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 the GPL v2 or later, see the file LICENSE in this tarball.
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 */
23
24#include <arpa/telnet.h>
25#include <netinet/in.h>
26#include "libbb.h"
27
28#ifdef DOTRACE
29#define TRACE(x, y) do { if (x) printf y; } while (0)
30#else
31#define TRACE(x, y)
32#endif
33
34enum {
35	DATABUFSIZE = 128,
36	IACBUFSIZE  = 128,
37
38	CHM_TRY = 0,
39	CHM_ON = 1,
40	CHM_OFF = 2,
41
42	UF_ECHO = 0x01,
43	UF_SGA = 0x02,
44
45	TS_0 = 1,
46	TS_IAC = 2,
47	TS_OPT = 3,
48	TS_SUB1 = 4,
49	TS_SUB2 = 5,
50};
51
52typedef unsigned char byte;
53
54enum { netfd = 3 };
55
56struct globals {
57	int	iaclen; /* could even use byte, but it's a loss on x86 */
58	byte	telstate; /* telnet negotiation state from network input */
59	byte	telwish;  /* DO, DONT, WILL, WONT */
60	byte    charmode;
61	byte    telflags;
62	byte	do_termios;
63#if ENABLE_FEATURE_TELNET_TTYPE
64	char	*ttype;
65#endif
66#if ENABLE_FEATURE_TELNET_AUTOLOGIN
67	const char *autologin;
68#endif
69#if ENABLE_FEATURE_AUTOWIDTH
70	unsigned win_width, win_height;
71#endif
72	/* same buffer used both for network and console read/write */
73	char    buf[DATABUFSIZE];
74	/* buffer to handle telnet negotiations */
75	char    iacbuf[IACBUFSIZE];
76	struct termios termios_def;
77	struct termios termios_raw;
78} FIX_ALIASING;
79#define G (*(struct globals*)&bb_common_bufsiz1)
80#define INIT_G() do { \
81	struct G_sizecheck { \
82		char G_sizecheck[sizeof(G) > COMMON_BUFSIZE ? -1 : 1]; \
83	}; \
84} while (0)
85
86/* Function prototypes */
87static void rawmode(void);
88static void cookmode(void);
89static void do_linemode(void);
90static void will_charmode(void);
91static void telopt(byte c);
92static int subneg(byte c);
93
94static void iac_flush(void)
95{
96	write(netfd, G.iacbuf, G.iaclen);
97	G.iaclen = 0;
98}
99
100#define write_str(fd, str) write(fd, str, sizeof(str) - 1)
101
102static void doexit(int ev) NORETURN;
103static void doexit(int ev)
104{
105	cookmode();
106	exit(ev);
107}
108
109static void con_escape(void)
110{
111	char b;
112
113	if (bb_got_signal) /* came from line mode... go raw */
114		rawmode();
115
116	write_str(1, "\r\nConsole escape. Commands are:\r\n\n"
117			" l	go to line mode\r\n"
118			" c	go to character mode\r\n"
119			" z	suspend telnet\r\n"
120			" e	exit telnet\r\n");
121
122	if (read(STDIN_FILENO, &b, 1) <= 0)
123		doexit(EXIT_FAILURE);
124
125	switch (b) {
126	case 'l':
127		if (!bb_got_signal) {
128			do_linemode();
129			goto ret;
130		}
131		break;
132	case 'c':
133		if (bb_got_signal) {
134			will_charmode();
135			goto ret;
136		}
137		break;
138	case 'z':
139		cookmode();
140		kill(0, SIGTSTP);
141		rawmode();
142		break;
143	case 'e':
144		doexit(EXIT_SUCCESS);
145	}
146
147	write_str(1, "continuing...\r\n");
148
149	if (bb_got_signal)
150		cookmode();
151 ret:
152	bb_got_signal = 0;
153
154}
155
156static void handle_net_output(int len)
157{
158	/* here we could do smart tricks how to handle 0xFF:s in output
159	 * stream like writing twice every sequence of FF:s (thus doing
160	 * many write()s. But I think interactive telnet application does
161	 * not need to be 100% 8-bit clean, so changing every 0xff:s to
162	 * 0x7f:s
163	 *
164	 * 2002-mar-21, Przemyslaw Czerpak (druzus@polbox.com)
165	 * I don't agree.
166	 * first - I cannot use programs like sz/rz
167	 * second - the 0x0D is sent as one character and if the next
168	 *	char is 0x0A then it's eaten by a server side.
169	 * third - why do you have to make 'many write()s'?
170	 *	I don't understand.
171	 * So I implemented it. It's really useful for me. I hope that
172	 * other people will find it interesting too.
