CVE-2021-47560

What it actually does

NULL pointer dereference in netif_carrier_on/off when mlxsw spectrum driver processes firmware-generated port up/down events for the CPU port (local port 0), which exists but has no associated netdev.

Why it matters to the business

Kernel instability or crashes on systems using affected Mellanox networking hardware, resulting in network downtime and potential service disruption; low exploitability reduces immediate urgency despite long exposure window.

How an attack unfolds

An attacker with ability to influence or emulate buggy firmware sends a port event for local port 0; the driver skips non-existent port checks for the CPU port and calls carrier functions on a NULL pointer, causing a crash.

How to fix it

Update to a kernel version containing the fix that bails early on CPU port events; apply the corresponding package updates for affected distributions.

How to confirm the fix worked

Confirm driver source contains the early return for local port 0 events; test with emulator or hardware that can generate port events for the CPU port and verify no crash occurs.

Typical attack path

1. Obtain or emulate access to trigger firmware port events
2. Cause event generation for CPU port (local port 0)
3. Driver processes event without early bail
4. NULL dereference occurs in netif_carrier handling

How to detect it

Inspect kernel logs for NULL pointer dereference traces involving netif_carrier_on/off or mlxsw spectrum port event handling; look for mentions of local port 0 events from firmware.

What your security team should do

• Prioritize kernel updates on systems using mlxsw spectrum hardware
• Monitor for firmware updates from device vendors
• Review logs for unexpected port events during testing