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 #include "lstun.h"
38 
39 #define MAXSOCK 32
40 #define BACKOFF 1
41 #define RETRIES 16
42 
43 const char	*addr;		/* our addr */
44 const char	*ssh_tflag;
45 const char	*ssh_dest;
46 
47 char		 ssh_host[256];
48 char		 ssh_port[16];
49 
50 struct event	 sockev[MAXSOCK];
51 int		 socks[MAXSOCK];
52 int		 nsock;
53 
54 int		 debug;
55 int		 verbose;
56 
57 struct event	 sighupev;
58 struct event	 sigintev;
59 struct event	 sigtermev;
60 struct event	 sigchldev;
61 struct event	 siginfoev;
62 
63 struct timeval	 timeout = {600, 0}; /* 10 minutes */
64 struct event	 timeoutev;
65 
66 pid_t		 ssh_pid = -1;
67 
68 int		 conn;
69 
70 static void
71 sig_handler(int sig, short event, void *data)
72 {
73 	int status;
74 
75 	switch (sig) {
76 	case SIGHUP:
77 	case SIGINT:
78 	case SIGTERM:
79 		log_info("quitting");
80 		event_loopbreak();
81 		break;
82 	case SIGCHLD:
83 		if (waitpid(ssh_pid, &status, WNOHANG) == -1)
84 			fatal("waitpid");
85 		ssh_pid = -1;
86 		break;
87 #ifdef SIGINFO
88 	case SIGINFO:
89 #else
90 	case SIGUSR1:
91 #endif
92 		log_info("connections: %d", conn);
93 	}
94 }
95 
96 static int
97 spawn_ssh(void)
98 {
99 	log_debug("spawning ssh");
100 
101 	switch (ssh_pid = fork()) {
102 	case -1:
103 		log_warnx("fork");
104 		return -1;
105 	case 0:
106 		execl(SSH_PROG, "ssh", "-L", ssh_tflag, "-NTq", ssh_dest,
107 		    NULL);
108 		fatal("exec");
109 	default:
110 		return 0;
111 	}
112 }
113 
114 static void
115 killing_time(int fd, short event, void *data)
116 {
117 	if (ssh_pid == -1)
118 		return;
119 
120 	log_debug("timeout expired, killing ssh (%d)", ssh_pid);
121 	kill(ssh_pid, SIGTERM);
122 	ssh_pid = -1;
123 }
124 
125 void
126 conn_free(struct conn *c)
127 {
128 	if (c->sourcebev != NULL)
129 		bufferevent_free(c->sourcebev);
130 	if (c->tobev != NULL)
131 		bufferevent_free(c->tobev);
132 
133 	if (evtimer_pending(&c->waitev, NULL))
134 		evtimer_del(&c->waitev);
135 
136 	close(c->source);
137 	if (c->to != -1)
138 		close(c->to);
139 
140 	free(c);
141 
142 	if (--conn == 0) {
143 		log_debug("scheduling ssh termination (%llds)",
144 		    (long long)timeout.tv_sec);
145 		if (timeout.tv_sec != 0) {
146 			evtimer_set(&timeoutev, killing_time, NULL);
147 			evtimer_add(&timeoutev, &timeout);
148 		}
149 	}
150 }
151 
152 static int
153 connect_to_ssh(void)
154 {
155 	struct addrinfo hints, *res, *res0;
156 	int r, saved_errno, sock;
157 	const char *cause;
158 
159 	memset(&hints, 0, sizeof(hints));
160 	hints.ai_family = AF_UNSPEC;
161 	hints.ai_socktype = SOCK_STREAM;
162 
163 	r = getaddrinfo(ssh_host, ssh_port, &hints, &res0);
164 	if (r != 0) {
165 		log_warnx("getaddrinfo(\"%s\", \"%s\"): %s",
166 		    ssh_host, ssh_port, gai_strerror(r));
167 		return -1;
168 	}
169 
170 	for (res = res0; res; res = res->ai_next) {
171 		sock = socket(res->ai_family, res->ai_socktype,
172 		    res->ai_protocol);
173 		if (sock == -1) {
174 			cause = "socket";
175 			continue;
176 		}
177 
178 		if (connect(sock, res->ai_addr, res->ai_addrlen) == -1) {
179 			cause = "connect";
180 			saved_errno = errno;
181 			close(sock);
182 			errno = saved_errno;
183 			sock = -1;
184 			continue;
185 		}
186 
187 		break;
188 	}
189 
190 	if (sock == -1)
191 		log_warn("%s", cause);
192 
193 	freeaddrinfo(res0);
194 	return sock;
195 }
196 
197 static void
198 try_to_connect(int fd, short event, void *d)
199 {
200 	struct conn *c = d;
201 
202 	/* ssh may have died in the meantime */
203 	if (ssh_pid == -1) {
204 		conn_free(c);
205 		return;
206 	}
207 
208 	c->ntentative++;
209 	log_info("trying to connect to %s:%s (%d/%d)", ssh_host, ssh_port,
210 	    c->ntentative, RETRIES);
211 
212 	if ((c->to = connect_to_ssh()) == -1) {
213 		if (c->ntentative == RETRIES) {
214 			log_warnx("giving up connecting");
