1 /*
2  * Copyright (c) 2021, 2022 Omar Polo <op@omarpolo.com>
3  *
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose with or without fee is hereby granted, provided that the above
6  * copyright notice and this permission notice appear in all copies.
7  *
8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15  */
16 
17 #include "config.h"
18 
19 #include <sys/types.h>
20 #include <sys/stat.h>
21 #include <sys/socket.h>
22 #include <sys/wait.h>
23 
24 #include <ctype.h>
25 #include <errno.h>
26 #include <fcntl.h>
27 #include <limits.h>
28 #include <netdb.h>
29 #include <signal.h>
30 #include <stdio.h>
31 #include <stdlib.h>
32 #include <string.h>
33 #include <syslog.h>
34 #include <unistd.h>
35 
36 #include "log.h"
37 
38 #ifndef SSH_PATH
39 #define SSH_PATH "/usr/bin/ssh"
40 #endif
41 
42 #define MAXSOCK 32
43 #define BACKOFF 1
44 #define RETRIES 16
45 
46 #ifndef __OpenBSD__
47 #define pledge(p, e) 0
48 #define unveil(p, m) 0
49 #endif
50 
51 const char	*addr;		/* our addr */
52 const char	*ssh_tflag;
53 const char	*ssh_dest;
54 
55 char		 ssh_host[256];
56 char		 ssh_port[16];
57 
58 struct event	 sockev[MAXSOCK];
59 int		 socks[MAXSOCK];
60 int		 nsock;
61 
62 int		 debug;
63 int		 verbose;
64 
65 struct event	 sighupev;
66 struct event	 sigintev;
67 struct event	 sigtermev;
68 struct event	 sigchldev;
69 struct event	 siginfoev;
70 
71 struct timeval	 timeout = {600, 0}; /* 10 minutes */
72 struct event	 timeoutev;
73 
74 pid_t		 ssh_pid = -1;
75 
76 int		 conn;
77 
78 struct conn {
79 	int			 ntentative;
80 	struct timeval		 retry;
81 	struct event		 waitev;
82 	int			 source;
83 	struct bufferevent	*sourcebev;
84 	int			 to;
85 	struct bufferevent	*tobev;
86 };
87 
88 static void
89 sig_handler(int sig, short event, void *data)
90 {
91 	int status;
92 
93 	switch (sig) {
94 	case SIGHUP:
95 	case SIGINT:
96 	case SIGTERM:
97 		log_info("quitting");
98 		event_loopbreak();
99 		break;
100 	case SIGCHLD:
101 		if (waitpid(ssh_pid, &status, WNOHANG) == -1)
102 			fatal("waitpid");
103 		ssh_pid = -1;
104 		break;
105 #ifdef SIGINFO
106 	case SIGINFO:
107 #else
108 	case SIGUSR1:
109 #endif
110 		log_info("connections: %d", conn);
111 	}
112 }
113 
114 static int
115 spawn_ssh(void)
116 {
117 	log_debug("spawning ssh");
118 
119 	switch (ssh_pid = fork()) {
120 	case -1:
121 		log_warnx("fork");
122 		return -1;
123 	case 0:
124 		execl(SSH_PATH, "ssh", "-L", ssh_tflag, "-NTq", ssh_dest,
125 		    NULL);
126 		fatal("exec");
127 	default:
128 		return 0;
129 	}
130 }
131 
132 static void
133 conn_free(struct conn *c)
134 {
135 	if (c->sourcebev != NULL)
136 		bufferevent_free(c->sourcebev);
137 	if (c->tobev != NULL)
138 		bufferevent_free(c->tobev);
139 
140 	if (evtimer_pending(&c->waitev, NULL))
141 		evtimer_del(&c->waitev);
142 
143 	close(c->source);
144 	if (c->to != -1)
145 		close(c->to);
146 
147 	free(c);
148 }
149 
150 static void
151 killing_time(int fd, short event, void *data)
152 {
153 	if (ssh_pid == -1)
154 		return;
155 
156 	log_debug("timeout expired, killing ssh (%d)", ssh_pid);
157 	kill(ssh_pid, SIGTERM);
158 	ssh_pid = -1;
159 }
160 
161 static void
162 nopcb(struct bufferevent *bev, void *d)
163 {
164 	return;
165 }
166 
