Toby Ovod-Everett > Win32-Security > Win32::Security::ACE

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NAME ^

Win32::Security::ACE - Win32 ACE manipulation

SYNOPSIS ^

        use Win32::Security::ACE;

        my $ace = Win32::Security::ACE->new('FILE', $rawace);
        my $ace2 = Win32::Security::ACE->new('FILE', $type, $flags, $mask, $trustee);
        my $ace3 = Win32::Security::ACE->new('FILE', $type, $flags, $mask, $sid);

        $ace->objectType();

        $ace->aceType();
        $ace->aceFlags();
        $ace->accessMask();
        $ace->sid();
        $ace->trustee();

        $ace->explainAceFlags();
        $ace->explainAccessMask();

        $ace->rawAce();
        $ace->rawAceType();
        $ace->rawAceFlags();
        $ace->rawAccessMask();

        my(@container_inheritable_aces) = $ace->inheritable('CONTAINER');
        my(@object_inheritable_aces) = $ace->inheritable('OBJECT');

DESCRIPTION ^

Win32::Security::ACE and its subclasses provide an interface for interacting with Win32 ACEs (Access Control Entries). The subclasses allow for variation in mask behavior (different privileges apply to files than apply to registry keys and so forth) and for variation in ACE behavior (OBJECT_ACE_TYPE varieties).

Win32::Security::ACE uses the flyweight design pattern in conjunction with an in-memory cache of demand-computed properties. The result is that parsing of ACEs is only done once for each unique ACE, and that the ACE objects themselves are very lightweight. Double-indirection is used in the ACE objects to provide for mutability without invalidating the cache.

Installation instructions

This installs as part of Win32-Security. See Win32::Security::NamedObject for more information.

It depends upon Class::Prototyped and Data::BitMask, which should be installable via PPM or available on CPAN. It also depends upon Win32::Security::Raw and Win32::Security::SID , which are installed as part of Win32-Security.

ARCHITECTURE ^

Win32::Security::ACE uses some OO tricks to boost performance and clean up the design. Here's a quick overview of the internal architecture, should you care! It is possible to use Win32::Security::ACE objects without understanding or reading any of this, because the public interface is designed to hide as much of the details as possible. After all, that's the point of OO design. If, however, you want to boost performance or to muck about in the internals, it's worth understanding how things were done.

Class Structure

Win32::Security::ACE uses multiple inheritance in a diamond pattern. This was deemed to be the best solution to an otherwise ugly situation.

Each ACE comes in a variety of forms - six at current count - and some of these forms (notably the OBJECT_ACE_TYPE varieties) use a different internal structure. While the code doesn't currently support the OBJECT_ACE_TYPE varieties, it was important to architect the code to support that for future expansion.

Each ACE can be applied to a wide variety of Named Objects as well. For better or worse, the behavior of the Access Masks for Named Objects varies according to the type of Named Object (think files vs. Active Directory objects). This behavioral variation extends to the realm of applying inherited GENERIC Access Masks to objects.

Much internal debate (I love arguing with myself) was expended over attempting to reconcile these two orthogonal forms of variation without multiple inheritance before deciding to just bite the bullet.

The obvious ugliness is that number_of_ace_types * number_of_object_types classes have to be created. Luckily I'd already made Win32::Security::Recursor dependent upon Class::Prototyped, so it was deemed acceptable to make Win32::Security::ACE and Win32::Security::ACL dependent upon it as well.

With that in mind, the base class hierarchy looks like this:

The concrete classes are named Win32::Security::ACE::$objectType::$aceType (i.e. Win32::Security::ACE::SE_FILE_OBJECT::ACCESS_ALLOWED_ACE_TYPE) and inherit from both the Win32::Security::ACE::$objectType and Win32::Security::ACE::$aceType classes in that order. The concrete classes are automatically generated using Class::Prototyped.

Flyweight Objects w/ Cached Demand-Computed Properties

On the typical computer systems, there are very few unique ACEs. There may be hundred or thousands, but usually there are orders of magnitude fewer ACEs than there are objects to which they are applied. In order to reduce the computation involved in analyzing them, Win32::Security::ACE caches all the information computed about each ACE in a central store (actually, multiple central stores - one for each Named Object type) based on the binary form (rawAce). The object returned by a call to new is a reference to a reference to the hash for that rawAce in the central store. Because it isn't a direct reference to the hash, it is possible to switch which hash the object points to on the fly. This allows the Win32::Security::ACE objects to be mutable while maintaining the immutability of the central store. It also makes each individual Win32::Security::ACE object incredibly lightweight, since it is only composed of a single blessed scalar. The properties are computed as needed, but the results are cached in the central store.

