crypto/openssh/dns.c

   1 /* $OpenBSD: dns.c,v 1.37 2017/09/14 04:32:21 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 "sshkey.h"
  42 #include "ssherr.h"
  43 #include "dns.h"
  44 #include "log.h"
  45 #include "digest.h"
  46
  47 static const char *errset_text[] = {
  48         "success",              /* 0 ERRSET_SUCCESS */
  49         "out of memory",        /* 1 ERRSET_NOMEMORY */
  50         "general failure",      /* 2 ERRSET_FAIL */
  51         "invalid parameter",    /* 3 ERRSET_INVAL */
  52         "name does not exist",  /* 4 ERRSET_NONAME */
  53         "data does not exist",  /* 5 ERRSET_NODATA */
  54 };
  55
  56 static const char *
  57 dns_result_totext(unsigned int res)
  58 {
  59         switch (res) {
  60         case ERRSET_SUCCESS:
  61                 return errset_text[ERRSET_SUCCESS];
  62         case ERRSET_NOMEMORY:
  63                 return errset_text[ERRSET_NOMEMORY];
  64         case ERRSET_FAIL:
  65                 return errset_text[ERRSET_FAIL];
  66         case ERRSET_INVAL:
  67                 return errset_text[ERRSET_INVAL];
  68         case ERRSET_NONAME:
  69                 return errset_text[ERRSET_NONAME];
  70         case ERRSET_NODATA:
  71                 return errset_text[ERRSET_NODATA];
  72         default:
  73                 return "unknown error";
  74         }
  75 }
  76
  77 /*
  78  * Read SSHFP parameters from key buffer.
  79  */
  80 static int
  81 dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
  82     u_char **digest, size_t *digest_len, struct sshkey *key)
  83 {
  84         int r, success = 0;
  85         int fp_alg = -1;
  86
  87         switch (key->type) {
  88         case KEY_RSA:
  89                 *algorithm = SSHFP_KEY_RSA;
  90                 if (!*digest_type)
  91                         *digest_type = SSHFP_HASH_SHA1;
  92                 break;
  93         case KEY_DSA:
  94                 *algorithm = SSHFP_KEY_DSA;
  95                 if (!*digest_type)
  96                         *digest_type = SSHFP_HASH_SHA1;
  97                 break;
  98         case KEY_ECDSA:
  99                 *algorithm = SSHFP_KEY_ECDSA;
 100                 if (!*digest_type)
 101                         *digest_type = SSHFP_HASH_SHA256;
 102                 break;
 103         case KEY_ED25519:
 104                 *algorithm = SSHFP_KEY_ED25519;
 105                 if (!*digest_type)
 106                         *digest_type = SSHFP_HASH_SHA256;
 107                 break;
 108         default:
 109                 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
 110                 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
 111         }
 112
 113         switch (*digest_type) {
 114         case SSHFP_HASH_SHA1:
 115                 fp_alg = SSH_DIGEST_SHA1;
 116                 break;
 117         case SSHFP_HASH_SHA256:
 118                 fp_alg = SSH_DIGEST_SHA256;
 119                 break;
 120         default:
 121                 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
 122         }
 123
 124         if (*algorithm && *digest_type) {
 125                 if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
 126                     digest_len)) != 0)
 127                         fatal("%s: sshkey_fingerprint_raw: %s", __func__,
 128                            ssh_err(r));
 129                 success = 1;
 130         } else {
 131                 *digest = NULL;
 132                 *digest_len = 0;
 133                 success = 0;
 134         }
 135
 136         return success;
 137 }
 138
 139 /*
 140  * Read SSHFP parameters from rdata buffer.
 141  */
 142 static int
 143 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
 144     u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
 145 {
 146         int success = 0;
 147
 148         *algorithm = SSHFP_KEY_RESERVED;
 149         *digest_type = SSHFP_HASH_RESERVED;
 150
 151         if (rdata_len >= 2) {
 152                 *algorithm = rdata[0];
 153                 *digest_type = rdata[1];
 154                 *digest_len = rdata_len - 2;
 155
 156                 if (*digest_len > 0) {
 157                         *digest = xmalloc(*digest_len);
 158                         memcpy(*digest, rdata + 2, *digest_len);
 159                 } else {
 160                         *digest = (u_char *)xstrdup("");
 161                 }
 162
 163                 success = 1;
 164         }
 165
 166         return success;
 167 }
 168
 169 /*
 170  * Check if hostname is numerical.
 171  * Returns -1 if hostname is numeric, 0 otherwise
 172  */
 173 static int
 174 is_numeric_hostname(const char *hostname)
 175 {
 176         struct addrinfo hints, *ai;
 177
 178         /*
 179          * We shouldn't ever get a null host but if we do then log an error
 180          * and return -1 which stops DNS key fingerprint processing.
 181          */
 182         if (hostname == NULL) {
 183                 error("is_numeric_hostname called with NULL hostname");
 184                 return -1;
 185         }
 186
 187         memset(&hints, 0, sizeof(hints));
 188         hints.ai_socktype = SOCK_DGRAM;
 189         hints.ai_flags = AI_NUMERICHOST;
 190
 191         if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
 192                 freeaddrinfo(ai);
 193                 return -1;
 194         }
 195
 196         return 0;
 197 }
 198
 199 /*
 200  * Verify the given hostname, address and host key using DNS.
