CVE-2021-47564

What it actually does

Double-free vulnerability in prestera_bridge_port_join error path that invokes prestera_bridge_destroy on an already-freed object, resulting in kernel oops and crash.

Why it matters to the business

Unexpected kernel panics on systems using Marvell Prestera network hardware can cause unplanned downtime, loss of network connectivity, and require manual intervention or reboot.

How an attack unfolds

An attacker with local or network-adjacent access triggers netdevice notifier events that exercise the error path inside prestera_bridge_port_join; the flawed handling then calls prestera_bridge_destroy twice, dereferencing freed memory and crashing the kernel.

How to fix it

Upgrade to a Linux kernel containing the upstream fix for the prestera double-free error path; rebuild and reboot with the corrected prestera driver module.

How to confirm the fix worked

Confirm the prestera.c source no longer contains the double-free sequence in prestera_bridge_port_join; reproduce bridge-port join failures without triggering an oops.

Typical attack path

1. Obtain ability to trigger netdev upper-device link or bridge-port events
2. Force an error condition during prestera_bridge_port_join processing
3. Execute the buggy error path that calls prestera_bridge_destroy on a freed object
4. Kernel dereferences poisoned pointer (0xdead000000000122) and panics

How to detect it

Search kernel logs and dmesg for 'Internal error: Oops', 'prestera_bridge_destroy', and the listed call trace involving prestera_netdev_event_handler.

• prestera_bridge_destroy+0x2c/0xb0 [prestera]
• prestera_bridge_port_join+0x2cc/0x350 [prestera]
• prestera_netdev_port_event.constprop.0+0x3c4/0x450 [prestera]
• Internal error: Oops: 96000044
• x0 : dead000000000122

What your security team should do

• Prioritize kernel upgrade on all hosts exposing the prestera driver
• Add kernel oops monitoring for prestera call traces
• Limit unprivileged users' ability to create bridges or manipulate netdev links where feasible