1 /* vi: set sw=4 ts=4: */
2 /*
3 * telnet implementation for busybox
4 *
5 * Author: Tomi Ollila <too@iki.fi>
6 * Copyright (C) 1994-2000 by Tomi Ollila
7 *
8 * Created: Thu Apr 7 13:29:41 1994 too
9 * Last modified: Fri Jun 9 14:34:24 2000 too
10 *
11 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
12 *
13 * HISTORY
14 * Revision 3.1 1994/04/17 11:31:54 too
15 * initial revision
16 * Modified 2000/06/13 for inclusion into BusyBox by Erik Andersen <andersen@codepoet.org>
17 * Modified 2001/05/07 to add ability to pass TTYPE to remote host by Jim McQuillan
18 * <jam@ltsp.org>
19 * Modified 2004/02/11 to add ability to pass the USER variable to remote host
20 * by Fernando Silveira <swrh@gmx.net>
21 */
22 //config:config TELNET
23 //config: bool "telnet (8.8 kb)"
24 //config: default y
25 //config: help
26 //config: Telnet is an interface to the TELNET protocol, but is also commonly
27 //config: used to test other simple protocols.
28 //config:
29 //config:config FEATURE_TELNET_TTYPE
30 //config: bool "Pass TERM type to remote host"
31 //config: default y
32 //config: depends on TELNET
33 //config: help
34 //config: Setting this option will forward the TERM environment variable to the
35 //config: remote host you are connecting to. This is useful to make sure that
36 //config: things like ANSI colors and other control sequences behave.
37 //config:
38 //config:config FEATURE_TELNET_AUTOLOGIN
39 //config: bool "Pass USER type to remote host"
40 //config: default y
41 //config: depends on TELNET
42 //config: help
43 //config: Setting this option will forward the USER environment variable to the
44 //config: remote host you are connecting to. This is useful when you need to
45 //config: log into a machine without telling the username (autologin). This
46 //config: option enables '-a' and '-l USER' options.
47 //config:
48 //config:config FEATURE_TELNET_WIDTH
49 //config: bool "Enable window size autodetection"
50 //config: default y
51 //config: depends on TELNET
52
53 //applet:IF_TELNET(APPLET(telnet, BB_DIR_USR_BIN, BB_SUID_DROP))
54
55 //kbuild:lib-$(CONFIG_TELNET) += telnet.o
56
57 //usage:#if ENABLE_FEATURE_TELNET_AUTOLOGIN
58 //usage:#define telnet_trivial_usage
59 //usage: "[-a] [-l USER] HOST [PORT]"
60 //usage:#define telnet_full_usage "\n\n"
61 //usage: "Connect to telnet server\n"
62 //usage: "\n -a Automatic login with $USER variable"
63 //usage: "\n -l USER Automatic login as USER"
64 //usage:
65 //usage:#else
66 //usage:#define telnet_trivial_usage
67 //usage: "HOST [PORT]"
68 //usage:#define telnet_full_usage "\n\n"
69 //usage: "Connect to telnet server"
70 //usage:#endif
71
72 #include <arpa/telnet.h>
73 #include <netinet/in.h>
74 #include "libbb.h"
75 #include "common_bufsiz.h"
76
77 #ifdef __BIONIC__
78 /* should be in arpa/telnet.h */
79 # define IAC 255 /* interpret as command: */
80 # define DONT 254 /* you are not to use option */
81 # define DO 253 /* please, you use option */
82 # define WONT 252 /* I won't use option */
83 # define WILL 251 /* I will use option */
84 # define SB 250 /* interpret as subnegotiation */
85 # define SE 240 /* end sub negotiation */
86 # define TELOPT_ECHO 1 /* echo */
87 # define TELOPT_SGA 3 /* suppress go ahead */
