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Damien Miller4ca108d2006-03-26 13:57:07 +11001/* $OpenBSD: dns.c,v 1.17 2006/03/19 18:51:18 deraadt 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"
29
Damien Miller37876e92003-05-15 10:19:46 +100030#include <netdb.h>
Damien Miller37876e92003-05-15 10:19:46 +100031
32#include "xmalloc.h"
33#include "key.h"
34#include "dns.h"
35#include "log.h"
Damien Miller37876e92003-05-15 10:19:46 +100036
Damien Miller37876e92003-05-15 10:19:46 +100037static const char *errset_text[] = {
38 "success", /* 0 ERRSET_SUCCESS */
39 "out of memory", /* 1 ERRSET_NOMEMORY */
40 "general failure", /* 2 ERRSET_FAIL */
41 "invalid parameter", /* 3 ERRSET_INVAL */
42 "name does not exist", /* 4 ERRSET_NONAME */
43 "data does not exist", /* 5 ERRSET_NODATA */
44};
45
46static const char *
Darren Tucker3f9fdc72004-06-22 12:56:01 +100047dns_result_totext(unsigned int res)
Damien Miller37876e92003-05-15 10:19:46 +100048{
Darren Tucker3f9fdc72004-06-22 12:56:01 +100049 switch (res) {
Damien Miller37876e92003-05-15 10:19:46 +100050 case ERRSET_SUCCESS:
51 return errset_text[ERRSET_SUCCESS];
52 case ERRSET_NOMEMORY:
53 return errset_text[ERRSET_NOMEMORY];
54 case ERRSET_FAIL:
55 return errset_text[ERRSET_FAIL];
56 case ERRSET_INVAL:
57 return errset_text[ERRSET_INVAL];
58 case ERRSET_NONAME:
59 return errset_text[ERRSET_NONAME];
60 case ERRSET_NODATA:
61 return errset_text[ERRSET_NODATA];
62 default:
63 return "unknown error";
64 }
65}
Damien Miller37876e92003-05-15 10:19:46 +100066
67/*
68 * Read SSHFP parameters from key buffer.
69 */
70static int
71dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
Damien Miller150b5572003-11-17 21:19:29 +110072 u_char **digest, u_int *digest_len, const Key *key)
Damien Miller37876e92003-05-15 10:19:46 +100073{
74 int success = 0;
75
76 switch (key->type) {
77 case KEY_RSA:
78 *algorithm = SSHFP_KEY_RSA;
79 break;
80 case KEY_DSA:
81 *algorithm = SSHFP_KEY_DSA;
82 break;
83 default:
Damien Miller65712492005-11-05 15:09:27 +110084 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
Damien Miller37876e92003-05-15 10:19:46 +100085 }
86
87 if (*algorithm) {
88 *digest_type = SSHFP_HASH_SHA1;
89 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
Damien Miller65712492005-11-05 15:09:27 +110090 if (*digest == NULL)
91 fatal("dns_read_key: null from key_fingerprint_raw()");
Damien Miller37876e92003-05-15 10:19:46 +100092 success = 1;
93 } else {
94 *digest_type = SSHFP_HASH_RESERVED;
95 *digest = NULL;
96 *digest_len = 0;
97 success = 0;
98 }
99
100 return success;
101}
102
103/*
104 * Read SSHFP parameters from rdata buffer.
105 */
106static int
107dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
108 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
109{
110 int success = 0;
111
112 *algorithm = SSHFP_KEY_RESERVED;
113 *digest_type = SSHFP_HASH_RESERVED;
114
115 if (rdata_len >= 2) {
116 *algorithm = rdata[0];
117 *digest_type = rdata[1];
118 *digest_len = rdata_len - 2;
119
120 if (*digest_len > 0) {
121 *digest = (u_char *) xmalloc(*digest_len);
122 memcpy(*digest, rdata + 2, *digest_len);
123 } else {
Damien Miller59962942006-03-26 00:06:48 +1100124 *digest = (u_char *)xstrdup("");
Damien Miller37876e92003-05-15 10:19:46 +1000125 }
126
127 success = 1;
128 }
129
130 return success;
131}
132
Damien Millera31c9292005-05-26 12:03:31 +1000133/*
134 * Check if hostname is numerical.