215 			conn_free(c);
216 			return;
217 		}
218 
219 		evtimer_set(&c->waitev, try_to_connect, c);
220 		evtimer_add(&c->waitev, &c->retry);
221 		return;
222 	}
223 
224 	log_info("connected!");
225 
226 	if (conn_splice(c) == -1)
227 		conn_free(c);
228 }
229 
230 static void
231 do_accept(int fd, short event, void *data)
232 {
233 	struct conn *c;
234 	int s;
235 
236 	log_debug("incoming connection");
237 
238 	if ((s = accept(fd, NULL, 0)) == -1) {
239 		log_warn("accept");
240 		return;
241 	}
242 
243 	if (ssh_pid == -1 && spawn_ssh() == -1) {
244 		close(s);
245 		return;
246 	}
247 
248 	if ((c = calloc(1, sizeof(*c))) == NULL) {
249 		log_warn("calloc");
250 		close(s);
251 		return;
252 	}
253 
254 	conn++;
255 	if (evtimer_pending(&timeoutev, NULL))
256 		evtimer_del(&timeoutev);
257 
258 	c->source = s;
259 	c->to = -1;
260 	c->retry.tv_sec = BACKOFF;
261 	evtimer_set(&c->waitev, try_to_connect, c);
262 	evtimer_add(&c->waitev, &c->retry);
263 }
264 
265 static const char *
266 copysec(const char *s, char *d, size_t len)
267 {
268 	const char *c;
269 
270 	if ((c = strchr(s, ':')) == NULL)
271 		return NULL;
272 	if ((size_t)(c - s) >= len-1)
273 		return NULL;
274 	memset(d, 0, len);
275 	memcpy(d, s, c - s);
276 	return c;
277 }
278 
279 static void
280 bind_socket(void)
281 {
282 	struct addrinfo hints, *res, *res0;
283 	int v, r, saved_errno;
284 	char host[64];
285 	const char *c, *h, *port, *cause;
286 
287 	if ((c = strchr(addr, ':')) == NULL) {
288 		h = "localhost";
289 		port = addr;
290 	} else {
291 		if ((c = copysec(addr, host, sizeof(host))) == NULL)
292 			fatalx("name too long: %s", addr);
293 
294 		h = host;
295 		port = c+1;
296 	}
297 
298 	memset(&hints, 0, sizeof(hints));
299 	hints.ai_family = AF_UNSPEC;
300 	hints.ai_socktype = SOCK_STREAM;
301 	hints.ai_flags = AI_PASSIVE;
302 
303 	r = getaddrinfo(h, port, &hints, &res0);
304 	if (r != 0)
305 		fatalx("getaddrinfo(%s): %s", addr, gai_strerror(r));
306 
307 	for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
308 		socks[nsock] = socket(res->ai_family, res->ai_socktype,
309 		    res->ai_protocol);
310 		if (socks[nsock] == -1) {
311 			cause = "socket";
312 			continue;
313 		}
314 
315 		v = 1;
316 		if (setsockopt(socks[nsock], SOL_SOCKET, SO_REUSEADDR, &v,
317 		    sizeof(v)) == -1)
318 			fatal("setsockopt(SO_REUSEADDR)");
319 
320 		v = 1;
321 		if (setsockopt(socks[nsock], SOL_SOCKET, SO_REUSEPORT, &v,
322 		    sizeof(v)) == -1)
323 			fatal("setsockopt(SO_REUSEPORT)");
324 
325 		if (bind(socks[nsock], res->ai_addr, res->ai_addrlen) == -1) {
326 			cause = "bind";
327 			saved_errno = errno;
328 			close(socks[nsock]);
329 			errno = saved_errno;
330 			continue;
331 		}
332 
333 		if (listen(socks[nsock], 5) == -1)
334 			fatal("listen");
335 
336 		nsock++;
337 	}
338 	if (nsock == 0)
339 		fatal("%s", cause);
340 
341 	freeaddrinfo(res0);
342 }
343 
344 static void
345 parse_sshaddr(void)
346 {
347 	const char *c;
348 
349 	if (isdigit((unsigned char)*ssh_tflag)) {
350 		strlcpy(ssh_host, "localhost", sizeof(ssh_host));
351 		if (copysec(ssh_tflag, ssh_port, sizeof(ssh_port)) == NULL)
352 			goto err;
353 		return;
354 	}
355 
356 	if ((c = copysec(ssh_tflag, ssh_host, sizeof(ssh_host))) == NULL)
357 		goto err;
358 	if (copysec(c+1, ssh_port, sizeof(ssh_port)) == NULL)
359 		goto err;
360 	return;
361 
362 err:
363 	fatalx("wrong value for -B");
364 }
365 
366 static void __dead
367 usage(void)
368 {
369 	fprintf(stderr, "usage: %s [-dv] -B sshaddr -b addr [-t timeout]"
370 	    " destination\n", getprogname());
371 	exit(1);
372 }
373 
374 int
375 main(int argc, char **argv)
376 {
377 	int ch, i, fd;
378 	const char *errstr;
379 	struct stat sb;
380 
381 	/*
382 	 * Ensure we have fds 0-2 open so that we have no issue with
383 	 * calling bind_socket before daemon(3).
