Annotation of src/usr.bin/ssh/dns.c, Revision 1.32
1.32 ! djm 1: /* $OpenBSD: dns.c,v 1.31 2014/06/24 01:13:21 djm Exp $ */
1.1 jakob 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: */
1.20 stevesk 27:
28: #include <sys/types.h>
29: #include <sys/socket.h>
1.1 jakob 30:
31: #include <netdb.h>
1.22 stevesk 32: #include <stdio.h>
1.21 stevesk 33: #include <string.h>
1.31 djm 34: #include <stdarg.h>
35: #include <stdlib.h>
1.1 jakob 36:
37: #include "xmalloc.h"
38: #include "key.h"
39: #include "dns.h"
40: #include "log.h"
1.32 ! djm 41: #include "digest.h"
1.1 jakob 42:
43: static const char *errset_text[] = {
44: "success", /* 0 ERRSET_SUCCESS */
45: "out of memory", /* 1 ERRSET_NOMEMORY */
46: "general failure", /* 2 ERRSET_FAIL */
47: "invalid parameter", /* 3 ERRSET_INVAL */
48: "name does not exist", /* 4 ERRSET_NONAME */
49: "data does not exist", /* 5 ERRSET_NODATA */
50: };
51:
52: static const char *
1.10 avsm 53: dns_result_totext(unsigned int res)
1.1 jakob 54: {
1.10 avsm 55: switch (res) {
1.1 jakob 56: case ERRSET_SUCCESS:
57: return errset_text[ERRSET_SUCCESS];
58: case ERRSET_NOMEMORY:
59: return errset_text[ERRSET_NOMEMORY];
60: case ERRSET_FAIL:
61: return errset_text[ERRSET_FAIL];
62: case ERRSET_INVAL:
63: return errset_text[ERRSET_INVAL];
64: case ERRSET_NONAME:
65: return errset_text[ERRSET_NONAME];
66: case ERRSET_NODATA:
67: return errset_text[ERRSET_NODATA];
68: default:
69: return "unknown error";
70: }
71: }
72:
73: /*
74: * Read SSHFP parameters from key buffer.
75: */
76: static int
77: dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
1.26 djm 78: u_char **digest, u_int *digest_len, Key *key)
1.1 jakob 79: {
80: int success = 0;
1.32 ! djm 81: int fp_alg = -1;
1.1 jakob 82:
83: switch (key->type) {
84: case KEY_RSA:
1.3 jakob 85: *algorithm = SSHFP_KEY_RSA;
1.28 djm 86: if (!*digest_type)
87: *digest_type = SSHFP_HASH_SHA1;
1.1 jakob 88: break;
89: case KEY_DSA:
1.3 jakob 90: *algorithm = SSHFP_KEY_DSA;
1.28 djm 91: if (!*digest_type)
92: *digest_type = SSHFP_HASH_SHA1;
93: break;
94: case KEY_ECDSA:
95: *algorithm = SSHFP_KEY_ECDSA;
1.30 logan 96: if (!*digest_type)
97: *digest_type = SSHFP_HASH_SHA256;
98: break;
99: case KEY_ED25519:
100: *algorithm = SSHFP_KEY_ED25519;
1.28 djm 101: if (!*digest_type)
102: *digest_type = SSHFP_HASH_SHA256;
1.1 jakob 103: break;
104: default:
1.14 stevesk 105: *algorithm = SSHFP_KEY_RESERVED; /* 0 */
1.28 djm 106: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
107: }
108:
109: switch (*digest_type) {
110: case SSHFP_HASH_SHA1:
1.32 ! djm 111: fp_alg = SSH_DIGEST_SHA1;
1.28 djm 112: break;
113: case SSHFP_HASH_SHA256:
1.32 ! djm 114: fp_alg = SSH_DIGEST_SHA256;
1.28 djm 115: break;
116: default:
117: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
1.1 jakob 118: }
119:
1.28 djm 120: if (*algorithm && *digest_type) {
1.32 ! djm 121: *digest = key_fingerprint_raw(key, fp_alg, digest_len);
1.14 stevesk 122: if (*digest == NULL)
123: fatal("dns_read_key: null from key_fingerprint_raw()");
1.1 jakob 124: success = 1;
125: } else {
126: *digest = NULL;
127: *digest_len = 0;
128: success = 0;
129: }
130:
131: return success;
132: }
133:
134: /*
135: * Read SSHFP parameters from rdata buffer.
