233 lines
9.2 KiB
Groff
233 lines
9.2 KiB
Groff
.\"-
|
|
.\" Copyright (c) 1999-2002 Robert N. M. Watson
|
|
.\" Copyright (c) 2002-2004 Networks Associates Technology, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This software was developed by Robert Watson for the TrustedBSD Project.
|
|
.\"
|
|
.\" This software was developed for the FreeBSD Project in part 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.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd February 27, 2021
|
|
.Dt MAC 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm mac
|
|
.Nd TrustedBSD Mandatory Access Control framework
|
|
.Sh SYNOPSIS
|
|
.In sys/types.h
|
|
.In sys/mac.h
|
|
.Pp
|
|
In the kernel configuration file:
|
|
.Cd "options MAC"
|
|
.Cd "options MAC_DEBUG"
|
|
.Sh DESCRIPTION
|
|
.Ss Introduction
|
|
The
|
|
.Tn TrustedBSD
|
|
mandatory access control framework permits dynamically
|
|
introduced system security modules to modify system security functionality.
|
|
This can be used to support a variety of new security services, including
|
|
traditional labeled mandatory access control models.
|
|
The framework provides a series of entry points which must be called by
|
|
code supporting various kernel services, especially with respects to access
|
|
control points and object creation.
|
|
The framework then calls out to security modules to offer them the
|
|
opportunity to modify security behavior at those MAC API entry points.
|
|
Both consumers of the API (normal kernel services) and security modules
|
|
must be aware of the semantics of the API calls, particularly with respect
|
|
to synchronization primitives (such as locking).
|
|
.Ss Kernel Objects Supported by the Framework
|
|
The MAC framework manages labels on a variety of types of in-kernel
|
|
objects, including process credentials, vnodes, devfs_dirents, mount
|
|
points, sockets, mbufs, bpf descriptors, network interfaces, IP fragment
|
|
queues, and pipes.
|
|
Label data on kernel objects, represented by
|
|
.Vt "struct label" ,
|
|
is policy-unaware, and may be used in the manner seen fit by policy modules.
|
|
.Ss API for Consumers
|
|
The MAC API provides a large set of entry points, too broad to specifically
|
|
document here.
|
|
In general, these entry points represent an access control check or other
|
|
MAC-relevant operations, accept one or more subjects (credentials)
|
|
authorizing the activity, a set of objects on which the operation
|
|
is to be performed, and a set of operation arguments providing information
|
|
about the type of operation being requested.
|
|
.Ss Locking for Consumers
|
|
Consumers of the MAC API must be aware of the locking requirements for
|
|
each API entry point: generally, appropriate locks must be held over each
|
|
subject or object being passed into the call, so that MAC modules may
|
|
make use of various aspects of the object for access control purposes.
|
|
For example, vnode locks are frequently required in order that the MAC
|
|
framework and modules may retrieve security labels and attributes from the
|
|
vnodes for the purposes of access control.
|
|
Similarly, the caller must be aware of the reference counting semantics
|
|
of any subject or object passed into the MAC API: all calls require that
|
|
a valid reference to the object be held for the duration of the
|
|
(potentially lengthy) MAC API call.
|
|
Under some circumstances, objects must be held in either a shared or
|
|
exclusive manner.
|
|
.Ss API for Module Writers
|
|
Each module exports a structure describing the MAC API operations that
|
|
the module chooses to implement, including initialization and destruction
|
|
API entry points, a variety of object creation and destruction calls,
|
|
and a large set of access control check points.
|
|
In the future, additional audit entry points will also be present.
|
|
Module authors may choose to only implement a subset of the entry points,
|
|
setting API function pointers in the description structure to
|
|
.Dv NULL ,
|
|
permitting the framework to avoid calling into the module.
|
|
.Ss Locking for Module Writers
|
|
Module writers must be aware of the locking semantics of entry points
|
|
that they implement: MAC API entry points will have specific locking
|
|
or reference counting semantics for each argument, and modules must follow
|
|
the locking and reference counting protocol or risk a variety of failure
|
|
modes (including race conditions, inappropriate pointer dereferences,
|
|
etc).
|
|
.Pp
|
|
MAC module writers must also be aware that MAC API entry points will
|
|
frequently be invoked from deep in a kernel stack, and as such must be
|
|
careful to avoid violating more global locking requirements, such as
|
|
global lock order requirements.
|
|
For example, it may be inappropriate to lock additional objects not
|
|
specifically maintained and ordered by the policy module, or the
|
|
policy module might violate a global ordering requirement relating
|
|
to those additional objects.
|
|
.Pp
|
|
Finally, MAC API module implementors must be careful to avoid
|
|
inappropriately calling back into the MAC framework: the framework
|
|
makes use of locking to prevent inconsistencies during policy module
|
|
attachment and detachment.
