crypto/openssh/dns.c

   1 /* $OpenBSD: dns.c,v 1.42 2022/02/01 23:32:51 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 <stdlib.h>
  38
  39 #include "xmalloc.h"
  40 #include "sshkey.h"
  41 #include "ssherr.h"
  42 #include "dns.h"
  43 #include "log.h"
  44 #include "digest.h"
  45
  46 static const char * const errset_text[] = {
  47         "success",              /* 0 ERRSET_SUCCESS */
  48         "out of memory",        /* 1 ERRSET_NOMEMORY */
  49         "general failure",      /* 2 ERRSET_FAIL */
  50         "invalid parameter",    /* 3 ERRSET_INVAL */
  51         "name does not exist",  /* 4 ERRSET_NONAME */
  52         "data does not exist",  /* 5 ERRSET_NODATA */
  53 };
  54
  55 static const char *
  56 dns_result_totext(unsigned int res)
  57 {
  58         switch (res) {
  59         case ERRSET_SUCCESS:
  60                 return errset_text[ERRSET_SUCCESS];
  61         case ERRSET_NOMEMORY:
  62                 return errset_text[ERRSET_NOMEMORY];
  63         case ERRSET_FAIL:
  64                 return errset_text[ERRSET_FAIL];
  65         case ERRSET_INVAL:
  66                 return errset_text[ERRSET_INVAL];
  67         case ERRSET_NONAME:
  68                 return errset_text[ERRSET_NONAME];
  69         case ERRSET_NODATA:
  70                 return errset_text[ERRSET_NODATA];
  71         default:
  72                 return "unknown error";
  73         }
  74 }
  75
  76 /*
  77  * Read SSHFP parameters from key buffer.
  78  * Caller must free digest which is allocated by sshkey_fingerprint_raw().
  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                 break;
  91         case KEY_DSA:
  92                 *algorithm = SSHFP_KEY_DSA;
  93                 break;
  94         case KEY_ECDSA:
  95                 *algorithm = SSHFP_KEY_ECDSA;
  96                 break;
  97         case KEY_ED25519:
  98                 *algorithm = SSHFP_KEY_ED25519;
  99                 break;
 100         case KEY_XMSS:
 101                 *algorithm = SSHFP_KEY_XMSS;
 102                 break;
 103         default:
 104                 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
 105         }
 106
 107         switch (*digest_type) {
 108         case SSHFP_HASH_SHA1:
 109                 fp_alg = SSH_DIGEST_SHA1;
 110                 break;
 111         case SSHFP_HASH_SHA256:
 112                 fp_alg = SSH_DIGEST_SHA256;
 113                 break;
 114         default:
 115                 *digest_type = SSHFP_HASH_RESERVED; /* 0 */
 116         }
 117
 118         if (*algorithm && *digest_type) {
 119                 if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,
 120                     digest_len)) != 0)
 121                         fatal_fr(r, "sshkey_fingerprint_raw");
 122                 success = 1;
 123         } else {
 124                 *digest = NULL;
 125                 *digest_len = 0;
 126         }
 127
 128         return success;
 129 }
 130
 131 /*
 132  * Read SSHFP parameters from rdata buffer.
 133  */
 134 static int
 135 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
 136     u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)
 137 {
 138         int success = 0;
 139
 140         *algorithm = SSHFP_KEY_RESERVED;
 141         *digest_type = SSHFP_HASH_RESERVED;
 142
 143         if (rdata_len >= 2) {
 144                 *algorithm = rdata[0];
 145                 *digest_type = rdata[1];
 146                 *digest_len = rdata_len - 2;
 147
 148                 if (*digest_len > 0) {
 149                         *digest = xmalloc(*digest_len);
 150                         memcpy(*digest, rdata + 2, *digest_len);
 151                 } else {
 152                         *digest = (u_char *)xstrdup("");
 153                 }
 154
 155                 success = 1;
 156         }
 157
 158         return success;
 159 }
 160
 161 /*
 162  * Check if hostname is numerical.
 163  * Returns -1 if hostname is numeric, 0 otherwise
 164  */
 165 static int
 166 is_numeric_hostname(const char *hostname)
 167 {
 168         struct addrinfo hints, *ai;
 169
 170         /*
 171          * We shouldn't ever get a null host but if we do then log an error
 172          * and return -1 which stops DNS key fingerprint processing.
 173          */
 174         if (hostname == NULL) {
 175                 error("is_numeric_hostname called with NULL hostname");
 176                 return -1;
 177         }
 178
 179         memset(&hints, 0, sizeof(hints));
 180         hints.ai_socktype = SOCK_DGRAM;
 181         hints.ai_flags = AI_NUMERICHOST;
 182
 183         if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
 184                 freeaddrinfo(ai);
 185                 return -1;
 186         }
 187
 188         return 0;
 189 }
 190
 191 /*
 192  * Verify the given hostname, address and host key using DNS.
