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Damien Miller319550a2005-11-05 15:11:15 +11001/* $OpenBSD: dns.c,v 1.16 2005/10/17 14:13:35 stevesk 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
Damien Miller37876e92003-05-15 10:19:46 +100028#include "includes.h"
Damien Miller319550a2005-11-05 15:11:15 +110029RCSID("$OpenBSD: dns.c,v 1.16 2005/10/17 14:13:35 stevesk Exp $");
Damien Miller37876e92003-05-15 10:19:46 +100030
Damien Miller37876e92003-05-15 10:19:46 +100031#include <netdb.h>
Damien Miller37876e92003-05-15 10:19:46 +100032
33#include "xmalloc.h"
34#include "key.h"
35#include "dns.h"
36#include "log.h"
Damien Miller37876e92003-05-15 10:19:46 +100037
Damien Miller37876e92003-05-15 10:19:46 +100038static const char *errset_text[] = {
39 "success", /* 0 ERRSET_SUCCESS */
40 "out of memory", /* 1 ERRSET_NOMEMORY */
41 "general failure", /* 2 ERRSET_FAIL */
42 "invalid parameter", /* 3 ERRSET_INVAL */
43 "name does not exist", /* 4 ERRSET_NONAME */
44 "data does not exist", /* 5 ERRSET_NODATA */
45};
46
47static const char *
Darren Tucker3f9fdc72004-06-22 12:56:01 +100048dns_result_totext(unsigned int res)
Damien Miller37876e92003-05-15 10:19:46 +100049{
Darren Tucker3f9fdc72004-06-22 12:56:01 +100050 switch (res) {
Damien Miller37876e92003-05-15 10:19:46 +100051 case ERRSET_SUCCESS:
52 return errset_text[ERRSET_SUCCESS];
53 case ERRSET_NOMEMORY:
54 return errset_text[ERRSET_NOMEMORY];
55 case ERRSET_FAIL:
56 return errset_text[ERRSET_FAIL];
57 case ERRSET_INVAL:
58 return errset_text[ERRSET_INVAL];
59 case ERRSET_NONAME:
60 return errset_text[ERRSET_NONAME];
61 case ERRSET_NODATA:
62 return errset_text[ERRSET_NODATA];
63 default:
64 return "unknown error";
65 }
66}
Damien Miller37876e92003-05-15 10:19:46 +100067
68/*
69 * Read SSHFP parameters from key buffer.
70 */
71static int
72dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
Damien Miller150b5572003-11-17 21:19:29 +110073 u_char **digest, u_int *digest_len, const Key *key)
Damien Miller37876e92003-05-15 10:19:46 +100074{
75 int success = 0;
76
77 switch (key->type) {
78 case KEY_RSA:
79 *algorithm = SSHFP_KEY_RSA;
80 break;
81 case KEY_DSA:
82 *algorithm = SSHFP_KEY_DSA;
83 break;
84 default:
Damien Miller65712492005-11-05 15:09:27 +110085 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
Damien Miller37876e92003-05-15 10:19:46 +100086 }
87
88 if (*algorithm) {
89 *digest_type = SSHFP_HASH_SHA1;
90 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
Damien Miller65712492005-11-05 15:09:27 +110091 if (*digest == NULL)
92 fatal("dns_read_key: null from key_fingerprint_raw()");
Damien Miller37876e92003-05-15 10:19:46 +100093 success = 1;
94 } else {
95 *digest_type = SSHFP_HASH_RESERVED;
96 *digest = NULL;
97 *digest_len = 0;
98 success = 0;
99 }
100
101 return success;
102}
103
104/*
105 * Read SSHFP parameters from rdata buffer.
