Multi-Level Security confidentiality policy
SYNOPSISTo compile MLS into your kernel, place the following lines in your kernel configuration file:
Alternately, to load the MLS module at boot time, place the following line in your kernel configuration file:
and in loader.conf(5):
In MLS, all system subjects and objects are assigned confidentiality labels, made up of a sensitivity level and zero or more compartments. Together, these label elements permit all labels to be placed in a partial order, with confidentiality protections based on a dominance operator describing the order. The sensitivity level is expressed as a value between 0 and 65535, with higher values reflecting higher sensitivity levels. The compartment field is expressed as a set of up to 256 components, numbered from 1 to 256. A complete label consists of both sensitivity and compartment elements.
With normal labels, dominance is defined as a label having a
higher or equal active sensitivity level, and having at least all of the
same compartments as the label to which it is being compared. With respect
to label comparisons, “
Three special label values exist:
The MLS model enforces the following basic restrictions:
These rules prevent subjects of lower clearance from gaining access information classified beyond its clearance level in order to protect the confidentiality of classified information, subjects of higher clearance from writing to objects of lower classification in order to prevent the accidental or malicious leaking of information, and subjects of lower clearance from observing subjects of higher clearance altogether. In traditional trusted operating systems, the MLS confidentiality model is used in concert with the Biba integrity model (mac_biba(4)) in order to protect the Trusted Code Base (TCB).
Label FormatAlmost all system objects are tagged with an effective, active label element, reflecting the classification of the object, or classification of the data contained in the object. In general, object labels are represented in the following form:
Subject labels consist of three label elements: an effective (active) label, as well as a range of available labels. This range is represented using two ordered MLS label elements, and when set on a process, permits the process to change its active label to any label of greater or equal integrity to the low end of the range, and lesser or equal integrity to the high end of the range. In general, subject labels are represented in the following form:
Valid ranged labels must meet the following requirement regarding their elements:
rangehigh ≥ effective ≥ rangelow
One class of objects with ranges currently exists, the network interface. In the case of the network interface, the effective label element references the default label for packets received over the interface, and the range represents the range of acceptable labels of packets to be transmitted over the interface.
Runtime ConfigurationThe following sysctl(8) MIBs are available for fine-tuning the enforcement of this MAC policy.
IMPLEMENTATION NOTESCurrently, the
SEE ALSOmac(4), mac_biba(4), mac_bsdextended(4), mac_ifoff(4), mac_lomac(4), mac_none(4), mac_partition(4), mac_portacl(4), mac_seeotheruids(4), mac_test(4), maclabel(7), mac(9)
AUTHORSThis software was contributed to the FreeBSD Project by Network Associates Laboratories, the Security Research Division of Network Associates Inc. under DARPA/SPAWAR contract N66001-01-C-8035 (“CBOSS”), as part of the DARPA CHATS research program.
BUGSWhile the MAC Framework design is intended to support the containment of the root user, not all attack channels are currently protected by entry point checks. As such, MAC Framework policies should not be relied on, in isolation, to protect against a malicious privileged user.
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