1 /* $OpenBSD: dns.c,v 1.31 2014/06/24 01:13:21 djm 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 "key.h" 42 #include "dns.h" 43 #include "log.h" 44 45 static const char *errset_text[] = { 46 "success", /* 0 ERRSET_SUCCESS */ 47 "out of memory", /* 1 ERRSET_NOMEMORY */ 48 "general failure", /* 2 ERRSET_FAIL */ 49 "invalid parameter", /* 3 ERRSET_INVAL */ 50 "name does not exist", /* 4 ERRSET_NONAME */ 51 "data does not exist", /* 5 ERRSET_NODATA */ 52 }; 53 54 static const char * 55 dns_result_totext(unsigned int res) 56 { 57 switch (res) { 58 case ERRSET_SUCCESS: 59 return errset_text[ERRSET_SUCCESS]; 60 case ERRSET_NOMEMORY: 61 return errset_text[ERRSET_NOMEMORY]; 62 case ERRSET_FAIL: 63 return errset_text[ERRSET_FAIL]; 64 case ERRSET_INVAL: 65 return errset_text[ERRSET_INVAL]; 66 case ERRSET_NONAME: 67 return errset_text[ERRSET_NONAME]; 68 case ERRSET_NODATA: 69 return errset_text[ERRSET_NODATA]; 70 default: 71 return "unknown error"; 72 } 73 } 74 75 /* 76 * Read SSHFP parameters from key buffer. 77 */ 78 static int 79 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type, 80 u_char **digest, u_int *digest_len, Key *key) 81 { 82 int success = 0; 83 enum fp_type fp_type = 0; 84 85 switch (key->type) { 86 case KEY_RSA: 87 *algorithm = SSHFP_KEY_RSA; 88 if (!*digest_type) 89 *digest_type = SSHFP_HASH_SHA1; 90 break; 91 case KEY_DSA: 92 *algorithm = SSHFP_KEY_DSA; 93 if (!*digest_type) 94 *digest_type = SSHFP_HASH_SHA1; 95 break; 96 case KEY_ECDSA: 97 *algorithm = SSHFP_KEY_ECDSA; 98 if (!*digest_type) 99 *digest_type = SSHFP_HASH_SHA256; 100 break; 101 case KEY_ED25519: 102 *algorithm = SSHFP_KEY_ED25519; 103 if (!*digest_type) 104 *digest_type = SSHFP_HASH_SHA256; 105 break; 106 default: 107 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 108 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 109 } 110 111 switch (*digest_type) { 112 case SSHFP_HASH_SHA1: 113 fp_type = SSH_FP_SHA1; 114 break; 115 case SSHFP_HASH_SHA256: 116 fp_type = SSH_FP_SHA256; 117 break; 118 default: 119 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 120 } 121 122 if (*algorithm && *digest_type) { 123 *digest = key_fingerprint_raw(key, fp_type, digest_len); 124 if (*digest == NULL) 125 fatal("dns_read_key: null from key_fingerprint_raw()"); 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, 141 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) 142 { 143 int success = 0; 144 145 *algorithm = SSHFP_KEY_RESERVED; 146 *digest_type = SSHFP_HASH_RESERVED; 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 { 157 *digest = (u_char *)xstrdup(""); 158 } 159 160 success = 1; 161 } 162 163 return success; 164 } 165 166 /* 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; 174 175 /* 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 } 183 184 memset(&hints, 0, sizeof(hints)); 185 hints.ai_socktype = SOCK_DGRAM; 186 hints.ai_flags = AI_NUMERICHOST; 187 188 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 189 freeaddrinfo(ai); 190 return -1; 191 } 192 193 return 0; 194 } 195 196 /* 197 * Verify the given hostname, address and host key using DNS. 198 * Returns 0 if lookup succeeds, -1 otherwise 199 */ 200 int 201 verify_host_key_dns(const char *hostname, struct sockaddr *address, 202 Key *hostkey, int *flags) 203 { 204 u_int counter; 205 int result; 206 struct rrsetinfo *fingerprints = NULL; 207 208 u_int8_t hostkey_algorithm; 209 u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED; 210 u_char *hostkey_digest; 211 u_int hostkey_digest_len; 212 213 u_int8_t dnskey_algorithm; 214 u_int8_t dnskey_digest_type; 215 u_char *dnskey_digest; 216 u_int dnskey_digest_len; 217 218 *flags = 0; 219 220 debug3("verify_host_key_dns"); 221 if (hostkey == NULL) 222 fatal("No key to look up!"); 223 224 if (is_numeric_hostname(hostname)) { 225 debug("skipped DNS lookup for numerical hostname"); 226 return -1; 227 } 228 229 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 230 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 231 if (result) { 232 verbose("DNS lookup error: %s", dns_result_totext(result)); 233 return -1; 234 } 235 236 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); 243 } 244 245 /* Initialize default host key parameters */ 246 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 247 &hostkey_digest, &hostkey_digest_len, hostkey)) { 248 error("Error calculating host key fingerprint."); 249 freerrset(fingerprints); 250 return -1; 251 } 252 253 if (fingerprints->rri_nrdatas) 254 *flags |= DNS_VERIFY_FOUND; 255 256 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 257 /* 258 * Extract the key from the answer. Ignore any badly 259 * formatted fingerprints. 260 */ 261 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 262 &dnskey_digest, &dnskey_digest_len, 263 fingerprints->rri_rdatas[counter].rdi_data, 264 fingerprints->rri_rdatas[counter].rdi_length)) { 265 verbose("Error parsing fingerprint from DNS."); 266 continue; 267 } 268 269 if (hostkey_digest_type != dnskey_digest_type) { 270 hostkey_digest_type = dnskey_digest_type; 271 free(hostkey_digest); 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 } 282 283 /* 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 && 287 timingsafe_bcmp(hostkey_digest, dnskey_digest, 288 hostkey_digest_len) == 0) 289 *flags |= DNS_VERIFY_MATCH; 290 } 291 free(dnskey_digest); 292 } 293 294 free(hostkey_digest); /* from key_fingerprint_raw() */ 295 freerrset(fingerprints); 296 297 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"); 304 305 return 0; 306 } 307 308 /* 309 * Export the fingerprint of a key as a DNS resource record 310 */ 311 int 312 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic) 313 { 314 u_int8_t rdata_pubkey_algorithm = 0; 315 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED; 316 u_int8_t dtype; 317 u_char *rdata_digest; 318 u_int i, rdata_digest_len; 319 int success = 0; 320 321 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) { 326 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", 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"); 337 free(rdata_digest); /* from key_fingerprint_raw() */ 338 success = 1; 339 } 340 } 341 342 /* No SSHFP record was generated at all */ 343 if (success == 0) { 344 error("%s: unsupported algorithm and/or digest_type", __func__); 345 } 346 347 return success; 348 } 349