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 FIXME - if we mean to send 0xFF to the terminal then it will be escaped,
78 what is the escape character? We aren't handling that situation here.
80 CR-LF ->'s CR mapping is also done here, for convenience.
82 NB: may fail to remove iacs which wrap around buffer!
84 static unsigned char *
85 remove_iacs(struct tsession *ts, int *pnum_totty)
87 unsigned char *ptr0 = TS_BUF1 + ts->wridx1;
88 unsigned char *ptr = ptr0;
89 unsigned char *totty = ptr;
90 unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
99 /* We now map \r\n ==> \r for pragmatic reasons.
100 * Many client implementations send \r\n when
101 * the user hits the CarriageReturn key.
103 if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
107 * TELOPT_NAWS support!
109 if ((ptr+2) >= end) {
110 /* only the beginning of the IAC is in the
111 buffer we were asked to process, we can't
112 process this char. */
117 * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
119 else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
123 break; /* incomplete, can't process */
124 ws.ws_col = (ptr[3] << 8) | ptr[4];
125 ws.ws_row = (ptr[5] << 8) | ptr[6];
126 ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
129 /* skip 3-byte IAC non-SB cmd */
131 fprintf(stderr, "Ignoring IAC %s,%s\n",
132 TELCMD(ptr[1]), TELOPT(ptr[2]));
139 num_totty = totty - ptr0;
140 *pnum_totty = num_totty;
141 /* the difference between ptr and totty is number of iacs
142 we removed from the stream. Adjust buf1 accordingly. */
143 if ((ptr - totty) == 0) /* 99.999% of cases */
145 ts->wridx1 += ptr - totty;
146 ts->size1 -= ptr - totty;
147 /* move chars meant for the terminal towards the end of the buffer */
148 return memmove(ptr - num_totty, ptr0, num_totty);
152 static struct tsession *
154 USE_FEATURE_TELNETD_STANDALONE(int sock)
155 SKIP_FEATURE_TELNETD_STANDALONE(void)
157 const char *login_argv[2];
158 struct termios termbuf;
160 char tty_name[GETPTY_BUFSIZE];
161 struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
163 /*ts->buf1 = (char *)(ts + 1);*/
164 /*ts->buf2 = ts->buf1 + BUFSIZE;*/
166 /* Got a new connection, set up a tty. */
167 fd = xgetpty(tty_name);
172 #if ENABLE_FEATURE_TELNETD_STANDALONE
173 ts->sockfd_read = sock;
175 if (!sock) { /* We are called with fd 0 - we are in inetd mode */
176 sock++; /* so use fd 1 for output */
179 ts->sockfd_write = sock;
183 /* ts->sockfd_read = 0; - done by xzalloc */
184 ts->sockfd_write = 1;
188 /* Make the telnet client understand we will echo characters so it
189 * should not do it locally. We don't tell the client to run linemode,
190 * because we want to handle line editing and tab completion and other
191 * stuff that requires char-by-char support. */
193 static const char iacs_to_send[] ALIGN1 = {
194 IAC, DO, TELOPT_ECHO,
195 IAC, DO, TELOPT_NAWS,
196 IAC, DO, TELOPT_LFLOW,
197 IAC, WILL, TELOPT_ECHO,
198 IAC, WILL, TELOPT_SGA
200 memcpy(TS_BUF2, iacs_to_send, sizeof(iacs_to_send));
201 ts->rdidx2 = sizeof(iacs_to_send);
202 ts->size2 = sizeof(iacs_to_send);
205 fflush(NULL); /* flush all streams */
206 pid = vfork(); /* NOMMU-friendly */
210 /* sock will be closed by caller */
211 bb_perror_msg("vfork");
221 /* Careful - we are after vfork! */
223 /* make new session and process group */
226 /* Restore default signal handling */
227 bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
229 /* open the child's side of the tty. */
230 /* NB: setsid() disconnects from any previous ctty's. Therefore
231 * we must open child's side of the tty AFTER setsid! */
233 xopen(tty_name, O_RDWR); /* becomes our ctty */
236 tcsetpgrp(0, getpid()); /* switch this tty's process group to us */
238 /* The pseudo-terminal allocated to the client is configured to operate in
239 * cooked mode, and with XTABS CRMOD enabled (see tty(4)). */
240 tcgetattr(0, &termbuf);
241 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
242 termbuf.c_oflag |= ONLCR | XTABS;
243 termbuf.c_iflag |= ICRNL;
244 termbuf.c_iflag &= ~IXOFF;
245 /*termbuf.c_lflag &= ~ICANON;*/
246 tcsetattr(0, TCSANOW, &termbuf);
248 /* Uses FILE-based I/O to stdout, but does fflush(stdout),
249 * so should be safe with vfork.
