24 Repository Resource Security

Overview of Oracle XML DB Resource Security and ACLs

Oracle XML DB maintains object-level security for all resources in Oracle XML DB Repository.

Oracle XML DB uses an access control list (ACL) mechanism to restrict access to any Oracle XML DB resource or database object mapped to the repository. An ACL is a list of access control entries that determine which principals have access to a given resource or resources. ACLs are a standard security mechanism used in Java, Windows NT, and other systems.

Access Control List Concepts

This section describes several access control list (ACL) terms and concepts:

• Principal. An entity that may be granted access control privileges to an Oracle XML DB resource. Oracle XML DB supports the following as principals:

  • Database users

  • Database roles. A database role can be understood as a group; for example, the DBA role represents the group of all database administrators.

  • LDAP users and groups. For details on using LDAP principals see "Integrating Oracle XML DB with LDAP".

  The special principal, dav:owner, corresponds to the owner of the resource being secured. The owner of the resource is one of the properties of the resource. Use of the dav:owner principal allows greater ACL sharing between users, because the owner of the document often has special rights. See Also "Access Privileges".

• Privilege: This is a particular right that can be granted or denied to a principal. Oracle XML DB has a set of system-defined rights (such as READ or UPDATE) that can be referenced in any ACL. Privileges can be granted or denied to the principal dav:owner, that represents the owner of the document, regardless of who the owner is. Privileges can be one of the following:

  • Aggregate (containing other privileges)

  • Atomic (which cannot be subdivided)

  Aggregate privileges are a naming convenience to simplify usability when the number of privileges becomes large, as well as to promote inter operability between ACL clients. Please see "Access Privileges" for the list of atomic and aggregate privileges that can be used in ACLs.

  The set of privileges granted to a principal controls the ability of that principal to perform a given operation or method on an Oracle XML DB resource. For example, if the principal HR wants to perform the read operation on a given resource, then the read privileges must be granted to HR prior to the read operation. Therefore, privileges control how users can operate on resources.

• ACE (access control entry): ACE is an entry in the ACL that grants or denies access to a particular principal (database user). An ACL consists of a list of ACEs where ordering is irrelevant. There can be only one grant ACE and one deny ACE for a particular principal in a single ACL.

  
  

  Note: More than one grant ACE (or deny ACE) can apply to a particular user because a user can be granted more than one role.

  
  

  An Oracle XML DB ACE element has the following properties:

  • Operation: Either grant or deny

  • Principal: A valid principal, as described previously.

  • Privileges Set: A particular set of privileges to be granted or denied for a particular principal

  • Principal Format (optional): The format of the principal. An LDAP distinguished name (DN), a short name (DB user/role or LDAP nickname), or an LDAP GUID. The default is short name. If the principal name matches both a DB user and an LDAP nickname, it is assumed to refer to the LDAP nickname.

  • Collection (optional): A BOOLEAN attribute that specifies whether the principal is a collection of users (LDAP group or DB role) or a single user (LDAP or DB user).

• Access control list (ACL): A list of access control entry elements, with the element name ace, that defines access control to a resource. An ACE either grants or denies privileges for a principal.

  The following example shows entries in an ACL:

  <acl description="myacl"
       xmlns="http://xmlns.oracle.com/xdb/acl.xsd"
       xmlns:dav="DAV:"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
                           http://xmlns.oracle.com/xdb/acl.xsd">
    <ace>
      <principal>dav:owner</principal>
      <grant>true</grant>
      <privilege>
        <dav:all/>
      </privilege>
    </ace>
  </acl>
  
  

  In this ACL there is only one ACE. The ACE grants all privileges to the owner of the resource.

• Default ACL: When a resource is inserted into Oracle XML DB Repository, by default the ACL on its parent folder is used to protect the resource. After the resource is created, a new ACL can be set on it.

• ACL file-naming conventions: Supplied ACLs use the following file-naming convention: <privilege>_<users>_acl.xml

  where <privilege> represents the privilege granted and <users> represents the users that are granted access to the resource.

• ACL Evaluation Rules: Privileges are checked before a user is allowed to access a resource. This is done by evaluating the resource ACL for the current user. To evaluate an ACL, the database collects the list of ACEs in the ACL that apply to the user logged into the current database session. The list of currently active roles for the user is maintained as part of the session, and it is used to match ACEs, which specify roles as principals, with the current users. To resolve conflicts between ACEs, the following rule is used: if a privilege is denied by any ACE, then the privilege is denied for the entire ACL.

