1 /* $OpenBSD: dns.c,v 1.44 2023/03/10 04:06:21 dtucker 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 <sys/types.h>
29 #include <sys/socket.h>
30
31 #include <netdb.h>
32 #include <stdarg.h>
33 #include <stdio.h>
34 #include <string.h>
35 #include <stdlib.h>
36
37 #include "xmalloc.h"
38 #include "sshkey.h"
39 #include "ssherr.h"
40 #include "dns.h"
41 #include "log.h"
42 #include "digest.h"
43
44 static const char * const errset_text[] = {
45 "success", /* 0 ERRSET_SUCCESS */
46 "out of memory", /* 1 ERRSET_NOMEMORY */
47 "general failure", /* 2 ERRSET_FAIL */
48 "invalid parameter", /* 3 ERRSET_INVAL */
49 "name does not exist", /* 4 ERRSET_NONAME */
50 "data does not exist", /* 5 ERRSET_NODATA */
51 };
52
53 static const char *
dns_result_totext(unsigned int res)54 dns_result_totext(unsigned int res)
55 {
56 switch (res) {
57 case ERRSET_SUCCESS:
58 return errset_text[ERRSET_SUCCESS];
59 case ERRSET_NOMEMORY:
60 return errset_text[ERRSET_NOMEMORY];
61 case ERRSET_FAIL:
62 return errset_text[ERRSET_FAIL];
63 case ERRSET_INVAL:
64 return errset_text[ERRSET_INVAL];
65 case ERRSET_NONAME:
66 return errset_text[ERRSET_NONAME];
67 case ERRSET_NODATA:
68 return errset_text[ERRSET_NODATA];
69 default:
70 return "unknown error";
71 }
72 }
73
74 /*
75 * Read SSHFP parameters from key buffer.
76 * Caller must free digest which is allocated by sshkey_fingerprint_raw().
77 */
78 static int
dns_read_key(u_int8_t * algorithm,u_int8_t * digest_type,u_char ** digest,size_t * digest_len,struct sshkey * key)79 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
80 u_char **digest, size_t *digest_len, struct sshkey *key)
81 {
82 int r, success = 0;
83 int fp_alg = -1;
84
85 switch (key->type) {
86 case KEY_RSA:
87 *algorithm = SSHFP_KEY_RSA;
88 break;
89 case KEY_DSA:
90 *algorithm = SSHFP_KEY_DSA;
91 break;
92 case KEY_ECDSA:
93 *algorithm = SSHFP_KEY_ECDSA;
94 break;
95 case KEY_ED25519:
96 *algorithm = SSHFP_KEY_ED25519;
97 break;
98 case KEY_XMSS:
99 *algorithm = SSHFP_KEY_XMSS;
100 break;
101 default:
102 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
103 }
104
105 switch (*digest_type) {
106 case SSHFP_HASH_SHA1:
107 fp_alg = SSH_DIGEST_SHA1;
108 break;
109 case SSHFP_HASH_SHA256:
110 fp_alg = SSH_DIGEST_SHA256;
111 break;
112 default:
113 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
114 }
115
116 if (*algorithm && *digest_type) {
117 if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
118 digest_len)) != 0)
119 fatal_fr(r, "sshkey_fingerprint_raw");
120 success = 1;
121 } else {
122 *digest = NULL;
123 *digest_len = 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,size_t * 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, size_t *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 = 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,struct sshkey * hostkey,int * flags)194 verify_host_key_dns(const char *hostname, struct sockaddr *address,
195 struct sshkey *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_char *hostkey_digest;
203 size_t hostkey_digest_len;
204
205 u_int8_t dnskey_algorithm;
206 u_int8_t dnskey_digest_type;
207 u_char *dnskey_digest;
208 size_t dnskey_digest_len;
209
210 *flags = 0;
211
212 debug3("verify_host_key_dns");
213 if (hostkey == NULL)
214 fatal("No key to look up!");
215
216 if (is_numeric_hostname(hostname)) {
217 debug("skipped DNS lookup for numerical hostname");
218 return -1;
219 }
220
221 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
222 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
223 if (result) {
224 verbose("DNS lookup error: %s", dns_result_totext(result));
225 return -1;
226 }
227
228 if (fingerprints->rri_flags & RRSET_VALIDATED) {
229 *flags |= DNS_VERIFY_SECURE;
230 debug("found %d secure fingerprints in DNS",
231 fingerprints->rri_nrdatas);
232 } else {
233 debug("found %d insecure fingerprints in DNS",
234 fingerprints->rri_nrdatas);
235 }
236
237 if (fingerprints->rri_nrdatas)
238 *flags |= DNS_VERIFY_FOUND;
239
240 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
241 /*
242 * Extract the key from the answer. Ignore any badly
243 * formatted fingerprints.
