1 /* $OpenBSD: dns.c,v 1.29 2013/05/17 00:13:13 djm 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
38 #include "xmalloc.h"
39 #include "key.h"
40 #include "dns.h"
41 #include "log.h"
42
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 */
50 };
51
52 static const char *
dns_result_totext(unsigned int res)53 dns_result_totext(unsigned int res)
54 {
55 switch (res) {
56 case ERRSET_SUCCESS:
57 return errset_text[ERRSET_SUCCESS];
58 case ERRSET_NOMEMORY:
59 return errset_text[ERRSET_NOMEMORY];
60 case ERRSET_FAIL:
61 return errset_text[ERRSET_FAIL];
62 case ERRSET_INVAL:
63 return errset_text[ERRSET_INVAL];
64 case ERRSET_NONAME:
65 return errset_text[ERRSET_NONAME];
66 case ERRSET_NODATA:
67 return errset_text[ERRSET_NODATA];
68 default:
69 return "unknown error";
70 }
71 }
72
73 /*
74 * Read SSHFP parameters from key buffer.
75 */
76 static int
dns_read_key(u_int8_t * algorithm,u_int8_t * digest_type,u_char ** digest,u_int * digest_len,Key * key)77 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
78 u_char **digest, u_int *digest_len, Key *key)
79 {
80 int success = 0;
81 enum fp_type fp_type = 0;
82
83 switch (key->type) {
84 case KEY_RSA:
85 *algorithm = SSHFP_KEY_RSA;
86 if (!*digest_type)
87 *digest_type = SSHFP_HASH_SHA1;
88 break;
89 case KEY_DSA:
90 *algorithm = SSHFP_KEY_DSA;
91 if (!*digest_type)
92 *digest_type = SSHFP_HASH_SHA1;
93 break;
94 case KEY_ECDSA:
95 *algorithm = SSHFP_KEY_ECDSA;
96 if (!*digest_type)
97 *digest_type = SSHFP_HASH_SHA256;
98 break;
99 default:
100 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
101 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
102 }
103
104 switch (*digest_type) {
105 case SSHFP_HASH_SHA1:
106 fp_type = SSH_FP_SHA1;
107 break;
108 case SSHFP_HASH_SHA256:
109 fp_type = SSH_FP_SHA256;
110 break;
111 default:
112 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
113 }
114
115 if (*algorithm && *digest_type) {
116 *digest = key_fingerprint_raw(key, fp_type, digest_len);
117 if (*digest == NULL)
118 fatal("dns_read_key: null from key_fingerprint_raw()");
119 success = 1;
120 } else {
121 *digest = NULL;
122 *digest_len = 0;
123 success = 0;
124 }
125
126 return success;
127 }
128
129 /*
130 * Read SSHFP parameters from rdata buffer.
131 */
132 static int
dns_read_rdata(u_int8_t * algorithm,u_int8_t * digest_type,u_char ** digest,u_int * digest_len,u_char * rdata,int rdata_len)133 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
134 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
135 {
136 int success = 0;
137
138 *algorithm = SSHFP_KEY_RESERVED;
139 *digest_type = SSHFP_HASH_RESERVED;
140
141 if (rdata_len >= 2) {
142 *algorithm = rdata[0];
143 *digest_type = rdata[1];
144 *digest_len = rdata_len - 2;
145
146 if (*digest_len > 0) {
147 *digest = (u_char *) xmalloc(*digest_len);
148 memcpy(*digest, rdata + 2, *digest_len);
149 } else {
150 *digest = (u_char *)xstrdup("");
151 }
152
153 success = 1;
154 }
155
156 return success;
157 }
158
159 /*
160 * Check if hostname is numerical.
161 * Returns -1 if hostname is numeric, 0 otherwise
162 */
163 static int
is_numeric_hostname(const char * hostname)164 is_numeric_hostname(const char *hostname)
165 {
166 struct addrinfo hints, *ai;
167
168 /*
169 * We shouldn't ever get a null host but if we do then log an error
170 * and return -1 which stops DNS key fingerprint processing.
171 */
172 if (hostname == NULL) {
173 error("is_numeric_hostname called with NULL hostname");
174 return -1;
175 }
176
177 memset(&hints, 0, sizeof(hints));
178 hints.ai_socktype = SOCK_DGRAM;
179 hints.ai_flags = AI_NUMERICHOST;
180
181 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
182 freeaddrinfo(ai);
183 return -1;
184 }
185
186 return 0;
187 }
188
189 /*
190 * Verify the given hostname, address and host key using DNS.
