2 = sizeof(iacs_to_send);
261 fflush(NULL); /* flush all streams */
262 pid = vfork(); /* NOMMU-friendly */
266 /* sock will be closed by caller */
267 bb_perror_msg("vfork");
277 /* Careful - we are after vfork! */
279 /* make new session and process group */
282 /* open the child's side of the tty. */
283 /* NB: setsid() disconnects from any previous ctty's. Therefore
284 * we must open child's side of the tty AFTER setsid! */
285 fd = xopen(tty_name, O_RDWR); /* becomes our ctty */
289 while (fd > 2) close(fd--);
290 tcsetpgrp(0, getpid()); /* switch this tty's process group to us */
292 /* The pseudo-terminal allocated to the client is configured to operate in
293 * cooked mode, and with XTABS CRMOD enabled (see tty(4)). */
294 tcgetattr(0, &termbuf);
295 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
296 termbuf.c_oflag |= ONLCR | XTABS;
297 termbuf.c_iflag |= ICRNL;
298 termbuf.c_iflag &= ~IXOFF;
299 /*termbuf.c_lflag &= ~ICANON;*/
300 tcsetattr(0, TCSANOW, &termbuf);
302 /* Uses FILE-based I/O to stdout, but does fflush(stdout),
303 * so should be safe with vfork.
304 * I fear, though, that some users will have ridiculously big
305 * issue files, and they may block writing to fd 1. */
306 print_login_issue(issuefile, NULL);
308 /* Exec shell / login / whatever */
309 login_argv[0] = loginpath;
310 login_argv[1] = NULL;
311 execvp(loginpath, (char **)login_argv);
312 /* Safer with vfork, and we shouldn't send message
313 * to remote clients anyway */
314 _exit(1); /*bb_perror_msg_and_die("execv %s", loginpath);*/
317 #if ENABLE_FEATURE_TELNETD_STANDALONE
320 free_session(struct tsession *ts)
322 struct tsession *t = sessions;
324 /* Unlink this telnet session from the session list */
328 while (t->next != ts)
334 /* It was said that "normal" telnetd just closes ptyfd,
335 * doesn't send SIGKILL. When we close ptyfd,
336 * kernel sends SIGHUP to processes having slave side opened. */
337 kill(ts->shell_pid, SIGKILL);
338 wait4(ts->shell_pid, NULL, 0, NULL);
341 close(ts->sockfd_read);
342 /* We do not need to close(ts->sockfd_write), it's the same
343 * as sockfd_read unless we are in inetd mode. But in inetd mode
344 * we do not free_session(), ever */
347 /* Scan all sessions and find new maxfd */
351 if (maxfd < ts->ptyfd)
353 if (maxfd < ts->sockfd_read)
354 maxfd = ts->sockfd_read;
356 /* Again, sockfd_write == sockfd_read here */
357 if (maxfd < ts->sockfd_write)
358 maxfd = ts->sockfd_write;
364 #else /* !FEATURE_TELNETD_STANDALONE */
366 /* Never actually called */
367 void free_session(struct tsession *ts);
371 static void handle_sigchld(int sig)
376 pid = waitpid(-1, &sig, WNOHANG);
380 if (ts->shell_pid == pid) {
390 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
391 int telnetd_main(int argc, char **argv)
393 fd_set rdfdset, wrfdset;
397 #if ENABLE_FEATURE_TELNETD_STANDALONE
398 #define IS_INETD (opt & OPT_INETD)
399 int master_fd = master_fd; /* be happy, gcc */
400 unsigned portnbr = 23;
401 char *opt_bindaddr = NULL;
411 OPT_WATCHCHILD = (1 << 2), /* -K */
412 OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
413 OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p */
414 OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
417 /* Even if !STANDALONE, we accept (and ignore) -i, thus people
418 * don't need to guess whether it's ok to pass -i to us */
419 opt = getopt32(argv, "f:l:Ki" USE_FEATURE_TELNETD_STANDALONE("p:b:F"),
420 &issuefile, &loginpath
421 USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
422 if (!IS_INETD /*&& !re_execed*/) {
423 /* inform that we start in standalone mode?
424 * May be useful when people forget to give -i */
425 /*bb_error_msg("listening for connections");*/
426 if (!(opt & OPT_FOREGROUND)) {
427 /* DAEMON_CHDIR_ROOT was giving inconsistent
428 * behavior with/without -F, -i */
429 bb_daemonize_or_rexec(0 /*DAEMON_CHDIR_ROOT*/, argv);
432 /* Redirect log to syslog early, if needed */
433 if (IS_INETD || !(opt & OPT_FOREGROUND)) {
434 openlog(applet_name, 0, LOG_USER);
435 logmode = LOGMODE_SYSLOG;
437 USE_FEATURE_TELNETD_STANDALONE(
439 portnbr = xatou16(opt_portnbr);
442 /* Used to check access(loginpath, X_OK) here. Pointless.
