1 /*
2  * Copyright (c) 2022 Stefan Sperling <stsp@openbsd.org>
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/queue.h>
19 #include <sys/socket.h>
20 #include <sys/uio.h>
21 
22 #include <errno.h>
23 #include <event.h>
24 #include <siphash.h>
25 #include <stdint.h>
26 #include <stdio.h>
27 #include <stdlib.h>
28 #include <string.h>
29 #include <imsg.h>
30 #include <limits.h>
31 #include <sha1.h>
32 #include <sha2.h>
33 #include <signal.h>
34 #include <unistd.h>
35 
36 #include "got_error.h"
37 #include "got_path.h"
38 
39 #include "gotd.h"
40 #include "log.h"
41 #include "listen.h"
42 
43 #ifndef nitems
44 #define nitems(_a)	(sizeof((_a)) / sizeof((_a)[0]))
45 #endif
46 
47 struct gotd_listen_client {
48 	STAILQ_ENTRY(gotd_listen_client)	 entry;
49 	uint32_t			 id;
50 	int				 fd;
51 	uid_t				 euid;
52 };
53 STAILQ_HEAD(gotd_listen_clients, gotd_listen_client);
54 
55 static struct gotd_listen_clients gotd_listen_clients[GOTD_CLIENT_TABLE_SIZE];
56 static SIPHASH_KEY clients_hash_key;
57 static volatile int listen_client_cnt;
58 static int inflight;
59 
60 struct gotd_uid_connection_counter {
61 	STAILQ_ENTRY(gotd_uid_connection_counter) entry;
62 	uid_t euid;
63 	int nconnections;
64 };
65 STAILQ_HEAD(gotd_client_uids, gotd_uid_connection_counter);
66 static struct gotd_client_uids gotd_client_uids[GOTD_CLIENT_TABLE_SIZE];
67 static SIPHASH_KEY uid_hash_key;
68 
69 static struct {
70 	pid_t pid;
71 	const char *title;
72 	int fd;
73 	struct gotd_imsgev iev;
74 	struct gotd_imsgev pause;
75 	struct gotd_uid_connection_limit *connection_limits;
76 	size_t nconnection_limits;
77 } gotd_listen;
78 
79 static int inflight;
80 
81 static void listen_shutdown(void);
82 
83 static void
84 listen_sighdlr(int sig, short event, void *arg)
85 {
86 	/*
87 	 * Normal signal handler rules don't apply because libevent
88 	 * decouples for us.
89 	 */
90 
91 	switch (sig) {
92 	case SIGHUP:
93 		break;
94 	case SIGUSR1:
95 		break;
96 	case SIGTERM:
97 	case SIGINT:
98 		listen_shutdown();
99 		/* NOTREACHED */
100 		break;
101 	default:
102 		fatalx("unexpected signal");
103 	}
104 }
105 
106 static uint64_t
107 client_hash(uint32_t client_id)
108 {
109 	return SipHash24(&clients_hash_key, &client_id, sizeof(client_id));
110 }
111 
112 static void
113 add_client(struct gotd_listen_client *client)
114 {
115 	uint64_t slot = client_hash(client->id) % nitems(gotd_listen_clients);
116 	STAILQ_INSERT_HEAD(&gotd_listen_clients[slot], client, entry);
117 	listen_client_cnt++;
118 }
119 
120 static struct gotd_listen_client *
121 find_client(uint32_t client_id)
122 {
123 	uint64_t slot;
124 	struct gotd_listen_client *c;
125 
126 	slot = client_hash(client_id) % nitems(gotd_listen_clients);
127 	STAILQ_FOREACH(c, &gotd_listen_clients[slot], entry) {
128 		if (c->id == client_id)
129 			return c;
130 	}
131 
132 	return NULL;
133 }
134 
135 static uint32_t
136 get_client_id(void)
137 {
138 	int duplicate = 0;
139 	uint32_t id;
140 
141 	do {
142 		id = arc4random();
143 		duplicate = (find_client(id) != NULL);
144 	} while (duplicate || id == 0);
145 
146 	return id;
147 }
148 
149 static uint64_t
150 uid_hash(uid_t euid)
151 {
152 	return SipHash24(&uid_hash_key, &euid, sizeof(euid));
153 }
154 
