1 /* $OpenBSD: dns.c,v 1.6 2003/06/11 10:18:47 jakob 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 29 #include "includes.h" 30 31 #ifdef DNS 32 #include <openssl/bn.h> 33 #ifdef LWRES 34 #include <lwres/netdb.h> 35 #include <dns/result.h> 36 #else /* LWRES */ 37 #include <netdb.h> 38 #endif /* LWRES */ 39 40 #include "xmalloc.h" 41 #include "key.h" 42 #include "dns.h" 43 #include "log.h" 44 #include "uuencode.h" 45 46 extern char *__progname; 47 RCSID("$OpenBSD: dns.c,v 1.6 2003/06/11 10:18:47 jakob Exp $"); 48 49 #ifndef LWRES 50 static const char *errset_text[] = { 51 "success", /* 0 ERRSET_SUCCESS */ 52 "out of memory", /* 1 ERRSET_NOMEMORY */ 53 "general failure", /* 2 ERRSET_FAIL */ 54 "invalid parameter", /* 3 ERRSET_INVAL */ 55 "name does not exist", /* 4 ERRSET_NONAME */ 56 "data does not exist", /* 5 ERRSET_NODATA */ 57 }; 58 59 static const char * 60 dns_result_totext(unsigned int error) 61 { 62 switch (error) { 63 case ERRSET_SUCCESS: 64 return errset_text[ERRSET_SUCCESS]; 65 case ERRSET_NOMEMORY: 66 return errset_text[ERRSET_NOMEMORY]; 67 case ERRSET_FAIL: 68 return errset_text[ERRSET_FAIL]; 69 case ERRSET_INVAL: 70 return errset_text[ERRSET_INVAL]; 71 case ERRSET_NONAME: 72 return errset_text[ERRSET_NONAME]; 73 case ERRSET_NODATA: 74 return errset_text[ERRSET_NODATA]; 75 default: 76 return "unknown error"; 77 } 78 } 79 #endif /* LWRES */ 80 81 82 /* 83 * Read SSHFP parameters from key buffer. 84 */ 85 static int 86 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type, 87 u_char **digest, u_int *digest_len, Key *key) 88 { 89 int success = 0; 90 91 switch (key->type) { 92 case KEY_RSA: 93 *algorithm = SSHFP_KEY_RSA; 94 break; 95 case KEY_DSA: 96 *algorithm = SSHFP_KEY_DSA; 97 break; 98 default: 99 *algorithm = SSHFP_KEY_RESERVED; 100 } 101 102 if (*algorithm) { 103 *digest_type = SSHFP_HASH_SHA1; 104 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len); 105 success = 1; 106 } else { 107 *digest_type = SSHFP_HASH_RESERVED; 108 *digest = NULL; 109 *digest_len = 0; 110 success = 0; 111 } 112 113 return success; 114 } 115 116 /* 117 * Read SSHFP parameters from rdata buffer. 118 */ 119 static int 120 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, 121 u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len) 122 { 123 int success = 0; 124 125 *algorithm = SSHFP_KEY_RESERVED; 126 *digest_type = SSHFP_HASH_RESERVED; 127 128 if (rdata_len >= 2) { 129 *algorithm = rdata[0]; 130 *digest_type = rdata[1]; 131 *digest_len = rdata_len - 2; 132 133 if (*digest_len > 0) { 134 *digest = (u_char *) xmalloc(*digest_len); 135 memcpy(*digest, rdata + 2, *digest_len); 136 } else { 137 *digest = NULL; 138 } 139 140 success = 1; 141 } 142 143 return success; 144 } 145 146 147 /* 148 * Verify the given hostname, address and host key using DNS. 149 * Returns 0 if key verifies or -1 if key does NOT verify 150 */ 151 int 152 verify_host_key_dns(const char *hostname, struct sockaddr *address, 153 Key *hostkey) 154 { 155 int counter; 156 int result; 157 struct rrsetinfo *fingerprints = NULL; 158 int failures = 0; 159 160 u_int8_t hostkey_algorithm; 161 u_int8_t hostkey_digest_type; 162 u_char *hostkey_digest; 163 u_int hostkey_digest_len; 164 165 u_int8_t dnskey_algorithm; 166 u_int8_t dnskey_digest_type; 167 u_char *dnskey_digest; 168 u_int dnskey_digest_len; 169 170 171 debug3("verify_hostkey_dns"); 172 if (hostkey == NULL) 173 fatal("No key to look up!"); 174 175 result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, 