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 {
            unsigned int            acl_maxcnt;
            unsigned int            acl_cnt;
            int                     acl_spare[4];
            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. In this implementation, the acl_maxcnt field is always set to ACL_MAX_ENTRIES.

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. This is only valid for POSIX.1e ACLs.
    ACL_OTHER
        Discretionary access rights for processes not covered by any other ACL entry. This is only valid for POSIX.1e ACLs.
    ACL_OTHER_OBJ
        Same as ACL_OTHER.
    ACL_EVERYONE
        Discretionary access rights for all users. This is only valid for NFSv4 ACLs.

    Each POSIX.1e ACL 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. For entries other than ACL_USER and ACL_GROUP, this field should be set to ACL_UNDEFINED_ID.

acl_perm_t ae_perm
    This field defines what kind of access the process matching this ACL has for accessing the associated file. For POSIX.1e ACLs, the following are valid:

    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.

    For NFSv4 ACLs, the following are valid:

    ACL_READ_DATA
        The process may read from the associated file.

    ACL_LIST_DIRECTORY
        Same as ACL_READ_DATA.

    ACL_WRITE_DATA
        The process may write to the associated file.

    ACL_ADD_FILE
        Same as ACL_ACL_WRITE_DATA.

    ACL_APPEND_DATA

    ACL_ADD_SUBDIRECTORY
        Same as ACL_APPEND_DATA.

    ACL_READ_NAMED_ATTRS
        Ignored.

    ACL_WRITE_NAMED_ATTRS
        Ignored.

    ACL_EXECUTE
        The process may execute the associated file.

    ACL_DELETE_CHILD

    ACL_READ_ATTRIBUTES

    ACL_WRITE_ATTRIBUTES

    ACL_DELETE

    ACL_READ_ACL

    ACL_WRITE_ACL

    ACL_WRITE_OWNER

    ACL_SYNCHRONIZE
        Ignored.

acl_entry_type_t ae_entry_type
    This field defines the type of NFSv4 ACL entry. It is not used with POSIX.1e ACLs. The following values are valid:

    ACL_ENTRY_TYPE_ALLOW

    ACL_ENTRY_TYPE_DENY

acl_flag_t ae_flags
    This field defines the inheritance flags of NFSv4 ACL entry. It is not used with POSIX.1e ACLs. The following values are valid:

    ACL_ENTRY_FILE_INHERIT

    ACL_ENTRY_DIRECTORY_INHERIT

    ACL_ENTRY_NO_PROPAGATE_INHERIT

    ACL_ENTRY_INHERIT_ONLY

    ACL_ENTRY_INHERITED
    The ACL_ENTRY_INHERITED flag is set on an ACE that has been inherited from its parent. It may also be set programmatically, and is valid on both files and directories.

SEE ALSO
acl(3), genfs(9), genfs_can_access(9), genfs_can_access_acl_nfs4(9), genfs_can_access_acl_posix1e(9), VOP_ACLCHECK(9), VOP_GETACL(9), VOP_SETACL(9)

AUTHORS
This manual page was written by Robert Watson.