1 /* $OpenBSD: dns.c,v 1.29 2013/05/17 00:13:13 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 38 #include "xmalloc.h" 39 #include "key.h" 40 #include "dns.h" 41 #include "log.h" 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 * 53 dns_result_totext(unsigned int res) 54 { 55 switch (res) { 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, 78 u_char **digest, u_int *digest_len, Key *key) 79 { 80 int success = 0; 81 enum fp_type fp_type = 0; 82 83 switch (key->type) { 84 case KEY_RSA: 85 *algorithm = SSHFP_KEY_RSA; 86 if (!*digest_type) 87 *digest_type = SSHFP_HASH_SHA1; 88 break; 89 case KEY_DSA: 90 *algorithm = SSHFP_KEY_DSA; 91 if (!*digest_type) 92 *digest_type = SSHFP_HASH_SHA1; 93 break; 94 case KEY_ECDSA: 95 *algorithm = SSHFP_KEY_ECDSA; 96 if (!*digest_type) 97 *digest_type = SSHFP_HASH_SHA256; 98 break; 99 default: 100 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 101 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 102 } 103 104 switch (*digest_type) { 105 case SSHFP_HASH_SHA1: 106 fp_type = SSH_FP_SHA1; 107 break; 108 case SSHFP_HASH_SHA256: 109 fp_type = SSH_FP_SHA256; 110 break; 111 default: 112 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 113 } 114 115 if (*algorithm && *digest_type) { 116 *digest = key_fingerprint_raw(key, fp_type, digest_len); 117 if (*digest == NULL) 118 fatal("dns_read_key: null from key_fingerprint_raw()"); 119 success = 1; 120 } else { 121 *digest = NULL; 122 *digest_len = 0; 123 success = 0; 124 } 125 126 return success; 127 } 128 129 /* 130 * Read SSHFP parameters from rdata buffer. 131 */ 132 static int 133 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 134 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) 135 { 136 int success = 0; 137 138 *algorithm = SSHFP_KEY_RESERVED; 139 *digest_type = SSHFP_HASH_RESERVED; 140 141 if (rdata_len >= 2) { 142 *algorithm = rdata[0]; 143 *digest_type = rdata[1]; 144 *digest_len = rdata_len - 2; 145 146 if (*digest_len > 0) { 147 *digest = (u_char *) xmalloc(*digest_len); 148 memcpy(*digest, rdata + 2, *digest_len); 149 } else { 150 *digest = (u_char *)xstrdup(""); 151 } 152 153 success = 1; 154 } 155 156 return success; 157 } 158 159 /* 160 * Check if hostname is numerical. 161 * Returns -1 if hostname is numeric, 0 otherwise 162 */ 163 static int 164 is_numeric_hostname(const char *hostname) 165 { 166 struct addrinfo hints, *ai; 167 168 /* 169 * We shouldn't ever get a null host but if we do then log an error 170 * and return -1 which stops DNS key fingerprint processing. 171 */ 172 if (hostname == NULL) { 173 error("is_numeric_hostname called with NULL hostname"); 174 return -1; 175 } 176 177 memset(&hints, 0, sizeof(hints)); 178 hints.ai_socktype = SOCK_DGRAM; 179 hints.ai_flags = AI_NUMERICHOST; 180 181 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 182 freeaddrinfo(ai); 183 return -1; 184 } 185 186 return 0; 187 } 188 189 /* 190 * Verify the given hostname, address and host key using DNS. 191 * Returns 0 if lookup succeeds, -1 otherwise 192 */ 193 int 194 verify_host_key_dns(const char *hostname, struct sockaddr *address, 195 Key *hostkey, int *flags) 196 { 197 u_int counter; 198 int result; 199 struct rrsetinfo *fingerprints = NULL; 200 201 u_int8_t hostkey_algorithm; 202 u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED; 203 u_char *hostkey_digest; 204 u_int hostkey_digest_len; 205 206 u_int8_t dnskey_algorithm; 207 u_int8_t dnskey_digest_type; 208 u_char *dnskey_digest; 209 u_int dnskey_digest_len; 210 211 *flags = 0; 212 213 debug3("verify_host_key_dns"); 214 if (hostkey == NULL) 215 fatal("No key to look up!"); 216 217 if (is_numeric_hostname(hostname)) { 218 debug("skipped DNS lookup