1 /* $OpenBSD: dns.c,v 1.27 2010/08/31 11:54:45 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
82 switch (key->type) {
83 case KEY_RSA:
84 *algorithm = SSHFP_KEY_RSA;
85 break;
86 case KEY_DSA:
87 *algorithm = SSHFP_KEY_DSA;
88 break;
89 /* XXX KEY_ECDSA */
90 default:
91 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
92 }
93
94 if (*algorithm) {
95 *digest_type = SSHFP_HASH_SHA1;
96 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
97 if (*digest == NULL)
98 fatal("dns_read_key: null from key_fingerprint_raw()");
99 success = 1;
100 } else {
101 *digest_type = SSHFP_HASH_RESERVED;
102 *digest = NULL;
103 *digest_len = 0;
104 success = 0;
105 }
106
107 return success;
108 }
109
110 /*
111 * Read SSHFP parameters from rdata buffer.
112 */
113 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)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)
116 {
117 int success = 0;
118
119 *algorithm = SSHFP_KEY_RESERVED;
120 *digest_type = SSHFP_HASH_RESERVED;
121
122 if (rdata_len >= 2) {
123 *algorithm = rdata[0];
124 *digest_type = rdata[1];
125 *digest_len = rdata_len - 2;
126
127 if (*digest_len > 0) {
128 *digest = (u_char *) xmalloc(*digest_len);
129 memcpy(*digest, rdata + 2, *digest_len);
130 } else {
131 *digest = (u_char *)xstrdup("");
132 }
133
134 success = 1;
135 }
136
137 return success;
138 }
139
140 /*
141 * Check if hostname is numerical.
142 * Returns -1 if hostname is numeric, 0 otherwise
143 */
144 static int
is_numeric_hostname(const char * hostname)145 is_numeric_hostname(const char *hostname)
146 {
147 struct addrinfo hints, *ai;
148
149 /*
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.
152 */
153 if (hostname == NULL) {
154 error("is_numeric_hostname called with NULL hostname");
155 return -1;
156 }
157
158 memset(&hints, 0, sizeof(hints));
159 hints.ai_socktype = SOCK_DGRAM;
160 hints.ai_flags = AI_NUMERICHOST;
161
162 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
163 freeaddrinfo(ai);
164 return -1;
165 }
166
167 return 0;
168 }
169
170 /*
171 * Verify the given hostname, address and host key using DNS.
172 * Returns 0 if lookup succeeds, -1 otherwise
173 */
174 int
verify_host_key_dns(const char * hostname,struct sockaddr * address,Key * hostkey,int * flags)175 verify_host_key_dns(const char *hostname, struct sockaddr *address,
176 Key *hostkey, int *flags)
177 {
178 u_int counter;
179 int result;
180 struct rrsetinfo *fingerprints = NULL;
181
182 u_int8_t hostkey_algorithm;
183 u_int8_t hostkey_digest_type;
184 u_char *hostkey_digest;
185 u_int hostkey_digest_len;
186
187 u_int8_t dnskey_algorithm;
188 u_int8_t dnskey_digest_type;
189 u_char *dnskey_digest;
190 u_int dnskey_digest_len;
191
192 *flags = 0;
193
194 debug3("verify_host_key_dns");
195 if (hostkey == NULL)
196 fatal("No key to look up!");
197
198 if (is_numeric_hostname(hostname)) {
199 debug("skipped DNS lookup for numerical hostname");
200 return -1;
201 }
202
203 #ifndef ANDROID
204 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
205 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
206 #else
207 /* unsupported in android */
208 result = -1;
209 #endif
210 if (result) {
211 verbose("DNS lookup error: %s", dns_result_totext(result));
212 return -1;
213 }
214
215 if (fingerprints->rri_flags & RRSET_VALIDATED) {
216 *flags |= DNS_VERIFY_SECURE;
217 debug("found %d secure fingerprints in DNS",
218 fingerprints->rri_nrdatas);
219 } else {
220 debug("found %d insecure fingerprints in DNS",
221 fingerprints->rri_nrdatas);
222 }
223
224 /* Initialize host key parameters */
225 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
226 &hostkey_digest, &hostkey_digest_len, hostkey)) {
227 error("Error calculating host key fingerprint.");
228 #ifndef ANDROID
229 freerrset(fingerprints);
230 #endif
231 return -1;
232 }
233
234 if (fingerprints->rri_nrdatas)
235 *flags |= DNS_VERIFY_FOUND;
236
237 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
238 /*
239 * Extract the key from the answer. Ignore any badly
240 * formatted fingerprints.
241 */
242 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
243 &dnskey_digest, &dnskey_digest_len,
244 fingerprints->rri_rdatas[counter].rdi_data,
245 fingerprints->rri_rdatas[counter].rdi_length)) {
246 verbose("Error parsing fingerprint from DNS.");
247 continue;
248 }
249
250 /* Check if the current key is the same as the given key */
251 if (hostkey_algorithm == dnskey_algorithm &&
252 hostkey_digest_type == dnskey_digest_type) {
253
254 if (hostkey_digest_len == dnskey_digest_len &&
255 memcmp(hostkey_digest, dnskey_digest,
256 hostkey_digest_len) == 0) {
257
258 *flags |= DNS_VERIFY_MATCH;
259 }
260 }
261 xfree(dnskey_digest);
262 }
263
264 xfree(hostkey_digest); /* from key_fingerprint_raw() */
265 #ifndef ANDROID
266 freerrset(fingerprints);
267 #endif
268
269 if (*flags & DNS_VERIFY_FOUND)
270 if (*flags & DNS_VERIFY_MATCH)
271 debug("matching host key fingerprint found in DNS");
272 else
273 debug("mismatching host key fingerprint found in DNS");
274 else
275 debug("no host key fingerprint found in DNS");
276
277 return 0;
278 }
279
280 /*
281 * Export the fingerprint of a key as a DNS resource record
282 */
283 int
export_dns_rr(const char * hostname,Key * key,FILE * f,int generic)284 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
285 {
286 u_int8_t rdata_pubkey_algorithm = 0;
287 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
288 u_char *rdata_digest;
289 u_int rdata_digest_len;
290
291 u_int i;
292 int success = 0;
293
294 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
295 &rdata_digest, &rdata_digest_len, key)) {
296
297 if (generic)
298 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
299 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
300 rdata_pubkey_algorithm, rdata_digest_type);
301 else
302 fprintf(f, "%s IN SSHFP %d %d ", hostname,
303 rdata_pubkey_algorithm, rdata_digest_type);
304
305 for (i = 0; i < rdata_digest_len; i++)
306 fprintf(f, "%02x", rdata_digest[i]);
307 fprintf(f, "\n");
308 xfree(rdata_digest); /* from key_fingerprint_raw() */
309 success = 1;
310 } else {
311 error("export_dns_rr: unsupported algorithm");
312 }
313
314 return success;
315 }
316