dns.c

   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 <stdio.h>
  35 #include <string.h>
  36
  37 #include "xmalloc.h"
  38 #include "key.h"
  39 #include "dns.h"
  40 #include "log.h"
  41
  42 static const char *errset_text[] = {
  43         "success",              /* 0 ERRSET_SUCCESS */
  44         "out of memory",        /* 1 ERRSET_NOMEMORY */
  45         "general failure",      /* 2 ERRSET_FAIL */
  46         "invalid parameter",    /* 3 ERRSET_INVAL */
  47         "name does not exist",  /* 4 ERRSET_NONAME */
  48         "data does not exist",  /* 5 ERRSET_NODATA */
  49 };
  50
  51 static const char *
  52 dns_result_totext(unsigned int res)
  53 {
  54         switch (res) {
  55         case ERRSET_SUCCESS:
  56                 return errset_text[ERRSET_SUCCESS];
  57         case ERRSET_NOMEMORY:
  58                 return errset_text[ERRSET_NOMEMORY];
  59         case ERRSET_FAIL:
  60                 return errset_text[ERRSET_FAIL];
  61         case ERRSET_INVAL:
  62                 return errset_text[ERRSET_INVAL];
  63         case ERRSET_NONAME:
  64                 return errset_text[ERRSET_NONAME];
  65         case ERRSET_NODATA:
  66                 return errset_text[ERRSET_NODATA];
  67         default:
  68                 return "unknown error";
  69         }
  70 }
  71
  72 /*
  73  * Read SSHFP parameters from key buffer.
  74  */
  75 static int
  76 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
  77     u_char **digest, u_int *digest_len, const Key *key)
  78 {
  79         int success = 0;
  80
  81         switch (key->type) {
  82         case KEY_RSA:
  83                 *algorithm = SSHFP_KEY_RSA;
  84                 break;
  85         case KEY_DSA:
  86                 *algorithm = SSHFP_KEY_DSA;
  87                 break;
  88         default:
  89                 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
  90         }
  91
  92         if (*algorithm) {
  93                 *digest_type = SSHFP_HASH_SHA1;
  94                 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
  95                 if (*digest == NULL)
  96                         fatal("dns_read_key: null from key_fingerprint_raw()");
  97                 success = 1;
  98         } else {
  99                 *digest_type = SSHFP_HASH_RESERVED;
 100                 *digest = NULL;
 101                 *digest_len = 0;
 102                 success = 0;
 103         }
 104
 105         return success;
 106 }
 107
 108 /*
 109  * Read SSHFP parameters from rdata buffer.
 110  */
 111 static int
 112 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
 113     u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
 114 {
 115         int success = 0;
 116
 117         *algorithm = SSHFP_KEY_RESERVED;
 118         *digest_type = SSHFP_HASH_RESERVED;
 119
 120         if (rdata_len >= 2) {
 121                 *algorithm = rdata[0];
 122                 *digest_type = rdata[1];
 123                 *digest_len = rdata_len - 2;
 124
 125                 if (*digest_len > 0) {
 126                         *digest = (u_char *) xmalloc(*digest_len);
 127                         memcpy(*digest, rdata + 2, *digest_len);
 128                 } else {
 129                         *digest = (u_char *)xstrdup("");
 130                 }
 131
 132                 success = 1;
 133         }
 134
 135         return success;
 136 }
 137
 138 /*
 139  * Check if hostname is numerical.
 140  * Returns -1 if hostname is numeric, 0 otherwise
 141  */
 142 static int
 143 is_numeric_hostname(const char *hostname)
 144 {
 145         struct addrinfo hints, *ai;
 146
 147         memset(&hints, 0, sizeof(hints));
 148         hints.ai_socktype = SOCK_DGRAM;
 149         hints.ai_flags = AI_NUMERICHOST;
 150
 151         if (getaddrinfo(hostname, "0", &hints, &ai) == 0) {
 152                 freeaddrinfo(ai);
 153                 return -1;
 154         }
 155
 156         return 0;
 157 }
 158
 159 /*
 160  * Verify the given hostname, address and host key using DNS.
