CVE-2025-39745 rcutorture: Fix rcutorture_one_extend_check() splat in RT kernels
A bug in the Linux kernel's RCU torture test module causes a kernel warning splat on RT kernels, potentially leading to system instability or denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-39745?
CVE-2025-39745 is a medium-severity denial of service vulnerability in Linux kernel, published on 11 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2025-39745?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39745?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-39745 being exploited?
There is no known exploitation of CVE-2025-39745 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-39745, GHSA-59f6-f4pc-ww92, ROOT-OS-DEBIAN-12-CVE-2025-39745, ROOT-OS-DEBIAN-13-CVE-2025-39745, ROOT-OS-UBUNTU-2204-CVE-2025-39745, ROOT-OS-UBUNTU-2404-CVE-2025-39745 and 1 more.