dns.c

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