1 /* vi: set sw=4 ts=4: */
2 /*
3 * Simple telnet server
4 * Bjorn Wesen, Axis Communications AB (bjornw@axis.com)
5 *
6 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
7 *
8 * ---------------------------------------------------------------------------
9 * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN
10 ****************************************************************************
11 *
12 * The telnetd manpage says it all:
13 *
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.
19 *
20 * Vladimir Oleynik <dzo@simtreas.ru> 2001
21 * Set process group corrections, initial busybox port
22 */
23 //config:config TELNETD
24 //config: bool "telnetd (12 kb)"
25 //config: default y
26 //config: select FEATURE_SYSLOG
27 //config: help
28 //config: A daemon for the TELNET protocol, allowing you to log onto the host
29 //config: running the daemon. Please keep in mind that the TELNET protocol
30 //config: sends passwords in plain text. If you can't afford the space for an
31 //config: SSH daemon and you trust your network, you may say 'y' here. As a
32 //config: more secure alternative, you should seriously consider installing the
33 //config: very small Dropbear SSH daemon instead:
34 //config: http://matt.ucc.asn.au/dropbear/dropbear.html
35 //config:
36 //config: Note that for busybox telnetd to work you need several things:
37 //config: First of all, your kernel needs:
38 //config: CONFIG_UNIX98_PTYS=y
39 //config:
40 //config: Next, you need a /dev/pts directory on your root filesystem:
41 //config:
42 //config: $ ls -ld /dev/pts
43 //config: drwxr-xr-x 2 root root 0 Sep 23 13:21 /dev/pts/
44 //config:
45 //config: Next you need the pseudo terminal master multiplexer /dev/ptmx:
46 //config:
47 //config: $ ls -la /dev/ptmx
48 //config: crw-rw-rw- 1 root tty 5, 2 Sep 23 13:55 /dev/ptmx
49 //config:
50 //config: Any /dev/ttyp[0-9]* files you may have can be removed.
51 //config: Next, you need to mount the devpts filesystem on /dev/pts using:
52 //config:
53 //config: mount -t devpts devpts /dev/pts
54 //config:
55 //config: You need to be sure that busybox has LOGIN and
56 //config: FEATURE_SUID enabled. And finally, you should make
57 //config: certain that busybox has been installed setuid root:
58 //config:
59 //config: chown root.root /bin/busybox
60 //config: chmod 4755 /bin/busybox
61 //config:
62 //config: with all that done, telnetd _should_ work....
63 //config:
64 //config:config FEATURE_TELNETD_STANDALONE
65 //config: bool "Support standalone telnetd (not inetd only)"
66 //config: default y
67 //config: depends on TELNETD
68 //config: help
69 //config: Selecting this will make telnetd able to run standalone.
70 //config:
71 //config:config FEATURE_TELNETD_PORT_DEFAULT
72 //config: int "Default port"
73 //config: default 23
74 //config: range 1 65535
75 //config: depends on FEATURE_TELNETD_STANDALONE
76 //config:
77 //config:config FEATURE_TELNETD_INETD_WAIT
78 //config: bool "Support -w SEC option (inetd wait mode)"
79 //config: default y
80 //config: depends on FEATURE_TELNETD_STANDALONE
81 //config: help
82 //config: This option allows you to run telnetd in "inet wait" mode.
83 //config: Example inetd.conf line (note "wait", not usual "nowait"):
84 //config:
85 //config: telnet stream tcp wait root /bin/telnetd telnetd -w10
86 //config:
87 //config: In this example, inetd passes _listening_ socket_ as fd 0
88 //config: to telnetd when connection appears.
89 //config: telnetd will wait for connections until all existing
90 //config: connections are closed, and no new connections
91 //config: appear during 10 seconds. Then it exits, and inetd continues
92 //config: to listen for new connections.
93 //config:
94 //config: This option is rarely used. "tcp nowait" is much more usual
95 //config: way of running tcp services, including telnetd.
96 //config: You most probably want to say N here.
