File: dns.c

package info (click to toggle)
openssh 1:7.9p1-10
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, buster, sid
  • size: 14,136 kB
  • sloc: ansic: 101,922; sh: 11,876; makefile: 1,338; awk: 341; cpp: 82; python: 37; csh: 1
file content (368 lines) | stat: -rw-r--r-- 9,757 bytes parent folder | download | duplicates (2)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
/* $OpenBSD: dns.c,v 1.38 2018/02/23 15:58:37 markus Exp $ */

/*
 * Copyright (c) 2003 Wesley Griffin. All rights reserved.
 * Copyright (c) 2003 Jakob Schlyter. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/socket.h>

#include <netdb.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>
#include <stdlib.h>

#include "xmalloc.h"
#include "sshkey.h"
#include "ssherr.h"
#include "dns.h"
#include "log.h"
#include "digest.h"

static const char *errset_text[] = {
	"success",		/* 0 ERRSET_SUCCESS */
	"out of memory",	/* 1 ERRSET_NOMEMORY */
	"general failure",	/* 2 ERRSET_FAIL */
	"invalid parameter",	/* 3 ERRSET_INVAL */
	"name does not exist",	/* 4 ERRSET_NONAME */
	"data does not exist",	/* 5 ERRSET_NODATA */
};

static const char *
dns_result_totext(unsigned int res)
{
	switch (res) {
	case ERRSET_SUCCESS:
		return errset_text[ERRSET_SUCCESS];
	case ERRSET_NOMEMORY:
		return errset_text[ERRSET_NOMEMORY];
	case ERRSET_FAIL:
		return errset_text[ERRSET_FAIL];
	case ERRSET_INVAL:
		return errset_text[ERRSET_INVAL];
	case ERRSET_NONAME:
		return errset_text[ERRSET_NONAME];
	case ERRSET_NODATA:
		return errset_text[ERRSET_NODATA];
	default:
		return "unknown error";
	}
}

/*
 * Read SSHFP parameters from key buffer.
 */
static int
dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
    u_char **digest, size_t *digest_len, struct sshkey *key)
{
	int r, success = 0;
	int fp_alg = -1;

	switch (key->type) {
	case KEY_RSA:
		*algorithm = SSHFP_KEY_RSA;
		if (!*digest_type)
			*digest_type = SSHFP_HASH_SHA1;
		break;
	case KEY_DSA:
		*algorithm = SSHFP_KEY_DSA;
		if (!*digest_type)
			*digest_type = SSHFP_HASH_SHA1;
		break;
	case KEY_ECDSA:
		*algorithm = SSHFP_KEY_ECDSA;
		if (!*digest_type)
			*digest_type = SSHFP_HASH_SHA256;
		break;
	case KEY_ED25519:
		*algorithm = SSHFP_KEY_ED25519;
		if (!*digest_type)
			*digest_type = SSHFP_HASH_SHA256;
		break;
	case KEY_XMSS:
		*algorithm = SSHFP_KEY_XMSS;
		if (!*digest_type)
			*digest_type = SSHFP_HASH_SHA256;
		break;
	default:
		*algorithm = SSHFP_KEY_RESERVED; /* 0 */
		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
	}

	switch (*digest_type) {
	case SSHFP_HASH_SHA1:
		fp_alg = SSH_DIGEST_SHA1;
		break;
	case SSHFP_HASH_SHA256:
		fp_alg = SSH_DIGEST_SHA256;
		break;
	default:
		*digest_type = SSHFP_HASH_RESERVED; /* 0 */
	}

	if (*algorithm && *digest_type) {
		if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
		    digest_len)) != 0)
			fatal("%s: sshkey_fingerprint_raw: %s", __func__,
			   ssh_err(r));
		success = 1;
	} else {
		*digest = NULL;
		*digest_len = 0;
		success = 0;
	}

	return success;
}

/*
 * Read SSHFP parameters from rdata buffer.
 */
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)
{
	int success = 0;

	*algorithm = SSHFP_KEY_RESERVED;
	*digest_type = SSHFP_HASH_RESERVED;

	if (rdata_len >= 2) {
		*algorithm = rdata[0];
		*digest_type = rdata[1];
		*digest_len = rdata_len - 2;

		if (*digest_len > 0) {
			*digest = xmalloc(*digest_len);
			memcpy(*digest, rdata + 2, *digest_len);
		} else {
			*digest = (u_char *)xstrdup("");
		}

		success = 1;
	}

	return success;
}

/*
 * Check if hostname is numerical.
 * Returns -1 if hostname is numeric, 0 otherwise
 */
static int
is_numeric_hostname(const char *hostname)
{
	struct addrinfo hints, *ai;

