1 /* $OpenBSD: dns.c,v 1.39 2020/10/18 11:32:01 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 <sys/types.h> 29 #include <sys/socket.h> 30 31 #include <netdb.h> 32 #include <stdio.h> 33 #include <string.h> 34 #include <stdarg.h> 35 #include <stdlib.h> 36 37 #include "xmalloc.h" 38 #include "sshkey.h" 39 #include "ssherr.h" 40 #include "dns.h" 41 #include "log.h" 42 #include "digest.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, size_t *digest_len, struct sshkey *key) 80 { 81 int r, success = 0; 82 int fp_alg = -1; 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 case KEY_ED25519: 101 *algorithm = SSHFP_KEY_ED25519; 102 if (!*digest_type) 103 *digest_type = SSHFP_HASH_SHA256; 104 break; 105 case KEY_XMSS: 106 *algorithm = SSHFP_KEY_XMSS; 107 if (!*digest_type) 108 *digest_type = SSHFP_HASH_SHA256; 109 break; 110 default: 111 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 112 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 113 } 114 115 switch (*digest_type) { 116 case SSHFP_HASH_SHA1: 117 fp_alg = SSH_DIGEST_SHA1; 118 break; 119 case SSHFP_HASH_SHA256: 120 fp_alg = SSH_DIGEST_SHA256; 121 break; 122 default: 123 *digest_type = SSHFP_HASH_RESERVED; /* 0 */ 124 } 125 126 if (*algorithm && *digest_type) { 127 if ((r = sshkey_fingerprint_raw(key, fp_alg, digest, 128 digest_len)) != 0) 129 fatal_fr(r, "sshkey_fingerprint_raw"); 130 success = 1; 131 } else { 132 *digest = NULL; 133 *digest_len = 0; 134 success = 0; 135 } 136 137 return success; 138 } 139 140 /* 141 * Read SSHFP parameters from rdata buffer. 142 */ 143 static int 144 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 145 u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len) 146 { 147 int success = 0; 148 149 *algorithm = SSHFP_KEY_RESERVED; 150 *digest_type = SSHFP_HASH_RESERVED; 151 152 if (rdata_len >= 2) { 153 *algorithm = rdata[0]; 154 *digest_type = rdata[1]; 155 *digest_len = rdata_len - 2; 156 157 if (*digest_len > 0) { 158 *digest = xmalloc(*digest_len); 159 memcpy(*digest, rdata + 2, *digest_len); 160 } else { 161 *digest = (u_char *)xstrdup(""); 162 } 163 164 success = 1; 165 } 166 167 return success; 168 } 169 170 /* 171 * Check if hostname is numerical. 172 * Returns -1 if hostname is numeric, 0 otherwise 173 */ 174 static int 175 is_numeric_hostname(const char *hostname) 176 { 177 struct addrinfo hints, *ai; 178 179 /* 180 * We shouldn't ever get a null host but if we do then log an error 181 * and return -1 which stops DNS key fingerprint processing. 182 */ 183 if (hostname == NULL) { 184 error("is_numeric_hostname called with NULL hostname"); 185 return -1; 186 } 187 188 memset(&hints, 0, sizeof(hints)); 189 hints.ai_socktype = SOCK_DGRAM; 190 hints.ai_flags = AI_NUMERICHOST; 191 192 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 193 freeaddrinfo(ai); 194 return -1; 195 } 196 197 return 0; 198 } 199 200 /* 201 * Verify the given hostname, address and host key using DNS. 202 * Returns 0 if lookup succeeds, -1 otherwise 203 */ 204 int 205 verify_host_key_dns(const char *hostname, struct sockaddr *address, 206 struct sshkey *hostkey, int *flags) 207 { 208 u_int counter; 209 int result; 210 struct rrsetinfo *fingerprints = NULL; 211 212 u_int8_t hostkey_algorithm; 213 u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED; 214 u_char *hostkey_digest; 215 size_t hostkey_digest_len; 216 217 u_int8_t dnskey_algorithm; 218 u_int8_t dnskey_digest_type; 219 u_char *dnskey_digest; 220 size_t dnskey_digest_len; 221 222 *flags = 0; 223 224 debug3("verify_host_key_dns"); 225 if (hostkey == NULL) 226 fatal("No key to look up!"); 227 228 if (is_numeric_hostname(hostname)) { 229 debug("skipped DNS lookup for