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