NetworkPkg/DnsDxe: [CVE-2018-12178] Check the received packet size before parsing the message.

Fix CVE-2018-12178
REF: https://bugzilla.tianocore.org/show_bug.cgi?id=809

The DNS driver only checks the received packet size against the
minimum DNS header size in DnsOnPacketReceived(), later it accesses
the QueryName and QuerySection beyond the header scope, which might
cause the pointer within DNS driver points to an invalid entry or
modifies the memory content beyond the header scope.

This patch is to fix above problem.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Wang Fan <fan.wang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Siyuan Fu <siyuan.fu@intel.com>

NetworkPkg/DnsDxe/DnsImpl.h

@@ -583,6 +583,7 @@ IsValidDnsResponse (
 
   @param  Instance              The DNS instance
   @param  RxString              Received buffer.
+  @param  Length                Received buffer length.
   @param  Completed             Flag to indicate that Dns response is valid.
 
   @retval EFI_SUCCESS           Parse Dns Response successfully.
@@ -593,6 +594,7 @@ EFI_STATUS
 ParseDnsResponse (
   IN OUT DNS_INSTANCE              *Instance,
   IN     UINT8                     *RxString,
+  IN     UINT32                    Length,
      OUT BOOLEAN                   *Completed
   );