1 /* $OpenBSD: dns.c,v 1.27 2010/08/31 11:54:45 djm 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>
43 static const char *errset_text[] = {
44 "success", /* 0 ERRSET_SUCCESS */
45 "out of memory", /* 1 ERRSET_NOMEMORY */
46 "general failure", /* 2 ERRSET_FAIL */
47 "invalid parameter", /* 3 ERRSET_INVAL */
48 "name does not exist", /* 4 ERRSET_NONAME */
49 "data does not exist", /* 5 ERRSET_NODATA */
53 dns_result_totext(unsigned int res)
57 return errset_text[ERRSET_SUCCESS];
59 return errset_text[ERRSET_NOMEMORY];
61 return errset_text[ERRSET_FAIL];
63 return errset_text[ERRSET_INVAL];
65 return errset_text[ERRSET_NONAME];
67 return errset_text[ERRSET_NODATA];
69 return "unknown error";
74 * Read SSHFP parameters from key buffer.
77 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
78 u_char **digest, u_int *digest_len, Key *key)
84 *algorithm = SSHFP_KEY_RSA;
87 *algorithm = SSHFP_KEY_DSA;
91 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
95 *digest_type = SSHFP_HASH_SHA1;
96 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
98 fatal("dns_read_key: null from key_fingerprint_raw()");
101 *digest_type = SSHFP_HASH_RESERVED;
111 * Read SSHFP parameters from rdata buffer.
114 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
115 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
119 *algorithm = SSHFP_KEY_RESERVED;
120 *digest_type = SSHFP_HASH_RESERVED;
122 if (rdata_len >= 2) {
123 *algorithm = rdata[0];
124 *digest_type = rdata[1];
125 *digest_len = rdata_len - 2;
127 if (*digest_len > 0) {
128 *digest = (u_char *) xmalloc(*digest_len);
129 memcpy(*digest, rdata + 2, *digest_len);
131 *digest = (u_char *)xstrdup("");
141 * Check if hostname is numerical.
142 * Returns -1 if hostname is numeric, 0 otherwise
145 is_numeric_hostname(const char *hostname)
147 struct addrinfo hints, *ai;
150 * We shouldn't ever get a null host but if we do then log an error
151 * and return -1 which stops DNS key fingerprint processing.
153 if (hostname == NULL) {
154 error("is_numeric_hostname called with NULL hostname");
158 memset(&hints, 0, sizeof(hints));
159 hints.ai_socktype = SOCK_DGRAM;
160 hints.ai_flags = AI_NUMERICHOST;
162 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
171 * Verify the given hostname, address and host key using DNS.
172 * Returns 0 if lookup succeeds, -1 otherwise
175 verify_host_key_dns(const char *hostname, struct sockaddr *address,
176 Key *hostkey, int *flags)
180 unsigned int rrset_flags = 0;
181 struct rrsetinfo *fingerprints = NULL;
183 u_int8_t hostkey_algorithm;
184 u_int8_t hostkey_digest_type;
185 u_char *hostkey_digest;
186 u_int hostkey_digest_len;
188 u_int8_t dnskey_algorithm;
189 u_int8_t dnskey_digest_type;
190 u_char *dnskey_digest;
191 u_int dnskey_digest_len;
195 debug3("verify_host_key_dns");
197 fatal("No key to look up!");
199 if (is_numeric_hostname(hostname)) {
200 debug("skipped DNS lookup for numerical hostname");
205 * Original getrrsetbyname function, found on OpenBSD for example,
206 * doesn't accept any flag and prerequisite for obtaining AD bit in
207 * DNS response is set by "options edns0" in resolv.conf.
209 * Our version is more clever and use RRSET_FORCE_EDNS0 flag.
211 #ifndef HAVE_GETRRSETBYNAME
212 rrset_flags |= RRSET_FORCE_EDNS0;
214 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
215 DNS_RDATATYPE_SSHFP, rrset_flags, &fingerprints);
218 verbose("DNS lookup error: %s", dns_result_totext(result));
222 if (fingerprints->rri_flags & RRSET_VALIDATED) {
223 *flags |= DNS_VERIFY_SECURE;
224 debug("found %d secure fingerprints in DNS",
225 fingerprints->rri_nrdatas);
227 debug("found %d insecure fingerprints in DNS",
228 fingerprints->rri_nrdatas);
231 /* Initialize host key parameters */
232 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
233 &hostkey_digest, &hostkey_digest_len, hostkey)) {
234 error("Error calculating host key fingerprint.");
235 freerrset(fingerprints);
239 if (fingerprints->rri_nrdatas)
240 *flags |= DNS_VERIFY_FOUND;
242 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
244 * Extract the key from the answer. Ignore any badly
245 * formatted fingerprints.
247 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
248 &dnskey_digest, &dnskey_digest_len,
249 fingerprints->rri_rdatas[counter].rdi_data,
250 fingerprints->rri_rdatas[counter].rdi_length)) {
251 verbose("Error parsing fingerprint from DNS.");
255 /* Check if the current key is the same as the given key */
256 if (hostkey_algorithm == dnskey_algorithm &&
257 hostkey_digest_type == dnskey_digest_type) {
259 if (hostkey_digest_len == dnskey_digest_len &&
260 memcmp(hostkey_digest, dnskey_digest,
261 hostkey_digest_len) == 0) {
263 *flags |= DNS_VERIFY_MATCH;
266 xfree(dnskey_digest);
269 xfree(hostkey_digest); /* from key_fingerprint_raw() */
270 freerrset(fingerprints);
272 if (*flags & DNS_VERIFY_FOUND)
273 if (*flags & DNS_VERIFY_MATCH)
274 debug("matching host key fingerprint found in DNS");
276 debug("mismatching host key fingerprint found in DNS");
278 debug("no host key fingerprint found in DNS");
284 * Export the fingerprint of a key as a DNS resource record
287 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
289 u_int8_t rdata_pubkey_algorithm = 0;
290 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
291 u_char *rdata_digest;
292 u_int rdata_digest_len;
297 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
298 &rdata_digest, &rdata_digest_len, key)) {
301 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
302 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
303 rdata_pubkey_algorithm, rdata_digest_type);
305 fprintf(f, "%s IN SSHFP %d %d ", hostname,
306 rdata_pubkey_algorithm, rdata_digest_type);
308 for (i = 0; i < rdata_digest_len; i++)
309 fprintf(f, "%02x", rdata_digest[i]);
311 xfree(rdata_digest); /* from key_fingerprint_raw() */
314 error("export_dns_rr: unsupported algorithm");