---
id: CVE-2026-31422
title: 'net/sched: cls_flow: fix NULL pointer dereference on shared blocks'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: cls_flow: fix NULL pointer dereference on shared blocks

  flow_change() calls tcf_block_q() and dereferences q->handle to derive
  a default baseclass.  Shared …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db <
    57f94ac7e953eece5ed4819605a18f3cdfc63dcc
  - >-
    Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db <
    942813276edeb1741fa5b0a73471beb4e495fa08
  - >-
    Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db <
    cc707a4fd4c3b6ab2722e06bc359aa010e13d408
  - >-
    Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db <
    4a09f72007201c9f667dc47f64517ec23eea65e5
  - >-
    Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db <
    9bf5fc36a43f7b8b5507c96e74fb81f1e8b4957e
  - >-
    Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db <
    a208c3e1232997e9317887294c20008dfcb75449
  - >-
    Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db <
    415ea0c973c754b9f375225807810eb9045f4293
  - >-
    Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db <
    1a280dd4bd1d616a01d6ffe0de284c907b555504
  - Linux 4.15
published: '2026-04-13'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:46:58.481Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-31422'
references:
  - url: 'https://git.kernel.org/stable/c/57f94ac7e953eece5ed4819605a18f3cdfc63dcc'
  - url: 'https://git.kernel.org/stable/c/942813276edeb1741fa5b0a73471beb4e495fa08'
  - url: 'https://git.kernel.org/stable/c/cc707a4fd4c3b6ab2722e06bc359aa010e13d408'
  - url: 'https://git.kernel.org/stable/c/4a09f72007201c9f667dc47f64517ec23eea65e5'
  - url: 'https://git.kernel.org/stable/c/9bf5fc36a43f7b8b5507c96e74fb81f1e8b4957e'
  - url: 'https://git.kernel.org/stable/c/a208c3e1232997e9317887294c20008dfcb75449'
  - url: 'https://git.kernel.org/stable/c/415ea0c973c754b9f375225807810eb9045f4293'
  - url: 'https://git.kernel.org/stable/c/1a280dd4bd1d616a01d6ffe0de284c907b555504'
tags:
  - cve.org
epss: 0.00171
epssPercentile: 0.05625
ingestedAt: '2026-09-08T15:33:26.991Z'
---

## Overview

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

net/sched: cls_flow: fix NULL pointer dereference on shared blocks

flow_change() calls tcf_block_q() and dereferences q->handle to derive
a default baseclass.  Shared blocks leave block->q NULL, causing a NULL
deref when a flow filter without a fully qualified baseclass is created
on a shared block.

Check tcf_block_shared() before accessing block->q and return -EINVAL
for shared blocks.  This avoids the null-deref shown below:

=======================================================================
KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f]
RIP: 0010:flow_change (net/sched/cls_flow.c:508)
Call Trace:
 tc_new_tfilter (net/sched/cls_api.c:2432)
 rtnetlink_rcv_msg (net/core/rtnetlink.c:6980)
 [...]
=======================================================================

## Affected

- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 57f94ac7e953eece5ed4819605a18f3cdfc63dcc`
- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 942813276edeb1741fa5b0a73471beb4e495fa08`
- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < cc707a4fd4c3b6ab2722e06bc359aa010e13d408`
- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 4a09f72007201c9f667dc47f64517ec23eea65e5`
- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 9bf5fc36a43f7b8b5507c96e74fb81f1e8b4957e`
- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < a208c3e1232997e9317887294c20008dfcb75449`
- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 415ea0c973c754b9f375225807810eb9045f4293`
- `Linux >= 1abf272022cf1d18469405f47b4ec49c6a3125db < 1a280dd4bd1d616a01d6ffe0de284c907b555504`
- `Linux 4.15`

## Remediation

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