88 # define TELOPT_TTYPE 24 /* terminal type */
89 # define TELOPT_NAWS 31 /* window size */
90 #endif
91
92 enum {
93 DATABUFSIZE = 128,
94 IACBUFSIZE = 128,
95
96 CHM_TRY = 0,
97 CHM_ON = 1,
98 CHM_OFF = 2,
99
100 UF_ECHO = 0x01,
101 UF_SGA = 0x02,
102
103 TS_NORMAL = 0,
104 TS_COPY = 1,
105 TS_IAC = 2,
106 TS_OPT = 3,
107 TS_SUB1 = 4,
108 TS_SUB2 = 5,
109 TS_CR = 6,
110 };
111
112 typedef unsigned char byte;
113
114 enum { netfd = 3 };
115
116 struct globals {
117 int iaclen; /* could even use byte, but it's a loss on x86 */
118 byte telstate; /* telnet negotiation state from network input */
119 byte telwish; /* DO, DONT, WILL, WONT */
120 byte charmode;
121 byte telflags;
122 byte do_termios;
123 #if ENABLE_FEATURE_TELNET_TTYPE
124 char *ttype;
125 #endif
126 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
127 const char *autologin;
128 #endif
129 #if ENABLE_FEATURE_TELNET_WIDTH
130 unsigned win_width, win_height;
131 #endif
132 /* same buffer used both for network and console read/write */
133 char buf[DATABUFSIZE];
134 /* buffer to handle telnet negotiations */
135 char iacbuf[IACBUFSIZE];
136 struct termios termios_def;
137 struct termios termios_raw;
138 } FIX_ALIASING;
139 #define G (*(struct globals*)bb_common_bufsiz1)
140 #define INIT_G() do { \
141 setup_common_bufsiz(); \
142 BUILD_BUG_ON(sizeof(G) > COMMON_BUFSIZE); \
143 } while (0)
144
145
146 static void rawmode(void);
147 static void cookmode(void);
148 static void do_linemode(void);
149 static void will_charmode(void);
150 static void telopt(byte c);
151 static void subneg(byte c);
152
iac_flush(void)153 static void iac_flush(void)
154 {
155 if (G.iaclen != 0) {
156 full_write(netfd, G.iacbuf, G.iaclen);
157 G.iaclen = 0;
158 }
159 }
160
161 static void doexit(int ev) NORETURN;
doexit(int ev)162 static void doexit(int ev)
163 {
164 cookmode();
165 exit(ev);
166 }
167
con_escape(void)168 static void con_escape(void)
169 {
170 char b;
171
172 if (bb_got_signal) /* came from line mode... go raw */
173 rawmode();
174
175 full_write1_str("\r\nConsole escape. Commands are:\r\n\n"
176 " l go to line mode\r\n"
177 " c go to character mode\r\n"
178 " z suspend telnet\r\n"
179 " e exit telnet\r\n");
180
181 if (read(STDIN_FILENO, &b, 1) <= 0)
182 doexit(EXIT_FAILURE);
183
184 switch (b) {
185 case 'l':
186 if (!bb_got_signal) {
187 do_linemode();
188 goto ret;
189 }
190 break;
191 case 'c':
192 if (bb_got_signal) {
193 will_charmode();
194 goto ret;
195 }
196 break;
197 case 'z':
198 cookmode();
199 kill(0, SIGTSTP);
200 rawmode();
201 break;
202 case 'e':
203 doexit(EXIT_SUCCESS);
204 }
205
206 full_write1_str("continuing...\r\n");
207
208 if (bb_got_signal)
209 cookmode();
210 ret:
211 bb_got_signal = 0;
212 }
213
handle_net_output(int len)214 static void handle_net_output(int len)
215 {
216 byte outbuf[2 * DATABUFSIZE];
217 byte *dst = outbuf;
218 byte *src = (byte*)G.buf;
219 byte *end = src + len;
220
221 while (src < end) {
222 byte c = *src++;
223 if (c == 0x1d) {
224 con_escape();
225 return;
226 }
227 *dst = c;
228 if (c == IAC)
229 *++dst = c; /* IAC -> IAC IAC */
230 else
231 if (c == '\r' || c == '\n') {
232 /* Enter key sends '\r' in raw mode and '\n' in cooked one.
