CVE-2021-47467

What it actually does

Reference count leak occurs in the normal execution path of kfree_at_end() because kunit_alloc_and_get_resource() increments the refcount on the returned resource object without a corresponding decrement, leaving the object with an elevated reference count.

Why it matters to the business

Kernel testing infrastructure may experience gradual resource exhaustion or unexpected object lifetime issues during prolonged test runs, potentially destabilizing development and CI environments over time; low urgency given age and low exploitability metrics.

How an attack unfolds

An attacker would need to trigger kunit test paths that invoke kfree_at_end() repeatedly; the leak accumulates without any known public exploit chains or threat actor usage, and the issue was resolved by switching to kunit_alloc_resource().

How to fix it

Update to a kernel version containing commit 65c44883f9d24f3ccef066fb523c93d8fdd7afc1 or later that replaces the call with kunit_alloc_resource(); rebuild and redeploy the kernel image.

How to confirm the fix worked

Inspect the kunit resource allocation code for use of kunit_alloc_resource() instead of kunit_alloc_and_get_resource(); run KUnit test suites and monitor reference counts or memory usage for leaks.

Typical attack path

1. Identify or control execution of KUnit tests that allocate resources via kfree_at_end
2. Cause repeated invocations of the affected allocation path
3. Accumulate unreleased references leading to resource pressure

How to detect it

Examine kernel logs and test output for repeated resource allocation warnings; search source history for the original kunit_alloc_and_get_resource call site; no runtime IOCs are known because the flaw is a coding defect rather than an attacker-triggered condition.

What your security team should do

• Prioritize kernel updates in development and test environments where KUnit is active
• Monitor upstream stable kernel releases for backports of the fix
• Review any custom KUnit extensions for similar reference counting patterns