Annotation of src/usr.bin/ssh/dns.c, Revision 1.33
1.33 ! djm 1: /* $OpenBSD: dns.c,v 1.32 2014/12/21 22:27:56 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"
1.33 ! djm 38: #include "sshkey.h"
! 39: #include "ssherr.h"
1.1 jakob 40: #include "dns.h"
41: #include "log.h"
1.32 djm 42: #include "digest.h"
1.1 jakob 43:
44: static const char *errset_text[] = {
45: "success", /* 0 ERRSET_SUCCESS */
46: "out of memory", /* 1 ERRSET_NOMEMORY */
47: "general failure", /* 2 ERRSET_FAIL */
48: "invalid parameter", /* 3 ERRSET_INVAL */
49: "name does not exist", /* 4 ERRSET_NONAME */
50: "data does not exist", /* 5 ERRSET_NODATA */
51: };
52:
53: static const char *
1.10 avsm 54: dns_result_totext(unsigned int res)
1.1 jakob 55: {
1.10 avsm 56: switch (res) {
1.1 jakob 57: case ERRSET_SUCCESS:
58: return errset_text[ERRSET_SUCCESS];
59: case ERRSET_NOMEMORY:
60: return errset_text[ERRSET_NOMEMORY];
61: case ERRSET_FAIL:
62: return errset_text[ERRSET_FAIL];
63: case ERRSET_INVAL:
64: return errset_text[ERRSET_INVAL];
65: case ERRSET_NONAME:
66: return errset_text[ERRSET_NONAME];
67: case ERRSET_NODATA:
68: return errset_text[ERRSET_NODATA];
69: default:
70: return "unknown error";
71: }
72: }
73:
74: /*
75: * Read SSHFP parameters from key buffer.
76: */
77: static int
78: dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
1.33 ! djm 79: u_char **digest, size_t *digest_len, struct sshkey *key)
1.1 jakob 80: {
1.33 ! djm 81: int r, success = 0;
1.32 djm 82: int fp_alg = -1;
1.1 jakob 83:
84: switch (key->type) {
85: case KEY_RSA:
1.3 jakob 86: *algorithm = SSHFP_KEY_RSA;
1.28 djm 87: if (!*digest_type)
88: *digest_type = SSHFP_HASH_SHA1;
1.1 jakob 89: break;
90: case KEY_DSA:
1.3 jakob 91: *algorithm = SSHFP_KEY_DSA;
1.28 djm 92: if (!*digest_type)
93: *digest_type = SSHFP_HASH_SHA1;
94: break;
95: case KEY_ECDSA:
96: *algorithm = SSHFP_KEY_ECDSA;
1.30 logan 97: if (!*digest_type)
98: *digest_type = SSHFP_HASH_SHA256;
99: break;
100: case KEY_ED25519:
101: *algorithm = SSHFP_KEY_ED25519;
1.28 djm 102: if (!*digest_type)
103: *digest_type = SSHFP_HASH_SHA256;
1.1 jakob 104: break;
105: default:
1.14 stevesk 106: *algorithm = SSHFP_KEY_RESERVED; /* 0 */
1.28 djm 107: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
108: }
109:
110: switch (*digest_type) {
111: case SSHFP_HASH_SHA1:
1.32 djm 112: fp_alg = SSH_DIGEST_SHA1;
1.28 djm 113: break;
114: case SSHFP_HASH_SHA256:
1.32 djm 115: fp_alg = SSH_DIGEST_SHA256;
1.28 djm 116: break;
117: default:
118: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
1.1 jakob 119: }
120:
1.28 djm 121: if (*algorithm && *digest_type) {
1.33 ! djm 122: if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
! 123: digest_len)) != 0)
! 124: fatal("%s: sshkey_fingerprint_raw: %s", __func__,
! 125: ssh_err(r));
1.1 jakob 126: success = 1;
127: } else {
128: *digest = NULL;
129: *digest_len = 0;
130: success = 0;
131: }
132:
133: return success;
134: }
135:
136: /*
137: * Read SSHFP parameters from rdata buffer.
