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 <err.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 <unistd.h>
31 
32 #include <stdint.h>
33 
34 #ifndef SSH_PATH
35 #define SSH_PATH "/usr/bin/ssh"
36 #endif
37 
38 #define MAXSOCK 4
39 #define MAXCONN 16
40 
41 int		 rport;		/* ssh port */
42 const char	*addr;		/* our addr */
43 const char	*ssh_tunnel_flag;
44 const char	*ssh_dest;
45 
46 struct event	 sockev[MAXSOCK];
47 int		 socks[MAXSOCK];
48 int		 nsock;
49 
50 struct event	 sighupev;
51 struct event	 sigintev;
52 struct event	 sigtermev;
53 struct event	 sigchldev;
54 struct event	 siginfoev;
55 
56 struct timeval	 timeout;
57 struct event	 timeoutev;
58 
59 pid_t		 ssh_pid = -1;
60 
61 int		 conn;
62 
63 struct conn {
64 	int		source;
65 	struct bufferevent *sourcebev;
66 	int		to;
67 	struct bufferevent *tobev;
68 } conns[MAXCONN];
69 
70 static void
71 terminate(int fd, short event, void *data)
72 {
73 	event_loopbreak();
74 }
75 
76 static void
77 chld(int fd, short event, void *data)
78 {
79 	int status;
80 	pid_t pid;
81 
82 	if ((pid = waitpid(ssh_pid, &status, WNOHANG)) == -1)
83 		err(1, "waitpid");
84 }
85 
86 static void
87 info(int fd, short event, void *data)
88 {
89 	warnx("connections: %d", conn);
90 }
91 
92 static void
93 spawn_ssh(void)
94 {
95 	warnx("spawning ssh...");
96 
97 	switch (ssh_pid = fork()) {
98 	case -1:
99 		err(1, "fork");
100 	case 0:
101 		execl(SSH_PATH, "ssh", "-L", ssh_tunnel_flag,
102 		    "-NTq", ssh_dest, NULL);
103 		err(1, "exec");
104 	default:
105 		sleep(5); /* XXX: wait for ssh to bind the port... */
106 	}
107 }
108 
109 static void
110 killing_time(int fd, short event, void *data)
111 {
112 	if (ssh_pid == -1)
113 		return;
114 
115 	warnx("killing time!");
116 	kill(ssh_pid, SIGTERM);
117 	ssh_pid = -1;
118 }
119 
120 static void
121 nopcb(struct bufferevent *bev, void *d)
122 {
123 	return;
124 }
125 
126 static void
127 sreadcb(struct bufferevent *bev, void *d)
128 {
129 	struct conn *c = d;
130 
131 	bufferevent_write_buffer(c->tobev, EVBUFFER_INPUT(bev));
132 }
133 
134 static void
135 treadcb(struct bufferevent *bev, void *d)
136 {
137 	struct conn *c = d;
138 
139 	bufferevent_write_buffer(c->sourcebev, EVBUFFER_INPUT(bev));
140 }
141 
142 static void
143 errcb(struct bufferevent *bev, short event, void *d)
144 {
145 	struct conn *c = d;
146 
147 	warnx("in errcb, closing connection");
148 
149 	bufferevent_free(c->sourcebev);
150 	bufferevent_free(c->tobev);
151 
152 	close(c->source);
153 	close(c->to);
154 
155 	c->source = -1;
156 	c->to = -1;
157 
158 	if (--conn == 0) {
159 		warnx("scheduling ssh termination (%lds)",
160 		    timeout.tv_sec);
161 		evtimer_set(&timeoutev, killing_time, NULL);
162 		evtimer_add(&timeoutev, &timeout);
163 	}
164 }
165 
166 static int
167 connect_to_ssh(void)
168 {
169 	struct addrinfo hints, *res, *res0;
170 	int r, saved_errno, sock;
171 	char port[16];
172 	const char *c, *cause;
