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/* $OpenBSD: dns.c,v 1.37 2017/09/14 04:32:21 djm Exp $ */ |
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/* |
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* Copyright (c) 2003 Wesley Griffin. All rights reserved. |
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* Copyright (c) 2003 Jakob Schlyter. All rights reserved. |
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* |
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* Redistribution and use in source and binary forms, with or without |
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* modification, are permitted provided that the following conditions |
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* are met: |
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* 1. Redistributions of source code must retain the above copyright |
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* notice, this list of conditions and the following disclaimer. |
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* 2. Redistributions in binary form must reproduce the above copyright |
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* notice, this list of conditions and the following disclaimer in the |
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* documentation and/or other materials provided with the distribution. |
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* |
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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*/ |
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#include <sys/types.h> |
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#include <sys/socket.h> |
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#include <netdb.h> |
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#include <stdio.h> |
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#include <string.h> |
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#include <stdarg.h> |
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#include <stdlib.h> |
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#include "xmalloc.h" |
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#include "sshkey.h" |
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#include "ssherr.h" |
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#include "dns.h" |
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#include "log.h" |
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#include "digest.h" |
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static const char *errset_text[] = { |
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"success", /* 0 ERRSET_SUCCESS */ |
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"out of memory", /* 1 ERRSET_NOMEMORY */ |
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"general failure", /* 2 ERRSET_FAIL */ |
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"invalid parameter", /* 3 ERRSET_INVAL */ |
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"name does not exist", /* 4 ERRSET_NONAME */ |
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"data does not exist", /* 5 ERRSET_NODATA */ |
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}; |
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static const char * |
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dns_result_totext(unsigned int res) |
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{ |
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switch (res) { |
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case ERRSET_SUCCESS: |
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return errset_text[ERRSET_SUCCESS]; |
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case ERRSET_NOMEMORY: |
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return errset_text[ERRSET_NOMEMORY]; |
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case ERRSET_FAIL: |
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return errset_text[ERRSET_FAIL]; |
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case ERRSET_INVAL: |
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return errset_text[ERRSET_INVAL]; |
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case ERRSET_NONAME: |
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return errset_text[ERRSET_NONAME]; |
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case ERRSET_NODATA: |
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return errset_text[ERRSET_NODATA]; |
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default: |
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return "unknown error"; |
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} |
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} |
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/* |
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* Read SSHFP parameters from key buffer. |
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*/ |
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static int |
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dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type, |
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u_char **digest, size_t *digest_len, struct sshkey *key) |
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{ |
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int r, success = 0; |
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int fp_alg = -1; |
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switch (key->type) { |
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case KEY_RSA: |
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*algorithm = SSHFP_KEY_RSA; |
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if (!*digest_type) |
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*digest_type = SSHFP_HASH_SHA1; |
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break; |
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case KEY_DSA: |
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*algorithm = SSHFP_KEY_DSA; |
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if (!*digest_type) |
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*digest_type = SSHFP_HASH_SHA1; |
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break; |
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case KEY_ECDSA: |
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*algorithm = SSHFP_KEY_ECDSA; |
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if (!*digest_type) |
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*digest_type = SSHFP_HASH_SHA256; |
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break; |
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case KEY_ED25519: |
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*algorithm = SSHFP_KEY_ED25519; |
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if (!*digest_type) |
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*digest_type = SSHFP_HASH_SHA256; |
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break; |
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default: |
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*algorithm = SSHFP_KEY_RESERVED; /* 0 */ |
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*digest_type = SSHFP_HASH_RESERVED; /* 0 */ |
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} |
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switch (*digest_type) { |
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case SSHFP_HASH_SHA1: |
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fp_alg = SSH_DIGEST_SHA1; |
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break; |
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case SSHFP_HASH_SHA256: |
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fp_alg = SSH_DIGEST_SHA256; |
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break; |
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default: |
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*digest_type = SSHFP_HASH_RESERVED; /* 0 */ |
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} |
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if (*algorithm && *digest_type) { |
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if ((r = sshkey_fingerprint_raw(key, fp_alg, digest, |
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digest_len)) != 0) |
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fatal("%s: sshkey_fingerprint_raw: %s", __func__, |
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ssh_err(r)); |
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success = 1; |
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} else { |
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*digest = NULL; |
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*digest_len = 0; |
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success = 0; |
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} |
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return success; |
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} |
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/* |
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* Read SSHFP parameters from rdata buffer. |
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*/ |
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static int |
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dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type, |
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u_char **digest, size_t *digest_len, u_char *rdata, int rdata_len) |
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{ |
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int success = 0; |
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*algorithm = SSHFP_KEY_RESERVED; |
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*digest_type = SSHFP_HASH_RESERVED; |
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if (rdata_len >= 2) { |
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*algorithm = rdata[0]; |
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*digest_type = rdata[1]; |
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*digest_len = rdata_len - 2; |
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if (*digest_len > 0) { |
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*digest = xmalloc(*digest_len); |
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memcpy(*digest, rdata + 2, *digest_len); |
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} else { |
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*digest = (u_char *)xstrdup(""); |
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} |
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success = 1; |
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} |
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return success; |
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} |
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/* |
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* Check if hostname is numerical. |
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* Returns -1 if hostname is numeric, 0 otherwise |
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*/ |
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static int |
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is_numeric_hostname(const char *hostname) |
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{ |
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struct addrinfo hints, *ai; |
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/* |
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* We shouldn't ever get a null host but if we do then log an error |
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* and return -1 which stops DNS key fingerprint processing. |
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*/ |
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if (hostname == NULL) { |
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error("is_numeric_hostname called with NULL hostname"); |