155 static void
156 add_uid_connection_counter(struct gotd_uid_connection_counter *counter)
157 {
158 	uint64_t slot = uid_hash(counter->euid) % nitems(gotd_client_uids);
159 	STAILQ_INSERT_HEAD(&gotd_client_uids[slot], counter, entry);
160 }
161 
162 static void
163 remove_uid_connection_counter(struct gotd_uid_connection_counter *counter)
164 {
165 	uint64_t slot = uid_hash(counter->euid) % nitems(gotd_client_uids);
166 	STAILQ_REMOVE(&gotd_client_uids[slot], counter,
167 	    gotd_uid_connection_counter, entry);
168 }
169 
170 static struct gotd_uid_connection_counter *
171 find_uid_connection_counter(uid_t euid)
172 {
173 	uint64_t slot;
174 	struct gotd_uid_connection_counter *c;
175 
176 	slot = uid_hash(euid) % nitems(gotd_client_uids);
177 	STAILQ_FOREACH(c, &gotd_client_uids[slot], entry) {
178 		if (c->euid == euid)
179 			return c;
180 	}
181 
182 	return NULL;
183 }
184 
185 struct gotd_uid_connection_limit *
186 gotd_find_uid_connection_limit(struct gotd_uid_connection_limit *limits,
187     size_t nlimits, uid_t uid)
188 {
189 	/* This array is always sorted to allow for binary search. */
190 	int i, left = 0, right = nlimits - 1;
191 
192 	while (left <= right) {
193 		i = ((left + right) / 2);
194 		if (limits[i].uid == uid)
195 			return &limits[i];
196 		if (limits[i].uid > uid)
197 			left = i + 1;
198 		else
199 			right = i - 1;
200 	}
201 
202 	return NULL;
203 }
204 
205 static const struct got_error *
206 disconnect(struct gotd_listen_client *client)
207 {
208 	struct gotd_uid_connection_counter *counter;
209 	uint64_t slot;
210 	int client_fd;
211 
212 	log_debug("client on fd %d disconnecting", client->fd);
213 
214 	slot = client_hash(client->id) % nitems(gotd_listen_clients);
215 	STAILQ_REMOVE(&gotd_listen_clients[slot], client,
216 	    gotd_listen_client, entry);
217 
218 	counter = find_uid_connection_counter(client->euid);
219 	if (counter) {
220 		if (counter->nconnections > 0)
221 			counter->nconnections--;
222 		if (counter->nconnections == 0) {
223 			remove_uid_connection_counter(counter);
224 			free(counter);
225 		}
226 	}
227 
228 	client_fd = client->fd;
229 	free(client);
230 	inflight--;
231 	listen_client_cnt--;
232 	if (close(client_fd) == -1)
233 		return got_error_from_errno("close");
234 
235 	return NULL;
236 }
237 
238 static int
239 accept_reserve(int fd, struct sockaddr *addr, socklen_t *addrlen,
240     int reserve, volatile int *counter)
241 {
242 	int ret;
243 
244 	if (getdtablecount() + reserve +
245 	    ((*counter + 1) * GOTD_FD_NEEDED) >= getdtablesize()) {
246 		log_debug("inflight fds exceeded");
247 		errno = EMFILE;
248 		return -1;
249 	}
250 
251 	if ((ret = accept4(fd, addr, addrlen,
252 	    SOCK_NONBLOCK | SOCK_CLOEXEC)) > -1) {
253 		(*counter)++;
254 	}
255 
256 	return ret;
257 }
258 
259 static void
260 gotd_accept_paused(int fd, short event, void *arg)
261 {
262 	event_add(&gotd_listen.iev.ev, NULL);
263 }
264 
265 static void
266 gotd_accept(int fd, short event, void *arg)
267 {
268 	struct gotd_imsgev *iev = arg;
269 	struct sockaddr_storage ss;
270 	struct timeval backoff;
271 	socklen_t len;
272 	int s = -1;
273 	struct gotd_listen_client *client = NULL;
274 	struct gotd_uid_connection_counter *counter = NULL;
