lsm_interface.rst (2545B)
1======================================== 2NetLabel Linux Security Module Interface 3======================================== 4 5Paul Moore, paul.moore@hp.com 6 7May 17, 2006 8 9Overview 10======== 11 12NetLabel is a mechanism which can set and retrieve security attributes from 13network packets. It is intended to be used by LSM developers who want to make 14use of a common code base for several different packet labeling protocols. 15The NetLabel security module API is defined in 'include/net/netlabel.h' but a 16brief overview is given below. 17 18NetLabel Security Attributes 19============================ 20 21Since NetLabel supports multiple different packet labeling protocols and LSMs 22it uses the concept of security attributes to refer to the packet's security 23labels. The NetLabel security attributes are defined by the 24'netlbl_lsm_secattr' structure in the NetLabel header file. Internally the 25NetLabel subsystem converts the security attributes to and from the correct 26low-level packet label depending on the NetLabel build time and run time 27configuration. It is up to the LSM developer to translate the NetLabel 28security attributes into whatever security identifiers are in use for their 29particular LSM. 30 31NetLabel LSM Protocol Operations 32================================ 33 34These are the functions which allow the LSM developer to manipulate the labels 35on outgoing packets as well as read the labels on incoming packets. Functions 36exist to operate both on sockets as well as the sk_buffs directly. These high 37level functions are translated into low level protocol operations based on how 38the administrator has configured the NetLabel subsystem. 39 40NetLabel Label Mapping Cache Operations 41======================================= 42 43Depending on the exact configuration, translation between the network packet 44label and the internal LSM security identifier can be time consuming. The 45NetLabel label mapping cache is a caching mechanism which can be used to 46sidestep much of this overhead once a mapping has been established. Once the 47LSM has received a packet, used NetLabel to decode its security attributes, 48and translated the security attributes into a LSM internal identifier the LSM 49can use the NetLabel caching functions to associate the LSM internal 50identifier with the network packet's label. This means that in the future 51when a incoming packet matches a cached value not only are the internal 52NetLabel translation mechanisms bypassed but the LSM translation mechanisms are 53bypassed as well which should result in a significant reduction in overhead.