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return -1; |
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} |
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memset(&hints, 0, sizeof(hints)); |
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hints.ai_socktype = SOCK_DGRAM; |
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hints.ai_flags = AI_NUMERICHOST; |
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if (getaddrinfo(hostname, NULL, &hints, &ai) == 0) { |
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freeaddrinfo(ai); |
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return -1; |
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} |
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return 0; |
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} |
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/* |
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* Verify the given hostname, address and host key using DNS. |
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* Returns 0 if lookup succeeds, -1 otherwise |
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*/ |
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int |
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verify_host_key_dns(const char *hostname, struct sockaddr *address, |
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struct sshkey *hostkey, int *flags) |
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{ |
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u_int counter; |
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int result; |
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struct rrsetinfo *fingerprints = NULL; |
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u_int8_t hostkey_algorithm; |
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u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED; |
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u_char *hostkey_digest; |
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size_t hostkey_digest_len; |
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u_int8_t dnskey_algorithm; |
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u_int8_t dnskey_digest_type; |
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u_char *dnskey_digest; |
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size_t dnskey_digest_len; |
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*flags = 0; |
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debug3("verify_host_key_dns"); |
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if (hostkey == NULL) |
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fatal("No key to look up!"); |
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if (is_numeric_hostname(hostname)) { |
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debug("skipped DNS lookup for numerical hostname"); |
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return -1; |
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} |
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result = getrrsetbyname(hostname, DNS_RDATACLASS_IN, |
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DNS_RDATATYPE_SSHFP, 0, &fingerprints); |
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if (result) { |
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verbose("DNS lookup error: %s", dns_result_totext(result)); |
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return -1; |
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} |
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if (fingerprints->rri_flags & RRSET_VALIDATED) { |
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*flags |= DNS_VERIFY_SECURE; |
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debug("found %d secure fingerprints in DNS", |
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fingerprints->rri_nrdatas); |
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} else { |
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debug("found %d insecure fingerprints in DNS", |
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fingerprints->rri_nrdatas); |
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} |
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/* Initialize default host key parameters */ |
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if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type, |
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&hostkey_digest, &hostkey_digest_len, hostkey)) { |
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error("Error calculating host key fingerprint."); |
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freerrset(fingerprints); |
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return -1; |
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} |
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if (fingerprints->rri_nrdatas) |
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*flags |= DNS_VERIFY_FOUND; |
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for (counter = 0; counter < fingerprints->rri_nrdatas; counter++) { |
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/* |
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* Extract the key from the answer. Ignore any badly |
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* formatted fingerprints. |
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*/ |
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if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type, |
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&dnskey_digest, &dnskey_digest_len, |
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fingerprints->rri_rdatas[counter].rdi_data, |
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fingerprints->rri_rdatas[counter].rdi_length)) { |
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verbose("Error parsing fingerprint from DNS."); |
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continue; |
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} |
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if (hostkey_digest_type != dnskey_digest_type) { |
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hostkey_digest_type = dnskey_digest_type; |
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free(hostkey_digest); |
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/* Initialize host key parameters */ |
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if (!dns_read_key(&hostkey_algorithm, |
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&hostkey_digest_type, &hostkey_digest, |
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&hostkey_digest_len, hostkey)) { |
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error("Error calculating key fingerprint."); |
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freerrset(fingerprints); |
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return -1; |
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} |
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} |
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/* Check if the current key is the same as the given key */ |
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if (hostkey_algorithm == dnskey_algorithm && |
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hostkey_digest_type == dnskey_digest_type) { |
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if (hostkey_digest_len == dnskey_digest_len && |
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timingsafe_bcmp(hostkey_digest, dnskey_digest, |
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hostkey_digest_len) == 0) |
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*flags |= DNS_VERIFY_MATCH; |
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} |
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free(dnskey_digest); |
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} |
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free(hostkey_digest); /* from sshkey_fingerprint_raw() */ |
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freerrset(fingerprints); |
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if (*flags & DNS_VERIFY_FOUND) |
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if (*flags & DNS_VERIFY_MATCH) |
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debug("matching host key fingerprint found in DNS"); |
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else |
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debug("mismatching host key fingerprint found in DNS"); |
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else |
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debug("no host key fingerprint found in DNS"); |
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return 0; |
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} |
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/* |
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* Export the fingerprint of a key as a DNS resource record |
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*/ |
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int |
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export_dns_rr(const char *hostname, struct sshkey *key, FILE *f, int generic) |
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{ |
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u_int8_t rdata_pubkey_algorithm = 0; |
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u_int8_t rdata_digest_type = SSHFP_HASH_RESERVED; |
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u_int8_t dtype; |
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u_char *rdata_digest; |
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size_t i, rdata_digest_len; |
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int success = 0; |
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for (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) { |
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rdata_digest_type = dtype; |
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if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type, |
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&rdata_digest, &rdata_digest_len, key)) { |
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if (generic) { |
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fprintf(f, "%s IN TYPE%d \\# %zu %02x %02x ", |
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hostname, DNS_RDATATYPE_SSHFP, |
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2 + rdata_digest_len, |
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rdata_pubkey_algorithm, rdata_digest_type); |
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} else { |
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fprintf(f, "%s IN SSHFP %d %d ", hostname, |
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rdata_pubkey_algorithm, rdata_digest_type); |
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} |
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for (i = 0; i < rdata_digest_len; i++) |
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fprintf(f, "%02x", rdata_digest[i]); |
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fprintf(f, "\n"); |
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free(rdata_digest); /* from sshkey_fingerprint_raw() */ |
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success = 1; |
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} |
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} |
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/* No SSHFP record was generated at all */ |
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if (success == 0) { |
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error("%s: unsupported algorithm and/or digest_type", __func__); |
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} |
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return success; |
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} |