233 *
234 * See RFC 1123 3.3.1 Telnet End-of-Line Convention.
235 * Using CR LF instead of other allowed possibilities
236 * like CR NUL - easier to talk to HTTP/SMTP servers.
237 */
238 *dst = '\r'; /* Enter -> CR LF */
239 *++dst = '\n';
240 }
241 #if 0
242 /* putty's "special commands" mode does this: */
243 /* Korenix 3005 switch needs at least the backspace tweak */
244 if (c == 0x08 || c == 0x7f) { /* ctrl+h || backspace */
245 *dst = IAC;
246 *++dst = EC;
247 }
248 if (c == 0x03) { /* ctrl+c */
249 *dst = IAC;
250 *++dst = IP;
251 }
252 #endif
253 dst++;
254 }
255 if (dst - outbuf != 0)
256 full_write(netfd, outbuf, dst - outbuf);
257 }
258
handle_net_input(int len)259 static void handle_net_input(int len)
260 {
261 byte c;
262 int i;
263 int cstart = 0;
264
265 i = 0;
266 //bb_error_msg("[%u,'%.*s']", G.telstate, len, G.buf);
267 if (G.telstate == TS_NORMAL) { /* most typical state */
268 while (i < len) {
269 c = G.buf[i];
270 i++;
271 if (c == IAC) /* unlikely */
272 goto got_IAC;
273 if (c != '\r') /* likely */
274 continue;
275 G.telstate = TS_CR;
276 cstart = i;
277 goto got_special;
278 }
279 full_write(STDOUT_FILENO, G.buf, len);
280 return;
281 got_IAC:
282 G.telstate = TS_IAC;
283 cstart = i - 1;
284 got_special: ;
285 }
286
287 for (; i < len; i++) {
288 c = G.buf[i];
289
290 switch (G.telstate) {
291 case TS_CR:
292 /* Prev char was CR. If cur one is NUL, ignore it.
293 * See RFC 1123 section 3.3.1 for discussion of telnet EOL handling.
294 */
295 G.telstate = TS_COPY;
296 if (c == '\0')
297 break;
298 /* else: fall through - need to handle CR IAC ... properly */
299
300 case TS_COPY: /* Prev char was ordinary */
301 /* Similar to NORMAL, but in TS_COPY we need to copy bytes */
302 if (c == IAC)
303 G.telstate = TS_IAC;
304 else {
305 G.buf[cstart++] = c;
306 if (c == '\r')
307 G.telstate = TS_CR;
308 }
309 break;
310
311 case TS_IAC: /* Prev char was IAC */
312 switch (c) {
313 case IAC: /* IAC IAC -> one IAC */
314 G.buf[cstart++] = c;
315 G.telstate = TS_COPY;
316 break;
317 case SB:
318 G.telstate = TS_SUB1;
319 break;
320 case DO:
321 case DONT:
322 case WILL:
323 case WONT:
324 G.telwish = c;
325 G.telstate = TS_OPT;
326 break;
327 /* DATA MARK must be added later */
328 default:
329 G.telstate = TS_COPY;
330 }
331 break;
332
333 case TS_OPT: /* Prev chars were IAC WILL/WONT/DO/DONT */
334 telopt(c);
335 G.telstate = TS_COPY;
336 break;
337
338 case TS_SUB1: /* Subnegotiation */
339 case TS_SUB2: /* Subnegotiation */
340 subneg(c); /* can change G.telstate */
341 break;
342 }
343 }
344
345 /* We had some IACs, or CR */
346 iac_flush();
347 if (G.telstate == TS_COPY) /* we aren't in the middle of IAC */
348 G.telstate = TS_NORMAL;
349 if (cstart != 0)
350 full_write(STDOUT_FILENO, G.buf, cstart);
351 }
352
put_iac(int c)353 static void put_iac(int c)
354 {
355 int iaclen = G.iaclen;