136: */
137: static int
138: dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
139: u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
140: {
141: int success = 0;
142:
1.3 jakob 143: *algorithm = SSHFP_KEY_RESERVED;
144: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 145:
146: if (rdata_len >= 2) {
147: *algorithm = rdata[0];
148: *digest_type = rdata[1];
149: *digest_len = rdata_len - 2;
150:
151: if (*digest_len > 0) {
152: *digest = (u_char *) xmalloc(*digest_len);
153: memcpy(*digest, rdata + 2, *digest_len);
154: } else {
1.18 deraadt 155: *digest = (u_char *)xstrdup("");
1.1 jakob 156: }
157:
158: success = 1;
159: }
160:
161: return success;
162: }
163:
1.11 jakob 164: /*
165: * Check if hostname is numerical.
166: * Returns -1 if hostname is numeric, 0 otherwise
167: */
168: static int
169: is_numeric_hostname(const char *hostname)
170: {
171: struct addrinfo hints, *ai;
172:
1.25 dtucker 173: /*
174: * We shouldn't ever get a null host but if we do then log an error
175: * and return -1 which stops DNS key fingerprint processing.
176: */
177: if (hostname == NULL) {
178: error("is_numeric_hostname called with NULL hostname");
179: return -1;
180: }
181:
1.11 jakob 182: memset(&hints, 0, sizeof(hints));
183: hints.ai_socktype = SOCK_DGRAM;
184: hints.ai_flags = AI_NUMERICHOST;
185:
1.25 dtucker 186: if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
1.11 jakob 187: freeaddrinfo(ai);
188: return -1;
189: }
190:
191: return 0;
192: }
1.1 jakob 193:
194: /*
195: * Verify the given hostname, address and host key using DNS.
1.9 djm 196: * Returns 0 if lookup succeeds, -1 otherwise
1.1 jakob 197: */
198: int
199: verify_host_key_dns(const char *hostname, struct sockaddr *address,
1.26 djm 200: Key *hostkey, int *flags)
1.1 jakob 201: {
1.12 djm 202: u_int counter;
1.1 jakob 203: int result;
1.4 jakob 204: struct rrsetinfo *fingerprints = NULL;
1.1 jakob 205:
206: u_int8_t hostkey_algorithm;
1.28 djm 207: u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 208: u_char *hostkey_digest;
209: u_int hostkey_digest_len;
210:
211: u_int8_t dnskey_algorithm;
212: u_int8_t dnskey_digest_type;
213: u_char *dnskey_digest;
214: u_int dnskey_digest_len;
215:
1.8 jakob 216: *flags = 0;
1.1 jakob 217:
1.16 stevesk 218: debug3("verify_host_key_dns");
1.1 jakob 219: if (hostkey == NULL)
220: fatal("No key to look up!");
1.11 jakob 221:
222: if (is_numeric_hostname(hostname)) {
223: debug("skipped DNS lookup for numerical hostname");
224: return -1;
225: }
1.1 jakob 226:
227: result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
1.4 jakob 228: DNS_RDATATYPE_SSHFP, 0, &fingerprints);
1.1 jakob 229: if (result) {
230: verbose("DNS lookup error: %s", dns_result_totext(result));
1.8 jakob 231: return -1;
1.1 jakob 232: }
233:
1.8 jakob 234: if (fingerprints->rri_flags & RRSET_VALIDATED) {
235: *flags |= DNS_VERIFY_SECURE;
236: debug("found %d secure fingerprints in DNS",
237: fingerprints->rri_nrdatas);
238: } else {
239: debug("found %d insecure fingerprints in DNS",
240: fingerprints->rri_nrdatas);
1.1 jakob 241: }
242:
1.28 djm 243: /* Initialize default host key parameters */
1.1 jakob 244: if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
245: &hostkey_digest, &hostkey_digest_len, hostkey)) {
246: error("Error calculating host key fingerprint.");
1.5 jakob 247: freerrset(fingerprints);
1.8 jakob 248: return -1;
1.1 jakob 249: }
250:
1.8 jakob 251: if (fingerprints->rri_nrdatas)
252: *flags |= DNS_VERIFY_FOUND;
253:
1.24 stevesk 254: for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
1.1 jakob 255: /*
256: * Extract the key from the answer. Ignore any badly
1.4 jakob 257: * formatted fingerprints.
