1/* $OpenBSD: dns.c,v 1.44 2023/03/10 04:06:21 dtucker 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 <stdlib.h>
38
39#include "xmalloc.h"
40#include "sshkey.h"
41#include "ssherr.h"
42#include "dns.h"
43#include "log.h"
44#include "digest.h"
45
46static const char * const errset_text[] = {
47	"success",		/* 0 ERRSET_SUCCESS */
48	"out of memory",	/* 1 ERRSET_NOMEMORY */
49	"general failure",	/* 2 ERRSET_FAIL */
50	"invalid parameter",	/* 3 ERRSET_INVAL */
51	"name does not exist",	/* 4 ERRSET_NONAME */
52	"data does not exist",	/* 5 ERRSET_NODATA */
53};
54
55static const char *
56dns_result_totext(unsigned int res)
57{
58	switch (res) {
59	case ERRSET_SUCCESS:
60		return errset_text[ERRSET_SUCCESS];
61	case ERRSET_NOMEMORY:
62		return errset_text[ERRSET_NOMEMORY];
63	case ERRSET_FAIL:
64		return errset_text[ERRSET_FAIL];
65	case ERRSET_INVAL:
66		return errset_text[ERRSET_INVAL];
67	case ERRSET_NONAME:
68		return errset_text[ERRSET_NONAME];
69	case ERRSET_NODATA:
70		return errset_text[ERRSET_NODATA];
71	default:
72		return "unknown error";
73	}
74}
75
76/*
77 * Read SSHFP parameters from key buffer.
78 * Caller must free digest which is allocated by sshkey_fingerprint_raw().
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		break;
91	case KEY_DSA:
92		*algorithm = SSHFP_KEY_DSA;
93		break;
94	case KEY_ECDSA:
95		*algorithm = SSHFP_KEY_ECDSA;
96		break;
97	case KEY_ED25519:
98		*algorithm = SSHFP_KEY_ED25519;
99		break;
100	case KEY_XMSS:
101		*algorithm = SSHFP_KEY_XMSS;
102		break;
103	default:
104		*algorithm = SSHFP_KEY_RESERVED; /* 0 */
105	}
106
107	switch (*digest_type) {
108	case SSHFP_HASH_SHA1:
109		fp_alg = SSH_DIGEST_SHA1;
110		break;
111	case SSHFP_HASH_SHA256:
112		fp_alg = SSH_DIGEST_SHA256;
113		break;
114	default:
115		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
116	}
117
118	if (*algorithm && *digest_type) {
119		if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
120		    digest_len)) != 0)
121			fatal_fr(r, "sshkey_fingerprint_raw");
122		success = 1;
123	} else {
124		*digest = NULL;
125		*digest_len = 0;
126	}
127
128	return success;
129}
130
131/*
132 * Read SSHFP parameters from rdata buffer.
133 */
134static int
135dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
136    u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
137{
138	int success = 0;
139
140	*algorithm = SSHFP_KEY_RESERVED;
141	*digest_type = SSHFP_HASH_RESERVED;
142
143	if (rdata_len >= 2) {
144		*algorithm = rdata[0];
145		*digest_type = rdata[1];
146		*digest_len = rdata_len - 2;
147
148		if (*digest_len > 0) {
149			*digest = xmalloc(*digest_len);
150			memcpy(*digest, rdata + 2, *digest_len);
151		} else {
152			*digest = (u_char *)xstrdup("");
153		}
154
155		success = 1;
156	}
157
158	return success;
159}
160
161/*
162 * Check if hostname is numerical.
163 * Returns -1 if hostname is numeric, 0 otherwise
164 */
165static int
166is_numeric_hostname(const char *hostname)
167{
168	struct addrinfo hints, *ai;
169
170	/*
171	 * We shouldn't ever get a null host but if we do then log an error
172	 * and return -1 which stops DNS key fingerprint processing.
173	 */
174	if (hostname == NULL) {
175		error("is_numeric_hostname called with NULL hostname");
176		return -1;
177	}
178
179	memset(&hints, 0, sizeof(hints));
180	hints.ai_socktype = SOCK_DGRAM;
181	hints.ai_flags = AI_NUMERICHOST;
182
183	if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
184		freeaddrinfo(ai);
185		return -1;
186	}
187
188	return 0;
189}
190
191/*
192 * Verify the given hostname, address and host key using DNS.