Access Privileges

Oracle XML DB provides a set of privileges to control access to Oracle XML DB resources. Access privileges in an ACE are stored in the privilege element. Privileges can be either aggregate (composed of other privileges) or atomic.

When an ACL is stored in Oracle XML DB, the aggregate privileges retain their identity: they are not decomposed into the corresponding leaf privileges. In WebDAV terms, these are aggregate privileges that are not abstract.

Interaction with Database Table Security

Resources in Oracle XML DB Repository are of two types:

• LOB-based (content is stored in a LOB which is part of the resource). Access is determined only by the ACL that protects the resource.

• REF-based (content is XML and is stored in a database table). Users must have the appropriate privilege in the underlying table (or view) where the XML content is stored, as well as permissions through the ACL for the resource.

Since the content of a REF-based resource may actually be stored in a table, it is possible to access this data directly using SQL queries on the table. A uniform access control mechanism is one where the privileges needed are independent of the method of access (for example, FTP, HTTP, or SQL). To provide a uniform security mechanism using ACLs, the underlying table must first be hierarchy-enabled before resources that reference the rows in the table are inserted into Oracle XML DB. This is done using procedure DBMS_XDBZ.enable_hierarchy. This procedure adds two hidden columns to store the ACLOID and the OWNER of the resources that reference the rows in the table. It also adds a Row Level Security (RLS) policy to the table, which checks the ACL whenever a SELECT, UPDATE, or DELETE statement is executed on the table. The default tables produced by XML schema registration are already hierarchy-enabled.

In a particular table, some, but not all, objects may be mapped to Oracle XML DB resources. Only those objects mapped into Oracle XML DB Repository undergo ACL checking, but they will all have table-level security.

Working with Oracle XML DB ACLs

Oracle XML DB ACLs are (file) resources, so all of the methods that operate on resources also apply to ACLs. In addition, there are several APIs specific to ACLsin package DBMS_XDB. Those procedures and functions let you use PL/SQL to access Oracle XML DB security mechanisms, check user privileges based on a particular ACL, and list the set of privileges the current user has for a particular ACL and resource.

DECLARE
  b BOOLEAN;
BEGIN
  b := DBMS_XDB.createFolder('/TESTUSER');
  b := DBMS_XDB.createResource(
         '/TESTUSER/acl1.xml', 
         '<acl description="myacl"
               xmlns="http://xmlns.oracle.com/xdb/acl.xsd"
               xmlns:dav="DAV:"
               xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
               xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
                                   http://xmlns.oracle.com/xdb/acl.xsd">
            <ace>
              <principal>dav:owner</principal>
              <grant>true</grant>
              <privilege>
                <dav:all/>
              </privilege>
            </ace>
          </acl>');
END;

DECLARE
  b BOOLEAN;
BEGIN
  b := DBMS_XDB.createResource('/TESTUSER/po1.xml', 'Hello');
END;
/
 
CALL DBMS_XDB.setACL('/TESTUSER/po1.xml', '/TESTUSER/acl1.xml');

CALL DBMS_XDB.deleteResource('/TESTUSER/acl1.xml');

UPDATE RESOURCE_VIEW r
  SET r.RES =
        updateXML(
          r.RES,
          '/r:Resource/r:Contents/a:acl',
          '<acl description="myacl"
                xmlns="http://xmlns.oracle.com/xdb/acl.xsd"
                xmlns:dav="DAV:"
                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
                                    http://xmlns.oracle.com/xdb/acl.xsd">
             <ace>
               <principal>TESTUSER</principal>
               <grant>true</grant>
               <privilege>
                 <dav:all/>
               </privilege>
             </ace>
           </acl>',
          'xmlns:r="http://xmlns.oracle.com/xdb/XDBResource.xsd"
           xmlns:a="http://xmlns.oracle.com/xdb/acl.xsd"')
  WHERE r.ANY_PATH='/TESTUSER/acl1.xml';