97
98 //applet:IF_TELNETD(APPLET(telnetd, BB_DIR_USR_SBIN, BB_SUID_DROP))
99
100 //kbuild:lib-$(CONFIG_TELNETD) += telnetd.o
101
102 //usage:#define telnetd_trivial_usage
103 //usage: "[OPTIONS]"
104 //usage:#define telnetd_full_usage "\n\n"
105 //usage: "Handle incoming telnet connections"
106 //usage: IF_NOT_FEATURE_TELNETD_STANDALONE(" via inetd") "\n"
107 //usage: "\n -l LOGIN Exec LOGIN on connect"
108 //usage: "\n -f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue"
109 //usage: "\n -K Close connection as soon as login exits"
110 //usage: "\n (normally wait until all programs close slave pty)"
111 //usage: IF_FEATURE_TELNETD_STANDALONE(
112 //usage: "\n -p PORT Port to listen on. Default "STR(CONFIG_FEATURE_TELNETD_PORT_DEFAULT)
113 //usage: "\n -b ADDR[:PORT] Address to bind to"
114 //usage: "\n -F Run in foreground"
115 //usage: "\n -i Inetd mode"
116 //usage: IF_FEATURE_TELNETD_INETD_WAIT(
117 //usage: "\n -w SEC Inetd 'wait' mode, linger time SEC"
118 //usage: "\n inetd.conf line: 23 stream tcp wait root telnetd telnetd -w10"
119 //usage: "\n -S Log to syslog (implied by -i or without -F and -w)"
120 //usage: )
121 //usage: )
122
123 #define DEBUG 0
124
125 #include "libbb.h"
126 #include "common_bufsiz.h"
127 #include <syslog.h>
128
129 #if DEBUG
130 # define TELCMDS
131 # define TELOPTS
132 #endif
133 #include <arpa/telnet.h>
134
135
136 struct tsession {
137 struct tsession *next;
138 pid_t shell_pid;
139 int sockfd_read;
140 int sockfd_write;
141 int ptyfd;
142 smallint buffered_IAC_for_pty;
143
144 /* two circular buffers */
145 /*char *buf1, *buf2;*/
146 /*#define TS_BUF1(ts) ts->buf1*/
147 /*#define TS_BUF2(ts) TS_BUF2(ts)*/
148 #define TS_BUF1(ts) ((unsigned char*)(ts + 1))
149 #define TS_BUF2(ts) (((unsigned char*)(ts + 1)) + BUFSIZE)
150 int rdidx1, wridx1, size1;
151 int rdidx2, wridx2, size2;
152 };
153
154 /* Two buffers are directly after tsession in malloced memory.
155 * Make whole thing fit in 4k */
156 enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
157
158
159 /* Globals */
160 struct globals {
161 struct tsession *sessions;
162 const char *loginpath;
163 const char *issuefile;
164 int maxfd;
165 } FIX_ALIASING;
166 #define G (*(struct globals*)bb_common_bufsiz1)
167 #define INIT_G() do { \
168 setup_common_bufsiz(); \
169 G.loginpath = "/bin/login"; \
170 G.issuefile = "/etc/issue.net"; \
171 } while (0)
172
173
174 /* Write some buf1 data to pty, processing IACs.
175 * Update wridx1 and size1. Return < 0 on error.
176 * Buggy if IAC is present but incomplete: skips them.
177 */
178 static ssize_t
safe_write_to_pty_decode_iac(struct tsession * ts)179 safe_write_to_pty_decode_iac(struct tsession *ts)
180 {
181 unsigned wr;
182 ssize_t rc;
183 unsigned char *buf;
184 unsigned char *found;
185
186 buf = TS_BUF1(ts) + ts->wridx1;
187 wr = MIN(BUFSIZE - ts->wridx1, ts->size1);
188 /* wr is at least 1 here */
189
190 if (ts->buffered_IAC_for_pty) {
191 /* Last time we stopped on a "dangling" IAC byte.
192 * We removed it from the buffer back then.
193 * Now pretend it's still there, and jump to IAC processing.
194 */
195 ts->buffered_IAC_for_pty = 0;
196 wr++;
197 ts->size1++;
198 buf--; /* Yes, this can point before the buffer. It's ok */
199 ts->wridx1--;
200 goto handle_iac;
201 }
202
203 found = memchr(buf, IAC, wr);
204 if (found != buf) {
205 /* There is a "prefix" of non-IAC chars.
206 * Write only them, and return.
207 */
208 if (found)
209 wr = found - buf;
210
211 /* We map \r\n ==> \r for pragmatic reasons:
212 * many client implementations send \r\n when
213 * the user hits the CarriageReturn key.
214 * See RFC 1123 3.3.1 Telnet End-of-Line Convention.
