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 		event_loopbreak();
96 		break;
97 	case SIGCHLD:
98 		if (waitpid(ssh_pid, &status, WNOHANG) == -1)
99 			fatal("waitpid");
100 		ssh_pid = -1;
101 		break;
102 #ifdef SIGINFO
103 	case SIGINFO:
104 #else
105 	case SIGUSR1:
106 #endif
107 		log_info("connections: %d", conn);
108 	}
109 }
110 
111 static void
112 spawn_ssh(void)
113 {
114 	log_debug("spawning ssh");
115 
116 	switch (ssh_pid = fork()) {
117 	case -1:
118 		fatal("fork");
119 	case 0:
120 		execl(SSH_PATH, "ssh", "-L", ssh_tflag, "-NTq", ssh_dest,
121 		    NULL);
122 		fatal("exec");
123 	default:
124 		return;
125 	}
126 }
127 
128 static void
129 conn_free(struct conn *c)
130 {
131 	if (c->sourcebev != NULL)
132 		bufferevent_free(c->sourcebev);
133 	if (c->tobev != NULL)
134 		bufferevent_free(c->tobev);
135 
136 	if (evtimer_pending(&c->waitev, NULL))
137 		evtimer_del(&c->waitev);
138 
139 	close(c->source);
140 	if (c->to != -1)
141 		close(c->to);
142 
143 	free(c);
144 }
145 
146 static void
147 killing_time(int fd, short event, void *data)
148 {
149 	if (ssh_pid == -1)
150 		return;
151 
152 	log_debug("timeout expired, killing ssh (%d)", ssh_pid);
153 	kill(ssh_pid, SIGTERM);
154 	ssh_pid = -1;
155 }
156 
157 static void
158 nopcb(struct bufferevent *bev, void *d)
159 {
160 	return;
161 }
162 
163 static void
164 sreadcb(struct bufferevent *bev, void *d)
165 {
166 	struct conn *c = d;
167 
168 	bufferevent_write_buffer(c->tobev, EVBUFFER_INPUT(bev));
169 }
170 
171 static void
172 treadcb(struct bufferevent *bev, void *d)
173 {
174 	struct conn *c = d;
175 
176 	bufferevent_write_buffer(c->sourcebev, EVBUFFER_INPUT(bev));
177 }
178 
179 static void
180 errcb(struct bufferevent *bev, short event, void *d)
181 {
182 	struct conn *c = d;
183 
184 	log_info("closing connection (event=%x)", event);
185 
186 	conn_free(c);
187 
188 	if (--conn == 0) {
189 		log_debug("scheduling ssh termination (%llds)",
190 		    (long long)timeout.tv_sec);
191 		if (timeout.tv_sec != 0) {
192 			evtimer_set(&timeoutev, killing_time, NULL);
193 			evtimer_add(&timeoutev, &timeout);
194 		}
195 	}
196 }
197 
198 static int
199 connect_to_ssh(void)
200 {
201 	struct addrinfo hints, *res, *res0;
202 	int r, saved_errno, sock;
203 	const char *cause;
204 
205 	memset(&hints, 0, sizeof(hints));
206 	hints.ai_family = AF_UNSPEC;
207 	hints.ai_socktype = SOCK_STREAM;
208 
209 	r = getaddrinfo(ssh_host, ssh_port, &hints, &res0);
210 	if (r != 0) {
211 		log_warnx("getaddrinfo(\"%s\", \"%s\"): %s",
212 		    ssh_host, ssh_port, gai_strerror(r));
213 		return -1;
214 	}
215 
216 	for (res = res0; res; res = res->ai_next) {
217 		sock = socket(res->ai_family, res->ai_socktype,
218 		    res->ai_protocol);
219 		if (sock == -1) {
220 			cause = "socket";
221 			continue;
222 		}
223 
224 		if (connect(sock, res->ai_addr, res->ai_addrlen) == -1) {
225 			cause = "connect";
226 			saved_errno = errno;
227 			close(sock);
228 			errno = saved_errno;
229 			sock = -1;
230 			continue;
231 		}
232 
233 		break;
234 	}
235 
236 	if (sock == -1)
237 		log_warn("%s", cause);
238 
239 	freeaddrinfo(res0);
240 	return sock;
241 }
242 
243 static void
244 try_to_connect(int fd, short event, void *d)
245 {
246 	struct conn *c = d;
247 
248 	/* ssh may die in the meantime */
249 	if (ssh_pid == -1) {
250 		close(c->source);
251 		c->source = -1;
252 		return;
253 	}
254 
255 	c->ntentative++;
256 	log_info("trying to connect to %s:%s (%d/%d)", ssh_host, ssh_port,
257 	    c->ntentative, RETRIES);
258 
259 	if ((c->to = connect_to_ssh()) == -1) {
260 		if (c->ntentative == RETRIES) {
261 			log_warnx("giving up connecting");
262 			close(c->source);
263 			c->source = -1;
264 			return;
265 		}
266 
267 		evtimer_set(&c->waitev, try_to_connect, c);
268 		evtimer_add(&c->waitev, &c->retry);
269 		return;
270 	}
271 
272 	log_info("connected!");