 201  * Returns 0 if lookup succeeds, -1 otherwise
 202  */
 203 int
 204 verify_host_key_dns(const char *hostname, struct sockaddr *address,
 205     struct sshkey *hostkey, int *flags)
 206 {
 207         u_int counter;
 208         int result;
 209         struct rrsetinfo *fingerprints = NULL;
 210
 211         u_int8_t hostkey_algorithm;
 212         u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
 213         u_char *hostkey_digest;
 214         size_t hostkey_digest_len;
 215
 216         u_int8_t dnskey_algorithm;
 217         u_int8_t dnskey_digest_type;
 218         u_char *dnskey_digest;
 219         size_t dnskey_digest_len;
 220
 221         *flags = 0;
 222
 223         debug3("verify_host_key_dns");
 224         if (hostkey == NULL)
 225                 fatal("No key to look up!");
 226
 227         if (is_numeric_hostname(hostname)) {
 228                 debug("skipped DNS lookup for numerical hostname");
 229                 return -1;
 230         }
 231
 232         result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
 233             DNS_RDATATYPE_SSHFP, 0, &fingerprints);
 234         if (result) {
 235                 verbose("DNS lookup error: %s", dns_result_totext(result));
 236                 return -1;
 237         }
 238
 239         if (fingerprints->rri_flags & RRSET_VALIDATED) {
 240                 *flags |= DNS_VERIFY_SECURE;
 241                 debug("found %d secure fingerprints in DNS",
 242                     fingerprints->rri_nrdatas);
 243         } else {
 244                 debug("found %d insecure fingerprints in DNS",
 245                     fingerprints->rri_nrdatas);
 246         }
 247
 248         /* Initialize default host key parameters */
 249         if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
 250             &hostkey_digest, &hostkey_digest_len, hostkey)) {
 251                 error("Error calculating host key fingerprint.");
 252                 freerrset(fingerprints);
 253                 return -1;
 254         }
 255
 256         if (fingerprints->rri_nrdatas)
 257                 *flags |= DNS_VERIFY_FOUND;
 258
 259         for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
 260                 /*
 261                  * Extract the key from the answer. Ignore any badly
 262                  * formatted fingerprints.
 263                  */
 264                 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
 265                     &dnskey_digest, &dnskey_digest_len,
 266                     fingerprints->rri_rdatas[counter].rdi_data,
 267                     fingerprints->rri_rdatas[counter].rdi_length)) {
 268                         verbose("Error parsing fingerprint from DNS.");
 269                         continue;
 270                 }
 271
 272                 if (hostkey_digest_type != dnskey_digest_type) {
 273                         hostkey_digest_type = dnskey_digest_type;
 274                         free(hostkey_digest);
 275
 276                         /* Initialize host key parameters */
 277                         if (!dns_read_key(&hostkey_algorithm,
 278                             &hostkey_digest_type, &hostkey_digest,
 279                             &hostkey_digest_len, hostkey)) {
 280                                 error("Error calculating key fingerprint.");
 281                                 freerrset(fingerprints);
 282                                 return -1;
 283                         }
 284                 }
 285
 286                 /* Check if the current key is the same as the given key */
 287                 if (hostkey_algorithm == dnskey_algorithm &&
 288                     hostkey_digest_type == dnskey_digest_type) {
 289                         if (hostkey_digest_len == dnskey_digest_len &&
 290                             timingsafe_bcmp(hostkey_digest, dnskey_digest,
 291                             hostkey_digest_len) == 0)
 292                                 *flags |= DNS_VERIFY_MATCH;
 293                 }
 294                 free(dnskey_digest);
 295         }
 296
 297         free(hostkey_digest); /* from sshkey_fingerprint_raw() */
 298         freerrset(fingerprints);
 299
 300         if (*flags & DNS_VERIFY_FOUND)
 301                 if (*flags & DNS_VERIFY_MATCH)
 302                         debug("matching host key fingerprint found in DNS");
 303                 else
 304                         debug("mismatching host key fingerprint found in DNS");
 305         else
 306                 debug("no host key fingerprint found in DNS");
 307
 308         return 0;
 309 }
 310
 311 /*
 312  * Export the fingerprint of a key as a DNS resource record
 313  */
 314 int
 315 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
 316 {
 317         u_int8_t rdata_pubkey_algorithm = 0;
 318         u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
 319         u_int8_t dtype;
 320         u_char *rdata_digest;
 321         size_t i, rdata_digest_len;
 322         int success = 0;
 323
 324         for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
 325                 rdata_digest_type = dtype;
 326                 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
 327                     &rdata_digest, &rdata_digest_len, key)) {
 328                         if (generic) {
 329                                 fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
 330                                     hostname, DNS_RDATATYPE_SSHFP,
 331                                     2 + rdata_digest_len,
 332                                     rdata_pubkey_algorithm, rdata_digest_type);
 333                         } else {
 334                                 fprintf(f, "%s IN SSHFP %d %d ", hostname,
 335                                     rdata_pubkey_algorithm, rdata_digest_type);
 336                         }
 337                         for (i = 0; i < rdata_digest_len; i++)
 338                                 fprintf(f, "%02x", rdata_digest[i]);
 339                         fprintf(f, "\n");
 340                         free(rdata_digest); /* from sshkey_fingerprint_raw() */
 341                         success = 1;
 342                 }
 343         }
 344
 345         /* No SSHFP record was generated at all */
 346         if (success == 0) {
 347                 error("%s: unsupported algorithm and/or digest_type", __func__);
 348         }
 349
 350         return success;
 351 }