215 */
216 rc = wr;
217 found = memchr(buf, '\r', wr);
218 if (found)
219 rc = found - buf + 1;
220 rc = safe_write(ts->ptyfd, buf, rc);
221 if (rc <= 0)
222 return rc;
223 if (rc < wr /* don't look past available data */
224 && buf[rc-1] == '\r' /* need this: imagine that write was _short_ */
225 && (buf[rc] == '\n' || buf[rc] == '\0')
226 ) {
227 rc++;
228 }
229 goto update_and_return;
230 }
231
232 /* buf starts with IAC char. Process that sequence.
233 * Example: we get this from our own (bbox) telnet client:
234 * read(5, "\377\374\1""\377\373\37""\377\372\37\0\262\0@\377\360""\377\375\1""\377\375\3"):
235 * IAC WONT ECHO, IAC WILL NAWS, IAC SB NAWS <cols> <rows> IAC SE, IAC DO SGA
236 * Another example (telnet-0.17 from old-netkit):
237 * read(4, "\377\375\3""\377\373\30""\377\373\37""\377\373 ""\377\373!""\377\373\"""\377\373'"
238 * "\377\375\5""\377\373#""\377\374\1""\377\372\37\0\257\0I\377\360""\377\375\1"):
239 * IAC DO SGA, IAC WILL TTYPE, IAC WILL NAWS, IAC WILL TSPEED, IAC WILL LFLOW, IAC WILL LINEMODE, IAC WILL NEW_ENVIRON,
240 * IAC DO STATUS, IAC WILL XDISPLOC, IAC WONT ECHO, IAC SB NAWS <cols> <rows> IAC SE, IAC DO ECHO
241 */
242 if (wr <= 1) {
243 /* Only the single IAC byte is in the buffer, eat it
244 * and set a flag "process the rest of the sequence
245 * next time we are here".
246 */
247 //bb_error_msg("dangling IAC!");
248 ts->buffered_IAC_for_pty = 1;
249 rc = 1;
250 goto update_and_return;
251 }
252
253 handle_iac:
254 /* 2-byte commands (240..250 and 255):
255 * IAC IAC (255) Literal 255. Supported.
256 * IAC SE (240) End of subnegotiation. Treated as NOP.
257 * IAC NOP (241) NOP. Supported.
258 * IAC BRK (243) Break. Like serial line break. TODO via tcsendbreak()?
259 * IAC AYT (246) Are you there.
260 * These don't look useful:
261 * IAC DM (242) Data mark. What is this?
262 * IAC IP (244) Suspend, interrupt or abort the process. (Ancient cousin of ^C).
263 * IAC AO (245) Abort output. "You can continue running, but do not send me the output".
264 * IAC EC (247) Erase character. The receiver should delete the last received char.
265 * IAC EL (248) Erase line. The receiver should delete everything up tp last newline.
266 * IAC GA (249) Go ahead. For half-duplex lines: "now you talk".
267 * Implemented only as part of NAWS:
268 * IAC SB (250) Subnegotiation of an option follows.
269 */
270 if (buf[1] == IAC) {
271 /* Literal 255 (emacs M-DEL) */
272 //bb_error_msg("255!");
273 rc = safe_write(ts->ptyfd, &buf[1], 1);
274 /*
275 * If we went through buffered_IAC_for_pty==1 path,
276 * bailing out on error like below messes up the buffer.
277 * EAGAIN is highly unlikely here, other errors will be
278 * repeated on next write, let's just skip error check.
279 */
280 #if 0
281 if (rc <= 0)
282 return rc;
283 #endif
284 rc = 2;
285 goto update_and_return;
286 }
287 if (buf[1] == AYT) {
288 if (ts->size2 == 0) { /* if nothing buffered yet... */
289 /* Send back evidence that AYT was seen */
290 unsigned char *buf2 = TS_BUF2(ts);
291 buf2[0] = IAC;
292 buf2[1] = NOP;
293 ts->wridx2 = 0;
294 ts->rdidx2 = ts->size2 = 2;
295 }
296 rc = 2;
297 goto update_and_return;
298 }
299 if (buf[1] >= 240 && buf[1] <= 249) {
300 /* NOP (241). Ignore (putty keepalive, etc) */
301 /* All other 2-byte commands also treated as NOPs here */
302 rc = 2;
303 goto update_and_return;
304 }
305
306 if (wr <= 2) {
307 /* BUG: only 2 bytes of the IAC is in the buffer, we just eat them.