For instance, once explainAccessMask has been computed for a given rawAce, it can be found from the object as $$self->{explainAccessMask}. This should be used with care, although in some instances it is possible to reduce the number of method calls (should this be necessary for performance reasons) by making calls like so:

    $$ace->{explainAccessMask} || $ace->explainAccessMask();

That provides a fail-safe should the explainAccessMask value have not yet been computed while eliminating the method call if it has been.

In order to defend against accidental manipulation, return values from the calls (although not from the direct access, obviously) are deep-copied one layer deep. That means that the results of $ace->explainAccessMask() can be safely manipulated without harming the ACE, but that the results of $$ace->{explainAccessMask} should be treated as read-only. Win32::Security::ACE objects returned are cloned (using inlined code to reduce the performance hit). The values returned from the /^dbm.*/ calls are not cloned, however, so be careful there.

Method Reference ^

new

Creates a new Win32::Security::ACE object.

The various calling forms are:

Note that when using $objectType and $aceType in the package name, the values need to be canonicalized (i.e. SE_FILE_OBJECT, not the alias FILE). Also note that the $aceType is extractable from the $rawAce. When those values are passed as part of the parameter list, any of the valid aliases are permitted. If the $objectType or $aceType has already been canonicalized, improved performance can be realized by making the call on the more fully-qualified package name and thus avoiding the calls to redo the canonicalization. It is important that if $aceType is specified for a $rawAce that the values match. The backslash preceding the final :: in the final two class name calls is a fast way of ensuring that $objectType rather than $objectType:: is the interpolated variable name.

For ACCESS_ALLOWED_ACE_TYPE, ACCESS_DENIED_ACE_TYPE, and SYSTEM_AUDIT_ACE_TYPE, the @aceParams array consists of aceFlags, accessMask, and either the sid or trustee. The aceType, aceFlags, and accessMask can be passed as integers or in any acceptable format for Data::BitMask (i.e. '|' separated constants in a string, an anonmous array of constants, or an anonymous hash of constants). See Data::BitMask::buildRawMask for more information.

clone

This creates a new Win32::Security::ACE object that is identical in all forms, except for identity, to the original object. Because of the flyweight design pattern, this is a very inexpensive operation. However, should you wish to avoid the overhead of a method call, you can inline the code like so:

    bless(\(my $o = ${$obj}), ref($obj));

Basically, it derefences the scalar reference, assigns it to a temporary lexical, creates a reference to that, and then blesses it into the original package. Nifty, eh? Syntax stolen (with a few modifications) from Data::Dumper output.

dump

This returns a dump of the Win32::Security::ACL object in a format useful for debugging.

rawAce

Returns the binary string form of the ACE. If passed a value, changes the binary string form of the ACE to the new value and returns $self.

dbmAceType

Returns the Data::BitMask object for interacting with ACE Types. Standard Win32 constants for ACE_TYPE are supported along with several aliases. The standard ACE_TYPE constants are ACCESS_ALLOWED_ACE_TYPE, ACCESS_DENIED_ACE_TYPE, SYSTEM_AUDIT_ACE_TYPE, SYSTEM_ALARM_ACE_TYPE, ACCESS_ALLOWED_COMPOUND_ACE_TYPE, ACCESS_ALLOWED_OBJECT_ACE_TYPE, ACCESS_DENIED_OBJECT_ACE_TYPE, SYSTEM_AUDIT_OBJECT_ACE_TYPE, SYSTEM_ALARM_OBJECT_ACE_TYPE, ACCESS_MIN_MS_ACE_TYPE, ACCESS_MAX_MS_V2_ACE_TYPE, ACCESS_MAX_MS_V3_ACE_TYPE, ACCESS_MIN_MS_OBJECT_ACE_TYPE, ACCESS_MAX_MS_OBJECT_ACE_TYPE, ACCESS_MAX_MS_V4_ACE_TYPE, and ACCESS_MAX_MS_ACE_TYPE.

The aliases are:

dbmObjectType

Returns the Data::BitMask object for interacting with Named Object Types. The standard Object Types are SE_UNKNOWN_OBJECT_TYPE, SE_FILE_OBJECT, SE_SERVICE, SE_PRINTER, SE_REGISTRY_KEY, SE_LMSHARE, SE_KERNEL_OBJECT, SE_WINDOW_OBJECT, SE_DS_OBJECT, SE_DS_OBJECT_ALL, and SE_PROVIDER_DEFINED_OBJECT.

