znc/src/SSLVerifyHost.cpp

/*
 * Copyright (C) 2004-2015 ZNC, see the NOTICE file for details.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <znc/SSLVerifyHost.h>

#ifdef HAVE_LIBSSL

#include <openssl/x509v3.h>

namespace ZNC_Curl {
///////////////////////////////////////////////////////////////////////////
//
// This block is from https://github.com/bagder/curl/blob/master/lib/
// Copyright: Daniel Stenberg, <daniel@haxx.se>, license: MIT
//

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at http://curl.haxx.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/

/* Portable, consistent toupper (remember EBCDIC). Do not use toupper() because
   its behavior is altered by the current locale. */
inline char Curl_raw_toupper(char in)
{
	switch (in) {
		case 'a':
			return 'A';
		case 'b':
			return 'B';
		case 'c':
			return 'C';
		case 'd':
			return 'D';
		case 'e':
			return 'E';
		case 'f':
			return 'F';
		case 'g':
			return 'G';
		case 'h':
			return 'H';
		case 'i':
			return 'I';
		case 'j':
			return 'J';
		case 'k':
			return 'K';
		case 'l':
			return 'L';
		case 'm':
			return 'M';
		case 'n':
			return 'N';
		case 'o':
			return 'O';
		case 'p':
			return 'P';
		case 'q':
			return 'Q';
		case 'r':
			return 'R';
		case 's':
			return 'S';
		case 't':
			return 'T';
		case 'u':
			return 'U';
		case 'v':
			return 'V';
		case 'w':
			return 'W';
		case 'x':
			return 'X';
		case 'y':
			return 'Y';
		case 'z':
			return 'Z';
	}
	return in;
}

/*
* Curl_raw_equal() is for doing "raw" case insensitive strings. This is meant
* to be locale independent and only compare strings we know are safe for
* this. See http://daniel.haxx.se/blog/2008/10/15/strcasecmp-in-turkish/ for
* some further explanation to why this function is necessary.
*
* The function is capable of comparing a-z case insensitively even for
* non-ascii.
*/
static int Curl_raw_equal(const char *first, const char *second)
{
	while(*first && *second) {
		if(Curl_raw_toupper(*first) != Curl_raw_toupper(*second))
			/* get out of the loop as soon as they don't match */
			break;
		first++;
		second++;
	}
	/* we do the comparison here (possibly again), just to make sure that if the
	   loop above is skipped because one of the strings reached zero, we must not
	   return this as a successful match */
	return (Curl_raw_toupper(*first) == Curl_raw_toupper(*second));
}
static int Curl_raw_nequal(const char *first, const char *second, size_t max)
{
	while(*first && *second && max) {
		if(Curl_raw_toupper(*first) != Curl_raw_toupper(*second)) {
			break;
		}
		max--;
		first++;
		second++;
	}
	if(0 == max)
		return 1; /* they are equal this far */
	return Curl_raw_toupper(*first) == Curl_raw_toupper(*second);
}

static const int CURL_HOST_NOMATCH = 0;
static const int CURL_HOST_MATCH = 1;

/*
 * Match a hostname against a wildcard pattern.
 * E.g.
 *  "foo.host.com" matches "*.host.com".
 *
 * We use the matching rule described in RFC6125, section 6.4.3.
 * http://tools.ietf.org/html/rfc6125#section-6.4.3
 *
 * In addition: ignore trailing dots in the host names and wildcards, so that
 * the names are used normalized. This is what the browsers do.
 *
 * Do not allow wildcard matching on IP numbers. There are apparently
 * certificates being used with an IP address in the CN field, thus making no
 * apparent distinction between a name and an IP. We need to detect the use of
 * an IP address and not wildcard match on such names.
 *
 * NOTE: hostmatch() gets called with copied buffers so that it can modify the
 * contents at will.
 */

static int hostmatch(char *hostname, char *pattern)
{
  const char *pattern_label_end, *pattern_wildcard, *hostname_label_end;
  int wildcard_enabled;
  size_t prefixlen, suffixlen;
  struct in_addr ignored;
#ifdef ENABLE_IPV6
  struct sockaddr_in6 si6;
#endif

  /* normalize pattern and hostname by stripping off trailing dots */
  size_t len = strlen(hostname);
  if(hostname[len-1]=='.')
    hostname[len-1]=0;
  len = strlen(pattern);
  if(pattern[len-1]=='.')
    pattern[len-1]=0;

  pattern_wildcard = strchr(pattern, '*');
  if(pattern_wildcard == nullptr)
    return Curl_raw_equal(pattern, hostname) ?
      CURL_HOST_MATCH : CURL_HOST_NOMATCH;