308 * This is not a practical problem since >2 byte IACs are seen only
309 * in initial negotiation, when buffer is empty
310 */
311 rc = 2;
312 goto update_and_return;
313 }
314
315 if (buf[1] == SB) {
316 if (buf[2] == TELOPT_NAWS) {
317 /* IAC SB, TELOPT_NAWS, 4-byte, IAC SE */
318 struct winsize ws;
319 if (wr <= 6) {
320 /* BUG: incomplete, can't process */
321 rc = wr;
322 goto update_and_return;
323 }
324 memset(&ws, 0, sizeof(ws)); /* pixel sizes are set to 0 */
325 ws.ws_col = (buf[3] << 8) | buf[4];
326 ws.ws_row = (buf[5] << 8) | buf[6];
327 ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
328 rc = 7;
329 /* trailing IAC SE will be eaten separately, as 2-byte NOP */
330 goto update_and_return;
331 }
332 /* else: other subnegs not supported yet */
333 }
334
335 /* Assume it is a 3-byte WILL/WONT/DO/DONT 251..254 command and skip it */
336 #if DEBUG
337 fprintf(stderr, "Ignoring IAC %s,%s\n",
338 TELCMD(buf[1]), TELOPT(buf[2]));
339 #endif
340 rc = 3;
341
342 update_and_return:
343 ts->wridx1 += rc;
344 if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
345 ts->wridx1 = 0;
346 ts->size1 -= rc;
347 /*
348 * Hack. We cannot process IACs which wrap around buffer's end.
349 * Since properly fixing it requires writing bigger code,
350 * we rely instead on this code making it virtually impossible
351 * to have wrapped IAC (people don't type at 2k/second).
352 * It also allows for bigger reads in common case.
353 */
354 if (ts->size1 == 0) { /* very typical */
355 //bb_error_msg("zero size1");
356 ts->rdidx1 = 0;
357 ts->wridx1 = 0;
358 return rc;
359 }
360 wr = ts->wridx1;
361 if (wr != 0 && wr < ts->rdidx1) {
362 /* Buffer is not wrapped yet.
363 * We can easily move it to the beginning.
364 */
365 //bb_error_msg("moved %d", wr);
366 memmove(TS_BUF1(ts), TS_BUF1(ts) + wr, ts->size1);
367 ts->rdidx1 -= wr;
368 ts->wridx1 = 0;
369 }
370 return rc;
371 }
372
373 /*
374 * Converting single IAC into double on output
375 */
safe_write_double_iac(int fd,const char * buf,size_t count)376 static size_t safe_write_double_iac(int fd, const char *buf, size_t count)
377 {
378 const char *IACptr;
379 size_t wr, rc, total;
380
381 total = 0;
382 while (1) {
383 if (count == 0)
384 return total;
385 if (*buf == (char)IAC) {
386 static const char IACIAC[] ALIGN1 = { IAC, IAC };
387 rc = safe_write(fd, IACIAC, 2);
388 /* BUG: if partial write was only 1 byte long, we end up emitting just one IAC */
389 if (rc != 2)
390 break;
391 buf++;
392 total++;
393 count--;
394 continue;
395 }
396 /* count != 0, *buf != IAC */
397 IACptr = memchr(buf, IAC, count);
398 wr = count;
399 if (IACptr)
400 wr = IACptr - buf;
401 rc = safe_write(fd, buf, wr);
402 if (rc != wr)
403 break;
404 buf += rc;
405 total += rc;
406 count -= rc;
407 }
408 /* here: rc - result of last short write */
409 if ((ssize_t)rc < 0) { /* error? */
410 if (total == 0)
411 return rc;
412 rc = 0;
413 }
414 return total + rc;
415 }
416
417 /* Must match getopt32 string */
418 enum {
419 OPT_WATCHCHILD = (1 << 2), /* -K */
420 OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
421 OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p PORT */
422 OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
423 OPT_SYSLOG = (1 << 7) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -S */
424 OPT_WAIT = (1 << 8) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -w SEC */
425 };
426
427 static struct tsession *
make_new_session(IF_FEATURE_TELNETD_STANDALONE (int sock)IF_NOT_FEATURE_TELNETD_STANDALONE (void))428 make_new_session(
429 IF_FEATURE_TELNETD_STANDALONE(int sock)
430 IF_NOT_FEATURE_TELNETD_STANDALONE(void)
431 ) {
432 #if !ENABLE_FEATURE_TELNETD_STANDALONE
433 enum { sock = 0 };
434 #endif
