Oracle Solaris Trusted Extensions Administrator's Procedures

Labels in Trusted Extensions Software

Labels and clearances are at the center of mandatory access control (MAC) in Trusted Extensions. They determine which users can access which programs, files, and directories. Labels and clearances consist of one classification component and zero or more compartment components. The classification component indicates a hierarchical level of security such as TOP SECRET or CONFIDENTIAL. The compartment component represents a group of users who might need access to a common body of information. Some typical types of compartments are projects, departments, or physical locations. Labels are readable by authorized users, but internally, labels are manipulated as numbers. The numbers and their readable versions are defined in the label_encodings file.

Trusted Extensions mediates all attempted security-related transactions. The software compares the labels of the accessing entity, typically a process, and the entity being accessed, usually a filesystem object. The software then permits or disallows the transaction depending on which label is dominant. Labels are also used to determine access to other system resources, such as allocatable devices, networks, frame buffers, and other hosts.

Dominance Relationships Between Labels

One entity's label is said to dominate another label if the following two conditions are met:

Two labels are said to be equal if they have the same classification and the same set of compartments. If the labels are equal, they dominate each other and access is permitted.

If one label has a higher classification or if it has the same classification and its compartments are a superset of the second label's compartments, or both, the first label is said to strictly dominate the second label.

Two labels are said to be disjoint or noncomparable if neither label dominates the other label.

The following table presents examples of label comparisons for dominance. In the example, NEED_TO_KNOW is a higher classification than INTERNAL. There are three compartments: Eng, Mkt, and Fin.

Table 1–1 Examples of Label Relationships

Label 1 


Label 2 


(strictly) dominates 



(strictly) dominates 



(strictly) dominates 



dominates (equals) 



is disjoint with 



is disjoint with 



is disjoint with 


Administrative Labels

Trusted Extensions provides two special administrative labels that are used as labels or clearances: ADMIN_HIGH and ADMIN_LOW. These labels are used to protect system resources and are intended for administrators rather than regular users.

ADMIN_HIGH is the highest label. ADMIN_HIGH dominates all other labels in the system and is used to protect system data, such as administration databases or audit trails, from being read. You must be in the global zone to read data that is labeled ADMIN_HIGH.

ADMIN_LOW is the lowest label. ADMIN_LOW is dominated by all other labels in a system, including labels for regular users. Mandatory access control does not permit users to write data to files with labels lower than the user's label. Thus, a file at the label ADMIN_LOW can be read by regular users, but cannot be modified. ADMIN_LOW is typically used to protect public executables that are shared, such as files in /usr/bin.

Label Encodings File

All label components for a system, that is, classifications, compartments, and the associated rules, are stored in an ADMIN_HIGH file, the label_encodings file. This file is located in the /etc/security/tsol directory. The security administrator sets up the label_encodings file for the site. A label encodings file contains:

For more information, see the label_encodings(4) man page. Detailed information can also be found in Oracle Solaris Trusted Extensions Label Administration and Compartmented Mode Workstation Labeling: Encodings Format.

Label Ranges

A label range is the set of potentially usable labels at which users can operate. Both users and resources both have label ranges. Resources that can be protected by label ranges include such things as allocatable devices, networks, interfaces, frame buffers, and commands or actions. A label range is defined by a clearance at the top of the range and a minimum label at the bottom.

A range does not necessarily include all combinations of labels that fall between a maximum and minimum label. Rules in the label_encodings file can disqualify certain combinations. A label must be well-formed, that is, permitted by all applicable rules in the label encodings file, in order to be included in a range.

However, a clearance does not have to be well-formed. Suppose, for example, that a label_encodings file prohibits any combination of compartments Eng, Mkt, and Fin in a label. INTERNAL Eng Mkt Fin would be a valid clearance but not a valid label. As a clearance, this combination would let a user access files that are labeled INTERNAL Eng, INTERNAL Mkt, and INTERNAL Fin.

Account Label Range

When you assign a clearance and a minimum label to a user, you define the upper and lower boundaries of the account label range in which that user is permitted to operate. The following equation describes the account label range, using ≤ to indicate “dominated by or the same as”:

minimum label ≤ permitted label ≤ clearance

Thus, the user is permitted to operate at any label that is dominated by the clearance as long as that label dominates the minimum label. When a user's clearance or minimum label is not expressly set, the defaults that are defined in the label_encodings file take effect.

Users can be assigned a clearance and a minimum label that enable them to operate at more than one label, or at a single label. When a user's clearance and minimum label are equal, the user can operate at only one label.

Session Range

The session range is the set of labels that is available to a user during a Trusted Extensions session. The session range must be within the user's account label range and the label range set for the system. At login, if the user selects single-label session mode, the session range is limited to that label. If the user selects multilabel session mode, then the label that the user selects becomes the session clearance. The session clearance defines the upper boundary of the session range. The user's minimum label defines the lower bound. The user begins the session in a workspace at the minimum label. During the session, the user can switch to a workspace at any label within the session range.

What Labels Protect and Where Labels Appear

Labels appear on the desktop and on output that is executed on the desktop, such as printer output.