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DnsServer: updated ProcessUdpRequestAsync() to handle truncation for MX response to allow trying once after removing glue records before sending a TC response due to issues with some old mail servers that do not retry over TCP when TC response is received. Updated ProcessRecursiveQueryAsync() to use EDNS request to allow relaying extended DNS error response from blocked zone to client.

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This commit is contained in:
Shreyas Zare
2023-03-05 19:26:05 +05:30
parent 157115b48e
commit bbf4a2e773
1 changed files with 30 additions and 8 deletions
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38
DnsServerCore/Dns/DnsServer.cs
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@@ -435,10 +435,32 @@ namespace DnsServerCore.Dns
}
else
{
if (response.Question[0].Type == DnsResourceRecordType.IXFR)
response = new DnsDatagram(response.Identifier, true, response.OPCODE, response.AuthoritativeAnswer, false, response.RecursionDesired, response.RecursionAvailable, response.AuthenticData, response.CheckingDisabled, response.RCODE, response.Question, new DnsResourceRecord[] { response.Answer[0] }, null, null, request.EDNS is null ? ushort.MinValue : _udpPayloadSize) { Tag = DnsServerResponseType.Authoritative }; //truncate response
else
response = new DnsDatagram(response.Identifier, true, response.OPCODE, response.AuthoritativeAnswer, true, response.RecursionDesired, response.RecursionAvailable, response.AuthenticData, response.CheckingDisabled, response.RCODE, response.Question, null, null, null, request.EDNS is null ? ushort.MinValue : _udpPayloadSize) { Tag = DnsServerResponseType.Authoritative };
switch (response.Question[0].Type)
{
case DnsResourceRecordType.MX:
//removing glue records and trying again since some mail servers fail to fallback to TCP on truncation
response = response.CloneWithoutGlueRecords();
sendBufferStream.Position = 0;
try
{
response.WriteTo(sendBufferStream);
}
catch (NotSupportedException)
{
//send TC since response is still big even after removing glue records
response = new DnsDatagram(response.Identifier, true, response.OPCODE, response.AuthoritativeAnswer, true, response.RecursionDesired, response.RecursionAvailable, response.AuthenticData, response.CheckingDisabled, response.RCODE, response.Question, null, null, null, request.EDNS is null ? ushort.MinValue : _udpPayloadSize) { Tag = DnsServerResponseType.Authoritative };
}
break;
case DnsResourceRecordType.IXFR:
response = new DnsDatagram(response.Identifier, true, response.OPCODE, response.AuthoritativeAnswer, false, response.RecursionDesired, response.RecursionAvailable, response.AuthenticData, response.CheckingDisabled, response.RCODE, response.Question, new DnsResourceRecord[] { response.Answer[0] }, null, null, request.EDNS is null ? ushort.MinValue : _udpPayloadSize) { Tag = DnsServerResponseType.Authoritative }; //truncate response
break;
default:
response = new DnsDatagram(response.Identifier, true, response.OPCODE, response.AuthoritativeAnswer, true, response.RecursionDesired, response.RecursionAvailable, response.AuthenticData, response.CheckingDisabled, response.RCODE, response.Question, null, null, null, request.EDNS is null ? ushort.MinValue : _udpPayloadSize) { Tag = DnsServerResponseType.Authoritative };
break;
}
}
sendBufferStream.Position = 0;
@@ -1932,7 +1954,7 @@ namespace DnsServerCore.Dns
}
}
DnsDatagram response = _authZoneManager.Query(request);
DnsDatagram response = _authZoneManager.Query(request, isRecursionAllowed);
if (response is not null)
{
response.Tag = DnsServerResponseType.Authoritative;
@@ -2514,7 +2536,7 @@ namespace DnsServerCore.Dns
if (record.Type != DnsResourceRecordType.CNAME)
break; //no further CNAME records exists
DnsDatagram newRequest = new DnsDatagram(0, false, DnsOpcode.StandardQuery, false, false, true, false, false, false, DnsResponseCode.NoError, new DnsQuestionRecord[] { new DnsQuestionRecord((record.RDATA as DnsCNAMERecordData).Domain, request.Question[0].Type, request.Question[0].Class) });
DnsDatagram newRequest = new DnsDatagram(0, false, DnsOpcode.StandardQuery, false, false, true, false, false, false, DnsResponseCode.NoError, new DnsQuestionRecord[] { new DnsQuestionRecord((record.RDATA as DnsCNAMERecordData).Domain, request.Question[0].Type, request.Question[0].Class) }, null, null, null, _udpPayloadSize);
//check allowed zone
inAllowedZone = _allowedZoneManager.IsAllowed(newRequest) || _blockListZoneManager.IsAllowed(newRequest);
@@ -2535,8 +2557,8 @@ namespace DnsServerCore.Dns
//copy last response answers
answer.AddRange(blockedResponse.Answer);
//cname response cannot be for type NS, MX, SRV so no additional section in response
return new DnsDatagram(request.Identifier, true, DnsOpcode.StandardQuery, false, false, true, true, false, false, DnsResponseCode.NoError, request.Question, answer, blockedResponse.Authority) { Tag = blockedResponse.Tag };
//include blocked response additional section to pass on Extended DNS Errors
return new DnsDatagram(request.Identifier, true, DnsOpcode.StandardQuery, false, false, true, true, false, false, DnsResponseCode.NoError, request.Question, answer, blockedResponse.Authority, blockedResponse.Additional) { Tag = blockedResponse.Tag };
}
}
}