ACL(9) MidnightBSD Kernel Developer’s Manual ACL(9)

NAME

acl — virtual file system access control lists

SYNOPSIS

#include <sys/param.h>
#include <sys/vnode.h>
#include <sys/acl.h>

In the kernel configuration file:

options UFS_ACL

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 file systems with differing ACL semantics, the vnode interface is aware only of the syntax of ACLs, relying on the underlying file system to implement the details. Depending on the underlying file system, each file or directory may have zero or more ACLs associated with it, named using the type field of the appropriate vnode ACL calls: VOP_ACLCHECK(9), VOP_GETACL(9), and VOP_SETACL(9).

Currently, each ACL is represented in-kernel by a fixed-size acl structure, defined as follows:

struct acl {
int acl_cnt;
struct acl_entry acl_entry[ACL_MAX_ENTRIES];
};

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.

Each individual ACL entry is of the type acl_entry_t, which is a structure with the following members:

acl_tag_t ae_tag

The following is a list of definitions of ACL types to be set in ae_tag:

ACL_UNDEFINED_FIELD

Undefined ACL type.

ACL_USER_OBJ

Discretionary access rights for processes whose effective user ID matches the user ID of the file’s owner.

ACL_USER

Discretionary access rights for processes whose effective user ID matches the ACL entry qualifier.

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.

ACL_GROUP

Discretionary access rights for processes whose effective group ID or any supplemental groups match the ACL entry qualifier.

ACL_MASK

The maximum discretionary access rights that can be granted to a process in the file group class.

ACL_OTHER

Discretionary access rights for processes not covered by any other ACL entry.

ACL_OTHER_OBJ

Same as ACL_OTHER. Each ACL entry must contain exactly one ACL_USER_OBJ, one ACL_GROUP_OBJ, and one ACL_OTHER. If any of ACL_USER, ACL_GROUP, or ACL_OTHER are present, then exactly one ACL_MASK entry should be present.

uid_t ae_id

The ID of user for whom this ACL describes access permissions.

acl_perm_t ae_perm

This field defines what kind of access the process matching this ACL has for accessing the associated file.

ACL_EXECUTE

The process may execute the associated file.

ACL_WRITE

The process may write to the associated file.

ACL_READ

The process may read from the associated file.

ACL_PERM_NONE

The process has no read, write or execute permissions to the associated file.

IMPLEMENTATION NOTES

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)

SEE ALSO

acl(3), vaccess_acl_posix1e(9), VFS(9), vnaccess(9), VOP_ACLCHECK(9), VOP_GETACL(9), VOP_SETACL(9)

AUTHORS

This manual page was written by Robert Watson.

MidnightBSD 0.3 December 23, 1999 MidnightBSD 0.3