135 * Returns -1 if hostname is numeric, 0 otherwise
136 */
137static int
138is_numeric_hostname(const char *hostname)
139{
140 struct addrinfo hints, *ai;
141
142 memset(&hints, 0, sizeof(hints));
143 hints.ai_socktype = SOCK_DGRAM;
144 hints.ai_flags = AI_NUMERICHOST;
145
146 if (getaddrinfo(hostname, "0", &hints, &ai) == 0) {
147 freeaddrinfo(ai);
148 return -1;
149 }
150
151 return 0;
152}
Damien Miller37876e92003-05-15 10:19:46 +1000153
154/*
155 * Verify the given hostname, address and host key using DNS.
Damien Millera8e06ce2003-11-21 23:48:55 +1100156 * Returns 0 if lookup succeeds, -1 otherwise
Damien Miller37876e92003-05-15 10:19:46 +1000157 */
158int
159verify_host_key_dns(const char *hostname, struct sockaddr *address,
Damien Miller150b5572003-11-17 21:19:29 +1100160 const Key *hostkey, int *flags)
Damien Miller37876e92003-05-15 10:19:46 +1000161{
Damien Millereccb9de2005-06-17 12:59:34 +1000162 u_int counter;
Damien Miller37876e92003-05-15 10:19:46 +1000163 int result;
164 struct rrsetinfo *fingerprints = NULL;
Damien Miller37876e92003-05-15 10:19:46 +1000165
166 u_int8_t hostkey_algorithm;
167 u_int8_t hostkey_digest_type;
168 u_char *hostkey_digest;
169 u_int hostkey_digest_len;
170
171 u_int8_t dnskey_algorithm;
172 u_int8_t dnskey_digest_type;
173 u_char *dnskey_digest;
174 u_int dnskey_digest_len;
175
Damien Miller150b5572003-11-17 21:19:29 +1100176 *flags = 0;
Damien Miller37876e92003-05-15 10:19:46 +1000177
Damien Miller319550a2005-11-05 15:11:15 +1100178 debug3("verify_host_key_dns");
Damien Miller37876e92003-05-15 10:19:46 +1000179 if (hostkey == NULL)
180 fatal("No key to look up!");
181
Damien Millera31c9292005-05-26 12:03:31 +1000182 if (is_numeric_hostname(hostname)) {
183 debug("skipped DNS lookup for numerical hostname");
184 return -1;
185 }
186
Damien Miller37876e92003-05-15 10:19:46 +1000187 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
188 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
189 if (result) {
190 verbose("DNS lookup error: %s", dns_result_totext(result));
Damien Miller150b5572003-11-17 21:19:29 +1100191 return -1;
Damien Miller37876e92003-05-15 10:19:46 +1000192 }
193
Damien Miller150b5572003-11-17 21:19:29 +1100194 if (fingerprints->rri_flags & RRSET_VALIDATED) {
195 *flags |= DNS_VERIFY_SECURE;
196 debug("found %d secure fingerprints in DNS",
197 fingerprints->rri_nrdatas);
198 } else {
199 debug("found %d insecure fingerprints in DNS",
200 fingerprints->rri_nrdatas);
Damien Miller37876e92003-05-15 10:19:46 +1000201 }
Damien Miller37876e92003-05-15 10:19:46 +1000202
203 /* Initialize host key parameters */
204 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
205 &hostkey_digest, &hostkey_digest_len, hostkey)) {
206 error("Error calculating host key fingerprint.");
Damien Millerb0622652003-05-15 13:27:28 +1000207 freerrset(fingerprints);
Damien Miller150b5572003-11-17 21:19:29 +1100208 return -1;
Damien Miller37876e92003-05-15 10:19:46 +1000209 }
210
Damien Miller150b5572003-11-17 21:19:29 +1100211 if (fingerprints->rri_nrdatas)
212 *flags |= DNS_VERIFY_FOUND;
213
Damien Miller20afc242005-11-05 15:06:38 +1100214 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
Damien Miller37876e92003-05-15 10:19:46 +1000215 /*
216 * Extract the key from the answer. Ignore any badly
217 * formatted fingerprints.
