From 02c8ae8400276879eef86fd66e6881e809c53369 Mon Sep 17 00:00:00 2001
From: Shreyas Zare <shreyas@technitium.com>
Date: Sun, 28 Jun 2020 19:38:34 +0530
Subject: [PATCH] AuthZone: added checks in GetNameServerAddresses() to prevent
 exceptions. Made GetPrimaryNameServerAddresses() public, used GetRecords()
 for getting NS records and updated implementation to use addresses from NS
 record and from glue records. Made GetSecondaryNameServerAddresses() public
 and used GetRecords() for getting NS records. Updated GetRecords() to return
 empty array if no records are found. Optimized ContainsNameServerRecords()
 code.

---
 DnsServerCore/Dns/Zones/AuthZone.cs | 99 +++++++++++++++++++++--------
 1 file changed, 73 insertions(+), 26 deletions(-)

diff --git a/DnsServerCore/Dns/Zones/AuthZone.cs b/DnsServerCore/Dns/Zones/AuthZone.cs
index 1865c568..7ca7ca6d 100644
--- a/DnsServerCore/Dns/Zones/AuthZone.cs
+++ b/DnsServerCore/Dns/Zones/AuthZone.cs
@@ -136,24 +136,34 @@ namespace DnsServerCore.Dns.Zones
             else
             {
                 //resolve addresses
-                DnsDatagram response = dnsServer.DirectQuery(new DnsQuestionRecord(nsDomain, DnsResourceRecordType.A, DnsClass.IN));
-                if (response != null)
+                try
                 {
-                    IReadOnlyList<IPAddress> addresses = DnsClient.ParseResponseA(response);
-                    foreach (IPAddress address in addresses)
-                        nameServers.Add(new NameServerAddress(nsDomain, address));
-                }
-
-                if (dnsServer.PreferIPv6)
-                {
-                    response = dnsServer.DirectQuery(new DnsQuestionRecord(nsDomain, DnsResourceRecordType.AAAA, DnsClass.IN));
-                    if (response != null)
+                    DnsDatagram response = dnsServer.DirectQuery(new DnsQuestionRecord(nsDomain, DnsResourceRecordType.A, DnsClass.IN));
+                    if ((response != null) && (response.Answer.Count > 0))
                     {
-                        IReadOnlyList<IPAddress> addresses = DnsClient.ParseResponseAAAA(response);
+                        IReadOnlyList<IPAddress> addresses = DnsClient.ParseResponseA(response);
                         foreach (IPAddress address in addresses)
                             nameServers.Add(new NameServerAddress(nsDomain, address));
                     }
                 }
+                catch
+                { }
+
+                if (dnsServer.PreferIPv6)
+                {
+                    try
+                    {
+                        DnsDatagram response = dnsServer.DirectQuery(new DnsQuestionRecord(nsDomain, DnsResourceRecordType.AAAA, DnsClass.IN));
+                        if ((response != null) && (response.Answer.Count > 0))
+                        {
+                            IReadOnlyList<IPAddress> addresses = DnsClient.ParseResponseAAAA(response);
+                            foreach (IPAddress address in addresses)
+                                nameServers.Add(new NameServerAddress(nsDomain, address));
+                        }
+                    }
+                    catch
+                    { }
+                }
             }
 
             return nameServers;
@@ -161,24 +171,52 @@ namespace DnsServerCore.Dns.Zones
 
         #endregion
 
-        #region protected
+        #region public
 
-        protected IReadOnlyList<NameServerAddress> GetPrimaryNameServerAddresses(DnsServer dnsServer)
+        public IReadOnlyList<NameServerAddress> GetPrimaryNameServerAddresses(DnsServer dnsServer)
         {
-            DnsResourceRecord soaRecord = _entries[DnsResourceRecordType.SOA][0];
+            List<NameServerAddress> nameServers = new List<NameServerAddress>();
 
