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>
34 #if ENABLE_FEATURE_UTMP
35 # include <utmp.h> /* LOGIN_PROCESS */
40 struct tsession *next;
46 /* two circular buffers */
47 /*char *buf1, *buf2;*/
48 /*#define TS_BUF1(ts) ts->buf1*/
49 /*#define TS_BUF2(ts) TS_BUF2(ts)*/
50 #define TS_BUF1(ts) ((unsigned char*)(ts + 1))
51 #define TS_BUF2(ts) (((unsigned char*)(ts + 1)) + BUFSIZE)
52 int rdidx1, wridx1, size1;
53 int rdidx2, wridx2, size2;
56 /* Two buffers are directly after tsession in malloced memory.
57 * Make whole thing fit in 4k */
58 enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
63 struct tsession *sessions;
64 const char *loginpath;
65 const char *issuefile;
68 #define G (*(struct globals*)&bb_common_bufsiz1)
69 #define INIT_G() do { \
70 G.loginpath = "/bin/login"; \
71 G.issuefile = "/etc/issue.net"; \
76 Remove all IAC's from buf1 (received IACs are ignored and must be removed
77 so as to not be interpreted by the terminal). Make an uninterrupted
78 string of characters fit for the terminal. Do this by packing
79 all characters meant for the terminal sequentially towards the end of buf.
81 Return a pointer to the beginning of the characters meant for the terminal
82 and make *num_totty the number of characters that should be sent to
85 Note - if an IAC (3 byte quantity) starts before (bf + len) but extends
86 past (bf + len) then that IAC will be left unprocessed and *processed
87 will be less than len.
89 CR-LF ->'s CR mapping is also done here, for convenience.
91 NB: may fail to remove iacs which wrap around buffer!
93 static unsigned char *
94 remove_iacs(struct tsession *ts, int *pnum_totty)
96 unsigned char *ptr0 = TS_BUF1(ts) + ts->wridx1;
97 unsigned char *ptr = ptr0;
98 unsigned char *totty = ptr;
99 unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
108 /* We map \r\n ==> \r for pragmatic reasons.
109 * Many client implementations send \r\n when
110 * the user hits the CarriageReturn key.
112 if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
119 if (ptr[1] == NOP) { /* Ignore? (putty keepalive, etc.) */
123 if (ptr[1] == IAC) { /* Literal IAC? (emacs M-DEL) */
130 * TELOPT_NAWS support!
132 if ((ptr+2) >= end) {
133 /* Only the beginning of the IAC is in the
134 buffer we were asked to process, we can't
139 * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
141 if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
144 break; /* incomplete, can't process */
145 ws.ws_col = (ptr[3] << 8) | ptr[4];
146 ws.ws_row = (ptr[5] << 8) | ptr[6];
147 ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
151 /* skip 3-byte IAC non-SB cmd */
153 fprintf(stderr, "Ignoring IAC %s,%s\n",
154 TELCMD(ptr[1]), TELOPT(ptr[2]));
159 num_totty = totty - ptr0;
160 *pnum_totty = num_totty;
161 /* The difference between ptr and totty is number of iacs
162 we removed from the stream. Adjust buf1 accordingly */
163 if ((ptr - totty) == 0) /* 99.999% of cases */
165 ts->wridx1 += ptr - totty;
166 ts->size1 -= ptr - totty;
167 /* Move chars meant for the terminal towards the end of the buffer */
168 return memmove(ptr - num_totty, ptr0, num_totty);
172 * Converting single IAC into double on output
174 static size_t iac_safe_write(int fd, const char *buf, size_t count)
177 size_t wr, rc, total;
183 if (*buf == (char)IAC) {
184 static const char IACIAC[] ALIGN1 = { IAC, IAC };
185 rc = safe_write(fd, IACIAC, 2);
193 /* count != 0, *buf != IAC */
194 IACptr = memchr(buf, IAC, count);
198 rc = safe_write(fd, buf, wr);
205 /* here: rc - result of last short write */
206 if ((ssize_t)rc < 0) { /* error? */
214 /* Must match getopt32 string */
216 OPT_WATCHCHILD = (1 << 2), /* -K */
217 OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
218 OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p PORT */
219 OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
