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Damien Millerb0622652003-05-15 13:27:28 +10001/* $OpenBSD: dns.c,v 1.5 2003/05/15 02:27:15 jakob Exp $ */
Damien Miller37876e92003-05-15 10:19:46 +10002
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#ifdef DNS
32#include <openssl/bn.h>
33#ifdef LWRES
34#include <lwres/netdb.h>
35#include <dns/result.h>
36#else /* LWRES */
37#include <netdb.h>
38#endif /* LWRES */
39
40#include "xmalloc.h"
41#include "key.h"
42#include "dns.h"
43#include "log.h"
44#include "uuencode.h"
45
46extern char *__progname;
Damien Millerb0622652003-05-15 13:27:28 +100047RCSID("$OpenBSD: dns.c,v 1.5 2003/05/15 02:27:15 jakob Exp $");
Damien Miller37876e92003-05-15 10:19:46 +100048
49#ifndef LWRES
50static const char *errset_text[] = {
51 "success", /* 0 ERRSET_SUCCESS */
52 "out of memory", /* 1 ERRSET_NOMEMORY */
53 "general failure", /* 2 ERRSET_FAIL */
54 "invalid parameter", /* 3 ERRSET_INVAL */
55 "name does not exist", /* 4 ERRSET_NONAME */
56 "data does not exist", /* 5 ERRSET_NODATA */
57};
58
59static const char *
60dns_result_totext(unsigned int error)
61{
62 switch (error) {
63 case ERRSET_SUCCESS:
64 return errset_text[ERRSET_SUCCESS];
65 case ERRSET_NOMEMORY:
66 return errset_text[ERRSET_NOMEMORY];
67 case ERRSET_FAIL:
68 return errset_text[ERRSET_FAIL];
69 case ERRSET_INVAL:
70 return errset_text[ERRSET_INVAL];
71 case ERRSET_NONAME:
72 return errset_text[ERRSET_NONAME];
73 case ERRSET_NODATA:
74 return errset_text[ERRSET_NODATA];
75 default:
76 return "unknown error";
77 }
78}
79#endif /* LWRES */
80
81
82/*
83 * Read SSHFP parameters from key buffer.
84 */
85static int
86dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
87 u_char **digest, u_int *digest_len, Key *key)
88{
89 int success = 0;
90
91 switch (key->type) {
92 case KEY_RSA:
93 *algorithm = SSHFP_KEY_RSA;
94 break;
95 case KEY_DSA:
96 *algorithm = SSHFP_KEY_DSA;
97 break;
98 default:
99 *algorithm = SSHFP_KEY_RESERVED;
100 }
101
102 if (*algorithm) {
103 *digest_type = SSHFP_HASH_SHA1;
104 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
105 success = 1;
106 } else {
107 *digest_type = SSHFP_HASH_RESERVED;
108 *digest = NULL;
109 *digest_len = 0;
110 success = 0;
111 }
112
113 return success;
114}
115
116/*
117 * Read SSHFP parameters from rdata buffer.
118 */
119static int
120dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
121 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
122{
123 int success = 0;
124
125 *algorithm = SSHFP_KEY_RESERVED;
126 *digest_type = SSHFP_HASH_RESERVED;
127
128 if (rdata_len >= 2) {
129 *algorithm = rdata[0];
130 *digest_type = rdata[1];
131 *digest_len = rdata_len - 2;
132
133 if (*digest_len > 0) {
134 *digest = (u_char *) xmalloc(*digest_len);
135 memcpy(*digest, rdata + 2, *digest_len);
136 } else {
137 *digest = NULL;
138 }
139
140 success = 1;
141 }
142
143 return success;
144}
145
146
147/*
148 * Verify the given hostname, address and host key using DNS.
149 * Returns 0 if key verifies or -1 if key does NOT verify
150 */
151int
152verify_host_key_dns(const char *hostname, struct sockaddr *address,
153 Key *hostkey)
154{
155 int counter;
156 int result;
157 struct rrsetinfo *fingerprints = NULL;
158 int failures = 0;
159
160 u_int8_t hostkey_algorithm;
161 u_int8_t hostkey_digest_type;
162 u_char *hostkey_digest;
163 u_int hostkey_digest_len;
164
165 u_int8_t dnskey_algorithm;
166 u_int8_t dnskey_digest_type;
167 u_char *dnskey_digest;
168 u_int dnskey_digest_len;
169
170
171 debug3("verify_hostkey_dns");
172 if (hostkey == NULL)
173 fatal("No key to look up!");
174
175 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
176 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
177 if (result) {
178 verbose("DNS lookup error: %s", dns_result_totext(result));
179 return DNS_VERIFY_ERROR;
180 }
181
182#ifdef DNSSEC
183 /* Only accept validated answers */
184 if (!fingerprints->rri_flags & RRSET_VALIDATED) {
185 error("Ignored unvalidated fingerprint from DNS.");
Damien Millerb0622652003-05-15 13:27:28 +1000186 freerrset(fingerprints);
Damien Miller37876e92003-05-15 10:19:46 +1000187 return DNS_VERIFY_ERROR;
188 }
189#endif
190
191 debug("found %d fingerprints in DNS", fingerprints->rri_nrdatas);
192
193 /* Initialize host key parameters */
194 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
195 &hostkey_digest, &hostkey_digest_len, hostkey)) {
196 error("Error calculating host key fingerprint.");
Damien Millerb0622652003-05-15 13:27:28 +1000197 freerrset(fingerprints);
Damien Miller37876e92003-05-15 10:19:46 +1000198 return DNS_VERIFY_ERROR;
199 }
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 /* Matching algoritm and digest. */
223 freerrset(fingerprints);
224#ifdef DNSSEC
225 debug("matching host key fingerprint found in DNS");
226 return DNS_VERIFY_OK;
227#else
228 logit("Matching host key fingerprint found in DNS.");
229 return DNS_VERIFY_ERROR;
230#endif
231 } else {
232 /* Correct algorithm but bad digest */
233 debug("verify_hostkey_dns: failed");
234 failures++;
235 }
236 }
237 }
238
239 freerrset(fingerprints);
240
241 if (failures) {
242 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
243 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
244 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
245 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
246 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
247 error("It is also possible that the %s host key has just been changed.",
248 key_type(hostkey));
249 error("Please contact your system administrator.");
250 return DNS_VERIFY_FAILED;
251 }
252
253 debug("fingerprints found in DNS, but none of them matched");
254
255 return DNS_VERIFY_ERROR;
256}
257
258
259/*
260 * Export the fingerprint of a key as a DNS resource record
261 */
262int
263export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
264{
265 u_int8_t rdata_pubkey_algorithm = 0;
266 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
267 u_char *rdata_digest;
268 u_int rdata_digest_len;
269
270 int i;
271 int success = 0;
272
273 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
274 &rdata_digest, &rdata_digest_len, key)) {
275
276 if (generic)
277 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
278 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
279 rdata_pubkey_algorithm, rdata_digest_type);
280 else
281 fprintf(f, "%s IN SSHFP %d %d ", hostname,
282 rdata_pubkey_algorithm, rdata_digest_type);
283
284 for (i = 0; i < rdata_digest_len; i++)
285 fprintf(f, "%02x", rdata_digest[i]);
286 fprintf(f, "\n");
287 success = 1;
288 } else {
289 error("dns_export_rr: unsupported algorithm");
290 }
291
292 return success;
293}
294
295#endif /* DNS */