356 if (iaclen >= IACBUFSIZE) {
357 iac_flush();
358 iaclen = 0;
359 }
360 G.iacbuf[iaclen] = c; /* "... & 0xff" is implicit */
361 G.iaclen = iaclen + 1;
362 }
363
put_iac2_msb_lsb(unsigned x_y)364 static void put_iac2_msb_lsb(unsigned x_y)
365 {
366 put_iac(x_y >> 8); /* "... & 0xff" is implicit */
367 put_iac(x_y); /* "... & 0xff" is implicit */
368 }
369 #define put_iac2_x_y(x,y) put_iac2_msb_lsb(((x)<<8) + (y))
370
371 #if ENABLE_FEATURE_TELNET_WIDTH \
372 || ENABLE_FEATURE_TELNET_TTYPE \
373 || ENABLE_FEATURE_TELNET_AUTOLOGIN
put_iac4_msb_lsb(unsigned x_y_z_t)374 static void put_iac4_msb_lsb(unsigned x_y_z_t)
375 {
376 put_iac2_msb_lsb(x_y_z_t >> 16);
377 put_iac2_msb_lsb(x_y_z_t); /* "... & 0xffff" is implicit */
378 }
379 #define put_iac4_x_y_z_t(x,y,z,t) put_iac4_msb_lsb(((x)<<24) + ((y)<<16) + ((z)<<8) + (t))
380 #endif
381
put_iac3_IAC_x_y_merged(unsigned wwdd_and_c)382 static void put_iac3_IAC_x_y_merged(unsigned wwdd_and_c)
383 {
384 put_iac(IAC);
385 put_iac2_msb_lsb(wwdd_and_c);
386 }
387 #define put_iac3_IAC_x_y(wwdd,c) put_iac3_IAC_x_y_merged(((wwdd)<<8) + (c))
388
389 #if ENABLE_FEATURE_TELNET_TTYPE
put_iac_subopt(byte c,char * str)390 static void put_iac_subopt(byte c, char *str)
391 {
392 put_iac4_x_y_z_t(IAC, SB, c, 0);
393
394 while (*str)
395 put_iac(*str++);
396
397 put_iac2_x_y(IAC, SE);
398 }
399 #endif
400
401 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
put_iac_subopt_autologin(void)402 static void put_iac_subopt_autologin(void)
403 {
404 const char *p;
405
406 put_iac4_x_y_z_t(IAC, SB, TELOPT_NEW_ENVIRON, TELQUAL_IS);
407 put_iac4_x_y_z_t(NEW_ENV_VAR, 'U', 'S', 'E'); /* "USER" */
408 put_iac2_x_y('R', NEW_ENV_VALUE);
409
410 p = G.autologin;
411 while (*p)
412 put_iac(*p++);
413
414 put_iac2_x_y(IAC, SE);
415 }
416 #endif
417
418 #if ENABLE_FEATURE_TELNET_WIDTH
put_iac_naws(byte c,int x,int y)419 static void put_iac_naws(byte c, int x, int y)
420 {
421 put_iac3_IAC_x_y(SB, c);
422
423 put_iac4_msb_lsb((x << 16) + y);
424
425 put_iac2_x_y(IAC, SE);
426 }
427 #endif
428
setConMode(void)429 static void setConMode(void)
430 {
431 if (G.telflags & UF_ECHO) {
432 if (G.charmode == CHM_TRY) {
433 G.charmode = CHM_ON;
434 printf("\r\nEntering %s mode"
435 "\r\nEscape character is '^%c'.\r\n", "character", ']');
436 rawmode();
437 }
438 } else {
439 if (G.charmode != CHM_OFF) {
440 G.charmode = CHM_OFF;
441 printf("\r\nEntering %s mode"
442 "\r\nEscape character is '^%c'.\r\n", "line", 'C');
443 cookmode();
444 }
445 }
446 }
447
will_charmode(void)448 static void will_charmode(void)
449 {
450 G.charmode = CHM_TRY;
451 G.telflags |= (UF_ECHO | UF_SGA);
452 setConMode();
453
454 put_iac3_IAC_x_y(DO, TELOPT_ECHO);
455 put_iac3_IAC_x_y(DO, TELOPT_SGA);
456 iac_flush();
457 }
458
do_linemode(void)459 static void do_linemode(void)
460 {
461 G.charmode = CHM_TRY;
