CVE-2025-21767
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.
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
No mitigations published for this CVE yet.
The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.
✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here withsource_tier=community-verified.
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| sles | affected | | |
| debian | bookworm | fixed | 6.1.129-1 |
| debian | bullseye | fixed | 5.10.237-1 |
| debian | forky | fixed | 6.12.16-1 |
| debian | sid | fixed | 6.12.16-1 |
| debian | trixie | fixed | 6.12.16-1 |
| linux-kernel | affected | 5.10.235 | |
| linux-kernel | 6.14 | affected | |
References
- https://git.kernel.org/stable/c/0fb534187d2355f6c8f995321e76d1ccd1262ac1
- https://git.kernel.org/stable/c/60f54f0d4ea530950549a8263e6fdd70a40490a4
- https://git.kernel.org/stable/c/6bb05a33337b2c842373857b63de5c9bf1ae2a09
- 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/d9c217fadfcff7a8df58567517d1e4253f3fd243
- https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
- https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
- https://cert-portal.siemens.com/productcert/html/ssa-082556.html
- https://www.suse.com/security/cve/CVE-2025-21767.html
- https://security-tracker.debian.org/tracker/CVE-2025-21767
CWEs
CWE-667
Community-verified mitigations for this CVE will appear above when contributors publish them.
Verify integrity in audit chain (admin only). AS-IS.