---
id: CVE-2025-21767
title: >-
  In the Linux kernel, the following vulnerability has been resolved:


  clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic
  context


  The following bug report happened with a PREEMPT_RT kernel:

    BUG: sleeping fun…
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic
  context


  The following bug report happened with a PREEMPT_RT kernel:

    BUG: sleeping fun…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-667
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.10.50, < 5.10.235'
  - 'linux_kernel >= 5.12.17, < 5.13'
  - 'linux_kernel >= 5.13.2, < 5.15.179'
  - 'linux_kernel >= 5.16, < 6.1.129'
  - 'linux_kernel >= 6.2, < 6.6.79'
  - 'linux_kernel >= 6.7, < 6.12.16'
  - 'linux_kernel >= 6.13, < 6.13.4'
  - linux_kernel = 6.14
patched:
  - linux_kernel 6.13.4
published: '2025-02-27'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:17:34.557'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-21767'
references:
  - url: 'https://git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8783ceeee797d9aa9cfe150690fb9d0bac8cc459'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d9c217fadfcff7a8df58567517d1e4253f3fd243'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-082556.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-784472.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00178
epssPercentile: 0.07339
ingestedAt: '2026-10-15T03:30:12.795Z'
---

## Overview

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

clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context

The following bug report happened with a PREEMPT_RT kernel:

  BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2012, name: kwatchdog
  preempt_count: 1, expected: 0
  RCU nest depth: 0, expected: 0
  get_random_u32+0x4f/0x110
  clocksource_verify_choose_cpus+0xab/0x1a0
  clocksource_verify_percpu.part.0+0x6b/0x330
  clocksource_watchdog_kthread+0x193/0x1a0

It is due to the fact that clocksource_verify_choose_cpus() is invoked with
preemption disabled.  This function invokes get_random_u32() to obtain
random numbers for choosing CPUs.  The batched_entropy_32 local lock and/or
the base_crng.lock spinlock in driver/char/random.c will be acquired during
the call. In PREEMPT_RT kernel, they are both sleeping locks and so cannot
be acquired in atomic context.

Fix this problem by using migrate_disable() to allow smp_processor_id() to
be reliably used without introducing atomic context. preempt_disable() is
then called after clocksource_verify_choose_cpus() but before the
clocksource measurement is being run to avoid introducing unexpected
latency.

## Affected

- `linux_kernel >= 5.10.50, < 5.10.235`
- `linux_kernel >= 5.12.17, < 5.13`
- `linux_kernel >= 5.13.2, < 5.15.179`
- `linux_kernel >= 5.16, < 6.1.129`
- `linux_kernel >= 6.2, < 6.6.79`
- `linux_kernel >= 6.7, < 6.12.16`
- `linux_kernel >= 6.13, < 6.13.4`
- `linux_kernel = 6.14`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.13.4`