dns.c revision 162852 
1/* $OpenBSD: dns.c,v 1.23 2006/08/03 03:34:42 deraadt 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, const Key *key)
79{
80	int success = 0;
81
82	switch (key->type) {
83	case KEY_RSA:
84		*algorithm = SSHFP_KEY_RSA;
85		break;
86	case KEY_DSA:
87		*algorithm = SSHFP_KEY_DSA;
88		break;
89	default:
90		*algorithm = SSHFP_KEY_RESERVED; /* 0 */
91	}
92
93	if (*algorithm) {
94		*digest_type = SSHFP_HASH_SHA1;
95		*digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
96		if (*digest == NULL)
97			fatal("dns_read_key: null from key_fingerprint_raw()");
98		success = 1;
99	} else {
100		*digest_type = SSHFP_HASH_RESERVED;
101		*digest = NULL;
102		*digest_len = 0;
103		success = 0;
104	}
105
106	return success;
107}
108
109/*
110 * Read SSHFP parameters from rdata buffer.
111 */
112static int
113dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
114    u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
115{
116	int success = 0;
117
118	*algorithm = SSHFP_KEY_RESERVED;
119	*digest_type = SSHFP_HASH_RESERVED;
120
121	if (rdata_len >= 2) {
122		*algorithm = rdata[0];
123		*digest_type = rdata[1];
124		*digest_len = rdata_len - 2;
125
126		if (*digest_len > 0) {
127			*digest = (u_char *) xmalloc(*digest_len);
128			memcpy(*digest, rdata + 2, *digest_len);
129		} else {
130			*digest = (u_char *)xstrdup("");
131		}
132
133		success = 1;
134	}
135
136	return success;
137}
138
139/*
140 * Check if hostname is numerical.
141 * Returns -1 if hostname is numeric, 0 otherwise
142 */
143static int
144is_numeric_hostname(const char *hostname)
145{
146	struct addrinfo hints, *ai;
147
148	memset(&hints, 0, sizeof(hints));
149	hints.ai_socktype = SOCK_DGRAM;
150	hints.ai_flags = AI_NUMERICHOST;
151
152	if (getaddrinfo(hostname, "0", &hints, &ai) == 0) {
153		freeaddrinfo(ai);
154		return -1;
155	}
156
157	return 0;
158}
159
160/*
161 * Verify the given hostname, address and host key using DNS.
162 * Returns 0 if lookup succeeds, -1 otherwise
163 */
164int
165verify_host_key_dns(const char *hostname, struct sockaddr *address,
166    const Key *hostkey, int *flags)
167{
168	u_int counter;
169	int result;
170	struct rrsetinfo *fingerprints = NULL;
171
172	u_int8_t hostkey_algorithm;
173	u_int8_t hostkey_digest_type;
174	u_char *hostkey_digest;
175	u_int hostkey_digest_len;
176
177	u_int8_t dnskey_algorithm;
178	u_int8_t dnskey_digest_type;
179	u_char *dnskey_digest;
180	u_int dnskey_digest_len;
181
182	*flags = 0;
183
184	debug3("verify_host_key_dns");
185	if (hostkey == NULL)
186		fatal("No key to look up!");
187
188	if (is_numeric_hostname(hostname)) {
189		debug("skipped DNS lookup for numerical hostname");
190		return -1;
191	}
192
193	result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
194	    DNS_RDATATYPE_SSHFP, 0, &fingerprints);
195	if (result) {
196		verbose("DNS lookup error: %s", dns_result_totext(result));
197		return -1;
198	}
199
200	if (fingerprints->rri_flags & RRSET_VALIDATED) {
201		*flags |= DNS_VERIFY_SECURE;
202		debug("found %d secure fingerprints in DNS",
203		    fingerprints->rri_nrdatas);
204	} else {
205		debug("found %d insecure fingerprints in DNS",
206		    fingerprints->rri_nrdatas);
207	}
208
209	/* Initialize host key parameters */
210	if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
211	    &hostkey_digest, &hostkey_digest_len, hostkey)) {
212		error("Error calculating host key fingerprint.");
213		freerrset(fingerprints);
214		return -1;
215	}
216
217	if (fingerprints->rri_nrdatas)
218		*flags |= DNS_VERIFY_FOUND;
219
220	for (counter = 0; counter < fingerprints->rri_nrdatas; counter++)  {
221		/*
222		 * Extract the key from the answer. Ignore any badly
223		 * formatted fingerprints.
224		 */
225		if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
226		    &dnskey_digest, &dnskey_digest_len,
227		    fingerprints->rri_rdatas[counter].rdi_data,
228		    fingerprints->rri_rdatas[counter].rdi_length)) {
229			verbose("Error parsing fingerprint from DNS.");
230			continue;
231		}
232
233		/* Check if the current key is the same as the given key */
234		if (hostkey_algorithm == dnskey_algorithm &&
235		    hostkey_digest_type == dnskey_digest_type) {
236
237			if (hostkey_digest_len == dnskey_digest_len &&
238			    memcmp(hostkey_digest, dnskey_digest,
239			    hostkey_digest_len) == 0) {
240
241				*flags |= DNS_VERIFY_MATCH;
242			}
243		}
244		xfree(dnskey_digest);
245	}
246
247	xfree(hostkey_digest); /* from key_fingerprint_raw() */
248	freerrset(fingerprints);
249
250	if (*flags & DNS_VERIFY_FOUND)
251		if (*flags & DNS_VERIFY_MATCH)
252			debug("matching host key fingerprint found in DNS");
253		else
254			debug("mismatching host key fingerprint found in DNS");
255	else
256		debug("no host key fingerprint found in DNS");
257
258	return 0;
259}
260
261/*
262 * Export the fingerprint of a key as a DNS resource record
263 */
264int
265export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
266{
267	u_int8_t rdata_pubkey_algorithm = 0;
268	u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
269	u_char *rdata_digest;
270	u_int rdata_digest_len;
271
272	u_int i;
273	int success = 0;
274
275	if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
276	    &rdata_digest, &rdata_digest_len, key)) {
277
278		if (generic)
279			fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
280			    DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
281			    rdata_pubkey_algorithm, rdata_digest_type);
282		else
283			fprintf(f, "%s IN SSHFP %d %d ", hostname,
284			    rdata_pubkey_algorithm, rdata_digest_type);
285
286		for (i = 0; i < rdata_digest_len; i++)
287			fprintf(f, "%02x", rdata_digest[i]);
288		fprintf(f, "\n");
289		xfree(rdata_digest); /* from key_fingerprint_raw() */
290		success = 1;
291	} else {
292		error("export_dns_rr: unsupported algorithm");
293	}
294
295	return success;
296}
297