275 	struct gotd_imsg_connect iconn;
276 	uid_t euid;
277 	gid_t egid;
278 
279 	backoff.tv_sec = 1;
280 	backoff.tv_usec = 0;
281 
282 	if (event_add(&gotd_listen.iev.ev, NULL) == -1) {
283 		log_warn("event_add");
284 		return;
285 	}
286 	if (event & EV_TIMEOUT)
287 		return;
288 
289 	len = sizeof(ss);
290 
291 	/* Other backoff conditions apart from EMFILE/ENFILE? */
292 	s = accept_reserve(fd, (struct sockaddr *)&ss, &len, GOTD_FD_RESERVE,
293 	    &inflight);
294 	if (s == -1) {
295 		switch (errno) {
296 		case EINTR:
297 		case EWOULDBLOCK:
298 		case ECONNABORTED:
299 			return;
300 		case EMFILE:
301 		case ENFILE:
302 			event_del(&gotd_listen.iev.ev);
303 			evtimer_add(&gotd_listen.pause.ev, &backoff);
304 			return;
305 		default:
306 			log_warn("accept");
307 			return;
308 		}
309 	}
310 
311 	if (listen_client_cnt >= GOTD_MAXCLIENTS)
312 		goto err;
313 
314 	if (getpeereid(s, &euid, &egid) == -1) {
315 		log_warn("getpeerid");
316 		goto err;
317 	}
318 
319 	counter = find_uid_connection_counter(euid);
320 	if (counter == NULL) {
321 		counter = calloc(1, sizeof(*counter));
322 		if (counter == NULL) {
323 			log_warn("%s: calloc", __func__);
324 			goto err;
325 		}
326 		counter->euid = euid;
327 		counter->nconnections = 1;
328 		add_uid_connection_counter(counter);
329 	} else {
330 		int max_connections = GOTD_MAX_CONN_PER_UID;
331 		struct gotd_uid_connection_limit *limit;
332 
333 		limit = gotd_find_uid_connection_limit(
334 		    gotd_listen.connection_limits,
335 		    gotd_listen.nconnection_limits, euid);
336 		if (limit)
337 			max_connections = limit->max_connections;
338 
339 		if (counter->nconnections >= max_connections) {
340 			log_warnx("maximum connections exceeded for uid %d",
341 			    euid);
342 			goto err;
343 		}
344 		counter->nconnections++;
345 	}
346 
347 	client = calloc(1, sizeof(*client));
348 	if (client == NULL) {
349 		log_warn("%s: calloc", __func__);
350 		goto err;
351 	}
352 	client->id = get_client_id();
353 	client->fd = s;
354 	client->euid = euid;
355 	s = -1;
356 	add_client(client);
357 	log_debug("%s: new client connected on fd %d uid %d gid %d", __func__,
358 	    client->fd, euid, egid);
359 
360 	memset(&iconn, 0, sizeof(iconn));
361 	iconn.client_id = client->id;
362 	iconn.euid = euid;
363 	iconn.egid = egid;
364 	s = dup(client->fd);
365 	if (s == -1) {
366 		log_warn("%s: dup", __func__);
367 		goto err;
368 	}
369 	if (gotd_imsg_compose_event(iev, GOTD_IMSG_CONNECT, PROC_LISTEN, s,
370 	    &iconn, sizeof(iconn)) == -1) {
371 		log_warn("imsg compose CONNECT");
372 		goto err;
373 	}
374 
375 	return;
376 err:
377 	inflight--;
378 	if (client)
379 		disconnect(client);
380 	if (s != -1)
381 		close(s);
382 }
383 
384 static const struct got_error *
385 recv_disconnect(struct imsg *imsg)
386 {
387 	struct gotd_imsg_disconnect idisconnect;
388 	size_t datalen;
389 	struct gotd_listen_client *client = NULL;
390 
391 	datalen = imsg->hdr.len - IMSG_HEADER_SIZE;
392 	if (datalen != sizeof(idisconnect))
393 		return got_error(GOT_ERR_PRIVSEP_LEN);
394 	memcpy(&idisconnect, imsg->data, sizeof(idisconnect));
395 
396 	log_debug("client disconnecting");
397 
398 	client = find_client(idisconnect.client_id);
399 	if (client == NULL)
