1 /*
2  * Copyright (c) 2019 Martijn van Duren <martijn@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 #include <sys/types.h>
17 #include <sys/socket.h>
18 
19 #include <arpa/inet.h>
20 #include <errno.h>
21 #include <event.h>
22 #include <inttypes.h>
23 #include <netdb.h>
24 #include <stdlib.h>
25 #include <stdarg.h>
26 #include <stdio.h>
27 #include <string.h>
28 #include <syslog.h>
29 #include <unistd.h>
30 #include <asr.h>
31 
32 #include "opensmtpd.h"
33 
34 struct dnsbl_session;
35 
36 struct dnsbl_query {
37 	struct event_asr *event;
38 	int running;
39 	int blacklist;
40 	struct dnsbl_session *session;
41 };
42 
43 struct dnsbl_session {
44 	int listed;
45 	int set_header;
46 	int logged_mark;
47 	struct dnsbl_query *query;
48 	struct osmtpd_ctx *ctx;
49 };
50 
51 static const char **blacklists = NULL;
52 static const char **printblacklists;
53 static size_t nblacklists = 0;
54 static int markspam = 0;
55 static int verbose = 0;
56 
57 const char *dnsbl_printblacklist(const char *);
58 int dnsbl_connect(struct osmtpd_ctx *, const char *,
59     struct sockaddr_storage *);
60 int dnsbl_begin(struct osmtpd_ctx *, uint32_t);
61 int dnsbl_dataline(struct osmtpd_ctx *, const char *);
62 void dnsbl_resolve(struct asr_result *, void *);
63 void dnsbl_session_query_done(struct dnsbl_session *);
64 void *dnsbl_session_new(struct osmtpd_ctx *);
65 void dnsbl_session_free(struct osmtpd_ctx *, void *);
66 void usage(void);
67 
68 int
69 main(int argc, char *argv[])
70 {
71 	int ch;
72 	size_t i;
73 
74 	while ((ch = getopt(argc, argv, "mv")) != -1) {
75 		switch (ch) {
76 		case 'm':
77 			markspam = 1;
78 			break;
79 		case 'v':
80 			verbose = 1;
81 			break;
82 		default:
83 			usage();
84 		}
85 	}
86 
87 	if (pledge("stdio dns", NULL) == -1)
88 		osmtpd_err(1, "pledge");
89 
90 	if ((nblacklists = argc - optind) == 0)
91 		osmtpd_errx(1, "No blacklist specified");
92 
93 	blacklists = calloc(nblacklists, sizeof(*blacklists));
94 	printblacklists = calloc(nblacklists, sizeof(*printblacklists));
95 	if (printblacklists == NULL || blacklists == NULL)
96 		osmtpd_err(1, "malloc");
97 	for (i = 0; i < nblacklists; i++) {
98 		blacklists[i] = argv[optind + i];
99 		printblacklists[i] = dnsbl_printblacklist(argv[optind + i]);
100 	}
101 
102 	osmtpd_register_filter_connect(dnsbl_connect);
103 	osmtpd_local_session(dnsbl_session_new, dnsbl_session_free);
104 	if (markspam) {
105 		osmtpd_register_report_begin(1, dnsbl_begin);
106 		osmtpd_register_filter_dataline(dnsbl_dataline);
107 	}
108 	osmtpd_run();
109 
110 	return 0;
111 }
112 
113 const char *
114 dnsbl_printblacklist(const char *blacklist)
115 {
116 	/* All of abusix is paid and has a key in the first spot */
117 	if (strcasestr(blacklist, ".mail.abusix.zone") != NULL)
118 		return strchr(blacklist, '.') + 1;
119 	/* XXX assume dq.spamhaus.net is paid and has a key in the first spot */
120 	if (strcasestr(blacklist, ".dq.spamhaus.net") != NULL)
121 		return strchr(blacklist, '.') + 1;
122 	return blacklist;
123 }
124 
125 int
126 dnsbl_connect(struct osmtpd_ctx *ctx, const char *hostname,
127     struct sockaddr_storage *ss)
128 {
129 	struct dnsbl_session *session = ctx->local_session;
130 	struct asr_query *aq;
131 	char query[255];
132 	u_char *addr;
133 	size_t i;
134 
135 	if (ss->ss_family == AF_INET)
136 		addr = (u_char *)(&(((struct sockaddr_in *)ss)->sin_addr));
137 	else
138 		addr = (u_char *)(&(((struct sockaddr_in6 *)ss)->sin6_addr));
139 	for (i = 0; i < nblacklists; i++) {
140 		if (ss->ss_family == AF_INET) {
141 			if (snprintf(query, sizeof(query), "%u.%u.%u.%u.%s",
142 			    addr[3], addr[2], addr[1], addr[0],
143 			    blacklists[i]) >= (int) sizeof(query))
144 				osmtpd_errx(1,
145 				    "Can't create query, domain too long");
146 		} else if (ss->ss_family == AF_INET6) {
147 			if (snprintf(query, sizeof(query), "%hhx.%hhx.%hhx.%hhx"
148 			    ".%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx"
149 			    ".%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx"
150 			    ".%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%hhx.%s",
151 			    (u_char) (addr[15] & 0xf), (u_char) (addr[15] >> 4),
152 			    (u_char) (addr[14] & 0xf), (u_char) (addr[14] >> 4),
153 			    (u_char) (addr[13] & 0xf), (u_char) (addr[13] >> 4),
154 			    (u_char) (addr[12] & 0xf), (u_char) (addr[12] >> 4),
155 			    (u_char) (addr[11] & 0xf), (u_char) (addr[11] >> 4),
