[NetLabel]: documentation

Documentation for the NetLabel system, this includes a basic overview
of how NetLabel works, how LSM developers can integrate it into their
favorite LSM, as well as documentation on the CIPSO related sysctl
variables.  Also, due to the difficulty of finding expired IETF
drafts, I am including the IETF CIPSO draft that is the basis of the
NetLabel CIPSO implementation.
Signed-off-by: NPaul Moore <paul.moore@hp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

CREDITS

@@ -2384,6 +2384,13 @@ N: Thomas Molina
 E: tmolina@cablespeed.com
 D: bug fixes, documentation, minor hackery
 
+N: Paul Moore
+E: paul.moore@hp.com
+D: NetLabel author
+S: Hewlett-Packard
+S: 110 Spit Brook Road
+S: Nashua, NH 03062
+
 N: James Morris
 E: jmorris@namei.org
 W: http://namei.org/

Documentation/00-INDEX

@@ -184,6 +184,8 @@ mtrr.txt
 	- how to use PPro Memory Type Range Registers to increase performance.
 nbd.txt
 	- info on a TCP implementation of a network block device.
+netlabel/
+	- directory with information on the NetLabel subsystem.
 networking/
 	- directory with info on various aspects of networking with Linux.
 nfsroot.txt

Documentation/netlabel/00-INDEX

+00-INDEX
+	- this file.
+cipso_ipv4.txt
+	- documentation on the IPv4 CIPSO protocol engine.
+draft-ietf-cipso-ipsecurity-01.txt
+	- IETF draft of the CIPSO protocol, dated 16 July 1992.
+introduction.txt
+	- NetLabel introduction, READ THIS FIRST.
+lsm_interface.txt
+	- documentation on the NetLabel kernel security module API.

Documentation/netlabel/cipso_ipv4.txt

+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.

Documentation/netlabel/introduction.txt

+NetLabel Introduction
+==============================================================================
+Paul Moore, paul.moore@hp.com
+
+August 2, 2006
+
+ * Overview
+
+NetLabel is a mechanism which can be used by kernel security modules to attach
+security attributes to outgoing network packets generated from user space
+applications and read security attributes from incoming network packets.  It
+is composed of three main components, the protocol engines, the communication
+layer, and the kernel security module API.
+
+ * Protocol Engines
+
+The protocol engines are responsible for both applying and retrieving the
+network packet's security attributes.  If any translation between the network
+security attributes and those on the host are required then the protocol
+engine will handle those tasks as well.  Other kernel subsystems should
+refrain from calling the protocol engines directly, instead they should use
+the NetLabel kernel security module API described below.
+
+Detailed information about each NetLabel protocol engine can be found in this
+directory, consult '00-INDEX' for filenames.
+
+ * Communication Layer
+
+The communication layer exists to allow NetLabel configuration and monitoring
+from user space.  The NetLabel communication layer uses a message based
+protocol built on top of the Generic NETLINK transport mechanism.  The exact
+formatting of these NetLabel messages as well as the Generic NETLINK family
+names can be found in the the 'net/netlabel/' directory as comments in the
+header files as well as in 'include/net/netlabel.h'.
+
+ * Security Module API
+
+The purpose of the NetLabel security module API is to provide a protocol
+independent interface to the underlying NetLabel protocol engines.  In addition
+to protocol independence, the security module API is designed to be completely
+LSM independent which should allow multiple LSMs to leverage the same code
+base.
+
+Detailed information about the NetLabel security module API can be found in the
+'include/net/netlabel.h' header file as well as the 'lsm_interface.txt' file
+found in this directory.

Documentation/netlabel/lsm_interface.txt

+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 it's 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.

Documentation/networking/ip-sysctl.txt

@@ -375,6 +375,41 @@ tcp_slow_start_after_idle - BOOLEAN
 	be timed out after an idle period.
 	Default: 1
 
+CIPSOv4 Variables:
+
+cipso_cache_enable - BOOLEAN
+	If set, enable additions to and lookups from the CIPSO label mapping
+	cache.  If unset, additions are ignored and lookups always result in a
+	miss.  However, regardless of the setting the cache is still
+	invalidated when required when means you can safely toggle this on and
+	off and the cache will always be "safe".
+	Default: 1
+
+cipso_cache_bucket_size - INTEGER
+	The CIPSO label cache consists of a fixed size hash table with each
+	hash bucket containing a number of cache entries.  This variable limits
+	the number of entries in each hash bucket; the larger the value the
+	more CIPSO label mappings that can be cached.  When the number of
+	entries in a given hash bucket reaches this limit adding new entries
+	causes the oldest entry in the bucket to be removed to make room.
+	Default: 10
+
+cipso_rbm_optfmt - BOOLEAN
+	Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
+	the CIPSO draft specification (see Documentation/netlabel for details).
+	This means that when set the CIPSO tag will be padded with empty
+	categories in order to make the packet data 32-bit aligned.
+	Default: 0
+
+cipso_rbm_structvalid - BOOLEAN
+	If set, do a very strict check of the CIPSO option when
+	ip_options_compile() is called.  If unset, relax the checks done during
+	ip_options_compile().  Either way is "safe" as errors are caught else
+	where in the CIPSO processing code but setting this to 0 (False) should
+	result in less work (i.e. it should be faster) but could cause problems
+	with other implementations that require strict checking.
+	Default: 0
+
 IP Variables:
 
 ip_local_port_range - 2 INTEGERS