250 * I fear, though, that some users will have ridiculously big
251 * issue files, and they may block writing to fd 1,
252 * (parent is supposed to read it, but parent waits
253 * for vforked child to exec!) */
254 print_login_issue(issuefile, tty_name);
256 /* Exec shell / login / whatever */
257 login_argv[0] = loginpath;
258 login_argv[1] = NULL;
259 /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
260 * exec external program */
261 BB_EXECVP(loginpath, (char **)login_argv);
262 /* _exit is safer with vfork, and we shouldn't send message
263 * to remote clients anyway */
264 _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", loginpath);*/
267 /* Must match getopt32 string */
269 OPT_WATCHCHILD = (1 << 2), /* -K */
270 OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
271 OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p */
272 OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
275 #if ENABLE_FEATURE_TELNETD_STANDALONE
278 free_session(struct tsession *ts)
280 struct tsession *t = sessions;
282 if (option_mask32 & OPT_INETD)
285 /* Unlink this telnet session from the session list */
289 while (t->next != ts)
295 /* It was said that "normal" telnetd just closes ptyfd,
296 * doesn't send SIGKILL. When we close ptyfd,
297 * kernel sends SIGHUP to processes having slave side opened. */
298 kill(ts->shell_pid, SIGKILL);
299 wait4(ts->shell_pid, NULL, 0, NULL);
302 close(ts->sockfd_read);
303 /* We do not need to close(ts->sockfd_write), it's the same
304 * as sockfd_read unless we are in inetd mode. But in inetd mode
305 * we do not reach this */
308 /* Scan all sessions and find new maxfd */
312 if (maxfd < ts->ptyfd)
314 if (maxfd < ts->sockfd_read)
315 maxfd = ts->sockfd_read;
317 /* Again, sockfd_write == sockfd_read here */
318 if (maxfd < ts->sockfd_write)
319 maxfd = ts->sockfd_write;
325 #else /* !FEATURE_TELNETD_STANDALONE */
327 /* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
328 #define free_session(ts) return 0
332 static void handle_sigchld(int sig UNUSED_PARAM)
337 /* Looping: more than one child may have exited */
339 pid = wait_any_nohang(NULL);
344 if (ts->shell_pid == pid) {
353 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
354 int telnetd_main(int argc UNUSED_PARAM, char **argv)
356 fd_set rdfdset, wrfdset;
360 #if ENABLE_FEATURE_TELNETD_STANDALONE
361 #define IS_INETD (opt & OPT_INETD)
362 int master_fd = master_fd; /* be happy, gcc */
363 unsigned portnbr = 23;
364 char *opt_bindaddr = NULL;
373 /* Even if !STANDALONE, we accept (and ignore) -i, thus people
374 * don't need to guess whether it's ok to pass -i to us */
375 opt = getopt32(argv, "f:l:Ki" USE_FEATURE_TELNETD_STANDALONE("p:b:F"),
376 &issuefile, &loginpath
377 USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
378 if (!IS_INETD /*&& !re_execed*/) {
379 /* inform that we start in standalone mode?
380 * May be useful when people forget to give -i */
381 /*bb_error_msg("listening for connections");*/
382 if (!(opt & OPT_FOREGROUND)) {
383 /* DAEMON_CHDIR_ROOT was giving inconsistent
384 * behavior with/without -F, -i */
385 bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
388 /* Redirect log to syslog early, if needed */
389 if (IS_INETD || !(opt & OPT_FOREGROUND)) {
390 openlog(applet_name, 0, LOG_USER);
391 logmode = LOGMODE_SYSLOG;
393 USE_FEATURE_TELNETD_STANDALONE(
395 portnbr = xatou16(opt_portnbr);
398 /* Used to check access(loginpath, X_OK) here. Pointless.