435 const char *login_argv[2];
436 struct termios termbuf;
437 int fd, pid;
438 char tty_name[GETPTY_BUFSIZE];
439 struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
440
441 /*ts->buf1 = (char *)(ts + 1);*/
442 /*ts->buf2 = ts->buf1 + BUFSIZE;*/
443
444 /* Got a new connection, set up a tty */
445 fd = xgetpty(tty_name);
446 if (fd > G.maxfd)
447 G.maxfd = fd;
448 ts->ptyfd = fd;
449 ndelay_on(fd);
450 close_on_exec_on(fd);
451
452 /* SO_KEEPALIVE by popular demand */
453 setsockopt_keepalive(sock);
454 #if ENABLE_FEATURE_TELNETD_STANDALONE
455 ts->sockfd_read = sock;
456 ndelay_on(sock);
457 if (sock == 0) { /* We are called with fd 0 - we are in inetd mode */
458 sock++; /* so use fd 1 for output */
459 ndelay_on(sock);
460 }
461 ts->sockfd_write = sock;
462 if (sock > G.maxfd)
463 G.maxfd = sock;
464 #else
465 /* ts->sockfd_read = 0; - done by xzalloc */
466 ts->sockfd_write = 1;
467 ndelay_on(0);
468 ndelay_on(1);
469 #endif
470
471 /* Make the telnet client understand we will echo characters so it
472 * should not do it locally. We don't tell the client to run linemode,
473 * because we want to handle line editing and tab completion and other
474 * stuff that requires char-by-char support. */
475 {
476 static const char iacs_to_send[] ALIGN1 = {
477 IAC, DO, TELOPT_ECHO,
478 IAC, DO, TELOPT_NAWS,
479 /* This requires telnetd.ctrlSQ.patch (incomplete) */
480 /*IAC, DO, TELOPT_LFLOW,*/
481 IAC, WILL, TELOPT_ECHO,
482 IAC, WILL, TELOPT_SGA
483 };
484 /* This confuses safe_write_double_iac(), it will try to duplicate
485 * each IAC... */
486 //memcpy(TS_BUF2(ts), iacs_to_send, sizeof(iacs_to_send));
487 //ts->rdidx2 = sizeof(iacs_to_send);
488 //ts->size2 = sizeof(iacs_to_send);
489 /* So just stuff it into TCP stream! (no error check...) */
490 #if ENABLE_FEATURE_TELNETD_STANDALONE
491 safe_write(sock, iacs_to_send, sizeof(iacs_to_send));
492 #else
493 safe_write(1, iacs_to_send, sizeof(iacs_to_send));
494 #endif
495 /*ts->rdidx2 = 0; - xzalloc did it */
496 /*ts->size2 = 0;*/
497 }
498
499 fflush_all();
500 pid = vfork(); /* NOMMU-friendly */
501 if (pid < 0) {
502 free(ts);
503 close(fd);
504 /* sock will be closed by caller */
505 bb_simple_perror_msg("vfork");
506 return NULL;
507 }
508 if (pid > 0) {
509 /* Parent */
510 ts->shell_pid = pid;
511 return ts;
512 }
513
514 /* Child */
515 /* Careful - we are after vfork! */
516
517 /* Restore default signal handling ASAP */
518 bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
519
520 pid = getpid();
521
522 if (ENABLE_FEATURE_UTMP) {
523 len_and_sockaddr *lsa = get_peer_lsa(sock);
524 char *hostname = NULL;
525 if (lsa) {
526 hostname = xmalloc_sockaddr2dotted(&lsa->u.sa);
527 free(lsa);
528 }
529 write_new_utmp(pid, LOGIN_PROCESS, tty_name, /*username:*/ "LOGIN", hostname);
530 free(hostname);
531 }
532
533 /* Make new session and process group */
534 setsid();
535
536 /* Open the child's side of the tty */
537 /* NB: setsid() disconnects from any previous ctty's. Therefore
538 * we must open child's side of the tty AFTER setsid! */
539 close(0);
540 xopen(tty_name, O_RDWR); /* becomes our ctty */
541 xdup2(0, 1);
542 xdup2(0, 2);
543 tcsetpgrp(0, pid); /* switch this tty's process group to us */
544
545 /* The pseudo-terminal allocated to the client is configured to operate
546 * in cooked mode, and with XTABS CRMOD enabled (see tty(4)) */
547 tcgetattr(0, &termbuf);
548 termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
549 termbuf.c_oflag |= ONLCR | XTABS;
550 termbuf.c_iflag |= ICRNL;
551 termbuf.c_iflag &= ~IXOFF;
552 /*termbuf.c_lflag &= ~ICANON;*/
553 tcsetattr_stdin_TCSANOW(&termbuf);
554
555 /* Uses FILE-based I/O to stdout, but does fflush_all(),
556 * so should be safe with vfork.
