Annotation of src/usr.bin/ssh/dns.c, Revision 1.28
1.28 ! djm 1: /* $OpenBSD: dns.c,v 1.27 2010/08/31 11:54:45 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>
1.1 jakob 34:
35: #include "xmalloc.h"
36: #include "key.h"
37: #include "dns.h"
38: #include "log.h"
39:
40: static const char *errset_text[] = {
41: "success", /* 0 ERRSET_SUCCESS */
42: "out of memory", /* 1 ERRSET_NOMEMORY */
43: "general failure", /* 2 ERRSET_FAIL */
44: "invalid parameter", /* 3 ERRSET_INVAL */
45: "name does not exist", /* 4 ERRSET_NONAME */
46: "data does not exist", /* 5 ERRSET_NODATA */
47: };
48:
49: static const char *
1.10 avsm 50: dns_result_totext(unsigned int res)
1.1 jakob 51: {
1.10 avsm 52: switch (res) {
1.1 jakob 53: case ERRSET_SUCCESS:
54: return errset_text[ERRSET_SUCCESS];
55: case ERRSET_NOMEMORY:
56: return errset_text[ERRSET_NOMEMORY];
57: case ERRSET_FAIL:
58: return errset_text[ERRSET_FAIL];
59: case ERRSET_INVAL:
60: return errset_text[ERRSET_INVAL];
61: case ERRSET_NONAME:
62: return errset_text[ERRSET_NONAME];
63: case ERRSET_NODATA:
64: return errset_text[ERRSET_NODATA];
65: default:
66: return "unknown error";
67: }
68: }
69:
70: /*
71: * Read SSHFP parameters from key buffer.
72: */
73: static int
74: dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
1.26 djm 75: u_char **digest, u_int *digest_len, Key *key)
1.1 jakob 76: {
77: int success = 0;
1.28 ! djm 78: enum fp_type fp_type = 0;
1.1 jakob 79:
80: switch (key->type) {
81: case KEY_RSA:
1.3 jakob 82: *algorithm = SSHFP_KEY_RSA;
1.28 ! djm 83: if (!*digest_type)
! 84: *digest_type = SSHFP_HASH_SHA1;
1.1 jakob 85: break;
86: case KEY_DSA:
1.3 jakob 87: *algorithm = SSHFP_KEY_DSA;
1.28 ! djm 88: if (!*digest_type)
! 89: *digest_type = SSHFP_HASH_SHA1;
! 90: break;
! 91: case KEY_ECDSA:
! 92: *algorithm = SSHFP_KEY_ECDSA;
! 93: if (!*digest_type)
! 94: *digest_type = SSHFP_HASH_SHA256;
1.1 jakob 95: break;
96: default:
1.14 stevesk 97: *algorithm = SSHFP_KEY_RESERVED; /* 0 */
1.28 ! djm 98: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
! 99: }
! 100:
! 101: switch (*digest_type) {
! 102: case SSHFP_HASH_SHA1:
! 103: fp_type = SSH_FP_SHA1;
! 104: break;
! 105: case SSHFP_HASH_SHA256:
! 106: fp_type = SSH_FP_SHA256;
! 107: break;
! 108: default:
! 109: *digest_type = SSHFP_HASH_RESERVED; /* 0 */
1.1 jakob 110: }
111:
1.28 ! djm 112: if (*algorithm && *digest_type) {
! 113: *digest = key_fingerprint_raw(key, fp_type, digest_len);
1.14 stevesk 114: if (*digest == NULL)
115: fatal("dns_read_key: null from key_fingerprint_raw()");
1.1 jakob 116: success = 1;
117: } else {
118: *digest = NULL;
119: *digest_len = 0;
120: success = 0;
121: }
122:
123: return success;
124: }
125:
126: /*
127: * Read SSHFP parameters from rdata buffer.
