Each Oracle Label Security user has authorizations that include special components.

• A maximum and minimum level

• A set of authorized compartments

• A set of authorized groups

• For each compartment and group, a specification of read-only access, or read/write access

The administrator also specifies the user's initial session label when setting up these authorizations for the user. The session label is the particular combination of levels, compartments, and groups at which a user works at any given time. The user can change the session label to any combination of components for which the user is authorized.

When a user writes data without specifying its label, a row label is assigned automatically, using the user's session label.

However, the user can set the label for the written row, within certain restrictions on the components of the label he specifies. The level of this label can be set to any level within the range specified by the administrator. For example, it can be set to the level of the user's current session label down to the user's minimum level. However, the compartments and groups for this row's new label are more restricted. The new label can include only those compartments and groups contained in the current session label and, among those, only the ones for which the user has write access.

When the administrator sets up the user authorizations, he or she also specifies an initial default row label.

The session label and the row label can fall anywhere within the range of the user's level, compartment, and group authorizations.

In Figure 3-2, the user's maximum level is SENSITIVE and the minimum level is UNCLASSIFIED. However, his default session label is C:FIN,OP:WR. In this example, the administrator has set the user's session label so that the user connects to the database at the CONFIDENTIAL level.

Similarly, although the user is authorized for compartments FIN and OP, and group WR, the administrator could set the session label so that the user connects with only compartment FIN and group WR.

The administrator explicitly sets authorizations for levels, compartments, and groups.

• Authorized Levels
  The administrator explicitly sets the level authorization for an Oracle Label Security policy.
• Authorized Compartments
  The administrator specifies the list of compartments that a user can place in his or her session label.
• Authorized Groups
  You must specify a list of groups that a user can place in a session label and grant write access for each group.

Oracle Label Security automatically computes a number of labels based on the value of the session label.

Table 3-2 lists the computed session labels.

Although data labels are stored in a column within data records, information about user authorizations is stored in relational tables.

When a user logs on, the tables are used to dynamically generate user labels for use during the session.

• Difference Between Read and Write Operations
  Two fundamental types of access mediation on Data Manipulation language (DML) operations exist within protected tables: read access and write access.
• Propagation of Read/Write Authorizations on Groups
  When groups are organized hierarchically, a user's assigned groups include all subgroups that are subordinate to the group to which the user belongs.

The READ_CONTROL enforcement determines the ability to read data in a row.

The following rules are used, in the sequence listed, to determine a user's read access to a row of data:

1. The user's level must be greater than or equal to the level of the data.

2. The user's label must include at least one of the groups that belong to the data (or the parent group of one such subgroup).

3. The user's label must include all the compartments that belong to the data.

If the user's label passes these tests, then it is said to dominate the row's label.

Note that there is no notion of read or write access connected with levels. This is because the administrator specifies a range of levels (minimum to maximum) within which a user can potentially read and write. At any time, the user can read all data equal to or less than the current session level. No privileges (other than FULL) allow the user to write below the minimum authorized level.

Figure 3-6 illustrates how the label evaluation process proceeds from levels to groups to compartments. Note that if the data label is null or invalid, then the user is denied access.

As a read access request comes in, Oracle Label Security evaluates each row to determine the following:

1. Is the user's level equal to, or greater than, the level of the data?

2. If so, does the user have access to at least one of the groups present in the data label?

3. If so, does the user have access to all the compartments present in the data label? (That is, are the data's compartments a subset of the user's compartments?)

If the answer is no at any stage in this evaluation process, then Oracle Label Security denies access to the row and moves on to evaluate the next row of data.

Oracle Label Security policies allow user sessions to read rows at their label and below, which is called reading down. Sessions cannot read rows at labels that they do not dominate.

For example, if you are logged in at SENSITIVE:ALPHA,BETA, you can read a row labeled SENSITIVE:ALPHA because your label dominates that of the row. However, you cannot read a row labeled SENSITIVE:ALPHA,GAMMA because your label does not dominate that of the row.

Note that the user can gain access to the rows otherwise denied, if she or he has special Oracle Label Security privileges.

In the context of Oracle Label Security, WRITE_CONTROL enforcement determines the ability to insert, update, or delete data in a row.

WRITE_CONTROL enables you to control data access with ever finer granularity. Granularity increases when compartments are added to levels. It increases again when groups are added to compartments. Access control becomes even more fine grained when you can manage the user's ability to write the data that he can read.

To determine whether a user can write a particular row of data, Oracle Label Security evaluates the following rules, in the order given:

1. The level in the data label must be greater than or equal to the user's minimum level and less than or equal to the user's session level.

2. When groups are present, the user's label must include at least one of the groups with write access that appear in the data label (or the parent of one such subgroup). In addition, the user's label must include all the compartments in the data label.

3. When no groups are present, the user's label must have write access on all of the compartments in the data label.

To state tests 2 and 3 another way:

• If the label has no groups, then the user must have write access on all the compartments in the label in order to write the data.

• If the label does have groups and the user has write access to one of the groups, she only needs read access to the compartments in order to write the data.

Just as with read operations, the label evaluation process proceeds from levels to groups to compartments. Note that the user cannot write any data below the authorized minimum level, nor above the current session level. The user can always read below the minimum level.

Figure 3-7 illustrates how the process works with INSERT, UPDATE, and DELETE operations. Note that if the data label is null or invalid, then the user is denied access.

As an access request comes in, Oracle Label Security evaluates each row to determine the following:

1. Is the data's level equal to, or less than the level of the user?

2. Is the data's level equal to, or greater than the user's minimum level?

3. If the data's level falls within the foregoing bounds, then does the user have write access to at least one of the groups present in the data label?