There are a number of aliases as well:

rawAceType

Returns the integer form of the ACE Type. Useful for equality checks with other calls to rawAceType.

aceType

Returns the Data::BitMask::explain_const form of the ACE Type (i.e. a string constant, such as 'ACCESS_ALLOWED_ACE_TYPE' or 'ACCESS_DENIED_ACE_TYPE').

dbmAceFlags

Returns the Data::BitMask object for interacting with ACE Flags. Standard Win32 constants for ACE_FLAGS are supported along with some aliases. The standard ACE_FLAGS constants are OBJECT_INHERIT_ACE, CONTAINER_INHERIT_ACE, NO_PROPAGATE_INHERIT_ACE, INHERIT_ONLY_ACE, INHERITED_ACE, SUCCESSFUL_ACCESS_ACE_FLAG, and FAILED_ACCESS_ACE_FLAG.

The aliases are:

rawAceFlags

Returns the integer form of the ACE Flags. Useful for equality checks with other calls to rawAceFlags.

If called with a passed parameter, mutates the ACE to that new aceFlags value. All forms of aceFlags access accept all forms as parameters when used as a setter.

aceFlags

Returns the Data::BitMask::break_mask form of the ACE Flags (i.e. a hash containing all matching constants for the Flags mask of the ACE).

If called with a passed parameter, mutates the ACE to that new aceFlags value. All forms of aceFlags access accept all forms as parameters when used as a setter.

explainAceFlags

Returns the Data::BitMask::explain_mask form of the ACE Flags (i.e. a hash containing a set of constants sufficient to recreate and explain the flags mask of the ACE).

If called with a passed parameter, mutates the ACE to that new aceFlags value. All forms of aceFlags access accept all forms as parameters when used as a setter.

sid

Returns the SID in binary form. Useful for equality checks with other SIDs.

If called with a passed parameter, mutates the ACE to that new SID. Both sid and trustee accepts SID and Trustee names as passed parameters when used as a setter.

trustee

Returns the Trustee for the SID as generated by Win32::Security::SID::ConvertSidToName.

If called with a passed parameter, mutates the ACE to that new trustee. Both sid and trustee accepts SID and Trustee names as passed parameters when used as a setter.

buildRawAce

Creates a binary string ACE from parameters. This should always be called on a full class (i.e. Win32::Security::ACE::$objectType::$aceType). Each implementation accepts different parameters.

ACCESS_ALLOWED_ACE_TYPE, ACCESS_DENIED_ACE_TYPE, SYSTEM_AUDIT_ACE_TYPE

These accept AceFlags, AccessMask, and either Sid or Trustee.

buildRawAceNamed

Creates a binary string ACE from named parameters. This should always be called on a full class (i.e. Win32::Security::ACE::$objectType::$aceType) or on an existing ACE. Each implementation accepts different parameters. If called on an existing ACE, missing parameters will be supplied from the existing ACE. As an example, to create a new rawAce value based on an existing ACE, but with the Access Mask set to READ:

    $ace->buildRawAceNamed(accessMask => 'READ');
ACCESS_ALLOWED_ACE_TYPE, ACCESS_DENIED_ACE_TYPE, SYSTEM_AUDIT_ACE_TYPE

These accept aceFlags, accessMask, and trustee (as either a SID or Trustee name). The names are case-sensitive.

inheritable

Accepts a type (either 'OBJECT' or 'CONTAINER') and calls inheritable_OBJECT or inheritable_CONTAINER as appropriate.

Those methods return the list of ACEs that would be inherited by a newly created child OBJECT or CONTAINER if the parent has this ACE. In most cases, there will be either none (non-inheritable ACE) or one (inheritable ACE) ACEs returned. In the case of ACEs that use GENERIC_.* permissions or that use CREATOR OWNER, there may be two ACEs returned - one to implement the permissions on that specific container, and the other to perpetuate the inheritable ACE. In the case of an CREATOR OWNER ACE, the ACE that implements the actual permissions on the container will be given a null SID.

The methods take care of checking the flags to determine whether the ACE should be inherited as well as adjusting the flags for any inherited ACE appropriately.