462 G.telflags &= ~(UF_ECHO | UF_SGA);
463 setConMode();
464
465 put_iac3_IAC_x_y(DONT, TELOPT_ECHO);
466 put_iac3_IAC_x_y(DONT, TELOPT_SGA);
467 iac_flush();
468 }
469
to_notsup(char c)470 static void to_notsup(char c)
471 {
472 if (G.telwish == WILL)
473 put_iac3_IAC_x_y(DONT, c);
474 else if (G.telwish == DO)
475 put_iac3_IAC_x_y(WONT, c);
476 }
477
to_echo(void)478 static void to_echo(void)
479 {
480 /* if server requests ECHO, don't agree */
481 if (G.telwish == DO) {
482 put_iac3_IAC_x_y(WONT, TELOPT_ECHO);
483 return;
484 }
485 if (G.telwish == DONT)
486 return;
487
488 if (G.telflags & UF_ECHO) {
489 if (G.telwish == WILL)
490 return;
491 } else if (G.telwish == WONT)
492 return;
493
494 if (G.charmode != CHM_OFF)
495 G.telflags ^= UF_ECHO;
496
497 if (G.telflags & UF_ECHO)
498 put_iac3_IAC_x_y(DO, TELOPT_ECHO);
499 else
500 put_iac3_IAC_x_y(DONT, TELOPT_ECHO);
501
502 setConMode();
503 full_write1_str("\r\n"); /* sudden modec */
504 }
505
to_sga(void)506 static void to_sga(void)
507 {
508 /* daemon always sends will/wont, client do/dont */
509
510 if (G.telflags & UF_SGA) {
511 if (G.telwish == WILL)
512 return;
513 } else if (G.telwish == WONT)
514 return;
515
516 G.telflags ^= UF_SGA; /* toggle */
517 if (G.telflags & UF_SGA)
518 put_iac3_IAC_x_y(DO, TELOPT_SGA);
519 else
520 put_iac3_IAC_x_y(DONT, TELOPT_SGA);
521 }
522
523 #if ENABLE_FEATURE_TELNET_TTYPE
to_ttype(void)524 static void to_ttype(void)
525 {
526 /* Tell server we will (or won't) do TTYPE */
527 if (G.ttype)
528 put_iac3_IAC_x_y(WILL, TELOPT_TTYPE);
529 else
530 put_iac3_IAC_x_y(WONT, TELOPT_TTYPE);
531 }
532 #endif
533
534 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
to_new_environ(void)535 static void to_new_environ(void)
536 {
537 /* Tell server we will (or will not) do AUTOLOGIN */
538 if (G.autologin)
539 put_iac3_IAC_x_y(WILL, TELOPT_NEW_ENVIRON);
540 else
541 put_iac3_IAC_x_y(WONT, TELOPT_NEW_ENVIRON);
542 }
543 #endif
544
545 #if ENABLE_FEATURE_TELNET_WIDTH
to_naws(void)546 static void to_naws(void)
547 {
548 /* Tell server we will do NAWS */
549 put_iac3_IAC_x_y(WILL, TELOPT_NAWS);
550 }
551 #endif
552
telopt(byte c)553 static void telopt(byte c)
554 {
555 switch (c) {
556 case TELOPT_ECHO:
557 to_echo(); break;
558 case TELOPT_SGA:
559 to_sga(); break;
560 #if ENABLE_FEATURE_TELNET_TTYPE
561 case TELOPT_TTYPE:
562 to_ttype(); break;
563 #endif
564 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
565 case TELOPT_NEW_ENVIRON:
566 to_new_environ(); break;
567 #endif
568 #if ENABLE_FEATURE_TELNET_WIDTH
569 case TELOPT_NAWS:
570 to_naws();
571 put_iac_naws(c, G.win_width, G.win_height);
572 break;
573 #endif
574 default:
575 to_notsup(c);
576 break;
577 }
578 }
579
580 /* subnegotiation -- ignore all (except TTYPE,NAWS) */
subneg(byte c)581 static void subneg(byte c)
582 {
583 switch (G.telstate) {
584 case TS_SUB1:
