crypto/openssh/dns.c

   1 /* $OpenBSD: dns.c,v 1.31 2014/06/24 01:13:21 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 #include <stdarg.h>
  38 #include <stdlib.h>
  39
  40 #include "xmalloc.h"
  41 #include "key.h"
  42 #include "dns.h"
  43 #include "log.h"
  44
  45 static const char *errset_text[] = {
  46         "success",              /* 0 ERRSET_SUCCESS */
  47         "out of memory",        /* 1 ERRSET_NOMEMORY */
  48         "general failure",      /* 2 ERRSET_FAIL */
  49         "invalid parameter",    /* 3 ERRSET_INVAL */
  50         "name does not exist",  /* 4 ERRSET_NONAME */
  51         "data does not exist",  /* 5 ERRSET_NODATA */
  52 };
  53
  54 static const char *
  55 dns_result_totext(unsigned int res)
  56 {
  57         switch (res) {
  58         case ERRSET_SUCCESS:
  59                 return errset_text[ERRSET_SUCCESS];
  60         case ERRSET_NOMEMORY:
  61                 return errset_text[ERRSET_NOMEMORY];
  62         case ERRSET_FAIL:
  63                 return errset_text[ERRSET_FAIL];
  64         case ERRSET_INVAL:
  65                 return errset_text[ERRSET_INVAL];
  66         case ERRSET_NONAME:
  67                 return errset_text[ERRSET_NONAME];
  68         case ERRSET_NODATA:
  69                 return errset_text[ERRSET_NODATA];
  70         default:
  71                 return "unknown error";
  72         }
  73 }
  74
  75 /*
  76  * Read SSHFP parameters from key buffer.
  77  */
  78 static int
  79 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
  80     u_char **digest, u_int *digest_len, Key *key)
  81 {
  82         int success = 0;
  83         enum fp_type fp_type = 0;
  84
  85         switch (key->type) {
  86         case KEY_RSA:
  87                 *algorithm = SSHFP_KEY_RSA;
  88                 if (!*digest_type)
  89                         *digest_type = SSHFP_HASH_SHA1;
  90                 break;
  91         case KEY_DSA:
  92                 *algorithm = SSHFP_KEY_DSA;
  93                 if (!*digest_type)
  94                         *digest_type = SSHFP_HASH_SHA1;
  95                 break;
  96         case KEY_ECDSA:
  97                 *algorithm = SSHFP_KEY_ECDSA;
  98                 if (!*digest_type)
  99                         *digest_type = SSHFP_HASH_SHA256;
 100                 break;
 101         case KEY_ED25519:
 102                 *algorithm = SSHFP_KEY_ED25519;
 103                 if (!*digest_type)
 104                         *digest_type = SSHFP_HASH_SHA256;
 105                 break;
 106         default:
 107                 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
 108                 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
 109         }
 110
 111         switch (*digest_type) {
 112         case SSHFP_HASH_SHA1:
 113                 fp_type = SSH_FP_SHA1;
 114                 break;
 115         case SSHFP_HASH_SHA256:
 116                 fp_type = SSH_FP_SHA256;
 117                 break;
 118         default:
 119                 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
 120         }
 121
 122         if (*algorithm && *digest_type) {
 123                 *digest = key_fingerprint_raw(key, fp_type, digest_len);
 124                 if (*digest == NULL)
 125                         fatal("dns_read_key: null from key_fingerprint_raw()");
 126                 success = 1;
 127         } else {
 128                 *digest = NULL;
 129                 *digest_len = 0;
 130                 success = 0;
 131         }
 132
 133         return success;
 134 }
 135
 136 /*
 137  * Read SSHFP parameters from rdata buffer.
 138  */
 139 static int
 140 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
 141     u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
 142 {
 143         int success = 0;
 144
 145         *algorithm = SSHFP_KEY_RESERVED;
 146         *digest_type = SSHFP_HASH_RESERVED;
 147
 148         if (rdata_len >= 2) {
 149                 *algorithm = rdata[0];
 150                 *digest_type = rdata[1];
 151                 *digest_len = rdata_len - 2;
 152
 153                 if (*digest_len > 0) {
 154                         *digest = (u_char *) xmalloc(*digest_len);
 155                         memcpy(*digest, rdata + 2, *digest_len);
 156                 } else {
 157                         *digest = (u_char *)xstrdup("");
 158                 }
 159
 160                 success = 1;
 161         }
 162
 163         return success;
 164 }
 165
 166 /*
 167  * Check if hostname is numerical.
 168  * Returns -1 if hostname is numeric, 0 otherwise
 169  */
 170 static int
 171 is_numeric_hostname(const char *hostname)
 172 {
 173         struct addrinfo hints, *ai;
 174
 175         /*
 176          * We shouldn't ever get a null host but if we do then log an error
 177          * and return -1 which stops DNS key fingerprint processing.
 178          */
 179         if (hostname == NULL) {
 180                 error("is_numeric_hostname called with NULL hostname");
 181                 return -1;
 182         }
 183
 184         memset(&hints, 0, sizeof(hints));
 185         hints.ai_socktype = SOCK_DGRAM;
 186         hints.ai_flags = AI_NUMERICHOST;
 187
 188         if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
 189                 freeaddrinfo(ai);
 190                 return -1;
 191         }
 192
 193         return 0;
 194 }
 195
 196 /*
 197  * Verify the given hostname, address and host key using DNS.