384 	 */
385 	for (i = 0; i < 3; ++i) {
386 		if (fstat(i, &sb) == -1) {
387 			if ((fd = open("/dev/null", O_RDWR)) != -1) {
388 				if (dup2(fd, i) == -1)
389 					exit(1);
390 				if (fd > i)
391 					close(fd);
392 			} else
393 				exit(1);
394 		}
395 	}
396 
397 	log_init(1, LOG_DAEMON);
398 	log_setverbose(1);
399 
400 	while ((ch = getopt(argc, argv, "B:b:dt:v")) != -1) {
401 		switch (ch) {
402 		case 'B':
403 			ssh_tflag = optarg;
404 			parse_sshaddr();
405 			break;
406 		case 'b':
407 			addr = optarg;
408 			break;
409 		case 'd':
410 			debug = 1;
411 			break;
412 		case 't':
413 			timeout.tv_sec = strtonum(optarg, 0, INT_MAX, &errstr);
414 			if (errstr != NULL)
415 				fatalx("timeout is %s: %s", errstr, optarg);
416 			break;
417 		case 'v':
418 			verbose = 1;
419 			break;
420 		default:
421 			usage();
422 		}
423 	}
424 	argc -= optind;
425 	argv += optind;
426 
427 	if (argc != 1 || addr == NULL || ssh_tflag == NULL)
428 		usage();
429 
430 	ssh_dest = argv[0];
431 
432 	bind_socket();
433 
434 	log_init(debug, LOG_DAEMON);
435 	log_setverbose(verbose);
436 
437 	if (!debug)
438 		daemon(1, 0);
439 
440 	signal(SIGPIPE, SIG_IGN);
441 
442 	event_init();
443 
444 	/* initialize the timer */
445 	evtimer_set(&timeoutev, killing_time, NULL);
446 
447 	signal_set(&sighupev, SIGHUP, sig_handler, NULL);
448 	signal_set(&sigintev, SIGINT, sig_handler, NULL);
449 	signal_set(&sigtermev, SIGTERM, sig_handler, NULL);
450 	signal_set(&sigchldev, SIGCHLD, sig_handler, NULL);
451 #ifdef SIGINFO
452 	signal_set(&siginfoev, SIGINFO, sig_handler, NULL);
453 #else
454 	signal_set(&siginfoev, SIGUSR1, sig_handler, NULL);
455 #endif
456 
457 	signal_add(&sighupev, NULL);
458 	signal_add(&sigintev, NULL);
459 	signal_add(&sigtermev, NULL);
460 	signal_add(&sigchldev, NULL);
461 	signal_add(&siginfoev, NULL);
462 
463 	for (i = 0; i < nsock; ++i) {
464 		event_set(&sockev[i], socks[i], EV_READ|EV_PERSIST,
465 		    do_accept, NULL);
466 		event_add(&sockev[i], NULL);
467 	}
468 
469 	if (unveil(SSH_PROG, "x") == -1)
470 		fatal("unveil(%s)", SSH_PROG);
471 
472 	/*
473 	 * dns, inet: bind the socket and connect to the childs.
474 	 * proc, exec: execute ssh on demand.
475 	 */
476 	if (pledge("stdio dns inet proc exec", NULL) == -1)
477 		fatal("pledge");
478 
479 	log_info("starting");
480 	event_dispatch();
481 
482 	if (ssh_pid != -1)
483 		kill(ssh_pid, SIGINT);
484 
485 	return 0;
486 }