CVE-2025-40142 ALSA: pcm: Disable bottom softirqs as part of spin_lock_irq() on PREEMPT_RT
A race condition in the Linux kernel ALSA PCM driver on PREEMPT_RT systems can cause a deadlock, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40142?
CVE-2025-40142 is a vulnerability in Linux, published on 12 Nov 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:
ALSA: pcm: Disable bottom softirqs as part of spin_lock_irq() on PREEMPT_RT
snd_pcm_group_lock_irq() acquires a spinlock_t and disables interrupts via spin_lock_irq(). This also implicitly disables the handling of softirqs such as TIMER_SOFTIRQ. On PREEMPT_RT softirqs are preemptible and spin_lock_irq() does not disable them. That means a timer can be invoked during spin_lock_irq() on the same CPU. Due to synchronisations reasons local_bh_disable() has a per-CPU lock named softirq_ctrl.lock which synchronizes individual softirq against each other. syz-bot managed to trigger a lockdep report where softirq_ctrl.lock is acquired in hrtimer_cancel() in addition to hrtimer_run_softirq(). This is a possible deadlock.
The softirq_ctrl.lock can not be made part of spin_lock_irq() as this would lead to too much synchronisation against individual threads on the system. To avoid the possible deadlock, softirqs must be manually disabled before the lock is acquired.
Disable softirqs before the lock is acquired on PREEMPT_RT.
Which versions are affected by CVE-2025-40142?
How do I fix CVE-2025-40142?
Apply the vendor's patch.
Is CVE-2025-40142 being exploited?
There is no known exploitation of CVE-2025-40142 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40142, DEBIAN-CVE-2025-40142, GHSA-5f4r-vh38-xfwr, ROOT-OS-DEBIAN-13-CVE-2025-40142, UBUNTU-CVE-2025-40142.