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/*
* This file is part of PowerDNS or dnsdist.
* Copyright -- PowerDNS.COM B.V. and its contributors
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
*
* In addition, for the avoidance of any doubt, permission is granted to
* link this program with OpenSSL and to (re)distribute the binaries
* produced as the result of such linking.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "ednscookies.hh"
#include "misc.hh"
#ifdef HAVE_CRYPTO_SHORTHASH
#include <sodium.h>
#endif
EDNSCookiesOpt::EDNSCookiesOpt(const std::string& option)
{
getEDNSCookiesOptFromString(option.c_str(), option.length());
}
EDNSCookiesOpt::EDNSCookiesOpt(const char* option, unsigned int len)
{
getEDNSCookiesOptFromString(option, len);
}
bool EDNSCookiesOpt::makeFromString(const std::string& option)
{
getEDNSCookiesOptFromString(option.c_str(), option.length());
return isWellFormed();
}
bool EDNSCookiesOpt::makeFromString(const char* option, unsigned int len)
{
getEDNSCookiesOptFromString(option, len);
return isWellFormed();
}
string EDNSCookiesOpt::makeOptString() const
{
string ret;
if (!isWellFormed())
return ret;
ret.assign(client);
if (server.length() != 0)
ret.append(server);
return ret;
}
void EDNSCookiesOpt::getEDNSCookiesOptFromString(const char* option, unsigned int len)
{
client.clear();
server.clear();
if (len < 8)
return;
client = string(option, 8);
if (len > 8) {
server = string(option + 8, len - 8);
}
}
bool EDNSCookiesOpt::isValid(const string& secret, const ComboAddress& source) const
{
#ifdef HAVE_CRYPTO_SHORTHASH
if (server.length() != 16 || client.length() != 8) {
return false;
}
if (server[0] != '\x01') {
// Version is not 1, can't verify
return false;
}
uint32_t ts;
memcpy(&ts, &server[4], sizeof(ts));
ts = ntohl(ts);
uint32_t now = static_cast<uint32_t>(time(nullptr));
// RFC 9018 section 4.3:
// The DNS server
// SHOULD allow cookies within a 1-hour period in the past and a
// 5-minute period into the future
if (rfc1982LessThan(now + 300, ts) && rfc1982LessThan(ts + 3600, now)) {
return false;
}
if (secret.length() != crypto_shorthash_KEYBYTES) {
return false;
}
string toHash = client + server.substr(0, 8) + source.toByteString();
string hashResult;
hashResult.resize(8);
crypto_shorthash(
reinterpret_cast<unsigned char*>(&hashResult[0]),
reinterpret_cast<const unsigned char*>(&toHash[0]),
toHash.length(),
reinterpret_cast<const unsigned char*>(&secret[0]));
return constantTimeStringEquals(server.substr(8), hashResult);
#else
return false;
#endif
}
bool EDNSCookiesOpt::shouldRefresh() const
{
if (server.size() < 16) {
return true;
}
uint32_t ts;
memcpy(&ts, &server[4], sizeof(ts));
ts = ntohl(ts);
uint32_t now = static_cast<uint32_t>(time(nullptr));
// RFC 9018 section 4.3:
// The DNS server
// SHOULD allow cookies within a 1-hour period in the past and a
// 5-minute period into the future
// If this is not the case, we need to refresh
if (rfc1982LessThan(now + 300, ts) && rfc1982LessThan(ts + 3600, now)) {
return true;
}
// RFC 9018 section 4.3:
// The DNS server SHOULD generate a new Server Cookie at least if the
// received Server Cookie from the client is more than half an hour old
return rfc1982LessThan(ts + 1800, now);
}
bool EDNSCookiesOpt::makeServerCookie(const string& secret, const ComboAddress& source)
{
#ifdef HAVE_CRYPTO_SHORTHASH
static_assert(EDNSCookieSecretSize == crypto_shorthash_KEYBYTES * 2, "The EDNSCookieSecretSize is not twice crypto_shorthash_KEYBYTES");
if (isValid(secret, source) && !shouldRefresh()) {
return true;
}
if (secret.length() != crypto_shorthash_KEYBYTES) {
return false;
}
server.clear();
server.reserve(16);
server = "\x01"; // Version
server.resize(4, '\0'); // 3 reserved bytes
uint32_t now = htonl(static_cast<uint32_t>(time(nullptr)));
server += string(reinterpret_cast<const char*>(&now), sizeof(now));
server.resize(8);
string toHash = client;
toHash += server;
toHash += source.toByteString();
server.resize(16);
crypto_shorthash(
reinterpret_cast<unsigned char*>(&server[8]),
reinterpret_cast<const unsigned char*>(&toHash[0]),
toHash.length(),
reinterpret_cast<const unsigned char*>(&secret[0]));
return true;
#else
return false;
#endif
}
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