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1 /* $OpenBSD: dns.c,v 1.35 2015/08/20 22:32:42 deraadt 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 <stdarg.h>
38 #include <stdlib.h>
39 
40 #include "xmalloc.h"
41 #include "sshkey.h"
42 #include "ssherr.h"
43 #include "dns.h"
44 #include "log.h"
45 #include "digest.h"
46 
47 static const char *errset_text[] = {
48 	"success",		/* 0 ERRSET_SUCCESS */
49 	"out of memory",	/* 1 ERRSET_NOMEMORY */
50 	"general failure",	/* 2 ERRSET_FAIL */
51 	"invalid parameter",	/* 3 ERRSET_INVAL */
52 	"name does not exist",	/* 4 ERRSET_NONAME */
53 	"data does not exist",	/* 5 ERRSET_NODATA */
54 };
55 
56 static const char *
dns_result_totext(unsigned int res)57 dns_result_totext(unsigned int res)
58 {
59 	switch (res) {
60 	case ERRSET_SUCCESS:
61 		return errset_text[ERRSET_SUCCESS];
62 	case ERRSET_NOMEMORY:
63 		return errset_text[ERRSET_NOMEMORY];
64 	case ERRSET_FAIL:
65 		return errset_text[ERRSET_FAIL];
66 	case ERRSET_INVAL:
67 		return errset_text[ERRSET_INVAL];
68 	case ERRSET_NONAME:
69 		return errset_text[ERRSET_NONAME];
70 	case ERRSET_NODATA:
71 		return errset_text[ERRSET_NODATA];
72 	default:
73 		return "unknown error";
74 	}
75 }
76 
77 /*
78  * Read SSHFP parameters from key buffer.
79  */
80 static int
dns_read_key(u_int8_t * algorithm,u_int8_t * digest_type,u_char ** digest,size_t * digest_len,struct sshkey * key)81 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
82     u_char **digest, size_t *digest_len, struct sshkey *key)
83 {
84 	int r, success = 0;
85 	int fp_alg = -1;
86 
87 	switch (key->type) {
88 	case KEY_RSA:
89 		*algorithm = SSHFP_KEY_RSA;
90 		if (!*digest_type)
91 			*digest_type = SSHFP_HASH_SHA1;
92 		break;
93 	case KEY_DSA:
94 		*algorithm = SSHFP_KEY_DSA;
95 		if (!*digest_type)
96 			*digest_type = SSHFP_HASH_SHA1;
97 		break;
98 	case KEY_ECDSA:
99 		*algorithm = SSHFP_KEY_ECDSA;
100 		if (!*digest_type)
101 			*digest_type = SSHFP_HASH_SHA256;
102 		break;
103 	case KEY_ED25519:
104 		*algorithm = SSHFP_KEY_ED25519;
105 		if (!*digest_type)
106 			*digest_type = SSHFP_HASH_SHA256;
107 		break;
108 	default:
109 		*algorithm = SSHFP_KEY_RESERVED; /* 0 */
110 		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
111 	}
112 
113 	switch (*digest_type) {
114 	case SSHFP_HASH_SHA1:
115 		fp_alg = SSH_DIGEST_SHA1;
116 		break;
117 	case SSHFP_HASH_SHA256:
118 		fp_alg = SSH_DIGEST_SHA256;
119 		break;
120 	default:
121 		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
122 	}
123 
124 	if (*algorithm && *digest_type) {
125 		if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
126 		    digest_len)) != 0)
127 			fatal("%s: sshkey_fingerprint_raw: %s", __func__,
128 			   ssh_err(r));
129 		success = 1;
130 	} else {
131 		*digest = NULL;
132 		*digest_len = 0;
133 		success = 0;
134 	}
135 
136 	return success;
137 }
138 
139 /*
140  * Read SSHFP parameters from rdata buffer.
141  */
142 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)143 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
144     u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
145 {
146 	int success = 0;
147 
148 	*algorithm = SSHFP_KEY_RESERVED;
149 	*digest_type = SSHFP_HASH_RESERVED;
150 
151 	if (rdata_len >= 2) {
152 		*algorithm = rdata[0];
153 		*digest_type = rdata[1];
154 		*digest_len = rdata_len - 2;
155 
156 		if (*digest_len > 0) {
157 			*digest = xmalloc(*digest_len);
158 			memcpy(*digest, rdata + 2, *digest_len);
159 		} else {
160 			*digest = (u_char *)xstrdup("");
161 		}
162 
163 		success = 1;
164 	}
165 
166 	return success;
167 }
168 
169 /*
170  * Check if hostname is numerical.
171  * Returns -1 if hostname is numeric, 0 otherwise
172  */
173 static int
is_numeric_hostname(const char * hostname)174 is_numeric_hostname(const char *hostname)
175 {
176 	struct addrinfo hints, *ai;
177 
178 	/*
179 	 * We shouldn't ever get a null host but if we do then log an error
180 	 * and return -1 which stops DNS key fingerprint processing.
181 	 */
182 	if (hostname == NULL) {
183 		error("is_numeric_hostname called with NULL hostname");
184 		return -1;
185 	}
186 
187 	memset(&hints, 0, sizeof(hints));
188 	hints.ai_socktype = SOCK_DGRAM;
189 	hints.ai_flags = AI_NUMERICHOST;
190 
191 	if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
192 		freeaddrinfo(ai);
193 		return -1;
194 	}
195 
196 	return 0;
197 }
198 
199 /*
200  * Verify the given hostname, address and host key using DNS.