273 
274 	c->sourcebev = bufferevent_new(c->source, sreadcb, nopcb, errcb, c);
275 	c->tobev = bufferevent_new(c->to, treadcb, nopcb, errcb, c);
276 	if (c->sourcebev == NULL || c->tobev == NULL) {
277 		log_warn("bufferevent_new");
278 		conn_free(c);
279 		return;
280 	}
281 
282 	bufferevent_enable(c->sourcebev, EV_READ|EV_WRITE);
283 	bufferevent_enable(c->tobev, EV_READ|EV_WRITE);
284 }
285 
286 static void
287 do_accept(int fd, short event, void *data)
288 {
289 	struct conn *c;
290 	int s;
291 
292 	log_debug("incoming connection");
293 
294 	if (evtimer_pending(&timeoutev, NULL))
295 		evtimer_del(&timeoutev);
296 
297 	if ((s = accept(fd, NULL, 0)) == -1)
298 		fatal("accept");
299 
300 	conn++;
301 
302 	if (ssh_pid == -1)
303 		spawn_ssh();
304 
305 	if ((c = calloc(1, sizeof(*c))) == NULL) {
306 		log_warn("calloc");
307 		close(s);
308 		return;
309 	}
310 
311 	c->source = s;
312 	c->to = -1;
313 	c->retry.tv_sec = BACKOFF;
314 	evtimer_set(&c->waitev, try_to_connect, c);
315 	evtimer_add(&c->waitev, &c->retry);
316 }
317 
318 static const char *
319 copysec(const char *s, char *d, size_t len)
320 {
321 	const char *c;
322 
323 	if ((c = strchr(s, ':')) == NULL)
324 		return NULL;
325 	if ((size_t)(c - s) >= len-1)
326 		return NULL;
327 	memset(d, 0, len);
328 	memcpy(d, s, c - s);
329 	return c;
330 }
331 
332 static void
333 bind_socket(void)
334 {
335 	struct addrinfo hints, *res, *res0;
336 	int v, r, saved_errno;
337 	char host[64];
338 	const char *c, *h, *port, *cause;
339 
340 	if ((c = strchr(addr, ':')) == NULL) {
341 		h = NULL;
342 		port = addr;
343 	} else {
344 		if ((c = copysec(addr, host, sizeof(host))) == NULL)
345 			fatalx("name too long: %s", addr);
346 
347 		h = host;
348 		port = c+1;
349 	}
350 
351 	memset(&hints, 0, sizeof(hints));
352 	hints.ai_family = AF_UNSPEC;
353 	hints.ai_socktype = SOCK_STREAM;
354 	hints.ai_flags = AI_PASSIVE;
355 
356 	r = getaddrinfo(h, port, &hints, &res0);
357 	if (r != 0)
358 		fatalx("getaddrinfo(%s): %s", addr, gai_strerror(r));
359 
360 	for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
361 		socks[nsock] = socket(res->ai_family, res->ai_socktype,
362 		    res->ai_protocol);
363 		if (socks[nsock] == -1) {
364 			cause = "socket";
365 			continue;
366 		}
367 
368 		if (bind(socks[nsock], res->ai_addr, res->ai_addrlen) == -1) {
369 			cause = "bind";
370 			saved_errno = errno;
371 			close(socks[nsock]);
372 			errno = saved_errno;
373 			continue;
374 		}
375 
376 		v = 1;
377 		if (setsockopt(socks[nsock], SOL_SOCKET, SO_REUSEADDR, &v,
378 		    sizeof(v)) == -1)
379 			fatal("setsockopt(SO_REUSEADDR)");
380 
381 		v = 1;
382 		if (setsockopt(socks[nsock], SOL_SOCKET, SO_REUSEPORT, &v,
383 		    sizeof(v)) == -1)
384 			fatal("setsockopt(SO_REUSEPORT)");
385 
386 		listen(socks[nsock], 5);
387 
388 		nsock++;
389 	}
390 	if (nsock == 0)
391 		fatal("%s", cause);
392 
393 	freeaddrinfo(res0);
394 }
395 
396 static void
397 parse_tflag(void)
398 {
399 	const char *c;
400 
401 	if (isdigit((unsigned char)*ssh_tflag)) {
402 		strlcpy(ssh_host, "localhost", sizeof(ssh_host));
403 		if (copysec(ssh_tflag, ssh_port, sizeof(ssh_port)) == NULL)
404 			goto err;
405 		return;
406 	}
407 
408 	if ((c = copysec(ssh_tflag, ssh_host, sizeof(ssh_host))) == NULL)
409 		goto err;
410 	if (copysec(c+1, ssh_port, sizeof(ssh_port)) == NULL)
411 		goto err;
412 	return;
413 
414 err:
415 	fatal("wrong value for -B");
416 }
417 
418 static void __dead
419 usage(void)
420 {
421 	fprintf(stderr, "usage: %s [-dv] -B sshaddr -b addr [-t timeout]"
422 	    " destination\n", getprogname());
423 	exit(1);
424 }
425 
426 int
427 main(int argc, char **argv)
428 {
429 	int ch, i, fd;
430 	const char *errstr;
431 	struct stat sb;
432 
433 	/*
434 	 * Ensure we have fds 0-2 open so that we have no issue with
435 	 * calling bind_socket before daemon(3).
