1/* $OpenBSD: dns.c,v 1.38 2018/02/23 15:58:37 markus 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
47static 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
56static const char *
57dns_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 */
80static int
81dns_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	case KEY_XMSS:
109		*algorithm = SSHFP_KEY_XMSS;
110		if (!*digest_type)
111			*digest_type = SSHFP_HASH_SHA256;
112		break;
113	default:
114		*algorithm = SSHFP_KEY_RESERVED; /* 0 */
115		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
116	}
117
118	switch (*digest_type) {
119	case SSHFP_HASH_SHA1:
120		fp_alg = SSH_DIGEST_SHA1;
121		break;
122	case SSHFP_HASH_SHA256:
123		fp_alg = SSH_DIGEST_SHA256;
124		break;
125	default:
126		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
127	}
128
129	if (*algorithm && *digest_type) {
130		if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
131		    digest_len)) != 0)
132			fatal("%s: sshkey_fingerprint_raw: %s", __func__,
133			   ssh_err(r));
134		success = 1;
135	} else {
136		*digest = NULL;
137		*digest_len = 0;
138		success = 0;
139	}
140
141	return success;
142}
143
144/*
145 * Read SSHFP parameters from rdata buffer.
146 */
147static int
148dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
149    u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
150{
151	int success = 0;
152
153	*algorithm = SSHFP_KEY_RESERVED;
154	*digest_type = SSHFP_HASH_RESERVED;
155
156	if (rdata_len >= 2) {
157		*algorithm = rdata[0];
158		*digest_type = rdata[1];
159		*digest_len = rdata_len - 2;
160
161		if (*digest_len > 0) {
162			*digest = xmalloc(*digest_len);
163			memcpy(*digest, rdata + 2, *digest_len);
164		} else {
165			*digest = (u_char *)xstrdup("");
166		}
167
168		success = 1;
169	}
170
171	return success;
172}
173
174/*
175 * Check if hostname is numerical.
176 * Returns -1 if hostname is numeric, 0 otherwise
177 */
178static int
179is_numeric_hostname(const char *hostname)
180{
181	struct addrinfo hints, *ai;
182
183	/*
184	 * We shouldn't ever get a null host but if we do then log an error
185	 * and return -1 which stops DNS key fingerprint processing.
186	 */
187	if (hostname == NULL) {
188		error("is_numeric_hostname called with NULL hostname");
189		return -1;
190	}
191
192	memset(&hints, 0, sizeof(hints));
193	hints.ai_socktype = SOCK_DGRAM;
194	hints.ai_flags = AI_NUMERICHOST;
195
196	if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
197		freeaddrinfo(ai);
198		return -1;
199	}
200
201	return 0;
202}
203
204/*
205 * Verify the given hostname, address and host key using DNS.
206 * Returns 0 if lookup succeeds, -1 otherwise
207 */
208int
209verify_host_key_dns(const char *hostname, struct sockaddr *address,
210    struct sshkey *hostkey, int *flags)
211{
212	u_int counter;
213	int result;
214	struct rrsetinfo *fingerprints = NULL;
215
216	u_int8_t hostkey_algorithm;
217	u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
218	u_char *hostkey_digest;
219	size_t hostkey_digest_len;
220
221	u_int8_t dnskey_algorithm;
222	u_int8_t dnskey_digest_type;
223	u_char *dnskey_digest;
224	size_t dnskey_digest_len;
225
226	*flags = 0;
227
228	debug3("verify_host_key_dns");
229	if (hostkey == NULL)
230		fatal("No key to look up!");
231
232	if (is_numeric_hostname(hostname)) {
233		debug("skipped DNS lookup for numerical hostname");
234		return -1;
235	}
236
237	result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
238	    DNS_RDATATYPE_SSHFP, 0, &fingerprints);
239	if (result) {
240		verbose("DNS lookup error: %s", dns_result_totext(result));
241		return -1;
242	}
243
244	if (fingerprints->rri_flags & RRSET_VALIDATED) {
245		*flags |= DNS_VERIFY_SECURE;
246		debug("found %d secure fingerprints in DNS",
247		    fingerprints->rri_nrdatas);
248	} else {
249		debug("found %d insecure fingerprints in DNS",
250		    fingerprints->rri_nrdatas);
251	}
252
253	/* Initialize default host key parameters */
254	if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
255	    &hostkey_digest, &hostkey_digest_len, hostkey)) {
256		error("Error calculating host key fingerprint.");
257		freerrset(fingerprints);
258		return -1;
259	}
260
261	if (fingerprints->rri_nrdatas)
262		*flags |= DNS_VERIFY_FOUND;
263
264	for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
265		/*
266		 * Extract the key from the answer. Ignore any badly
267		 * formatted fingerprints.
