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