Label APIs

Labels, label ranges, and a label limit determine who can access information on a system that is configured with Trusted Extensions.

The label APIs are used to access, convert, and perform comparisons for labels, label ranges and limits, and the relationship between labels. A label can dominate another label, or a label can be disjoint from another label.

The label_encodings file defines the sensitivity labels, clearance labels, label ranges, and label relationships that pertain to your Trusted Extensions environment. This file also controls the appearance of labels. The security administrator is responsible for creating and maintaining the label_encodings file. See the label_encodings(4) man page.

The label of a process is determined by the zone in which the process executes.

All objects are associated with a label or sometimes with a label range. An object can be accessed at a particular label within the defined label range. The objects that are associated with a label range include the following:

• All users and all roles

• All hosts with which communications are permitted

• Zone interfaces and network interfaces

• Allocatable devices, such as tape drives, diskette drives, CD-ROM devices, and audio devices

• Other devices that are not allocatable, such as printers and workstations

  Workstation access is controlled by the label range that is set for the frame buffer or video display device. The security administrator sets this range by using the Device Manager GUI. By default, devices have a range from ADMIN_LOW to ADMIN_HIGH.

For more information about labels, see Label Types.

How Labels Are Used in Access Control Decisions

MAC compares the label of the process that is running an application with the label or the label range of any object that the process tries to access. MAC permits a process to read down to a lower label and permits a process to write to an equal label.

Label[Process] >= Label[Object]

A process bound to a multilevel port (MLP) can listen for requests at multiple labels and send replies to the originator of the request. In Trusted Extensions, such replies are write-equal.

Label[Process] = Label[Object]

Types of Label APIs

Sensitivity Label APIs

Sensitivity label APIs can be used to do the following:

• Obtain a process label

• Initialize labels

• Find the greatest lower bound or the least upper bound between two labels

• Compare labels for dominance and equality

• Check and set label types

• Convert labels to a readable format

• Obtain information from the label_encodings file

• Check that a sensitivity label is valid and within the system range

For a description of these APIs, see Chapter 2, Labels and Clearances.

Clearance Label APIs

Users, devices, and network interfaces have label ranges. The upper bound of the range is effectively the clearance. If the upper bound of the range and the lower bound of the range are equal, the range is a single label.

Clearance label APIs can be used to do the following:

• Find the greatest lower bound or the least upper bound between two labels

• Compare labels for dominance and equality

• Convert clearances between the internal format and the hexadecimal format

For a description of these APIs, see Chapter 2, Labels and Clearances.

Label Range APIs

A label range is used to set limits on the following:

• The labels at which hosts can send and receive information

• The labels at which processes acting on behalf of users and roles can work on the system

• The labels at which users can allocate devices

  This use of a label range restricts the labels at which files can be written to storage media on these devices.

Label ranges are assigned administratively. Label ranges can apply to users, roles, hosts, zones, network interfaces, printers, and other objects.

You can use the following methods to obtain information about label ranges:

• getuserrange() obtains the user's label range.

• getdevicerange() obtains the label range of a device.

• tninfo -t template-name shows the label range of a template that is associated with a network interface.

For a description of these APIs, see Chapter 2, Labels and Clearances.