176 DNS_RDATATYPE_SSHFP, 0, &fingerprints); 177 if (result) { 178 verbose("DNS lookup error: %s", dns_result_totext(result)); 179 return DNS_VERIFY_ERROR; 180 } 181 182 #ifdef DNSSEC 183 /* Only accept validated answers */ 184 if (!fingerprints->rri_flags & RRSET_VALIDATED) { 185 error("Ignored unvalidated fingerprint from DNS."); 186 freerrset(fingerprints); 187 return DNS_VERIFY_ERROR; 188 } 189 #endif 190 191 debug("found %d fingerprints in DNS", fingerprints->rri_nrdatas); 192 193 /* Initialize host key parameters */ 194 if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, 195 &hostkey_digest, &hostkey_digest_len, hostkey)) { 196 error("Error calculating host key fingerprint."); 197 freerrset(fingerprints); 198 return DNS_VERIFY_ERROR; 199 } 200 201 for (counter = 0 ; counter < fingerprints->rri_nrdatas ; counter++) { 202 /* 203 * Extract the key from the answer. Ignore any badly 204 * formatted fingerprints. 205 */ 206 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, 207 &dnskey_digest, &dnskey_digest_len, 208 fingerprints->rri_rdatas[counter].rdi_data, 209 fingerprints->rri_rdatas[counter].rdi_length)) { 210 verbose("Error parsing fingerprint from DNS."); 211 continue; 212 } 213 214 /* Check if the current key is the same as the given key */ 215 if (hostkey_algorithm == dnskey_algorithm && 216 hostkey_digest_type == dnskey_digest_type) { 217 218 if (hostkey_digest_len == dnskey_digest_len && 219 memcmp(hostkey_digest, dnskey_digest, 220 hostkey_digest_len) == 0) { 221 222 /* Matching algoritm and digest. */ 223 freerrset(fingerprints); 224 debug("matching host key fingerprint found in DNS"); 225 return DNS_VERIFY_OK; 226 } else { 227 /* Correct algorithm but bad digest */ 228 debug("verify_hostkey_dns: failed"); 229 failures++; 230 } 231 } 232 } 233 234 freerrset(fingerprints); 235 236 if (failures) { 237 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); 238 error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @"); 239 error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); 240 error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!"); 241 error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!"); 242 error("It is also possible that the %s host key has just been changed.", 243 key_type(hostkey)); 244 error("Please contact your system administrator."); 245 return DNS_VERIFY_FAILED; 246 } 247 248 debug("fingerprints found in DNS, but none of them matched"); 249 250 return DNS_VERIFY_ERROR; 251 } 252 253 254 /* 255 * Export the fingerprint of a key as a DNS resource record 256 */ 257 int 258 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic) 259 { 260 u_int8_t rdata_pubkey_algorithm = 0; 261 u_int8_t rdata_digest_type = SSHFP_HASH_SHA1; 262 u_char *rdata_digest; 263 u_int rdata_digest_len; 264 265 int i; 266 int success = 0; 267 268 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, 269 &rdata_digest, &rdata_digest_len, key)) { 270 271 if (generic) 272 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname, 273 DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len, 274 rdata_pubkey_algorithm, rdata_digest_type); 275 else 276 fprintf(f, "%s IN SSHFP %d %d ", hostname, 277 rdata_pubkey_algorithm, rdata_digest_type); 278 279 for (i = 0; i < rdata_digest_len; i++) 280 fprintf(f, "%02x", rdata_digest[i]); 281 fprintf(f, "\n"); 282 success = 1; 283 } else { 284 error("dns_export_rr: unsupported algorithm"); 285 } 286 287 return success; 288 } 289 290 #endif /* DNS */ 291