|
|
MAC API modules should avoid producing scenarios in which deadlocks
|
|
or inconsistencies might occur.
|
|
.Ss Adding New MAC Entry Points
|
|
The MAC API is intended to be easily expandable as new services are
|
|
added to the kernel.
|
|
In order that policies may be guaranteed the opportunity to ubiquitously
|
|
protect system subjects and objects, it is important that kernel
|
|
developers maintain awareness of when security checks or relevant
|
|
subject or object operations occur in newly written or modified kernel
|
|
code.
|
|
New entry points must be carefully documented so as to prevent any
|
|
confusion regarding lock orders and semantics.
|
|
Introducing new entry points requires four distinct pieces of work:
|
|
introducing new MAC API entries reflecting the operation arguments,
|
|
scattering these MAC API entry points throughout the new or modified
|
|
kernel service, extending the front-end implementation of the MAC API
|
|
framework, and modifying appropriate modules to take advantage of
|
|
the new entry points so that they may consistently enforce their
|
|
policies.
|
|
.Sh ENTRY POINTS
|
|
System service and module authors should reference the
|
|
.%T "FreeBSD Architecture Handbook"
|
|
for information on the MAC Framework APIs.
|
|
.Sh SEE ALSO
|
|
.Xr acl 3 ,
|
|
.Xr mac 3 ,
|
|
.Xr posix1e 3 ,
|
|
.Xr mac_biba 4 ,
|
|
.Xr mac_bsdextended 4 ,
|
|
.Xr mac_ifoff 4 ,
|
|
.Xr mac_lomac 4 ,
|
|
.Xr mac_mls 4 ,
|
|
.Xr mac_none 4 ,
|
|
.Xr mac_partition 4 ,
|
|
.Xr mac_seeotheruids 4 ,
|
|
.Xr mac_test 4 ,
|
|
.Xr ucred 9 ,
|
|
.Xr vaccess 9 ,
|
|
.Xr vaccess_acl_posix1e 9 ,
|
|
.Xr VFS 9 ,
|
|
.Xr VOP_SETLABEL 9 .
|
|
.Rs
|
|
.%T "The FreeBSD Architecture Handbook"
|
|
.%U "https://www.FreeBSD.org/doc/en_US.ISO8859-1/books/arch-handbook/"
|
|
.Re
|
|
.Sh HISTORY
|
|
The
|
|
.Tn TrustedBSD
|
|
MAC Framework first appeared in
|
|
.Fx 5.0 .
|
|
.Sh AUTHORS
|
|
This manual page was written by
|
|
.An Robert Watson .
|
|
This software was contributed to the
|
|
.Fx
|
|
Project by Network Associates Laboratories, the Security Research
|
|
Division of Network Associates Inc.\& under DARPA/SPAWAR contract
|
|
N66001-01-C-8035
|
|
.Pq Dq CBOSS ,
|
|
as part of the DARPA CHATS research program.
|
|
.Pp
|
|
.An -nosplit
|
|
The
|
|
.Tn TrustedBSD
|
|
MAC Framework was designed by
|
|
.An Robert Watson ,
|
|
and implemented by the Network Associates Laboratories Network Security
|
|
(NETSEC), Secure Execution Environment (SEE), and Adaptive
|
|
Network Defense research groups.
|
|
Network Associates Laboratory staff contributing to the CBOSS Project
|
|
include (in alphabetical order):
|
|
.An Lee Badger ,
|
|
.An Brian Feldman ,
|
|
.An Hrishikesh Dandekar ,
|
|
.An Tim Fraser ,
|
|
.An Doug Kilpatrick ,
|
|
.An Suresh Krishnaswamy ,
|
|
.An Adam Migus ,
|
|
.An Wayne Morrison ,
|
|
.An Andrew Reisse ,
|
|
.An Chris Vance ,
|
|
and
|
|
.An Robert Watson .
|
|
.Pp
|
|
Sub-contracted staff include:
|
|
.An Chris Costello ,
|
|
.An Poul-Henning Kamp ,
|
|
.An Jonathan Lemon ,
|
|
.An Kirk McKusick ,
|
|
.An Dag-Erling Sm\(/orgrav .
|
|
.Pp
|
|
Additional contributors include:
|
|
.An Pawel Dawidek ,
|
|
.An Chris Faulhaber ,
|
|
.An Ilmar Habibulin ,
|
|
.An Mike Halderman ,
|
|
.An Bosko Milekic ,
|
|
.An Thomas Moestl ,
|
|
.An Andrew Reiter ,
|
|
and
|
|
.An Tim Robbins .
|
|
.Sh BUGS
|
|
While 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.
|