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.Dd May 8, 2023
.Dt ACL 3
.Os
.Sh NAME
.Nm acl
.Nd introduction to the POSIX.1e/NFSv4 ACL security API
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/acl.h
.Sh DESCRIPTION
.Fx
permits file systems to export Access Control Lists via the VFS, and
provides a library for userland access to and manipulation of these ACLs.
.Fx
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.
.Pp
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
.Fx .
.Pp
Available functions, sorted by behavior, include:
.Bl -tag -width indent
.It Fn acl_add_flag_np
This function is described in
.Xr acl_add_flag_np 3 ,
and may be used to add flags to a flagset.
.It Fn acl_add_perm
This function is described in
.Xr acl_add_perm 3 ,
and may be used to add permissions to a permission set.
.It Fn acl_calc_mask
This function is described in
.Xr acl_calc_mask 3 ,
and may be used to calculate and set the permissions associated with
the
.Dv ACL_MASK
entry.
.It Fn acl_clear_flags_np
This function is described in
.Xr acl_clear_flags_np 3 ,
and may be used to clear all flags from a flagset.
.It Fn acl_clear_perms
This function is described in
.Xr acl_clear_perms 3 ,
and may be used to clear all permissions from a permission set.
.It Fn acl_copy_entry
This function is described in
.Xr acl_copy_entry 3 ,
and may be used to copy the contents of an ACL entry.
.It Xo
.Fn acl_create_entry ,
.Fn acl_create_entry_np
.Xc
These functions are described in
.Xr acl_create_entry 3 ,
and may be used to create an empty entry in an ACL.
.It Xo
.Fn acl_delete_def_file ,
.Fn acl_delete_def_link_np ,
.Fn acl_delete_fd_np ,
.Fn acl_delete_file_np ,
.Fn acl_delete_link_np
.Xc
These functions are described in
.Xr acl_delete 3 ,
and may be used to delete ACLs from file system objects.
.It Xo
.Fn acl_delete_entry ,
.Fn acl_delete_entry_np ,
.Xc
This functions are described in
.Xr acl_delete_entry 3 ,
and may be used to delete an entry from an ACL.
.It Fn acl_delete_flag_np
This function is described in
.Xr acl_delete_flag_np 3 ,
and may be used to delete flags from a flagset.
.It Fn acl_delete_perm
This function is described in
.Xr acl_delete_perm 3 ,
and may be used to delete permissions from a permset.
.It Fn acl_dup
This function is described in
.Xr acl_dup 3 ,
and may be used to duplicate an ACL structure.
.It Fn acl_free
This function is described in
.Xr acl_free 3 ,
and may be used to free userland working ACL storage.
.It Fn acl_from_text
This function is described in
.Xr 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.
.It Fn acl_get_brand_np
This function is described in
.Xr acl_get_brand_np 3
and may be used to determine whether the ACL has POSIX.1e or NFSv4 semantics.
.It Fn acl_get_entry
This function is described in
.Xr acl_get_entry 3 ,
and may be used to retrieve a designated ACL entry from an ACL.
.It Xo
.Fn acl_get_fd ,
.Fn acl_get_fd_np ,
.Fn acl_get_file ,
.Fn acl_get_link_np
.Xc
These functions are described in
.Xr acl_get 3 ,
and may be used to retrieve ACLs from file system objects.
.It Fn acl_get_entry_type_np
This function is described in
.Xr acl_get_entry_type_np 3 ,
and may be used to retrieve an ACL type from an ACL entry.
.It Fn acl_get_flagset_np
This function is described in
.Xr acl_get_flagset_np 3 ,
and may be used to retrieve a flagset from an ACL entry.
.It Fn acl_get_perm_np
This function is described in
.Xr acl_get_perm_np 3 ,
and may be used to check if a permission is set in a permset.
.It Fn acl_get_permset
This function is described in
.Xr acl_get_permset 3 ,
and may be used to retrieve a permset from an ACL entry.
.It Fn acl_get_qualifier
This function is described in
.Xr acl_get_qualifier 3 ,
and may be used to retrieve the qualifier from an ACL entry.
.It Fn acl_get_tag_type
This function is described in
.Xr acl_get_tag_type 3 ,
and may be used to retrieve the tag type from an ACL entry.