400 		return got_error(GOT_ERR_CLIENT_ID);
401 
402 	return disconnect(client);
403 }
404 
405 static void
406 listen_dispatch(int fd, short event, void *arg)
407 {
408 	const struct got_error *err = NULL;
409 	struct gotd_imsgev *iev = arg;
410 	struct imsgbuf *ibuf = &iev->ibuf;
411 	struct imsg imsg;
412 	ssize_t n;
413 	int shut = 0;
414 
415 	if (event & EV_READ) {
416 		if ((n = imsg_read(ibuf)) == -1 && errno != EAGAIN)
417 			fatal("imsg_read error");
418 		if (n == 0)	/* Connection closed. */
419 			shut = 1;
420 	}
421 
422 	if (event & EV_WRITE) {
423 		n = msgbuf_write(&ibuf->w);
424 		if (n == -1 && errno != EAGAIN)
425 			fatal("msgbuf_write");
426 		if (n == 0)	/* Connection closed. */
427 			shut = 1;
428 	}
429 
430 	for (;;) {
431 		if ((n = imsg_get(ibuf, &imsg)) == -1)
432 			fatal("%s: imsg_get", __func__);
433 		if (n == 0)	/* No more messages. */
434 			break;
435 
436 		switch (imsg.hdr.type) {
437 		case GOTD_IMSG_DISCONNECT:
438 			err = recv_disconnect(&imsg);
439 			if (err)
440 				log_warnx("disconnect: %s", err->msg);
441 			break;
442 		default:
443 			log_debug("unexpected imsg %d", imsg.hdr.type);
444 			break;
445 		}
446 
447 		imsg_free(&imsg);
448 	}
449 
450 	if (!shut) {
451 		gotd_imsg_event_add(iev);
452 	} else {
453 		/* This pipe is dead. Remove its event handler */
454 		event_del(&iev->ev);
455 		event_loopexit(NULL);
456 	}
457 }
458 
459 void
460 listen_main(const char *title, int gotd_socket,
461     struct gotd_uid_connection_limit *connection_limits,
462     size_t nconnection_limits)
463 {
464 	struct gotd_imsgev iev;
465 	struct event evsigint, evsigterm, evsighup, evsigusr1;
466 
467 	arc4random_buf(&clients_hash_key, sizeof(clients_hash_key));
468 	arc4random_buf(&uid_hash_key, sizeof(uid_hash_key));
469 
470 	gotd_listen.title = title;
471 	gotd_listen.pid = getpid();
472 	gotd_listen.fd = gotd_socket;
473 	gotd_listen.connection_limits = connection_limits;
474 	gotd_listen.nconnection_limits = nconnection_limits;
475 
476 	signal_set(&evsigint, SIGINT, listen_sighdlr, NULL);
477 	signal_set(&evsigterm, SIGTERM, listen_sighdlr, NULL);
478 	signal_set(&evsighup, SIGHUP, listen_sighdlr, NULL);
479 	signal_set(&evsigusr1, SIGUSR1, listen_sighdlr, NULL);
480 	signal(SIGPIPE, SIG_IGN);
481 
482 	signal_add(&evsigint, NULL);
483 	signal_add(&evsigterm, NULL);
484 	signal_add(&evsighup, NULL);
485 	signal_add(&evsigusr1, NULL);
486 
487 	imsg_init(&iev.ibuf, GOTD_FILENO_MSG_PIPE);
488 	iev.handler = listen_dispatch;
489 	iev.events = EV_READ;
490 	iev.handler_arg = NULL;
491 	event_set(&iev.ev, iev.ibuf.fd, EV_READ, listen_dispatch, &iev);
492 	if (event_add(&iev.ev, NULL) == -1)
493 		fatalx("event add");
494 
495 	event_set(&gotd_listen.iev.ev, gotd_listen.fd, EV_READ | EV_PERSIST,
496 	    gotd_accept, &iev);
497 	if (event_add(&gotd_listen.iev.ev, NULL))
498 		fatalx("event add");
499 	evtimer_set(&gotd_listen.pause.ev, gotd_accept_paused, NULL);
500 
501 	event_dispatch();
502 
503 	listen_shutdown();
504 }
505 
506 static void
507 listen_shutdown(void)
508 {
509 	log_debug("shutting down");
510 
511 	free(gotd_listen.connection_limits);
512 	if (gotd_listen.fd != -1)
513 		close(gotd_listen.fd);
514 
515 	exit(0);
516 }