173 
174 	if ((c = strchr(ssh_tunnel_flag, ':')) == NULL)
175 		errx(1, "wrong flag format: %s", ssh_tunnel_flag);
176 
177 	if ((size_t)(c - ssh_tunnel_flag) >= sizeof(port)-1)
178 		errx(1, "EPORTTOOLONG");
179 
180 	memset(port, 0, sizeof(port));
181 	memcpy(port, ssh_tunnel_flag, c - ssh_tunnel_flag);
182 
183 	memset(&hints, 0, sizeof(hints));
184 	hints.ai_family = AF_UNSPEC;
185 	hints.ai_socktype = SOCK_STREAM;
186 
187 	/* XXX: hardcoded */
188 	r = getaddrinfo("localhost", port, &hints, &res0);
189 	if (r != 0)
190 		errx(1, "getaddrinfo(\"localhost\", \"%s\"): %s",
191 		    port, gai_strerror(r));
192 
193 	for (res = res0; res; res = res->ai_next) {
194 		sock = socket(res->ai_family, res->ai_socktype,
195 		    res->ai_protocol);
196 		if (sock == -1) {
197 			cause = "socket";
198 			continue;
199 		}
200 
201 		if (connect(sock, res->ai_addr, res->ai_addrlen) == -1) {
202 			cause = "connect";
203 			saved_errno = errno;
204 			close(sock);
205 			errno = saved_errno;
206 			sock = -1;
207 			continue;
208 		}
209 
210 		break;
211 	}
212 
213 	if (sock == -1)
214 		err(1, "%s", cause);
215 
216 	freeaddrinfo(res0);
217 	return sock;
218 }
219 
220 static void
221 do_accept(int fd, short event, void *data)
222 {
223 	int s, sock, i;
224 
225 	warnx("handling connection");
226 
227 	if (evtimer_pending(&timeoutev, NULL))
228 		evtimer_del(&timeoutev);
229 
230 	if ((s = accept(fd, NULL, 0)) == -1)
231 		err(1, "accept");
232 
233 	if (conn == MAXCONN) {
234 		/* oops */
235 		close(s);
236 		return;
237 	}
238 
239 	conn++;
240 
241 	if (ssh_pid == -1)
242 		spawn_ssh();
243 
244 	warnx("binding the socket to ssh");
245 	sock = connect_to_ssh();
246 
247 	for (i = 0; i < MAXCONN; ++i) {
248 		if (conns[i].source == -1) {
249 			conns[i].source = s;
250 			conns[i].to = sock;
251 			conns[i].sourcebev = bufferevent_new(s,
252 			    sreadcb, nopcb, errcb, &conns[i]);
253 			conns[i].tobev = bufferevent_new(sock,
254 			    treadcb, nopcb, errcb, &conns[i]);
255 			if (conns[i].sourcebev == NULL ||
256 			    conns[i].tobev == NULL)
257 				err(1, "bufferevent_new");
258 			bufferevent_enable(conns[i].sourcebev, 
259 			    EV_READ|EV_WRITE);
260 			bufferevent_enable(conns[i].tobev, 
261 			    EV_READ|EV_WRITE);
262 			break;
263 		}
264 	}
265 }
266 
267 static void __dead
268 usage(void)
269 {
270 	fprintf(stderr, "usage: %s -B port:host:hostport -b addr [-t timeout]"
271 	    " destination\n", getprogname());
272 	exit(1);
273 }
274 
275 static void
276 bind_socket(void)
277 {
278 	struct addrinfo hints, *res, *res0;
279 	int r, saved_errno;
280 	char host[64];
281 	const char *c, *h, *port, *cause;
282 
283 	if ((c = strchr(addr, ':')) == NULL) {
284 		h = NULL;
285 		port = addr;
286 	} else {
287 		if ((size_t)(c - addr) >= sizeof(host) -1)
288 			errx(1, "ENAMETOOLONG");
289 		memset(host, 0, sizeof(host));
290 		memcpy(host, c, c - addr);
291 
