Type enforcement

The concept of type enforcement (TE) in the field of information technology is related to access control. Implementing TE gives priority to “mandatory access control” (MAC) over “discretionary access control” (DAC). Access clearance is first given to a subject (e.g. process) accessing objects (e.g. files, records, messages) based on rules defined in an attached security context. A security context in a domain is defined by a domain security policy. In the Linux security module (LSM) in SELinux, the security context is an extended attribute. Type enforcement implementation is a prerequisite for MAC, and a first step before “multi-level security” (MLS) or its replacement “multi categories security” (MCS). It is a complement of “role based access control” (RBAC).

Type enforcement implies fine grained control over the operating system, not only to have control over process execution, but also over “domain transition” or authorization scheme. This is why it is best implemented as a kernel module, as is the case with SELinux. Using type enforcement is a way to implement the FLASK architecture.

Using type enforcement, users may (as in Microsoft Active Directory) or may not (as in SELinux) be associated with a Kerberos realm, although the original type enforcement model implies so. It is always necessary to define a TE access matrix containing rules about clearance granted to a given security context, or subject's rights over objects according to an authorization scheme.

Practically, type enforcement evaluates a set of rules from the source security context of a subject, against a set of rules from the target security context of the object. A clearance decision occurs depending on the TE access description (matrix). Then, DAC or other access control mechanisms (MLS / MCS, …) apply.

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