CVE-2021-47442

What it actually does

Unconditional skb allocation in digital_in_send_sdd_req is not released when digital_in_send_cmd fails, producing a kernel memory leak on the error path.

Why it matters to the business

Repeated triggering of the failure condition can gradually exhaust kernel memory, leading to degraded performance or denial of service on systems using NFC digital functionality; low public exploit activity reduces immediate risk but long publication window increases exposure for unpatched kernels.

How an attack unfolds

An attacker with local or adjacent NFC access crafts conditions that cause digital_in_send_cmd to return failure after skb allocation, repeating the sequence to accumulate unreleased buffers until memory pressure impacts the system.

How to fix it

Apply the upstream fix that adds the missing skb free on digital_in_send_cmd failure; rebuild and deploy updated kernels to all affected systems.

How to confirm the fix worked

Inspect the digital_in_send_sdd_req function in the running kernel source or binary for the presence of the skb free call after the send_cmd failure check; confirm via kernel changelog or git history that the leak fix commit is included.

Typical attack path

1. Obtain local or NFC-adjacent access to a vulnerable kernel
2. Trigger digital_in_send_sdd_req with parameters that cause digital_in_send_cmd to fail
3. Repeat the sequence to accumulate leaked skb buffers
4. Observe system-wide memory pressure or OOM events

How to detect it

Review kernel logs and memory accounting for repeated NFC digital allocation failures without corresponding frees; correlate with process or driver activity involving nfc or digital_in_send.

What your security team should do

• Prioritize kernel updates for any systems exposing NFC digital interfaces
• Monitor kernel memory statistics and NFC-related error rates for anomalous growth
• Disable NFC digital support where not required as a temporary control