avoid processing incorrect ICMP message on Unix (dotnet/corefx#34084)

* use connect on unicast ping addresses to avoild processing incorrect responses

* feedback from review


Commit migrated from dotnet/corefx@3172386

src/libraries/System.Net.Ping/src/System/Net/NetworkInformation/Ping.Unix.cs

@@ -88,15 +88,28 @@ private SocketConfig GetSocketConfig(IPAddress address, byte[] buffer, int timeo
 
         private Socket GetRawSocket(SocketConfig socketConfig)
         {
+            IPEndPoint ep = (IPEndPoint)socketConfig.EndPoint;
+
             // Setting Socket.DontFragment and .Ttl is not supported on Unix, so socketConfig.Options is ignored.
-            AddressFamily addrFamily = ((IPEndPoint)socketConfig.EndPoint).Address.AddressFamily;
+            AddressFamily addrFamily = ep.Address.AddressFamily;
             Socket socket = new Socket(addrFamily, SocketType.Raw, socketConfig.ProtocolType);
             socket.ReceiveTimeout = socketConfig.Timeout;
             socket.SendTimeout = socketConfig.Timeout;
             if (socketConfig.Options != null && socketConfig.Options.Ttl > 0)
             {
                 socket.Ttl = (short)socketConfig.Options.Ttl;
             }
+
+#pragma warning disable 618
+            // Disable warning about obsolete property. We could use GetAddressBytes but that allocates.
+            // IPv4 multicast address starts with 1110 bits so mask rest and test if we get correct value e.g. 0xe0.
+            if (!ep.Address.IsIPv6Multicast && !(addrFamily == AddressFamily.InterNetwork && (ep.Address.Address & 0xf0) == 0xe0))
+            {
+                // If it is not multicast, use Connect to scope responses only to the target address.
+                socket.Connect(socketConfig.EndPoint);
+            }
+#pragma warning restore 618
+
             return socket;
         }
 
@@ -129,7 +142,7 @@ private bool TryGetPingReply(SocketConfig socketConfig, byte[] receiveBuffer, in
             {
                 return false;
             }
-            
+
             sw.Stop();
             long roundTripTime = sw.ElapsedMilliseconds;
             int dataOffset = ipHeaderLength + IcmpHeaderLengthInBytes;