128: */
129: static int
130: dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
131: u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
132: {
133: int success = 0;
134:
1.3 jakob 135: *algorithm = SSHFP_KEY_RESERVED;
136: *digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 137:
138: if (rdata_len >= 2) {
139: *algorithm = rdata[0];
140: *digest_type = rdata[1];
141: *digest_len = rdata_len - 2;
142:
143: if (*digest_len > 0) {
144: *digest = (u_char *) xmalloc(*digest_len);
145: memcpy(*digest, rdata + 2, *digest_len);
146: } else {
1.18 deraadt 147: *digest = (u_char *)xstrdup("");
1.1 jakob 148: }
149:
150: success = 1;
151: }
152:
153: return success;
154: }
155:
1.11 jakob 156: /*
157: * Check if hostname is numerical.
158: * Returns -1 if hostname is numeric, 0 otherwise
159: */
160: static int
161: is_numeric_hostname(const char *hostname)
162: {
163: struct addrinfo hints, *ai;
164:
1.25 dtucker 165: /*
166: * We shouldn't ever get a null host but if we do then log an error
167: * and return -1 which stops DNS key fingerprint processing.
168: */
169: if (hostname == NULL) {
170: error("is_numeric_hostname called with NULL hostname");
171: return -1;
172: }
173:
1.11 jakob 174: memset(&hints, 0, sizeof(hints));
175: hints.ai_socktype = SOCK_DGRAM;
176: hints.ai_flags = AI_NUMERICHOST;
177:
1.25 dtucker 178: if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
1.11 jakob 179: freeaddrinfo(ai);
180: return -1;
181: }
182:
183: return 0;
184: }
1.1 jakob 185:
186: /*
187: * Verify the given hostname, address and host key using DNS.
1.9 djm 188: * Returns 0 if lookup succeeds, -1 otherwise
1.1 jakob 189: */
190: int
191: verify_host_key_dns(const char *hostname, struct sockaddr *address,
1.26 djm 192: Key *hostkey, int *flags)
1.1 jakob 193: {
1.12 djm 194: u_int counter;
1.1 jakob 195: int result;
1.4 jakob 196: struct rrsetinfo *fingerprints = NULL;
1.1 jakob 197:
198: u_int8_t hostkey_algorithm;
1.28 ! djm 199: u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
1.1 jakob 200: u_char *hostkey_digest;
201: u_int hostkey_digest_len;
202:
203: u_int8_t dnskey_algorithm;
204: u_int8_t dnskey_digest_type;
205: u_char *dnskey_digest;
206: u_int dnskey_digest_len;
207:
1.8 jakob 208: *flags = 0;
1.1 jakob 209:
1.16 stevesk 210: debug3("verify_host_key_dns");
1.1 jakob 211: if (hostkey == NULL)
212: fatal("No key to look up!");
1.11 jakob 213:
214: if (is_numeric_hostname(hostname)) {
215: debug("skipped DNS lookup for numerical hostname");
216: return -1;
217: }
1.1 jakob 218:
219: result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
1.4 jakob 220: DNS_RDATATYPE_SSHFP, 0, &fingerprints);
1.1 jakob 221: if (result) {
222: verbose("DNS lookup error: %s", dns_result_totext(result));
1.8 jakob 223: return -1;
1.1 jakob 224: }
225:
1.8 jakob 226: if (fingerprints->rri_flags & RRSET_VALIDATED) {
227: *flags |= DNS_VERIFY_SECURE;
228: debug("found %d secure fingerprints in DNS",
229: fingerprints->rri_nrdatas);
230: } else {
231: debug("found %d insecure fingerprints in DNS",
232: fingerprints->rri_nrdatas);
1.1 jakob 233: }
234:
1.28 ! djm 235: /* Initialize default host key parameters */
1.1 jakob 236: if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
237: &hostkey_digest, &hostkey_digest_len, hostkey)) {
238: error("Error calculating host key fingerprint.");
1.5 jakob 239: freerrset(fingerprints);
1.8 jakob 240: return -1;
1.1 jakob 241: }
242:
1.8 jakob 243: if (fingerprints->rri_nrdatas)
244: *flags |= DNS_VERIFY_FOUND;
245:
1.24 stevesk 246: for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
1.1 jakob 247: /*
248: * Extract the key from the answer. Ignore any badly
1.4 jakob 249: * formatted fingerprints.
