1 /* $OpenBSD: dns.c,v 1.27 2010/08/31 11:54:45 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 82 switch (key->type) { 83 case KEY_RSA: 84 *algorithm = SSHFP_KEY_RSA; 85 break; 86 case KEY_DSA: 87 *algorithm = SSHFP_KEY_DSA; 88 break; 89 /* XXX KEY_ECDSA */ 90 default: 91 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 92 } 93 94 if (*algorithm) { 95 *digest_type = SSHFP_HASH_SHA1; 96 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len); 97 if (*digest == NULL) 98 fatal("dns_read_key: null from key_fingerprint_raw()"); 99 success = 1; 100 } else { 101 *digest_type = SSHFP_HASH_RESERVED; 102 *digest = NULL; 103 *digest_len = 0; 104 success = 0; 105 } 106 107 return success; 108 } 109 110 /* 111 * Read SSHFP parameters from rdata buffer. 112 */ 113 static int 114 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 115 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) 116 { 117 int success = 0; 118 119 *algorithm = SSHFP_KEY_RESERVED; 120 *digest_type = SSHFP_HASH_RESERVED; 121 122 if (rdata_len >= 2) { 123 *algorithm = rdata[0]; 124 *digest_type = rdata[1]; 125 *digest_len = rdata_len - 2; 126 127 if (*digest_len > 0) { 128 *digest = (u_char *) xmalloc(*digest_len); 129 memcpy(*digest, rdata + 2, *digest_len); 130 } else { 131 *digest = (u_char *)xstrdup(""); 132 } 133 134 success = 1; 135 } 136 137 return success; 138 } 139 140 /* 141 * Check if hostname is numerical. 142 * Returns -1 if hostname is numeric, 0 otherwise 143 */ 144 static int 145 is_numeric_hostname(const char *hostname) 146 { 147 struct addrinfo hints, *ai; 148 149 /* 150 * We shouldn't ever get a null host but if we do then log an error 151 * and return -1 which stops DNS key fingerprint processing. 152 */ 153 if (hostname == NULL) { 154 error("is_numeric_hostname called with NULL hostname"); 155 return -1; 156 } 157 158 memset(&hints, 0, sizeof(hints)); 159 hints.ai_socktype = SOCK_DGRAM; 160 hints.ai_flags = AI_NUMERICHOST; 161 162 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 163 freeaddrinfo(ai); 164 return -1; 165 } 166 167 return 0; 168 } 169 170 /* 171 * Verify the given hostname, address and host key using DNS. 172 * Returns 0 if lookup succeeds, -1 otherwise 173 */ 174 int 175 verify_host_key_dns(const char *hostname, struct sockaddr *address, 176 Key *hostkey, int *flags) 177 { 178 u_int counter; 179 int result; 180 struct rrsetinfo *fingerprints = NULL; 181 182 u_int8_t hostkey_algorithm; 183 u_int8_t hostkey_digest_type; 184 u_char *hostkey_digest; 185 u_int hostkey_digest_len; 186 187 u_int8_t dnskey_algorithm; 188 u_int8_t dnskey_digest_type; 189 u_char *dnskey_digest; 190 u_int dnskey_digest_len; 191 192 *flags = 0; 193 194 debug3("verify_host_key_dns"); 195 if (hostkey == NULL) 196 fatal("No key to look up!"); 197 198 if (is_numeric_hostname(hostname)) { 199 debug("skipped DNS lookup for numerical hostname"); 200 return -1; 201 } 202 203 #ifndef ANDROID 204 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 205 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 206 #else 207 /* unsupported in android */ 208 result = -1; 209 #endif 210 if (result) { 211 verbose("DNS lookup error: %s", dns_result_totext(result)); 212 return -1; 213 } 214 215 if (fingerprints->rri_flags & RRSET_VALIDATED) { 216 *flags |= DNS_VERIFY_SECURE; 217 debug("found %d secure fingerprints in DNS", 218 fingerprints->rri_nrdatas); 219 } else { 220 debug("found %d insecure fingerprints in DNS", 221 fingerprints->rri_nrdatas); 222 } 223 224 /* Initialize host key parameters */ 225 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 226 &hostkey_digest, &hostkey_digest_len, hostkey)) { 227 error("Error calculating host key fingerprint."); 228 #ifndef ANDROID 229 freerrset(fingerprints); 230 #endif 231 return -1; 232 } 233 234 if (fingerprints->rri_nrdatas) 235 *flags |= DNS_VERIFY_FOUND; 236 237 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 238 /* 239 * Extract the key from the answer. Ignore any badly 240 * formatted fingerprints. 241 */ 242 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 243 &dnskey_digest, &dnskey_digest_len, 244 fingerprints->rri_rdatas[counter].rdi_data, 245 fingerprints->rri_rdatas[counter].rdi_length)) { 246 verbose("Error parsing fingerprint from DNS."); 247 continue; 248 } 249 250 /* Check if the current key is the same as the given key */ 251 if (hostkey_algorithm == dnskey_algorithm && 252 hostkey_digest_type == dnskey_digest_type) { 253 254 if (hostkey_digest_len == dnskey_digest_len && 255 memcmp(hostkey_digest, dnskey_digest, 256 hostkey_digest_len) == 0) { 257 258 *flags |= DNS_VERIFY_MATCH; 259 } 260 } 261 xfree(dnskey_digest); 262 } 263 264 xfree(hostkey_digest); /* from key_fingerprint_raw() */ 265 #ifndef ANDROID 266 freerrset(fingerprints); 267 #endif 268 269 if (*flags & DNS_VERIFY_FOUND) 270 if (*flags & DNS_VERIFY_MATCH) 271 debug("matching host key fingerprint found in DNS"); 272 else 273 debug("mismatching host key fingerprint found in DNS"); 274 else 275 debug("no host key fingerprint found in DNS"); 276 277 return 0; 278 } 279 280 /* 281 * Export the fingerprint of a key as a DNS resource record 282 */ 283 int 284 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic) 285 { 286 u_int8_t rdata_pubkey_algorithm = 0; 287 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; 288 u_char *rdata_digest; 289 u_int rdata_digest_len; 290 291 u_int i; 292 int success = 0; 293 294 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 295 &rdata_digest, &rdata_digest_len, key)) { 296 297 if (generic) 298 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, 299 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, 300 rdata_pubkey_algorithm, rdata_digest_type); 301 else 302 fprintf(f, "%s IN SSHFP %d %d ", hostname, 303 rdata_pubkey_algorithm, rdata_digest_type); 304 305 for (i = 0; i < rdata_digest_len; i++) 306 fprintf(f, "%02x", rdata_digest[i]); 307 fprintf(f, "\n"); 308 xfree(rdata_digest); /* from key_fingerprint_raw() */ 309 success = 1; 310 } else { 311 error("export_dns_rr: unsupported algorithm"); 312 } 313 314 return success; 315 } 316