UPDATE RESOURCE_VIEW r
  SET r.RES =
        appendChildXML(
          r.RES,
          '/r:Resource/r:Contents/a:acl',
          XMLType('<ace xmlns="http://xmlns.oracle.com/xdb/acl.xsd">
                     <principal>HR</principal>
                     <grant>true</grant>
                     <privilege>
                       <read-properties/>
                       <read-contents/>
                     </privilege>
                   </ace>'),
                  'xmlns:r="http://xmlns.oracle.com/xdb/XDBResource.xsd"
                   xmlns:a="http://xmlns.oracle.com/xdb/acl.xsd"')
  WHERE r.ANY_PATH='/TESTUSER/acl1.xml';

UPDATE RESOURCE_VIEW r
  SET r.RES =
        deleteXML(r.RES,
                  '/r:Resource/r:Contents/a:acl/a:ace',
                  'xmlns:r="http://xmlns.oracle.com/xdb/XDBResource.xsd"
                   xmlns:a="http://xmlns.oracle.com/xdb/acl.xsd"')
  WHERE r.ANY_PATH='/TESTUSER/acl1.xml';

SELECT DBMS_XDB.getACLDocument('/TESTUSER/po1.xml').getClobVal() FROM DUAL;
 
DBMS_XDB.GETACLDOCUMENT('/TESTUSER/PO1.XML').GETCLOBVAL()
--------------------------------------------------------------------------------
<acl description="myacl" xmlns="http://xmlns.oracle.com/xdb/acl.xsd" xmlns:dav="
DAV:" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="
http://xmlns.oracle.com/xdb/acl.xsd                                     http://x
mlns.oracle.com/xdb/acl.xsd">
  <ace>
    <principal>TESTUSER</principal>
    <grant>true</grant>
    <privilege>
      <dav:all/>
    </privilege>
  </ace>
  <ace xmlns="http://xmlns.oracle.com/xdb/acl.xsd">
    <principal>HR</principal>
    <grant>true</grant>
    <privilege>
      <read-properties/>
      <read-contents/>
    </privilege>
  </ace>
</acl>
 
1 row selected.

SELECT DBMS_XDB.getPrivileges('/TESTUSER/po1.xml').getClobVal() FROM DUAL;
 
DBMS_XDB.GETPRIVILEGES('/TESTUSER/PO1.XML').GETCLOBVAL()
--------------------------------------------------------------------------------
<privilege xmlns="http://xmlns.oracle.com/xdb/acl.xsd" xmlns:xsi="http://www.w3.
org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl
.xsd http://xmlns.oracle.com/xdb/acl.xsd DAV: http://xmlns.oracle.com/xdb/dav.xs
d" xmlns:xdbacl="http://xmlns.oracle.com/xdb/acl.xsd" xmlns:dav="DAV:">
  <read-properties/>
  <read-contents/>
  <update/>
  <link/>
  <unlink/>
  <read-acl/>
  <write-acl-ref/>
  <update-acl/>
  <resolve/>
  <unlink-from/>
  <dav:lock/>
  <dav:unlock/>
</privilege>
 
1 row selected.

SELECT DBMS_XDB.checkPrivileges(
         '/TESTUSER/po1.xml',
         XMLType('<privilege
                      xmlns="http://xmlns.oracle.com/xdb/acl.xsd"
                      xmlns:dav="DAV:"
                      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                      xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
                                          http://xmlns.oracle.com/xdb/acl.xsd">
                    <read-contents/>
                    <read-properties/>
                  </privilege>'))
  FROM DUAL;
 
DBMS_XDB.CHECKPRIVILEGES('/TESTUSER/PO1.XML',
---------------------------------------------
                                            1
 
1 row selected.

CONNECT SH/SH

SELECT DBMS_XDB.ACLCheckPrivileges(
         '/TESTUSER/acl1.xml',
         'TESTUSER',
         XMLType('<privilege
                      xmlns="http://xmlns.oracle.com/xdb/acl.xsd"
                      xmlns:dav="DAV:"
                      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                      xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
                                          http://xmlns.oracle.com/xdb/acl.xsd">
                    <read-contents/>
                    <read-properties/>
                  </privilege>'))
  FROM DUAL;
 
DBMS_XDB.ACLCHECKPRIVILEGES('/TESTUSER/ACL1.XML','TESTUSER',
------------------------------------------------------------
                                                           0
 
1 row selected.

SELECT a.ANY_PATH
  FROM RESOURCE_VIEW a
  WHERE extractValue(a.RES, '/Resource/XMLRef')
        = make_ref(XDB.XDB$ACL,
                   (SELECT extractValue(r.RES, '/Resource/ACLOID')
                      FROM RESOURCE_VIEW r
                      WHERE equals_path(r.RES, '/TESTUSER/po1.xml') = 1));
 
ANY_PATH
------------------
/TESTUSER/acl1.xml
 
1 row selected.

