---
id: CVE-2026-74284
title: 'net/sched: sch_hfsc: Don''t make class passive twice'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: sch_hfsc: Don't make class passive twice

  update_vf() is called from two places for the same class during a single
  dequeue when the class's child qdisc (e.g.…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 72c61ffbeeb8c50f6d4d70c65d3283aa1bac57a7 <
    a425c82ff06cda5165e0de3de8c2a445ec1f863e
  - >-
    Linux >= a5efc95a33bd4fcb879250852828cc58c7862970 <
    fc973ecd1a079b9a87c360478542f3a56dea085b
  - >-
    Linux >= 0475c85426b18eccdcb7f9fb58d8f8e9c6c58c87 <
    15720cd8fa3fc625146128f89a8e11b0449a20a7
  - >-
    Linux >= 9030a91235ae4845ec71902c3e0cecfc9ed1f2df <
    b2a017bfcf565721918ec7355a373911d2f2a227
  - >-
    Linux >= d06476714d2819b550e0cc39222347e2c8941c9d <
    9221a594c72a1446137926d4c2aa04e345f798dc
  - >-
    Linux >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb <
    66dbb13eeb2fc339f8f548a9076be4c1a94857b0
  - >-
    Linux >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb <
    3a49bbae676fef1ffe548971e6229ae2adeb9d10
  - >-
    Linux >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb <
    90b662ea25f5e83bb3b8ccec5b93ced810b92fb8
  - Linux 9a5fd5c2f4d4afdd5e405083ee53e0789ce76956
  - Linux c1175c4ad01dbc9c979d099861fa90a754f72059
  - Linux >= 5.10.241 < 5.10.261
  - Linux >= 5.15.190 < 5.15.212
  - Linux >= 6.1.138 < 6.1.178
  - Linux >= 6.6.90 < 6.6.145
  - Linux >= 6.12.28 < 6.12.97
  - Linux >= 5.4.297 < 5.5
  - Linux >= 6.14.6 < 6.15
  - Linux 6.15
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-06T16:55:52.211339Z'
published: '2026-08-15'
updated: '2026-11-06'
sourceUpdated: '2026-11-06T17:05:43.463Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-74284'
references:
  - url: 'https://git.kernel.org/stable/c/a425c82ff06cda5165e0de3de8c2a445ec1f863e'
  - url: 'https://git.kernel.org/stable/c/fc973ecd1a079b9a87c360478542f3a56dea085b'
  - url: 'https://git.kernel.org/stable/c/15720cd8fa3fc625146128f89a8e11b0449a20a7'
  - url: 'https://git.kernel.org/stable/c/b2a017bfcf565721918ec7355a373911d2f2a227'
  - url: 'https://git.kernel.org/stable/c/9221a594c72a1446137926d4c2aa04e345f798dc'
  - url: 'https://git.kernel.org/stable/c/66dbb13eeb2fc339f8f548a9076be4c1a94857b0'
  - url: 'https://git.kernel.org/stable/c/3a49bbae676fef1ffe548971e6229ae2adeb9d10'
  - url: 'https://git.kernel.org/stable/c/90b662ea25f5e83bb3b8ccec5b93ced810b92fb8'
tags:
  - cve.org
epss: 0.00216
epssPercentile: 0.12151
ingestedAt: '2026-11-06T18:00:12.565Z'
---

## Overview

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

net/sched: sch_hfsc: Don't make class passive twice

update_vf() is called from two places for the same class during a single
dequeue when the class's child qdisc (e.g. codel/fq_codel) drops its last
packets while dequeuing:

1. The child calls qdisc_tree_reduce_backlog(), which, now that the child
   is empty, invokes hfsc_qlen_notify() -> update_vf(cl, 0, 0) and turns
   the class passive (cl_nactive is decremented up the hierarchy).

2. hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time)
   to charge the dequeued bytes.

On the second call the class is already passive, but its child qdisc is
still empty, so update_vf() arms go_passive again:

      if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC)
              go_passive = 1;

The leaf is then skipped by the cl_nactive == 0 check inside the loop,
which does not clear go_passive, so the stale go_passive propagates to the
parent and decrements its cl_nactive a second time. A parent that still
has other active children is driven to cl_nactive == 0 and removed from
the vttree, even though those siblings are still backlogged. They are
never dequeued again and the qdisc stalls.

Fix this by only arming go_passive when the class is actually active, so an
already-passive class no longer triggers a second passive transition. The
byte accounting (cl->cl_total += len) still runs for every ancestor, so
dequeued bytes continue to be counted exactly once.

## Affected

- `Linux >= 72c61ffbeeb8c50f6d4d70c65d3283aa1bac57a7 < a425c82ff06cda5165e0de3de8c2a445ec1f863e`
- `Linux >= a5efc95a33bd4fcb879250852828cc58c7862970 < fc973ecd1a079b9a87c360478542f3a56dea085b`
- `Linux >= 0475c85426b18eccdcb7f9fb58d8f8e9c6c58c87 < 15720cd8fa3fc625146128f89a8e11b0449a20a7`
- `Linux >= 9030a91235ae4845ec71902c3e0cecfc9ed1f2df < b2a017bfcf565721918ec7355a373911d2f2a227`
- `Linux >= d06476714d2819b550e0cc39222347e2c8941c9d < 9221a594c72a1446137926d4c2aa04e345f798dc`
- `Linux >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb < 66dbb13eeb2fc339f8f548a9076be4c1a94857b0`
- `Linux >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb < 3a49bbae676fef1ffe548971e6229ae2adeb9d10`
- `Linux >= 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb < 90b662ea25f5e83bb3b8ccec5b93ced810b92fb8`
- `Linux 9a5fd5c2f4d4afdd5e405083ee53e0789ce76956`
- `Linux c1175c4ad01dbc9c979d099861fa90a754f72059`
- `Linux >= 5.10.241 < 5.10.261`
- `Linux >= 5.15.190 < 5.15.212`
- `Linux >= 6.1.138 < 6.1.178`
- `Linux >= 6.6.90 < 6.6.145`
- `Linux >= 6.12.28 < 6.12.97`
- `Linux >= 5.4.297 < 5.5`
- `Linux >= 6.14.6 < 6.15`
- `Linux 6.15`

## Remediation

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