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