138: */
139: static int
140: dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
1.33 ! djm 141: u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
1.1 jakob 142: {
143: int success = 0;
144:
1.3 jakob 145: *algorithm = SSHFP_KEY_RESERVED;
146: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 147:
148: if (rdata_len >= 2) {
149: *algorithm = rdata[0];
150: *digest_type = rdata[1];
151: *digest_len = rdata_len - 2;
152:
153: if (*digest_len > 0) {
154: *digest = (u_char *) xmalloc(*digest_len);
155: memcpy(*digest, rdata + 2, *digest_len);
156: } else {
1.18 deraadt 157: *digest = (u_char *)xstrdup("");
1.1 jakob 158: }
159:
160: success = 1;
161: }
162:
163: return success;
164: }
165:
1.11 jakob 166: /*
167: * Check if hostname is numerical.
168: * Returns -1 if hostname is numeric, 0 otherwise
169: */
170: static int
171: is_numeric_hostname(const char *hostname)
172: {
173: struct addrinfo hints, *ai;
174:
1.25 dtucker 175: /*
176: * We shouldn't ever get a null host but if we do then log an error
177: * and return -1 which stops DNS key fingerprint processing.
178: */
179: if (hostname == NULL) {
180: error("is_numeric_hostname called with NULL hostname");
181: return -1;
182: }
183:
1.11 jakob 184: memset(&hints, 0, sizeof(hints));
185: hints.ai_socktype = SOCK_DGRAM;
186: hints.ai_flags = AI_NUMERICHOST;
187:
1.25 dtucker 188: if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
1.11 jakob 189: freeaddrinfo(ai);
190: return -1;
191: }
192:
193: return 0;
194: }
1.1 jakob 195:
196: /*
197: * Verify the given hostname, address and host key using DNS.
1.9 djm 198: * Returns 0 if lookup succeeds, -1 otherwise
1.1 jakob 199: */
200: int
201: verify_host_key_dns(const char *hostname, struct sockaddr *address,
1.33 ! djm 202: struct sshkey *hostkey, int *flags)
1.1 jakob 203: {
1.12 djm 204: u_int counter;
1.1 jakob 205: int result;
1.4 jakob 206: struct rrsetinfo *fingerprints = NULL;
1.1 jakob 207:
208: u_int8_t hostkey_algorithm;
1.28 djm 209: u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 210: u_char *hostkey_digest;
1.33 ! djm 211: size_t hostkey_digest_len;
1.1 jakob 212:
213: u_int8_t dnskey_algorithm;
214: u_int8_t dnskey_digest_type;
215: u_char *dnskey_digest;
1.33 ! djm 216: size_t dnskey_digest_len;
1.1 jakob 217:
1.8 jakob 218: *flags = 0;
1.1 jakob 219:
1.16 stevesk 220: debug3("verify_host_key_dns");
1.1 jakob 221: if (hostkey == NULL)
222: fatal("No key to look up!");
1.11 jakob 223:
224: if (is_numeric_hostname(hostname)) {
225: debug("skipped DNS lookup for numerical hostname");
226: return -1;
227: }
1.1 jakob 228:
229: result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
1.4 jakob 230: DNS_RDATATYPE_SSHFP, 0, &fingerprints);
1.1 jakob 231: if (result) {
232: verbose("DNS lookup error: %s", dns_result_totext(result));
1.8 jakob 233: return -1;
1.1 jakob 234: }
235:
1.8 jakob 236: if (fingerprints->rri_flags & RRSET_VALIDATED) {
237: *flags |= DNS_VERIFY_SECURE;
238: debug("found %d secure fingerprints in DNS",
239: fingerprints->rri_nrdatas);
240: } else {
241: debug("found %d insecure fingerprints in DNS",
242: fingerprints->rri_nrdatas);
1.1 jakob 243: }
244:
1.28 djm 245: /* Initialize default host key parameters */
1.1 jakob 246: if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
247: &hostkey_digest, &hostkey_digest_len, hostkey)) {
248: error("Error calculating host key fingerprint.");
1.5 jakob 249: freerrset(fingerprints);
1.8 jakob 250: return -1;
1.1 jakob 251: }
252:
1.8 jakob 253: if (fingerprints->rri_nrdatas)
254: *flags |= DNS_VERIFY_FOUND;
255:
1.24 stevesk 256: for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
1.1 jakob 257: /*
258: * Extract the key from the answer. Ignore any badly
1.4 jakob 259: * formatted fingerprints.
