In this lesson, you will learn how to synchronize Mandatory Access Control (MAC) labels with the identity of the end-user behind an Identity-Aware Proxy (IAP) to enforce fine-grained security policies.
The Challenge of Proxy Transparency
When a user accesses a service through an IAP, the incoming request often arrives at the backend with the proxy’s own service identity. From the perspective of the kernel’s MAC system (like SELinux or AppArmor), the request appears to originate from the proxy process, not the human user. This creates a security gap where the MAC system cannot distinguish between a legitimate request from an authorized user and a compromised proxy service.
Bridging Identity to MAC Contexts
To resolve this, we must extend the security context of the thread handling the request to reflect the user's identity verified by the proxy. Instead of relying on a static label for the proxy process, we use dynamic transition mechanisms.
When the proxy authenticates a user, it passes the user’s identity—typically via headers or metadata—to the backend. The backend service then performs a security context transition. By using a specialized interface, the service thread temporarily adopts an execution label associated with that specific user identity before accessing local resources.
For example, in SELinux, a service can utilize setexeccon() to transition its process context based on the authenticated user:
// Pseudo-code for context transition
char *user_context = get_context_for_user(authenticated_id);
if (setexeccon(user_context) == 0) {
// Access the resource; the kernel now sees the user's context
read_file("/data/secure_resource");
}
// Revert context after the task is complete
setexeccon(NULL);
By binding the MAC context to the user identity provided by the proxy, you ensure that even if the proxy itself is hijacked, the underlying system prevents it from accessing files or data that the specific authenticated user is not explicitly permitted to see. The MAC policy remains the final arbiter of truth, anchored in the user's identity rather than the proxy's privileges.
Key Takeaway: Integrating MAC with Identity-Aware Proxies requires dynamically transitioning the thread's security context to match the authenticated user, ensuring that access enforcement is tied to the identity rather than the transit mechanism.