193 * Returns 0 if lookup succeeds, -1 otherwise
194 */
195int
196verify_host_key_dns(const char *hostname, struct sockaddr *address,
197    struct sshkey *hostkey, int *flags)
198{
199	u_int counter;
200	int result;
201	struct rrsetinfo *fingerprints = NULL;
202
203	u_int8_t hostkey_algorithm;
204	u_char *hostkey_digest;
205	size_t hostkey_digest_len;
206
207	u_int8_t dnskey_algorithm;
208	u_int8_t dnskey_digest_type;
209	u_char *dnskey_digest;
210	size_t dnskey_digest_len;
211
212	*flags = 0;
213
214	debug3("verify_host_key_dns");
215	if (hostkey == NULL)
216		fatal("No key to look up!");
217
218	if (is_numeric_hostname(hostname)) {
219		debug("skipped DNS lookup for numerical hostname");
220		return -1;
221	}
222
223	result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
224	    DNS_RDATATYPE_SSHFP, 0, &fingerprints);
225	if (result) {
226		verbose("DNS lookup error: %s", dns_result_totext(result));
227		return -1;
228	}
229
230	if (fingerprints->rri_flags & RRSET_VALIDATED) {
231		*flags |= DNS_VERIFY_SECURE;
232		debug("found %d secure fingerprints in DNS",
233		    fingerprints->rri_nrdatas);
234	} else {
235		debug("found %d insecure fingerprints in DNS",
236		    fingerprints->rri_nrdatas);
237	}
238
239	if (fingerprints->rri_nrdatas)
240		*flags |= DNS_VERIFY_FOUND;
241
242	for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
243		/*
244		 * Extract the key from the answer. Ignore any badly
245		 * formatted fingerprints.
246		 */
247		if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
248		    &dnskey_digest, &dnskey_digest_len,
249		    fingerprints->rri_rdatas[counter].rdi_data,
250		    fingerprints->rri_rdatas[counter].rdi_length)) {
251			verbose("Error parsing fingerprint from DNS.");
252			continue;
253		}
254		debug3_f("checking SSHFP type %d fptype %d", dnskey_algorithm,
255		    dnskey_digest_type);
256
257		/* Calculate host key fingerprint. */
258		if (!dns_read_key(&hostkey_algorithm, &dnskey_digest_type,
259		    &hostkey_digest, &hostkey_digest_len, hostkey)) {
260			error("Error calculating key fingerprint.");
261			free(dnskey_digest);
262			freerrset(fingerprints);
263			return -1;
264		}
265
266		/* Check if the current key is the same as the given key */
267		if (hostkey_algorithm == dnskey_algorithm &&
268		    hostkey_digest_len == dnskey_digest_len) {
269			if (timingsafe_bcmp(hostkey_digest, dnskey_digest,
270			    hostkey_digest_len) == 0) {
271				debug_f("matched SSHFP type %d fptype %d",
272				    dnskey_algorithm, dnskey_digest_type);
273				*flags |= DNS_VERIFY_MATCH;
274			} else {
275				debug_f("failed SSHFP type %d fptype %d",
276				    dnskey_algorithm, dnskey_digest_type);
277				*flags |= DNS_VERIFY_FAILED;
278			}
279		}
280		free(dnskey_digest);
281		free(hostkey_digest); /* from sshkey_fingerprint_raw() */
282	}
283
284	freerrset(fingerprints);
285
286	/* If any fingerprint failed to validate, return failure. */
287	if (*flags & DNS_VERIFY_FAILED)
288		*flags &= ~DNS_VERIFY_MATCH;
289
290	if (*flags & DNS_VERIFY_FOUND)
291		if (*flags & DNS_VERIFY_MATCH)
292			debug("matching host key fingerprint found in DNS");
293		else
294			debug("mismatching host key fingerprint found in DNS");
295	else
296		debug("no host key fingerprint found in DNS");
297
298	return 0;
299}
300
301/*
302 * Export the fingerprint of a key as a DNS resource record
303 */
304int
305export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic,
306    int alg)
307{
308	u_int8_t rdata_pubkey_algorithm = 0;
309	u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
310	u_int8_t dtype;
311	u_char *rdata_digest;
312	size_t i, rdata_digest_len;
313	int success = 0;
314
315	for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
316		if (alg != -1 && dtype != alg)
317			continue;
318		rdata_digest_type = dtype;
319		if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
320		    &rdata_digest, &rdata_digest_len, key)) {
321			if (generic) {
322				fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
323				    hostname, DNS_RDATATYPE_SSHFP,
324				    2 + rdata_digest_len,
325				    rdata_pubkey_algorithm, rdata_digest_type);
326			} else {
327				fprintf(f, "%s IN SSHFP %d %d ", hostname,
328				    rdata_pubkey_algorithm, rdata_digest_type);
329			}
330			for (i = 0; i < rdata_digest_len; i++)
331				fprintf(f, "%02x", rdata_digest[i]);
332			fprintf(f, "\n");
333			free(rdata_digest); /* from sshkey_fingerprint_raw() */
334			success = 1;
335		}
336	}
337
338	/* No SSHFP record was generated at all */
339	if (success == 0) {
340		error_f("unsupported algorithm and/or digest_type");
341	}
342
343	return success;
344}
345