1.1 jakob 260: */
261: if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
262: &dnskey_digest, &dnskey_digest_len,
1.4 jakob 263: fingerprints->rri_rdatas[counter].rdi_data,
264: fingerprints->rri_rdatas[counter].rdi_length)) {
1.1 jakob 265: verbose("Error parsing fingerprint from DNS.");
266: continue;
267: }
268:
1.28 djm 269: if (hostkey_digest_type != dnskey_digest_type) {
270: hostkey_digest_type = dnskey_digest_type;
1.29 djm 271: free(hostkey_digest);
1.28 djm 272:
273: /* Initialize host key parameters */
274: if (!dns_read_key(&hostkey_algorithm,
275: &hostkey_digest_type, &hostkey_digest,
276: &hostkey_digest_len, hostkey)) {
277: error("Error calculating key fingerprint.");
278: freerrset(fingerprints);
279: return -1;
280: }
281: }
282:
1.1 jakob 283: /* Check if the current key is the same as the given key */
284: if (hostkey_algorithm == dnskey_algorithm &&
285: hostkey_digest_type == dnskey_digest_type) {
286: if (hostkey_digest_len == dnskey_digest_len &&
1.28 djm 287: timingsafe_bcmp(hostkey_digest, dnskey_digest,
288: hostkey_digest_len) == 0)
1.8 jakob 289: *flags |= DNS_VERIFY_MATCH;
1.1 jakob 290: }
1.29 djm 291: free(dnskey_digest);
1.1 jakob 292: }
293:
1.29 djm 294: free(hostkey_digest); /* from key_fingerprint_raw() */
1.4 jakob 295: freerrset(fingerprints);
1.1 jakob 296:
1.8 jakob 297: if (*flags & DNS_VERIFY_FOUND)
298: if (*flags & DNS_VERIFY_MATCH)
299: debug("matching host key fingerprint found in DNS");
300: else
301: debug("mismatching host key fingerprint found in DNS");
302: else
303: debug("no host key fingerprint found in DNS");
1.1 jakob 304:
1.8 jakob 305: return 0;
1.1 jakob 306: }
307:
308: /*
309: * Export the fingerprint of a key as a DNS resource record
310: */
311: int
1.33 ! djm 312: export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
1.1 jakob 313: {
314: u_int8_t rdata_pubkey_algorithm = 0;
1.28 djm 315: u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
316: u_int8_t dtype;
1.1 jakob 317: u_char *rdata_digest;
1.33 ! djm 318: size_t i, rdata_digest_len;
1.1 jakob 319: int success = 0;
320:
1.28 djm 321: for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
322: rdata_digest_type = dtype;
323: if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
324: &rdata_digest, &rdata_digest_len, key)) {
325: if (generic) {
1.33 ! djm 326: fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
1.28 djm 327: hostname, DNS_RDATATYPE_SSHFP,
328: 2 + rdata_digest_len,
329: rdata_pubkey_algorithm, rdata_digest_type);
330: } else {
331: fprintf(f, "%s IN SSHFP %d %d ", hostname,
332: rdata_pubkey_algorithm, rdata_digest_type);
333: }
334: for (i = 0; i < rdata_digest_len; i++)
335: fprintf(f, "%02x", rdata_digest[i]);
336: fprintf(f, "\n");
1.29 djm 337: free(rdata_digest); /* from key_fingerprint_raw() */
1.28 djm 338: success = 1;
339: }
340: }
1.1 jakob 341:
1.28 djm 342: /* No SSHFP record was generated at all */
343: if (success == 0) {
344: error("%s: unsupported algorithm and/or digest_type", __func__);
1.1 jakob 345: }
346:
347: return success;
348: }
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