---
id: CVE-2026-80630
title: >-
  In the Linux kernel, the following vulnerability has been resolved:


  net/sched: sch_fq_codel: Do not call qdisc_tree_reduce_backlog during peek
  before restoring qlen


  Whenever fq_codel drops packets during peek, it calls

  qdisc_tree_reduc…
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  net/sched: sch_fq_codel: Do not call qdisc_tree_reduce_backlog during peek
  before restoring qlen


  Whenever fq_codel drops packets during peek, it calls

  qdisc_tree_reduc…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
published: '2026-08-28'
updated: '2026-08-29'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-80630'
references:
  - url: 'https://git.kernel.org/stable/c/0500af8630c3253f0dde879bd3a73a06bb2f2b3f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/097f6fc7b1ae362dd7a9444b2572162fda73b284'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/20dd591d8f951e1e6aca5052be8785e6181055e2'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/3e515188393e62a718ccebee651ee74514104ff6'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7c09843fd2b44d9bf0de798683861d1aecd62a08'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/94a5f1efdefb01f82cd228bf4e7ef1e8fc075c80'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/acc08a0c7f37ebb1901144e03a7cba7d4afd9203'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/af54df2f44d9605614bc7ed96640302a240a9a62'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00755
epssPercentile: 0.53173
ingestedAt: '2026-08-29T23:43:56.447Z'
---

## Overview

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

net/sched: sch_fq_codel: Do not call qdisc_tree_reduce_backlog during peek before restoring qlen

Whenever fq_codel drops packets during peek, it calls
qdisc_tree_reduce_backlog. An issue arises because it calls
qdisc_tree_reduce_backlog before it reincrements the qlen. If qlen drops
to zero, but peek returns an skb, the parent's qlen_notify callback will be
executed even though fq_codel still has 1 packet on the queue and, thus,
will mistakenly deactivate the parent's class causing issues like a recent
report [1] and a wild memory access in qfq:

[   29.371146][  T360] Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI
[   29.371666][  T360] KASAN: maybe wild-memory-access in range [0xdead000000000120-0xdead000000000127]
[   29.371987][  T360] CPU: 6 UID: 0 PID: 360 Comm: tc Not tainted 7.1.0-rc5-00285-gc530e5b2dbc6-dirty #82 PREEMPT(full)
[   29.372384][  T360] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
[   29.372620][  T360] RIP: 0010:qfq_deactivate_agg (include/linux/list.h:1029 (discriminator 2) include/linux/list.h:1043 (discriminator 2) net/sched/sch_qfq.c:1369 (discriminator 2) net/sched/sch_qfq.c:1395 (discriminator 2)) sch_qfq
[   29.373544][  T360] RSP: 0018:ffff888102417370 EFLAGS: 00010216
[   29.373800][  T360] RAX: 0000000000000000 RBX: ffff88811224d568 RCX: dffffc0000000000
[   29.374079][  T360] RDX: 1ffff11021fe1543 RSI: ffff88810ff0aa00 RDI: dffffc0000000000
[   29.374368][  T360] RBP: ffff88811224c280 R08: dead000000000122 R09: 1bd5a00000000024
[   29.374649][  T360] R10: fffffbfff7940329 R11: fffffbfff7940329 R12: 0000000000000000
[   29.374926][  T360] R13: dead000000000100 R14: ffff88811224d580 R15: ffff88811224d578
[   29.375207][  T360] FS:  00007f5b794e5780(0000) GS:ffff88815d1e9000(0000) knlGS:0000000000000000
[   29.375545][  T360] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   29.375823][  T360] CR2: 000055ffb091f000 CR3: 000000010a305000 CR4: 0000000000750ef0
[   29.376103][  T360] PKRU: 55555554
[   29.376258][  T360] Call Trace:
[   29.376401][  T360]  <TASK>
...
[   29.376885][  T360] qfq_reset_qdisc (net/sched/sch_qfq.c:357 net/sched/sch_qfq.c:1487) sch_qfq
[   29.377074][  T360]  qdisc_reset (net/sched/sch_generic.c:1057)
[   29.377414][  T360]  __qdisc_destroy (net/sched/sch_generic.c:1096)
[   29.377600][  T360]  qdisc_graft (net/sched/sch_api.c:1062 net/sched/sch_api.c:1053 net/sched/sch_api.c:1159)
[   29.378593][  T360]  tc_get_qdisc (net/sched/sch_api.c:1528 net/sched/sch_api.c:1556)

Fix this by only calling qdisc_tree_reduce_backlog in peek after the
qlen is restored.

[1] http://lore.kernel.org/netdev/CAN2cbVe79oj0O9==m4+4x3v+O+qzRagA=2=wkrp9i9=CqYvyZA@mail.gmail.com/

## Remediation

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