220 OPT_SYSLOG = (1 << 7) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -S */
221 OPT_WAIT = (1 << 8) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -w SEC */
224 static struct tsession *
226 IF_FEATURE_TELNETD_STANDALONE(int sock)
227 IF_NOT_FEATURE_TELNETD_STANDALONE(void)
229 const char *login_argv[2];
230 struct termios termbuf;
232 char tty_name[GETPTY_BUFSIZE];
233 struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
235 /*ts->buf1 = (char *)(ts + 1);*/
236 /*ts->buf2 = ts->buf1 + BUFSIZE;*/
238 /* Got a new connection, set up a tty */
239 fd = xgetpty(tty_name);
244 close_on_exec_on(fd);
246 #if ENABLE_FEATURE_TELNETD_STANDALONE
247 /* SO_KEEPALIVE by popular demand */
248 setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
249 ts->sockfd_read = sock;
251 if (sock == 0) { /* We are called with fd 0 - we are in inetd mode */
252 sock++; /* so use fd 1 for output */
255 ts->sockfd_write = sock;
259 /* SO_KEEPALIVE by popular demand */
260 setsockopt(0, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
261 /* ts->sockfd_read = 0; - done by xzalloc */
262 ts->sockfd_write = 1;
267 /* Make the telnet client understand we will echo characters so it
268 * should not do it locally. We don't tell the client to run linemode,
269 * because we want to handle line editing and tab completion and other
270 * stuff that requires char-by-char support. */
272 static const char iacs_to_send[] ALIGN1 = {
273 IAC, DO, TELOPT_ECHO,
274 IAC, DO, TELOPT_NAWS,
275 /* This requires telnetd.ctrlSQ.patch (incomplete) */
276 /* IAC, DO, TELOPT_LFLOW, */
277 IAC, WILL, TELOPT_ECHO,
278 IAC, WILL, TELOPT_SGA
280 /* This confuses iac_safe_write(), it will try to duplicate
282 //memcpy(TS_BUF2(ts), iacs_to_send, sizeof(iacs_to_send));
283 //ts->rdidx2 = sizeof(iacs_to_send);
284 //ts->size2 = sizeof(iacs_to_send);
285 /* So just stuff it into TCP stream! (no error check...) */
286 #if ENABLE_FEATURE_TELNETD_STANDALONE
287 safe_write(sock, iacs_to_send, sizeof(iacs_to_send));
289 safe_write(1, iacs_to_send, sizeof(iacs_to_send));
291 /*ts->rdidx2 = 0; - xzalloc did it */
296 pid = vfork(); /* NOMMU-friendly */
300 /* sock will be closed by caller */
301 bb_perror_msg("vfork");
311 /* Careful - we are after vfork! */
313 /* Restore default signal handling ASAP */
314 bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
316 /* Make new session and process group */
319 /* Open the child's side of the tty */
320 /* NB: setsid() disconnects from any previous ctty's. Therefore
321 * we must open child's side of the tty AFTER setsid! */
323 xopen(tty_name, O_RDWR); /* becomes our ctty */
327 tcsetpgrp(0, pid); /* switch this tty's process group to us */
329 //TODO: fetch remote addr via getpeername (see ftpd.c)
330 write_new_utmp(pid, LOGIN_PROCESS, tty_name, /*username:*/ "LOGIN", /*hostname:*/ NULL);
332 /* The pseudo-terminal allocated to the client is configured to operate
333 * in cooked mode, and with XTABS CRMOD enabled (see tty(4)) */
334 tcgetattr(0, &termbuf);
335 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
336 termbuf.c_oflag |= ONLCR | XTABS;
337 termbuf.c_iflag |= ICRNL;
338 termbuf.c_iflag &= ~IXOFF;
339 /*termbuf.c_lflag &= ~ICANON;*/
340 tcsetattr_stdin_TCSANOW(&termbuf);
342 /* Uses FILE-based I/O to stdout, but does fflush_all(),
343 * so should be safe with vfork.
344 * I fear, though, that some users will have ridiculously big
345 * issue files, and they may block writing to fd 1,
346 * (parent is supposed to read it, but parent waits
347 * for vforked child to exec!) */
348 print_login_issue(G.issuefile, tty_name);
350 /* Exec shell / login / whatever */
351 login_argv[0] = G.loginpath;
352 login_argv[1] = NULL;
353 /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
354 * exec external program.
355 * NB: sock is either 0 or has CLOEXEC set on it.
356 * fd has CLOEXEC set on it too. These two fds will be closed here.