557 * I fear, though, that some users will have ridiculously big
558 * issue files, and they may block writing to fd 1,
559 * (parent is supposed to read it, but parent waits
560 * for vforked child to exec!) */
561 print_login_issue(G.issuefile, tty_name);
562
563 /* Exec shell / login / whatever */
564 login_argv[0] = G.loginpath;
565 login_argv[1] = NULL;
566 /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
567 * exec external program.
568 * NB: sock is either 0 or has CLOEXEC set on it.
569 * fd has CLOEXEC set on it too. These two fds will be closed here.
570 */
571 BB_EXECVP(G.loginpath, (char **)login_argv);
572 /* _exit is safer with vfork, and we shouldn't send message
573 * to remote clients anyway */
574 _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", G.loginpath);*/
575 }
576
577 #if ENABLE_FEATURE_TELNETD_STANDALONE
578
579 static void
free_session(struct tsession * ts)580 free_session(struct tsession *ts)
581 {
582 struct tsession *t;
583
584 if (option_mask32 & OPT_INETD)
585 exit(EXIT_SUCCESS);
586
587 /* Unlink this telnet session from the session list */
588 t = G.sessions;
589 if (t == ts)
590 G.sessions = ts->next;
591 else {
592 while (t->next != ts)
593 t = t->next;
594 t->next = ts->next;
595 }
596
597 #if 0
598 /* It was said that "normal" telnetd just closes ptyfd,
599 * doesn't send SIGKILL. When we close ptyfd,
600 * kernel sends SIGHUP to processes having slave side opened. */
601 kill(ts->shell_pid, SIGKILL);
602 waitpid(ts->shell_pid, NULL, 0);
603 #endif
604 close(ts->ptyfd);
605 close(ts->sockfd_read);
606 /* We do not need to close(ts->sockfd_write), it's the same
607 * as sockfd_read unless we are in inetd mode. But in inetd mode
608 * we do not reach this */
609 free(ts);
610
611 /* Scan all sessions and find new maxfd */
612 G.maxfd = 0;
613 ts = G.sessions;
614 while (ts) {
615 if (G.maxfd < ts->ptyfd)
616 G.maxfd = ts->ptyfd;
617 if (G.maxfd < ts->sockfd_read)
618 G.maxfd = ts->sockfd_read;
619 #if 0
620 /* Again, sockfd_write == sockfd_read here */
621 if (G.maxfd < ts->sockfd_write)
622 G.maxfd = ts->sockfd_write;
623 #endif
624 ts = ts->next;
625 }
626 }
627
628 #else /* !FEATURE_TELNETD_STANDALONE */
629
630 /* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
631 #define free_session(ts) return 0
632
633 #endif
634
handle_sigchld(int sig UNUSED_PARAM)635 static void handle_sigchld(int sig UNUSED_PARAM)
636 {
637 pid_t pid;
638 struct tsession *ts;
639 int save_errno = errno;
640
641 /* Looping: more than one child may have exited */
642 while (1) {
643 pid = wait_any_nohang(NULL);
644 if (pid <= 0)
645 break;
646 ts = G.sessions;
647 while (ts) {
648 if (ts->shell_pid == pid) {
649 ts->shell_pid = -1;
650 update_utmp_DEAD_PROCESS(pid);
651 break;
652 }
653 ts = ts->next;
654 }
655 }
656
657 errno = save_errno;
658 }
659
660 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
telnetd_main(int argc UNUSED_PARAM,char ** argv)661 int telnetd_main(int argc UNUSED_PARAM, char **argv)
662 {
663 fd_set rdfdset, wrfdset;
664 unsigned opt;
665 int count;
666 struct tsession *ts;
667 #if ENABLE_FEATURE_TELNETD_STANDALONE
668 #define IS_INETD (opt & OPT_INETD)
669 int master_fd = master_fd; /* for compiler */
670 int sec_linger = sec_linger;
671 char *opt_bindaddr = NULL;
672 char *opt_portnbr;
673 #else
674 enum {
675 IS_INETD = 1,
676 master_fd = -1,
677 };
678 #endif
679 INIT_G();
680
681 /* Even if !STANDALONE, we accept (and ignore) -i, thus people
682 * don't need to guess whether it's ok to pass -i to us */
683 opt = getopt32(argv, "^"
684 "f:l:Ki"
685 IF_FEATURE_TELNETD_STANDALONE("p:b:F")
686 IF_FEATURE_TELNETD_INETD_WAIT("Sw:+") /* -w NUM */
687 "\0"
688 /* -w implies -F. -w and -i don't mix */
689 IF_FEATURE_TELNETD_INETD_WAIT("wF:i--w:w--i"),
690 &G.issuefile, &G.loginpath
691 IF_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr)
692 IF_FEATURE_TELNETD_INETD_WAIT(, &sec_linger)
693 );
694 if (!IS_INETD /*&& !re_execed*/) {
695 /* inform that we start in standalone mode?
