xref: /openbsd/usr.sbin/smtpd/smtp.c (revision eed85469) 
1 /*	$OpenBSD: smtp.c,v 1.167 2021/03/05 12:37:32 eric Exp $	*/
2 
3 /*
4  * Copyright (c) 2008 Gilles Chehade <gilles@poolp.org>
5  * Copyright (c) 2008 Pierre-Yves Ritschard <pyr@openbsd.org>
6  * Copyright (c) 2009 Jacek Masiulaniec <jacekm@dobremiasto.net>
7  *
8  * Permission to use, copy, modify, and distribute this software for any
9  * purpose with or without fee is hereby granted, provided that the above
10  * copyright notice and this permission notice appear in all copies.
11  *
12  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
13  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
14  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
15  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
16  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
17  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
18  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
19  */
20 
21 #include <sys/types.h>
22 #include <sys/queue.h>
23 #include <sys/tree.h>
24 #include <sys/socket.h>
25 
26 #include <err.h>
27 #include <errno.h>
28 #include <event.h>
29 #include <imsg.h>
30 #include <netdb.h>
31 #include <pwd.h>
32 #include <signal.h>
33 #include <limits.h>
34 #include <stdio.h>
35 #include <stdlib.h>
36 #include <string.h>
37 #include <tls.h>
38 #include <unistd.h>
39 
40 #include <openssl/ssl.h>
41 
42 #include "smtpd.h"
43 #include "log.h"
44 #include "ssl.h"
45 
46 static void smtp_setup_events(void);
47 static void smtp_pause(void);
48 static void smtp_resume(void);
49 static void smtp_accept(int, short, void *);
50 static void smtp_dropped(struct listener *, int, const struct sockaddr_storage *);
51 static int smtp_enqueue(void);
52 static int smtp_can_accept(void);
53 static void smtp_setup_listeners(void);
54 static void smtp_setup_listener_tls(struct listener *);
55 
56 int
57 proxy_session(struct listener *listener, int sock,
58     const struct sockaddr_storage *ss,
59     void (*accepted)(struct listener *, int,
60 	const struct sockaddr_storage *, struct io *),
61     void (*dropped)(struct listener *, int,
62 	const struct sockaddr_storage *));
63 
64 static void smtp_accepted(struct listener *, int, const struct sockaddr_storage *, struct io *);
65 
66 /*
67  * This function are not publicy exported because it is a hack until libtls
68  * has a proper privsep setup
69  */
70 void tls_config_use_fake_private_key(struct tls_config *config);
71 
72 #define	SMTP_FD_RESERVE	5
73 static size_t	sessions;
74 static size_t	maxsessions;
75 
76 void
77 smtp_imsg(struct mproc *p, struct imsg *imsg)
78 {
79 	switch (imsg->hdr.type) {
80 	case IMSG_SMTP_CHECK_SENDER:
81 	case IMSG_SMTP_EXPAND_RCPT:
82 	case IMSG_SMTP_LOOKUP_HELO:
83 	case IMSG_SMTP_AUTHENTICATE:
84 	case IMSG_FILTER_SMTP_PROTOCOL:
85 	case IMSG_FILTER_SMTP_DATA_BEGIN:
86 		smtp_session_imsg(p, imsg);
87 		return;
88 
89 	case IMSG_SMTP_MESSAGE_COMMIT:
90 	case IMSG_SMTP_MESSAGE_CREATE:
91 	case IMSG_SMTP_MESSAGE_OPEN:
92 	case IMSG_QUEUE_ENVELOPE_SUBMIT:
93 	case IMSG_QUEUE_ENVELOPE_COMMIT:
94 		smtp_session_imsg(p, imsg);
95 		return;
96 
97 	case IMSG_QUEUE_SMTP_SESSION:
98 		m_compose(p, IMSG_QUEUE_SMTP_SESSION, 0, 0, smtp_enqueue(),
99 		    imsg->data, imsg->hdr.len - sizeof imsg->hdr);
100 		return;
101 
102 	case IMSG_CTL_SMTP_SESSION:
103 		m_compose(p, IMSG_CTL_SMTP_SESSION, imsg->hdr.peerid, 0,
104 		    smtp_enqueue(), NULL, 0);
105 		return;
106 
107 	case IMSG_CTL_PAUSE_SMTP:
108 		log_debug("debug: smtp: pausing listening sockets");
109 		smtp_pause();
110 		env->sc_flags |= SMTPD_SMTP_PAUSED;
111 		return;
112 
113 	case IMSG_CTL_RESUME_SMTP:
114 		log_debug("debug: smtp: resuming listening sockets");
115 		env->sc_flags &= ~SMTPD_SMTP_PAUSED;
116 		smtp_resume();
117 		return;
118 	}
119 
120 	errx(1, "smtp_imsg: unexpected %s imsg", imsg_to_str(imsg->hdr.type));
121 }
122 
123 void
124 smtp_postfork(void)
125 {
126 	smtp_setup_listeners();
127 }
128 
129 void
130 smtp_postprivdrop(void)
131 {
132 }
133 
134 void
135 smtp_configure(void)
136 {
137 	smtp_setup_events();
138 }
139 
140 static void
