1 /* $OpenBSD: dns.c,v 1.35 2015/08/20 22:32:42 deraadt Exp $ */
2
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 #include "includes.h"
29
30 #include <sys/types.h>
31 #include <sys/socket.h>
32
33 #include <netdb.h>
34 #include <stdarg.h>
35 #include <stdio.h>
36 #include <string.h>
37 #include <stdarg.h>
38 #include <stdlib.h>
39
40 #include "xmalloc.h"
41 #include "sshkey.h"
42 #include "ssherr.h"
43 #include "dns.h"
44 #include "log.h"
45 #include "digest.h"
46
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 */
54 };
55
56 static const char *
dns_result_totext(unsigned int res)57 dns_result_totext(unsigned int res)
58 {
59 switch (res) {
60 case ERRSET_SUCCESS:
61 return errset_text[ERRSET_SUCCESS];
62 case ERRSET_NOMEMORY:
63 return errset_text[ERRSET_NOMEMORY];
64 case ERRSET_FAIL:
65 return errset_text[ERRSET_FAIL];
66 case ERRSET_INVAL:
67 return errset_text[ERRSET_INVAL];
68 case ERRSET_NONAME:
69 return errset_text[ERRSET_NONAME];
70 case ERRSET_NODATA:
71 return errset_text[ERRSET_NODATA];
72 default:
73 return "unknown error";
74 }
75 }
76
77 /*
78 * Read SSHFP parameters from key buffer.
79 */
80 static int
dns_read_key(u_int8_t * algorithm,u_int8_t * digest_type,u_char ** digest,size_t * digest_len,struct sshkey * key)81 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
82 u_char **digest, size_t *digest_len, struct sshkey *key)
83 {
84 int r, success = 0;
85 int fp_alg = -1;
86
87 switch (key->type) {
88 case KEY_RSA:
89 *algorithm = SSHFP_KEY_RSA;
90 if (!*digest_type)
91 *digest_type = SSHFP_HASH_SHA1;
92 break;
93 case KEY_DSA:
94 *algorithm = SSHFP_KEY_DSA;
95 if (!*digest_type)
96 *digest_type = SSHFP_HASH_SHA1;
97 break;
98 case KEY_ECDSA:
99 *algorithm = SSHFP_KEY_ECDSA;
100 if (!*digest_type)
101 *digest_type = SSHFP_HASH_SHA256;
102 break;
103 case KEY_ED25519:
104 *algorithm = SSHFP_KEY_ED25519;
105 if (!*digest_type)
106 *digest_type = SSHFP_HASH_SHA256;
107 break;
108 default:
109 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
110 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
111 }
112
113 switch (*digest_type) {
114 case SSHFP_HASH_SHA1:
115 fp_alg = SSH_DIGEST_SHA1;
116 break;
117 case SSHFP_HASH_SHA256:
118 fp_alg = SSH_DIGEST_SHA256;
119 break;
120 default:
121 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
122 }
123
124 if (*algorithm && *digest_type) {
125 if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
126 digest_len)) != 0)
127 fatal("%s: sshkey_fingerprint_raw: %s", __func__,
128 ssh_err(r));
129 success = 1;
130 } else {
131 *digest = NULL;
132 *digest_len = 0;
133 success = 0;
134 }
135
136 return success;
137 }
138
139 /*
140 * Read SSHFP parameters from rdata buffer.
141 */
142 static int
dns_read_rdata(u_int8_t * algorithm,u_int8_t * digest_type,u_char ** digest,size_t * digest_len,u_char * rdata,int rdata_len)143 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
144 u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
145 {
146 int success = 0;
147
148 *algorithm = SSHFP_KEY_RESERVED;
149 *digest_type = SSHFP_HASH_RESERVED;
150
151 if (rdata_len >= 2) {
152 *algorithm = rdata[0];
153 *digest_type = rdata[1];
154 *digest_len = rdata_len - 2;
155
156 if (*digest_len > 0) {
157 *digest = xmalloc(*digest_len);
158 memcpy(*digest, rdata + 2, *digest_len);
159 } else {
160 *digest = (u_char *)xstrdup("");
161 }
162
163 success = 1;
164 }
165
166 return success;
167 }
168
169 /*
170 * Check if hostname is numerical.
171 * Returns -1 if hostname is numeric, 0 otherwise
172 */
173 static int
is_numeric_hostname(const char * hostname)174 is_numeric_hostname(const char *hostname)
175 {
176 struct addrinfo hints, *ai;
177
178 /*
179 * We shouldn't ever get a null host but if we do then log an error
180 * and return -1 which stops DNS key fingerprint processing.
181 */
182 if (hostname == NULL) {
183 error("is_numeric_hostname called with NULL hostname");
184 return -1;
185 }
186
187 memset(&hints, 0, sizeof(hints));
188 hints.ai_socktype = SOCK_DGRAM;
189 hints.ai_flags = AI_NUMERICHOST;
190
191 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
192 freeaddrinfo(ai);
193 return -1;
194 }
195
196 return 0;
197 }
198
199 /*
200 * Verify the given hostname, address and host key using DNS.