696 * May be useful when people forget to give -i */
697 /*bb_error_msg("listening for connections");*/
698 if (!(opt & OPT_FOREGROUND)) {
699 /* DAEMON_CHDIR_ROOT was giving inconsistent
700 * behavior with/without -F, -i */
701 bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
702 }
703 }
704 /* Redirect log to syslog early, if needed */
705 if (IS_INETD || (opt & OPT_SYSLOG) || !(opt & OPT_FOREGROUND)) {
706 openlog(applet_name, LOG_PID, LOG_DAEMON);
707 logmode = LOGMODE_SYSLOG;
708 }
709 #if ENABLE_FEATURE_TELNETD_STANDALONE
710 if (IS_INETD) {
711 G.sessions = make_new_session(0);
712 if (!G.sessions) /* pty opening or vfork problem, exit */
713 return 1; /* make_new_session printed error message */
714 } else {
715 master_fd = 0;
716 if (!(opt & OPT_WAIT)) {
717 unsigned portnbr = CONFIG_FEATURE_TELNETD_PORT_DEFAULT;
718 if (opt & OPT_PORT)
719 portnbr = xatou16(opt_portnbr);
720 master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
721 xlisten(master_fd, 1);
722 }
723 close_on_exec_on(master_fd);
724 }
725 #else
726 G.sessions = make_new_session();
727 if (!G.sessions) /* pty opening or vfork problem, exit */
728 return 1; /* make_new_session printed error message */
729 #endif
730
731 /* We don't want to die if just one session is broken */
732 signal(SIGPIPE, SIG_IGN);
733
734 if (opt & OPT_WATCHCHILD)
735 signal(SIGCHLD, handle_sigchld);
736 else /* prevent dead children from becoming zombies */
737 signal(SIGCHLD, SIG_IGN);
738
739 /*
740 This is how the buffers are used. The arrows indicate data flow.
741
742 +-------+ wridx1++ +------+ rdidx1++ +----------+
743 | | <-------------- | buf1 | <-------------- | |
744 | | size1-- +------+ size1++ | |
745 | pty | | socket |
746 | | rdidx2++ +------+ wridx2++ | |
747 | | --------------> | buf2 | --------------> | |
748 +-------+ size2++ +------+ size2-- +----------+
749
750 size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
751 size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
752
753 Each session has got two buffers. Buffers are circular. If sizeN == 0,
754 buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
755 rdidxN == wridxN.
756 */
757 again:
758 FD_ZERO(&rdfdset);
759 FD_ZERO(&wrfdset);
760
761 /* Select on the master socket, all telnet sockets and their
762 * ptys if there is room in their session buffers.
