aclv.5 (2010 09)

a
aclv(5) aclv(5)
NAME
aclv - introduction to JFS access control lists (ACLs)
DESCRIPTION
Access control lists (ACLs) are a key enforcement mechanism of discretionary access control (see
Definitions below), for specifying access to files by users and groups more selectively than traditional HP-
UX mechanisms allow.
HP-UX already enables non-privileged users or processes, such as file owners, to allow or deny other
users access to files and other objects on a "need to know" basis, as determined by their user and/or group
identity (see passwd(4) and group(4)). This level of control is accomplished by setting or manipulating a
file’s permission bits to grant or restrict access by owner, group, and others (see chmod(2)).
ACLs offer a greater degree of selectivity than permission bits. ACLs allow the file owner or superuser to
permit or deny access to a list of users and groups other than the file owner and owning group.
ACLs are supported as a superset of the UNIX operating system discretionary access control (DAC)
mechanism for files, but not for other objects such as inter-process communication (IPC) objects.
This manual page describes ACLs as implemented on JFS file systems only. See acl(5) for a description
of ACLs in HFS file systems.
Definitions
Because control of access to data is a key concern of computer security, we provide the following
definitions, based on those of the Department of Defense Trusted Computer System Evaluation Criteria, to
explain further both the concepts of access control and its relevance to HP-UX security features:
access "A specific type of interaction between a subject and an object that results in the flow of
information from one to the other." Subjects include "persons, processes, or devices that
cause information to flow among objects or change the system state." Objects include files
(ordinary files, directories, special files, FIFOs, etc.) and inter-process communication
(IPC) features (shared memory, message queues, semaphores, sockets).
access control list (ACL)
An access control list is a set of (user|group, mode) entries associated with a file that
specify permissions for all possible user-IDs and/or group-IDs.
access control list (ACL) entry
An entry in an ACL that specifies access rights for a file’s owner, owning group, group
class, additional user, additional group, or all others.
change permission
The right to alter DAC information (permission bits or ACL entries). Change permission
is granted to object (file) owners and to privileged users.
discretionary access control (DAC)
"A means of restricting access to objects based on the identity of subjects and/or groups to
which they belong. The controls are discretionary in the sense that a subject with a cer-
tain access permission is capable of passing that permission (perhaps indirectly) to any
other subject."
mode Three bits in each ACL entry that represent read, write, and execute/search permissions.
These bits may exist in addition to the 16 mode bits associated with every file in the file
system (see glossary (9)).
privilege The ability to ignore access restrictions and change restrictions imposed by security pol-
icy and implemented in an access control mechanism. In HP-UX, superusers and
members of certain groups (see privgrp (4)) are the only privileged users.
restrictive versus permissive
An individual ACL entry is considered restrictive or permissive, depending on context.
Restrictive entries deny a user and/or group access that would otherwise be granted by
less-specific base or optional ACL entries (see below). Permissive entries grant a user
and/or group access that would otherwise be denied by less-specific base or optional ACL
entries.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1