# CVE-2025-39745: rcutorture: Fix rcutorture_one_extend_check() splat in RT kernels

CVE-2025-39745 is fixed in linux on 1 platform by DEBIAN-CVE-2025-39745 (version 6.16.3-1), released September 11, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2025-39745
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0016
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 11, 2025
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-39745

## Description

In the Linux kernel, the following vulnerability has been resolved:  rcutorture: Fix rcutorture_one_extend_check() splat in RT kernels  For built with CONFIG_PREEMPT_RT=y kernels, running rcutorture tests resulted in the following splat:  [   68.797425] rcutorture_one_extend_check during change: Current 0x1  To add 0x1  To remove 0x0  preempt_count() 0x0 [   68.797533] WARNING: CPU: 2 PID: 512 at kernel/rcu/rcutorture.c:1993 rcutorture_one_extend_check+0x419/0x560 [rcutorture] [   68.797601] Call Trace: [   68.797602]  <TASK> [   68.797619]  ? lockdep_softirqs_off+0xa5/0x160 [   68.797631]  rcutorture_one_extend+0x18e/0xcc0 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [   68.797646]  ? local_clock+0x19/0x40 [   68.797659]  rcu_torture_one_read+0xf0/0x280 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [   68.797678]  ? __pfx_rcu_torture_one_read+0x10/0x10 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [   68.797804]  ? __pfx_rcu_torture_timer+0x10/0x10 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [   68.797815] rcu-torture: rcu_torture_reader task started [   68.797824] rcu-torture: Creating rcu_torture_reader task [   68.797824]  rcu_torture_reader+0x238/0x580 [rcutorture 2466dbd2ff34dbaa36049cb323a80c3306ac997c] [   68.797836]  ? kvm_sched_clock_read+0x15/0x30  Disable BH does not change the SOFTIRQ corresponding bits in preempt_count() for RT kernels, this commit therefore use softirq_count() to check the if BH is disabled.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 6.16.3-1 | [DEBIAN-CVE-2025-39745](https://patchblox.com/security/data/fix/linux/debian-cve-2025-39745.md) | Sep 11, 2025 |

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