  /* detect IP address as hostname and fail the match if so */
  if(inet_pton(AF_INET, hostname, &ignored) > 0)
    return CURL_HOST_NOMATCH;
#ifdef ENABLE_IPV6
  else if(Curl_inet_pton(AF_INET6, hostname, &si6.sin6_addr) > 0)
    return CURL_HOST_NOMATCH;
#endif

  /* We require at least 2 dots in pattern to avoid too wide wildcard
     match. */
  wildcard_enabled = 1;
  pattern_label_end = strchr(pattern, '.');
  if(pattern_label_end == nullptr || strchr(pattern_label_end+1, '.') == nullptr ||
     pattern_wildcard > pattern_label_end ||
     Curl_raw_nequal(pattern, "xn--", 4)) {
    wildcard_enabled = 0;
  }
  if(!wildcard_enabled)
    return Curl_raw_equal(pattern, hostname) ?
      CURL_HOST_MATCH : CURL_HOST_NOMATCH;

  hostname_label_end = strchr(hostname, '.');
  if(hostname_label_end == nullptr ||
     !Curl_raw_equal(pattern_label_end, hostname_label_end))
    return CURL_HOST_NOMATCH;

  /* The wildcard must match at least one character, so the left-most
     label of the hostname is at least as large as the left-most label
     of the pattern. */
  if(hostname_label_end - hostname < pattern_label_end - pattern)
    return CURL_HOST_NOMATCH;

  prefixlen = pattern_wildcard - pattern;
  suffixlen = pattern_label_end - (pattern_wildcard+1);
  return Curl_raw_nequal(pattern, hostname, prefixlen) &&
    Curl_raw_nequal(pattern_wildcard+1, hostname_label_end - suffixlen,
                    suffixlen) ?
    CURL_HOST_MATCH : CURL_HOST_NOMATCH;
}

static int Curl_cert_hostcheck(const char *match_pattern, const char *hostname)
{
  char *matchp;
  char *hostp;
  int res = 0;
  if(!match_pattern || !*match_pattern ||
      !hostname || !*hostname) /* sanity check */
    ;
  else {
    matchp = strdup(match_pattern);
    if(matchp) {
      hostp = strdup(hostname);
      if(hostp) {
        if(hostmatch(hostp, matchp) == CURL_HOST_MATCH)
          res= 1;
        free(hostp);
      }
      free(matchp);
    }
  }

  return res;
}

//
// End of https://github.com/bagder/curl/blob/master/lib/
//
///////////////////////////////////////////////////////////////////////////
}  // namespace ZNC_Curl

namespace ZNC_iSECPartners {
///////////////////////////////////////////////////////////////////////////
//
// This block is from https://github.com/iSECPartners/ssl-conservatory/
// Copyright: Alban Diquet, license: MIT
//

/*
 * Helper functions to perform basic hostname validation using OpenSSL.
 *
 * Please read "everything-you-wanted-to-know-about-openssl.pdf" before
 * attempting to use this code. This whitepaper describes how the code works, 
 * how it should be used, and what its limitations are.
 *
 * Author:  Alban Diquet
 * License: See LICENSE
 *
 */
 
typedef enum {
	MatchFound,
	MatchNotFound,
	NoSANPresent,
	MalformedCertificate,
	Error
} HostnameValidationResult;

#define HOSTNAME_MAX_SIZE 255

/**
* Tries to find a match for hostname in the certificate's Common Name field.
*
* Returns MatchFound if a match was found.
* Returns MatchNotFound if no matches were found.
* Returns MalformedCertificate if the Common Name had a NUL character embedded in it.
* Returns Error if the Common Name could not be extracted.
*/
static HostnameValidationResult matches_common_name(const char *hostname, const X509 *server_cert) {
	int common_name_loc = -1;
	X509_NAME_ENTRY *common_name_entry = nullptr;
	ASN1_STRING *common_name_asn1 = nullptr;
	char *common_name_str = nullptr;

	// Find the position of the CN field in the Subject field of the certificate
	common_name_loc = X509_NAME_get_index_by_NID(X509_get_subject_name((X509 *) server_cert), NID_commonName, -1);
	if (common_name_loc < 0) {
		return Error;
	}

	// Extract the CN field
	common_name_entry = X509_NAME_get_entry(X509_get_subject_name((X509 *) server_cert), common_name_loc);
	if (common_name_entry == nullptr) {
		return Error;
	}

