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DnsServer: implemented draft-ietf-dnsop-serve-stale-04 in RecursiveResolve().

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This commit is contained in:
Shreyas Zare
2019-03-30 17:07:48 +05:30
parent bab78ec014
commit ea5a1aab45
1 changed files with 148 additions and 51 deletions
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159
DnsServerCore/DnsServer.cs
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@@ -70,7 +70,7 @@ namespace DnsServerCore
X509Certificate2 _certificate;
readonly Zone _authoritativeZoneRoot = new Zone(true);
readonly Zone _cacheZoneRoot = new Zone(false);
readonly Zone _cacheZoneRoot = new Zone(false) { ServeStaleTtl = 7 * 24 * 60 * 60 }; //7 days serve stale ttl as per draft-ietf-dnsop-serve-stale-04
readonly Zone _allowedZoneRoot = new Zone(true);
Zone _blockedZoneRoot = new Zone(true);
@@ -83,7 +83,7 @@ namespace DnsServerCore
DnsTransportProtocol _forwarderProtocol = DnsTransportProtocol.Udp;
DnsTransportProtocol _recursiveResolveProtocol = DnsTransportProtocol.Udp;
bool _preferIPv6 = false;
int _retries = 3;
int _retries = 2;
int _timeout = 2000;
int _maxStackCount = 10;
LogManager _log;
@@ -93,7 +93,7 @@ namespace DnsServerCore
int _tcpSendTimeout = 10000;
int _tcpReceiveTimeout = 10000;
readonly ConcurrentDictionary<DnsQuestionRecord, object> _recursiveQueryLocks = new ConcurrentDictionary<DnsQuestionRecord, object>();
readonly ConcurrentDictionary<DnsQuestionRecord, RecursiveQueryLock> _recursiveQueryLocks = new ConcurrentDictionary<DnsQuestionRecord, RecursiveQueryLock>(Environment.ProcessorCount * 64, Environment.ProcessorCount * 32);
volatile ServiceState _state = ServiceState.Stopped;
@@ -1119,36 +1119,20 @@ namespace DnsServerCore
{
//query cache zone to see if answer available
{
DnsDatagram cacheResponse = QueryCache(request);
DnsDatagram cacheResponse = QueryCache(request, false, true);
if (cacheResponse != null)
return cacheResponse;
}
//recursion with locking
{
object newLockObj = new object();
object actualLockObj = _recursiveQueryLocks.GetOrAdd(request.Question[0], newLockObj);
RecursiveQueryLock newLockObj = new RecursiveQueryLock();
RecursiveQueryLock actualLockObj = _recursiveQueryLocks.GetOrAdd(request.Question[0], newLockObj);
if (!actualLockObj.Equals(newLockObj))
if (actualLockObj.Equals(newLockObj))
{
//question already being recursively resolved by another thread, wait till timeout or pulse signal
lock (actualLockObj)
//got lock so question not being resolved; do recursive resolution in worker thread
ThreadPool.QueueUserWorkItem(delegate (object state)
{
Monitor.Wait(actualLockObj, _timeout * _retries);
}
//query cache zone again to see if answer available
{
DnsDatagram cacheResponse = QueryCache(request);
if (cacheResponse != null)
return cacheResponse;
}
//no response available in cache so respond with server failure
return new DnsDatagram(new DnsHeader(request.Header.Identifier, true, DnsOpcode.StandardQuery, false, false, request.Header.RecursionDesired, true, false, false, DnsResponseCode.ServerFailure, request.Header.QDCOUNT, 0, 0, 0), request.Question, null, null, null);
}
}
//select protocol
DnsTransportProtocol protocol;
@@ -1164,31 +1148,111 @@ namespace DnsServerCore
try
{
return DnsClient.RecursiveResolve(request.Question[0], viaNameServers, _dnsCache, _proxy, _preferIPv6, protocol, _retries, _timeout, _recursiveResolveProtocol, _maxStackCount);
//recursive resolve and update cache
DnsClient.RecursiveResolve(request.Question[0], viaNameServers, _dnsCache, _proxy, _preferIPv6, protocol, _retries, _timeout, _recursiveResolveProtocol, _maxStackCount);
}
catch (Exception ex)
{
LogManager log = _log;
if (log != null)
{
string nameServers = null;
