1 /* $OpenBSD: dns.c,v 1.35 2015/08/20 22:32:42 deraadt 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 <stdarg.h> 38 #include <stdlib.h> 39 40 #include "xmalloc.h" 41 #include "sshkey.h" 42 #include "ssherr.h" 43 #include "dns.h" 44 #include "log.h" 45 #include "digest.h" 46 47 static const char *errset_text[] = { 48 "success", /* 0 ERRSET_SUCCESS */ 49 "out of memory", /* 1 ERRSET_NOMEMORY */ 50 "general failure", /* 2 ERRSET_FAIL */ 51 "invalid parameter", /* 3 ERRSET_INVAL */ 52 "name does not exist", /* 4 ERRSET_NONAME */ 53 "data does not exist", /* 5 ERRSET_NODATA */ 54 }; 55 56 static const char * 57 dns_result_totext(unsigned int res) 58 { 59 switch (res) { 60 case ERRSET_SUCCESS: 61 return errset_text[ERRSET_SUCCESS]; 62 case ERRSET_NOMEMORY: 63 return errset_text[ERRSET_NOMEMORY]; 64 case ERRSET_FAIL: 65 return errset_text[ERRSET_FAIL]; 66 case ERRSET_INVAL: 67 return errset_text[ERRSET_INVAL]; 68 case ERRSET_NONAME: 69 return errset_text[ERRSET_NONAME]; 70 case ERRSET_NODATA: 71 return errset_text[ERRSET_NODATA]; 72 default: 73 return "unknown error"; 74 } 75 } 76 77 /* 78 * Read SSHFP parameters from key buffer. 79 */ 80 static int 81 dns_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 if (!*digest_type) 91 *digest_type = SSHFP_HASH_SHA1; 92 break; 93 case KEY_DSA: 94 *algorithm = SSHFP_KEY_DSA; 95 if (!*digest_type) 96 *digest_type = SSHFP_HASH_SHA1; 97 break; 98 case KEY_ECDSA: 99 *algorithm = SSHFP_KEY_ECDSA; 100 if (!*digest_type) 101 *digest_type = SSHFP_HASH_SHA256; 102 break; 103 case KEY_ED25519: 104 *algorithm = SSHFP_KEY_ED25519; 105 if (!*digest_type) 106 *digest_type = SSHFP_HASH_SHA256; 107 break; 108 default: 109 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 110 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 111 } 112 113 switch (*digest_type) { 114 case SSHFP_HASH_SHA1: 115 fp_alg = SSH_DIGEST_SHA1; 116 break; 117 case SSHFP_HASH_SHA256: 118 fp_alg = SSH_DIGEST_SHA256; 119 break; 120 default: 121 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 122 } 123 124 if (*algorithm && *digest_type) { 125 if ((r = sshkey_fingerprint_raw(key, fp_alg, digest, 126 digest_len)) != 0) 127 fatal("%s: sshkey_fingerprint_raw: %s", __func__, 128 ssh_err(r)); 129 success = 1; 130 } else { 131 *digest = NULL; 132 *digest_len = 0; 133 success = 0; 134 } 135 136 return success; 137 } 138 139 /* 140 * Read SSHFP parameters from rdata buffer. 141 */ 142 static int 143 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 144 u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len) 145 { 146 int success = 0; 147 148 *algorithm = SSHFP_KEY_RESERVED; 149 *digest_type = SSHFP_HASH_RESERVED; 150 151 if (rdata_len >= 2) { 152 *algorithm = rdata[0]; 153 *digest_type = rdata[1]; 154 *digest_len = rdata_len - 2; 155 156 if (*digest_len > 0) { 157 *digest = xmalloc(*digest_len); 158 memcpy(*digest, rdata + 2, *digest_len); 159 } else { 160 *digest = (u_char *)xstrdup(""); 161 } 162 163 success = 1; 164 } 165 166 return success; 167 } 168 169 /* 170 * Check if hostname is numerical. 171 * Returns -1 if hostname is numeric, 0 otherwise 172 */ 173 static int 174 is_numeric_hostname(const char *hostname) 175 { 176 struct addrinfo hints, *ai; 177 178 /* 179 * We shouldn't ever get a null host but if we do then log an error 180 * and return -1 which stops DNS key fingerprint processing. 181 */ 182 if (hostname == NULL) { 183 error("is_numeric_hostname called with NULL hostname"); 184 return -1; 185 } 186 187 memset(&hints, 0, sizeof(hints)); 188 hints.ai_socktype = SOCK_DGRAM; 189 hints.ai_flags = AI_NUMERICHOST; 190 191 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 192 freeaddrinfo(ai); 193 return -1; 194 } 195 196 return 0; 197 } 198 199 /* 200 * Verify the given hostname, address and host key using DNS. 201 * Returns 0 if lookup succeeds, -1 otherwise 202 */ 203 int 204 verify_host_key_dns(const char *hostname, struct sockaddr *address, 205 struct sshkey *hostkey, int *flags) 206 { 207 u_int counter; 208 int result; 209 struct rrsetinfo *fingerprints = NULL; 210 211 u_int8_t hostkey_algorithm; 212 u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED; 213 u_char *hostkey_digest; 214 size_t hostkey_digest_len; 215 