106 */
107static int
108dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
109 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
110{
111 int success = 0;
112
113 *algorithm = SSHFP_KEY_RESERVED;
114 *digest_type = SSHFP_HASH_RESERVED;
115
116 if (rdata_len >= 2) {
117 *algorithm = rdata[0];
118 *digest_type = rdata[1];
119 *digest_len = rdata_len - 2;
120
121 if (*digest_len > 0) {
122 *digest = (u_char *) xmalloc(*digest_len);
123 memcpy(*digest, rdata + 2, *digest_len);
124 } else {
Damien Miller65712492005-11-05 15:09:27 +1100125 *digest = xstrdup("");
Damien Miller37876e92003-05-15 10:19:46 +1000126 }
127
128 success = 1;
129 }
130
131 return success;
132}
133
Damien Millera31c9292005-05-26 12:03:31 +1000134/*
135 * Check if hostname is numerical.
136 * Returns -1 if hostname is numeric, 0 otherwise
137 */
138static int
139is_numeric_hostname(const char *hostname)
140{
141 struct addrinfo hints, *ai;
142
143 memset(&hints, 0, sizeof(hints));
144 hints.ai_socktype = SOCK_DGRAM;
145 hints.ai_flags = AI_NUMERICHOST;
146
147 if (getaddrinfo(hostname, "0", &hints, &ai) == 0) {
148 freeaddrinfo(ai);
149 return -1;
150 }
151
152 return 0;
153}
Damien Miller37876e92003-05-15 10:19:46 +1000154
155/*
156 * Verify the given hostname, address and host key using DNS.
Damien Millera8e06ce2003-11-21 23:48:55 +1100157 * Returns 0 if lookup succeeds, -1 otherwise
Damien Miller37876e92003-05-15 10:19:46 +1000158 */
159int
160verify_host_key_dns(const char *hostname, struct sockaddr *address,
Damien Miller150b5572003-11-17 21:19:29 +1100161 const Key *hostkey, int *flags)
Damien Miller37876e92003-05-15 10:19:46 +1000162{
Damien Millereccb9de2005-06-17 12:59:34 +1000163 u_int counter;
Damien Miller37876e92003-05-15 10:19:46 +1000164 int result;
165 struct rrsetinfo *fingerprints = NULL;
Damien Miller37876e92003-05-15 10:19:46 +1000166
167 u_int8_t hostkey_algorithm;
168 u_int8_t hostkey_digest_type;
169 u_char *hostkey_digest;
170 u_int hostkey_digest_len;
171
172 u_int8_t dnskey_algorithm;
173 u_int8_t dnskey_digest_type;
174 u_char *dnskey_digest;
175 u_int dnskey_digest_len;
176
Damien Miller150b5572003-11-17 21:19:29 +1100177 *flags = 0;
Damien Miller37876e92003-05-15 10:19:46 +1000178
Damien Miller319550a2005-11-05 15:11:15 +1100179 debug3("verify_host_key_dns");
Damien Miller37876e92003-05-15 10:19:46 +1000180 if (hostkey == NULL)
181 fatal("No key to look up!");
182
Damien Millera31c9292005-05-26 12:03:31 +1000183 if (is_numeric_hostname(hostname)) {
184 debug("skipped DNS lookup for numerical hostname");
185 return -1;
186 }
187
Damien Miller37876e92003-05-15 10:19:46 +1000188 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
189 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
190 if (result) {
191 verbose("DNS lookup error: %s", dns_result_totext(result));
Damien Miller150b5572003-11-17 21:19:29 +1100192 return -1;
Damien Miller37876e92003-05-15 10:19:46 +1000193 }
194
Damien Miller150b5572003-11-17 21:19:29 +1100195 if (fingerprints->rri_flags & RRSET_VALIDATED) {
196 *flags |= DNS_VERIFY_SECURE;
197 debug("found %d secure fingerprints in DNS",
198 fingerprints->rri_nrdatas);
199 } else {
200 debug("found %d insecure fingerprints in DNS",
201 fingerprints->rri_nrdatas);
Damien Miller37876e92003-05-15 10:19:46 +1000202 }
Damien Miller37876e92003-05-15 10:19:46 +1000203
204 /* Initialize host key parameters */
205 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
206 &hostkey_digest, &hostkey_digest_len, hostkey)) {
207 error("Error calculating host key fingerprint.");
Damien Millerb0622652003-05-15 13:27:28 +1000208 freerrset(fingerprints);
Damien Miller150b5572003-11-17 21:19:29 +1100209 return -1;
Damien Miller37876e92003-05-15 10:19:46 +1000210 }
211
Damien Miller150b5572003-11-17 21:19:29 +1100212 if (fingerprints->rri_nrdatas)
213 *flags |= DNS_VERIFY_FOUND;
214
Damien Miller20afc242005-11-05 15:06:38 +1100215 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
Damien Miller37876e92003-05-15 10:19:46 +1000216 /*
217 * Extract the key from the answer. Ignore any badly
218 * formatted fingerprints.