167 static void
168 sreadcb(struct bufferevent *bev, void *d)
169 {
170 	struct conn *c = d;
171 
172 	bufferevent_write_buffer(c->tobev, EVBUFFER_INPUT(bev));
173 }
174 
175 static void
176 treadcb(struct bufferevent *bev, void *d)
177 {
178 	struct conn *c = d;
179 
180 	bufferevent_write_buffer(c->sourcebev, EVBUFFER_INPUT(bev));
181 }
182 
183 static void
184 errcb(struct bufferevent *bev, short event, void *d)
185 {
186 	struct conn *c = d;
187 
188 	log_info("closing connection (event=%x)", event);
189 
190 	conn_free(c);
191 
192 	if (--conn == 0) {
193 		log_debug("scheduling ssh termination (%llds)",
194 		    (long long)timeout.tv_sec);
195 		if (timeout.tv_sec != 0) {
196 			evtimer_set(&timeoutev, killing_time, NULL);
197 			evtimer_add(&timeoutev, &timeout);
198 		}
199 	}
200 }
201 
202 static int
203 connect_to_ssh(void)
204 {
205 	struct addrinfo hints, *res, *res0;
206 	int r, saved_errno, sock;
207 	const char *cause;
208 
209 	memset(&hints, 0, sizeof(hints));
210 	hints.ai_family = AF_UNSPEC;
211 	hints.ai_socktype = SOCK_STREAM;
212 
213 	r = getaddrinfo(ssh_host, ssh_port, &hints, &res0);
214 	if (r != 0) {
215 		log_warnx("getaddrinfo(\"%s\", \"%s\"): %s",
216 		    ssh_host, ssh_port, gai_strerror(r));
217 		return -1;
218 	}
219 
220 	for (res = res0; res; res = res->ai_next) {
221 		sock = socket(res->ai_family, res->ai_socktype,
222 		    res->ai_protocol);
223 		if (sock == -1) {
224 			cause = "socket";
225 			continue;
226 		}
227 
228 		if (connect(sock, res->ai_addr, res->ai_addrlen) == -1) {
229 			cause = "connect";
230 			saved_errno = errno;
231 			close(sock);
232 			errno = saved_errno;
233 			sock = -1;
234 			continue;
235 		}
236 
237 		break;
238 	}
239 
240 	if (sock == -1)
241 		log_warn("%s", cause);
242 
243 	freeaddrinfo(res0);
244 	return sock;
245 }
246 
247 static void
248 try_to_connect(int fd, short event, void *d)
249 {
250 	struct conn *c = d;
251 
252 	/* ssh may have died in the meantime */
253 	if (ssh_pid == -1) {
254 		conn_free(c);
255 		return;
256 	}
257 
258 	c->ntentative++;
259 	log_info("trying to connect to %s:%s (%d/%d)", ssh_host, ssh_port,
260 	    c->ntentative, RETRIES);
261 
262 	if ((c->to = connect_to_ssh()) == -1) {
263 		if (c->ntentative == RETRIES) {
264 			log_warnx("giving up connecting");
265 			conn_free(c);
266 			return;
267 		}
268 
269 		evtimer_set(&c->waitev, try_to_connect, c);
270 		evtimer_add(&c->waitev, &c->retry);
271 		return;
272 	}
273 
274 	log_info("connected!");
275 
276 	c->sourcebev = bufferevent_new(c->source, sreadcb, nopcb, errcb, c);
277 	c->tobev = bufferevent_new(c->to, treadcb, nopcb, errcb, c);
278 	if (c->sourcebev == NULL || c->tobev == NULL) {
279 		log_warn("bufferevent_new");
280 		conn_free(c);
281 		return;
282 	}
283 
284 	bufferevent_enable(c->sourcebev, EV_READ|EV_WRITE);
285 	bufferevent_enable(c->tobev, EV_READ|EV_WRITE);
286 }
287 
288 static void
289 do_accept(int fd, short event, void *data)
290 {
291 	struct conn *c;
292 	int s;
293 
294 	log_debug("incoming connection");
295 
296 	if ((s = accept(fd, NULL, 0)) == -1) {
297 		log_warn("accept");
298 		return;
299 	}
300 
301 	if (ssh_pid == -1 && spawn_ssh() == -1) {
302 		close(s);
303 		return;
