Count any incoming packet that could not be recognized as an LLUDP packet as a malformed packet. Record this as stat clientstack.<scene>.IncomingPacketsMalformedCount

Used to detect if a simulator is receiving significant junk UDP
Decimates the number of packets between which a warning is logged and prints the IP source of the last malformed packet when logging

OpenSim/Region/ClientStack/Linden/UDP/LLUDPServer.cs

@@ -106,6 +106,19 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                     stat => stat.Value = m_udpServer.IncomingPacketsProcessed,
                     StatVerbosity.Debug));
 
+            StatsManager.RegisterStat(
+                new Stat(
+                    "IncomingPacketsMalformedCount",
+                    "Number of inbound UDP packets that could not be recognized as LL protocol packets.",
+                    "",
+                    "",
+                    "clientstack",
+                    scene.Name,
+                    StatType.Pull,
+                    MeasuresOfInterest.AverageChangeOverTime,
+                    stat => stat.Value = m_udpServer.IncomingMalformedPacketCount,
+                    StatVerbosity.Info));
+
             StatsManager.RegisterStat(
                 new Stat(
                     "OutgoingUDPSendsCount",
@@ -268,7 +281,10 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
         public Socket Server { get { return null; } }
 
-        private int m_malformedCount = 0; // Guard against a spamming attack
+        /// <summary>
+        /// Record how many inbound packets could not be recognized as LLUDP packets.
+        /// </summary>
+        public int IncomingMalformedPacketCount { get; private set; }
 
         /// <summary>
         /// Record current outgoing client for monitoring purposes.
@@ -1181,6 +1197,19 @@ namespace OpenSim.Region.ClientStack.LindenUDP
             outgoingPacket.TickCount = Environment.TickCount & Int32.MaxValue;
         }
 
+        private void RecordMalformedInboundPacket(IPEndPoint endPoint)
+        {
+//                if (m_malformedCount < 100)
+//                    m_log.DebugFormat("[LLUDPSERVER]: Dropped malformed packet: " + e.ToString());
+
+            IncomingMalformedPacketCount++;
+
+            if ((IncomingMalformedPacketCount % 10000) == 0)
+                m_log.WarnFormat(
+                    "[LLUDPSERVER]: Received {0} malformed packets so far, probable network attack.  Last malformed was from {1}", 
+                    IncomingMalformedPacketCount, endPoint);
+        }
+
         public override void PacketReceived(UDPPacketBuffer buffer)
         {
             // Debugging/Profiling
@@ -1202,6 +1231,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 //                    "[LLUDPSERVER]: Dropping undersized packet with {0} bytes received from {1} in {2}",
 //                    buffer.DataLength, buffer.RemoteEndPoint, m_scene.RegionInfo.RegionName);
 
+                RecordMalformedInboundPacket(endPoint);
+
                 return; // Drop undersized packet
             }
 
@@ -1220,6 +1251,8 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 //                    "[LLUDPSERVER]: Dropping packet with malformed header received from {0} in {1}",
 //                    buffer.RemoteEndPoint, m_scene.RegionInfo.RegionName);
 
+                RecordMalformedInboundPacket(endPoint);
+
                 return; // Malformed header
             }
 
@@ -1235,34 +1268,24 @@ namespace OpenSim.Region.ClientStack.LindenUDP
                     // Only allocate a buffer for zerodecoding if the packet is zerocoded
                     ((buffer.Data[0] & Helpers.MSG_ZEROCODED) != 0) ? new byte[4096] : null);
             }
-            catch (MalformedDataException)
-            {
-            }
-            catch (IndexOutOfRangeException)
-            {
-//                m_log.WarnFormat(
-//                    "[LLUDPSERVER]: Dropping short packet received from {0} in {1}",
-//                    buffer.RemoteEndPoint, m_scene.RegionInfo.RegionName);
-
-                return; // Drop short packet
-            }
             catch (Exception e)
             {
-                if (m_malformedCount < 100)
+                if (IncomingMalformedPacketCount < 100)
                     m_log.DebugFormat("[LLUDPSERVER]: Dropped malformed packet: " + e.ToString());
-
-                m_malformedCount++;
-
-                if ((m_malformedCount % 100000) == 0)
-                    m_log.DebugFormat("[LLUDPSERVER]: Received {0} malformed packets so far, probable network attack.", m_malformedCount);
             }
 
             // Fail-safe check
             if (packet == null)
             {
-                m_log.ErrorFormat("[LLUDPSERVER]: Malformed data, cannot parse {0} byte packet from {1}:",
+                if (IncomingMalformedPacketCount < 100)
-                    buffer.DataLength, buffer.RemoteEndPoint);
+                {
-                m_log.Error(Utils.BytesToHexString(buffer.Data, buffer.DataLength, null));
+                    m_log.ErrorFormat("[LLUDPSERVER]: Malformed data, cannot parse {0} byte packet from {1}:",
+                        buffer.DataLength, buffer.RemoteEndPoint);
+                    m_log.Error(Utils.BytesToHexString(buffer.Data, buffer.DataLength, null));
+                }
+
+                RecordMalformedInboundPacket(endPoint);
+
                 return;
             }