244 */
245 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
246 &dnskey_digest, &dnskey_digest_len,
247 fingerprints->rri_rdatas[counter].rdi_data,
248 fingerprints->rri_rdatas[counter].rdi_length)) {
249 verbose("Error parsing fingerprint from DNS.");
250 continue;
251 }
252 debug3_f("checking SSHFP type %d fptype %d", dnskey_algorithm,
253 dnskey_digest_type);
254
255 /* Calculate host key fingerprint. */
256 if (!dns_read_key(&hostkey_algorithm, &dnskey_digest_type,
257 &hostkey_digest, &hostkey_digest_len, hostkey)) {
258 error("Error calculating key fingerprint.");
259 free(dnskey_digest);
260 freerrset(fingerprints);
261 return -1;
262 }
263
264 /* Check if the current key is the same as the given key */
265 if (hostkey_algorithm == dnskey_algorithm &&
266 hostkey_digest_len == dnskey_digest_len) {
267 if (timingsafe_bcmp(hostkey_digest, dnskey_digest,
268 hostkey_digest_len) == 0) {
269 debug_f("matched SSHFP type %d fptype %d",
270 dnskey_algorithm, dnskey_digest_type);
271 *flags |= DNS_VERIFY_MATCH;
272 } else {
273 debug_f("failed SSHFP type %d fptype %d",
274 dnskey_algorithm, dnskey_digest_type);
275 *flags |= DNS_VERIFY_FAILED;
276 }
277 }
278 free(dnskey_digest);
279 free(hostkey_digest); /* from sshkey_fingerprint_raw() */
280 }
281
282 freerrset(fingerprints);
283
284 /* If any fingerprint failed to validate, return failure. */
285 if (*flags & DNS_VERIFY_FAILED)
286 *flags &= ~DNS_VERIFY_MATCH;
287
288 if (*flags & DNS_VERIFY_FOUND)
289 if (*flags & DNS_VERIFY_MATCH)
290 debug("matching host key fingerprint found in DNS");
291 else
292 debug("mismatching host key fingerprint found in DNS");
293 else
294 debug("no host key fingerprint found in DNS");
295
296 return 0;
297 }
298
299 /*
300 * Export the fingerprint of a key as a DNS resource record
301 */
302 int
export_dns_rr(const char * hostname,struct sshkey * key,FILE * f,int generic,int alg)303 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic,
304 int alg)
305 {
306 u_int8_t rdata_pubkey_algorithm = 0;
307 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
308 u_int8_t dtype;
309 u_char *rdata_digest;
310 size_t i, rdata_digest_len;
311 int success = 0;
312
313 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
314 if (alg != -1 && dtype != alg)
315 continue;
316 rdata_digest_type = dtype;
317 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
318 &rdata_digest, &rdata_digest_len, key)) {
319 if (generic) {
320 fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
321 hostname, DNS_RDATATYPE_SSHFP,
322 2 + rdata_digest_len,
323 rdata_pubkey_algorithm, rdata_digest_type);
324 } else {
325 fprintf(f, "%s IN SSHFP %d %d ", hostname,
326 rdata_pubkey_algorithm, rdata_digest_type);
327 }
328 for (i = 0; i < rdata_digest_len; i++)
329 fprintf(f, "%02x", rdata_digest[i]);
330 fprintf(f, "\n");
331 free(rdata_digest); /* from sshkey_fingerprint_raw() */
332 success = 1;
333 }
334 }
335
336 /* No SSHFP record was generated at all */
337 if (success == 0) {
338 error_f("unsupported algorithm and/or digest_type");
339 }
340
341 return success;
342 }
343