1 /* $OpenBSD: dns.c,v 1.23 2006/08/03 03:34:42 deraadt 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 memset(&hints, 0, sizeof(hints)); 149 hints.ai_socktype = SOCK_DGRAM; 150 hints.ai_flags = AI_NUMERICHOST; 151 152 if (getaddrinfo(hostname, "0", &hints, &ai) == 0) { 153 freeaddrinfo(ai); 154 return -1; 155 } 156 157 return 0; 158 } 159 160 /* 161 * Verify the given hostname, address and host key using DNS. 162 * Returns 0 if lookup succeeds, -1 otherwise 163 */ 164 int 165 verify_host_key_dns(const char *hostname, struct sockaddr *address, 166 const Key *hostkey, int *flags) 167 { 168 u_int counter; 169 int result; 170 struct rrsetinfo *fingerprints = NULL; 171 172 u_int8_t hostkey_algorithm; 173 u_int8_t hostkey_digest_type; 174 u_char *hostkey_digest; 175 u_int hostkey_digest_len; 176 177 u_int8_t dnskey_algorithm; 178 u_int8_t dnskey_digest_type; 179 u_char *dnskey_digest; 180 u_int dnskey_digest_len; 181 182 *flags = 0; 183 184 debug3("verify_host_key_dns"); 185 if (hostkey == NULL) 186 fatal("No key to look up!"); 187 188 if (is_numeric_hostname(hostname)) { 189 debug("skipped DNS lookup for numerical hostname"); 190 return -1; 191 } 192 193 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 194 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 195 if (result) { 196 verbose("DNS lookup error: %s", dns_result_totext(result)); 197 return -1; 198 } 199 200 if (fingerprints->rri_flags & RRSET_VALIDATED) { 201 *flags |= DNS_VERIFY_SECURE; 202 debug("found %d secure fingerprints in DNS", 203 fingerprints->rri_nrdatas); 204 } else { 205 debug("found %d insecure fingerprints in DNS", 206 fingerprints->rri_nrdatas); 207 } 208 209 /* Initialize host key parameters */ 210 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 211 &hostkey_digest, &hostkey_digest_len, hostkey)) { 212 error("Error calculating host key fingerprint."); 213 freerrset(fingerprints); 214 return -1; 215 } 216 217 if (fingerprints->rri_nrdatas) 218 *flags |= DNS_VERIFY_FOUND; 219 220 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 221 /* 222 * Extract the key from the answer. Ignore any badly 223 * formatted fingerprints. 224 */ 225 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 226 &dnskey_digest, &dnskey_digest_len, 227 fingerprints->rri_rdatas[counter].rdi_data, 228 fingerprints->rri_rdatas[counter].rdi_length)) { 229 verbose("Error parsing fingerprint from DNS."); 230 continue; 231 } 232 233 /* Check if the current key is the same as the given key */ 234 if (hostkey_algorithm == dnskey_algorithm && 235 hostkey_digest_type == dnskey_digest_type) { 236 237 if (hostkey_digest_len == dnskey_digest_len && 238 memcmp(hostkey_digest, dnskey_digest, 239 hostkey_digest_len) == 0) { 240 241 *flags |= DNS_VERIFY_MATCH; 242 } 243 } 244 xfree(dnskey_digest); 245 } 246 247 xfree(hostkey_digest); /* from key_fingerprint_raw() */ 248 freerrset(fingerprints); 249 250 if (*flags & DNS_VERIFY_FOUND) 251 if (*flags & DNS_VERIFY_MATCH) 252 debug("matching host key fingerprint found in DNS"); 253 else 254 debug("mismatching host key fingerprint found in DNS"); 255 else 256 debug("no host key fingerprint found in DNS"); 257 258 return 0; 259 } 260 261 /* 262 * Export the fingerprint of a key as a DNS resource record 263 */ 264 int 265 export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic) 266 { 267 u_int8_t rdata_pubkey_algorithm = 0; 268 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; 269 u_char *rdata_digest; 270 u_int rdata_digest_len; 271 272 u_int i; 273 int success = 0; 274 275 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 276 &rdata_digest, &rdata_digest_len, key)) { 277 278 if (generic) 279 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, 280 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, 281 rdata_pubkey_algorithm, rdata_digest_type); 282 else 283 fprintf(f, "%s IN SSHFP %d %d ", hostname, 284 rdata_pubkey_algorithm, rdata_digest_type); 285 286 for (i = 0; i < rdata_digest_len; i++) 287 fprintf(f, "%02x", rdata_digest[i]); 288 fprintf(f, "\n"); 289 xfree(rdata_digest); /* from key_fingerprint_raw() */ 290 success = 1; 291 } else { 292 error("export_dns_rr: unsupported algorithm"); 293 } 294 295 return success; 296 } 297