acl
—
introduction to the POSIX.1e/NFSv4 ACL security API
Standard C Library (libc, -lc)
FreeBSD permits file systems to export Access Control
Lists via the VFS, and provides a library for userland access to and
manipulation of these ACLs. FreeBSD supports POSIX.1e
and NFSv4 ACLs, but not all file systems provide support for ACLs, and some
may require that ACL support be explicitly enabled by the administrator. The
library calls 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 ACL
semantics alternative to POSIX.1e, such as NFSv4. 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; almost all
of these support routines are implemented in
FreeBSD.
Available functions, sorted by behavior, include:
acl_add_flag_np
()
- This function is described in
acl_add_flag_np(3),
and may be used to add flags to a flagset.
acl_add_perm
()
- This function is described in
acl_add_perm(3), and
may be used to add permissions to a permission set.
acl_calc_mask
()
- This function is described in
acl_calc_mask(3), and
may be used to calculate and set the permissions associated with the
ACL_MASK
entry.
acl_clear_flags_np
()
- This function is described in
acl_clear_flags_np(3),
and may be used to clear all flags from a flagset.
acl_clear_perms
()
- This function is described in
acl_clear_perms(3),
and may be used to clear all permissions from a permission set.
acl_copy_entry
()
- This function is described in
acl_copy_entry(3),
and may be used to copy the contents of an ACL entry.
acl_create_entry
(),
acl_create_entry_np
()
- These functions are described in
acl_create_entry(3),
and may be used to create an empty entry in an ACL.
acl_delete_def_file
(),
acl_delete_def_link_np
(),
acl_delete_fd_np
(),
acl_delete_file_np
(),
acl_delete_link_np
()
- These functions are described in
acl_delete(3), and may
be used to delete ACLs from file system objects.
acl_delete_entry
(),
acl_delete_entry_np
(),
- This functions are described in
acl_delete_entry(3),
and may be used to delete an entry from an ACL.
acl_delete_flag_np
()
- This function is described in
acl_delete_flag_np(3),
and may be used to delete flags from a flagset.
acl_delete_perm
()
- This function is described in
acl_delete_perm(3),
and may be used to delete permissions from a permset.
acl_dup
()
- This function is described in
acl_dup(3), and may be used
to duplicate an ACL structure.
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 or NFSv4 semantics.
acl_get_brand_np
()
- This function is described in
acl_get_brand_np(3)
and may be used to determine whether the ACL has POSIX.1e or NFSv4
semantics.
acl_get_entry
()
- This function is described in
acl_get_entry(3), and
may be used to retrieve a designated ACL entry from an ACL.
acl_get_fd
(),
acl_get_fd_np
(),
acl_get_file
(),
acl_get_link_np
()
- These functions are described in
acl_get(3), and may be used
to retrieve ACLs from file system objects.
acl_get_entry_type_np
()
- This function is described in
acl_get_entry_type_np(3),
and may be used to retrieve an ACL type from an ACL entry.
acl_get_flagset_np
()
- This function is described in
acl_get_flagset_np(3),
and may be used to retrieve a flagset from an ACL entry.
acl_get_permset
()
- This function is described in
acl_get_permset(3),
and may be used to retrieve a permset from an ACL entry.
acl_get_qualifier
()
- This function is described in
acl_get_qualifier(3),
and may be used to retrieve the qualifier from an ACL entry.
acl_get_tag_type
()
- This function is described in
acl_get_tag_type(3),
and may be used to retrieve the tag type from an ACL entry.
acl_init
()
- This function is described in
acl_init(3), and may be
used to allocate a fresh (empty) ACL structure.
acl_is_trivial_np
()
- This function is described in
acl_is_trivial_np(3),
and may be used to find out whether ACL is trivial.
acl_set_fd
(),
acl_set_fd_np
(),
acl_set_file
(),
acl_set_link_np
()
- These functions are described in
acl_set(3), and may be used
to assign an ACL to a file system object.
acl_set_entry_type_np
()
- This function is described in
acl_set_entry_type_np(3),
and may be used to set the ACL type of an ACL entry.
acl_set_flagset_np
()
- This function is described in
acl_set_flagset_np(3),
and may be used to set the flags of an ACL entry from a flagset.
acl_set_permset
()
- This function is described in
acl_set_permset(3),
and may be used to set the permissions of an ACL entry from a
permset.
acl_set_qualifier
()
- This function is described in
acl_set_qualifier(3),
and may be used to set the qualifier of an ACL.
acl_set_tag_type
()
- This function is described in
acl_set_tag_type(3),
and may be used to set the tag type of an ACL.
acl_strip_np
()
- This function is described in
acl_strip_np(3), and
may be used to remove extended entries from an ACL.
acl_to_text
(),
acl_to_text_np
()
- These functions are described in
acl_to_text(3), and may
be used to generate a text-form of a POSIX.1e or NFSv4 semantics ACL.
acl_valid
(),
acl_valid_fd_np
(),
acl_valid_file_np
(),
acl_valid_link_np
()
- These 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.
getfacl(1),
setfacl(1),
acl_add_flag_np(3),
acl_add_perm(3),
acl_calc_mask(3),
acl_clear_flags_np(3),
acl_clear_perms(3),
acl_copy_entry(3),
acl_create_entry(3),
acl_delete_entry(3),
acl_delete_flag_np(3),
acl_delete_perm(3),
acl_dup(3),
acl_free(3),
acl_from_text(3),
acl_get(3),
acl_get_brand_np(3),
acl_get_entry_type_np(3),
acl_get_flagset_np(3),
acl_get_permset(3),
acl_get_qualifier(3),
acl_get_tag_type(3),
acl_init(3),
acl_is_trivial_np(3),
acl_set(3),
acl_set_entry_type_np(3),
acl_set_flagset_np(3),
acl_set_permset(3),
acl_set_qualifier(3),
acl_set_tag_type(3),
acl_strip_np(3),
acl_to_text(3),
acl_valid(3),
posix1e(3),
acl(9)
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.
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.
Both NFSv4 and POSIX.1e ACL support were introduced in NetBSD
10.0. Support was ported from FreeBSD and is
based on extended attributes for the UFS and UFS2 file systems.
The getfacl(1) and
setfacl(1) utilities describe
the user tools that permit direct manipulation of complete file ACLs.