1/*	$NetBSD: dns.c,v 1.23 2023/07/26 17:58:15 christos Exp $	*/
2/* $OpenBSD: dns.c,v 1.44 2023/03/10 04:06:21 dtucker Exp $ */
3
4/*
5 * Copyright (c) 2003 Wesley Griffin. All rights reserved.
6 * Copyright (c) 2003 Jakob Schlyter. All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29#include "includes.h"
30__RCSID("$NetBSD: dns.c,v 1.23 2023/07/26 17:58:15 christos Exp $");
31#include <sys/types.h>
32#include <sys/socket.h>
33
34#include <netdb.h>
35#include <stdarg.h>
36#include <stdio.h>
37#include <string.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 "getrrsetbyname.h"
46#include "digest.h"
47
48static const char * const errset_text[] = {
49	"success",		/* 0 ERRSET_SUCCESS */
50	"out of memory",	/* 1 ERRSET_NOMEMORY */
51	"general failure",	/* 2 ERRSET_FAIL */
52	"invalid parameter",	/* 3 ERRSET_INVAL */
53	"name does not exist",	/* 4 ERRSET_NONAME */
54	"data does not exist",	/* 5 ERRSET_NODATA */
55};
56
57static const char *
58dns_result_totext(unsigned int res)
59{
60	switch (res) {
61	case ERRSET_SUCCESS:
62		return errset_text[ERRSET_SUCCESS];
63	case ERRSET_NOMEMORY:
64		return errset_text[ERRSET_NOMEMORY];
65	case ERRSET_FAIL:
66		return errset_text[ERRSET_FAIL];
67	case ERRSET_INVAL:
68		return errset_text[ERRSET_INVAL];
69	case ERRSET_NONAME:
70		return errset_text[ERRSET_NONAME];
71	case ERRSET_NODATA:
72		return errset_text[ERRSET_NODATA];
73	default:
74		return "unknown error";
75	}
76}
77
78/*
79 * Read SSHFP parameters from key buffer.
80 * Caller must free digest which is allocated by sshkey_fingerprint_raw().
81 */
82static int
83dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
84    u_char **digest, size_t *digest_len, struct sshkey *key)
85{
86	int r, success = 0;
87	int fp_alg = -1;
88
89	switch (key->type) {
90	case KEY_RSA:
91		*algorithm = SSHFP_KEY_RSA;
92		break;
93	case KEY_DSA:
94		*algorithm = SSHFP_KEY_DSA;
95		break;
96	case KEY_ECDSA:
97		*algorithm = SSHFP_KEY_ECDSA;
98		break;
99	case KEY_ED25519:
100		*algorithm = SSHFP_KEY_ED25519;
101		break;
102	case KEY_XMSS:
103		*algorithm = SSHFP_KEY_XMSS;
104		break;
105	default:
106		*algorithm = SSHFP_KEY_RESERVED; /* 0 */
107	}
108
109	switch (*digest_type) {
110	case SSHFP_HASH_SHA1:
111		fp_alg = SSH_DIGEST_SHA1;
112		break;
113	case SSHFP_HASH_SHA256:
114		fp_alg = SSH_DIGEST_SHA256;
115		break;
116	default:
117		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
118	}
119
120	if (*algorithm && *digest_type) {
121		if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
122		    digest_len)) != 0)
123			fatal_fr(r, "sshkey_fingerprint_raw");
124		success = 1;
125	} else {
126		*digest = NULL;
127		*digest_len = 0;
128	}
129
130	return success;
131}
132
133/*
134 * Read SSHFP parameters from rdata buffer.
135 */
136static int
137dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
138    u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
139{
140	int success = 0;
141
142	*algorithm = SSHFP_KEY_RESERVED;
143	*digest_type = SSHFP_HASH_RESERVED;
144
145	if (rdata_len >= 2) {
146		*algorithm = rdata[0];
147		*digest_type = rdata[1];
148		*digest_len = rdata_len - 2;
149
150		if (*digest_len > 0) {
151			*digest = xmalloc(*digest_len);
152			memcpy(*digest, rdata + 2, *digest_len);
153		} else {
154			*digest = (u_char *)xstrdup("");
155		}
156
157		success = 1;
158	}
159
160	return success;
161}
162
163/*
164 * Check if hostname is numerical.
165 * Returns -1 if hostname is numeric, 0 otherwise
166 */
167static int
168is_numeric_hostname(const char *hostname)
169{
170	struct addrinfo hints, *ai;
171
172	/*
173	 * We shouldn't ever get a null host but if we do then log an error
174	 * and return -1 which stops DNS key fingerprint processing.
175	 */
176	if (hostname == NULL) {
177		error("is_numeric_hostname called with NULL hostname");
178		return -1;
179	}
180
181	memset(&hints, 0, sizeof(hints));
182	hints.ai_socktype = SOCK_DGRAM;
183	hints.ai_flags = AI_NUMERICHOST;
184
185	if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
186		freeaddrinfo(ai);
187		return -1;
188	}
189
190	return 0;
191}
192
193/*
194 * Verify the given hostname, address and host key using DNS.
