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+NetLabel Linux Security Module Interface
+Paul Moore, paul.moore@hp.com
+May 17, 2006
+ * Overview
+NetLabel is a mechanism which can set and retrieve security attributes from
+network packets. It is intended to be used by LSM developers who want to make
+use of a common code base for several different packet labeling protocols.
+The NetLabel security module API is defined in 'include/net/netlabel.h' but a
+brief overview is given below.
+ * NetLabel Security Attributes
+Since NetLabel supports multiple different packet labeling protocols and LSMs
+it uses the concept of security attributes to refer to the packet's security
+labels. The NetLabel security attributes are defined by the
+'netlbl_lsm_secattr' structure in the NetLabel header file. Internally the
+NetLabel subsystem converts the security attributes to and from the correct
+low-level packet label depending on the NetLabel build time and run time
+configuration. It is up to the LSM developer to translate the NetLabel
+security attributes into whatever security identifiers are in use for their
+particular LSM.
+ * NetLabel LSM Protocol Operations
+These are the functions which allow the LSM developer to manipulate the labels
+on outgoing packets as well as read the labels on incoming packets. Functions
+exist to operate both on sockets as well as the sk_buffs directly. These high
+level functions are translated into low level protocol operations based on how
+the administrator has configured the NetLabel subsystem.
+ * NetLabel Label Mapping Cache Operations
+Depending on the exact configuration, translation between the network packet
+label and the internal LSM security identifier can be time consuming. The
+NetLabel label mapping cache is a caching mechanism which can be used to
+sidestep much of this overhead once a mapping has been established. Once the
+LSM has received a packet, used NetLabel to decode its security attributes,
+and translated the security attributes into a LSM internal identifier the LSM
+can use the NetLabel caching functions to associate the LSM internal
+identifier with the network packet's label. This means that in the future
+when a incoming packet matches a cached value not only are the internal
+NetLabel translation mechanisms bypassed but the LSM translation mechanisms are
+bypassed as well which should result in a significant reduction in overhead.