763 * NB: scalability problem: we recalculate entire bitmap
764 * before each select. Can be a problem with 500+ connections. */
765 ts = G.sessions;
766 while (ts) {
767 struct tsession *next = ts->next; /* in case we free ts */
768 if (ts->shell_pid == -1) {
769 /* Child died and we detected that */
770 free_session(ts);
771 } else {
772 if (ts->size1 > 0) /* can write to pty */
773 FD_SET(ts->ptyfd, &wrfdset);
774 if (ts->size1 < BUFSIZE) /* can read from socket */
775 FD_SET(ts->sockfd_read, &rdfdset);
776 if (ts->size2 > 0) /* can write to socket */
777 FD_SET(ts->sockfd_write, &wrfdset);
778 if (ts->size2 < BUFSIZE) /* can read from pty */
779 FD_SET(ts->ptyfd, &rdfdset);
780 }
781 ts = next;
782 }
783 if (!IS_INETD) {
784 FD_SET(master_fd, &rdfdset);
785 /* This is needed because free_session() does not
786 * take master_fd into account when it finds new
787 * maxfd among remaining fd's */
788 if (master_fd > G.maxfd)
789 G.maxfd = master_fd;
790 }
791
792 {
793 struct timeval *tv_ptr = NULL;
794 #if ENABLE_FEATURE_TELNETD_INETD_WAIT
795 struct timeval tv;
796 if ((opt & OPT_WAIT) && !G.sessions) {
797 tv.tv_sec = sec_linger;
798 tv.tv_usec = 0;
799 tv_ptr = &tv;
800 }
801 #endif
802 count = select(G.maxfd + 1, &rdfdset, &wrfdset, NULL, tv_ptr);
803 }
804 if (count == 0) /* "telnetd -w SEC" timed out */
805 return 0;
806 if (count < 0)
807 goto again; /* EINTR or ENOMEM */
808
809 #if ENABLE_FEATURE_TELNETD_STANDALONE
810 /* Check for and accept new sessions */
811 if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
812 int fd;
813 struct tsession *new_ts;
814
815 fd = accept(master_fd, NULL, NULL);
816 if (fd < 0)
817 goto again;
818 close_on_exec_on(fd);
819
820 /* Create a new session and link it into active list */
821 new_ts = make_new_session(fd);
822 if (new_ts) {
823 new_ts->next = G.sessions;
824 G.sessions = new_ts;
825 } else {
826 close(fd);
827 }
828 }
829 #endif
830
831 /* Then check for data tunneling */
832 ts = G.sessions;
833 while (ts) { /* For all sessions... */
834 struct tsession *next = ts->next; /* in case we free ts */
835
836 if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
837 /* Write to pty from buffer 1 */
838 count = safe_write_to_pty_decode_iac(ts);
839 if (count < 0) {
840 if (errno == EAGAIN)
841 goto skip1;
842 goto kill_session;
843 }
844 }
845 skip1:
846 if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
847 /* Write to socket from buffer 2 */
848 count = MIN(BUFSIZE - ts->wridx2, ts->size2);
849 count = safe_write_double_iac(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count);
850 if (count < 0) {
851 if (errno == EAGAIN)
852 goto skip2;
853 goto kill_session;
854 }
855 ts->wridx2 += count;
856 if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
857 ts->wridx2 = 0;
858 ts->size2 -= count;
859 if (ts->size2 == 0) {
860 ts->rdidx2 = 0;
861 ts->wridx2 = 0;
862 }
863 }
864 skip2:
865
866 if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
867 /* Read from socket to buffer 1 */
868 count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
869 count = safe_read(ts->sockfd_read, TS_BUF1(ts) + ts->rdidx1, count);
870 if (count <= 0) {
871 if (count < 0 && errno == EAGAIN)
872 goto skip3;
873 goto kill_session;
874 }
875 /* Ignore trailing NUL if it is there */
876 if (!TS_BUF1(ts)[ts->rdidx1 + count - 1]) {
877 --count;
878 }
879 ts->size1 += count;
880 ts->rdidx1 += count;
881 if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
882 ts->rdidx1 = 0;
883 }
884 skip3:
885 if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
886 /* Read from pty to buffer 2 */
887 int eio = 0;
888 read_pty:
889 count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
890 count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count);
891 if (count <= 0) {
892 if (count < 0) {
893 if (errno == EAGAIN)
894 goto skip4;
895 /* login process might call vhangup(),
896 * which causes intermittent EIOs on read above
897 * (observed on kernel 4.12.0). Try up to 10 ms.
898 */
899 if (errno == EIO && eio < 10) {
900 eio++;
901 //bb_error_msg("EIO pty %u", eio);
902 usleep(1000);
903 goto read_pty;
904 }
905 }
906 goto kill_session;
907 }
908 ts->size2 += count;
909 ts->rdidx2 += count;
910 if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */
911 ts->rdidx2 = 0;
912 }
913 skip4:
914 ts = next;
915 continue;
916 kill_session:
917 if (ts->shell_pid > 0)
918 update_utmp_DEAD_PROCESS(ts->shell_pid);
919 free_session(ts);
920 ts = next;
921 }
922
923 goto again;
924 }
925