 198  * Returns 0 if lookup succeeds, -1 otherwise
 199  */
 200 int
 201 verify_host_key_dns(const char *hostname, struct sockaddr *address,
 202     Key *hostkey, int *flags)
 203 {
 204         u_int counter;
 205         int result;
 206         struct rrsetinfo *fingerprints = NULL;
 207
 208         u_int8_t hostkey_algorithm;
 209         u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
 210         u_char *hostkey_digest;
 211         u_int hostkey_digest_len;
 212
 213         u_int8_t dnskey_algorithm;
 214         u_int8_t dnskey_digest_type;
 215         u_char *dnskey_digest;
 216         u_int dnskey_digest_len;
 217
 218         *flags = 0;
 219
 220         debug3("verify_host_key_dns");
 221         if (hostkey == NULL)
 222                 fatal("No key to look up!");
 223
 224         if (is_numeric_hostname(hostname)) {
 225                 debug("skipped DNS lookup for numerical hostname");
 226                 return -1;
 227         }
 228
 229         result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
 230             DNS_RDATATYPE_SSHFP, 0, &fingerprints);
 231         if (result) {
 232                 verbose("DNS lookup error: %s", dns_result_totext(result));
 233                 return -1;
 234         }
 235
 236         if (fingerprints->rri_flags & RRSET_VALIDATED) {
 237                 *flags |= DNS_VERIFY_SECURE;
 238                 debug("found %d secure fingerprints in DNS",
 239                     fingerprints->rri_nrdatas);
 240         } else {
 241                 debug("found %d insecure fingerprints in DNS",
 242                     fingerprints->rri_nrdatas);
 243         }
 244
 245         /* Initialize default host key parameters */
 246         if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
 247             &hostkey_digest, &hostkey_digest_len, hostkey)) {
 248                 error("Error calculating host key fingerprint.");
 249                 freerrset(fingerprints);
 250                 return -1;
 251         }
 252
 253         if (fingerprints->rri_nrdatas)
 254                 *flags |= DNS_VERIFY_FOUND;
 255
 256         for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
 257                 /*
 258                  * Extract the key from the answer. Ignore any badly
 259                  * formatted fingerprints.
 260                  */
 261                 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
 262                     &dnskey_digest, &dnskey_digest_len,
 263                     fingerprints->rri_rdatas[counter].rdi_data,
 264                     fingerprints->rri_rdatas[counter].rdi_length)) {
 265                         verbose("Error parsing fingerprint from DNS.");
 266                         continue;
 267                 }
 268
 269                 if (hostkey_digest_type != dnskey_digest_type) {
 270                         hostkey_digest_type = dnskey_digest_type;
 271                         free(hostkey_digest);
 272
 273                         /* Initialize host key parameters */
 274                         if (!dns_read_key(&hostkey_algorithm,
 275                             &hostkey_digest_type, &hostkey_digest,
 276                             &hostkey_digest_len, hostkey)) {
 277                                 error("Error calculating key fingerprint.");
 278                                 freerrset(fingerprints);
 279                                 return -1;
 280                         }
 281                 }
 282
 283                 /* Check if the current key is the same as the given key */
 284                 if (hostkey_algorithm == dnskey_algorithm &&
 285                     hostkey_digest_type == dnskey_digest_type) {
 286                         if (hostkey_digest_len == dnskey_digest_len &&
 287                             timingsafe_bcmp(hostkey_digest, dnskey_digest,
 288                             hostkey_digest_len) == 0)
 289                                 *flags |= DNS_VERIFY_MATCH;
 290                 }
 291                 free(dnskey_digest);
 292         }
 293
 294         free(hostkey_digest); /* from key_fingerprint_raw() */
 295         freerrset(fingerprints);
 296
 297         if (*flags & DNS_VERIFY_FOUND)
 298                 if (*flags & DNS_VERIFY_MATCH)
 299                         debug("matching host key fingerprint found in DNS");
 300                 else
 301                         debug("mismatching host key fingerprint found in DNS");
 302         else
 303                 debug("no host key fingerprint found in DNS");
 304
 305         return 0;
 306 }
 307
 308 /*
 309  * Export the fingerprint of a key as a DNS resource record
 310  */
 311 int
 312 export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
 313 {
 314         u_int8_t rdata_pubkey_algorithm = 0;
 315         u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
 316         u_int8_t dtype;
 317         u_char *rdata_digest;
 318         u_int i, rdata_digest_len;
 319         int success = 0;
 320
 321         for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
 322                 rdata_digest_type = dtype;
 323                 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
 324                     &rdata_digest, &rdata_digest_len, key)) {
 325                         if (generic) {
 326                                 fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ",
 327                                     hostname, DNS_RDATATYPE_SSHFP,
 328                                     2 + rdata_digest_len,
 329                                     rdata_pubkey_algorithm, rdata_digest_type);
 330                         } else {
 331                                 fprintf(f, "%s IN SSHFP %d %d ", hostname,
 332                                     rdata_pubkey_algorithm, rdata_digest_type);
 333                         }
 334                         for (i = 0; i < rdata_digest_len; i++)
 335                                 fprintf(f, "%02x", rdata_digest[i]);
 336                         fprintf(f, "\n");
 337                         free(rdata_digest); /* from key_fingerprint_raw() */
 338                         success = 1;
 339                 }
 340         }
 341
 342         /* No SSHFP record was generated at all */
 343         if (success == 0) {
 344                 error("%s: unsupported algorithm and/or digest_type", __func__);
 345         }
 346
 347         return success;
 348 }