1.1 jakob 258: */
259: if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
260: &dnskey_digest, &dnskey_digest_len,
1.4 jakob 261: fingerprints->rri_rdatas[counter].rdi_data,
262: fingerprints->rri_rdatas[counter].rdi_length)) {
1.1 jakob 263: verbose("Error parsing fingerprint from DNS.");
264: continue;
265: }
266:
1.28 djm 267: if (hostkey_digest_type != dnskey_digest_type) {
268: hostkey_digest_type = dnskey_digest_type;
1.29 djm 269: free(hostkey_digest);
1.28 djm 270:
271: /* Initialize host key parameters */
272: if (!dns_read_key(&hostkey_algorithm,
273: &hostkey_digest_type, &hostkey_digest,
274: &hostkey_digest_len, hostkey)) {
275: error("Error calculating key fingerprint.");
276: freerrset(fingerprints);
277: return -1;
278: }
279: }
280:
1.1 jakob 281: /* Check if the current key is the same as the given key */
282: if (hostkey_algorithm == dnskey_algorithm &&
283: hostkey_digest_type == dnskey_digest_type) {
284: if (hostkey_digest_len == dnskey_digest_len &&
1.28 djm 285: timingsafe_bcmp(hostkey_digest, dnskey_digest,
286: hostkey_digest_len) == 0)
1.8 jakob 287: *flags |= DNS_VERIFY_MATCH;
1.1 jakob 288: }
1.29 djm 289: free(dnskey_digest);
1.1 jakob 290: }
291:
1.29 djm 292: free(hostkey_digest); /* from key_fingerprint_raw() */
1.4 jakob 293: freerrset(fingerprints);
1.1 jakob 294:
1.8 jakob 295: if (*flags & DNS_VERIFY_FOUND)
296: if (*flags & DNS_VERIFY_MATCH)
297: debug("matching host key fingerprint found in DNS");
298: else
299: debug("mismatching host key fingerprint found in DNS");
300: else
301: debug("no host key fingerprint found in DNS");
1.1 jakob 302:
1.8 jakob 303: return 0;
1.1 jakob 304: }
305:
306: /*
307: * Export the fingerprint of a key as a DNS resource record
308: */
309: int
1.26 djm 310: export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
1.1 jakob 311: {
312: u_int8_t rdata_pubkey_algorithm = 0;
1.28 djm 313: u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
314: u_int8_t dtype;
1.1 jakob 315: u_char *rdata_digest;
1.28 djm 316: u_int i, rdata_digest_len;
1.1 jakob 317: int success = 0;
318:
1.28 djm 319: for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
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 \\# %d %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");
1.29 djm 335: free(rdata_digest); /* from key_fingerprint_raw() */
1.28 djm 336: success = 1;
337: }
338: }
1.1 jakob 339:
1.28 djm 340: /* No SSHFP record was generated at all */
341: if (success == 0) {
342: error("%s: unsupported algorithm and/or digest_type", __func__);
1.1 jakob 343: }
344:
345: return success;
346: }
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