CVE-2025-40142

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References