NetLabel CIPSO/IPv4 Protocol Engine
  ==============================================================================
  Paul Moore, paul.moore@hp.com
  
  May 17, 2006
  
   * Overview
  
  The NetLabel CIPSO/IPv4 protocol engine is based on the IETF Commercial IP
  Security Option (CIPSO) draft from July 16, 1992.  A copy of this draft can be
  found in this directory, consult '00-INDEX' for the filename.  While the IETF
  draft never made it to an RFC standard it has become a de-facto standard for
  labeled networking and is used in many trusted operating systems.
  
   * Outbound Packet Processing
  
  The CIPSO/IPv4 protocol engine applies the CIPSO IP option to packets by
  adding the CIPSO label to the socket.  This causes all packets leaving the
  system through the socket to have the CIPSO IP option applied.  The socket's
  CIPSO label can be changed at any point in time, however, it is recommended
  that it is set upon the socket's creation.  The LSM can set the socket's CIPSO
  label by using the NetLabel security module API; if the NetLabel "domain" is
  configured to use CIPSO for packet labeling then a CIPSO IP option will be
  generated and attached to the socket.
  
   * Inbound Packet Processing
  
  The CIPSO/IPv4 protocol engine validates every CIPSO IP option it finds at the
  IP layer without any special handling required by the LSM.  However, in order
  to decode and translate the CIPSO label on the packet the LSM must use the
  NetLabel security module API to extract the security attributes of the packet.
  This is typically done at the socket layer using the 'socket_sock_rcv_skb()'
  LSM hook.
  
   * Label Translation
  
  The CIPSO/IPv4 protocol engine contains a mechanism to translate CIPSO security
  attributes such as sensitivity level and category to values which are
  appropriate for the host.  These mappings are defined as part of a CIPSO
  Domain Of Interpretation (DOI) definition and are configured through the
  NetLabel user space communication layer.  Each DOI definition can have a
  different security attribute mapping table.
  
   * Label Translation Cache
  
  The NetLabel system provides a framework for caching security attribute
  mappings from the network labels to the corresponding LSM identifiers.  The
  CIPSO/IPv4 protocol engine supports this caching mechanism.