443 * exec will do this for us for free later. */
445 #if ENABLE_FEATURE_TELNETD_STANDALONE
447 sessions = make_new_session(0);
448 if (!sessions) /* pty opening or vfork problem, exit */
449 return 1; /* make_new_session prints error message */
451 master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
452 xlisten(master_fd, 1);
455 sessions = make_new_session();
456 if (!sessions) /* pty opening or vfork problem, exit */
457 return 1; /* make_new_session prints error message */
460 /* We don't want to die if just one session is broken */
461 signal(SIGPIPE, SIG_IGN);
463 if (opt & OPT_WATCHCHILD)
464 signal(SIGCHLD, handle_sigchld);
467 This is how the buffers are used. The arrows indicate the movement
469 +-------+ wridx1++ +------+ rdidx1++ +----------+
470 | | <-------------- | buf1 | <-------------- | |
471 | | size1-- +------+ size1++ | |
473 | | rdidx2++ +------+ wridx2++ | |
474 | | --------------> | buf2 | --------------> | |
475 +-------+ size2++ +------+ size2-- +----------+
477 size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
478 size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
480 Each session has got two buffers. Buffers are circular. If sizeN == 0,
481 buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
488 /* Select on the master socket, all telnet sockets and their
489 * ptys if there is room in their session buffers.
490 * NB: scalability problem: we recalculate entire bitmap
491 * before each select. Can be a problem with 500+ connections. */
494 struct tsession *next = ts->next; /* in case we free ts. */
495 if (ts->shell_pid == -1) {
496 #if !ENABLE_FEATURE_TELNETD_STANDALONE
502 if (ts->size1 > 0) /* can write to pty */
503 FD_SET(ts->ptyfd, &wrfdset);
504 if (ts->size1 < BUFSIZE) /* can read from socket */
505 FD_SET(ts->sockfd_read, &rdfdset);
506 if (ts->size2 > 0) /* can write to socket */
507 FD_SET(ts->sockfd_write, &wrfdset);
508 if (ts->size2 < BUFSIZE) /* can read from pty */
509 FD_SET(ts->ptyfd, &rdfdset);
514 FD_SET(master_fd, &rdfdset);
515 /* This is needed because free_session() does not
516 * take into account master_fd when it finds new
517 * maxfd among remaining fd's */
518 if (master_fd > maxfd)
522 count = select(maxfd + 1, &rdfdset, &wrfdset, NULL, NULL);
524 goto again; /* EINTR or ENOMEM */
526 #if ENABLE_FEATURE_TELNETD_STANDALONE
527 /* First check for and accept new sessions. */
528 if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
530 struct tsession *new_ts;
532 fd = accept(master_fd, NULL, NULL);
535 /* Create a new session and link it into our active list */
536 new_ts = make_new_session(fd);
538 new_ts->next = sessions;
546 /* Then check for data tunneling. */
548 while (ts) { /* For all sessions... */
549 struct tsession *next = ts->next; /* in case we free ts. */
551 if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
554 /* Write to pty from buffer 1. */
555 ptr = remove_iacs(ts, &num_totty);
556 count = safe_write(ts->ptyfd, ptr, num_totty);
564 if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
568 if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
569 /* Write to socket from buffer 2. */
570 count = MIN(BUFSIZE - ts->wridx2, ts->size2);
571 count = safe_write(ts->sockfd_write, TS_BUF2 + ts->wridx2, count);
579 if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
583 /* Should not be needed, but... remove_iacs is actually buggy
584 * (it cannot process iacs which wrap around buffer's end)!
585 * Since properly fixing it requires writing bigger code,
586 * we rely instead on this code making it virtually impossible
587 * to have wrapped iac (people don't type at 2k/second).
588 * It also allows for bigger reads in common case. */
589 if (ts->size1 == 0) {
593 if (ts->size2 == 0) {
598 if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
599 /* Read from socket to buffer 1. */
600 count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
601 count = safe_read(ts->sockfd_read, TS_BUF1 + ts->rdidx1, count);
603 if (count < 0 && errno == EAGAIN)
607 /* Ignore trailing NUL if it is there */
608 if (!TS_BUF1[ts->rdidx1 + count - 1]) {
613 if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
617 if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
618 /* Read from pty to buffer 2. */
619 count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
620 count = safe_read(ts->ptyfd, TS_BUF2 + ts->rdidx2, count);
622 if (count < 0 && errno == EAGAIN)
628 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */
635 #if !ENABLE_FEATURE_TELNETD_STANDALONE