1 /* $OpenBSD: dns.c,v 1.25 2008/06/12 00:03:49 dtucker 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, const 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 default: 90 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 91 } 92 93 if (*algorithm) { 94 *digest_type = SSHFP_HASH_SHA1; 95 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len); 96 if (*digest == NULL) 97 fatal("dns_read_key: null from key_fingerprint_raw()"); 98 success = 1; 99 } else { 100 *digest_type = SSHFP_HASH_RESERVED; 101 *digest = NULL; 102 *digest_len = 0; 103 success = 0; 104 } 105 106 return success; 107 } 108 109 /* 110 * Read SSHFP parameters from rdata buffer. 111 */ 112 static int 113 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 114 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) 115 { 116 int success = 0; 117 118 *algorithm = SSHFP_KEY_RESERVED; 119 *digest_type = SSHFP_HASH_RESERVED; 120 121 if (rdata_len >= 2) { 122 *algorithm = rdata[0]; 123 *digest_type = rdata[1]; 124 *digest_len = rdata_len - 2; 125 126 if (*digest_len > 0) { 127 *digest = (u_char *) xmalloc(*digest_len); 128 memcpy(*digest, rdata + 2, *digest_len); 129 } else { 130 *digest = (u_char *)xstrdup(""); 131 } 132 133 success = 1; 134 } 135 136 return success; 137 } 138 139 /* 140 * Check if hostname is numerical. 141 * Returns -1 if hostname is numeric, 0 otherwise 142 */ 143 static int 144 is_numeric_hostname(const char *hostname) 145 { 146 struct addrinfo hints, *ai; 147 148 /* 149 * We shouldn't ever get a null host but if we do then log an error 150 * and return -1 which stops DNS key fingerprint processing. 151 */ 152 if (hostname == NULL) { 153 error("is_numeric_hostname called with NULL hostname"); 154 return -1; 155 } 156 157 memset(&hints, 0, sizeof(hints)); 158 hints.ai_socktype = SOCK_DGRAM; 159 hints.ai_flags = AI_NUMERICHOST; 160 161 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 162 freeaddrinfo(ai); 163 return -1; 164 } 165 166 return 0; 167 } 168 169 /* 170 * Verify the given hostname, address and host key using DNS. 171 * Returns 0 if lookup succeeds, -1 otherwise 172 */ 173 int 174 verify_host_key_dns(const char *hostname, struct sockaddr *address, 175 const Key *hostkey, int *flags) 176 { 177 u_int counter; 178 int result; 179 struct rrsetinfo *fingerprints = NULL; 180 181 u_int8_t hostkey_algorithm; 182 u_int8_t hostkey_digest_type; 183 u_char *hostkey_digest; 184 u_int hostkey_digest_len; 185 186 u_int8_t dnskey_algorithm; 187 u_int8_t dnskey_digest_type; 188 u_char *dnskey_digest; 189 u_int dnskey_digest_len; 190 191 *flags = 0; 192 193 debug3("verify_host_key_dns"); 194 if (hostkey == NULL) 195 fatal("No key to look up!"); 196 197 if (is_numeric_hostname(hostname)) { 198 debug("skipped DNS lookup for numerical hostname"); 199 return -1; 200 } 201 202 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 203 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 204 if (result) { 205 verbose("DNS lookup error: %s", dns_result_totext(result)); 206 return -1; 207 } 208 209 if (fingerprints->rri_flags & RRSET_VALIDATED) { 210 *flags |= DNS_VERIFY_SECURE; 211 debug("found %d secure fingerprints in DNS", 212 fingerprints->rri_nrdatas); 213 } else { 214 debug("found %d insecure fingerprints in DNS", 215 fingerprints->rri_nrdatas); 216 } 217 218 /* Initialize host key parameters */ 219 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 220 &hostkey_digest, &hostkey_digest_len, hostkey)) { 221 error("Error calculating host key fingerprint."); 222 freerrset(fingerprints); 223 return -1; 224 } 225 226 if (fingerprints->rri_nrdatas) 227 *flags |= DNS_VERIFY_FOUND; 228 229 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 230 /* 231 * Extract the key from the answer. Ignore any badly 232 * formatted fingerprints. 233 */ 234 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 235 &dnskey_digest, &dnskey_digest_len, 236 fingerprints->rri_rdatas[counter].rdi_data, 237 fingerprints->rri_rdatas[counter].rdi_length)) { 238 verbose("Error parsing fingerprint from DNS."); 239 continue; 240 } 241 242 /* Check if the current key is the same as the given key */ 243 if (hostkey_algorithm == dnskey_algorithm && 244 hostkey_digest_type == dnskey_digest_type) { 245 246 if (hostkey_digest_len == dnskey_digest_len && 247 memcmp(hostkey_digest, dnskey_digest, 248 hostkey_digest_len) == 0) { 249 250 *flags |= DNS_VERIFY_MATCH; 251 } 252 } 253 xfree(dnskey_digest); 254 } 255 256 xfree(hostkey_digest); /* from key_fingerprint_raw() */ 257 freerrset(fingerprints); 258 259 if (*flags & DNS_VERIFY_FOUND) 260 if (*flags & DNS_VERIFY_MATCH) 261 debug("matching host key fingerprint found in DNS"); 262 else 263 debug("mismatching host key fingerprint found in DNS"); 264 else 265 debug("no host key fingerprint found in DNS"); 266 267 return 0; 268 } 269 270 /* 271 * Export the fingerprint of a key as a DNS resource record 272 */ 273 int 274 export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic) 275 { 276 u_int8_t rdata_pubkey_algorithm = 0; 277 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; 278 u_char *rdata_digest; 279 u_int rdata_digest_len; 280 281 u_int i; 282 int success = 0; 283 284 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 285 &rdata_digest, &rdata_digest_len, key)) { 286 287 if (generic) 288 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, 289 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, 290 rdata_pubkey_algorithm, rdata_digest_type); 291 else 292 fprintf(f, "%s IN SSHFP %d %d ", hostname, 293 rdata_pubkey_algorithm, rdata_digest_type); 294 295 for (i = 0; i < rdata_digest_len; i++) 296 fprintf(f, "%02x", rdata_digest[i]); 297 fprintf(f, "\n"); 298 xfree(rdata_digest); /* from key_fingerprint_raw() */ 299 success = 1; 300 } else { 301 error("export_dns_rr: unsupported algorithm"); 302 } 303 304 return success; 305 } 306