CVE-2021-47102

What it actually does

The flaw causes invalid memory access in the Prestera netdev event handler by unconditionally reading the upper_dev field from a structure that only exists for specific NETDEV_CHANGEUPPER events, resulting in stack-out-of-bounds reads for all other notifier events.

Why it matters to the business

Systems using the affected Marvell Prestera driver may experience kernel crashes or instability during routine network device registration and event processing, increasing downtime risk on embedded or networking hardware despite low observed exploitation activity over nearly three years since disclosure.

How an attack unfolds

An attacker triggers netdevice notifier chains (for example during interface registration) that invoke the handler with a generic info pointer; the code then dereferences fields that do not exist for the actual event type, producing memory corruption detectable by KASAN.

How to fix it

Upgrade the Linux kernel to a version containing the upstream fix that guards the upper_dev access behind an explicit NETDEV_CHANGEUPPER event-type check; rebuild and deploy the updated Prestera driver module.

How to confirm the fix worked

Confirm the corrected code path by inspecting prestera_netdev_port_event for an event == NETDEV_CHANGEUPPER guard before the upper_dev assignment, then exercise multiple netdevice notifier types while monitoring for KASAN violations.

Typical attack path

1. Register or modify network devices to generate non-CHANGEUPPER notifier events
2. Invoke prestera_netdev_event_handler which calls prestera_netdev_port_event without type validation
3. Access upper_dev field from an incompatible structure layout causing out-of-bounds stack read

How to detect it

Search kernel logs and KASAN reports for mentions of prestera_netdev_port_event or prestera_netdev_event_handler combined with stack-out-of-bounds or invalid memory access during udevd or netdevice registration activity.

• prestera_netdev_port_event
• prestera_netdev_event_handler
• BUG: KASAN: stack-out-of-bounds
• Read of size 8 at addr
• register_netdevice+0x3cc

What your security team should do

• Prioritize kernel updates on any systems shipping the Prestera driver
• Audit kernel logs for historical KASAN stack-out-of-bounds reports referencing prestera_netdev_port_event
• Test network interface bring-up sequences after patching to verify stability