173	 */
174
175	int i, j;
176	byte *p = (byte*)G.buf;
177	byte outbuf[4*DATABUFSIZE];
178
179	for (i = len, j = 0; i > 0; i--, p++) {
180		if (*p == 0x1d) {
181			con_escape();
182			return;
183		}
184		outbuf[j++] = *p;
185		if (*p == 0xff)
186			outbuf[j++] = 0xff;
187		else if (*p == 0x0d)
188			outbuf[j++] = 0x00;
189	}
190	if (j > 0)
191		write(netfd, outbuf, j);
192}
193
194static void handle_net_input(int len)
195{
196	int i;
197	int cstart = 0;
198
199	for (i = 0; i < len; i++) {
200		byte c = G.buf[i];
201
202		if (G.telstate == 0) { /* most of the time state == 0 */
203			if (c == IAC) {
204				cstart = i;
205				G.telstate = TS_IAC;
206			}
207			continue;
208		}
209		switch (G.telstate) {
210		case TS_0:
211			if (c == IAC)
212				G.telstate = TS_IAC;
213			else
214				G.buf[cstart++] = c;
215			break;
216
217		case TS_IAC:
218			if (c == IAC) { /* IAC IAC -> 0xFF */
219				G.buf[cstart++] = c;
220				G.telstate = TS_0;
221				break;
222			}
223			/* else */
224			switch (c) {
225			case SB:
226				G.telstate = TS_SUB1;
227				break;
228			case DO:
229			case DONT:
230			case WILL:
231			case WONT:
232				G.telwish =  c;
233				G.telstate = TS_OPT;
234				break;
235			default:
236				G.telstate = TS_0;	/* DATA MARK must be added later */
237			}
238			break;
239		case TS_OPT: /* WILL, WONT, DO, DONT */
240			telopt(c);
241			G.telstate = TS_0;
242			break;
243		case TS_SUB1: /* Subnegotiation */
244		case TS_SUB2: /* Subnegotiation */
245			if (subneg(c))
246				G.telstate = TS_0;
247			break;
248		}
249	}
250	if (G.telstate) {
251		if (G.iaclen)
252			iac_flush();
253		if (G.telstate == TS_0)
254			G.telstate = 0;
255		len = cstart;
256	}
257
258	if (len)
259		write(STDOUT_FILENO, G.buf, len);
260}
261
262static void put_iac(int c)
263{
264	G.iacbuf[G.iaclen++] = c;
265}
266
267static void put_iac2(byte wwdd, byte c)
268{
269	if (G.iaclen + 3 > IACBUFSIZE)
270		iac_flush();
271
272	put_iac(IAC);
273	put_iac(wwdd);
274	put_iac(c);
275}
276
277#if ENABLE_FEATURE_TELNET_TTYPE
278static void put_iac_subopt(byte c, char *str)
279{
280	int len = strlen(str) + 6;   // ( 2 + 1 + 1 + strlen + 2 )
281
282	if (G.iaclen + len > IACBUFSIZE)
283		iac_flush();
284
285	put_iac(IAC);
286	put_iac(SB);
287	put_iac(c);
288	put_iac(0);
289
290	while (*str)
291		put_iac(*str++);
292
293	put_iac(IAC);
294	put_iac(SE);
295}
296#endif
297
298#if ENABLE_FEATURE_TELNET_AUTOLOGIN
299static void put_iac_subopt_autologin(void)
300{
301	int len = strlen(G.autologin) + 6;	// (2 + 1 + 1 + strlen + 2)
302	const char *p = "USER";
303
304	if (G.iaclen + len > IACBUFSIZE)
305		iac_flush();
306
307	put_iac(IAC);
308	put_iac(SB);
309	put_iac(TELOPT_NEW_ENVIRON);
310	put_iac(TELQUAL_IS);
311	put_iac(NEW_ENV_VAR);
312
313	while (*p)
314		put_iac(*p++);
315
316	put_iac(NEW_ENV_VALUE);
317
318	p = G.autologin;
319	while (*p)
320		put_iac(*p++);
321
322	put_iac(IAC);
323	put_iac(SE);
324}
325#endif
326
327#if ENABLE_FEATURE_AUTOWIDTH
328static void put_iac_naws(byte c, int x, int y)
329{
330	if (G.iaclen + 9 > IACBUFSIZE)
331		iac_flush();
332
333	put_iac(IAC);
334	put_iac(SB);
335	put_iac(c);
336
337	put_iac((x >> 8) & 0xff);
338	put_iac(x & 0xff);
339	put_iac((y >> 8) & 0xff);
340	put_iac(y & 0xff);
341
342	put_iac(IAC);
343	put_iac(SE);
344}
345#endif
346
