1 /* $OpenBSD: dns.c,v 1.48 2026/03/03 09:57:25 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 "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 <stdlib.h>
38
39 #include "xmalloc.h"
40 #include "sshkey.h"
41 #include "dns.h"
42 #include "log.h"
43 #include "digest.h"
44
45 static const char * const errset_text[] = {
46 "success", /* 0 ERRSET_SUCCESS */
47 "out of memory", /* 1 ERRSET_NOMEMORY */
48 "general failure", /* 2 ERRSET_FAIL */
49 "invalid parameter", /* 3 ERRSET_INVAL */
50 "name does not exist", /* 4 ERRSET_NONAME */
51 "data does not exist", /* 5 ERRSET_NODATA */
52 };
53
54 static const char *
dns_result_totext(unsigned int res)55 dns_result_totext(unsigned int res)
56 {
57 switch (res) {
58 case ERRSET_SUCCESS:
59 return errset_text[ERRSET_SUCCESS];
60 case ERRSET_NOMEMORY:
61 return errset_text[ERRSET_NOMEMORY];
62 case ERRSET_FAIL:
63 return errset_text[ERRSET_FAIL];
64 case ERRSET_INVAL:
65 return errset_text[ERRSET_INVAL];
66 case ERRSET_NONAME:
67 return errset_text[ERRSET_NONAME];
68 case ERRSET_NODATA:
69 return errset_text[ERRSET_NODATA];
70 default:
71 return "unknown error";
72 }
73 }
74
75 /*
76 * Read SSHFP parameters from key buffer.
77 * Caller must free digest which is allocated by sshkey_fingerprint_raw().
78 */
79 static int
dns_read_key(uint8_t * algorithm,uint8_t * digest_type,u_char ** digest,size_t * digest_len,struct sshkey * key)80 dns_read_key(uint8_t *algorithm, uint8_t *digest_type,
81 u_char **digest, size_t *digest_len, struct sshkey *key)
82 {
83 int r, success = 0;
84 int fp_alg = -1;
85
86 switch (key->type) {
87 case KEY_RSA:
88 *algorithm = SSHFP_KEY_RSA;
89 break;
90 case KEY_ECDSA:
91 *algorithm = SSHFP_KEY_ECDSA;
92 break;
93 case KEY_ED25519:
94 *algorithm = SSHFP_KEY_ED25519;
95 break;
96 default:
97 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
98 }
99
100 switch (*digest_type) {
101 case SSHFP_HASH_SHA1:
102 fp_alg = SSH_DIGEST_SHA1;
103 break;
104 case SSHFP_HASH_SHA256:
105 fp_alg = SSH_DIGEST_SHA256;
106 break;
107 default:
108 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
109 }
110
111 if (*algorithm && *digest_type) {
112 if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
113 digest_len)) != 0)
114 fatal_fr(r, "sshkey_fingerprint_raw");
115 success = 1;
116 } else {
117 *digest = NULL;
118 *digest_len = 0;
119 }
120
121 return success;
122 }
123
124 /*
125 * Read SSHFP parameters from rdata buffer.
126 */
127 static int
dns_read_rdata(uint8_t * algorithm,uint8_t * digest_type,u_char ** digest,size_t * digest_len,u_char * rdata,int rdata_len)128 dns_read_rdata(uint8_t *algorithm, uint8_t *digest_type,
129 u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
130 {
131 int success = 0;
132
133 *algorithm = SSHFP_KEY_RESERVED;
134 *digest_type = SSHFP_HASH_RESERVED;
135
136 if (rdata_len >= 2) {
137 *algorithm = rdata[0];
138 *digest_type = rdata[1];
139 *digest_len = rdata_len - 2;
140
141 if (*digest_len > 0) {
142 *digest = xmalloc(*digest_len);
143 memcpy(*digest, rdata + 2, *digest_len);
144 } else {
145 *digest = (u_char *)xstrdup("");
146 }
147
148 success = 1;
149 }
150
151 return success;
152 }
153
154 /*
155 * Check if hostname is numerical.
156 * Returns -1 if hostname is numeric, 0 otherwise
157 */
158 static int
is_numeric_hostname(const char * hostname)159 is_numeric_hostname(const char *hostname)
160 {
161 struct addrinfo hints, *ai;
162
163 /*
164 * We shouldn't ever get a null host but if we do then log an error
165 * and return -1 which stops DNS key fingerprint processing.
166 */
167 if (hostname == NULL) {
168 error("is_numeric_hostname called with NULL hostname");
169 return -1;
170 }
171
172 memset(&hints, 0, sizeof(hints));
173 hints.ai_socktype = SOCK_DGRAM;
174 hints.ai_flags = AI_NUMERICHOST;
175
176 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
177 freeaddrinfo(ai);
178 return -1;
179 }
180
181 return 0;
182 }
183
184 /*
185 * Verify the given hostname, address and host key using DNS.