219 */
220 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
221 &dnskey_digest, &dnskey_digest_len,
222 fingerprints->rri_rdatas[counter].rdi_data,
223 fingerprints->rri_rdatas[counter].rdi_length)) {
224 verbose("Error parsing fingerprint from DNS.");
225 continue;
226 }
227
228 /* Check if the current key is the same as the given key */
229 if (hostkey_algorithm == dnskey_algorithm &&
230 hostkey_digest_type == dnskey_digest_type) {
231
232 if (hostkey_digest_len == dnskey_digest_len &&
233 memcmp(hostkey_digest, dnskey_digest,
234 hostkey_digest_len) == 0) {
235
Damien Miller150b5572003-11-17 21:19:29 +1100236 *flags |= DNS_VERIFY_MATCH;
Damien Miller37876e92003-05-15 10:19:46 +1000237 }
238 }
Damien Miller65712492005-11-05 15:09:27 +1100239 xfree(dnskey_digest);
Damien Miller37876e92003-05-15 10:19:46 +1000240 }
241
Damien Miller65712492005-11-05 15:09:27 +1100242 xfree(hostkey_digest); /* from key_fingerprint_raw() */
Damien Miller37876e92003-05-15 10:19:46 +1000243 freerrset(fingerprints);
244
Damien Miller150b5572003-11-17 21:19:29 +1100245 if (*flags & DNS_VERIFY_FOUND)
246 if (*flags & DNS_VERIFY_MATCH)
247 debug("matching host key fingerprint found in DNS");
248 else
249 debug("mismatching host key fingerprint found in DNS");
250 else
251 debug("no host key fingerprint found in DNS");
Damien Miller37876e92003-05-15 10:19:46 +1000252
Damien Miller150b5572003-11-17 21:19:29 +1100253 return 0;
Damien Miller37876e92003-05-15 10:19:46 +1000254}
255
Damien Miller37876e92003-05-15 10:19:46 +1000256/*
257 * Export the fingerprint of a key as a DNS resource record
258 */
259int
Damien Miller150b5572003-11-17 21:19:29 +1100260export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
Damien Miller37876e92003-05-15 10:19:46 +1000261{
262 u_int8_t rdata_pubkey_algorithm = 0;
263 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
264 u_char *rdata_digest;
265 u_int rdata_digest_len;
266
Damien Millereccb9de2005-06-17 12:59:34 +1000267 u_int i;
Damien Miller37876e92003-05-15 10:19:46 +1000268 int success = 0;
269
270 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
Damien Miller319550a2005-11-05 15:11:15 +1100271 &rdata_digest, &rdata_digest_len, key)) {
Damien Miller37876e92003-05-15 10:19:46 +1000272
273 if (generic)
274 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
275 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
276 rdata_pubkey_algorithm, rdata_digest_type);
277 else
278 fprintf(f, "%s IN SSHFP %d %d ", hostname,
279 rdata_pubkey_algorithm, rdata_digest_type);
280
281 for (i = 0; i < rdata_digest_len; i++)
282 fprintf(f, "%02x", rdata_digest[i]);
283 fprintf(f, "\n");
Damien Miller65712492005-11-05 15:09:27 +1100284 xfree(rdata_digest); /* from key_fingerprint_raw() */
Damien Miller37876e92003-05-15 10:19:46 +1000285 success = 1;
286 } else {
Damien Miller319550a2005-11-05 15:11:15 +1100287 error("export_dns_rr: unsupported algorithm");
Damien Miller37876e92003-05-15 10:19:46 +1000288 }
289
290 return success;
291}