1 /* $NetBSD: dns.c,v 1.4 2011/07/25 03:03:10 christos Exp $ */ 2 /* $OpenBSD: dns.c,v 1.27 2010/08/31 11:54:45 djm 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 1.4 2011/07/25 03:03:10 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, 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 /* XXX KEY_ECDSA */ 91 default: 92 *algorithm = SSHFP_KEY_RESERVED; /* 0 */ 93 } 94 95 if (*algorithm) { 96 *digest_type = SSHFP_HASH_SHA1; 97 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len); 98 if (*digest == NULL) 99 fatal("dns_read_key: null from key_fingerprint_raw()"); 100 success = 1; 101 } else { 102 *digest_type = SSHFP_HASH_RESERVED; 103 *digest = NULL; 104 *digest_len = 0; 105 success = 0; 106 } 107 108 return success; 109 } 110 111 /* 112 * Read SSHFP parameters from rdata buffer. 113 */ 114 static int 115 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 116 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) 117 { 118 int success = 0; 119 120 *algorithm = SSHFP_KEY_RESERVED; 121 *digest_type = SSHFP_HASH_RESERVED; 122 123 if (rdata_len >= 2) { 124 *algorithm = rdata[0]; 125 *digest_type = rdata[1]; 126 *digest_len = rdata_len - 2; 127 128 if (*digest_len > 0) { 129 *digest = (u_char *) xmalloc(*digest_len); 130 memcpy(*digest, rdata + 2, *digest_len); 131 } else { 132 *digest = (u_char *)xstrdup(""); 133 } 134 135 success = 1; 136 } 137 138 return success; 139 } 140 141 /* 142 * Check if hostname is numerical. 143 * Returns -1 if hostname is numeric, 0 otherwise 144 */ 145 static int 146 is_numeric_hostname(const char *hostname) 147 { 148 struct addrinfo hints, *ai; 149 150 /* 151 * We shouldn't ever get a null host but if we do then log an error 152 * and return -1 which stops DNS key fingerprint processing. 153 */ 154 if (hostname == NULL) { 155 error("is_numeric_hostname called with NULL hostname"); 156 return -1; 157 } 158 159 memset(&hints, 0, sizeof(hints)); 160 hints.ai_socktype = SOCK_DGRAM; 161 hints.ai_flags = AI_NUMERICHOST; 162 163 if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { 164 freeaddrinfo(ai); 165 return -1; 166 } 167 168 return 0; 169 } 170 171 /* 172 * Verify the given hostname, address and host key using DNS. 173 * Returns 0 if lookup succeeds, -1 otherwise 174 */ 175 int 176 verify_host_key_dns(const char *hostname, struct sockaddr *address, 177 Key *hostkey, int *flags) 178 { 179 u_int counter; 180 int result; 181 struct rrsetinfo *fingerprints = NULL; 182 183 u_int8_t hostkey_algorithm; 184 u_int8_t hostkey_digest_type; 185 u_char *hostkey_digest; 186 u_int hostkey_digest_len; 187 188 u_int8_t dnskey_algorithm; 189 u_int8_t dnskey_digest_type; 190 u_char *dnskey_digest; 191 u_int dnskey_digest_len; 192 193 *flags = 0; 194 195 debug3("verify_host_key_dns"); 196 if (hostkey == NULL) 197 fatal("No key to look up!"); 198 199 if (is_numeric_hostname(hostname)) { 200 debug("skipped DNS lookup for numerical hostname"); 201 return -1; 202 } 203 204 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 205 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 206 if (result) { 207 verbose("DNS lookup error: %s", dns_result_totext(result)); 208 return -1; 209 } 210 211 if (fingerprints->rri_flags & RRSET_VALIDATED) { 212 *flags |= DNS_VERIFY_SECURE; 213 debug("found %d secure fingerprints in DNS", 214 fingerprints->rri_nrdatas); 215 } else { 216 debug("found %d insecure fingerprints in DNS", 217 fingerprints->rri_nrdatas); 218 } 219 220 /* Initialize host key parameters */ 221 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 222 &hostkey_digest, &hostkey_digest_len, hostkey)) { 223 error("Error calculating host key fingerprint."); 224 freerrset(fingerprints); 225 return -1; 226 } 227 228 if (fingerprints->rri_nrdatas) 229 *flags |= DNS_VERIFY_FOUND; 230 231 for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { 232 /* 233 * Extract the key from the answer. Ignore any badly 234 * formatted fingerprints. 235 */ 236 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 237 &dnskey_digest, &dnskey_digest_len, 238 fingerprints->rri_rdatas[counter].rdi_data, 239 fingerprints->rri_rdatas[counter].rdi_length)) { 240 verbose("Error parsing fingerprint from DNS."); 241 continue; 242 } 243 244 /* Check if the current key is the same as the given key */ 245 if (hostkey_algorithm == dnskey_algorithm && 246 hostkey_digest_type == dnskey_digest_type) { 247 248 if (hostkey_digest_len == dnskey_digest_len && 249 memcmp(hostkey_digest, dnskey_digest, 250 hostkey_digest_len) == 0) { 251 252 *flags |= DNS_VERIFY_MATCH; 253 } 254 } 255 xfree(dnskey_digest); 256 } 257 258 xfree(hostkey_digest); /* from key_fingerprint_raw() */ 259 freerrset(fingerprints); 260 261 if (*flags & DNS_VERIFY_FOUND) 262 if (*flags & DNS_VERIFY_MATCH) 263 debug("matching host key fingerprint found in DNS"); 264 else 265 debug("mismatching host key fingerprint found in DNS"); 266 else 267 debug("no host key fingerprint found in DNS"); 268 269 return 0; 270 } 271 272 /* 273 * Export the fingerprint of a key as a DNS resource record 274 */ 275 int 276 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic) 277 { 278 u_int8_t rdata_pubkey_algorithm = 0; 279 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; 280 u_char *rdata_digest; 281 u_int rdata_digest_len; 282 283 u_int i; 284 int success = 0; 285 286 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 287 &rdata_digest, &rdata_digest_len, key)) { 288 289 if (generic) 290 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, 291 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, 292 rdata_pubkey_algorithm, rdata_digest_type); 293 else 294 fprintf(f, "%s IN SSHFP %d %d ", hostname, 295 rdata_pubkey_algorithm, rdata_digest_type); 296 297 for (i = 0; i < rdata_digest_len; i++) 298 fprintf(f, "%02x", rdata_digest[i]); 299 fprintf(f, "\n"); 300 xfree(rdata_digest); /* from key_fingerprint_raw() */ 301 success = 1; 302 } else { 303 error("export_dns_rr: unsupported algorithm"); 304 } 305 306 return success; 307 } 308