linux/Documentation/netlabel/lsm_interface.txt
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   1NetLabel Linux Security Module Interface
   2==============================================================================
   3Paul Moore, paul.moore@hp.com
   4
   5May 17, 2006
   6
   7 * Overview
   8
   9NetLabel is a mechanism which can set and retrieve security attributes from
  10network packets.  It is intended to be used by LSM developers who want to make
  11use of a common code base for several different packet labeling protocols.
  12The NetLabel security module API is defined in 'include/net/netlabel.h' but a
  13brief overview is given below.
  14
  15 * NetLabel Security Attributes
  16
  17Since NetLabel supports multiple different packet labeling protocols and LSMs
  18it uses the concept of security attributes to refer to the packet's security
  19labels.  The NetLabel security attributes are defined by the
  20'netlbl_lsm_secattr' structure in the NetLabel header file.  Internally the
  21NetLabel subsystem converts the security attributes to and from the correct
  22low-level packet label depending on the NetLabel build time and run time
  23configuration.  It is up to the LSM developer to translate the NetLabel
  24security attributes into whatever security identifiers are in use for their
  25particular LSM.
  26
  27 * NetLabel LSM Protocol Operations
  28
  29These are the functions which allow the LSM developer to manipulate the labels
  30on outgoing packets as well as read the labels on incoming packets.  Functions
  31exist to operate both on sockets as well as the sk_buffs directly.  These high
  32level functions are translated into low level protocol operations based on how
  33the administrator has configured the NetLabel subsystem.
  34
  35 * NetLabel Label Mapping Cache Operations
  36
  37Depending on the exact configuration, translation between the network packet
  38label and the internal LSM security identifier can be time consuming.  The
  39NetLabel label mapping cache is a caching mechanism which can be used to
  40sidestep much of this overhead once a mapping has been established.  Once the
  41LSM has received a packet, used NetLabel to decode its security attributes,
  42and translated the security attributes into a LSM internal identifier the LSM
  43can use the NetLabel caching functions to associate the LSM internal
  44identifier with the network packet's label.  This means that in the future
  45when a incoming packet matches a cached value not only are the internal
  46NetLabel translation mechanisms bypassed but the LSM translation mechanisms are
  47bypassed as well which should result in a significant reduction in overhead.
  48
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