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 <sys/types.h> 29 #include <sys/socket.h> 30 31 #include <netdb.h> 32 #include <stdio.h> 33 #include <string.h> 34 35 #include "xmalloc.h" 36 #include "key.h" 37 #include "dns.h" 38 #include "log.h" 39 40 static const char *errset_text[] = { 41 "success", /* 0 ERRSET_SUCCESS */ 42 "out of memory", /* 1 ERRSET_NOMEMORY */ 43 "general failure", /* 2 ERRSET_FAIL */ 44 "invalid parameter", /* 3 ERRSET_INVAL */ 45 "name does not exist", /* 4 ERRSET_NONAME */ 46 "data does not exist", /* 5 ERRSET_NODATA */ 47 }; 48 49 static const char * 50 dns_result_totext(unsigned int res) 51 { 52 switch (res) { 53 case ERRSET_SUCCESS: 54 return errset_text[ERRSET_SUCCESS]; 55 case ERRSET_NOMEMORY: 56 return errset_text[ERRSET_NOMEMORY]; 57 case ERRSET_FAIL: 58 return errset_text[ERRSET_FAIL]; 59 case ERRSET_INVAL: 60 return errset_text[ERRSET_INVAL]; 61 case ERRSET_NONAME: 62 return errset_text[ERRSET_NONAME]; 63 case ERRSET_NODATA: 64 return errset_text[ERRSET_NODATA]; 65 default: 66 return "unknown error"; 67 } 68 } 69 70 /* 71 * Read SSHFP parameters from key buffer. 72 */ 73 static int 74 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type, 75 u_char **digest, u_int *digest_len, const Key *key) 76 { 77 int success = 0; 78 79 switch (key->type) { 80 case KEY_RSA: 81 *algorithm = SSHFP_KEY_RSA; 82 break; 83 case KEY_DSA: 84 *algorithm = SSHFP_KEY_DSA; 85 break; 86 default: 87 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 88 } 89 90 if (*algorithm) { 91 *digest_type = SSHFP_HASH_SHA1; 92 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len); 93 if (*digest == NULL) 94 fatal("dns_read_key: null from key_fingerprint_raw()"); 95 success = 1; 96 } else { 97 *digest_type = SSHFP_HASH_RESERVED; 98 *digest = NULL; 99 *digest_len = 0; 100 success = 0; 101 } 102 103 return success; 104 } 105 106 /* 107 * Read SSHFP parameters from rdata buffer. 108 */ 109 static int 110 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 111 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) 112 { 113 int success = 0; 114 115 *algorithm = SSHFP_KEY_RESERVED; 116 *digest_type = SSHFP_HASH_RESERVED; 117 118 if (rdata_len >= 2) { 119 *algorithm = rdata[0]; 120 *digest_type = rdata[1]; 121 *digest_len = rdata_len - 2; 122 123 if (*digest_len > 0) { 124 *digest = (u_char *) xmalloc(*digest_len); 125 memcpy(*digest, rdata + 2, *digest_len); 126 } else { 127 *digest = (u_char *)xstrdup(""); 128 } 129 130 success = 1; 131 } 132 133 return success; 134 } 135 136 /* 137 * Check if hostname is numerical. 138 * Returns -1 if hostname is numeric, 0 otherwise 139 */ 140 static int 141 is_numeric_hostname(const char *hostname) 142 { 143 struct addrinfo hints, *ai; 144 145 /* 146 * We shouldn't ever get a null host but if we do then log an error 147 * and return -1 which stops DNS key fingerprint processing. 148 */ 149 if (hostname == NULL) { 150 error("is_numeric_hostname called with NULL hostname"); 151 return -1; 152 } 153 154 memset(&hints, 0, sizeof(hints)); 155 hints.ai_socktype = SOCK_DGRAM; 156 hints.ai_flags = AI_NUMERICHOST; 157 158 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 159 freeaddrinfo(ai); 160 return -1; 161 } 162 163 return 0; 164 } 165 166 /* 167 * Verify the given hostname, address and host key using DNS. 168 * Returns 0 if lookup succeeds, -1 otherwise 169 */ 170 int 171 verify_host_key_dns(const char *hostname, struct sockaddr *address, 172 const Key *hostkey, int *flags) 173 { 174 u_int counter; 175 int result; 176 struct rrsetinfo *fingerprints = NULL; 177 178 u_int8_t hostkey_algorithm; 179 u_int8_t hostkey_digest_type; 180 u_char *hostkey_digest; 181 u_int hostkey_digest_len; 182 183 u_int8_t dnskey_algorithm; 184 u_int8_t dnskey_digest_type; 185 u_char *dnskey_digest; 186 u_int dnskey_digest_len; 187 188 *flags = 0; 189 190 debug3("verify_host_key_dns"); 191 if (hostkey == NULL) 192 fatal("No key to look up!"); 193 194 if (is_numeric_hostname(hostname)) { 195 debug("skipped DNS lookup for numerical hostname"); 196 return -1; 197 } 198 199 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 200 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 201 if (result) { 202 verbose("DNS lookup error: %s", dns_result_totext(result)); 203 return -1; 204 } 205 206 if (fingerprints->rri_flags & RRSET_VALIDATED) { 207 *flags |= DNS_VERIFY_SECURE; 208 debug("found %d secure fingerprints in DNS", 209 fingerprints->rri_nrdatas); 210 } else { 211 debug("found %d insecure fingerprints in DNS", 212 fingerprints->rri_nrdatas); 213 } 214 215 /* Initialize host key parameters */ 216 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 217 &hostkey_digest, &hostkey_digest_len, hostkey)) { 218 error("Error calculating host key fingerprint."); 219 freerrset(fingerprints); 220 return -1; 221 } 222 223 if (fingerprints->rri_nrdatas) 224 *flags |= DNS_VERIFY_FOUND; 225 226 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 227 /* 228 * Extract the key from the answer. Ignore any badly 229 * formatted fingerprints. 230 */ 231 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 232 &dnskey_digest, &dnskey_digest_len, 233 fingerprints->rri_rdatas[counter].rdi_data, 234 fingerprints->rri_rdatas[counter].rdi_length)) { 235 verbose("Error parsing fingerprint from DNS."); 236 continue; 237 } 238 239 /* Check if the current key is the same as the given key */ 240 if (hostkey_algorithm == dnskey_algorithm && 241 hostkey_digest_type == dnskey_digest_type) { 242 243 if (hostkey_digest_len == dnskey_digest_len && 244 memcmp(hostkey_digest, dnskey_digest, 245 hostkey_digest_len) == 0) { 246 247 *flags |= DNS_VERIFY_MATCH; 248 } 249 } 250 xfree(dnskey_digest); 251 } 252 253 xfree(hostkey_digest); /* from key_fingerprint_raw() */ 254 freerrset(fingerprints); 255 256 if (*flags & DNS_VERIFY_FOUND) 257 if (*flags & DNS_VERIFY_MATCH) 258 debug("matching host key fingerprint found in DNS"); 259 else 260 debug("mismatching host key fingerprint found in DNS"); 261 else 262 debug("no host key fingerprint found in DNS"); 263 264 return 0; 265 } 266 267 /* 268 * Export the fingerprint of a key as a DNS resource record 269 */ 270 int 271 export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic) 272 { 273 u_int8_t rdata_pubkey_algorithm = 0; 274 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; 275 u_char *rdata_digest; 276 u_int rdata_digest_len; 277 278 u_int i; 279 int success = 0; 280 281 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 282 &rdata_digest, &rdata_digest_len, key)) { 283 284 if (generic) 285 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, 286 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, 287 rdata_pubkey_algorithm, rdata_digest_type); 288 else 289 fprintf(f, "%s IN SSHFP %d %d ", hostname, 290 rdata_pubkey_algorithm, rdata_digest_type); 291 292 for (i = 0; i < rdata_digest_len; i++) 293 fprintf(f, "%02x", rdata_digest[i]); 294 fprintf(f, "\n"); 295 xfree(rdata_digest); /* from key_fingerprint_raw() */ 296 success = 1; 297 } else { 298 error("export_dns_rr: unsupported algorithm"); 299 } 300 301 return success; 302 } 303