1NetLabel Linux Security Module Interface
3Paul Moore,
5May 17, 2006
7 * Overview
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.
15 * NetLabel Security Attributes
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.
27 * NetLabel LSM Protocol Operations
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.
35 * NetLabel Label Mapping Cache Operations
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.

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