4. If so, does the user have access to all the compartments with at least read access that are present in the data label?

5. If there are no groups but there are compartments, then does the user have write access to all of the compartments?

If the answer is no at any stage in this evaluation process, then Oracle Label Security denies access to the row, and moves on to evaluate the next row of data.

Consider a situation in which your session label is S:ALPHA,BETA but you have write access to only compartment ALPHA. In this case, you can read a row with the label S:ALPHA,BETA but you cannot update it.

In summary, write access is enforced on INSERT, UPDATE and DELETE operations upon the data in the row.

In addition, each user may have an associated minimum level below which the user cannot write. The user cannot update or delete any rows labeled with levels below the minimum, and cannot insert a row with a row label containing a level less than the minimum.

Oracle Label Security supports special privileges that allow authorized users to bypass certain parts of the policy.

Table 3-3 summarizes the full set of privileges that can be granted to users or trusted stored program units. Each privilege is more fully discussed after the table.

A user's authorizations can be modified with any of four privileges.

• READ Privilege
  A user with the READ privilege can read all data protected by the policy, regardless of the authorizations or session label.
• FULL Privilege
  The FULL privilege has the same effect and benefits as the READ privilege, with one difference.
• COMPACCESS Privilege
  The COMPACCESS privilege allows a user to access data based on the row label's compartments, independent of the row label's groups.
• PROFILE_ACCESS Privilege
  The PROFILE_ACCESS privilege allows a session to change its session labels and session privileges to those of a different user.

Once the label on a row has been set, Oracle Label Security privileges are required to modify the label.

Note that the LABEL_UPDATE enforcement option must be on for these label modification privileges to be enforced. When a user updates a row label, the new label and old label are compared, and the required privileges are determined.

The special row label privileges include:

• WRITEUP Privilege
  The WRITEUP privilege enables the user to raise the level of data within a row, without compromising the compartments or groups.
• WRITEDOWN Privilege
  The WRITEDOWN privilege enables the user to lower the level of data within a row, without compromising the compartments or groups.
• WRITEACROSS Privilege
  The WRITEACROSS privilege allows the user to change the compartments and groups of data, without altering its sensitivity level.

Oracle Label Security privileges are different from the standard Oracle Database system and object privileges.

Oracle Database enforces the discretionary access control privileges that a user has been granted. By default, a user has no privileges except those granted to the PUBLIC user group. A user must explicitly be granted the appropriate privilege to perform an operation.

For example, to read an object in Oracle Database, you must either be the object's owner, or be granted the SELECT privilege on the object, or be granted the SELECT ANY TABLE system privilege. Similarly, to update an object, you must either be the object's owner, or be granted the UPDATE privilege on the object, or be granted the UPDATE ANY TABLE privilege.

Prior to accessing data through a view, the users must have the appropriate system and object privileges on the view.

The privileges with which procedures that are owned by different users are executed differently in Oracle Database and Oracle Label Security.

For example, in Oracle Database, if user1 executes a procedure that belongs to user2, then the procedure runs with user2's system and object privileges. You can find the privileges that have been granted to a user by querying the DBA_SYS_PRIVS data dictionary view. However, any procedure executed by user1 runs with user1's own Oracle Label Security labels and privileges. This is true even when user1 executes stored program units owned by other users.

Figure 3-10 illustrates this process:

• Stored program units run with the DAC privileges of the procedure's owner (user2).

• In addition, stored program units accessing tables protected by Oracle Label Security mediate access to data rows based on the label attached to the row, and the Oracle Label Security labels and privileges of the invoker of the procedure (user1).

Stored program units can become trusted when an administrator assigns them Oracle Label Security privileges. A stored program unit can be run with its own autonomous Oracle Label Security privileges rather than those of the user who calls it. For example, if you possess no Oracle Label Security privileges in your own right but run a stored program unit that has the WRITEDOWN privilege, then you can update labels. In this case, the privileges used are those of the stored program unit, and not your own.

Trusted program units can encapsulate privileged operations in a controlled manner. By using procedures, packages, and functions with assigned privileges, you may be able to access data that your own labels and privileges would not authorize. For example, to perform aggregate functions over all data in a table, not just the data visible to you, you might use a trusted program set up by an administrator. This way program units can thus perform operations on behalf of users, without the need to grant privileges directly to users.

An administrator can choose from among a set of policy enforcement options when applying an Oracle Label Security policy to individual tables.

These options enable enforcement to be tailored differently for each database table. In addition to the access controls based on the labels, a SQL predicate can also be associated with each table. The predicate can further define which rows in the table are accessible to the user.

In cases where the label to be associated with a new or updated row should be automatically computed, an administrator can specify a labeling function when applying the policy. That function will thereafter always be invoked to provide the data labels written under that policy, because active labeling functions take precedence over any alternative means of supplying a label.

Except where noted, this guide assumes that all enforcement options are in effect.

Several Oracle Label Security policies can protect data in a single database.

Each defined policy is associated with a set of labels used only by that policy. Data labels are constrained by the set of defined labels for each policy.

Each policy may protect a different table, but multiple policies can also apply to a single table. To access data, you must have label authorizations for all policies protecting that data. To access any particular row, you must be authorized by all policies protecting the table containing your desired rows. If you require privileges, then you may need privileges for all of the policies affecting your work.

In a distributed environment that uses Oracle Label Security, remote connections are controlled by Oracle Label Security.