191 * Returns 0 if lookup succeeds, -1 otherwise
192 */
193 int
verify_host_key_dns(const char * hostname,struct sockaddr * address,Key * hostkey,int * flags)194 verify_host_key_dns(const char *hostname, struct sockaddr *address,
195 Key *hostkey, int *flags)
196 {
197 u_int counter;
198 int result;
199 struct rrsetinfo *fingerprints = NULL;
200
201 u_int8_t hostkey_algorithm;
202 u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
203 u_char *hostkey_digest;
204 u_int hostkey_digest_len;
205
206 u_int8_t dnskey_algorithm;
207 u_int8_t dnskey_digest_type;
208 u_char *dnskey_digest;
209 u_int dnskey_digest_len;
210
211 *flags = 0;
212
213 debug3("verify_host_key_dns");
214 if (hostkey == NULL)
215 fatal("No key to look up!");
216
217 if (is_numeric_hostname(hostname)) {
218 debug("skipped DNS lookup for numerical hostname");
219 return -1;
220 }
221
222 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
223 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
224 if (result) {
225 verbose("DNS lookup error: %s", dns_result_totext(result));
226 return -1;
227 }
228
229 if (fingerprints->rri_flags & RRSET_VALIDATED) {
230 *flags |= DNS_VERIFY_SECURE;
231 debug("found %d secure fingerprints in DNS",
232 fingerprints->rri_nrdatas);
233 } else {
234 debug("found %d insecure fingerprints in DNS",
235 fingerprints->rri_nrdatas);
236 }
237
238 /* Initialize default host key parameters */
239 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
240 &hostkey_digest, &hostkey_digest_len, hostkey)) {
241 error("Error calculating host key fingerprint.");
242 freerrset(fingerprints);
243 return -1;
244 }
245
246 if (fingerprints->rri_nrdatas)
247 *flags |= DNS_VERIFY_FOUND;
248
249 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
250 /*
251 * Extract the key from the answer. Ignore any badly
252 * formatted fingerprints.
253 */
254 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
255 &dnskey_digest, &dnskey_digest_len,
256 fingerprints->rri_rdatas[counter].rdi_data,
257 fingerprints->rri_rdatas[counter].rdi_length)) {
258 verbose("Error parsing fingerprint from DNS.");
259 continue;
260 }
261
262 if (hostkey_digest_type != dnskey_digest_type) {
263 hostkey_digest_type = dnskey_digest_type;
264 free(hostkey_digest);
265
266 /* Initialize host key parameters */
267 if (!dns_read_key(&hostkey_algorithm,
268 &hostkey_digest_type, &hostkey_digest,
269 &hostkey_digest_len, hostkey)) {
270 error("Error calculating key fingerprint.");
271 freerrset(fingerprints);
272 return -1;
273 }
274 }
275
276 /* Check if the current key is the same as the given key */
277 if (hostkey_algorithm == dnskey_algorithm &&
278 hostkey_digest_type == dnskey_digest_type) {
279 if (hostkey_digest_len == dnskey_digest_len &&
280 timingsafe_bcmp(hostkey_digest, dnskey_digest,
281 hostkey_digest_len) == 0)
282 *flags |= DNS_VERIFY_MATCH;
283 }
284 free(dnskey_digest);
285 }
286
287 free(hostkey_digest); /* from key_fingerprint_raw() */
288 freerrset(fingerprints);
289
290 if (*flags & DNS_VERIFY_FOUND)
291 if (*flags & DNS_VERIFY_MATCH)
292 debug("matching host key fingerprint found in DNS");
293 else
294 debug("mismatching host key fingerprint found in DNS");
295 else
296 debug("no host key fingerprint found in DNS");
297
298 return 0;
299 }
300
301 /*
302 * Export the fingerprint of a key as a DNS resource record
303 */
304 int
export_dns_rr(const char * hostname,Key * key,FILE * f,int generic)305 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
306 {
307 u_int8_t rdata_pubkey_algorithm = 0;
308 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
309 u_int8_t dtype;
310 u_char *rdata_digest;
311 u_int i, rdata_digest_len;
312 int success = 0;
313
314 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
315 rdata_digest_type = dtype;
316 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
317 &rdata_digest, &rdata_digest_len, key)) {
318 if (generic) {
319 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ",
320 hostname, DNS_RDATATYPE_SSHFP,
321 2 + rdata_digest_len,
322 rdata_pubkey_algorithm, rdata_digest_type);
323 } else {
324 fprintf(f, "%s IN SSHFP %d %d ", hostname,
325 rdata_pubkey_algorithm, rdata_digest_type);
326 }
327 for (i = 0; i < rdata_digest_len; i++)
328 fprintf(f, "%02x", rdata_digest[i]);
329 fprintf(f, "\n");
330 free(rdata_digest); /* from key_fingerprint_raw() */
331 success = 1;
332 }
333 }
334
335 /* No SSHFP record was generated at all */
336 if (success == 0) {
337 error("%s: unsupported algorithm and/or digest_type", __func__);
338 }
339
340 return success;
341 }
342