/* $OpenBSD: dns.c,v 1.48 2026/03/03 09:57:25 dtucker Exp $ */

/*

 * Copyright (c) 2003 Wesley Griffin. All rights reserved.

 * Copyright (c) 2003 Jakob Schlyter. All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include "includes.h"

#include <sys/types.h>

#include <sys/socket.h>

#include <netdb.h>

#include <stdarg.h>

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include "xmalloc.h"

#include "sshkey.h"

#include "dns.h"

#include "log.h"

#include "digest.h"

static const char * const errset_text[] = {

  "success",    /* 0 ERRSET_SUCCESS */

  "out of memory",  /* 1 ERRSET_NOMEMORY */

  "general failure",  /* 2 ERRSET_FAIL */

  "invalid parameter",  /* 3 ERRSET_INVAL */

  "name does not exist",  /* 4 ERRSET_NONAME */

  "data does not exist",  /* 5 ERRSET_NODATA */

};

static const char *

dns_result_totext(unsigned int res)

{

  switch (res) {

  case ERRSET_SUCCESS:

    return errset_text[ERRSET_SUCCESS];

  case ERRSET_NOMEMORY:

    return errset_text[ERRSET_NOMEMORY];

  case ERRSET_FAIL:

    return errset_text[ERRSET_FAIL];

  case ERRSET_INVAL:

    return errset_text[ERRSET_INVAL];

  case ERRSET_NONAME:

    return errset_text[ERRSET_NONAME];

  case ERRSET_NODATA:

    return errset_text[ERRSET_NODATA];

  default:

    return "unknown error";

  }

}

/*

 * Read SSHFP parameters from key buffer.

 * Caller must free digest which is allocated by sshkey_fingerprint_raw().

 */

static int

dns_read_key(uint8_t *algorithm, uint8_t *digest_type,

    u_char **digest, size_t *digest_len, struct sshkey *key)

{

  int r, success = 0;

  int fp_alg = -1;

  switch (key->type) {

  case KEY_RSA:

    *algorithm = SSHFP_KEY_RSA;

    break;

  case KEY_ECDSA:

    *algorithm = SSHFP_KEY_ECDSA;

    break;

  case KEY_ED25519:

    *algorithm = SSHFP_KEY_ED25519;

    break;

  default:

    *algorithm = SSHFP_KEY_RESERVED; /* 0 */

  }

  switch (*digest_type) {

  case SSHFP_HASH_SHA1:

    fp_alg = SSH_DIGEST_SHA1;

    break;

  case SSHFP_HASH_SHA256:

    fp_alg = SSH_DIGEST_SHA256;

    break;

  default:

    *digest_type = SSHFP_HASH_RESERVED; /* 0 */

  }

  if (*algorithm && *digest_type) {

    if ((r = sshkey_fingerprint_raw(key, fp_alg, digest,

        digest_len)) != 0)

      fatal_fr(r, "sshkey_fingerprint_raw");

    success = 1;

  } else {

    *digest = NULL;

    *digest_len = 0;

  }

  return success;

}

/*

 * Read SSHFP parameters from rdata buffer.

 */

static int

dns_read_rdata(uint8_t *algorithm, uint8_t *digest_type,

    u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len)

{

  int success = 0;

  *algorithm = SSHFP_KEY_RESERVED;

  *digest_type = SSHFP_HASH_RESERVED;

  if (rdata_len >= 2) {

    *algorithm = rdata[0];

    *digest_type = rdata[1];

    *digest_len = rdata_len - 2;

    if (*digest_len > 0) {

      *digest = xmalloc(*digest_len);

      memcpy(*digest, rdata + 2, *digest_len);

    } else {

      *digest = (u_char *)xstrdup("");

    }

    success = 1;

  }

  return success;

}

/*

 * Check if hostname is numerical.

 * Returns -1 if hostname is numeric, 0 otherwise

 */

static int

is_numeric_hostname(const char *hostname)

{

  struct addrinfo hints, *ai;

  /*

   * We shouldn't ever get a null host but if we do then log an error

   * and return -1 which stops DNS key fingerprint processing.

   */

  if (hostname == NULL) {

    error("is_numeric_hostname called with NULL hostname");

    return -1;

  }

  memset(&hints, 0, sizeof(hints));

  hints.ai_socktype = SOCK_DGRAM;

  hints.ai_flags = AI_NUMERICHOST;

  if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) {

    freeaddrinfo(ai);

    return -1;

  }

  return 0;

}

/*

 * Verify the given hostname, address and host key using DNS.

 * Returns 0 if lookup succeeds, -1 otherwise

 */

int

verify_host_key_dns(const char *hostname, struct sockaddr *address,

    struct sshkey *hostkey, int *flags)

{

  u_int counter;

  int result;

  struct rrsetinfo *fingerprints = NULL;

  uint8_t hostkey_algorithm;

  u_char *hostkey_digest;

  size_t hostkey_digest_len;

  uint8_t dnskey_algorithm;

  uint8_t dnskey_digest_type;

  u_char *dnskey_digest;

  size_t dnskey_digest_len;

  *flags = 0;

  debug3("verify_host_key_dns");

  if (hostkey == NULL)

    fatal("No key to look up!");

  if (is_numeric_hostname(hostname)) {

    debug("skipped DNS lookup for numerical hostname");

    return -1;

  }

  result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,

      DNS_RDATATYPE_SSHFP, 0, &fingerprints);

  if (result) {

    verbose("DNS lookup error: %s", dns_result_totext(result));

    return -1;

  }

  if (fingerprints->rri_flags & RRSET_VALIDATED) {

    *flags |= DNS_VERIFY_SECURE;

    debug("found %d secure fingerprints in DNS",

        fingerprints->rri_nrdatas);

  } else {

    debug("found %d insecure fingerprints in DNS",

        fingerprints->rri_nrdatas);

  }

  if (fingerprints->rri_nrdatas)

    *flags |= DNS_VERIFY_FOUND;

  for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) {

    /*

     * Extract the key from the answer. Ignore any badly

     * formatted fingerprints.

     */

    if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,

        &dnskey_digest, &dnskey_digest_len,

        fingerprints->rri_rdatas[counter].rdi_data,

        fingerprints->rri_rdatas[counter].rdi_length)) {

      verbose("Error parsing fingerprint from DNS.");

      continue;

    }

    debug3_f("checking SSHFP type %d fptype %d", dnskey_algorithm,

        dnskey_digest_type);

    /* Calculate host key fingerprint. */

    if (!dns_read_key(&hostkey_algorithm, &dnskey_digest_type,

        &hostkey_digest, &hostkey_digest_len, hostkey)) {

      error("Error calculating key fingerprint.");

      free(dnskey_digest);

      freerrset(fingerprints);

      return -1;

    }

    /* Check if the current key is the same as the given key */

    if (hostkey_algorithm == dnskey_algorithm &&

        hostkey_digest_len == dnskey_digest_len) {

      if (timingsafe_bcmp(hostkey_digest, dnskey_digest,

          hostkey_digest_len) == 0) {

        debug_f("matched SSHFP type %d fptype %d",

            dnskey_algorithm, dnskey_digest_type);

        *flags |= DNS_VERIFY_MATCH;

      } else {

        debug_f("failed SSHFP type %d fptype %d",

            dnskey_algorithm, dnskey_digest_type);

        *flags |= DNS_VERIFY_FAILED;

      }

    }

    free(dnskey_digest);

    free(hostkey_digest); /* from sshkey_fingerprint_raw() */

  }

  freerrset(fingerprints);

  /* If any fingerprint failed to validate, return failure. */

  if (*flags & DNS_VERIFY_FAILED)

    *flags &= ~DNS_VERIFY_MATCH;

  if (*flags & DNS_VERIFY_FOUND)

    if (*flags & DNS_VERIFY_MATCH)

      debug("matching host key fingerprint found in DNS");

    else

      debug("mismatching host key fingerprint found in DNS");

  else

    debug("no host key fingerprint found in DNS");

  return 0;

}

/*

 * Export the fingerprint of a key as a DNS resource record

 */

int

export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic,

    int alg)

{

  uint8_t rdata_pubkey_algorithm = 0;

  uint8_t rdata_digest_type = SSHFP_HASH_RESERVED;

  uint8_t dtype;

  u_char *rdata_digest;

  size_t i, rdata_digest_len;

  int success = 0;

  for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {

    if (alg != -1 && dtype != alg)

      continue;

    rdata_digest_type = dtype;

    if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,

        &rdata_digest, &rdata_digest_len, key)) {

      if (generic) {

        fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ",

            hostname, DNS_RDATATYPE_SSHFP,

            2 + rdata_digest_len,

            rdata_pubkey_algorithm, rdata_digest_type);

      } else {

        fprintf(f, "%s IN SSHFP %d %d ", hostname,

            rdata_pubkey_algorithm, rdata_digest_type);

      }

      for (i = 0; i < rdata_digest_len; i++)

        fprintf(f, "%02x", rdata_digest[i]);

      fprintf(f, "\n");

      free(rdata_digest); /* from sshkey_fingerprint_raw() */

      success = 1;

    }

  }

  /* No SSHFP record was generated at all */

  if (success == 0) {

    error_f("unsupported algorithm and/or digest_type");

  }

  return success;

}