216 u_int8_t dnskey_algorithm; 217 u_int8_t dnskey_digest_type; 218 u_char *dnskey_digest; 219 size_t dnskey_digest_len; 220 221 *flags = 0; 222 223 debug3("verify_host_key_dns"); 224 if (hostkey == NULL) 225 fatal("No key to look up!"); 226 227 if (is_numeric_hostname(hostname)) { 228 debug("skipped DNS lookup for numerical hostname"); 229 return -1; 230 } 231 232 #if !defined(ANDROID) 233 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 234 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 235 #else 236 /* unsupported in Android. */ 237 result = -1; 238 #endif 239 240 if (result) { 241 verbose("DNS lookup error: %s", dns_result_totext(result)); 242 return -1; 243 } 244 245 if (fingerprints->rri_flags & RRSET_VALIDATED) { 246 *flags |= DNS_VERIFY_SECURE; 247 debug("found %d secure fingerprints in DNS", 248 fingerprints->rri_nrdatas); 249 } else { 250 debug("found %d insecure fingerprints in DNS", 251 fingerprints->rri_nrdatas); 252 } 253 254 /* Initialize default host key parameters */ 255 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 256 &hostkey_digest, &hostkey_digest_len, hostkey)) { 257 error("Error calculating host key fingerprint."); 258 #if !defined(ANDROID) 259 freerrset(fingerprints); 260 #endif 261 return -1; 262 } 263 264 if (fingerprints->rri_nrdatas) 265 *flags |= DNS_VERIFY_FOUND; 266 267 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 268 /* 269 * Extract the key from the answer. Ignore any badly 270 * formatted fingerprints. 271 */ 272 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 273 &dnskey_digest, &dnskey_digest_len, 274 fingerprints->rri_rdatas[counter].rdi_data, 275 fingerprints->rri_rdatas[counter].rdi_length)) { 276 verbose("Error parsing fingerprint from DNS."); 277 continue; 278 } 279 280 if (hostkey_digest_type != dnskey_digest_type) { 281 hostkey_digest_type = dnskey_digest_type; 282 free(hostkey_digest); 283 284 /* Initialize host key parameters */ 285 if (!dns_read_key(&hostkey_algorithm, 286 &hostkey_digest_type, &hostkey_digest, 287 &hostkey_digest_len, hostkey)) { 288 error("Error calculating key fingerprint."); 289 #if !defined(ANDROID) 290 freerrset(fingerprints); 291 #endif 292 return -1; 293 } 294 } 295 296 /* Check if the current key is the same as the given key */ 297 if (hostkey_algorithm == dnskey_algorithm && 298 hostkey_digest_type == dnskey_digest_type) { 299 if (hostkey_digest_len == dnskey_digest_len && 300 timingsafe_bcmp(hostkey_digest, dnskey_digest, 301 hostkey_digest_len) == 0) 302 *flags |= DNS_VERIFY_MATCH; 303 } 304 free(dnskey_digest); 305 } 306 307 free(hostkey_digest); /* from sshkey_fingerprint_raw() */ 308 #if !defined(ANDROID) 309 freerrset(fingerprints); 310 #endif 311 312 if (*flags & DNS_VERIFY_FOUND) 313 if (*flags & DNS_VERIFY_MATCH) 314 debug("matching host key fingerprint found in DNS"); 315 else 316 debug("mismatching host key fingerprint found in DNS"); 317 else 318 debug("no host key fingerprint found in DNS"); 319 320 return 0; 321 } 322 323 /* 324 * Export the fingerprint of a key as a DNS resource record 325 */ 326 int 327 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic) 328 { 329 u_int8_t rdata_pubkey_algorithm = 0; 330 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED; 331 u_int8_t dtype; 332 u_char *rdata_digest; 333 size_t i, rdata_digest_len; 334 int success = 0; 335 336 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) { 337 rdata_digest_type = dtype; 338 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 339 &rdata_digest, &rdata_digest_len, key)) { 340 if (generic) { 341 fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ", 342 hostname, DNS_RDATATYPE_SSHFP, 343 2 + rdata_digest_len, 344 rdata_pubkey_algorithm, rdata_digest_type); 345 } else { 346 fprintf(f, "%s IN SSHFP %d %d ", hostname, 347 rdata_pubkey_algorithm, rdata_digest_type); 348 } 349 for (i = 0; i < rdata_digest_len; i++) 350 fprintf(f, "%02x", rdata_digest[i]); 351 fprintf(f, "\n"); 352 free(rdata_digest); /* from sshkey_fingerprint_raw() */ 353 success = 1; 354 } 355 } 356 357 /* No SSHFP record was generated at all */ 358 if (success == 0) { 359 error("%s: unsupported algorithm and/or digest_type", __func__); 360 } 361 362 return success; 363 } 364
