freebsd-skq/share/man/man9/acl.9

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.Dd December 23, 1999
.Os
.Dt ACL 9
.Sh NAME
.Nm acl
.Nd virtual filesystem access control lists
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.In sys/acl.h
.Pp
In the kernel configuration file:
.Cd "options UFS_ACL"
.Sh DESCRIPTION
Access control lists, or ACLs,
allow fine-grained specification of rights
for vnodes representing files and directories.
However, as there are a plethora of filesystems with differing ACL semantics,
the vnode interface is aware only of the syntax of ACLs,
relying on the underlying filesystem to implement the details.
Depending on the underlying filesystem, each file or directory
may have zero or more ACLs associated with it, named using the
.Fa type
field of the appropriate vnode ACL calls:
.Xr VOP_ACLCHECK 9 ,
.Xr VOP_GETACL 9 ,
and
.Xr VOP_SETACL 9 .
.Pp
Currently, each ACL is represented in-kernel by a fixed-size
.Vt acl
structure, defined as follows:
.Bd -literal -offset indent
struct acl {
        int                     acl_cnt;
        struct acl_entry        acl_entry[ACL_MAX_ENTRIES];
};
.Ed
.Pp
An ACL is constructed from a fixed size array of ACL entries,
each of which consists of a set of permissions, principal namespace,
and principal identifier.
.Pp
Each individual ACL entry is of the type
.Vt acl_entry_t ,
which is a structure with the following members:
.Bl -tag -width 2n
.It Vt acl_tag_t Va ae_tag
The following is a list of definitions of ACL types
to be set in
.Va ae_tag :
.Pp
.Bl -tag -width ".Dv ACL_UNDEFINED_FIELD" -offset indent -compact
.It Dv ACL_UNDEFINED_FIELD
Undefined ACL type.
.It Dv ACL_USER_OBJ
Discretionary access rights for processes whose effective user ID
matches the user ID of the file's owner.
.It Dv ACL_USER
Discretionary access rights for processes whose effective user ID
matches the ACL entry qualifier.
.It Dv ACL_GROUP_OBJ
Discretionary access rights for processes whose effective group ID
or any supplemental groups
match the group ID of the file's owner.
.It Dv ACL_GROUP
Discretionary access rights for processes whose effective group ID
or any supplemental groups
match the ACL entry qualifier.
.It Dv ACL_MASK
The maximum discretionary access rights that can be granted
to a process in the file group class.
.It Dv ACL_OTHER
Discretionary access rights for processes not covered by any other ACL
entry.
.It Dv ACL_OTHER_OBJ
Same as
.Dv ACL_OTHER .
Each ACL entry must contain exactly one
.Dv ACL_USER_OBJ ,
one
.Dv ACL_GROUP_OBJ ,
and one
.Dv ACL_OTHER .
If any of
.Dv ACL_USER ,
.Dv ACL_GROUP ,
or
.Dv ACL_OTHER
are present, then exactly one
.Dv ACL_MASK
entry should be present.
.El
.It Vt uid_t Va ae_id
The ID of user for whom this ACL describes access permissions.
.It Vt acl_perm_t Va ae_perm
This field defines what kind of access the process matching this ACL has
for accessing the associated file.
.Bl -tag -width ".Dv ACL_POSIX1E_BITS"
.It Dv ACL_EXECUTE
The process may execute the associated file.
.It Dv ACL_WRITE
The process may write to the associated file.
.It Dv ACL_READ
The process may read from the associated file.
.It Dv ACL_PERM_NONE
The process has no read, write or execute permissions
to the associated file.
.El
.El
.Pp
.Sh IMPLEMENTATION NOTES
.Bd -literal
typedef mode_t  *acl_permset_t;

/* internal ACL structure */
struct acl {
        int                     acl_cnt;
        struct acl_entry        acl_entry[ACL_MAX_ENTRIES];
};

/* external ACL structure */
struct acl_t_struct {
        struct acl              ats_acl;
        int                     ats_cur_entry;
};
typedef struct acl_t_struct *acl_t;

/*
 * Possible valid values for ae_tag field.
 */
#define ACL_UNDEFINED_TAG       0x00000000
#define ACL_USER_OBJ            0x00000001
#define ACL_USER                0x00000002
#define ACL_GROUP_OBJ           0x00000004
#define ACL_GROUP               0x00000008
#define ACL_MASK                0x00000010
#define ACL_OTHER               0x00000020
#define ACL_OTHER_OBJ           ACL_OTHER

/*
 * Possible valid values for acl_type_t arguments.
 */
#define ACL_TYPE_ACCESS         0x00000000
#define ACL_TYPE_DEFAULT        0x00000001
#define ACL_TYPE_AFS            0x00000002
#define ACL_TYPE_CODA           0x00000003
#define ACL_TYPE_NTFS           0x00000004
#define ACL_TYPE_NWFS           0x00000005

/*
 * Possible flags in ae_perm field.
 */
#define ACL_EXECUTE             0x0001
#define ACL_WRITE               0x0002
#define ACL_READ                0x0004
#define ACL_PERM_NONE           0x0000
#define ACL_PERM_BITS           (ACL_EXECUTE | ACL_WRITE | ACL_READ)
#define ACL_POSIX1E_BITS        (ACL_EXECUTE | ACL_WRITE | ACL_READ)

/*
 * Possible entry_id values for acl_get_entry()
 */
#define ACL_FIRST_ENTRY         0
#define ACL_NEXT_ENTRY          1

/*
 * Undefined value in ae_id field
 */
#define ACL_UNDEFINED_ID        ((uid_t)-1)
.Ed
.Sh SEE ALSO
.Xr acl 3 ,
.Xr vaccess_acl_posix1e 9 ,
.Xr VFS 9 ,
.Xr vnaccess 9 ,
.Xr VOP_ACLCHECK 9 ,
.Xr VOP_GETACL 9 ,
.Xr VOP_SETACL 9
.Sh AUTHORS
This man page was written by
.An Robert Watson .