.It Fn acl_init
This function is described in
.Xr acl_init 3 ,
and may be used to allocate a fresh (empty) ACL structure.
.It Fn acl_is_trivial_np
This function is described in
.Xr acl_is_trivial_np 3 ,
and may be used to find out whether ACL is trivial.
.It Xo
.Fn acl_set_fd ,
.Fn acl_set_fd_np ,
.Fn acl_set_file ,
.Fn acl_set_link_np
.Xc
These functions are described in
.Xr acl_set 3 ,
and may be used to assign an ACL to a file system object.
.It Fn acl_set_entry_type_np
This function is described in
.Xr acl_set_entry_type_np 3 ,
and may be used to set the ACL type of an ACL entry.
.It Fn acl_set_flagset_np
This function is described in
.Xr acl_set_flagset_np 3 ,
and may be used to set the flags of an ACL entry from a flagset.
.It Fn acl_set_permset
This function is described in
.Xr acl_set_permset 3 ,
and may be used to set the permissions of an ACL entry from a permset.
.It Fn acl_set_qualifier
This function is described in
.Xr acl_set_qualifier 3 ,
and may be used to set the qualifier of an ACL.
.It Fn acl_set_tag_type
This function is described in
.Xr acl_set_tag_type 3 ,
and may be used to set the tag type of an ACL.
.It Fn acl_strip_np
This function is described in
.Xr acl_strip_np 3 ,
and may be used to remove extended entries from an ACL.
.It Xo
.Fn acl_to_text ,
.Fn acl_to_text_np
.Xc
These functions are described in
.Xr acl_to_text 3 ,
and may be used to generate a text-form of a POSIX.1e or NFSv4 semantics ACL.
.It Xo
.Fn acl_valid ,
.Fn acl_valid_fd_np ,
.Fn acl_valid_file_np ,
.Fn acl_valid_link_np
.Xc
These functions are described in
.Xr 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.
.El
.Pp
Documentation of the internal kernel interfaces backing these calls may
be found in
.Xr 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.
.Sh SEE ALSO
.Xr getfacl 1 ,
.Xr setfacl 1 ,
.Xr acl_add_flag_np 3 ,
.Xr acl_add_perm 3 ,
.Xr acl_calc_mask 3 ,
.Xr acl_clear_flags_np 3 ,
.Xr acl_clear_perms 3 ,
.Xr acl_copy_entry 3 ,
.Xr acl_create_entry 3 ,
.Xr acl_delete_entry 3 ,
.Xr acl_delete_flag_np 3 ,
.Xr acl_delete_perm 3 ,
.Xr acl_dup 3 ,
.Xr acl_free 3 ,
.Xr acl_from_text 3 ,
.Xr acl_get 3 ,
.Xr acl_get_brand_np 3 ,
.Xr acl_get_entry_type_np 3 ,
.Xr acl_get_flagset_np 3 ,
.Xr acl_get_perm_np 3 ,
.Xr acl_get_permset 3 ,
.Xr acl_get_qualifier 3 ,
.Xr acl_get_tag_type 3 ,
.Xr acl_init 3 ,
.Xr acl_is_trivial_np 3 ,
.Xr acl_set 3 ,
.Xr acl_set_entry_type_np 3 ,
.Xr acl_set_flagset_np 3 ,
.Xr acl_set_permset 3 ,
.Xr acl_set_qualifier 3 ,
.Xr acl_set_tag_type 3 ,
.Xr acl_strip_np 3 ,
.Xr acl_to_text 3 ,
.Xr acl_valid 3 ,
.Xr posix1e 3 ,
.Xr acl 9
.Sh STANDARDS
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.
.Pp
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
.Fx
POSIX.1e implementation page for more information.
.Sh HISTORY
POSIX.1e support was introduced in
.Fx 4.0 ;
.Fx 5.0
was the first version to include a complete ACL implementation based
on extended attributes for the UFS and UFS2 file systems.
NFSv4 ACL support was introduced in
.Fx 8.0 .
.Pp
The
.Xr getfacl 1
and
.Xr setfacl 1
utilities describe the user tools that permit direct manipulation of complete
file ACLs.
.Sh AUTHORS
.An Robert N M Watson