-            return GetNameServerAddresses(dnsServer, soaRecord);
+            DnsResourceRecord soaRecord = _entries[DnsResourceRecordType.SOA][0];
+            DnsSOARecord soa = soaRecord.RDATA as DnsSOARecord;
+            IReadOnlyList<DnsResourceRecord> nsRecords = GetRecords(DnsResourceRecordType.NS); //stub zone has no authority so cant use QueryRecords
+
+            foreach (DnsResourceRecord nsRecord in nsRecords)
+            {
+                if (nsRecord.IsDisabled())
+                    continue;
+
+                string nsDomain = (nsRecord.RDATA as DnsNSRecord).NameServer;
+
+                if (soa.PrimaryNameServer.Equals(nsDomain, StringComparison.OrdinalIgnoreCase))
+                {
+                    //found primary NS
+                    nameServers.AddRange(GetNameServerAddresses(dnsServer, nsRecord));
+                    break;
+                }
+            }
+
+            foreach (NameServerAddress nameServer in GetNameServerAddresses(dnsServer, soaRecord))
+            {
+                if (!nameServers.Contains(nameServer))
+                    nameServers.Add(nameServer);
+            }
+
+            return nameServers;
         }
 
-        protected IReadOnlyList<NameServerAddress> GetSecondaryNameServerAddresses(DnsServer dnsServer)
+        public IReadOnlyList<NameServerAddress> GetSecondaryNameServerAddresses(DnsServer dnsServer)
         {
             List<NameServerAddress> nameServers = new List<NameServerAddress>();
 
             DnsSOARecord soa = _entries[DnsResourceRecordType.SOA][0].RDATA as DnsSOARecord;
-            IReadOnlyList<DnsResourceRecord> nsRecords = QueryRecords(DnsResourceRecordType.NS);
+            IReadOnlyList<DnsResourceRecord> nsRecords = GetRecords(DnsResourceRecordType.NS); //stub zone has no authority so cant use QueryRecords
 
             foreach (DnsResourceRecord nsRecord in nsRecords)
             {
+                if (nsRecord.IsDisabled())
+                    continue;
+
                 string nsDomain = (nsRecord.RDATA as DnsNSRecord).NameServer;
 
                 if (soa.PrimaryNameServer.Equals(nsDomain, StringComparison.OrdinalIgnoreCase))
@@ -190,10 +228,6 @@ namespace DnsServerCore.Dns.Zones
             return nameServers;
         }
 
-        #endregion
-
-        #region public
-
         public void SyncRecords(Dictionary<DnsResourceRecordType, List<DnsResourceRecord>> newEntries, bool dontRemoveRecords)
         {
             if (!dontRemoveRecords)
@@ -236,7 +270,7 @@ namespace DnsServerCore.Dns.Zones
                         if ((this is SecondaryZone) || (this is StubZone))
                         {
                             //copy existing SOA record's glue addresses to new SOA record
-                            newEntry.Value[0].SetGlueRecords(_entries[DnsResourceRecordType.SOA][0].GetGlueRecords());
+                            newEntry.Value[0].SyncGlueRecords(_entries[DnsResourceRecordType.SOA][0].GetGlueRecords());
                         }
                     }
 
@@ -363,13 +397,26 @@ namespace DnsServerCore.Dns.Zones
 
         public IReadOnlyList<DnsResourceRecord> GetRecords(DnsResourceRecordType type)
         {
-            return _entries[type];
+            if (_entries.TryGetValue(type, out IReadOnlyList<DnsResourceRecord> records))
+                return records;
+
+            return Array.Empty<DnsResourceRecord>();
         }
 
         public override bool ContainsNameServerRecords()
         {
-            IReadOnlyList<DnsResourceRecord> records = QueryRecords(DnsResourceRecordType.NS);
-            return (records.Count > 0) && (records[0].Type == DnsResourceRecordType.NS);
+            if (!_entries.TryGetValue(DnsResourceRecordType.NS, out IReadOnlyList<DnsResourceRecord> records))
+                return false;
+
+            foreach (DnsResourceRecord record in records)
+            {
+                if (record.IsDisabled())
+                    continue;
+
+                return true;
+            }
+
+            return false;
         }
 
         #endregion