358 BB_EXECVP(G.loginpath, (char **)login_argv);
359 /* _exit is safer with vfork, and we shouldn't send message
360 * to remote clients anyway */
361 _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", G.loginpath);*/
364 #if ENABLE_FEATURE_TELNETD_STANDALONE
367 free_session(struct tsession *ts)
371 if (option_mask32 & OPT_INETD)
374 /* Unlink this telnet session from the session list */
377 G.sessions = ts->next;
379 while (t->next != ts)
385 /* It was said that "normal" telnetd just closes ptyfd,
386 * doesn't send SIGKILL. When we close ptyfd,
387 * kernel sends SIGHUP to processes having slave side opened. */
388 kill(ts->shell_pid, SIGKILL);
389 waitpid(ts->shell_pid, NULL, 0);
392 close(ts->sockfd_read);
393 /* We do not need to close(ts->sockfd_write), it's the same
394 * as sockfd_read unless we are in inetd mode. But in inetd mode
395 * we do not reach this */
398 /* Scan all sessions and find new maxfd */
402 if (G.maxfd < ts->ptyfd)
404 if (G.maxfd < ts->sockfd_read)
405 G.maxfd = ts->sockfd_read;
407 /* Again, sockfd_write == sockfd_read here */
408 if (G.maxfd < ts->sockfd_write)
409 G.maxfd = ts->sockfd_write;
415 #else /* !FEATURE_TELNETD_STANDALONE */
417 /* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
418 #define free_session(ts) return 0
422 static void handle_sigchld(int sig UNUSED_PARAM)
426 int save_errno = errno;
428 /* Looping: more than one child may have exited */
430 pid = wait_any_nohang(NULL);
435 if (ts->shell_pid == pid) {
438 // When init(8) finds that a process has exited, it locates its utmp entry
439 // by ut_pid, sets ut_type to DEAD_PROCESS, and clears ut_user, ut_host
440 // and ut_time with null bytes.
441 // [same applies to other processes which maintain utmp entries, like telnetd]
443 // We do not bother actually clearing fields:
444 // it might be interesting to know who was logged in and from where
445 update_utmp(pid, DEAD_PROCESS, /*tty_name:*/ NULL, /*username:*/ NULL, /*hostname:*/ NULL);
455 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
456 int telnetd_main(int argc UNUSED_PARAM, char **argv)
458 fd_set rdfdset, wrfdset;
462 #if ENABLE_FEATURE_TELNETD_STANDALONE
463 #define IS_INETD (opt & OPT_INETD)
464 int master_fd = master_fd; /* for compiler */
465 int sec_linger = sec_linger;
466 char *opt_bindaddr = NULL;
476 /* -w NUM, and implies -F. -w and -i don't mix */
477 IF_FEATURE_TELNETD_INETD_WAIT(opt_complementary = "wF:w+:i--w:w--i";)
478 /* Even if !STANDALONE, we accept (and ignore) -i, thus people
479 * don't need to guess whether it's ok to pass -i to us */
480 opt = getopt32(argv, "f:l:Ki"
481 IF_FEATURE_TELNETD_STANDALONE("p:b:F")
482 IF_FEATURE_TELNETD_INETD_WAIT("Sw:"),
483 &G.issuefile, &G.loginpath
484 IF_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr)
485 IF_FEATURE_TELNETD_INETD_WAIT(, &sec_linger)
487 if (!IS_INETD /*&& !re_execed*/) {
488 /* inform that we start in standalone mode?
489 * May be useful when people forget to give -i */
490 /*bb_error_msg("listening for connections");*/
491 if (!(opt & OPT_FOREGROUND)) {
492 /* DAEMON_CHDIR_ROOT was giving inconsistent
493 * behavior with/without -F, -i */
494 bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
497 /* Redirect log to syslog early, if needed */
498 if (IS_INETD || (opt & OPT_SYSLOG) || !(opt & OPT_FOREGROUND)) {
499 openlog(applet_name, LOG_PID, LOG_DAEMON);
500 logmode = LOGMODE_SYSLOG;
502 #if ENABLE_FEATURE_TELNETD_STANDALONE
504 G.sessions = make_new_session(0);
505 if (!G.sessions) /* pty opening or vfork problem, exit */
506 return 1; /* make_new_session printed error message */
509 if (!(opt & OPT_WAIT)) {
510 unsigned portnbr = 23;
512 portnbr = xatou16(opt_portnbr);
513 master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
514 xlisten(master_fd, 1);
516 close_on_exec_on(master_fd);
519 G.sessions = make_new_session();
520 if (!G.sessions) /* pty opening or vfork problem, exit */
521 return 1; /* make_new_session printed error message */
524 /* We don't want to die if just one session is broken */
525 signal(SIGPIPE, SIG_IGN);
527 if (opt & OPT_WATCHCHILD)
528 signal(SIGCHLD, handle_sigchld);
529 else /* prevent dead children from becoming zombies */
530 signal(SIGCHLD, SIG_IGN);
