CVE-2025-21681

Published Jan 31, 2025

Last updated a year ago

CVSS medium 5.5

Overview

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's still easy to hit the infinite loop in the skb_tx_hash() from the OVS datapath. There might be other drivers that do the same, but dummy by itself is important for the OVS ecosystem, because it is frequently used as a packet sink for tcpdump while debugging OVS deployments. And when the issue is hit, the only way to recover is to reboot. Fix that by also checking if the device is running. The running state is handled by the net core during unregistering, so it covers unregistering case better, and we don't really need to send packets to devices that are not running anyway. While only checking the running state might be enough, the carrier check is preserved. The running and the carrier states seem disjoined throughout the code and different drivers. And other core functions like __dev_direct_xmit() check both before attempting to transmit a packet. So, it seems safer to check both flags in OVS as well.
Source
416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD status
Modified
Products
linux_kernel

Risk scores

CVSS 3.1

Type
Primary
Base score
5.5
Impact score
3.6
Exploitability score
1.8
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Severity
MEDIUM

Weaknesses

nvd@nist.gov
CWE-835

Social media

Hype score
Not currently trending

  1. 🔴 #Linux Kernel, Vulnerability type #CVE-2025-21681 (Critical) https://t.co/zA4Jphb0G7

    @dailycve

    21 Feb 2025

    21 Impressions

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  2. New post from https://t.co/uXvPWJy6tj (CVE-2025-21681 | Linux Kernel up to 6.1.126/6.6.73/6.12.10 skb_tx_hash infinite loop) has been published on https://t.co/qdv47tpl5o

    @WolfgangSesin

    31 Jan 2025

    49 Impressions

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  3. CVE-2025-21681 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 attempt… https://t.co/wQXl4LsDh3

    @CVEnew

    31 Jan 2025

    375 Impressions

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Configurations

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References

Sources include official advisories and independent security research.