292 		h = host;
293 		port = c+1;
294 	}
295 
296 	memset(&hints, 0, sizeof(hints));
297 	hints.ai_family = AF_UNSPEC;
298 	hints.ai_socktype = SOCK_STREAM;
299 	hints.ai_flags = AI_PASSIVE;
300 
301 	r = getaddrinfo(h, port, &hints, &res0);
302 	if (r != 0)
303 		errx(1, "getaddrinfo(%s): %s",
304 		    addr, gai_strerror(r));
305 
306 	for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) {
307 		socks[nsock] = socket(res->ai_family, res->ai_socktype,
308 		    res->ai_protocol);
309 		if (socks[nsock] == -1) {
310 			cause = "socket";
311 			continue;
312 		}
313 
314 		if (bind(socks[nsock], res->ai_addr, res->ai_addrlen) == -1) {
315 			cause = "bind";
316 			saved_errno = errno;
317 			close(socks[nsock]);
318 			errno = saved_errno;
319 			continue;
320 		}
321 
322 		listen(socks[nsock], 5);
323 
324 		nsock++;
325 	}
326 	if (nsock == 0)
327 		err(1, "%s", cause);
328 
329 	freeaddrinfo(res0);
330 }
331 
332 int
333 main(int argc, char **argv)
334 {
335 	pid_t pid;
336 	int ch, tout, i, status;
337 	const char *errstr;
338 
339 	while ((ch = getopt(argc, argv, "B:b:t:")) != -1) {
340 		switch (ch) {
341 		case 'B':
342 			ssh_tunnel_flag = optarg;
343 			break;
344 		case 'b':
345 			addr = optarg;
346 			break;
347 		case 't':
348 			tout = strtonum(optarg, 1, INT_MAX, &errstr);
349 			if (errstr != NULL)
350 				errx(1, "timeout is %s: %s", errstr, optarg);
351 			break;
352 		default:
353 			usage();
354 		}
355 	}
356 	argc -= optind;
357 	argv += optind;
358 
359 	if (argc != 1 || addr == NULL || ssh_tunnel_flag == NULL)
360 		usage();
361 
362 	if (tout == 0)
363 		tout = 120;
364 
365 	timeout.tv_sec = tout;
366 	timeout.tv_usec = 0;
367 
368 	ssh_dest = argv[0];
369 
370 	for (i = 0; i < MAXCONN; ++i) {
371 		conns[i].source = -1;
372 		conns[i].to = -1;
373 	}
374 
375 	bind_socket();
376 
377 	signal(SIGPIPE, SIG_IGN);
378 
379 	event_init();
380 
381 	/* initialize the timer */
382 	evtimer_set(&timeoutev, killing_time, NULL);
383 
384 	signal_set(&sighupev, SIGHUP, terminate, NULL);
385 	signal_set(&sigintev, SIGINT, terminate, NULL);
386 	signal_set(&sigtermev, SIGTERM, terminate, NULL);
387 	signal_set(&sigchldev, SIGCHLD, chld, NULL);
388 	signal_set(&siginfoev, SIGINFO, info, NULL);
389 
390 	signal_add(&sighupev, NULL);
391 	signal_add(&sigintev, NULL);
392 	signal_add(&sigtermev, NULL);
393 	signal_add(&sigchldev, NULL);
394 	signal_add(&siginfoev, NULL);
395 
396 	for (i = 0; i < nsock; ++i) {
397 		event_set(&sockev[i], socks[i], EV_READ|EV_PERSIST,
398 		    do_accept, NULL);
399 		event_add(&sockev[i], NULL);
400 	}
401 
402 	/*
403 	 * dns, inet: bind the socket and connect to the childs.
404 	 * proc, exec: execute ssh on demand.
405 	 */
406 	if (pledge("stdio dns inet proc exec", NULL) == -1)
407 		err(1, "pledge");
408 
409 	warnx("lift off!");
410 	event_dispatch();
411 
412 	if (ssh_pid != -1)
413 		kill(ssh_pid, SIGINT);
414 
415 	return 0;
416 }