201  * Returns 0 if lookup succeeds, -1 otherwise
202  */
203 int
verify_host_key_dns(const char * hostname,struct sockaddr * address,struct sshkey * hostkey,int * flags)204 verify_host_key_dns(const char *hostname, struct sockaddr *address,
205     struct sshkey *hostkey, int *flags)
206 {
207 	u_int counter;
208 	int result;
209 	struct rrsetinfo *fingerprints = NULL;
210 
211 	u_int8_t hostkey_algorithm;
212 	u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
213 	u_char *hostkey_digest;
214 	size_t hostkey_digest_len;
215 
216 	u_int8_t dnskey_algorithm;
217 	u_int8_t dnskey_digest_type;
218 	u_char *dnskey_digest;
219 	size_t dnskey_digest_len;
220 
221 	*flags = 0;
222 
223 	debug3("verify_host_key_dns");
224 	if (hostkey == NULL)
225 		fatal("No key to look up!");
226 
227 	if (is_numeric_hostname(hostname)) {
228 		debug("skipped DNS lookup for numerical hostname");
229 		return -1;
230 	}
231 
232 #if !defined(ANDROID)
233 	result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
234 	    DNS_RDATATYPE_SSHFP, 0, &fingerprints);
235 #else
236 	/* unsupported in Android. */
237 	result = -1;
238 #endif
239 
240 	if (result) {
241 		verbose("DNS lookup error: %s", dns_result_totext(result));
242 		return -1;
243 	}
244 
245 	if (fingerprints->rri_flags & RRSET_VALIDATED) {
246 		*flags |= DNS_VERIFY_SECURE;
247 		debug("found %d secure fingerprints in DNS",
248 		    fingerprints->rri_nrdatas);
249 	} else {
250 		debug("found %d insecure fingerprints in DNS",
251 		    fingerprints->rri_nrdatas);
252 	}
253 
254 	/* Initialize default host key parameters */
255 	if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
256 	    &hostkey_digest, &hostkey_digest_len, hostkey)) {
257 		error("Error calculating host key fingerprint.");
258 #if !defined(ANDROID)
259 		freerrset(fingerprints);
260 #endif
261 		return -1;
262 	}
263 
264 	if (fingerprints->rri_nrdatas)
265 		*flags |= DNS_VERIFY_FOUND;
266 
267 	for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
268 		/*
269 		 * Extract the key from the answer. Ignore any badly
270 		 * formatted fingerprints.
271 		 */
272 		if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
273 		    &dnskey_digest, &dnskey_digest_len,
274 		    fingerprints->rri_rdatas[counter].rdi_data,
275 		    fingerprints->rri_rdatas[counter].rdi_length)) {
276 			verbose("Error parsing fingerprint from DNS.");
277 			continue;
278 		}
279 
280 		if (hostkey_digest_type != dnskey_digest_type) {
281 			hostkey_digest_type = dnskey_digest_type;
282 			free(hostkey_digest);
283 
284 			/* Initialize host key parameters */
285 			if (!dns_read_key(&hostkey_algorithm,
286 			    &hostkey_digest_type, &hostkey_digest,
287 			    &hostkey_digest_len, hostkey)) {
288 				error("Error calculating key fingerprint.");
289 #if !defined(ANDROID)
290 				freerrset(fingerprints);
291 #endif
292 				return -1;
293 			}
294 		}
295 
296 		/* Check if the current key is the same as the given key */
297 		if (hostkey_algorithm == dnskey_algorithm &&
298 		    hostkey_digest_type == dnskey_digest_type) {
299 			if (hostkey_digest_len == dnskey_digest_len &&
300 			    timingsafe_bcmp(hostkey_digest, dnskey_digest,
301 			    hostkey_digest_len) == 0)
302 				*flags |= DNS_VERIFY_MATCH;
303 		}
304 		free(dnskey_digest);
305 	}
306 
307 	free(hostkey_digest); /* from sshkey_fingerprint_raw() */
308 #if !defined(ANDROID)
309 	freerrset(fingerprints);
310 #endif
311 
312 	if (*flags & DNS_VERIFY_FOUND)
313 		if (*flags & DNS_VERIFY_MATCH)
314 			debug("matching host key fingerprint found in DNS");
315 		else
316 			debug("mismatching host key fingerprint found in DNS");
317 	else
318 		debug("no host key fingerprint found in DNS");
319 
320 	return 0;
321 }
322 
323 /*
324  * Export the fingerprint of a key as a DNS resource record
325  */
326 int
export_dns_rr(const char * hostname,struct sshkey * key,FILE * f,int generic)327 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
328 {
329 	u_int8_t rdata_pubkey_algorithm = 0;
330 	u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
331 	u_int8_t dtype;
332 	u_char *rdata_digest;
333 	size_t i, rdata_digest_len;
334 	int success = 0;
335 
336 	for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
337 		rdata_digest_type = dtype;
338 		if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
339 		    &rdata_digest, &rdata_digest_len, key)) {
340 			if (generic) {
341 				fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
342 				    hostname, DNS_RDATATYPE_SSHFP,
343 				    2 + rdata_digest_len,
344 				    rdata_pubkey_algorithm, rdata_digest_type);
345 			} else {
346 				fprintf(f, "%s IN SSHFP %d %d ", hostname,
347 				    rdata_pubkey_algorithm, rdata_digest_type);
348 			}
349 			for (i = 0; i < rdata_digest_len; i++)
350 				fprintf(f, "%02x", rdata_digest[i]);
351 			fprintf(f, "\n");
352 			free(rdata_digest); /* from sshkey_fingerprint_raw() */
353 			success = 1;
354 		}
355 	}
356 
357 	/* No SSHFP record was generated at all */
358 	if (success == 0) {
359 		error("%s: unsupported algorithm and/or digest_type", __func__);
360 	}
361 
362 	return success;
363 }
364