436 	 */
437 	for (i = 0; i < 3; ++i) {
438 		if (fstat(i, &sb) == -1) {
439 			if ((fd = open("/dev/null", O_RDWR)) != -1) {
440 				if (dup2(fd, i) == -1)
441 					exit(1);
442 				if (fd > i)
443 					close(fd);
444 			} else
445 				exit(1);
446 		}
447 	}
448 
449 	log_init(1, LOG_DAEMON);
450 	log_setverbose(1);
451 
452 	while ((ch = getopt(argc, argv, "B:b:dt:v")) != -1) {
453 		switch (ch) {
454 		case 'B':
455 			ssh_tflag = optarg;
456 			parse_tflag();
457 			break;
458 		case 'b':
459 			addr = optarg;
460 			break;
461 		case 'd':
462 			debug = 1;
463 			break;
464 		case 't':
465 			timeout.tv_sec = strtonum(optarg, 0, INT_MAX, &errstr);
466 			if (errstr != NULL)
467 				fatalx("timeout is %s: %s", errstr, optarg);
468 			break;
469 		case 'v':
470 			verbose = 1;
471 			break;
472 		default:
473 			usage();
474 		}
475 	}
476 	argc -= optind;
477 	argv += optind;
478 
479 	if (argc != 1 || addr == NULL || ssh_tflag == NULL)
480 		usage();
481 
482 	ssh_dest = argv[0];
483 
484 	bind_socket();
485 
486 	log_init(debug, LOG_DAEMON);
487 	log_setverbose(verbose);
488 
489 	if (!debug)
490 		daemon(1, 0);
491 
492 	signal(SIGPIPE, SIG_IGN);
493 
494 	event_init();
495 
496 	/* initialize the timer */
497 	evtimer_set(&timeoutev, killing_time, NULL);
498 
499 	signal_set(&sighupev, SIGHUP, sig_handler, NULL);
500 	signal_set(&sigintev, SIGINT, sig_handler, NULL);
501 	signal_set(&sigtermev, SIGTERM, sig_handler, NULL);
502 	signal_set(&sigchldev, SIGCHLD, sig_handler, NULL);
503 #ifdef SIGINFO
504 	signal_set(&siginfoev, SIGINFO, sig_handler, NULL);
505 #else
506 	signal_set(&siginfoev, SIGUSR1, sig_handler, NULL);
507 #endif
508 
509 	signal_add(&sighupev, NULL);
510 	signal_add(&sigintev, NULL);
511 	signal_add(&sigtermev, NULL);
512 	signal_add(&sigchldev, NULL);
513 	signal_add(&siginfoev, NULL);
514 
515 	for (i = 0; i < nsock; ++i) {
516 		event_set(&sockev[i], socks[i], EV_READ|EV_PERSIST,
517 		    do_accept, NULL);
518 		event_add(&sockev[i], NULL);
519 	}
520 
521 	/*
522 	 * dns, inet: bind the socket and connect to the childs.
523 	 * proc, exec: execute ssh on demand.
524 	 */
525 	if (pledge("stdio dns inet proc exec", NULL) == -1)
526 		fatal("pledge");
527 
528 	log_info("starting");
529 	event_dispatch();
530 
531 	if (ssh_pid != -1)
532 		kill(ssh_pid, SIGINT);
533 
534 	return 0;
535 }