CVE-2021-47333

What it actually does

Null pointer dereference in the alcor_pci kernel driver when a device attaches directly to the root complex, causing bus->self to be NULL and triggering pci_read_config_byte on an invalid address during ASPM capability checks in the probe path.

Why it matters to the business

System crashes or instability on boot or device insertion for affected hardware configurations, leading to downtime and potential data loss in environments using the alcor_pci driver; low exploitation likelihood limits widespread impact but requires prompt patching for stability.

How an attack unfolds

An attacker with local access or control over hardware insertion triggers the alcor_pci module probe on a system where the device connects directly to the root complex; the missing NULL check on parent_pdev leads to a kernel NULL dereference panic during alcor_pci_find_cap_offset, denying service without further code execution.

How to fix it

Update the Linux kernel to a version containing the fix for this issue, which skips ASPM capability checks when bus->self is NULL and sets offsets to zero to disable ASPM safely.

How to confirm the fix worked

Confirm kernel version includes the alcor_pci NULL check patch; test device probe on root-complex-attached hardware and verify absence of NULL dereference oops in dmesg.

Typical attack path

1. Obtain local access or ability to insert compatible hardware
2. Ensure device attaches directly to root complex bypassing PCI bridge
3. Trigger alcor_pci_probe via module load or hotplug
4. Execute alcor_pci_init_check_aspm on NULL parent_pdev
5. Cause kernel panic via pci_read_config_byte on invalid address

How to detect it

Review kernel logs for NULL pointer dereference oops involving alcor_pci_probe or alcor_pci_find_cap_offset during boot or device insertion; no remote indicators exist.

What your security team should do

• Prioritize kernel updates on systems using alcor_pci hardware
• Monitor for related stability issues in production environments
• Apply vendor-supplied kernel packages containing the resolution