dns.c

   1 /*      $OpenBSD: dns.c,v 1.12 2005/06/17 02:44:32 djm 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 #include <openssl/bn.h>
  32 #ifdef LWRES
  33 #include <lwres/netdb.h>
  34 #include <dns/result.h>
  35 #else /* LWRES */
  36 #include <netdb.h>
  37 #endif /* LWRES */
  38
  39 #include "xmalloc.h"
  40 #include "key.h"
  41 #include "dns.h"
  42 #include "log.h"
  43 #include "uuencode.h"
  44
  45 extern char *__progname;
  46 RCSID("$OpenBSD: dns.c,v 1.12 2005/06/17 02:44:32 djm Exp $");
  47
  48 #ifndef LWRES
  49 static const char *errset_text[] = {
  50         "success",              /* 0 ERRSET_SUCCESS */
  51         "out of memory",        /* 1 ERRSET_NOMEMORY */
  52         "general failure",      /* 2 ERRSET_FAIL */
  53         "invalid parameter",    /* 3 ERRSET_INVAL */
  54         "name does not exist",  /* 4 ERRSET_NONAME */
  55         "data does not exist",  /* 5 ERRSET_NODATA */
  56 };
  57
  58 static const char *
  59 dns_result_totext(unsigned int res)
  60 {
  61         switch (res) {
  62         case ERRSET_SUCCESS:
  63                 return errset_text[ERRSET_SUCCESS];
  64         case ERRSET_NOMEMORY:
  65                 return errset_text[ERRSET_NOMEMORY];
  66         case ERRSET_FAIL:
  67                 return errset_text[ERRSET_FAIL];
  68         case ERRSET_INVAL:
  69                 return errset_text[ERRSET_INVAL];
  70         case ERRSET_NONAME:
  71                 return errset_text[ERRSET_NONAME];
  72         case ERRSET_NODATA:
  73                 return errset_text[ERRSET_NODATA];
  74         default:
  75                 return "unknown error";
  76         }
  77 }
  78 #endif /* LWRES */
  79
  80
  81 /*
  82  * Read SSHFP parameters from key buffer.
  83  */
  84 static int
  85 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
  86     u_char **digest, u_int *digest_len, const Key *key)
  87 {
  88         int success = 0;
  89
  90         switch (key->type) {
  91         case KEY_RSA:
  92                 *algorithm = SSHFP_KEY_RSA;
  93                 break;
  94         case KEY_DSA:
  95                 *algorithm = SSHFP_KEY_DSA;
  96                 break;
  97         default:
  98                 *algorithm = SSHFP_KEY_RESERVED;
  99         }
 100
 101         if (*algorithm) {
 102                 *digest_type = SSHFP_HASH_SHA1;
 103                 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
 104                 success = 1;
 105         } else {
 106                 *digest_type = SSHFP_HASH_RESERVED;
 107                 *digest = NULL;
 108                 *digest_len = 0;
 109                 success = 0;
 110         }
 111
 112         return success;
 113 }
 114
 115 /*
 116  * Read SSHFP parameters from rdata buffer.
 117  */
 118 static int
 119 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
 120     u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
 121 {
 122         int success = 0;
 123
 124         *algorithm = SSHFP_KEY_RESERVED;
 125         *digest_type = SSHFP_HASH_RESERVED;
 126
 127         if (rdata_len >= 2) {
 128                 *algorithm = rdata[0];
 129                 *digest_type = rdata[1];
 130                 *digest_len = rdata_len - 2;
 131
 132                 if (*digest_len > 0) {
 133                         *digest = (u_char *) xmalloc(*digest_len);
 134                         memcpy(*digest, rdata + 2, *digest_len);
 135                 } else {
 136                         *digest = NULL;
 137                 }
 138
 139                 success = 1;
 140         }
 141
 142         return success;
 143 }
 144
 145 /*
 146  * Check if hostname is numerical.
 147  * Returns -1 if hostname is numeric, 0 otherwise
 148  */
 149 static int
 150 is_numeric_hostname(const char *hostname)
 151 {
 152         struct addrinfo hints, *ai;
 153
 154         memset(&hints, 0, sizeof(hints));
 155         hints.ai_socktype = SOCK_DGRAM;
 156         hints.ai_flags = AI_NUMERICHOST;
 157
 158         if (getaddrinfo(hostname, "0", &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_hostkey_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         }
 251
 252         freerrset(fingerprints);
 253
 254         if (*flags & DNS_VERIFY_FOUND)
 255                 if (*flags & DNS_VERIFY_MATCH)
 256                         debug("matching host key fingerprint found in DNS");
 257                 else
 258                         debug("mismatching host key fingerprint found in DNS");
 259         else
 260                 debug("no host key fingerprint found in DNS");
 261
 262         return 0;
 263 }
 264
 265
 266 /*
 267  * Export the fingerprint of a key as a DNS resource record
 268  */
 269 int
 270 export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
 271 {
 272         u_int8_t rdata_pubkey_algorithm = 0;
 273         u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
 274         u_char *rdata_digest;
 275         u_int rdata_digest_len;
 276
 277         u_int i;
 278         int success = 0;
 279
 280         if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
 281                          &rdata_digest, &rdata_digest_len, key)) {
 282
 283                 if (generic)
 284                         fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
 285                             DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
 286                             rdata_pubkey_algorithm, rdata_digest_type);
 287                 else
 288                         fprintf(f, "%s IN SSHFP %d %d ", hostname,
 289                             rdata_pubkey_algorithm, rdata_digest_type);
 290
 291                 for (i = 0; i < rdata_digest_len; i++)
 292                         fprintf(f, "%02x", rdata_digest[i]);
 293                 fprintf(f, "\n");
 294                 success = 1;
 295         } else {
 296                 error("dns_export_rr: unsupported algorithm");
 297         }
 298
 299         return success;
 300 }