399 * exec will do this for us for free later. */
401 #if ENABLE_FEATURE_TELNETD_STANDALONE
403 sessions = make_new_session(0);
404 if (!sessions) /* pty opening or vfork problem, exit */
405 return 1; /* make_new_session prints error message */
407 master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
408 xlisten(master_fd, 1);
411 sessions = make_new_session();
412 if (!sessions) /* pty opening or vfork problem, exit */
413 return 1; /* make_new_session prints error message */
416 /* We don't want to die if just one session is broken */
417 signal(SIGPIPE, SIG_IGN);
419 if (opt & OPT_WATCHCHILD)
420 signal(SIGCHLD, handle_sigchld);
421 else /* prevent dead children from becoming zombies */
422 signal(SIGCHLD, SIG_IGN);
425 This is how the buffers are used. The arrows indicate the movement
427 +-------+ wridx1++ +------+ rdidx1++ +----------+
428 | | <-------------- | buf1 | <-------------- | |
429 | | size1-- +------+ size1++ | |
431 | | rdidx2++ +------+ wridx2++ | |
432 | | --------------> | buf2 | --------------> | |
433 +-------+ size2++ +------+ size2-- +----------+
435 size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
436 size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
438 Each session has got two buffers. Buffers are circular. If sizeN == 0,
439 buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
446 /* Select on the master socket, all telnet sockets and their
447 * ptys if there is room in their session buffers.
448 * NB: scalability problem: we recalculate entire bitmap
449 * before each select. Can be a problem with 500+ connections. */
452 struct tsession *next = ts->next; /* in case we free ts. */
453 if (ts->shell_pid == -1) {
454 /* Child died and we detected that */
457 if (ts->size1 > 0) /* can write to pty */
458 FD_SET(ts->ptyfd, &wrfdset);
459 if (ts->size1 < BUFSIZE) /* can read from socket */
460 FD_SET(ts->sockfd_read, &rdfdset);
461 if (ts->size2 > 0) /* can write to socket */
462 FD_SET(ts->sockfd_write, &wrfdset);
463 if (ts->size2 < BUFSIZE) /* can read from pty */
464 FD_SET(ts->ptyfd, &rdfdset);
469 FD_SET(master_fd, &rdfdset);
470 /* This is needed because free_session() does not
471 * take master_fd into account when it finds new
472 * maxfd among remaining fd's */
473 if (master_fd > maxfd)
477 count = select(maxfd + 1, &rdfdset, &wrfdset, NULL, NULL);
479 goto again; /* EINTR or ENOMEM */
481 #if ENABLE_FEATURE_TELNETD_STANDALONE
482 /* First check for and accept new sessions. */
483 if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
485 struct tsession *new_ts;
487 fd = accept(master_fd, NULL, NULL);
490 /* Create a new session and link it into our active list */
491 new_ts = make_new_session(fd);
493 new_ts->next = sessions;
501 /* Then check for data tunneling. */
503 while (ts) { /* For all sessions... */
504 struct tsession *next = ts->next; /* in case we free ts. */
506 if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
509 /* Write to pty from buffer 1. */
510 ptr = remove_iacs(ts, &num_totty);
511 count = safe_write(ts->ptyfd, ptr, num_totty);
519 if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
523 if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
524 /* Write to socket from buffer 2. */
525 count = MIN(BUFSIZE - ts->wridx2, ts->size2);
526 count = safe_write(ts->sockfd_write, TS_BUF2 + ts->wridx2, count);
534 if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
538 /* Should not be needed, but... remove_iacs is actually buggy
539 * (it cannot process iacs which wrap around buffer's end)!
540 * Since properly fixing it requires writing bigger code,
541 * we rely instead on this code making it virtually impossible
542 * to have wrapped iac (people don't type at 2k/second).
543 * It also allows for bigger reads in common case. */
544 if (ts->size1 == 0) {
548 if (ts->size2 == 0) {
553 if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
554 /* Read from socket to buffer 1. */
555 count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
556 count = safe_read(ts->sockfd_read, TS_BUF1 + ts->rdidx1, count);
558 if (count < 0 && errno == EAGAIN)
562 /* Ignore trailing NUL if it is there */
563 if (!TS_BUF1[ts->rdidx1 + count - 1]) {
568 if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
572 if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
573 /* Read from pty to buffer 2. */
574 count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
575 count = safe_read(ts->ptyfd, TS_BUF2 + ts->rdidx2, count);
577 if (count < 0 && errno == EAGAIN)
583 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */