OpenBSD-4.6/usr.bin/ssh/dns.c
/* $OpenBSD: dns.c,v 1.25 2008/06/12 00:03:49 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 <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include "xmalloc.h"
#include "key.h"
#include "dns.h"
#include "log.h"
static const char *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.
*/
static int
dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
u_char **digest, u_int *digest_len, const Key *key)
{
int success = 0;
switch (key->type) {
case KEY_RSA:
*algorithm = SSHFP_KEY_RSA;
break;
case KEY_DSA:
*algorithm = SSHFP_KEY_DSA;
break;
default:
*algorithm = SSHFP_KEY_RESERVED; /* 0 */
}
if (*algorithm) {
*digest_type = SSHFP_HASH_SHA1;
*digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
if (*digest == NULL)
fatal("dns_read_key: null from key_fingerprint_raw()");
success = 1;
} else {
*digest_type = SSHFP_HASH_RESERVED;
*digest = NULL;
*digest_len = 0;
success = 0;
}
return success;
}
/*
* Read SSHFP parameters from rdata buffer.
*/
static int
dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
u_char **digest, u_int *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 = (u_char *) 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,
const Key *hostkey, int *flags)
{
u_int counter;
int result;
struct rrsetinfo *fingerprints = NULL;
u_int8_t hostkey_algorithm;
u_int8_t hostkey_digest_type;
u_char *hostkey_digest;
u_int hostkey_digest_len;
u_int8_t dnskey_algorithm;
u_int8_t dnskey_digest_type;
u_char *dnskey_digest;
u_int 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);
}
/* Initialize host key parameters */
if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
&hostkey_digest, &hostkey_digest_len, hostkey)) {
error("Error calculating host key fingerprint.");
freerrset(fingerprints);
return -1;
}
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;
}
/* Check if the current key is the same as the given key */
if (hostkey_algorithm == dnskey_algorithm &&
hostkey_digest_type == dnskey_digest_type) {
if (hostkey_digest_len == dnskey_digest_len &&
memcmp(hostkey_digest, dnskey_digest,
hostkey_digest_len) == 0) {
*flags |= DNS_VERIFY_MATCH;
}
}
xfree(dnskey_digest);
}
xfree(hostkey_digest); /* from key_fingerprint_raw() */
freerrset(fingerprints);
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, const Key *key, FILE *f, int generic)
{
u_int8_t rdata_pubkey_algorithm = 0;
u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
u_char *rdata_digest;
u_int rdata_digest_len;
u_int i;
int success = 0;
if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
&rdata_digest, &rdata_digest_len, key)) {
if (generic)
fprintf(f, "%s IN TYPE%d \\# %d %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");
xfree(rdata_digest); /* from key_fingerprint_raw() */
success = 1;
} else {
error("export_dns_rr: unsupported algorithm");
}
return success;
}