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 void
113 spawn_ssh(void)
114 {
115 	log_debug("spawning ssh");
116 
117 	switch (ssh_pid = fork()) {
118 	case -1:
119 		fatal("fork");
120 	case 0:
121 		execl(SSH_PATH, "ssh", "-L", ssh_tflag, "-NTq", ssh_dest,
122 		    NULL);
123 		fatal("exec");
124 	default:
125 		return;
126 	}
127 }
128 
129 static void
130 conn_free(struct conn *c)
131 {
132 	if (c->sourcebev != NULL)
133 		bufferevent_free(c->sourcebev);
134 	if (c->tobev != NULL)
135 		bufferevent_free(c->tobev);
136 
137 	if (evtimer_pending(&c->waitev, NULL))
138 		evtimer_del(&c->waitev);
139 
140 	close(c->source);
141 	if (c->to != -1)
142 		close(c->to);
143 
144 	free(c);
145 }
146 
147 static void
148 killing_time(int fd, short event, void *data)
149 {
150 	if (ssh_pid == -1)
151 		return;
152 
153 	log_debug("timeout expired, killing ssh (%d)", ssh_pid);
154 	kill(ssh_pid, SIGTERM);
155 	ssh_pid = -1;
156 }
157 
158 static void
159 nopcb(struct bufferevent *bev, void *d)
160 {
161 	return;
162 }
163 
164 static void
165 sreadcb(struct bufferevent *bev, void *d)
166 {
167 	struct conn *c = d;
168 
169 	bufferevent_write_buffer(c->tobev, EVBUFFER_INPUT(bev));
170 }
171 
172 static void
173 treadcb(struct bufferevent *bev, void *d)
174 {
175 	struct conn *c = d;
176 
177 	bufferevent_write_buffer(c->sourcebev, EVBUFFER_INPUT(bev));
178 }
179 
180 static void
181 errcb(struct bufferevent *bev, short event, void *d)
182 {
183 	struct conn *c = d;
184 
185 	log_info("closing connection (event=%x)", event);
186 
187 	conn_free(c);
188 
189 	if (--conn == 0) {
190 		log_debug("scheduling ssh termination (%llds)",
191 		    (long long)timeout.tv_sec);
192 		if (timeout.tv_sec != 0) {
193 			evtimer_set(&timeoutev, killing_time, NULL);
194 			evtimer_add(&timeoutev, &timeout);
195 		}
196 	}
197 }
198 
199 static int
200 connect_to_ssh(void)
201 {
202 	struct addrinfo hints, *res, *res0;
203 	int r, saved_errno, sock;
204 	const char *cause;
205 
206 	memset(&hints, 0, sizeof(hints));
207 	hints.ai_family = AF_UNSPEC;
208 	hints.ai_socktype = SOCK_STREAM;
209 
210 	r = getaddrinfo(ssh_host, ssh_port, &hints, &res0);
211 	if (r != 0) {
212 		log_warnx("getaddrinfo(\"%s\", \"%s\"): %s",
213 		    ssh_host, ssh_port, gai_strerror(r));
214 		return -1;
215 	}
216 
217 	for (res = res0; res; res = res->ai_next) {
218 		sock = socket(res->ai_family, res->ai_socktype,
219 		    res->ai_protocol);
220 		if (sock == -1) {
221 			cause = "socket";
222 			continue;
223 		}
224 
225 		if (connect(sock, res->ai_addr, res->ai_addrlen) == -1) {
226 			cause = "connect";
227 			saved_errno = errno;
228 			close(sock);
229 			errno = saved_errno;
230 			sock = -1;
231 			continue;
232 		}
233 
234 		break;
235 	}
236 
237 	if (sock == -1)
238 		log_warn("%s", cause);
239 
240 	freeaddrinfo(res0);
241 	return sock;
242 }
243 
244 static void
245 try_to_connect(int fd, short event, void *d)
246 {
247 	struct conn *c = d;
248 
249 	/* ssh may die in the meantime */
250 	if (ssh_pid == -1) {
251 		close(c->source);
252 		c->source = -1;
253 		return;
254 	}
255 
256 	c->ntentative++;
257 	log_info("trying to connect to %s:%s (%d/%d)", ssh_host, ssh_port,
258 	    c->ntentative, RETRIES);
259 
260 	if ((c->to = connect_to_ssh()) == -1) {
261 		if (c->ntentative == RETRIES) {
262 			log_warnx("giving up connecting");
263 			close(c->source);
264 			c->source = -1;
265 			return;
266 		}
267 
268 		evtimer_set(&c->waitev, try_to_connect, c);
269 		evtimer_add(&c->waitev, &c->retry);
270 		return;
271 	}
272 
273 	log_info("connected!");
274 
275 	c->sourcebev = bufferevent_new(c->source, sreadcb, nopcb, errcb, c);
276 	c->tobev = bufferevent_new(c->to, treadcb, nopcb, errcb, c);
