1/* $OpenBSD: dns.c,v 1.28 2012/05/23 03:28:28 djm Exp $ */
2
3/*
4 * Copyright (c) 2003 Wesley Griffin. All rights reserved.
5 * Copyright (c) 2003 Jakob Schlyter. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28#include "includes.h"
29
30#include <sys/types.h>
31#include <sys/socket.h>
32
33#include <netdb.h>
34#include <stdarg.h>
35#include <stdio.h>
36#include <string.h>
37
38#include "xmalloc.h"
39#include "key.h"
40#include "dns.h"
41#include "log.h"
42
43static const char *errset_text[] = {
44	"success",		/* 0 ERRSET_SUCCESS */
45	"out of memory",	/* 1 ERRSET_NOMEMORY */
46	"general failure",	/* 2 ERRSET_FAIL */
47	"invalid parameter",	/* 3 ERRSET_INVAL */
48	"name does not exist",	/* 4 ERRSET_NONAME */
49	"data does not exist",	/* 5 ERRSET_NODATA */
50};
51
52static const char *
53dns_result_totext(unsigned int res)
54{
55	switch (res) {
56	case ERRSET_SUCCESS:
57		return errset_text[ERRSET_SUCCESS];
58	case ERRSET_NOMEMORY:
59		return errset_text[ERRSET_NOMEMORY];
60	case ERRSET_FAIL:
61		return errset_text[ERRSET_FAIL];
62	case ERRSET_INVAL:
63		return errset_text[ERRSET_INVAL];
64	case ERRSET_NONAME:
65		return errset_text[ERRSET_NONAME];
66	case ERRSET_NODATA:
67		return errset_text[ERRSET_NODATA];
68	default:
69		return "unknown error";
70	}
71}
72
73/*
74 * Read SSHFP parameters from key buffer.
75 */
76static int
77dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
78    u_char **digest, u_int *digest_len, Key *key)
79{
80	int success = 0;
81	enum fp_type fp_type = 0;
82
83	switch (key->type) {
84	case KEY_RSA:
85		*algorithm = SSHFP_KEY_RSA;
86		if (!*digest_type)
87			*digest_type = SSHFP_HASH_SHA1;
88		break;
89	case KEY_DSA:
90		*algorithm = SSHFP_KEY_DSA;
91		if (!*digest_type)
92			*digest_type = SSHFP_HASH_SHA1;
93		break;
94	case KEY_ECDSA:
95		*algorithm = SSHFP_KEY_ECDSA;
96		if (!*digest_type)
97			*digest_type = SSHFP_HASH_SHA256;
98		break;
99	default:
100		*algorithm = SSHFP_KEY_RESERVED; /* 0 */
101		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
102	}
103
104	switch (*digest_type) {
105	case SSHFP_HASH_SHA1:
106		fp_type = SSH_FP_SHA1;
107		break;
108	case SSHFP_HASH_SHA256:
109		fp_type = SSH_FP_SHA256;
110		break;
111	default:
112		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
113	}
114
115	if (*algorithm && *digest_type) {
116		*digest = key_fingerprint_raw(key, fp_type, digest_len);
117		if (*digest == NULL)
118			fatal("dns_read_key: null from key_fingerprint_raw()");
119		success = 1;
120	} else {
121		*digest = NULL;
122		*digest_len = 0;
123		success = 0;
124	}
125
126	return success;
127}
128
129/*
130 * Read SSHFP parameters from rdata buffer.
131 */
132static int
133dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
134    u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
135{
136	int success = 0;
137
138	*algorithm = SSHFP_KEY_RESERVED;
139	*digest_type = SSHFP_HASH_RESERVED;
140
141	if (rdata_len >= 2) {
142		*algorithm = rdata[0];
143		*digest_type = rdata[1];
144		*digest_len = rdata_len - 2;
145
146		if (*digest_len > 0) {
147			*digest = (u_char *) xmalloc(*digest_len);
148			memcpy(*digest, rdata + 2, *digest_len);
149		} else {
150			*digest = (u_char *)xstrdup("");
151		}
152
153		success = 1;
154	}
155
156	return success;
157}
158
159/*
160 * Check if hostname is numerical.
161 * Returns -1 if hostname is numeric, 0 otherwise
162 */
163static int
164is_numeric_hostname(const char *hostname)
165{
166	struct addrinfo hints, *ai;
167
168	/*
169	 * We shouldn't ever get a null host but if we do then log an error
170	 * and return -1 which stops DNS key fingerprint processing.
171	 */
172	if (hostname == NULL) {
173		error("is_numeric_hostname called with NULL hostname");
174		return -1;
175	}
176
177	memset(&hints, 0, sizeof(hints));
178	hints.ai_socktype = SOCK_DGRAM;
179	hints.ai_flags = AI_NUMERICHOST;
180
181	if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
182		freeaddrinfo(ai);
183		return -1;
184	}
185
186	return 0;
187}
188
189/*
190 * Verify the given hostname, address and host key using DNS.
