CVE-2025-40142
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-11-12

Last updated on: 2025-11-12

Assigner: kernel.org

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.
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Meta Information
Published
2025-11-12
Last Modified
2025-11-12
Generated
2026-05-07
AI Q&A
2025-11-13
EPSS Evaluated
2026-05-05
NVD
CVE-2025-40142
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability involves the Linux kernel's ALSA pcm component where the function snd_pcm_group_lock_irq() uses spin_lock_irq() to acquire a spinlock and disable interrupts. However, on PREEMPT_RT (a real-time kernel variant), softirqs remain preemptible and are not disabled by spin_lock_irq(), allowing timers to run during the lock on the same CPU. This leads to a potential deadlock involving the softirq_ctrl.lock, which synchronizes softirqs. The vulnerability arises because softirq_ctrl.lock can be acquired in conflicting contexts, causing a deadlock. The fix is to manually disable softirqs before acquiring the lock on PREEMPT_RT to prevent this deadlock.


How can this vulnerability impact me? :

This vulnerability can cause a deadlock in the Linux kernel on systems using PREEMPT_RT, potentially leading to system hangs or degraded performance. Such deadlocks can affect system stability and responsiveness, especially in real-time environments relying on PREEMPT_RT patches.


What immediate steps should I take to mitigate this vulnerability?

To mitigate this vulnerability, update the Linux kernel to a version where the ALSA pcm component disables bottom softirqs as part of spin_lock_irq() on PREEMPT_RT. This ensures that softirqs are manually disabled before acquiring the lock, preventing possible deadlocks. Applying the vendor's patch or kernel update that addresses this issue is recommended.


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