201 * Returns 0 if lookup succeeds, -1 otherwise
202 */
203 int
verify_host_key_dns(const char * hostname,struct sockaddr * address,struct sshkey * hostkey,int * flags)204 verify_host_key_dns(const char *hostname, struct sockaddr *address,
205 struct sshkey *hostkey, int *flags)
206 {
207 u_int counter;
208 int result;
209 struct rrsetinfo *fingerprints = NULL;
210
211 u_int8_t hostkey_algorithm;
212 u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
213 u_char *hostkey_digest;
214 size_t hostkey_digest_len;
215
216 u_int8_t dnskey_algorithm;
217 u_int8_t dnskey_digest_type;
218 u_char *dnskey_digest;
219 size_t dnskey_digest_len;
220
221 *flags = 0;
222
223 debug3("verify_host_key_dns");
224 if (hostkey == NULL)
225 fatal("No key to look up!");
226
227 if (is_numeric_hostname(hostname)) {
228 debug("skipped DNS lookup for numerical hostname");
229 return -1;
230 }
231
232 #if !defined(ANDROID)
233 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
234 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
235 #else
236 /* unsupported in Android. */
237 result = -1;
238 #endif
239
240 if (result) {
241 verbose("DNS lookup error: %s", dns_result_totext(result));
242 return -1;
243 }
244
245 if (fingerprints->rri_flags & RRSET_VALIDATED) {
246 *flags |= DNS_VERIFY_SECURE;
247 debug("found %d secure fingerprints in DNS",
248 fingerprints->rri_nrdatas);
249 } else {
250 debug("found %d insecure fingerprints in DNS",
251 fingerprints->rri_nrdatas);
252 }
253
254 /* Initialize default host key parameters */
255 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
256 &hostkey_digest, &hostkey_digest_len, hostkey)) {
257 error("Error calculating host key fingerprint.");
258 #if !defined(ANDROID)
259 freerrset(fingerprints);
260 #endif
261 return -1;
262 }
263
264 if (fingerprints->rri_nrdatas)
265 *flags |= DNS_VERIFY_FOUND;
266
267 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
268 /*
269 * Extract the key from the answer. Ignore any badly
270 * formatted fingerprints.
271 */
272 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
273 &dnskey_digest, &dnskey_digest_len,
274 fingerprints->rri_rdatas[counter].rdi_data,
275 fingerprints->rri_rdatas[counter].rdi_length)) {
276 verbose("Error parsing fingerprint from DNS.");
277 continue;
278 }
279
280 if (hostkey_digest_type != dnskey_digest_type) {
281 hostkey_digest_type = dnskey_digest_type;
282 free(hostkey_digest);
283
284 /* Initialize host key parameters */
285 if (!dns_read_key(&hostkey_algorithm,
286 &hostkey_digest_type, &hostkey_digest,
287 &hostkey_digest_len, hostkey)) {
288 error("Error calculating key fingerprint.");
289 #if !defined(ANDROID)
290 freerrset(fingerprints);
291 #endif
292 return -1;
293 }
294 }
295
296 /* Check if the current key is the same as the given key */
297 if (hostkey_algorithm == dnskey_algorithm &&
298 hostkey_digest_type == dnskey_digest_type) {
299 if (hostkey_digest_len == dnskey_digest_len &&
300 timingsafe_bcmp(hostkey_digest, dnskey_digest,
301 hostkey_digest_len) == 0)
302 *flags |= DNS_VERIFY_MATCH;
303 }
304 free(dnskey_digest);
305 }
306
307 free(hostkey_digest); /* from sshkey_fingerprint_raw() */
308 #if !defined(ANDROID)
309 freerrset(fingerprints);
310 #endif
311
312 if (*flags & DNS_VERIFY_FOUND)
313 if (*flags & DNS_VERIFY_MATCH)
314 debug("matching host key fingerprint found in DNS");
315 else
316 debug("mismatching host key fingerprint found in DNS");
317 else
318 debug("no host key fingerprint found in DNS");
319
320 return 0;
321 }
322
323 /*
324 * Export the fingerprint of a key as a DNS resource record
325 */
326 int
export_dns_rr(const char * hostname,struct sshkey * key,FILE * f,int generic)327 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
328 {
329 u_int8_t rdata_pubkey_algorithm = 0;
330 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
331 u_int8_t dtype;
332 u_char *rdata_digest;
333 size_t i, rdata_digest_len;
334 int success = 0;
335
336 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
337 rdata_digest_type = dtype;
338 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
339 &rdata_digest, &rdata_digest_len, key)) {
340 if (generic) {
341 fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
342 hostname, DNS_RDATATYPE_SSHFP,
343 2 + rdata_digest_len,
344 rdata_pubkey_algorithm, rdata_digest_type);
345 } else {
346 fprintf(f, "%s IN SSHFP %d %d ", hostname,
347 rdata_pubkey_algorithm, rdata_digest_type);
348 }
349 for (i = 0; i < rdata_digest_len; i++)
350 fprintf(f, "%02x", rdata_digest[i]);
351 fprintf(f, "\n");
352 free(rdata_digest); /* from sshkey_fingerprint_raw() */
353 success = 1;
354 }
355 }
356
357 /* No SSHFP record was generated at all */
358 if (success == 0) {
359 error("%s: unsupported algorithm and/or digest_type", __func__);
360 }
361
362 return success;
363 }
364