 193  * Returns 0 if lookup succeeds, -1 otherwise
 194  */
 195 int
 196 verify_host_key_dns(const char *hostname, struct sockaddr *address,
 197     struct sshkey *hostkey, int *flags)
 198 {
 199         u_int counter;
 200         int result;
 201         struct rrsetinfo *fingerprints = NULL;
 202
 203         u_int8_t hostkey_algorithm;
 204         u_char *hostkey_digest;
 205         size_t hostkey_digest_len;
 206
 207         u_int8_t dnskey_algorithm;
 208         u_int8_t dnskey_digest_type;
 209         u_char *dnskey_digest;
 210         size_t dnskey_digest_len;
 211
 212         *flags = 0;
 213
 214         debug3("verify_host_key_dns");
 215         if (hostkey == NULL)
 216                 fatal("No key to look up!");
 217
 218         if (is_numeric_hostname(hostname)) {
 219                 debug("skipped DNS lookup for numerical hostname");
 220                 return -1;
 221         }
 222
 223         result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
 224             DNS_RDATATYPE_SSHFP, 0, &fingerprints);
 225         if (result) {
 226                 verbose("DNS lookup error: %s", dns_result_totext(result));
 227                 return -1;
 228         }
 229
 230         if (fingerprints->rri_flags & RRSET_VALIDATED) {
 231                 *flags |= DNS_VERIFY_SECURE;
 232                 debug("found %d secure fingerprints in DNS",
 233                     fingerprints->rri_nrdatas);
 234         } else {
 235                 debug("found %d insecure fingerprints in DNS",
 236                     fingerprints->rri_nrdatas);
 237         }
 238
 239         if (fingerprints->rri_nrdatas)
 240                 *flags |= DNS_VERIFY_FOUND;
 241
 242         for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
 243                 /*
 244                  * Extract the key from the answer. Ignore any badly
 245                  * formatted fingerprints.
 246                  */
 247                 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
 248                     &dnskey_digest, &dnskey_digest_len,
 249                     fingerprints->rri_rdatas[counter].rdi_data,
 250                     fingerprints->rri_rdatas[counter].rdi_length)) {
 251                         verbose("Error parsing fingerprint from DNS.");
 252                         continue;
 253                 }
 254                 debug3_f("checking SSHFP type %d fptype %d", dnskey_algorithm,
 255                     dnskey_digest_type);
 256
 257                 /* Calculate host key fingerprint. */
 258                 if (!dns_read_key(&hostkey_algorithm, &dnskey_digest_type,
 259                     &hostkey_digest, &hostkey_digest_len, hostkey)) {
 260                         error("Error calculating key fingerprint.");
 261                         freerrset(fingerprints);
 262                         return -1;
 263                 }
 264
 265                 /* Check if the current key is the same as the given key */
 266                 if (hostkey_algorithm == dnskey_algorithm &&
 267                     hostkey_digest_len == dnskey_digest_len) {
 268                         if (timingsafe_bcmp(hostkey_digest, dnskey_digest,
 269                             hostkey_digest_len) == 0) {
 270                                 debug_f("matched SSHFP type %d fptype %d",
 271                                     dnskey_algorithm, dnskey_digest_type);
 272                                 *flags |= DNS_VERIFY_MATCH;
 273                         } else {
 274                                 debug_f("failed SSHFP type %d fptype %d",
 275                                     dnskey_algorithm, dnskey_digest_type);
 276                                 *flags |= DNS_VERIFY_FAILED;
 277                         }
 278                 }
 279                 free(dnskey_digest);
 280                 free(hostkey_digest); /* from sshkey_fingerprint_raw() */
 281         }
 282
 283         freerrset(fingerprints);
 284
 285         /* If any fingerprint failed to validate, return failure. */
 286         if (*flags & DNS_VERIFY_FAILED)
 287                 *flags &= ~DNS_VERIFY_MATCH;
 288
 289         if (*flags & DNS_VERIFY_FOUND)
 290                 if (*flags & DNS_VERIFY_MATCH)
 291                         debug("matching host key fingerprint found in DNS");
 292                 else
 293                         debug("mismatching host key fingerprint found in DNS");
 294         else
 295                 debug("no host key fingerprint found in DNS");
 296
 297         return 0;
 298 }
 299
 300 /*
 301  * Export the fingerprint of a key as a DNS resource record
 302  */
 303 int
 304 export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic)
 305 {
 306         u_int8_t rdata_pubkey_algorithm = 0;
 307         u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
 308         u_int8_t dtype;
 309         u_char *rdata_digest;
 310         size_t i, rdata_digest_len;
 311         int success = 0;
 312
 313         for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
 314                 rdata_digest_type = dtype;
 315                 if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
 316                     &rdata_digest, &rdata_digest_len, key)) {
 317                         if (generic) {
 318                                 fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",
 319                                     hostname, DNS_RDATATYPE_SSHFP,
 320                                     2 + rdata_digest_len,
 321                                     rdata_pubkey_algorithm, rdata_digest_type);
 322                         } else {
 323                                 fprintf(f, "%s IN SSHFP %d %d ", hostname,
 324                                     rdata_pubkey_algorithm, rdata_digest_type);
 325                         }
 326                         for (i = 0; i < rdata_digest_len; i++)
 327                                 fprintf(f, "%02x", rdata_digest[i]);
 328                         fprintf(f, "\n");
 329                         free(rdata_digest); /* from sshkey_fingerprint_raw() */
 330                         success = 1;
 331                 }
 332         }
 333
 334         /* No SSHFP record was generated at all */
 335         if (success == 0) {
 336                 error_f("unsupported algorithm and/or digest_type");
 337         }
 338
 339         return success;
 340 }