/* $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 <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;
}