diff options
Diffstat (limited to 'dns.c')
| -rw-r--r-- | dns.c | 293 |
1 files changed, 293 insertions, 0 deletions
@@ -0,0 +1,293 @@ +/* $OpenBSD: dns.c,v 1.4 2003/05/14 23:29:22 jakob 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" + +#ifdef DNS +#include <openssl/bn.h> +#ifdef LWRES +#include <lwres/netdb.h> +#include <dns/result.h> +#else /* LWRES */ +#include <netdb.h> +#endif /* LWRES */ + +#include "xmalloc.h" +#include "key.h" +#include "dns.h" +#include "log.h" +#include "uuencode.h" + +extern char *__progname; +RCSID("$OpenBSD: dns.c,v 1.4 2003/05/14 23:29:22 jakob Exp $"); + +#ifndef LWRES +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 error) +{ + switch (error) { + 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"; + } +} +#endif /* LWRES */ + + +/* + * 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, 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; + } + + if (*algorithm) { + *digest_type = SSHFP_HASH_SHA1; + *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len); + 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 = NULL; + } + + success = 1; + } + + return success; +} + + +/* + * Verify the given hostname, address and host key using DNS. + * Returns 0 if key verifies or -1 if key does NOT verify + */ +int +verify_host_key_dns(const char *hostname, struct sockaddr *address, + Key *hostkey) +{ + int counter; + int result; + struct rrsetinfo *fingerprints = NULL; + int failures = 0; + + 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; + + + debug3("verify_hostkey_dns"); + if (hostkey == NULL) + fatal("No key to look up!"); + + result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, + DNS_RDATATYPE_SSHFP, 0, &fingerprints); + if (result) { + verbose("DNS lookup error: %s", dns_result_totext(result)); + return DNS_VERIFY_ERROR; + } + +#ifdef DNSSEC + /* Only accept validated answers */ + if (!fingerprints->rri_flags & RRSET_VALIDATED) { + error("Ignored unvalidated fingerprint from DNS."); + return DNS_VERIFY_ERROR; + } +#endif + + debug("found %d 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."); + return DNS_VERIFY_ERROR; + } + + 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) { + + /* Matching algoritm and digest. */ + freerrset(fingerprints); +#ifdef DNSSEC + debug("matching host key fingerprint found in DNS"); + return DNS_VERIFY_OK; +#else + logit("Matching host key fingerprint found in DNS."); + return DNS_VERIFY_ERROR; +#endif + } else { + /* Correct algorithm but bad digest */ + debug("verify_hostkey_dns: failed"); + failures++; + } + } + } + + freerrset(fingerprints); + + if (failures) { + error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); + error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @"); + error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@"); + error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!"); + error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!"); + error("It is also possible that the %s host key has just been changed.", + key_type(hostkey)); + error("Please contact your system administrator."); + return DNS_VERIFY_FAILED; + } + + debug("fingerprints found in DNS, but none of them matched"); + + return DNS_VERIFY_ERROR; +} + + +/* + * Export the fingerprint of a key as a DNS resource record + */ +int +export_dns_rr(const char *hostname, 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; + + 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"); + success = 1; + } else { + error("dns_export_rr: unsupported algorithm"); + } + + return success; +} + +#endif /* DNS */ |