1 /* $OpenBSD: dns.c,v 1.38 2018/02/23 15:58:37 markus Exp $ */
4 * Copyright (c) 2003 Wesley Griffin. All rights reserved.
5 * Copyright (c) 2003 Jakob Schlyter. All rights reserved.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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.
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.
30 #include <sys/types.h>
31 #include <sys/socket.h>
47 static const char *errset_text[] = {
48 "success", /* 0 ERRSET_SUCCESS */
49 "out of memory", /* 1 ERRSET_NOMEMORY */
50 "general failure", /* 2 ERRSET_FAIL */
51 "invalid parameter", /* 3 ERRSET_INVAL */
52 "name does not exist", /* 4 ERRSET_NONAME */
53 "data does not exist", /* 5 ERRSET_NODATA */
57 dns_result_totext(unsigned int res)
61 return errset_text[ERRSET_SUCCESS];
63 return errset_text[ERRSET_NOMEMORY];
65 return errset_text[ERRSET_FAIL];
67 return errset_text[ERRSET_INVAL];
69 return errset_text[ERRSET_NONAME];
71 return errset_text[ERRSET_NODATA];
73 return "unknown error";
78 * Read SSHFP parameters from key buffer.
81 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
82 u_char **digest, size_t *digest_len, struct sshkey *key)
89 *algorithm = SSHFP_KEY_RSA;
91 *digest_type = SSHFP_HASH_SHA1;
94 *algorithm = SSHFP_KEY_DSA;
96 *digest_type = SSHFP_HASH_SHA1;
99 *algorithm = SSHFP_KEY_ECDSA;
101 *digest_type = SSHFP_HASH_SHA256;
104 *algorithm = SSHFP_KEY_ED25519;
106 *digest_type = SSHFP_HASH_SHA256;
109 *algorithm = SSHFP_KEY_XMSS;
111 *digest_type = SSHFP_HASH_SHA256;
114 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
115 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
118 switch (*digest_type) {
119 case SSHFP_HASH_SHA1:
120 fp_alg = SSH_DIGEST_SHA1;
122 case SSHFP_HASH_SHA256:
123 fp_alg = SSH_DIGEST_SHA256;
126 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
129 if (*algorithm && *digest_type) {
130 if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
132 fatal("%s: sshkey_fingerprint_raw: %s", __func__,
145 * Read SSHFP parameters from rdata buffer.
148 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
149 u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
153 *algorithm = SSHFP_KEY_RESERVED;
154 *digest_type = SSHFP_HASH_RESERVED;
156 if (rdata_len >= 2) {
157 *algorithm = rdata[0];
158 *digest_type = rdata[1];
159 *digest_len = rdata_len - 2;
161 if (*digest_len > 0) {
162 *digest = xmalloc(*digest_len);
163 memcpy(*digest, rdata + 2, *digest_len);
165 *digest = (u_char *)xstrdup("");
175 * Check if hostname is numerical.
176 * Returns -1 if hostname is numeric, 0 otherwise
179 is_numeric_hostname(const char *hostname)
181 struct addrinfo hints, *ai;
184 * We shouldn't ever get a null host but if we do then log an error
185 * and return -1 which stops DNS key fingerprint processing.
187 if (hostname == NULL) {
188 error("is_numeric_hostname called with NULL hostname");
192 memset(&hints, 0, sizeof(hints));
193 hints.ai_socktype = SOCK_DGRAM;
194 hints.ai_flags = AI_NUMERICHOST;
196 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
205 * Verify the given hostname, address and host key using DNS.
206 * Returns 0 if lookup succeeds, -1 otherwise
209 verify_host_key_dns(const char *hostname, struct sockaddr *address,
210 struct sshkey *hostkey, int *flags)
214 struct rrsetinfo *fingerprints = NULL;
216 u_int8_t hostkey_algorithm;
217 u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
218 u_char *hostkey_digest;
219 size_t hostkey_digest_len;
221 u_int8_t dnskey_algorithm;
222 u_int8_t dnskey_digest_type;
223 u_char *dnskey_digest;
224 size_t dnskey_digest_len;
228 debug3("verify_host_key_dns");
230 fatal("No key to look up!");
232 if (is_numeric_hostname(hostname)) {
233 debug("skipped DNS lookup for numerical hostname");
237 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
238 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
240 verbose("DNS lookup error: %s", dns_result_totext(result));
244 if (fingerprints->rri_flags & RRSET_VALIDATED) {
245 *flags |= DNS_VERIFY_SECURE;
246 debug("found %d secure fingerprints in DNS",
247 fingerprints->rri_nrdatas);
249 debug("found %d insecure fingerprints in DNS",
250 fingerprints->rri_nrdatas);
253 /* Initialize default host key parameters */
254 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
255 &hostkey_digest, &hostkey_digest_len, hostkey)) {
256 error("Error calculating host key fingerprint.");
257 freerrset(fingerprints);
261 if (fingerprints->rri_nrdatas)
262 *flags |= DNS_VERIFY_FOUND;
264 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
266 * Extract the key from the answer. Ignore any badly
267 * formatted fingerprints.
269 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
270 &dnskey_digest, &dnskey_digest_len,
271 fingerprints->rri_rdatas[counter].rdi_data,
272 fingerprints->rri_rdatas[counter].rdi_length)) {
273 verbose("Error parsing fingerprint from DNS.");
277 if (hostkey_digest_type != dnskey_digest_type) {
278 hostkey_digest_type = dnskey_digest_type;
279 free(hostkey_digest);
281 /* Initialize host key parameters */
282 if (!dns_read_key(&hostkey_algorithm,
283 &hostkey_digest_type, &hostkey_digest,
284 &hostkey_digest_len, hostkey)) {
285 error("Error calculating key fingerprint.");
286 freerrset(fingerprints);
291 /* Check if the current key is the same as the given key */
292 if (hostkey_algorithm == dnskey_algorithm &&
293 hostkey_digest_type == dnskey_digest_type) {
294 if (hostkey_digest_len == dnskey_digest_len &&
295 timingsafe_bcmp(hostkey_digest, dnskey_digest,
296 hostkey_digest_len) == 0)
297 *flags |= DNS_VERIFY_MATCH;
302 free(hostkey_digest); /* from sshkey_fingerprint_raw() */
303 freerrset(fingerprints);
305 if (*flags & DNS_VERIFY_FOUND)
306 if (*flags & DNS_VERIFY_MATCH)
307 debug("matching host key fingerprint found in DNS");
309 debug("mismatching host key fingerprint found in DNS");
311 debug("no host key fingerprint found in DNS");
317 * Export the fingerprint of a key as a DNS resource record
320 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
322 u_int8_t rdata_pubkey_algorithm = 0;
323 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
325 u_char *rdata_digest;
326 size_t i, rdata_digest_len;
329 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
330 rdata_digest_type = dtype;
331 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
332 &rdata_digest, &rdata_digest_len, key)) {
334 fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
335 hostname, DNS_RDATATYPE_SSHFP,
336 2 + rdata_digest_len,
337 rdata_pubkey_algorithm, rdata_digest_type);
339 fprintf(f, "%s IN SSHFP %d %d ", hostname,
340 rdata_pubkey_algorithm, rdata_digest_type);
342 for (i = 0; i < rdata_digest_len; i++)
343 fprintf(f, "%02x", rdata_digest[i]);
345 free(rdata_digest); /* from sshkey_fingerprint_raw() */
350 /* No SSHFP record was generated at all */
352 error("%s: unsupported algorithm and/or digest_type", __func__);