533 This is how the buffers are used. The arrows indicate data flow.
535 +-------+ wridx1++ +------+ rdidx1++ +----------+
536 | | <-------------- | buf1 | <-------------- | |
537 | | size1-- +------+ size1++ | |
539 | | rdidx2++ +------+ wridx2++ | |
540 | | --------------> | buf2 | --------------> | |
541 +-------+ size2++ +------+ size2-- +----------+
543 size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
544 size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
546 Each session has got two buffers. Buffers are circular. If sizeN == 0,
547 buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
554 /* Select on the master socket, all telnet sockets and their
555 * ptys if there is room in their session buffers.
556 * NB: scalability problem: we recalculate entire bitmap
557 * before each select. Can be a problem with 500+ connections. */
560 struct tsession *next = ts->next; /* in case we free ts */
561 if (ts->shell_pid == -1) {
562 /* Child died and we detected that */
565 if (ts->size1 > 0) /* can write to pty */
566 FD_SET(ts->ptyfd, &wrfdset);
567 if (ts->size1 < BUFSIZE) /* can read from socket */
568 FD_SET(ts->sockfd_read, &rdfdset);
569 if (ts->size2 > 0) /* can write to socket */
570 FD_SET(ts->sockfd_write, &wrfdset);
571 if (ts->size2 < BUFSIZE) /* can read from pty */
572 FD_SET(ts->ptyfd, &rdfdset);
577 FD_SET(master_fd, &rdfdset);
578 /* This is needed because free_session() does not
579 * take master_fd into account when it finds new
580 * maxfd among remaining fd's */
581 if (master_fd > G.maxfd)
586 struct timeval *tv_ptr = NULL;
587 #if ENABLE_FEATURE_TELNETD_INETD_WAIT
589 if ((opt & OPT_WAIT) && !G.sessions) {
590 tv.tv_sec = sec_linger;
595 count = select(G.maxfd + 1, &rdfdset, &wrfdset, NULL, tv_ptr);
597 if (count == 0) /* "telnetd -w SEC" timed out */
600 goto again; /* EINTR or ENOMEM */
602 #if ENABLE_FEATURE_TELNETD_STANDALONE
603 /* Check for and accept new sessions */
604 if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
606 struct tsession *new_ts;
608 fd = accept(master_fd, NULL, NULL);
611 close_on_exec_on(fd);
613 /* Create a new session and link it into active list */
614 new_ts = make_new_session(fd);
616 new_ts->next = G.sessions;
624 /* Then check for data tunneling */
626 while (ts) { /* For all sessions... */
627 struct tsession *next = ts->next; /* in case we free ts */
629 if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
632 /* Write to pty from buffer 1 */
633 ptr = remove_iacs(ts, &num_totty);
634 count = safe_write(ts->ptyfd, ptr, num_totty);
642 if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
646 if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
647 /* Write to socket from buffer 2 */
648 count = MIN(BUFSIZE - ts->wridx2, ts->size2);
649 count = iac_safe_write(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count);
657 if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
661 /* Should not be needed, but... remove_iacs is actually buggy
662 * (it cannot process iacs which wrap around buffer's end)!
663 * Since properly fixing it requires writing bigger code,
664 * we rely instead on this code making it virtually impossible
665 * to have wrapped iac (people don't type at 2k/second).
666 * It also allows for bigger reads in common case. */
667 if (ts->size1 == 0) {
671 if (ts->size2 == 0) {
676 if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
677 /* Read from socket to buffer 1 */
678 count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
679 count = safe_read(ts->sockfd_read, TS_BUF1(ts) + ts->rdidx1, count);
681 if (count < 0 && errno == EAGAIN)
685 /* Ignore trailing NUL if it is there */
686 if (!TS_BUF1(ts)[ts->rdidx1 + count - 1]) {
691 if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
695 if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
696 /* Read from pty to buffer 2 */
697 count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
698 count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count);
700 if (count < 0 && errno == EAGAIN)
706 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */
713 if (ts->shell_pid > 0)
714 update_utmp(ts->shell_pid, DEAD_PROCESS, /*tty_name:*/ NULL, /*username:*/ NULL, /*hostname:*/ NULL);