1 /* $OpenBSD: dns.c,v 1.25 2008/06/12 00:03:49 dtucker Exp $ */
2
3 /*
4 * Copyright © 2013
5 * Thorsten “mirabilos” Glaser <tg@mirbsd.org>
6 * Copyright (c) 2003 Wesley Griffin. All rights reserved.
7 * Copyright (c) 2003 Jakob Schlyter. All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
22 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
23 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
27 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28 */
29
30 #include <sys/types.h>
31 #include <sys/socket.h>
32
33 #include <netdb.h>
34 #include <stdio.h>
35 #include <string.h>
36
37 #include "xmalloc.h"
38 #include "key.h"
39 #include "dns.h"
40 #include "log.h"
41
42 __RCSID("$MirOS: src/usr.bin/ssh/dns.c,v 1.7 2013/10/31 20:07:11 tg Exp $");
43
44 static const char *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 */
77 static int
dns_read_key(u_int8_t * algorithm,u_int8_t * digest_type,u_char ** digest,u_int * digest_len,const Key * key)78 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
79 u_char **digest, u_int *digest_len, const Key *key)
80 {
81 int success = 0;
82
83 switch (key->type) {
84 case KEY_RSA:
85 *algorithm = SSHFP_KEY_RSA;
86 break;
87 case KEY_DSA:
88 *algorithm = SSHFP_KEY_DSA;
89 break;
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,const Key * hostkey,int * flags)175 verify_host_key_dns(const char *hostname,
176 struct sockaddr *address __attribute__((__unused__)),
177 const Key *hostkey, int *flags)
178 {
179 u_int counter;
180 int result;
181 struct rrsetinfo *fingerprints = NULL;
182
183 u_int8_t hostkey_algorithm;
184 u_int8_t hostkey_digest_type;
185 u_char *hostkey_digest;
186 u_int hostkey_digest_len;
187
188 u_int8_t dnskey_algorithm;
189 u_int8_t dnskey_digest_type;
190 u_char *dnskey_digest;
191 u_int dnskey_digest_len;
192
193 *flags = 0;
194
195 debug3("verify_host_key_dns");
196 if (hostkey == NULL)
197 fatal("No key to look up!");
198
199 if (is_numeric_hostname(hostname)) {
200 debug("skipped DNS lookup for numerical hostname");
201 return -1;
202 }
203
204 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
205 DNS_RDATATYPE_SSHFP, 0, &fingerprints);
206 if (result) {
207 verbose("DNS lookup error: %s", dns_result_totext(result));
208 return -1;
209 }
210
211 if (fingerprints->rri_flags & RRSET_VALIDATED) {
212 *flags |= DNS_VERIFY_SECURE;
213 debug("found %d secure fingerprints in DNS",
214 fingerprints->rri_nrdatas);
215 } else {
216 debug("found %d insecure fingerprints in DNS",
217 fingerprints->rri_nrdatas);
218 }
219
220 /* Initialize host key parameters */
221 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
222 &hostkey_digest, &hostkey_digest_len, hostkey)) {
223 error("Error calculating host key fingerprint.");
224 freerrset(fingerprints);
225 return -1;
226 }
227
228 if (fingerprints->rri_nrdatas)
229 *flags |= DNS_VERIFY_FOUND;
230
231 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
232 /*
233 * Extract the key from the answer. Ignore any badly
234 * formatted fingerprints.
235 */
236 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
237 &dnskey_digest, &dnskey_digest_len,
238 fingerprints->rri_rdatas[counter].rdi_data,
239 fingerprints->rri_rdatas[counter].rdi_length)) {
240 verbose("Error parsing fingerprint from DNS.");
241 continue;
242 }
243
244 /* Check if the current key is the same as the given key */
245 if (hostkey_algorithm == dnskey_algorithm &&
246 hostkey_digest_type == dnskey_digest_type) {
247
248 if (hostkey_digest_len == dnskey_digest_len &&
249 memcmp(hostkey_digest, dnskey_digest,
250 hostkey_digest_len) == 0) {
251
252 *flags |= DNS_VERIFY_MATCH;
253 }
254 }
255 xfree(dnskey_digest);
256 }
257
258 xfree(hostkey_digest); /* from key_fingerprint_raw() */
259 freerrset(fingerprints);
260
261 if (*flags & DNS_VERIFY_FOUND)
262 if (*flags & DNS_VERIFY_MATCH)
263 debug("matching host key fingerprint found in DNS");
264 else
265 debug("mismatching host key fingerprint found in DNS");
266 else
267 debug("no host key fingerprint found in DNS");
268
269 return 0;
270 }
271
272 /*
273 * Export the fingerprint of a key as a DNS resource record
274 */
275 int
export_dns_rr(const char * hostname,const Key * key,FILE * f,int generic)276 export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
277 {
278 u_int8_t rdata_pubkey_algorithm = 0;
279 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
280 u_char *rdata_digest;
281 u_int rdata_digest_len;
282
283 u_int i;
284 int success = 0;
285
286 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
287 &rdata_digest, &rdata_digest_len, key)) {
288
289 if (generic)
290 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
291 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
292 rdata_pubkey_algorithm, rdata_digest_type);
293 else
294 fprintf(f, "%s IN SSHFP %d %d ", hostname,
295 rdata_pubkey_algorithm, rdata_digest_type);
296
297 for (i = 0; i < rdata_digest_len; i++)
298 fprintf(f, "%02x", rdata_digest[i]);
299 fprintf(f, "\n");
300 xfree(rdata_digest); /* from key_fingerprint_raw() */
301 success = 1;
302 } else {
303 error("export_dns_rr: unsupported algorithm");
304 }
305
306 return success;
307 }
308