---
id: CVE-2026-98427
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: codel: bound the dropping loop per dequeue call

  The CoDel control law schedules the next drop one interval/sqrt(count)
  after the previous drop, using the co…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: codel: bound the dropping loop per dequeue call

  The CoDel control law schedules the next drop one interval/sqrt(count)
  after the previous drop, using the co…
severity: none
published: '2026-10-14'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T14:17:54.343'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-98427'
references:
  - url: 'https://git.kernel.org/stable/c/7f4a5ec6258fd7c92633ec4b0493fc51166d9398'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/bacd72289d34d8c05b7de5a12448b87b6dd93878'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
ingestedAt: '2026-10-14T15:36:13.990Z'
---

## Overview

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

net/sched: codel: bound the dropping loop per dequeue call

The CoDel control law schedules the next drop one interval/sqrt(count)
after the previous drop, using the configured interval
(codel_params.interval). For very small intervals the scheduled step
rounds down to zero, so the dropping loop in codel_dequeue() never
advances and drains the entire backlog under the qdisc lock in one
call - an unprivileged user can trigger a soft lockup this way.

Fix in the shared codel code used by both codel and fq_codel:

1. Make the control-law step at least 1 tick so the dropping loop
   always moves forward.

2. Cap the dropping loop at CODEL_MAX_DROPS_PER_DEQUEUE (256) drops
   per codel_dequeue() call, resyncing drop_next to now when the cap
   is hit: the catch-up owed to the loop grows with the idle gap and
   the backlog, which no interval threshold can bound. This is a
   deliberate behaviour change after long idle gaps.

The cap applies to fq_codel (4b549a2ef4be) and the mac80211 TXQ path
(fixed interval, cap only).

The target sojourn delay (codel_params.target) is not validated: it
does not feed the control law, so a sub-tick value is aggressive
rather than deadlock-prone.

Conditions to recreate the bug:
  - tc qdisc add dev lo root handle 1: tbf rate 1kbit burst 2kb limit 1000000
  - tc qdisc add dev lo parent 1:1 handle 10: codel interval 2us target 1ms noecn limit 1000000 (same for fq_codel)
  - unpatched kernel: tc accepts it; a UDP flood under the 1kbit tbf
    soft-lockups (watchdog: BUG: soft lockup) while one
    codel_dequeue() call drops the backlog under the qdisc lock
  - patched kernel: same setup, at most 256 drops per dequeue call,
    no soft lockup

Testing: claim reproducer and interval 2us/3us variants run clean;
tdc qdisc category passes (see the selftests patch).

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.