ABAC in PostgreSQL

Securing sensitive data in PostgreSQL databases requires fine-grained access control. ABAC is a method for setting and enforcing access rules. These rules rely on user, resource, and environmental attributes. In this article, we will discuss how to use ABAC in PostgreSQL to control access to your data with examples.

Understanding ABAC

ABAC is an access control model that determines access rights based on attributes. Users can connect these traits to job titles, teams, resources such as data, records, and surroundings like time and place. ABAC provides a flexible and dynamic way to set access policies. This allows for more detailed control than traditional role-based access models.

In PostgreSQL, you can use different methods like row-level security and security labels to implement ABAC. Let’s explore each of these techniques and see how you can apply them to enforce ABAC in your PostgreSQL database.

Row-Level Security

Row-level security in PostgreSQL lets you control access to specific rows in a table based on user attributes. RLS policies are rules written in SQL that users can apply to certain tables or all tables in a database.

Here is how to enable RLS and make a policy that limits access to rows based on a user’s department attribute.

CREATE TABLE employees (
id SERIAL PRIMARY KEY,
name TEXT,
department TEXT,
salary NUMERIC
);
ALTER TABLE employees ENABLE ROW LEVEL SECURITY;
CREATE POLICY department_access ON employees
USING (department = current_setting('app.current_user_department'));

In this example, we create an `employees` table and enable RLS on it. The `USING` clause defines the `department_access` policy, which specifies the condition for accessing rows.

The policy checks if the department column of each row matches the user’s current department attribute. The app stores the user’s current department attribute in app.current_user_department. setting.

To set the user’s department attribute, you can use the `set_config` function:

SELECT set_config('app.current_user_department', 'HR', false);

This policy lets users only view rows from their departments, ensuring strict access control based on their attributes.

Security Labels

Security labels provide another way to implement ABAC in PostgreSQL. Database objects assign key-value pairs known as labels. They categorize tables or rows based on security attributes. You can then define access policies based on these labels.

Here’s an example of how to create security labels and define an access policy using them:

CREATE EXTENSION sepgsql;
CREATE TABLE documents (
id SERIAL PRIMARY KEY,
content TEXT,
classification TEXT
);
SECURITY LABEL FOR selinux ON TABLE documents IS 'system_u:object_r:sepgsql_table_t:s0';
SECURITY LABEL FOR selinux ON COLUMN documents.classification IS 'system_u:object_r:sepgsql_column_t:s0';
CREATE POLICY document_access ON documents
USING (sepgsql_has_perm(current_user, classification, 'read') = 't');

In this example, we create a table named `documents`. We assign security labels to both the table and the `classification` column. We do this by using the `SECURITY LABEL` command. The labels follow the SELinux format and categorize the table and column based on security attributes.

Next, we define an access policy `document_access` using the `sepgsql_has_perm` function. This function verifies if the user has permission to read the classification label for each row. Only rows for which the function returns `true` (`’t’`) are accessible to the user.

Policy Expressions

Policy expressions allow you to define complex access control rules based on attributes and conditions. They provide a flexible way to combine multiple attributes and logic to determine access rights.

Here’s an example of using policy expressions to implement ABAC:

CREATE TABLE sales (
id SERIAL PRIMARY KEY,
product TEXT,
region TEXT,
amount NUMERIC
);
CREATE POLICY regional_sales ON sales
USING (
(region = current_setting('app.current_user_region') AND amount = 10000) OR
(current_setting('app.current_user_role') = 'manager')
);

In this example, we have a `sales` table that stores sales data, including the product, region, and amount. The `regional_sales` policy defines using a policy expression that combines multiple conditions.

The policy grants access to sales records if either of the following conditions is met:

The user’s region attribute matches the `region` column of the row, and the `amount` is less than or equal to 10,000.

The system sets the user’s role attribute to `’manager’`, granting them unrestricted access to all sales records.

The user can set their region and role attributes using the `set_config` function, similar to the previous examples.

Combining ABAC Techniques

You can implement ABAC in PostgreSQL using a combination of the techniques discussed above. Combine RLS, security labels, and policy expressions for a personalized access control system that fits your needs.

You can use RLS to control access by department. Use security labels to categorize sensitive data and policy expressions to create detailed access rules. Later you can base these rules on various attributes and conditions.

Performance Considerations

Implementing ABAC in PostgreSQL can affect query performance, especially when dealing with complex access policies. Important to consider the following performance aspects:

• Policy evaluation: The system evaluates each row-level policy for every query, which can add overhead to query execution. Optimize your policies to minimize the number of conditions and complexity.
• Indexing: Make sure to properly index the columns used in your access policies to speed up policy evaluation. Consider creating indexes on attributes frequently used in policy conditions.
• Caching: PostgreSQL caches the result of policy evaluations for a short period. Tune the `row_security_cache_size` configuration parameter to balance between cache efficiency and memory usage.
• Partitioning your tables based on specific attributes can help manage large tables and access policies more effectively. This can improve query performance by reducing the number of rows scanned during policy evaluation.

Testing and Auditing

When implementing ABAC in PostgreSQL, it’s crucial to thoroughly test your access policies to ensure they behave as expected. Test your rules by creating different scenarios with user attributes, resource attributes, and environmental conditions to ensure accuracy.

Additionally, enable logging and auditing to monitor access attempts and policy evaluations. PostgreSQL offers built-in logging mechanisms that users can configure to capture relevant access control events. Regularly review the logs to identify any unauthorized access attempts or policy misconfigurations.

Conclusion

ABAC is a powerful approach to enforce fine-grained access control in PostgreSQL databases. You can create access policies based on user attributes, resource attributes, and environment conditions. You can do this using techniques like row-level security, security labels, and policy expressions.

Using ABAC in PostgreSQL helps protect sensitive data, meet regulations, and maintain data privacy. Make sure to test and audit your access policies to make sure they work well and don’t cause problems.

This article shows you how to implement ABAC in your PostgreSQL database to improve your application’s security. Don’t forget to check and change your access rules as needed to keep your data access system strong and safe.