277 	if (c->sourcebev == NULL || c->tobev == NULL) {
278 		log_warn("bufferevent_new");
279 		conn_free(c);
280 		return;
281 	}
282 
283 	bufferevent_enable(c->sourcebev, EV_READ|EV_WRITE);
284 	bufferevent_enable(c->tobev, EV_READ|EV_WRITE);
285 }
286 
287 static void
288 do_accept(int fd, short event, void *data)
289 {
290 	struct conn *c;
291 	int s;
292 
293 	log_debug("incoming connection");
294 
295 	if (evtimer_pending(&timeoutev, NULL))
296 		evtimer_del(&timeoutev);
297 
298 	if ((s = accept(fd, NULL, 0)) == -1)
299 		fatal("accept");
300 
301 	conn++;
302 
303 	if (ssh_pid == -1)
304 		spawn_ssh();
305 
306 	if ((c = calloc(1, sizeof(*c))) == NULL) {
307 		log_warn("calloc");
308 		close(s);
309 		return;
310 	}
311 
312 	c->source = s;
313 	c->to = -1;
314 	c->retry.tv_sec = BACKOFF;
315 	evtimer_set(&c->waitev, try_to_connect, c);
316 	evtimer_add(&c->waitev, &c->retry);
317 }
318 
319 static const char *
320 copysec(const char *s, char *d, size_t len)
321 {
322 	const char *c;
323 
324 	if ((c = strchr(s, ':')) == NULL)
325 		return NULL;
326 	if ((size_t)(c - s) >= len-1)
327 		return NULL;
328 	memset(d, 0, len);
329 	memcpy(d, s, c - s);
330 	return c;
331 }
332 
333 static void
334 bind_socket(void)
335 {
336 	struct addrinfo hints, *res, *res0;
337 	int v, r, saved_errno;
338 	char host[64];
339 	const char *c, *h, *port, *cause;
340 
341 	if ((c = strchr(addr, ':')) == NULL) {
342 		h = NULL;
343 		port = addr;
344 	} else {
345 		if ((c = copysec(addr, host, sizeof(host))) == NULL)
346 			fatalx("name too long: %s", addr);
347 
348 		h = host;
349 		port = c+1;
350 	}
351 
352 	memset(&hints, 0, sizeof(hints));
353 	hints.ai_family = AF_UNSPEC;
354 	hints.ai_socktype = SOCK_STREAM;
355 	hints.ai_flags = AI_PASSIVE;
356 
357 	r = getaddrinfo(h, port, &hints, &res0);
358 	if (r != 0)
359 		fatalx("getaddrinfo(%s): %s", addr, gai_strerror(r));
360 
361 	for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
362 		socks[nsock] = socket(res->ai_family, res->ai_socktype,
363 		    res->ai_protocol);
364 		if (socks[nsock] == -1) {
365 			cause = "socket";
366 			continue;
367 		}
368 
369 		if (bind(socks[nsock], res->ai_addr, res->ai_addrlen) == -1) {
370 			cause = "bind";
371 			saved_errno = errno;
372 			close(socks[nsock]);
373 			errno = saved_errno;
374 			continue;
375 		}
376 
377 		v = 1;
378 		if (setsockopt(socks[nsock], SOL_SOCKET, SO_REUSEADDR, &v,
379 		    sizeof(v)) == -1)
380 			fatal("setsockopt(SO_REUSEADDR)");
381 
382 		v = 1;
383 		if (setsockopt(socks[nsock], SOL_SOCKET, SO_REUSEPORT, &v,
384 		    sizeof(v)) == -1)
385 			fatal("setsockopt(SO_REUSEPORT)");
386 
387 		listen(socks[nsock], 5);
388 
389 		nsock++;
390 	}
391 	if (nsock == 0)
392 		fatal("%s", cause);
393 
394 	freeaddrinfo(res0);
395 }
396 
397 static void
398 parse_sshaddr(void)
399 {
400 	const char *c;
401 
402 	if (isdigit((unsigned char)*ssh_tflag)) {
403 		strlcpy(ssh_host, "localhost", sizeof(ssh_host));
404 		if (copysec(ssh_tflag, ssh_port, sizeof(ssh_port)) == NULL)
405 			goto err;
406 		return;
407 	}
408 
409 	if ((c = copysec(ssh_tflag, ssh_host, sizeof(ssh_host))) == NULL)
410 		goto err;
411 	if (copysec(c+1, ssh_port, sizeof(ssh_port)) == NULL)
412 		goto err;
413 	return;
414 
415 err:
416 	fatal("wrong value for -B");
417 }
418 
419 static void __dead
420 usage(void)
421 {
422 	fprintf(stderr, "usage: %s [-dv] -B sshaddr -b addr [-t timeout]"
423 	    " destination\n", getprogname());
424 	exit(1);
425 }
426 
427 int
428 main(int argc, char **argv)
429 {
430 	int ch, i, fd;
431 	const char *errstr;
432 	struct stat sb;
433 
434 	/*
435 	 * Ensure we have fds 0-2 open so that we have no issue with
436 	 * calling bind_socket before daemon(3).