Note that it is not sufficient to simply concatenate the ACEs of a DACL to generate the inheritable DACL because Win2K and WinXP remove occluded permissions (for instance, if an container has an inherited permission granting READ access to Domain Users and someone grants explicit fully-inheritable FULL access to Domain Users to that container, child objects will not receive the inherited READ access because it is fully occluded by the also inherited FULL access).

inheritable_CONTAINER

See inheritable for an explanation.

inheritable_OBJECT

See inheritable for an explanation.

objectType

Returns the type of object to which the ACE is or should be attached.

dbmAccessMask

Returns the Data::BitMask object for interacting with the Access Mask. The default is Win32 constants for Standard Rights. Some of the Object Types define additional rights. The Standard Rights are DELETE, READ_CONTROL, WRITE_DAC, WRITE_OWNER, SYNCHRONIZE, STANDARD_RIGHTS_REQUIRED, STANDARD_RIGHTS_READ, STANDARD_RIGHTS_WRITE, STANDARD_RIGHTS_EXECUTE, STANDARD_RIGHTS_ALL, SPECIFIC_RIGHTS_ALL, ACCESS_SYSTEM_SECURITY, MAXIMUM_ALLOWED, GENERIC_READ, GENERIC_WRITE, GENERIC_EXECUTE, and GENERIC_ALL.

SE_FILE_OBJECT

Win32 constants for both Standard Rights and File Rights, along with a number of aliases. The File Rights are FILE_READ_DATA, FILE_LIST_DIRECTORY, FILE_WRITE_DATA, FILE_ADD_FILE, FILE_APPEND_DATA, FILE_ADD_SUBDIRECTORY, FILE_CREATE_PIPE_INSTANCE, FILE_READ_EA, FILE_WRITE_EA, FILE_EXECUTE, FILE_TRAVERSE, FILE_DELETE_CHILD, FILE_READ_ATTRIBUTES, FILE_WRITE_ATTRIBUTES, FILE_ALL_ACCESS, FILE_GENERIC_READ, FILE_GENERIC_WRITE, and FILE_GENERIC_EXECUTE.

The aliases are:

  • FULL or F (STANDARD_RIGHTS_ALL | FILE_GENERIC_READ |FILE_GENERIC_WRITE | FILE_GENERIC_EXECUTE | FILE_DELETE_CHILD)
  • MODIFY or M (FILE_GENERIC_READ | FILE_GENERIC_WRITE | FILE_GENERIC_EXECUTE | DELETE)
  • READ or R (FILE_GENERIC_READ | FILE_GENERIC_EXECUTE)
SE_REGISTRY_KEY

Win32 constants for Registry Key Rights. The Registry Key Rights are KEY_QUERY_VALUE, KEY_SET_VALUE, KEY_CREATE_SUB_KEY, KEY_ENUMERATE_SUB_KEYS, KEY_NOTIFY, KEY_CREATE_LINK, KEY_WOW64_64, KEY_WOW64_32KEY, KEY_READ, KEY_WRITE, KEY_EXECUTE, and KEY_ALL_ACCESS.

SE_REGISTRY_KEY support is still under development.

rawAccessMask

Returns the integer form of the Access Mask. Useful for equality checks and bitwise comparisons with other calls to rawmask.

If called with a passed parameter, mutates the ACE to that new accessMask value. All forms of accessMask access accept all forms as parameters when used as a setter.

accessMask

Returns the Data::BitMask::break_mask form of the Access Mask (i.e. a hash containing all matching constants for the Access Mask of the ACE).

If called with a passed parameter, mutates the ACE to that new accessMask value. All forms of accessMask access accept all forms as parameters when used as a setter.

explainAccessMask

Returns the Data::BitMask::explain_mask form of the Access Mask (i.e. a hash containing a set of constants sufficient to recreate and explain the Access Mask of the ACE).

If called with a passed parameter, mutates the ACE to that new accessMask value. All forms of accessMask access accept all forms as parameters when used as a setter.

cleansedAccessMask

This returns an Access Mask cleansed of GENERIC_ permissions for the ACE in question. Some of the Object Types define special behavior for this.

SE_FILE_OBJECT

Clears the GENERIC_READ, GENERIC_WRITE, GENERIC_EXECUTE, and GENERIC_ALL bits and replaces them with the constants FILE_GENERIC_READ, FILE_GENERIC_WRITE, FILE_GENERIC_EXECUTE, and FULL respectively. This is required for correctly interpreting inheritance of some INHERIT_ONLY_ACE ACEs.

AUTHOR ^

Toby Ovod-Everett, toby@ovod-everett.org

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