if (viaNameServers != null)
{
foreach (NameServerAddress nameServer in viaNameServers)
{
if (nameServers == null)
nameServers = nameServer.ToString();
else
nameServers += ", " + nameServer.ToString();
}
}
log.Write("DNS Server recursive resolution failed for QNAME: " + request.Question[0].Name + "; QTYPE: " + request.Question[0].Type.ToString() + "; QCLASS: " + request.Question[0].Class.ToString() + (nameServers == null ? "" : "; Name Servers: " + nameServers) + ";\r\n" + ex.ToString());
}
//fetch stale record and reset expiry
{
DnsDatagram cacheResponse = QueryCache(request, true, false);
if (cacheResponse != null)
{
foreach (DnsResourceRecord record in cacheResponse.Answer)
{
if (record.IsStale)
record.ResetExpiry(30); //reset expiry by 30 seconds so that resolver tries again only after 30 seconds as per draft-ietf-dnsop-serve-stale-04
}
}
}
}
finally
{
//remove question lock
if (_recursiveQueryLocks.TryRemove(request.Question[0], out object lockObj))
if (_recursiveQueryLocks.TryRemove(request.Question[0], out RecursiveQueryLock lockObj))
{
//pulse all waiting threads
lock (lockObj)
{
lockObj.SetComplete();
Monitor.PulseAll(lockObj);
}
}
}
});
}
private DnsDatagram QueryCache(DnsDatagram request)
//request is being recursively resolved by worker thread
bool timeout = false;
//wait till short timeout or pulse signal
lock (actualLockObj)
{
DnsDatagram cacheResponse = _cacheZoneRoot.Query(request);
if (!actualLockObj.Complete)
timeout = !Monitor.Wait(actualLockObj, _timeout - 200); //1.8 sec wait with default client timeout as 2 sec as per draft-ietf-dnsop-serve-stale-04
}
//query cache zone to get the cached answer
{
//if there was timeout then return stale answer (if available) as per draft-ietf-dnsop-serve-stale-04
DnsDatagram cacheResponse = QueryCache(request, timeout, timeout);
if (cacheResponse != null)
return cacheResponse;
}
if (timeout)
{
//wait till timeout or pulse signal for some more time before responding as ServerFailure
//this is required since, quickly returning ServerFailure results in clients giving up lookup attempt early causing DNS error messages in web browsers
lock (actualLockObj)
{
if (!actualLockObj.Complete)
Monitor.Wait(actualLockObj, _timeout + 200);
}
//query cache zone to see if answer is available now
{
DnsDatagram cacheResponse = QueryCache(request, false, false);
if (cacheResponse != null)
return cacheResponse;
}
}
//no response available in cache so respond with ServerFailure
return new DnsDatagram(new DnsHeader(request.Header.Identifier, true, DnsOpcode.StandardQuery, false, false, request.Header.RecursionDesired, true, false, false, DnsResponseCode.ServerFailure, request.Header.QDCOUNT, 0, 0, 0), request.Question, null, null, null);
}
private DnsDatagram QueryCache(DnsDatagram request, bool serveStale, bool tagAsCacheHit)
{
DnsDatagram cacheResponse = _cacheZoneRoot.Query(request, serveStale);
if (cacheResponse.Header.RCODE != DnsResponseCode.Refused)
{
if ((cacheResponse.Answer.Length > 0) || (cacheResponse.Authority.Length == 0) || (cacheResponse.Authority[0].Type == DnsResourceRecordType.SOA))
{
if (tagAsCacheHit)
cacheResponse.Tag = "cacheHit";
return cacheResponse;
}
}
@@ -1596,13 +1660,21 @@ namespace DnsServerCore
public int Retries
{
get { return _retries; }
set { _retries = value; }
set
{
if (value > 0)
_retries = value;
}
}
public int Timeout
{
get { return _timeout; }
set { _timeout = value; }
set
{
if (value >= 2000)
_timeout = value;
}
}
public int MaxStackCount
@@ -1674,5 +1746,30 @@ namespace DnsServerCore
#endregion
}
class RecursiveQueryLock
{
#region variables
bool _complete;
#endregion
#region public
public void SetComplete()
{
_complete = true;
}
#endregion
#region properties
public bool Complete
{ get { return _complete; } }
#endregion
}
}
}