1 /* $NetBSD: dns.c,v 1.2 2009/06/07 22:38:46 christos Exp $ */ 2 /* $OpenBSD: dns.c,v 1.25 2008/06/12 00:03:49 dtucker 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 1.2 2009/06/07 22:38:46 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, const Key *key) 80 { 81 int success = 0; 82 83 switch (key->type) { 84 case KEY_RSA: 85 *algorithm = SSHFP_KEY_RSA; 86 break; 87 case KEY_DSA: 88 *algorithm = SSHFP_KEY_DSA; 89 break; 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 const 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 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 204 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 205 if (result) { 206 verbose("DNS lookup error: %s", dns_result_totext(result)); 207 return -1; 208 } 209 210 if (fingerprints->rri_flags & RRSET_VALIDATED) { 211 *flags |= DNS_VERIFY_SECURE; 212 debug("found %d secure fingerprints in DNS", 213 fingerprints->rri_nrdatas); 214 } else { 215 debug("found %d insecure fingerprints in DNS", 216 fingerprints->rri_nrdatas); 217 } 218 219 /* Initialize host key parameters */ 220 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 221 &hostkey_digest, &hostkey_digest_len, hostkey)) { 222 error("Error calculating host key fingerprint."); 223 freerrset(fingerprints); 224 return -1; 225 } 226 227 if (fingerprints->rri_nrdatas) 228 *flags |= DNS_VERIFY_FOUND; 229 230 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 231 /* 232 * Extract the key from the answer. Ignore any badly 233 * formatted fingerprints. 234 */ 235 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 236 &dnskey_digest, &dnskey_digest_len, 237 fingerprints->rri_rdatas[counter].rdi_data, 238 fingerprints->rri_rdatas[counter].rdi_length)) { 239 verbose("Error parsing fingerprint from DNS."); 240 continue; 241 } 242 243 /* Check if the current key is the same as the given key */ 244 if (hostkey_algorithm == dnskey_algorithm && 245 hostkey_digest_type == dnskey_digest_type) { 246 247 if (hostkey_digest_len == dnskey_digest_len && 248 memcmp(hostkey_digest, dnskey_digest, 249 hostkey_digest_len) == 0) { 250 251 *flags |= DNS_VERIFY_MATCH; 252 } 253 } 254 xfree(dnskey_digest); 255 } 256 257 xfree(hostkey_digest); /* from key_fingerprint_raw() */ 258 freerrset(fingerprints); 259 260 if (*flags & DNS_VERIFY_FOUND) 261 if (*flags & DNS_VERIFY_MATCH) 262 debug("matching host key fingerprint found in DNS"); 263 else 264 debug("mismatching host key fingerprint found in DNS"); 265 else 266 debug("no host key fingerprint found in DNS"); 267 268 return 0; 269 } 270 271 /* 272 * Export the fingerprint of a key as a DNS resource record 273 */ 274 int 275 export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic) 276 { 277 u_int8_t rdata_pubkey_algorithm = 0; 278 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; 279 u_char *rdata_digest; 280 u_int rdata_digest_len; 281 282 u_int i; 283 int success = 0; 284 285 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 286 &rdata_digest, &rdata_digest_len, key)) { 287 288 if (generic) 289 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, 290 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, 291 rdata_pubkey_algorithm, rdata_digest_type); 292 else 293 fprintf(f, "%s IN SSHFP %d %d ", hostname, 294 rdata_pubkey_algorithm, rdata_digest_type); 295 296 for (i = 0; i < rdata_digest_len; i++) 297 fprintf(f, "%02x", rdata_digest[i]); 298 fprintf(f, "\n"); 299 xfree(rdata_digest); /* from key_fingerprint_raw() */ 300 success = 1; 301 } else { 302 error("export_dns_rr: unsupported algorithm"); 303 } 304 305 return success; 306 } 307