585 if (c == IAC)
586 G.telstate = TS_SUB2;
587 #if ENABLE_FEATURE_TELNET_TTYPE
588 else
589 if (c == TELOPT_TTYPE && G.ttype)
590 put_iac_subopt(TELOPT_TTYPE, G.ttype);
591 #endif
592 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
593 else
594 if (c == TELOPT_NEW_ENVIRON && G.autologin)
595 put_iac_subopt_autologin();
596 #endif
597 break;
598 case TS_SUB2:
599 if (c == SE) {
600 G.telstate = TS_COPY;
601 return;
602 }
603 G.telstate = TS_SUB1;
604 break;
605 }
606 }
607
rawmode(void)608 static void rawmode(void)
609 {
610 if (G.do_termios)
611 tcsetattr(0, TCSADRAIN, &G.termios_raw);
612 }
613
cookmode(void)614 static void cookmode(void)
615 {
616 if (G.do_termios)
617 tcsetattr(0, TCSADRAIN, &G.termios_def);
618 }
619
620 int telnet_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
telnet_main(int argc UNUSED_PARAM,char ** argv)621 int telnet_main(int argc UNUSED_PARAM, char **argv)
622 {
623 char *host;
624 int port;
625 int len;
626 struct pollfd ufds[2];
627
628 INIT_G();
629
630 #if ENABLE_FEATURE_TELNET_TTYPE
631 G.ttype = getenv("TERM");
632 #endif
633
634 if (tcgetattr(0, &G.termios_def) >= 0) {
635 G.do_termios = 1;
636 G.termios_raw = G.termios_def;
637 cfmakeraw(&G.termios_raw);
638 }
639
640 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
641 if (1 == getopt32(argv, "al:", &G.autologin)) {
642 /* Only -a without -l USER picks $USER from envvar */
643 G.autologin = getenv("USER");
644 }
645 argv += optind;
646 #else
647 argv++;
648 #endif
649 if (!*argv)
650 bb_show_usage();
651 host = *argv++;
652 port = *argv ? bb_lookup_port(*argv++, "tcp", 23)
653 : bb_lookup_std_port("telnet", "tcp", 23);
654 if (*argv) /* extra params?? */
655 bb_show_usage();
656
657 xmove_fd(create_and_connect_stream_or_die(host, port), netfd);
658 printf("Connected to %s\n", host);
659
660 setsockopt_keepalive(netfd);
661
662 #if ENABLE_FEATURE_TELNET_WIDTH
663 get_terminal_width_height(0, &G.win_width, &G.win_height);
664 //TODO: support dynamic resize?
665 #endif
666
667 signal(SIGINT, record_signo);
668
669 ufds[0].fd = STDIN_FILENO;
670 ufds[0].events = POLLIN;
671 ufds[1].fd = netfd;
672 ufds[1].events = POLLIN;
673
674 while (1) {
675 if (poll(ufds, 2, -1) < 0) {
676 /* error, ignore and/or log something, bay go to loop */
677 if (bb_got_signal)
678 con_escape();
679 else
680 sleep1();
681 continue;
682 }
683
684 // FIXME: reads can block. Need full bidirectional buffering.
685
686 if (ufds[0].revents) {
687 len = safe_read(STDIN_FILENO, G.buf, DATABUFSIZE);
688 if (len <= 0)
689 doexit(EXIT_SUCCESS);
690 handle_net_output(len);
691 }
692
693 if (ufds[1].revents) {
694 len = safe_read(netfd, G.buf, DATABUFSIZE);
695 if (len <= 0) {
696 full_write1_str("Connection closed by foreign host\r\n");
697 doexit(EXIT_FAILURE);
698 }
699 handle_net_input(len);
700 }
701 } /* while (1) */
702 }
703