for numerical hostname"); 219 return -1; 220 } 221 222 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 223 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 224 if (result) { 225 verbose("DNS lookup error: %s", dns_result_totext(result)); 226 return -1; 227 } 228 229 if (fingerprints->rri_flags & RRSET_VALIDATED) { 230 *flags |= DNS_VERIFY_SECURE; 231 debug("found %d secure fingerprints in DNS", 232 fingerprints->rri_nrdatas); 233 } else { 234 debug("found %d insecure fingerprints in DNS", 235 fingerprints->rri_nrdatas); 236 } 237 238 /* Initialize default host key parameters */ 239 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 240 &hostkey_digest, &hostkey_digest_len, hostkey)) { 241 error("Error calculating host key fingerprint."); 242 freerrset(fingerprints); 243 return -1; 244 } 245 246 if (fingerprints->rri_nrdatas) 247 *flags |= DNS_VERIFY_FOUND; 248 249 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 250 /* 251 * Extract the key from the answer. Ignore any badly 252 * formatted fingerprints. 253 */ 254 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 255 &dnskey_digest, &dnskey_digest_len, 256 fingerprints->rri_rdatas[counter].rdi_data, 257 fingerprints->rri_rdatas[counter].rdi_length)) { 258 verbose("Error parsing fingerprint from DNS."); 259 continue; 260 } 261 262 if (hostkey_digest_type != dnskey_digest_type) { 263 hostkey_digest_type = dnskey_digest_type; 264 free(hostkey_digest); 265 266 /* Initialize host key parameters */ 267 if (!dns_read_key(&hostkey_algorithm, 268 &hostkey_digest_type, &hostkey_digest, 269 &hostkey_digest_len, hostkey)) { 270 error("Error calculating key fingerprint."); 271 freerrset(fingerprints); 272 return -1; 273 } 274 } 275 276 /* Check if the current key is the same as the given key */ 277 if (hostkey_algorithm == dnskey_algorithm && 278 hostkey_digest_type == dnskey_digest_type) { 279 if (hostkey_digest_len == dnskey_digest_len && 280 timingsafe_bcmp(hostkey_digest, dnskey_digest, 281 hostkey_digest_len) == 0) 282 *flags |= DNS_VERIFY_MATCH; 283 } 284 free(dnskey_digest); 285 } 286 287 free(hostkey_digest); /* from key_fingerprint_raw() */ 288 freerrset(fingerprints); 289 290 if (*flags & DNS_VERIFY_FOUND) 291 if (*flags & DNS_VERIFY_MATCH) 292 debug("matching host key fingerprint found in DNS"); 293 else 294 debug("mismatching host key fingerprint found in DNS"); 295 else 296 debug("no host key fingerprint found in DNS"); 297 298 return 0; 299 } 300 301 /* 302 * Export the fingerprint of a key as a DNS resource record 303 */ 304 int 305 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic) 306 { 307 u_int8_t rdata_pubkey_algorithm = 0; 308 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED; 309 u_int8_t dtype; 310 u_char *rdata_digest; 311 u_int i, rdata_digest_len; 312 int success = 0; 313 314 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) { 315 rdata_digest_type = dtype; 316 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 317 &rdata_digest, &rdata_digest_len, key)) { 318 if (generic) { 319 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", 320 hostname, DNS_RDATATYPE_SSHFP, 321 2 + rdata_digest_len, 322 rdata_pubkey_algorithm, rdata_digest_type); 323 } else { 324 fprintf(f, "%s IN SSHFP %d %d ", hostname, 325 rdata_pubkey_algorithm, rdata_digest_type); 326 } 327 for (i = 0; i < rdata_digest_len; i++) 328 fprintf(f, "%02x", rdata_digest[i]); 329 fprintf(f, "\n"); 330 free(rdata_digest); /* from key_fingerprint_raw() */ 331 success = 1; 332 } 333 } 334 335 /* No SSHFP record was generated at all */ 336 if (success == 0) { 337 error("%s: unsupported algorithm and/or digest_type", __func__); 338 } 339 340 return success; 341 } 342