304 	}
305 
306 	if ((c = calloc(1, sizeof(*c))) == NULL) {
307 		log_warn("calloc");
308 		close(s);
309 		return;
310 	}
311 
312 	conn++;
313 	if (evtimer_pending(&timeoutev, NULL))
314 		evtimer_del(&timeoutev);
315 
316 	c->source = s;
317 	c->to = -1;
318 	c->retry.tv_sec = BACKOFF;
319 	evtimer_set(&c->waitev, try_to_connect, c);
320 	evtimer_add(&c->waitev, &c->retry);
321 }
322 
323 static const char *
324 copysec(const char *s, char *d, size_t len)
325 {
326 	const char *c;
327 
328 	if ((c = strchr(s, ':')) == NULL)
329 		return NULL;
330 	if ((size_t)(c - s) >= len-1)
331 		return NULL;
332 	memset(d, 0, len);
333 	memcpy(d, s, c - s);
334 	return c;
335 }
336 
337 static void
338 bind_socket(void)
339 {
340 	struct addrinfo hints, *res, *res0;
341 	int v, r, saved_errno;
342 	char host[64];
343 	const char *c, *h, *port, *cause;
344 
345 	if ((c = strchr(addr, ':')) == NULL) {
346 		h = NULL;
347 		port = addr;
348 	} else {
349 		if ((c = copysec(addr, host, sizeof(host))) == NULL)
350 			fatalx("name too long: %s", addr);
351 
352 		h = host;
353 		port = c+1;
354 	}
355 
356 	memset(&hints, 0, sizeof(hints));
357 	hints.ai_family = AF_UNSPEC;
358 	hints.ai_socktype = SOCK_STREAM;
359 	hints.ai_flags = AI_PASSIVE;
360 
361 	r = getaddrinfo(h, port, &hints, &res0);
362 	if (r != 0)
363 		fatalx("getaddrinfo(%s): %s", addr, gai_strerror(r));
364 
365 	for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
366 		socks[nsock] = socket(res->ai_family, res->ai_socktype,
367 		    res->ai_protocol);
368 		if (socks[nsock] == -1) {
369 			cause = "socket";
370 			continue;
371 		}
372 
373 		if (bind(socks[nsock], res->ai_addr, res->ai_addrlen) == -1) {
374 			cause = "bind";
375 			saved_errno = errno;
376 			close(socks[nsock]);
377 			errno = saved_errno;
378 			continue;
379 		}
380 
381 		v = 1;
382 		if (setsockopt(socks[nsock], SOL_SOCKET, SO_REUSEADDR, &v,
383 		    sizeof(v)) == -1)
384 			fatal("setsockopt(SO_REUSEADDR)");
385 
386 		v = 1;
387 		if (setsockopt(socks[nsock], SOL_SOCKET, SO_REUSEPORT, &v,
388 		    sizeof(v)) == -1)
389 			fatal("setsockopt(SO_REUSEPORT)");
390 
391 		listen(socks[nsock], 5);
392 
393 		nsock++;
394 	}
395 	if (nsock == 0)
396 		fatal("%s", cause);
397 
398 	freeaddrinfo(res0);
399 }
400 
401 static void
402 parse_sshaddr(void)
403 {
404 	const char *c;
405 
406 	if (isdigit((unsigned char)*ssh_tflag)) {
407 		strlcpy(ssh_host, "localhost", sizeof(ssh_host));
408 		if (copysec(ssh_tflag, ssh_port, sizeof(ssh_port)) == NULL)
409 			goto err;
410 		return;
411 	}
412 
413 	if ((c = copysec(ssh_tflag, ssh_host, sizeof(ssh_host))) == NULL)
414 		goto err;
415 	if (copysec(c+1, ssh_port, sizeof(ssh_port)) == NULL)
416 		goto err;
417 	return;
418 
419 err:
420 	fatalx("wrong value for -B");
421 }
422 
423 static void __dead
424 usage(void)
425 {
426 	fprintf(stderr, "usage: %s [-dv] -B sshaddr -b addr [-t timeout]"
427 	    " destination\n", getprogname());
428 	exit(1);
429 }
430 
431 int
432 main(int argc, char **argv)
433 {
434 	int ch, i, fd;
435 	const char *errstr;
436 	struct stat sb;
437 
438 	/*
439 	 * Ensure we have fds 0-2 open so that we have no issue with
440 	 * calling bind_socket before daemon(3).
