dns.c

   1 /* $OpenBSD: dns.c,v 1.25 2008/06/12 00:03:49 dtucker 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, const 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         default:
  90                 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
  91         }
  92
  93         if (*algorithm) {
  94                 *digest_type = SSHFP_HASH_SHA1;
  95                 *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
  96                 if (*digest == NULL)
  97                         fatal("dns_read_key: null from key_fingerprint_raw()");
  98                 success = 1;
  99         } else {
 100                 *digest_type = SSHFP_HASH_RESERVED;
 101                 *digest = NULL;
 102                 *digest_len = 0;
 103                 success = 0;
 104         }
 105
 106         return success;
 107 }
 108
 109 /*
 110  * Read SSHFP parameters from rdata buffer.
 111  */
 112 static int
 113 dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
 114     u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
 115 {
 116         int success = 0;
 117
 118         *algorithm = SSHFP_KEY_RESERVED;
 119         *digest_type = SSHFP_HASH_RESERVED;
 120
 121         if (rdata_len >= 2) {
 122                 *algorithm = rdata[0];
 123                 *digest_type = rdata[1];
 124                 *digest_len = rdata_len - 2;
 125
 126                 if (*digest_len > 0) {
 127                         *digest = (u_char *) xmalloc(*digest_len);
 128                         memcpy(*digest, rdata + 2, *digest_len);
 129                 } else {
 130                         *digest = (u_char *)xstrdup("");
 131                 }
 132
 133                 success = 1;
 134         }
 135
 136         return success;
 137 }
 138
 139 /*
 140  * Check if hostname is numerical.
 141  * Returns -1 if hostname is numeric, 0 otherwise
 142  */
 143 static int
 144 is_numeric_hostname(const char *hostname)
 145 {
 146         struct addrinfo hints, *ai;
 147
 148         /*
 149          * We shouldn't ever get a null host but if we do then log an error
 150          * and return -1 which stops DNS key fingerprint processing.
 151          */
 152         if (hostname == NULL) {
 153                 error("is_numeric_hostname called with NULL hostname");
 154                 return -1;
 155         }
 156
 157         memset(&hints, 0, sizeof(hints));
 158         hints.ai_socktype = SOCK_DGRAM;
 159         hints.ai_flags = AI_NUMERICHOST;
 160
 161         if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {
 162                 freeaddrinfo(ai);
 163                 return -1;
 164         }
 165
 166         return 0;
 167 }
 168
 169 /*
 170  * Verify the given hostname, address and host key using DNS.
 171  * Returns 0 if lookup succeeds, -1 otherwise
 172  */
 173 int
 174 verify_host_key_dns(const char *hostname, struct sockaddr *address,
 175     const Key *hostkey, int *flags)
 176 {
 177         u_int counter;
 178         int result;
 179         struct rrsetinfo *fingerprints = NULL;
 180
 181         u_int8_t hostkey_algorithm;
 182         u_int8_t hostkey_digest_type;
 183         u_char *hostkey_digest;
 184         u_int hostkey_digest_len;
 185
 186         u_int8_t dnskey_algorithm;
 187         u_int8_t dnskey_digest_type;
 188         u_char *dnskey_digest;
 189         u_int dnskey_digest_len;
 190
 191         *flags = 0;
 192
 193         debug3("verify_host_key_dns");
 194         if (hostkey == NULL)
 195                 fatal("No key to look up!");
 196
 197         if (is_numeric_hostname(hostname)) {
 198                 debug("skipped DNS lookup for numerical hostname");
 199                 return -1;
 200         }
 201
 202         result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
 203             DNS_RDATATYPE_SSHFP, 0, &fingerprints);
 204         if (result) {
 205                 verbose("DNS lookup error: %s", dns_result_totext(result));
 206                 return -1;
 207         }
 208
 209         if (fingerprints->rri_flags & RRSET_VALIDATED) {
 210                 *flags |= DNS_VERIFY_SECURE;
 211                 debug("found %d secure fingerprints in DNS",
 212                     fingerprints->rri_nrdatas);
 213         } else {
 214                 debug("found %d insecure fingerprints in DNS",
 215                     fingerprints->rri_nrdatas);
 216         }
 217
 218         /* Initialize host key parameters */
 219         if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
 220             &hostkey_digest, &hostkey_digest_len, hostkey)) {
 221                 error("Error calculating host key fingerprint.");
 222                 freerrset(fingerprints);
 223                 return -1;
 224         }
 225
 226         if (fingerprints->rri_nrdatas)
 227                 *flags |= DNS_VERIFY_FOUND;
 228
 229         for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {
 230                 /*
 231                  * Extract the key from the answer. Ignore any badly
 232                  * formatted fingerprints.
 233                  */
 234                 if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
 235                     &dnskey_digest, &dnskey_digest_len,
 236                     fingerprints->rri_rdatas[counter].rdi_data,
 237                     fingerprints->rri_rdatas[counter].rdi_length)) {
 238                         verbose("Error parsing fingerprint from DNS.");
 239                         continue;
 240                 }
 241
 242                 /* Check if the current key is the same as the given key */
 243                 if (hostkey_algorithm == dnskey_algorithm &&
 244                     hostkey_digest_type == dnskey_digest_type) {
 245
 246                         if (hostkey_digest_len == dnskey_digest_len &&
 247                             memcmp(hostkey_digest, dnskey_digest,
 248                             hostkey_digest_len) == 0) {
 249
 250                                 *flags |= DNS_VERIFY_MATCH;
 251                         }
 252                 }
 253                 xfree(dnskey_digest);
 254         }
 255
 256         xfree(hostkey_digest); /* from key_fingerprint_raw() */
 257         freerrset(fingerprints);
 258
 259         if (*flags & DNS_VERIFY_FOUND)
 260                 if (*flags & DNS_VERIFY_MATCH)
 261                         debug("matching host key fingerprint found in DNS");
 262                 else
 263                         debug("mismatching host key fingerprint found in DNS");
 264         else
 265                 debug("no host key fingerprint found in DNS");
 266
 267         return 0;
 268 }
 269
 270 /*
 271  * Export the fingerprint of a key as a DNS resource record
 272  */
 273 int
 274 export_dns_rr(const char *hostname, const Key *key, FILE *f, int generic)
 275 {
 276         u_int8_t rdata_pubkey_algorithm = 0;
 277         u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
 278         u_char *rdata_digest;
 279         u_int rdata_digest_len;
 280
 281         u_int i;
 282         int success = 0;
 283
 284         if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
 285             &rdata_digest, &rdata_digest_len, key)) {
 286
 287                 if (generic)
 288                         fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
 289                             DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
 290                             rdata_pubkey_algorithm, rdata_digest_type);
 291                 else
 292                         fprintf(f, "%s IN SSHFP %d %d ", hostname,
 293                             rdata_pubkey_algorithm, rdata_digest_type);
 294
 295                 for (i = 0; i < rdata_digest_len; i++)
 296                         fprintf(f, "%02x", rdata_digest[i]);
 297                 fprintf(f, "\n");
 298                 xfree(rdata_digest); /* from key_fingerprint_raw() */
 299                 success = 1;
 300         } else {
 301                 error("export_dns_rr: unsupported algorithm");
 302         }
 303
 304         return success;
 305 }