SELECT r.ANY_PATH
  FROM RESOURCE_VIEW r
  WHERE make_ref(XDB.XDB$ACL, extractValue(r.RES, '/Resource/ACLOID'))
        = (SELECT extractValue(a.RES, '/Resource/XMLRef')
             FROM RESOURCE_VIEW a
             WHERE equals_path(a.RES, '/TESTUSER/acl1.xml') = 1);
 
ANY_PATH
-----------------
/TESTUSER/po1.xml
 
1 row selected.

Integrating Oracle XML DB with LDAP

This section deals with allowing LDAP users to use the features of Oracle XML DB. The typical scenario is a single, shared database schema, to which multiple LDAP users are mapped. This mapping is maintained in the Oracle Internet Directory. Users can log in to the database using their LDAP username and password; they are then automatically mapped to the corresponding shared schema. (Users can log in using SQL or any of the supported Oracle XML DB protocols.) The implicit ACL resolution is based on the current LDAP user and the corresponding LDAP group membership information.

Before you can use LDAP users and groups as principals in Oracle XML DB ACLs, the following prerequisites must be satisfied:

• An Oracle Internet Directory must be set up, and the database must be registered with it.

• SSL authentication must be set up between the database and the Oracle Internet Directory.

• A database user must be created that corresponds to the shared database schema.

• The LDAP users must be created and mapped in the Oracle Internet Directory to the shared database schema.

• The LDAP groups must be created and their members must be specified.

• ACLs must be defined for the LDAP groups and users, and they must be used to protect the repository resources to be accessed by the LDAP users.

<acl description="/public/txmlacl1/acl1.xml"
     xmlns="http://xmlns.oracle.com/xdb/acl.xsd" xmlns:dav="DAV:"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd 
                         http://xmlns.oracle.com/xdb/acl.xsd">
  <ace principalFormat="DistinguishedName"> 
    <principal>cn=user1,ou=Americas,o=oracle,l=redwoodshores,st=CA,c=US
    </principal>
    <grant>true</grant>
    <privilege>
      <dav:all/>
    </privilege>
  </ace> 
</acl>

<acl xmlns="http://xmlns.oracle.com/xdb/acl.xsd" xmlns:dav="DAV:"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd 
                         http://xmlns.oracle.com/xdb/acl.xsd">
  <ace principalFormat="DistinguishedName"> 
    <principal>cn=grp1,ou=Americas,o=oracle,l=redwoodshores,st=CA,c=US</principal>
    <grant>true</grant>
    <privilege>
      <dav:read/>
    </privilege>
  </ace> 
</acl>

Performance Issues for Using ACLs

Since ACLs are checked for each access to Oracle XML DB Repository, the performance of the ACL check operation is critical to the performance of the repository. In Oracle XML DB, the required performance for this operation is achieved by employing several caches. ACLs are cached in a shared (shared by all sessions in the instance) cache. The performance of this cache is better when there are fewer ACLs in your system. Hence it is recommended that you share ACLs (between resources) as much as possible. Also, the cache works best when the number of ACEs in an ACL is at most 16.

There is also a session-specific cache of privileges granted to a given user by a given ACL. The entries in this cache have a time out (in seconds) specified by the element <acl-max-age> in the XDB configuration file (/xdbconfig.xml). For maximum performance this timeout should be as large as possible. But note that there is a trade-off here: the greater the timeout, the longer it will take for current sessions to pick up an updated ACL.

Oracle XML DB also maintains caches to improve performance when using ACLs that have LDAP principals (LDAP groups or users). The goal of these caches is to minimize network communication with the LDAP server. One is a shared cache that maps LDAP GUIDs to the corresponding LDAP nicknames and Distinguished Names (DNs). This is used when an ACL document is being displayed (or converted to CLOB or VARCHAR2 values from an XMLType instance). To purge this cache, use procedure DBMS_XDBZ.PurgeLDAPCache. The other cache is session-specific and maps LDAP groups to their members (nested membership). Note that whenever Oracle XML DB encounters an LDAP group for the first time (in a session) it will get the nested membership of that group from the LDAP server. Hence it is best to use groups with as few members and levels of nesting as possible.