numerical hostname"); 230 return -1; 231 } 232 233 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 234 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 235 if (result) { 236 verbose("DNS lookup error: %s", dns_result_totext(result)); 237 return -1; 238 } 239 240 if (fingerprints->rri_flags & RRSET_VALIDATED) { 241 *flags |= DNS_VERIFY_SECURE; 242 debug("found %d secure fingerprints in DNS", 243 fingerprints->rri_nrdatas); 244 } else { 245 debug("found %d insecure fingerprints in DNS", 246 fingerprints->rri_nrdatas); 247 } 248 249 /* Initialize default host key parameters */ 250 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 251 &hostkey_digest, &hostkey_digest_len, hostkey)) { 252 error("Error calculating host key fingerprint."); 253 freerrset(fingerprints); 254 return -1; 255 } 256 257 if (fingerprints->rri_nrdatas) 258 *flags |= DNS_VERIFY_FOUND; 259 260 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 261 /* 262 * Extract the key from the answer. Ignore any badly 263 * formatted fingerprints. 264 */ 265 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 266 &dnskey_digest, &dnskey_digest_len, 267 fingerprints->rri_rdatas[counter].rdi_data, 268 fingerprints->rri_rdatas[counter].rdi_length)) { 269 verbose("Error parsing fingerprint from DNS."); 270 continue; 271 } 272 273 if (hostkey_digest_type != dnskey_digest_type) { 274 hostkey_digest_type = dnskey_digest_type; 275 free(hostkey_digest); 276 277 /* Initialize host key parameters */ 278 if (!dns_read_key(&hostkey_algorithm, 279 &hostkey_digest_type, &hostkey_digest, 280 &hostkey_digest_len, hostkey)) { 281 error("Error calculating key fingerprint."); 282 freerrset(fingerprints); 283 return -1; 284 } 285 } 286 287 /* Check if the current key is the same as the given key */ 288 if (hostkey_algorithm == dnskey_algorithm && 289 hostkey_digest_type == dnskey_digest_type) { 290 if (hostkey_digest_len == dnskey_digest_len && 291 timingsafe_bcmp(hostkey_digest, dnskey_digest, 292 hostkey_digest_len) == 0) 293 *flags |= DNS_VERIFY_MATCH; 294 } 295 free(dnskey_digest); 296 } 297 298 free(hostkey_digest); /* from sshkey_fingerprint_raw() */ 299 freerrset(fingerprints); 300 301 if (*flags & DNS_VERIFY_FOUND) 302 if (*flags & DNS_VERIFY_MATCH) 303 debug("matching host key fingerprint found in DNS"); 304 else 305 debug("mismatching host key fingerprint found in DNS"); 306 else 307 debug("no host key fingerprint found in DNS"); 308 309 return 0; 310 } 311 312 /* 313 * Export the fingerprint of a key as a DNS resource record 314 */ 315 int 316 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic) 317 { 318 u_int8_t rdata_pubkey_algorithm = 0; 319 u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED; 320 u_int8_t dtype; 321 u_char *rdata_digest; 322 size_t i, rdata_digest_len; 323 int success = 0; 324 325 for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) { 326 rdata_digest_type = dtype; 327 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 328 &rdata_digest, &rdata_digest_len, key)) { 329 if (generic) { 330 fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ", 331 hostname, DNS_RDATATYPE_SSHFP, 332 2 + rdata_digest_len, 333 rdata_pubkey_algorithm, rdata_digest_type); 334 } else { 335 fprintf(f, "%s IN SSHFP %d %d ", hostname, 336 rdata_pubkey_algorithm, rdata_digest_type); 337 } 338 for (i = 0; i < rdata_digest_len; i++) 339 fprintf(f, "%02x", rdata_digest[i]); 340 fprintf(f, "\n"); 341 free(rdata_digest); /* from sshkey_fingerprint_raw() */ 342 success = 1; 343 } 344 } 345 346 /* No SSHFP record was generated at all */ 347 if (success == 0) { 348 error_f("unsupported algorithm and/or digest_type"); 349 } 350 351 return success; 352 } 353