dns.c revision 137015 
1/*	$OpenBSD: dns.c,v 1.10 2004/06/21 17:36:31 avsm 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
29#include "includes.h"
30
31#include <openssl/bn.h>
32#ifdef LWRES
33#include <lwres/netdb.h>
34#include <dns/result.h>
35#else /* LWRES */
36#include <netdb.h>
37#endif /* LWRES */
38
39#include "xmalloc.h"
40#include "key.h"
41#include "dns.h"
42#include "log.h"
43#include "uuencode.h"
44
45extern char *__progname;
46RCSID("$OpenBSD: dns.c,v 1.10 2004/06/21 17:36:31 avsm Exp $");
47
48#ifndef LWRES
49static const char *errset_text[] = {
50	"success",		/* 0 ERRSET_SUCCESS */
51	"out of memory",	/* 1 ERRSET_NOMEMORY */
52	"general failure",	/* 2 ERRSET_FAIL */
53	"invalid parameter",	/* 3 ERRSET_INVAL */
54	"name does not exist",	/* 4 ERRSET_NONAME */
55	"data does not exist",	/* 5 ERRSET_NODATA */
56};
57
58static const char *
59dns_result_totext(unsigned int res)
60{
61	switch (res) {
62	case ERRSET_SUCCESS:
63		return errset_text[ERRSET_SUCCESS];
64	case ERRSET_NOMEMORY:
65		return errset_text[ERRSET_NOMEMORY];
66	case ERRSET_FAIL:
67		return errset_text[ERRSET_FAIL];
68	case ERRSET_INVAL:
69		return errset_text[ERRSET_INVAL];
70	case ERRSET_NONAME:
71		return errset_text[ERRSET_NONAME];
72	case ERRSET_NODATA:
73		return errset_text[ERRSET_NODATA];
74	default:
75		return "unknown error";
76	}
77}
78#endif /* LWRES */
79
80
81/*
82 * Read SSHFP parameters from key buffer.
83 */
84static int
85dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
86    u_char **digest, u_int *digest_len, const Key *key)
87{
88	int success = 0;
89
90	switch (key->type) {
91	case KEY_RSA:
92		*algorithm = SSHFP_KEY_RSA;
93		break;
94	case KEY_DSA:
95		*algorithm = SSHFP_KEY_DSA;
96		break;
97	default:
98		*algorithm = SSHFP_KEY_RESERVED;
99	}
100
101	if (*algorithm) {
102		*digest_type = SSHFP_HASH_SHA1;
103		*digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
104		success = 1;
105	} else {
106		*digest_type = SSHFP_HASH_RESERVED;
107		*digest = NULL;
108		*digest_len = 0;
109		success = 0;
110	}
111
112	return success;
113}
114
115/*
116 * Read SSHFP parameters from rdata buffer.
117 */
118static int
119dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
120    u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
121{
122	int success = 0;
123
124	*algorithm = SSHFP_KEY_RESERVED;
125	*digest_type = SSHFP_HASH_RESERVED;
126
127	if (rdata_len >= 2) {
128		*algorithm = rdata[0];
129		*digest_type = rdata[1];
130		*digest_len = rdata_len - 2;
131
132		if (*digest_len > 0) {
133			*digest = (u_char *) xmalloc(*digest_len);
134			memcpy(*digest, rdata + 2, *digest_len);
135		} else {
136			*digest = NULL;
137		}
138
139		success = 1;
140	}
141
142	return success;
143}
144
145
146/*
147 * Verify the given hostname, address and host key using DNS.
148 * Returns 0 if lookup succeeds, -1 otherwise
149 */
150int
151verify_host_key_dns(const char *hostname, struct sockaddr *address,
152    const Key *hostkey, int *flags)
153{
154	int counter;
155	int result;
156	struct rrsetinfo *fingerprints = NULL;
157
158	u_int8_t hostkey_algorithm;
159	u_int8_t hostkey_digest_type;
160	u_char *hostkey_digest;
161	u_int hostkey_digest_len;
162
163	u_int8_t dnskey_algorithm;
164	u_int8_t dnskey_digest_type;
165	u_char *dnskey_digest;
166	u_int dnskey_digest_len;
167
168	*flags = 0;
169
170	debug3("verify_hostkey_dns");
171	if (hostkey == NULL)
172		fatal("No key to look up!");
173
174	result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
175	    DNS_RDATATYPE_SSHFP, 0, &fingerprints);
176	if (result) {
177		verbose("DNS lookup error: %s", dns_result_totext(result));
178		return -1;
179	}
180
181	if (fingerprints->rri_flags & RRSET_VALIDATED) {
182		*flags |= DNS_VERIFY_SECURE;
183		debug("found %d secure fingerprints in DNS",
184		    fingerprints->rri_nrdatas);
185	} else {
186		debug("found %d insecure fingerprints in DNS",
187		    fingerprints->rri_nrdatas);
188	}
189
190	/* Initialize host key parameters */
191	if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
192	    &hostkey_digest, &hostkey_digest_len, hostkey)) {
193		error("Error calculating host key fingerprint.");
194		freerrset(fingerprints);
195		return -1;
196	}
197
198	if (fingerprints->rri_nrdatas)
199		*flags |= DNS_VERIFY_FOUND;
200
201	for (counter = 0 ; counter < fingerprints->rri_nrdatas ; counter++)  {
202		/*
203		 * Extract the key from the answer. Ignore any badly
204		 * formatted fingerprints.
205		 */
206		if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
207		    &dnskey_digest, &dnskey_digest_len,
208		    fingerprints->rri_rdatas[counter].rdi_data,
209		    fingerprints->rri_rdatas[counter].rdi_length)) {
210			verbose("Error parsing fingerprint from DNS.");
211			continue;
212		}
213
214		/* Check if the current key is the same as the given key */
215		if (hostkey_algorithm == dnskey_algorithm &&
216		    hostkey_digest_type == dnskey_digest_type) {
217
218			if (hostkey_digest_len == dnskey_digest_len &&
219			    memcmp(hostkey_digest, dnskey_digest,
220			    hostkey_digest_len) == 0) {
221
222				*flags |= DNS_VERIFY_MATCH;
223			}
224		}
225	}
226
227	freerrset(fingerprints);
228
229	if (*flags & DNS_VERIFY_FOUND)
230		if (*flags & DNS_VERIFY_MATCH)
231			debug("matching host key fingerprint found in DNS");
232		else
233			debug("mismatching host key fingerprint found in DNS");
234	else
235		debug("no host key fingerprint found in DNS");
236
237	return 0;
238}
239
240
241/*
242 * Export the fingerprint of a key as a DNS resource record
243 */
244int
245export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
246{
247	u_int8_t rdata_pubkey_algorithm = 0;
248	u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
249	u_char *rdata_digest;
250	u_int rdata_digest_len;
251
252	int i;
253	int success = 0;
254
255	if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
256			 &rdata_digest, &rdata_digest_len, key)) {
257
258		if (generic)
259			fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
260			    DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
261			    rdata_pubkey_algorithm, rdata_digest_type);
262		else
263			fprintf(f, "%s IN SSHFP %d %d ", hostname,
264			    rdata_pubkey_algorithm, rdata_digest_type);
265
266		for (i = 0; i < rdata_digest_len; i++)
267			fprintf(f, "%02x", rdata_digest[i]);
268		fprintf(f, "\n");
269		success = 1;
270	} else {
271		error("dns_export_rr: unsupported algorithm");
272	}
273
274	return success;
275}
276