1.1 jakob 250: */
251: if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
252: &dnskey_digest, &dnskey_digest_len,
1.4 jakob 253: fingerprints->rri_rdatas[counter].rdi_data,
254: fingerprints->rri_rdatas[counter].rdi_length)) {
1.1 jakob 255: verbose("Error parsing fingerprint from DNS.");
256: continue;
257: }
258:
1.28 ! djm 259: if (hostkey_digest_type != dnskey_digest_type) {
! 260: hostkey_digest_type = dnskey_digest_type;
! 261: xfree(hostkey_digest);
! 262:
! 263: /* Initialize host key parameters */
! 264: if (!dns_read_key(&hostkey_algorithm,
! 265: &hostkey_digest_type, &hostkey_digest,
! 266: &hostkey_digest_len, hostkey)) {
! 267: error("Error calculating key fingerprint.");
! 268: freerrset(fingerprints);
! 269: return -1;
! 270: }
! 271: }
! 272:
1.1 jakob 273: /* Check if the current key is the same as the given key */
274: if (hostkey_algorithm == dnskey_algorithm &&
275: hostkey_digest_type == dnskey_digest_type) {
276: if (hostkey_digest_len == dnskey_digest_len &&
1.28 ! djm 277: timingsafe_bcmp(hostkey_digest, dnskey_digest,
! 278: hostkey_digest_len) == 0)
1.8 jakob 279: *flags |= DNS_VERIFY_MATCH;
1.1 jakob 280: }
1.14 stevesk 281: xfree(dnskey_digest);
1.1 jakob 282: }
283:
1.14 stevesk 284: xfree(hostkey_digest); /* from key_fingerprint_raw() */
1.4 jakob 285: freerrset(fingerprints);
1.1 jakob 286:
1.8 jakob 287: if (*flags & DNS_VERIFY_FOUND)
288: if (*flags & DNS_VERIFY_MATCH)
289: debug("matching host key fingerprint found in DNS");
290: else
291: debug("mismatching host key fingerprint found in DNS");
292: else
293: debug("no host key fingerprint found in DNS");
1.1 jakob 294:
1.8 jakob 295: return 0;
1.1 jakob 296: }
297:
298: /*
299: * Export the fingerprint of a key as a DNS resource record
300: */
301: int
1.26 djm 302: export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
1.1 jakob 303: {
304: u_int8_t rdata_pubkey_algorithm = 0;
1.28 ! djm 305: u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
! 306: u_int8_t dtype;
1.1 jakob 307: u_char *rdata_digest;
1.28 ! djm 308: u_int i, rdata_digest_len;
1.1 jakob 309: int success = 0;
310:
1.28 ! djm 311: for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
! 312: rdata_digest_type = dtype;
! 313: if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
! 314: &rdata_digest, &rdata_digest_len, key)) {
! 315: if (generic) {
! 316: fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ",
! 317: hostname, DNS_RDATATYPE_SSHFP,
! 318: 2 + rdata_digest_len,
! 319: rdata_pubkey_algorithm, rdata_digest_type);
! 320: } else {
! 321: fprintf(f, "%s IN SSHFP %d %d ", hostname,
! 322: rdata_pubkey_algorithm, rdata_digest_type);
! 323: }
! 324: for (i = 0; i < rdata_digest_len; i++)
! 325: fprintf(f, "%02x", rdata_digest[i]);
! 326: fprintf(f, "\n");
! 327: xfree(rdata_digest); /* from key_fingerprint_raw() */
! 328: success = 1;
! 329: }
! 330: }
1.1 jakob 331:
1.28 ! djm 332: /* No SSHFP record was generated at all */
! 333: if (success == 0) {
! 334: error("%s: unsupported algorithm and/or digest_type", __func__);
1.1 jakob 335: }
336:
337: return success;
338: }
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