1 /* $NetBSD: dns.c,v 1.9 2013/11/08 19:18:25 christos Exp $ */ 2 /* $OpenBSD: dns.c,v 1.29 2013/05/17 00:13:13 djm Exp $ */ 3 4 /* 5 * Copyright (c) 2003 Wesley Griffin. All rights reserved. 6 * Copyright (c) 2003 Jakob Schlyter. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 */ 28 29 #include "includes.h" 30 __RCSID("$NetBSD: dns.c,v 1.9 2013/11/08 19:18:25 christos Exp $"); 31 #include <sys/types.h> 32 #include <sys/socket.h> 33 34 #include <netdb.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 #include "getrrsetbyname.h" 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 * 54 dns_result_totext(unsigned int res) 55 { 56 switch (res) { 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, 79 u_char **digest, u_int *digest_len, Key *key) 80 { 81 int success = 0; 82 enum fp_type fp_type = 0; 83 84 switch (key->type) { 85 case KEY_RSA: 86 *algorithm = SSHFP_KEY_RSA; 87 if (!*digest_type) 88 *digest_type = SSHFP_HASH_SHA1; 89 break; 90 case KEY_DSA: 91 *algorithm = SSHFP_KEY_DSA; 92 if (!*digest_type) 93 *digest_type = SSHFP_HASH_SHA1; 94 break; 95 case KEY_ECDSA: 96 *algorithm = SSHFP_KEY_ECDSA; 97 if (!*digest_type) 98 *digest_type = SSHFP_HASH_SHA256; 99 break; 100 default: 101 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 102 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 103 } 104 105 switch (*digest_type) { 106 case SSHFP_HASH_SHA1: 107 fp_type = SSH_FP_SHA1; 108 break; 109 case SSHFP_HASH_SHA256: 110 fp_type = SSH_FP_SHA256; 111 break; 112 default: 113 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 114 } 115 116 if (*algorithm && *digest_type) { 117 *digest = key_fingerprint_raw(key, fp_type, digest_len); 118 if (*digest == NULL) 119 fatal("dns_read_key: null from key_fingerprint_raw()"); 120 success = 1; 121 } else { 122 *digest = NULL; 123 *digest_len = 0; 124 success = 0; 125 } 126 127 return success; 128 } 129 130 /* 131 * Read SSHFP parameters from rdata buffer. 132 */ 133 static int 134 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 135 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) 136 { 137 int success = 0; 138 139 *algorithm = SSHFP_KEY_RESERVED; 140 *digest_type = SSHFP_HASH_RESERVED; 141 142 if (rdata_len >= 2) { 143 *algorithm = rdata[0]; 144 *digest_type = rdata[1]; 145 *digest_len = rdata_len - 2; 146 147 if (*digest_len > 0) { 148 *digest = (u_char *) xmalloc(*digest_len); 149 memcpy(*digest, rdata + 2, *digest_len); 150 } else { 151 *digest = (u_char *)xstrdup(""); 152 } 153 154 success = 1; 155 } 156 157 return success; 158 } 159 160 /* 161 * Check if hostname is numerical. 162 * Returns -1 if hostname is numeric, 0 otherwise 163 */ 164 static int 165 is_numeric_hostname(const char *hostname) 166 { 167 struct addrinfo hints, *ai; 168 169 /* 170 * We shouldn't ever get a null host but if we do then log an error 171 * and return -1 which stops DNS key fingerprint processing. 172 */ 173 if (hostname == NULL) { 174 error("is_numeric_hostname called with NULL hostname"); 175 return -1; 176 } 177 178 memset(&hints, 0, sizeof(hints)); 179 hints.ai_socktype = SOCK_DGRAM; 180 hints.ai_flags = AI_NUMERICHOST; 181 182 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 183 freeaddrinfo(ai); 184 return -1; 185 } 186 187 return 0; 188 } 189 190 /* 191 * Verify the given hostname, address and host key using DNS. 192 * Returns 0 if lookup succeeds, -1 otherwise 193 */ 194 int 195 verify_host_key_dns(const char *hostname, struct sockaddr *address, 196 Key *hostkey, int *flags) 197 { 198 u_int counter; 199 int result; 200 struct rrsetinfo *fingerprints = NULL; 201 202 u_int8_t hostkey_algorithm; 203 u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED; 204 u_char *hostkey_digest; 205 u_int hostkey_digest_len; 206 207 u_int8_t dnskey_algorithm; 208 u_int8_t dnskey_digest_type; 209 u_char *dnskey_digest; 210 u_int dnskey_digest_len; 211 212 *flags = 0; 213 214 debug3("verify_host_key_dns"); 215 if (hostkey == NULL) 216 fatal("No key to look up!"); 217 218 if (is_numeric_hostname(hostname)) { 219 debug("skipped DNS lookup for numerical hostname"); 220 return -1; 221 } 222 223 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 224 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 225 if (result) { 226 verbose("DNS lookup error: %s", dns_result_totext(result)); 227 return -1; 228 } 229 230 if (fingerprints->rri_flags & RRSET_VALIDATED) { 231 *flags |= DNS_VERIFY_SECURE; 232 debug("found %d secure fingerprints in DNS", 233 fingerprints->rri_nrdatas); 234 } else { 235 debug("found %d insecure fingerprints in DNS", 236 fingerprints->rri_nrdatas); 237 } 238 239 /* Initialize default host key parameters */ 240 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 241 &hostkey_digest, &hostkey_digest_len, hostkey)) { 242 error("Error calculating host key fingerprint."); 243 freerrset(fingerprints); 244 return -1; 245 } 246 247 if (fingerprints->rri_nrdatas) 248 *flags |= DNS_VERIFY_FOUND; 249 250 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 251 /* 252 * Extract the key from the answer. Ignore any badly 253 * formatted fingerprints. 254 */ 255 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 256 &dnskey_digest, &dnskey_digest_len, 257 fingerprints->rri_rdatas[counter].rdi_data, 258 fingerprints->rri_rdatas[counter].rdi_length)) { 259 verbose("Error parsing fingerprint from DNS."); 260 continue; 261 } 262 263 if (hostkey_digest_type != dnskey_digest_type) { 264 hostkey_digest_type = dnskey_digest_type; 265 free(hostkey_digest); 266 267 /* Initialize host key parameters */ 268 if (!dns_read_key(&hostkey_algorithm, 269 &hostkey_digest_type, &hostkey_digest, 270 &hostkey_digest_len, hostkey)) { 271 error("Error calculating key fingerprint."); 272 freerrset(fingerprints); 273 return -1; 274 } 275 } 276 277 /* Check if the current key is the same as the given key */ 278 if (hostkey_algorithm == dnskey_algorithm && 279 hostkey_digest_type == dnskey_digest_type) { 280 if (hostkey_digest_len == dnskey_digest_len && 281 consttime_memequal(hostkey_digest, dnskey_digest, 282 hostkey_digest_len)) 283 *flags |= DNS_VERIFY_MATCH; 284 } 285 free(dnskey_digest); 286 } 287 288 free(hostkey_digest); /* from key_fingerprint_raw() */ 289 freerrset(fingerprints); 290 291 if (*flags & DNS_VERIFY_FOUND) 292 if (*flags & DNS_VERIFY_MATCH) 293 debug("matching host key fingerprint found in DNS"); 294 else 295 debug("mismatching host key fingerprint found in DNS"); 296 else 297 debug("no host key fingerprint found in DNS"); 298 299 return 0; 300 } 301 302 /* 303 * Export the fingerprint of a key as a DNS resource record 304 */ 305 int 306 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic) 307 { 308 u_int8_t rdata_pubkey_algorithm = 0; 309 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED; 310 u_int8_t dtype; 311 u_char *rdata_digest; 312 u_int i, rdata_digest_len; 313 int success = 0; 314 315 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) { 316 rdata_digest_type = dtype; 317 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 318 &rdata_digest, &rdata_digest_len, key)) { 319 if (generic) { 320 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", 321 hostname, DNS_RDATATYPE_SSHFP, 322 2 + rdata_digest_len, 323 rdata_pubkey_algorithm, rdata_digest_type); 324 } else { 325 fprintf(f, "%s IN SSHFP %d %d ", hostname, 326 rdata_pubkey_algorithm, rdata_digest_type); 327 } 328 for (i = 0; i < rdata_digest_len; i++) 329 fprintf(f, "%02x", rdata_digest[i]); 330 fprintf(f, "\n"); 331 free(rdata_digest); /* from key_fingerprint_raw() */ 332 success = 1; 333 } 334 } 335 336 /* No SSHFP record was generated at all */ 337 if (success == 0) { 338 error("%s: unsupported algorithm and/or digest_type", __func__); 339 } 340 341 return success; 342 } 343