141 smtp_setup_listeners(void)
142 {
143 	struct listener	       *l;
144 	int			opt;
145 
146 	TAILQ_FOREACH(l, env->sc_listeners, entry) {
147 		if ((l->fd = socket(l->ss.ss_family, SOCK_STREAM, 0)) == -1) {
148 			if (errno == EAFNOSUPPORT) {
149 				log_warn("smtpd: socket");
150 				continue;
151 			}
152 			fatal("smtpd: socket");
153 		}
154 
155 		if (l->flags & F_SSL)
156 			smtp_setup_listener_tls(l);
157 
158 		opt = 1;
159 		if (setsockopt(l->fd, SOL_SOCKET, SO_REUSEADDR, &opt,
160 		    sizeof(opt)) == -1)
161 			fatal("smtpd: setsockopt");
162 		if (bind(l->fd, (struct sockaddr *)&l->ss, l->ss.ss_len) == -1)
163 			fatal("smtpd: bind");
164 	}
165 }
166 
167 static void
168 smtp_setup_listener_tls(struct listener *l)
169 {
170 	static const char *dheparams[] = { "none", "auto", "legacy" };
171 	struct tls_config *config;
172 	struct pki *pki;
173 	struct ca *ca;
174 	int i;
175 
176 	if ((config = tls_config_new()) == NULL)
177 		fatal("smtpd: tls_config_new");
178 
179 	if (env->sc_tls_ciphers &&
180 	    tls_config_set_ciphers(config, env->sc_tls_ciphers) == -1)
181 			err(1, "%s", tls_config_error(config));
182 
183 	pki = l->pki[0];
184 	if (pki == NULL)
185 		fatal("no pki defined");
186 
187 	if (tls_config_set_dheparams(config, dheparams[pki->pki_dhe]) == -1)
188 		fatal("tls_config_set_dheparams");
189 
190 	tls_config_use_fake_private_key(config);
191 	for (i = 0; i < l->pkicount; i++) {
192 		pki = l->pki[i];
193 		if (i == 0) {
194 			if (tls_config_set_keypair_mem(config, pki->pki_cert,
195 			    pki->pki_cert_len, NULL, 0) == -1)
196 				fatal("tls_config_set_keypair_mem");
197 		} else {
198 			if (tls_config_add_keypair_mem(config, pki->pki_cert,
199 			    pki->pki_cert_len, NULL, 0) == -1)
200 				fatal("tls_config_add_keypair_mem");
201 		}
202 	}
203 	free(l->pki);
204 	l->pkicount = 0;
205 
206 	if (l->ca_name[0]) {
207 		ca = dict_get(env->sc_ca_dict, l->ca_name);
208 		if (tls_config_set_ca_mem(config, ca->ca_cert, ca->ca_cert_len)
209 		    == -1)
210 			fatal("tls_config_set_ca_mem");
211 	}
212 	else if (tls_config_set_ca_file(config, tls_default_ca_cert_file())
213 	    == -1)
214 		fatal("tls_config_set_ca_file");
215 
216 	if (l->flags & F_TLS_VERIFY)
217 		tls_config_verify_client(config);
218 	else
219 		tls_config_verify_client_optional(config);
220 
221 	l->tls = tls_server();
222 	if (l->tls == NULL)
223 		fatal("tls_server");
224 	if (tls_configure(l->tls, config) == -1) {
225 		fatal("tls_configure: %s", tls_error(l->tls));
226 	}
227 	tls_config_free(config);
228 }
229 
230 
231 static void
232 smtp_setup_events(void)
233 {
234 	struct listener *l;
235 
236 	TAILQ_FOREACH(l, env->sc_listeners, entry) {
237 		log_debug("debug: smtp: listen on %s port %d flags 0x%01x",
238 		    ss_to_text(&l->ss), ntohs(l->port), l->flags);
239 
240 		io_set_nonblocking(l->fd);
241 		if (listen(l->fd, SMTPD_BACKLOG) == -1)
242 			fatal("listen");
243 		event_set(&l->ev, l->fd, EV_READ|EV_PERSIST, smtp_accept, l);
244 
245 		if (!(env->sc_flags & SMTPD_SMTP_PAUSED))
246 			event_add(&l->ev, NULL);
247 	}
248 
249 	purge_config(PURGE_PKI_KEYS);
250 
251 	maxsessions = (getdtablesize() - getdtablecount()) / 2 - SMTP_FD_RESERVE;
252 	log_debug("debug: smtp: will accept at most %zu clients", maxsessions);
253 }
254 
255 static void
256 smtp_pause(void)
257 {
258 	struct listener *l;
259 
260 	if (env->sc_flags & (SMTPD_SMTP_DISABLED|SMTPD_SMTP_PAUSED))
261 		return;
262 
263 	TAILQ_FOREACH(l, env->sc_listeners, entry)
264 		event_del(&l->ev);
265 }
266 
267 static void
268 smtp_resume(void)
269 {
270 	struct listener *l;
271 
272 	if (env->sc_flags & (SMTPD_SMTP_DISABLED|SMTPD_SMTP_PAUSED))
273 		return;
274 
275 	TAILQ_FOREACH(l, env->sc_listeners, entry)
276 		event_add(&l->ev, NULL);
277 }
278 
279 static int
280 smtp_enqueue(void)
281 {
282 	struct listener	*listener = env->sc_sock_listener;
283 	int		 fd[2];
284 
285 	/*
286 	 * Some enqueue requests buffered in IMSG may still arrive even after
287 	 * call to smtp_pause() because enqueue listener is not a real socket
288 	 * and thus cannot be paused properly.