437 	 */
438 	for (i = 0; i < 3; ++i) {
439 		if (fstat(i, &sb) == -1) {
440 			if ((fd = open("/dev/null", O_RDWR)) != -1) {
441 				if (dup2(fd, i) == -1)
442 					exit(1);
443 				if (fd > i)
444 					close(fd);
445 			} else
446 				exit(1);
447 		}
448 	}
449 
450 	log_init(1, LOG_DAEMON);
451 	log_setverbose(1);
452 
453 	while ((ch = getopt(argc, argv, "B:b:dt:v")) != -1) {
454 		switch (ch) {
455 		case 'B':
456 			ssh_tflag = optarg;
457 			parse_sshaddr();
458 			break;
459 		case 'b':
460 			addr = optarg;
461 			break;
462 		case 'd':
463 			debug = 1;
464 			break;
465 		case 't':
466 			timeout.tv_sec = strtonum(optarg, 0, INT_MAX, &errstr);
467 			if (errstr != NULL)
468 				fatalx("timeout is %s: %s", errstr, optarg);
469 			break;
470 		case 'v':
471 			verbose = 1;
472 			break;
473 		default:
474 			usage();
475 		}
476 	}
477 	argc -= optind;
478 	argv += optind;
479 
480 	if (argc != 1 || addr == NULL || ssh_tflag == NULL)
481 		usage();
482 
483 	ssh_dest = argv[0];
484 
485 	bind_socket();
486 
487 	log_init(debug, LOG_DAEMON);
488 	log_setverbose(verbose);
489 
490 	if (!debug)
491 		daemon(1, 0);
492 
493 	signal(SIGPIPE, SIG_IGN);
494 
495 	event_init();
496 
497 	/* initialize the timer */
498 	evtimer_set(&timeoutev, killing_time, NULL);
499 
500 	signal_set(&sighupev, SIGHUP, sig_handler, NULL);
501 	signal_set(&sigintev, SIGINT, sig_handler, NULL);
502 	signal_set(&sigtermev, SIGTERM, sig_handler, NULL);
503 	signal_set(&sigchldev, SIGCHLD, sig_handler, NULL);
504 #ifdef SIGINFO
505 	signal_set(&siginfoev, SIGINFO, sig_handler, NULL);
506 #else
507 	signal_set(&siginfoev, SIGUSR1, sig_handler, NULL);
508 #endif
509 
510 	signal_add(&sighupev, NULL);
511 	signal_add(&sigintev, NULL);
512 	signal_add(&sigtermev, NULL);
513 	signal_add(&sigchldev, NULL);
514 	signal_add(&siginfoev, NULL);
515 
516 	for (i = 0; i < nsock; ++i) {
517 		event_set(&sockev[i], socks[i], EV_READ|EV_PERSIST,
518 		    do_accept, NULL);
519 		event_add(&sockev[i], NULL);
520 	}
521 
522 	/*
523 	 * dns, inet: bind the socket and connect to the childs.
524 	 * proc, exec: execute ssh on demand.
525 	 */
526 	if (pledge("stdio dns inet proc exec", NULL) == -1)
527 		fatal("pledge");
528 
529 	log_info("starting");
530 	event_dispatch();
531 
532 	if (ssh_pid != -1)
533 		kill(ssh_pid, SIGINT);
534 
535 	return 0;
536 }