441 	 */
442 	for (i = 0; i < 3; ++i) {
443 		if (fstat(i, &sb) == -1) {
444 			if ((fd = open("/dev/null", O_RDWR)) != -1) {
445 				if (dup2(fd, i) == -1)
446 					exit(1);
447 				if (fd > i)
448 					close(fd);
449 			} else
450 				exit(1);
451 		}
452 	}
453 
454 	log_init(1, LOG_DAEMON);
455 	log_setverbose(1);
456 
457 	while ((ch = getopt(argc, argv, "B:b:dt:v")) != -1) {
458 		switch (ch) {
459 		case 'B':
460 			ssh_tflag = optarg;
461 			parse_sshaddr();
462 			break;
463 		case 'b':
464 			addr = optarg;
465 			break;
466 		case 'd':
467 			debug = 1;
468 			break;
469 		case 't':
470 			timeout.tv_sec = strtonum(optarg, 0, INT_MAX, &errstr);
471 			if (errstr != NULL)
472 				fatalx("timeout is %s: %s", errstr, optarg);
473 			break;
474 		case 'v':
475 			verbose = 1;
476 			break;
477 		default:
478 			usage();
479 		}
480 	}
481 	argc -= optind;
482 	argv += optind;
483 
484 	if (argc != 1 || addr == NULL || ssh_tflag == NULL)
485 		usage();
486 
487 	ssh_dest = argv[0];
488 
489 	bind_socket();
490 
491 	log_init(debug, LOG_DAEMON);
492 	log_setverbose(verbose);
493 
494 	if (!debug)
495 		daemon(1, 0);
496 
497 	signal(SIGPIPE, SIG_IGN);
498 
499 	event_init();
500 
501 	/* initialize the timer */
502 	evtimer_set(&timeoutev, killing_time, NULL);
503 
504 	signal_set(&sighupev, SIGHUP, sig_handler, NULL);
505 	signal_set(&sigintev, SIGINT, sig_handler, NULL);
506 	signal_set(&sigtermev, SIGTERM, sig_handler, NULL);
507 	signal_set(&sigchldev, SIGCHLD, sig_handler, NULL);
508 #ifdef SIGINFO
509 	signal_set(&siginfoev, SIGINFO, sig_handler, NULL);
510 #else
511 	signal_set(&siginfoev, SIGUSR1, sig_handler, NULL);
512 #endif
513 
514 	signal_add(&sighupev, NULL);
515 	signal_add(&sigintev, NULL);
516 	signal_add(&sigtermev, NULL);
517 	signal_add(&sigchldev, NULL);
518 	signal_add(&siginfoev, NULL);
519 
520 	for (i = 0; i < nsock; ++i) {
521 		event_set(&sockev[i], socks[i], EV_READ|EV_PERSIST,
522 		    do_accept, NULL);
523 		event_add(&sockev[i], NULL);
524 	}
525 
526 	if (unveil(SSH_PATH, "x") == -1)
527 		fatal("unveil(%s)", SSH_PATH);
528 
529 	/*
530 	 * dns, inet: bind the socket and connect to the childs.
531 	 * proc, exec: execute ssh on demand.
532 	 */
533 	if (pledge("stdio dns inet proc exec", NULL) == -1)
534 		fatal("pledge");
535 
536 	log_info("starting");
537 	event_dispatch();
538 
539 	if (ssh_pid != -1)
540 		kill(ssh_pid, SIGINT);
541 
542 	return 0;
543 }