156 			    (u_char) (addr[10] & 0xf), (u_char) (addr[10] >> 4),
157 			    (u_char) (addr[9] & 0xf), (u_char) (addr[9] >> 4),
158 			    (u_char) (addr[8] & 0xf), (u_char) (addr[8] >> 4),
159 			    (u_char) (addr[7] & 0xf), (u_char) (addr[8] >> 4),
160 			    (u_char) (addr[6] & 0xf), (u_char) (addr[7] >> 4),
161 			    (u_char) (addr[5] & 0xf), (u_char) (addr[5] >> 4),
162 			    (u_char) (addr[4] & 0xf), (u_char) (addr[4] >> 4),
163 			    (u_char) (addr[3] & 0xf), (u_char) (addr[3] >> 4),
164 			    (u_char) (addr[2] & 0xf), (u_char) (addr[2] >> 4),
165 			    (u_char) (addr[1] & 0xf), (u_char) (addr[1] >> 4),
166 			    (u_char) (addr[0] & 0xf), (u_char) (addr[0] >> 4),
167 			    blacklists[i]) >= (int) sizeof(query))
168 				osmtpd_errx(1,
169 				    "Can't create query, domain too long");
170 		} else
171 			osmtpd_errx(1, "Invalid address family received");
172 
173 		aq = gethostbyname_async(query, NULL);
174 		session->query[i].event = event_asr_run(aq, dnsbl_resolve,
175 		    &(session->query[i]));
176 		session->query[i].blacklist = i;
177 		session->query[i].session = session;
178 		session->query[i].running = 1;
179 	}
180 
181 	return 0;
182 }
183 
184 void
185 dnsbl_resolve(struct asr_result *result, void *arg)
186 {
187 	struct dnsbl_query *query = arg;
188 	struct dnsbl_session *session = query->session;
189 	size_t i;
190 
191 	query->running = 0;
192 	query->event = NULL;
193 	if (result->ar_hostent != NULL) {
194 		if (!markspam) {
195 			osmtpd_filter_disconnect(session->ctx, "Listed at %s",
196 			    printblacklists[query->blacklist]);
197 			fprintf(stderr, "%016"PRIx64" listed at %s: rejected\n",
198 			    session->ctx->reqid,
199 			    printblacklists[query->blacklist]);
200 		} else {
201 			session->listed = query->blacklist;
202 			osmtpd_filter_proceed(session->ctx);
203 			/* Delay logging until we have a message */
204 		}
205 		dnsbl_session_query_done(session);
206 		return;
207 	}
208 	if (result->ar_h_errno != HOST_NOT_FOUND) {
209 		osmtpd_filter_disconnect(session->ctx, "DNS error on %s",
210 		    printblacklists[query->blacklist]);
211 		dnsbl_session_query_done(session);
212 		return;
213 	}
214 
215 	for (i = 0; i < nblacklists; i++) {
216 		if (session->query[i].running)
217 			return;
218 	}
219 	osmtpd_filter_proceed(session->ctx);
220 	if (verbose)
221 		fprintf(stderr, "%016"PRIx64" not listed\n",
222 		    session->ctx->reqid);
223 }
224 
225 int
226 dnsbl_begin(struct osmtpd_ctx *ctx, uint32_t msgid)
227 {
228 	struct dnsbl_session *session = ctx->local_session;
229 
230 	if (session->listed != -1) {
231 		if (!session->logged_mark) {
232 			fprintf(stderr, "%016"PRIx64" listed at %s: Marking as "
233 			    "spam\n", ctx->reqid,
234 			    printblacklists[session->listed]);
235 			session->logged_mark = 1;
236 		}
237 		session->set_header = 1;
238 	}
239 
240 	return 0;
241 }
242 
243 int
244 dnsbl_dataline(struct osmtpd_ctx *ctx, const char *line)
245 {
246 	struct dnsbl_session *session = ctx->local_session;
247 
248 	if (session->set_header) {
249 		osmtpd_filter_dataline(ctx, "X-Spam: yes");
250 		osmtpd_filter_dataline(ctx, "X-Spam-DNSBL: Listed at %s",
251 		    printblacklists[session->listed]);
252 		session->set_header = 0;
253 		
254 	}
255 	osmtpd_filter_dataline(ctx, "%s", line);
256 
257 	return 0;
258 }
259 
260 void
261 dnsbl_session_query_done(struct dnsbl_session *session)
262 {
263 	size_t i;
264 
265 	for (i = 0; i < nblacklists; i++) {
266 		if (session->query[i].running) {
267 			event_asr_abort(session->query[i].event);
268 			session->query[i].running = 0;
269 		}
270 	}
271 }
272 
273 void *
274 dnsbl_session_new(struct osmtpd_ctx *ctx)
275 {
276 	struct dnsbl_session *session;
277 
278 	if ((session = calloc(1, sizeof(*session))) == NULL)
279 		osmtpd_err(1, "malloc");
280 	if ((session->query = calloc(nblacklists, sizeof(*(session->query))))
281 	    == NULL)
282 		osmtpd_err(1, "malloc");
283 	session->listed = -1;
284 	session->set_header = 0;
285 	session->logged_mark = 0;
286 	session->ctx = ctx;
287 
288 	return session;
289 }
290 
291 void
292 dnsbl_session_free(struct osmtpd_ctx *ctx, void *data)
293 {
294 	struct dnsbl_session *session = data;
295 
296 	dnsbl_session_query_done(session);
297 	free(session->query);
298 	free(session);
299 }
300 
301 __dead void
302 usage(void)
303 {
304 	fprintf(stderr, "usage: filter-dnsbl [-m] blacklist [...]\n");
305 	exit(1);
306 }