268		 */
269		if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
270		    &dnskey_digest, &dnskey_digest_len,
271		    fingerprints->rri_rdatas[counter].rdi_data,
272		    fingerprints->rri_rdatas[counter].rdi_length)) {
273			verbose("Error parsing fingerprint from DNS.");
274			continue;
275		}
276
277		if (hostkey_digest_type != dnskey_digest_type) {
278			hostkey_digest_type = dnskey_digest_type;
279			free(hostkey_digest);
280
281			/* Initialize host key parameters */
282			if (!dns_read_key(&hostkey_algorithm,
283			    &hostkey_digest_type, &hostkey_digest,
284			    &hostkey_digest_len, hostkey)) {
285				error("Error calculating key fingerprint.");
286				freerrset(fingerprints);
287				return -1;
288			}
289		}
290
291		/* Check if the current key is the same as the given key */
292		if (hostkey_algorithm == dnskey_algorithm &&
293		    hostkey_digest_type == dnskey_digest_type) {
294			if (hostkey_digest_len == dnskey_digest_len &&
295			    timingsafe_bcmp(hostkey_digest, dnskey_digest,
296			    hostkey_digest_len) == 0)
297				*flags |= DNS_VERIFY_MATCH;
298		}
299		free(dnskey_digest);
300	}
301
302	free(hostkey_digest); /* from sshkey_fingerprint_raw() */
303	freerrset(fingerprints);
304
305	if (*flags & DNS_VERIFY_FOUND)
306		if (*flags & DNS_VERIFY_MATCH)
307			debug("matching host key fingerprint found in DNS");
308		else
309			debug("mismatching host key fingerprint found in DNS");
310	else
311		debug("no host key fingerprint found in DNS");
312
313	return 0;
314}
315
316/*
317 * Export the fingerprint of a key as a DNS resource record
318 */
319int
320export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
321{
322	u_int8_t rdata_pubkey_algorithm = 0;
323	u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
324	u_int8_t dtype;
325	u_char *rdata_digest;
326	size_t i, rdata_digest_len;
327	int success = 0;
328
329	for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
330		rdata_digest_type = dtype;
331		if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
332		    &rdata_digest, &rdata_digest_len, key)) {
333			if (generic) {
334				fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
335				    hostname, DNS_RDATATYPE_SSHFP,
336				    2 + rdata_digest_len,
337				    rdata_pubkey_algorithm, rdata_digest_type);
338			} else {
339				fprintf(f, "%s IN SSHFP %d %d ", hostname,
340				    rdata_pubkey_algorithm, rdata_digest_type);
341			}
342			for (i = 0; i < rdata_digest_len; i++)
343				fprintf(f, "%02x", rdata_digest[i]);
344			fprintf(f, "\n");
345			free(rdata_digest); /* from sshkey_fingerprint_raw() */
346			success = 1;
347		}
348	}
349
350	/* No SSHFP record was generated at all */
351	if (success == 0) {
352		error("%s: unsupported algorithm and/or digest_type", __func__);
353	}
354
355	return success;
356}
357