289 	 */
290 	if (env->sc_flags & SMTPD_SMTP_PAUSED)
291 		return (-1);
292 
293 	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, fd))
294 		return (-1);
295 
296 	if ((smtp_session(listener, fd[0], &listener->ss, env->sc_hostname, NULL)) == -1) {
297 		close(fd[0]);
298 		close(fd[1]);
299 		return (-1);
300 	}
301 
302 	sessions++;
303 	stat_increment("smtp.session", 1);
304 	stat_increment("smtp.session.local", 1);
305 
306 	return (fd[1]);
307 }
308 
309 static void
310 smtp_accept(int fd, short event, void *p)
311 {
312 	struct listener		*listener = p;
313 	struct sockaddr_storage	 ss;
314 	socklen_t		 len;
315 	int			 sock;
316 
317 	if (env->sc_flags & SMTPD_SMTP_PAUSED)
318 		fatalx("smtp_session: unexpected client");
319 
320 	if (!smtp_can_accept()) {
321 		log_warnx("warn: Disabling incoming SMTP connections: "
322 		    "Client limit reached");
323 		goto pause;
324 	}
325 
326 	len = sizeof(ss);
327 	if ((sock = accept(fd, (struct sockaddr *)&ss, &len)) == -1) {
328 		if (errno == ENFILE || errno == EMFILE) {
329 			log_warn("warn: Disabling incoming SMTP connections");
330 			goto pause;
331 		}
332 		if (errno == EINTR || errno == EWOULDBLOCK ||
333 		    errno == ECONNABORTED)
334 			return;
335 		fatal("smtp_accept");
336 	}
337 
338 	if (listener->flags & F_PROXY) {
339 		io_set_nonblocking(sock);
340 		if (proxy_session(listener, sock, &ss,
341 			smtp_accepted, smtp_dropped) == -1) {
342 			close(sock);
343 			return;
344 		}
345 		return;
346 	}
347 
348 	smtp_accepted(listener, sock, &ss, NULL);
349 	return;
350 
351 pause:
352 	smtp_pause();
353 	env->sc_flags |= SMTPD_SMTP_DISABLED;
354 	return;
355 }
356 
357 static int
358 smtp_can_accept(void)
359 {
360 	if (sessions + 1 == maxsessions)
361 		return 0;
362 	return (getdtablesize() - getdtablecount() - SMTP_FD_RESERVE >= 2);
363 }
364 
365 void
366 smtp_collect(void)
367 {
368 	sessions--;
369 	stat_decrement("smtp.session", 1);
370 
371 	if (!smtp_can_accept())
372 		return;
373 
374 	if (env->sc_flags & SMTPD_SMTP_DISABLED) {
375 		log_warnx("warn: smtp: "
376 		    "fd exhaustion over, re-enabling incoming connections");
377 		env->sc_flags &= ~SMTPD_SMTP_DISABLED;
378 		smtp_resume();
379 	}
380 }
381 
382 static void
383 smtp_accepted(struct listener *listener, int sock, const struct sockaddr_storage *ss, struct io *io)
384 {
385 	int     ret;
386 
387 	ret = smtp_session(listener, sock, ss, NULL, io);
388 	if (ret == -1) {
389 		log_warn("warn: Failed to create SMTP session");
390 		close(sock);
391 		return;
392 	}
393 	io_set_nonblocking(sock);
394 
395 	sessions++;
396 	stat_increment("smtp.session", 1);
397 	if (listener->ss.ss_family == AF_LOCAL)
398 		stat_increment("smtp.session.local", 1);
399 	if (listener->ss.ss_family == AF_INET)
400 		stat_increment("smtp.session.inet4", 1);
401 	if (listener->ss.ss_family == AF_INET6)
402 		stat_increment("smtp.session.inet6", 1);
403 }
404 
405 static void
406 smtp_dropped(struct listener *listener, int sock, const struct sockaddr_storage *ss)
407 {
408 	close(sock);
409 	sessions--;
410 }
411