CVE-2025-21681

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

openvswitch: fix lockup on tx to unregistering netdev with carrier

Commit in a fixes tag attempted to fix the issue in the following

sequence of calls:

do_output

-> ovs_vport_send

-> dev_queue_xmit

-> __dev_queue_xmit

-> netdev_core_pick_tx

-> skb_tx_hash

When device is unregistering, the 'dev->real_num_tx_queues' goes to

zero and the 'while (unlikely(hash >= qcount))' loop inside the

'skb_tx_hash' becomes infinite, locking up the core forever.

But unfortunately, checking just the carrier status is not enough to

fix the issue, because some devices may still be in unregistering

state while reporting carrier status OK.

One example of such device is a net/dummy. It sets carrier ON

on start, but it doesn't implement .ndo_stop to set the carrier off.

And it makes sense, because dummy doesn't really have a carrier.

Therefore, while this device is unregistering, it'

Remediation

Check the references section for vendor advisories and patches from linux. Update linux_kernel to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected Products

References