195 * Returns 0 if lookup succeeds, -1 otherwise
196 */
197int
198verify_host_key_dns(const char *hostname, struct sockaddr *address,
199    struct sshkey *hostkey, int *flags)
200{
201	u_int counter;
202	int result;
203	struct rrsetinfo *fingerprints = NULL;
204
205	u_int8_t hostkey_algorithm;
206	u_char *hostkey_digest;
207	size_t hostkey_digest_len;
208
209	u_int8_t dnskey_algorithm;
210	u_int8_t dnskey_digest_type;
211	u_char *dnskey_digest;
212	size_t dnskey_digest_len;
213
214	*flags = 0;
215
216	debug3("verify_host_key_dns");
217	if (hostkey == NULL)
218		fatal("No key to look up!");
219
220	if (is_numeric_hostname(hostname)) {
221		debug("skipped DNS lookup for numerical hostname");
222		return -1;
223	}
224
225	result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
226	    DNS_RDATATYPE_SSHFP, 0, &fingerprints);
227	if (result) {
228		verbose("DNS lookup error: %s", dns_result_totext(result));
229		return -1;
230	}
231
232	if (fingerprints->rri_flags & RRSET_VALIDATED) {
233		*flags |= DNS_VERIFY_SECURE;
234		debug("found %d secure fingerprints in DNS",
235		    fingerprints->rri_nrdatas);
236	} else {
237		debug("found %d insecure fingerprints in DNS",
238		    fingerprints->rri_nrdatas);
239	}
240
241	if (fingerprints->rri_nrdatas)
242		*flags |= DNS_VERIFY_FOUND;
243
244	for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
245		/*
246		 * Extract the key from the answer. Ignore any badly
247		 * formatted fingerprints.
248		 */
249		if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
250		    &dnskey_digest, &dnskey_digest_len,
251		    fingerprints->rri_rdatas[counter].rdi_data,
252		    fingerprints->rri_rdatas[counter].rdi_length)) {
253			verbose("Error parsing fingerprint from DNS.");
254			continue;
255		}
256		debug3_f("checking SSHFP type %d fptype %d", dnskey_algorithm,
257		    dnskey_digest_type);
258
259		/* Calculate host key fingerprint. */
260		if (!dns_read_key(&hostkey_algorithm, &dnskey_digest_type,
261		    &hostkey_digest, &hostkey_digest_len, hostkey)) {
262			error("Error calculating key fingerprint.");
263			free(dnskey_digest);
264			freerrset(fingerprints);
265			return -1;
266		}
267
268		/* Check if the current key is the same as the given key */
269		if (hostkey_algorithm == dnskey_algorithm &&
270		    hostkey_digest_len == dnskey_digest_len) {
271			if (timingsafe_bcmp(hostkey_digest, dnskey_digest,
272			    hostkey_digest_len) == 0) {
273				debug_f("matched SSHFP type %d fptype %d",
274				    dnskey_algorithm, dnskey_digest_type);
275				*flags |= DNS_VERIFY_MATCH;
276			} else {
277				debug_f("failed SSHFP type %d fptype %d",
278				    dnskey_algorithm, dnskey_digest_type);
279				*flags |= DNS_VERIFY_FAILED;
280			}
281		}
282		free(dnskey_digest);
283		free(hostkey_digest); /* from sshkey_fingerprint_raw() */
284	}
285
286	freerrset(fingerprints);
287
288	/* If any fingerprint failed to validate, return failure. */
289	if (*flags & DNS_VERIFY_FAILED)
290		*flags &= ~DNS_VERIFY_MATCH;
291
292	if (*flags & DNS_VERIFY_FOUND)
293		if (*flags & DNS_VERIFY_MATCH)
294			debug("matching host key fingerprint found in DNS");
295		else
296			debug("mismatching host key fingerprint found in DNS");
297	else
298		debug("no host key fingerprint found in DNS");
299
300	return 0;
301}
302
303/*
304 * Export the fingerprint of a key as a DNS resource record
305 */
306int
307export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic,
308    int alg)
309{
310	u_int8_t rdata_pubkey_algorithm = 0;
311	u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
312	u_int8_t dtype;
313	u_char *rdata_digest;
314	size_t i, rdata_digest_len;
315	int success = 0;
316
317	for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
318		if (alg != -1 && dtype != alg)
319			continue;
320		rdata_digest_type = dtype;
321		if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
322		    &rdata_digest, &rdata_digest_len, key)) {
323			if (generic) {
324				fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
325				    hostname, DNS_RDATATYPE_SSHFP,
326				    2 + rdata_digest_len,
327				    rdata_pubkey_algorithm, rdata_digest_type);
328			} else {
329				fprintf(f, "%s IN SSHFP %d %d ", hostname,
330				    rdata_pubkey_algorithm, rdata_digest_type);
331			}
332			for (i = 0; i < rdata_digest_len; i++)
333				fprintf(f, "%02x", rdata_digest[i]);
334			fprintf(f, "\n");
335			free(rdata_digest); /* from sshkey_fingerprint_raw() */
336			success = 1;
337		}
338	}
339
340	/* No SSHFP record was generated at all */
341	if (success == 0) {
342		error_f("unsupported algorithm and/or digest_type");
343	}
344
345	return success;
346}
347