186 * Returns 0 if lookup succeeds, -1 otherwise
187 */
188 int
verify_host_key_dns(const char * hostname,struct sockaddr * address,struct sshkey * hostkey,int * flags)189 verify_host_key_dns(const char *hostname, struct sockaddr *address,
190 struct sshkey *hostkey, int *flags)
191 {
192 u_int counter;
193 int result;
194 struct rrsetinfo *fingerprints = NULL;
195
196 uint8_t hostkey_algorithm;
197 u_char *hostkey_digest;
198 size_t hostkey_digest_len;
199
200 uint8_t dnskey_algorithm;
201 uint8_t dnskey_digest_type;
202 u_char *dnskey_digest;
203 size_t dnskey_digest_len;
204
205 *flags = 0;
206
207 debug3("verify_host_key_dns");
208 if (hostkey == NULL)
209 fatal("No key to look up!");
210
211 if (is_numeric_hostname(hostname)) {
212 debug("skipped DNS lookup for numerical hostname");
213 return -1;
214 }
215
216 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
217 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
218 if (result) {
219 verbose("DNS lookup error: %s", dns_result_totext(result));
220 return -1;
221 }
222
223 if (fingerprints->rri_flags & RRSET_VALIDATED) {
224 *flags |= DNS_VERIFY_SECURE;
225 debug("found %d secure fingerprints in DNS",
226 fingerprints->rri_nrdatas);
227 } else {
228 debug("found %d insecure fingerprints in DNS",
229 fingerprints->rri_nrdatas);
230 }
231
232 if (fingerprints->rri_nrdatas)
233 *flags |= DNS_VERIFY_FOUND;
234
235 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
236 /*
237 * Extract the key from the answer. Ignore any badly
238 * formatted fingerprints.
239 */
240 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
241 &dnskey_digest, &dnskey_digest_len,
242 fingerprints->rri_rdatas[counter].rdi_data,
243 fingerprints->rri_rdatas[counter].rdi_length)) {
244 verbose("Error parsing fingerprint from DNS.");
245 continue;
246 }
247 debug3_f("checking SSHFP type %d fptype %d", dnskey_algorithm,
248 dnskey_digest_type);
249
250 /* Calculate host key fingerprint. */
251 if (!dns_read_key(&hostkey_algorithm, &dnskey_digest_type,
252 &hostkey_digest, &hostkey_digest_len, hostkey)) {
253 error("Error calculating key fingerprint.");
254 free(dnskey_digest);
255 freerrset(fingerprints);
256 return -1;
257 }
258
259 /* Check if the current key is the same as the given key */
260 if (hostkey_algorithm == dnskey_algorithm &&
261 hostkey_digest_len == dnskey_digest_len) {
262 if (timingsafe_bcmp(hostkey_digest, dnskey_digest,
263 hostkey_digest_len) == 0) {
264 debug_f("matched SSHFP type %d fptype %d",
265 dnskey_algorithm, dnskey_digest_type);
266 *flags |= DNS_VERIFY_MATCH;
267 } else {
268 debug_f("failed SSHFP type %d fptype %d",
269 dnskey_algorithm, dnskey_digest_type);
270 *flags |= DNS_VERIFY_FAILED;
271 }
272 }
273 free(dnskey_digest);
274 free(hostkey_digest); /* from sshkey_fingerprint_raw() */
275 }
276
277 freerrset(fingerprints);
278
279 /* If any fingerprint failed to validate, return failure. */
280 if (*flags & DNS_VERIFY_FAILED)
281 *flags &= ~DNS_VERIFY_MATCH;
282
283 if (*flags & DNS_VERIFY_FOUND)
284 if (*flags & DNS_VERIFY_MATCH)
285 debug("matching host key fingerprint found in DNS");
286 else
287 debug("mismatching host key fingerprint found in DNS");
288 else
289 debug("no host key fingerprint found in DNS");
290
291 return 0;
292 }
293
294 /*
295 * Export the fingerprint of a key as a DNS resource record
296 */
297 int
export_dns_rr(const char * hostname,struct sshkey * key,FILE * f,int generic,int alg)298 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic,
299 int alg)
300 {
301 uint8_t rdata_pubkey_algorithm = 0;
302 uint8_t rdata_digest_type = SSHFP_HASH_RESERVED;
303 uint8_t dtype;
304 u_char *rdata_digest;
305 size_t i, rdata_digest_len;
306 int success = 0;
307
308 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
309 if (alg != -1 && dtype != alg)
310 continue;
311 rdata_digest_type = dtype;
312 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
313 &rdata_digest, &rdata_digest_len, key)) {
314 if (generic) {
315 fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
316 hostname, DNS_RDATATYPE_SSHFP,
317 2 + rdata_digest_len,
318 rdata_pubkey_algorithm, rdata_digest_type);
319 } else {
320 fprintf(f, "%s IN SSHFP %d %d ", hostname,
321 rdata_pubkey_algorithm, rdata_digest_type);
322 }
323 for (i = 0; i < rdata_digest_len; i++)
324 fprintf(f, "%02x", rdata_digest[i]);
325 fprintf(f, "\n");
326 free(rdata_digest); /* from sshkey_fingerprint_raw() */
327 success = 1;
328 }
329 }
330
331 /* No SSHFP record was generated at all */
332 if (success == 0) {
333 error_f("unsupported algorithm and/or digest_type");
334 }
335
336 return success;
337 }
338