	/*
	 * We shouldn't ever get a null host but if we do then log an error
	 * and return -1 which stops DNS key fingerprint processing.
	 */
	if (hostname == NULL) {
		error("is_numeric_hostname called with NULL hostname");
		return -1;
	}

	memset(&hints, 0, sizeof(hints));
	hints.ai_socktype = SOCK_DGRAM;
	hints.ai_flags = AI_NUMERICHOST;

	if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
		freeaddrinfo(ai);
		return -1;
	}

	return 0;
}

/*
 * Verify the given hostname, address and host key using DNS.
 * Returns 0 if lookup succeeds, -1 otherwise
 */
int
verify_host_key_dns(const char *hostname, struct sockaddr *address,
    struct sshkey *hostkey, int *flags)
{
	u_int counter;
	int result;
	unsigned int rrset_flags = 0;
	struct rrsetinfo *fingerprints = NULL;

	u_int8_t hostkey_algorithm;
	u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
	u_char *hostkey_digest;
	size_t hostkey_digest_len;

	u_int8_t dnskey_algorithm;
	u_int8_t dnskey_digest_type;
	u_char *dnskey_digest;
	size_t dnskey_digest_len;

	*flags = 0;

	debug3("verify_host_key_dns");
	if (hostkey == NULL)
		fatal("No key to look up!");

	if (is_numeric_hostname(hostname)) {
		debug("skipped DNS lookup for numerical hostname");
		return -1;
	}

	/*
	 * Original getrrsetbyname function, found on OpenBSD for example,
	 * doesn't accept any flag and prerequisite for obtaining AD bit in
	 * DNS response is set by "options edns0" in resolv.conf.
	 *
	 * Our version is more clever and use RRSET_FORCE_EDNS0 flag.
	 */
#ifndef HAVE_GETRRSETBYNAME
	rrset_flags |= RRSET_FORCE_EDNS0;
#endif
	result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
	    DNS_RDATATYPE_SSHFP, rrset_flags, &fingerprints);

	if (result) {
		verbose("DNS lookup error: %s", dns_result_totext(result));
		return -1;
	}

	if (fingerprints->rri_flags & RRSET_VALIDATED) {
		*flags |= DNS_VERIFY_SECURE;
		debug("found %d secure fingerprints in DNS",
		    fingerprints->rri_nrdatas);
	} else {
		debug("found %d insecure fingerprints in DNS",
		    fingerprints->rri_nrdatas);
	}

	/* Initialize default host key parameters */
	if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
	    &hostkey_digest, &hostkey_digest_len, hostkey)) {
		error("Error calculating host key fingerprint.");
		freerrset(fingerprints);
		return -1;
	}

	if (fingerprints->rri_nrdatas)
		*flags |= DNS_VERIFY_FOUND;

	for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
		/*
		 * Extract the key from the answer. Ignore any badly
		 * formatted fingerprints.
		 */
		if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
		    &dnskey_digest, &dnskey_digest_len,
		    fingerprints->rri_rdatas[counter].rdi_data,
		    fingerprints->rri_rdatas[counter].rdi_length)) {
			verbose("Error parsing fingerprint from DNS.");
			continue;
		}

		if (hostkey_digest_type != dnskey_digest_type) {
			hostkey_digest_type = dnskey_digest_type;
			free(hostkey_digest);

			/* Initialize host key parameters */
			if (!dns_read_key(&hostkey_algorithm,
			    &hostkey_digest_type, &hostkey_digest,
			    &hostkey_digest_len, hostkey)) {
				error("Error calculating key fingerprint.");
				freerrset(fingerprints);
				return -1;
			}
		}

		/* Check if the current key is the same as the given key */
		if (hostkey_algorithm == dnskey_algorithm &&
		    hostkey_digest_type == dnskey_digest_type) {
			if (hostkey_digest_len == dnskey_digest_len &&
			    timingsafe_bcmp(hostkey_digest, dnskey_digest,
			    hostkey_digest_len) == 0)
				*flags |= DNS_VERIFY_MATCH;
		}
		free(dnskey_digest);
	}

	free(hostkey_digest); /* from sshkey_fingerprint_raw() */
	freerrset(fingerprints);

	if (*flags & DNS_VERIFY_FOUND)
		if (*flags & DNS_VERIFY_MATCH)
			debug("matching host key fingerprint found in DNS");
		else
			debug("mismatching host key fingerprint found in DNS");
	else
		debug("no host key fingerprint found in DNS");

	return 0;
}

/*
 * Export the fingerprint of a key as a DNS resource record
 */
int
export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
{
	u_int8_t rdata_pubkey_algorithm = 0;
	u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
	u_int8_t dtype;
	u_char *rdata_digest;
	size_t i, rdata_digest_len;
	int success = 0;

	for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
		rdata_digest_type = dtype;
		if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
		    &rdata_digest, &rdata_digest_len, key)) {
			if (generic) {
				fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
				    hostname, DNS_RDATATYPE_SSHFP,
				    2 + rdata_digest_len,
				    rdata_pubkey_algorithm, rdata_digest_type);
			} else {
				fprintf(f, "%s IN SSHFP %d %d ", hostname,
				    rdata_pubkey_algorithm, rdata_digest_type);
			}
			for (i = 0; i < rdata_digest_len; i++)
				fprintf(f, "%02x", rdata_digest[i]);
			fprintf(f, "\n");
			free(rdata_digest); /* from sshkey_fingerprint_raw() */
			success = 1;
		}
	}

	/* No SSHFP record was generated at all */
	if (success == 0) {
		error("%s: unsupported algorithm and/or digest_type", __func__);
	}

	return success;
}