 161  * Returns 0 if lookup succeeds, -1 otherwise
 162  */
 163 int
 164 verify_host_key_dns(const char *hostname, struct sockaddr *address,
 165     const Key *hostkey, int *flags)
 166 {
 167         u_int counter;
 168         int result;
 169         struct rrsetinfo *fingerprints = NULL;
 170
 171         u_int8_t hostkey_algorithm;
 172         u_int8_t hostkey_digest_type;
 173         u_char *hostkey_digest;
 174         u_int hostkey_digest_len;
 175
 176         u_int8_t dnskey_algorithm;
 177         u_int8_t dnskey_digest_type;
 178         u_char *dnskey_digest;
 179         u_int dnskey_digest_len;
 180
 181         *flags = 0;
 182
 183         debug3("verify_host_key_dns");
 184         if (hostkey == NULL)
 185                 fatal("No key to look up!");
 186
 187         if (is_numeric_hostname(hostname)) {
 188                 debug("skipped DNS lookup for numerical hostname");
 189                 return -1;
 190         }
 191
 192         result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
 193             DNS_RDATATYPE_SSHFP, 0, &fingerprints);
 194         if (result) {
 195                 verbose("DNS lookup error: %s", dns_result_totext(result));
 196                 return -1;
 197         }
 198
 199         if (fingerprints->rri_flags & RRSET_VALIDATED) {
 200                 *flags |= DNS_VERIFY_SECURE;
 201                 debug("found %d secure fingerprints in DNS",
 202                     fingerprints->rri_nrdatas);
 203         } else {
 204                 debug("found %d insecure fingerprints in DNS",
 205                     fingerprints->rri_nrdatas);
 206         }
 207
 208         /* Initialize host key parameters */
 209         if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
 210             &hostkey_digest, &hostkey_digest_len, hostkey)) {
 211                 error("Error calculating host key fingerprint.");
 212                 freerrset(fingerprints);
 213                 return -1;
 214         }
 215
 216         if (fingerprints->rri_nrdatas)
 217                 *flags |= DNS_VERIFY_FOUND;
 218
 219         for (counter = 0; counter < fingerprints->rri_nrdatas; counter++)  {
 220                 /*
 221                  * Extract the key from the answer. Ignore any badly
 222                  * formatted fingerprints.
 223                  */
 224                 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
 225                     &dnskey_digest, &dnskey_digest_len,
 226                     fingerprints->rri_rdatas[counter].rdi_data,
 227                     fingerprints->rri_rdatas[counter].rdi_length)) {
 228                         verbose("Error parsing fingerprint from DNS.");
 229                         continue;
 230                 }
 231
 232                 /* Check if the current key is the same as the given key */
 233                 if (hostkey_algorithm == dnskey_algorithm &&
 234                     hostkey_digest_type == dnskey_digest_type) {
 235
 236                         if (hostkey_digest_len == dnskey_digest_len &&
 237                             memcmp(hostkey_digest, dnskey_digest,
 238                             hostkey_digest_len) == 0) {
 239
 240                                 *flags |= DNS_VERIFY_MATCH;
 241                         }
 242                 }
 243                 xfree(dnskey_digest);
 244         }
 245
 246         xfree(hostkey_digest); /* from key_fingerprint_raw() */
 247         freerrset(fingerprints);
 248
 249         if (*flags & DNS_VERIFY_FOUND)
 250                 if (*flags & DNS_VERIFY_MATCH)
 251                         debug("matching host key fingerprint found in DNS");
 252                 else
 253                         debug("mismatching host key fingerprint found in DNS");
 254         else
 255                 debug("no host key fingerprint found in DNS");
 256
 257         return 0;
 258 }
 259
 260 /*
 261  * Export the fingerprint of a key as a DNS resource record
 262  */
 263 int
 264 export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
 265 {
 266         u_int8_t rdata_pubkey_algorithm = 0;
 267         u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
 268         u_char *rdata_digest;
 269         u_int rdata_digest_len;
 270
 271         u_int i;
 272         int success = 0;
 273
 274         if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
 275             &rdata_digest, &rdata_digest_len, key)) {
 276
 277                 if (generic)
 278                         fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
 279                             DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
 280                             rdata_pubkey_algorithm, rdata_digest_type);
 281                 else
 282                         fprintf(f, "%s IN SSHFP %d %d ", hostname,
 283                             rdata_pubkey_algorithm, rdata_digest_type);
 284
 285                 for (i = 0; i < rdata_digest_len; i++)
 286                         fprintf(f, "%02x", rdata_digest[i]);
 287                 fprintf(f, "\n");
 288                 xfree(rdata_digest); /* from key_fingerprint_raw() */
 289                 success = 1;
 290         } else {
 291                 error("export_dns_rr: unsupported algorithm");
 292         }
 293
 294         return success;
 295 }