347static char const escapecharis[] ALIGN1 = "\r\nEscape character is ";
348
349static void setConMode(void)
350{
351	if (G.telflags & UF_ECHO) {
352		if (G.charmode == CHM_TRY) {
353			G.charmode = CHM_ON;
354			printf("\r\nEntering character mode%s'^]'.\r\n", escapecharis);
355			rawmode();
356		}
357	} else {
358		if (G.charmode != CHM_OFF) {
359			G.charmode = CHM_OFF;
360			printf("\r\nEntering line mode%s'^C'.\r\n", escapecharis);
361			cookmode();
362		}
363	}
364}
365
366static void will_charmode(void)
367{
368	G.charmode = CHM_TRY;
369	G.telflags |= (UF_ECHO | UF_SGA);
370	setConMode();
371
372	put_iac2(DO, TELOPT_ECHO);
373	put_iac2(DO, TELOPT_SGA);
374	iac_flush();
375}
376
377static void do_linemode(void)
378{
379	G.charmode = CHM_TRY;
380	G.telflags &= ~(UF_ECHO | UF_SGA);
381	setConMode();
382
383	put_iac2(DONT, TELOPT_ECHO);
384	put_iac2(DONT, TELOPT_SGA);
385	iac_flush();
386}
387
388static void to_notsup(char c)
389{
390	if (G.telwish == WILL)
391		put_iac2(DONT, c);
392	else if (G.telwish == DO)
393		put_iac2(WONT, c);
394}
395
396static void to_echo(void)
397{
398	/* if server requests ECHO, don't agree */
399	if (G.telwish == DO) {
400		put_iac2(WONT, TELOPT_ECHO);
401		return;
402	}
403	if (G.telwish == DONT)
404		return;
405
406	if (G.telflags & UF_ECHO) {
407		if (G.telwish == WILL)
408			return;
409	} else if (G.telwish == WONT)
410		return;
411
412	if (G.charmode != CHM_OFF)
413		G.telflags ^= UF_ECHO;
414
415	if (G.telflags & UF_ECHO)
416		put_iac2(DO, TELOPT_ECHO);
417	else
418		put_iac2(DONT, TELOPT_ECHO);
419
420	setConMode();
421	full_write1_str("\r\n");  /* sudden modec */
422}
423
424static void to_sga(void)
425{
426	/* daemon always sends will/wont, client do/dont */
427
428	if (G.telflags & UF_SGA) {
429		if (G.telwish == WILL)
430			return;
431	} else if (G.telwish == WONT)
432		return;
433
434	G.telflags ^= UF_SGA; /* toggle */
435	if (G.telflags & UF_SGA)
436		put_iac2(DO, TELOPT_SGA);
437	else
438		put_iac2(DONT, TELOPT_SGA);
439}
440
441#if ENABLE_FEATURE_TELNET_TTYPE
442static void to_ttype(void)
443{
444	/* Tell server we will (or won't) do TTYPE */
445	if (G.ttype)
446		put_iac2(WILL, TELOPT_TTYPE);
447	else
448		put_iac2(WONT, TELOPT_TTYPE);
449}
450#endif
451
452#if ENABLE_FEATURE_TELNET_AUTOLOGIN
453static void to_new_environ(void)
454{
455	/* Tell server we will (or will not) do AUTOLOGIN */
456	if (G.autologin)
457		put_iac2(WILL, TELOPT_NEW_ENVIRON);
458	else
459		put_iac2(WONT, TELOPT_NEW_ENVIRON);
460}
461#endif
462
463#if ENABLE_FEATURE_AUTOWIDTH
464static void to_naws(void)
465{
466	/* Tell server we will do NAWS */
467	put_iac2(WILL, TELOPT_NAWS);
468}
469#endif
470
471static void telopt(byte c)
472{
473	switch (c) {
474	case TELOPT_ECHO:
475		to_echo(); break;
476	case TELOPT_SGA:
477		to_sga(); break;
478#if ENABLE_FEATURE_TELNET_TTYPE
479	case TELOPT_TTYPE:
480		to_ttype(); break;
481#endif
482#if ENABLE_FEATURE_TELNET_AUTOLOGIN
483	case TELOPT_NEW_ENVIRON:
484		to_new_environ(); break;
485#endif
486#if ENABLE_FEATURE_AUTOWIDTH
487	case TELOPT_NAWS:
488		to_naws();
489		put_iac_naws(c, G.win_width, G.win_height);
490		break;
491#endif
492	default:
493		to_notsup(c);
494		break;
495	}
496}
497
498/* subnegotiation -- ignore all (except TTYPE,NAWS) */
499static int subneg(byte c)
500{
501	switch (G.telstate) {