191 * Returns 0 if lookup succeeds, -1 otherwise
192 */
193int
194verify_host_key_dns(const char *hostname, struct sockaddr *address,
195    Key *hostkey, int *flags)
196{
197	u_int counter;
198	int result;
199	struct rrsetinfo *fingerprints = NULL;
200
201	u_int8_t hostkey_algorithm;
202	u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
203	u_char *hostkey_digest;
204	u_int hostkey_digest_len;
205
206	u_int8_t dnskey_algorithm;
207	u_int8_t dnskey_digest_type;
208	u_char *dnskey_digest;
209	u_int dnskey_digest_len;
210
211	*flags = 0;
212
213	debug3("verify_host_key_dns");
214	if (hostkey == NULL)
215		fatal("No key to look up!");
216
217	if (is_numeric_hostname(hostname)) {
218		debug("skipped DNS lookup for numerical hostname");
219		return -1;
220	}
221
222	result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
223	    DNS_RDATATYPE_SSHFP, 0, &fingerprints);
224	if (result) {
225		verbose("DNS lookup error: %s", dns_result_totext(result));
226		return -1;
227	}
228
229	if (fingerprints->rri_flags & RRSET_VALIDATED) {
230		*flags |= DNS_VERIFY_SECURE;
231		debug("found %d secure fingerprints in DNS",
232		    fingerprints->rri_nrdatas);
233	} else {
234		debug("found %d insecure fingerprints in DNS",
235		    fingerprints->rri_nrdatas);
236	}
237
238	/* Initialize default host key parameters */
239	if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
240	    &hostkey_digest, &hostkey_digest_len, hostkey)) {
241		error("Error calculating host key fingerprint.");
242		freerrset(fingerprints);
243		return -1;
244	}
245
246	if (fingerprints->rri_nrdatas)
247		*flags |= DNS_VERIFY_FOUND;
248
249	for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
250		/*
251		 * Extract the key from the answer. Ignore any badly
252		 * formatted fingerprints.
253		 */
254		if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
255		    &dnskey_digest, &dnskey_digest_len,
256		    fingerprints->rri_rdatas[counter].rdi_data,
257		    fingerprints->rri_rdatas[counter].rdi_length)) {
258			verbose("Error parsing fingerprint from DNS.");
259			continue;
260		}
261
262		if (hostkey_digest_type != dnskey_digest_type) {
263			hostkey_digest_type = dnskey_digest_type;
264			xfree(hostkey_digest);
265
266			/* Initialize host key parameters */
267			if (!dns_read_key(&hostkey_algorithm,
268			    &hostkey_digest_type, &hostkey_digest,
269			    &hostkey_digest_len, hostkey)) {
270				error("Error calculating key fingerprint.");
271				freerrset(fingerprints);
272				return -1;
273			}
274		}
275
276		/* Check if the current key is the same as the given key */
277		if (hostkey_algorithm == dnskey_algorithm &&
278		    hostkey_digest_type == dnskey_digest_type) {
279			if (hostkey_digest_len == dnskey_digest_len &&
280			    timingsafe_bcmp(hostkey_digest, dnskey_digest,
281			    hostkey_digest_len) == 0)
282				*flags |= DNS_VERIFY_MATCH;
283		}
284		xfree(dnskey_digest);
285	}
286
287	xfree(hostkey_digest); /* from key_fingerprint_raw() */
288	freerrset(fingerprints);
289
290	if (*flags & DNS_VERIFY_FOUND)
291		if (*flags & DNS_VERIFY_MATCH)
292			debug("matching host key fingerprint found in DNS");
293		else
294			debug("mismatching host key fingerprint found in DNS");
295	else
296		debug("no host key fingerprint found in DNS");
297
298	return 0;
299}
300
301/*
302 * Export the fingerprint of a key as a DNS resource record
303 */
304int
305export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
306{
307	u_int8_t rdata_pubkey_algorithm = 0;
308	u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
309	u_int8_t dtype;
310	u_char *rdata_digest;
311	u_int i, rdata_digest_len;
312	int success = 0;
313
314	for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
315		rdata_digest_type = dtype;
316		if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
317		    &rdata_digest, &rdata_digest_len, key)) {
318			if (generic) {
319				fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ",
320				    hostname, DNS_RDATATYPE_SSHFP,
321				    2 + rdata_digest_len,
322				    rdata_pubkey_algorithm, rdata_digest_type);
323			} else {
324				fprintf(f, "%s IN SSHFP %d %d ", hostname,
325				    rdata_pubkey_algorithm, rdata_digest_type);
326			}
327			for (i = 0; i < rdata_digest_len; i++)
328				fprintf(f, "%02x", rdata_digest[i]);
329			fprintf(f, "\n");
330			xfree(rdata_digest); /* from key_fingerprint_raw() */
331			success = 1;
332		}
333	}
334
335	/* No SSHFP record was generated at all */
336	if (success == 0) {
337		error("%s: unsupported algorithm and/or digest_type", __func__);
338	}
339
340	return success;
341}
342