/*
Copyright (c) 2013-2020 Roger Light <roger@atchoo.org>

All rights reserved. This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
and Eclipse Distribution License v1.0 which accompany this distribution.

The Eclipse Public License is available at
   https://www.eclipse.org/legal/epl-2.0/
and the Eclipse Distribution License is available at
  http://www.eclipse.org/org/documents/edl-v10.php.

SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause

Contributors:
   Roger Light - initial implementation and documentation.
*/

#include "config.h"

#ifdef WITH_TLS

#ifdef WIN32
#  include <winsock2.h>
#  include <ws2tcpip.h>
#else
#  include <arpa/inet.h>
#  include <sys/socket.h>
#  include <strings.h>
#endif

#include <string.h>
#include <openssl/conf.h>
#include <openssl/x509v3.h>
#include <openssl/ssl.h>

#ifdef WITH_BROKER
#  include "mosquitto_broker_internal.h"
#endif
#include "mosquitto_internal.h"
#include "logging_mosq.h"
#include "tls_mosq.h"

extern int tls_ex_index_mosq;

int mosquitto__server_certificate_verify(int preverify_ok, X509_STORE_CTX *ctx)
{
	/* Preverify should have already checked expiry, revocation.
	 * We need to verify the hostname. */
	struct mosquitto *mosq;
	SSL *ssl;
	X509 *cert;

	/* Always reject if preverify_ok has failed. */
	if(!preverify_ok) return 0;

	ssl = X509_STORE_CTX_get_ex_data(ctx, SSL_get_ex_data_X509_STORE_CTX_idx());
	mosq = SSL_get_ex_data(ssl, tls_ex_index_mosq);
	if(!mosq) return 0;

	if(mosq->tls_insecure == false
#ifndef WITH_BROKER
			&& mosq->port != 0 /* no hostname checking for unix sockets */
#endif
			){
		if(X509_STORE_CTX_get_error_depth(ctx) == 0){
			/* FIXME - use X509_check_host() etc. for sufficiently new openssl (>=1.1.x) */
			cert = X509_STORE_CTX_get_current_cert(ctx);
			/* This is the peer certificate, all others are upwards in the chain. */
#if defined(WITH_BROKER)
			preverify_ok = mosquitto__verify_certificate_hostname(cert, mosq->bridge->addresses[mosq->bridge->cur_address].address);
#else
			preverify_ok = mosquitto__verify_certificate_hostname(cert, mosq->host);
#endif
			if (preverify_ok != 1) {
				log__printf(mosq, MOSQ_LOG_ERR, "Error: host name verification failed.");
			}
			return preverify_ok;
		}else{
			return preverify_ok;
		}
	}else{
		return preverify_ok;
	}
}

static int mosquitto__cmp_hostname_wildcard(char *certname, const char *hostname)
{
	size_t i;
	size_t len;

	if(!certname || !hostname){
		return 1;
	}

	if(certname[0] == '*'){
		if(certname[1] != '.'){
			return 1;
		}
		certname += 2;
		len = strlen(hostname);
		for(i=0; i<len-1; i++){
			if(hostname[i] == '.'){
				hostname += i+1;
				break;
			}
		}
		len = strlen(hostname);
		int dotcount = 0;
		for(i=0; i<len-1; i++){
			if(hostname[i] == '.'){
				dotcount++;
			}
		}
		if(dotcount < 1){
			/* Exclude e.g. *.com, allow e.g. *.example.com */
			return 1;
		}
		return strcasecmp(certname, hostname);
	}else{
		return strcasecmp(certname, hostname);
	}
}

/* This code is based heavily on the example provided in "Secure Programming
 * Cookbook for C and C++".
 */
int mosquitto__verify_certificate_hostname(X509 *cert, const char *hostname)
{
	int i;
	char name[256];
	X509_NAME *subj;
	bool have_san_dns = false;
	STACK_OF(GENERAL_NAME) *san;
	const GENERAL_NAME *nval;
	const unsigned char *data;
	unsigned char ipv6_addr[16];
	unsigned char ipv4_addr[4];
	int ipv6_ok;
	int ipv4_ok;

#ifdef WIN32
	ipv6_ok = InetPton(AF_INET6, hostname, &ipv6_addr);
	ipv4_ok = InetPton(AF_INET, hostname, &ipv4_addr);
#else
	ipv6_ok = inet_pton(AF_INET6, hostname, &ipv6_addr);
	ipv4_ok = inet_pton(AF_INET, hostname, &ipv4_addr);
#endif

	san = X509_get_ext_d2i(cert, NID_subject_alt_name, NULL, NULL);
	if(san){
		for(i=0; i<sk_GENERAL_NAME_num(san); i++){
			nval = sk_GENERAL_NAME_value(san, i);
			if(nval->type == GEN_DNS){
#if OPENSSL_VERSION_NUMBER < 0x10100000L
				data = ASN1_STRING_data(nval->d.dNSName);
#else
				data = ASN1_STRING_get0_data(nval->d.dNSName);
#endif
				if(data && !mosquitto__cmp_hostname_wildcard((char *)data, hostname)){
					sk_GENERAL_NAME_pop_free(san, GENERAL_NAME_free);
					return 1;
				}
				have_san_dns = true;
			}else if(nval->type == GEN_IPADD){
#if OPENSSL_VERSION_NUMBER < 0x10100000L
				data = ASN1_STRING_data(nval->d.iPAddress);
#else
				data = ASN1_STRING_get0_data(nval->d.iPAddress);
#endif
				if(nval->d.iPAddress->length == 4 && ipv4_ok){
					if(!memcmp(ipv4_addr, data, 4)){
						sk_GENERAL_NAME_pop_free(san, GENERAL_NAME_free);
						return 1;
					}
				}else if(nval->d.iPAddress->length == 16 && ipv6_ok){
					if(!memcmp(ipv6_addr, data, 16)){
						sk_GENERAL_NAME_pop_free(san, GENERAL_NAME_free);
						return 1;
					}
				}
			}
		}
		sk_GENERAL_NAME_pop_free(san, GENERAL_NAME_free);
		if(have_san_dns){
			/* Only check CN if subjectAltName DNS entry does not exist. */
			return 0;
		}
	}

	subj = X509_get_subject_name(cert);
	if(X509_NAME_get_text_by_NID(subj, NID_commonName, name, sizeof(name)) > 0){
		name[sizeof(name) - 1] = '\0';
		if (!mosquitto__cmp_hostname_wildcard(name, hostname)) return 1;
	}
	return 0;
}

#endif