502	case TS_SUB1:
503		if (c == IAC)
504			G.telstate = TS_SUB2;
505#if ENABLE_FEATURE_TELNET_TTYPE
506		else
507		if (c == TELOPT_TTYPE && G.ttype)
508			put_iac_subopt(TELOPT_TTYPE, G.ttype);
509#endif
510#if ENABLE_FEATURE_TELNET_AUTOLOGIN
511		else
512		if (c == TELOPT_NEW_ENVIRON && G.autologin)
513			put_iac_subopt_autologin();
514#endif
515		break;
516	case TS_SUB2:
517		if (c == SE)
518			return TRUE;
519		G.telstate = TS_SUB1;
520		/* break; */
521	}
522	return FALSE;
523}
524
525static void rawmode(void)
526{
527	if (G.do_termios)
528		tcsetattr(0, TCSADRAIN, &G.termios_raw);
529}
530
531static void cookmode(void)
532{
533	if (G.do_termios)
534		tcsetattr(0, TCSADRAIN, &G.termios_def);
535}
536
537/* poll gives smaller (-70 bytes) code */
538#define USE_POLL 1
539
540int telnet_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
541int telnet_main(int argc UNUSED_PARAM, char **argv)
542{
543	char *host;
544	int port;
545	int len;
546#ifdef USE_POLL
547	struct pollfd ufds[2];
548#else
549	fd_set readfds;
550	int maxfd;
551#endif
552
553	INIT_G();
554
555#if ENABLE_FEATURE_AUTOWIDTH
556	get_terminal_width_height(0, &G.win_width, &G.win_height);
557#endif
558
559#if ENABLE_FEATURE_TELNET_TTYPE
560	G.ttype = getenv("TERM");
561#endif
562
563	if (tcgetattr(0, &G.termios_def) >= 0) {
564		G.do_termios = 1;
565		G.termios_raw = G.termios_def;
566		cfmakeraw(&G.termios_raw);
567	}
568
569#if ENABLE_FEATURE_TELNET_AUTOLOGIN
570	if (1 & getopt32(argv, "al:", &G.autologin))
571		G.autologin = getenv("USER");
572	argv += optind;
573#else
574	argv++;
575#endif
576	if (!*argv)
577		bb_show_usage();
578	host = *argv++;
579	port = bb_lookup_port(*argv ? *argv++ : "telnet", "tcp", 23);
580	if (*argv) /* extra params?? */
581		bb_show_usage();
582
583	xmove_fd(create_and_connect_stream_or_die(host, port), netfd);
584
585	setsockopt(netfd, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
586
587	signal(SIGINT, record_signo);
588
589#ifdef USE_POLL
590	ufds[0].fd = 0; ufds[1].fd = netfd;
591	ufds[0].events = ufds[1].events = POLLIN;
592#else
593	FD_ZERO(&readfds);
594	FD_SET(STDIN_FILENO, &readfds);
595	FD_SET(netfd, &readfds);
596	maxfd = netfd + 1;
597#endif
598
599	while (1) {
600#ifndef USE_POLL
601		fd_set rfds = readfds;
602
603		switch (select(maxfd, &rfds, NULL, NULL, NULL))
604#else
605		switch (poll(ufds, 2, -1))
606#endif
607		{
608		case 0:
609			/* timeout */
610		case -1:
611			/* error, ignore and/or log something, bay go to loop */
612			if (bb_got_signal)
613				con_escape();
614			else
615				sleep(1);
616			break;
617		default:
618
619#ifdef USE_POLL
620			if (ufds[0].revents)
621#else
622			if (FD_ISSET(STDIN_FILENO, &rfds))
623#endif
624			{
625				len = safe_read(STDIN_FILENO, G.buf, DATABUFSIZE);
626				if (len <= 0)
627					doexit(EXIT_SUCCESS);
628				TRACE(0, ("Read con: %d\n", len));
629				handle_net_output(len);
630			}
631
632#ifdef USE_POLL
633			if (ufds[1].revents)
634#else
635			if (FD_ISSET(netfd, &rfds))
636#endif
637			{
638				len = safe_read(netfd, G.buf, DATABUFSIZE);
639				if (len <= 0) {
640					full_write1_str("Connection closed by foreign host\r\n");
641					doexit(EXIT_FAILURE);
642				}
643				TRACE(0, ("Read netfd (%d): %d\n", netfd, len));
644				handle_net_input(len);
645			}
646		}
647	} /* while (1) */
648}
649