	// Convert the CN field to a C string
	common_name_asn1 = X509_NAME_ENTRY_get_data(common_name_entry);
	if (common_name_asn1 == nullptr) {
		return Error;
	}			
	common_name_str = (char *) ASN1_STRING_data(common_name_asn1);

	// Make sure there isn't an embedded NUL character in the CN
	if (ASN1_STRING_length(common_name_asn1) != static_cast<int>(strlen(common_name_str))) {
		return MalformedCertificate;
	}

	DEBUG("SSLVerifyHost: Found CN " << common_name_str);
	// Compare expected hostname with the CN
	if (ZNC_Curl::Curl_cert_hostcheck(common_name_str, hostname)) {
		return MatchFound;
	}
	else {
		return MatchNotFound;
	}
}


/**
* Tries to find a match for hostname in the certificate's Subject Alternative Name extension.
*
* Returns MatchFound if a match was found.
* Returns MatchNotFound if no matches were found.
* Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it.
* Returns NoSANPresent if the SAN extension was not present in the certificate.
*/
static HostnameValidationResult matches_subject_alternative_name(const char *hostname, const X509 *server_cert) {
	HostnameValidationResult result = MatchNotFound;
	int i;
	int san_names_nb = -1;
	STACK_OF(GENERAL_NAME) *san_names = nullptr;

	// Try to extract the names within the SAN extension from the certificate
	san_names = reinterpret_cast<STACK_OF(GENERAL_NAME) *>(X509_get_ext_d2i((X509 *) server_cert, NID_subject_alt_name, nullptr, nullptr));
	if (san_names == nullptr) {
		return NoSANPresent;
	}
	san_names_nb = sk_GENERAL_NAME_num(san_names);

	// Check each name within the extension
	for (i=0; i<san_names_nb; i++) {
		const GENERAL_NAME *current_name = sk_GENERAL_NAME_value(san_names, i);

		if (current_name->type == GEN_DNS) {
			// Current name is a DNS name, let's check it
			char *dns_name = (char *) ASN1_STRING_data(current_name->d.dNSName);

			// Make sure there isn't an embedded NUL character in the DNS name
			if (ASN1_STRING_length(current_name->d.dNSName) != static_cast<int>(strlen(dns_name))) {
				result = MalformedCertificate;
				break;
			}
			else { // Compare expected hostname with the DNS name
				DEBUG("SSLVerifyHost: Found SAN " << dns_name);
				if (ZNC_Curl::Curl_cert_hostcheck(dns_name, hostname)) {
					result = MatchFound;
					break;
				}
			}
		}
	}
	sk_GENERAL_NAME_pop_free(san_names, GENERAL_NAME_free);

	return result;
}


/**
* Validates the server's identity by looking for the expected hostname in the
* server's certificate. As described in RFC 6125, it first tries to find a match
* in the Subject Alternative Name extension. If the extension is not present in
* the certificate, it checks the Common Name instead.
*
* Returns MatchFound if a match was found.
* Returns MatchNotFound if no matches were found.
* Returns MalformedCertificate if any of the hostnames had a NUL character embedded in it.
* Returns Error if there was an error.
*/
static HostnameValidationResult validate_hostname(const char *hostname, const X509 *server_cert) {
	HostnameValidationResult result;

	if((hostname == nullptr) || (server_cert == nullptr))
		return Error;

	// First try the Subject Alternative Names extension
	result = matches_subject_alternative_name(hostname, server_cert);
	if (result == NoSANPresent) {
		// Extension was not found: try the Common Name
		result = matches_common_name(hostname, server_cert);
	}

	return result;
}

//
// End of https://github.com/iSECPartners/ssl-conservatory/
//
///////////////////////////////////////////////////////////////////////////
}  // namespace ZNC_iSECPartners

bool ZNC_SSLVerifyHost(const CString& sHost, const X509* pCert, CString& sError) {
	DEBUG("SSLVerifyHost: checking " << sHost);
	ZNC_iSECPartners::HostnameValidationResult eResult = ZNC_iSECPartners::validate_hostname(sHost.c_str(), pCert);
	switch (eResult) {
		case ZNC_iSECPartners::MatchFound:
			DEBUG("SSLVerifyHost: verified");
			return true;
		case ZNC_iSECPartners::MatchNotFound:
			DEBUG("SSLVerifyHost: host doesn't match");
			sError = "hostname doesn't match";
			return false;
		case ZNC_iSECPartners::MalformedCertificate:
			DEBUG("SSLVerifyHost: malformed cert");
			sError = "malformed hostname in certificate";
			return false;
		default:
			DEBUG("SSLVerifyHost: error");
			sError = "hostname verification error";
			return false;
	}
}


#endif /* HAVE_LIBSSL */