218 */
219 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
220 &dnskey_digest, &dnskey_digest_len,
221 fingerprints->rri_rdatas[counter].rdi_data,
222 fingerprints->rri_rdatas[counter].rdi_length)) {
223 verbose("Error parsing fingerprint from DNS.");
224 continue;
225 }
226
227 /* Check if the current key is the same as the given key */
228 if (hostkey_algorithm == dnskey_algorithm &&
229 hostkey_digest_type == dnskey_digest_type) {
230
231 if (hostkey_digest_len == dnskey_digest_len &&
232 memcmp(hostkey_digest, dnskey_digest,
233 hostkey_digest_len) == 0) {
234
Damien Miller150b5572003-11-17 21:19:29 +1100235 *flags |= DNS_VERIFY_MATCH;
Damien Miller37876e92003-05-15 10:19:46 +1000236 }
237 }
Damien Miller65712492005-11-05 15:09:27 +1100238 xfree(dnskey_digest);
Damien Miller37876e92003-05-15 10:19:46 +1000239 }
240
Damien Miller65712492005-11-05 15:09:27 +1100241 xfree(hostkey_digest); /* from key_fingerprint_raw() */
Damien Miller37876e92003-05-15 10:19:46 +1000242 freerrset(fingerprints);
243
Damien Miller150b5572003-11-17 21:19:29 +1100244 if (*flags & DNS_VERIFY_FOUND)
245 if (*flags & DNS_VERIFY_MATCH)
246 debug("matching host key fingerprint found in DNS");
247 else
248 debug("mismatching host key fingerprint found in DNS");
249 else
250 debug("no host key fingerprint found in DNS");
Damien Miller37876e92003-05-15 10:19:46 +1000251
Damien Miller150b5572003-11-17 21:19:29 +1100252 return 0;
Damien Miller37876e92003-05-15 10:19:46 +1000253}
254
Damien Miller37876e92003-05-15 10:19:46 +1000255/*
256 * Export the fingerprint of a key as a DNS resource record
257 */
258int
Damien Miller150b5572003-11-17 21:19:29 +1100259export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
Damien Miller37876e92003-05-15 10:19:46 +1000260{
261 u_int8_t rdata_pubkey_algorithm = 0;
262 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
263 u_char *rdata_digest;
264 u_int rdata_digest_len;
265
Damien Millereccb9de2005-06-17 12:59:34 +1000266 u_int i;
Damien Miller37876e92003-05-15 10:19:46 +1000267 int success = 0;
268
269 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
Damien Miller319550a2005-11-05 15:11:15 +1100270 &rdata_digest, &rdata_digest_len, key)) {
Damien Miller37876e92003-05-15 10:19:46 +1000271
272 if (generic)
273 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
274 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
275 rdata_pubkey_algorithm, rdata_digest_type);
276 else
277 fprintf(f, "%s IN SSHFP %d %d ", hostname,
278 rdata_pubkey_algorithm, rdata_digest_type);
279
280 for (i = 0; i < rdata_digest_len; i++)
281 fprintf(f, "%02x", rdata_digest[i]);
282 fprintf(f, "\n");
Damien Miller65712492005-11-05 15:09:27 +1100283 xfree(rdata_digest); /* from key_fingerprint_raw() */
Damien Miller37876e92003-05-15 10:19:46 +1000284 success = 1;
285 } else {
Damien Miller319550a2005-11-05 15:11:15 +1100286 error("export_dns_rr: unsupported algorithm");
Damien Miller37876e92003-05-15 10:19:46 +1000287 }
288
289 return success;
290}