/*
  Helper functions to perform basic hostname validation using OpenSSL.

  Original Author:  Alban Diquet
  Copyright (C) 2012, iSEC Partners.
  Copyright 2020      Ismael Luceno

  Permission is hereby granted, free of charge, to any person obtaining a copy of
  this software and associated documentation files (the "Software"), to deal in
  the Software without restriction, including without limitation the rights to
  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
  of the Software, and to permit persons to whom the Software is furnished to do
  so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

#include "config.h"

#ifdef HAVE_WOLFSSL
#include <wolfssl/options.h>
#include <wolfssl/wolfcrypt/settings.h>
#include <wolfssl/openssl/ssl.h>
#include <wolfssl/openssl/x509v3.h>
#else
#include <openssl/ssl.h>
#include <openssl/x509v3.h>
#endif

#include "axel.h"

inline static int
match(const char *hostname, ASN1_STRING *certname)
{
	return dn_match(hostname,
			(const char *)ASN1_STRING_get0_data(certname),
			ASN1_STRING_length(certname));
}

/**
 * Match hostname against Certificate's CN field.
 *
 * @returns Negative on malformed input, Zero if matched, non-zero otherwise.
 */
static
int
matches_cn(const char *hostname, const X509 *cert)
{
	/* Find CN field in the Subject field */
	int loc = X509_NAME_get_index_by_NID(X509_get_subject_name(cert),
					     NID_commonName, -1);
	if (loc < 0)
		return 1;

	X509_NAME_ENTRY *entry;
	entry = X509_NAME_get_entry(X509_get_subject_name(cert), loc);
	if (!entry)
		return 1;

	ASN1_STRING *cn = X509_NAME_ENTRY_get_data(entry);
	if (!cn)
		return 1;

	return match(hostname, cn);
}

/**
 * Match hostname against Certificate's SAN fields if available,
 * or CN field otherwise.
 *
 * @returns Negative on malformed input, Zero if matched, non-zero otherwise.
 */
static
int
matches_cert(const char *hostname, const X509 *cert)
{
	/* Try to extract the names within the SAN extension */
	STACK_OF(GENERAL_NAME) *names;
	names = X509_get_ext_d2i(cert, NID_subject_alt_name, NULL, NULL);

	/* Iff extension was not found try the Common Name */
	if (!names)
		return matches_cn(hostname, cert);

	/* Check each name until a match or error */
	const int names_len = sk_GENERAL_NAME_num(names);
	int result = 1;
	for (int i = 0; i < names_len && result > 0; i++) {
		const GENERAL_NAME *cur = sk_GENERAL_NAME_value(names, i);
		/* Check DNS names only */
		if (cur->type == GEN_DNS)
			result = match(hostname, cur->d.dNSName);
	}
	sk_GENERAL_NAME_pop_free(names, GENERAL_NAME_free);
	return result;
}

bool
ssl_validate_hostname(const char *hostname, const X509 *cert)
{
	return hostname && cert && matches_cert(hostname, cert) == 0;
}