HP-UX Reference (11i v1 05/09) - 5 Miscellaneous Topics (vol 9)

a
acl(5) acl(5)
NAME
acl - introduction to HFS access control lists
DESCRIPTION
Access control lists 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 mechan-
isms 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 per-
mission 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, groups, or combinations thereof.
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 HFS file systems only. See aclv(5) for a description
of ACLs in JFS 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, sock-
ets).
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-ID/group-ID combinations.
access control list (ACL) entry
An entry in an ACL that specifies access rights for one user and group ID combina-
tion.
change permission
The right to alter DAC information (permission bits or ACL entries). Change permis-
sion 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 sub-
ject with a certain access permission is capable of passing that permission (perhaps
indirectly) to any other subject."
mode Three bits in each ACL entry which represent read, write, and execute/search permis-
sions. 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
policy 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.
Section 5−−2 Hewlett-Packard Company − 1 − HP-UX 11i Version 1: September 2005