ACL(3)

NAME
acl - introduction to the POSIX.1e ACL security API

LIBRARY
libposix1e

SYNOPSIS
#include <sys/types.h>
#include <sys/acl.h>

DESCRIPTION
As shipped, FreeBSD 4.0 permits file systems to export Access Control Lists via the VFS, and provides a library for userland access to and manipulation of these ACLs, but support for ACLs is not provided by any file systems shipped in the base operating system. The library calls shipped with 4.0 include routines to allocate, duplicate, retrieve, set, and validate ACLs associated with file objects. As well as the POSIX.1e routines, there are a number of non-portable extensions defined that allow for alternative ACL semantics than the POSIX.1e semantics, such as AFS, NTFS, Coda, and NWFS semantics. Where routines are non-standard, they are suffixed with _np to indicate that they are not portable. POSIX.1e describes a set of ACL manipulation routines to manage the contents of ACLs, as well as their relationships with files. This manipulation library is not currently implemented in FreeBSD, although a third party library was under development at the time this document was written. There is a general consensus that the POSIX.1e manipulation routines are ambiguously defined in the specification, and don't meet the needs of most applications. For the time being, applications may directly manipulate the ACL structures, defined in acl.h, although the recommended usage is to only ever handle text-form ACLs in applications, generated and maintained using acl_from_text() and acl_to_text(), passed directly to and from the management routines. In this manner, an application can remain safely unaware of the contents of ACLs. Available functions, sorted by behavior, include: acl_delete_def_file(), acl_delete_file_np(), acl_delete_fd_np() These functions are described in acl_delete(3), and may be used to delete ACLs from file system objects. acl_free() This function is described in acl_free(3), and may be used to free userland working ACL storage. acl_from_text() This function is described in acl_from_text(3), and may be used to convert a text-form ACL into working ACL state, if the ACL has POSIX.1e semantics. acl_get_file(), acl_get_fd(), acl_get_fd_np() These functions are described in acl_get(3), and may be used to retrieve ACLs from file system objects. acl_init() This function is described in acl_init(3), and may be used to allocate a fresh (empty) ACL structure. acl_dup() This function is described in acl_dup(3), and may be used to duplicate an ACL structure. acl_set_file(), acl_set_fd(), acl_set_fd_np() These functions are described in acl_set(3), and may be used to assign an ACL to a file system object. acl_to_text() This function is described in acl_to_text(3), and may be used to generate a text-form of a POSIX.1e semantics ACL. acl_valid(), acl_valid_file_np(), acl_valid_fd_np() Thee functions are described in acl_valid(3), and may be used to validate an ACL as correct POSIX.1e-semantics, or as appropriate for a particular file system object regardless of semantics. Documentation of the internal kernel interfaces backing these calls may be found in acl(9). The syscalls between the internal interfaces and the public library routines may change over time, and as such are not documented. They are not intended to be called directly without going through the library.

IMPLEMENTATION NOTES
FreeBSD's support for POSIX.1e interfaces and features is still under development at this time.

ENVIRONMENT
POSIX.1e assigns security labels to all objects, extending the security functionality described in POSIX.1. These additional labels provide fine-grained discretionary access control, fine-grained capabilities, and labels necessary for mandatory access control. POSIX.2c describes a set of userland utilities for manipulating these labels. These userland utilities are not bundled with FreeBSD 4.0 so as to discourage their use in the short term.

SEE ALSO
acl_dup(3), acl_free(3), acl_from_text(3), acl_get(3), acl_set(3), acl_to_text(3), acl_valid(3), acl(9), posix1e(3)

STANDARDS
POSIX.1e is described in IEEE POSIX.1e draft 17. Discussion of the draft continues on the cross-platform POSIX.1e implementation mailing list. To join this list, see the FreeBSD POSIX.1e implementation page for more information.

HISTORY
POSIX.1e support was introduced in FreeBSD 4.0, and development continues.

AUTHORS
Robert N M Watson

BUGS
These features are not yet fully implemented.