Linux Kernel PREEMPT_RT Softirq Handling Vulnerability in ALSA PCM Component

A vulnerability exists in the Linux kernel's Advanced Linux Sound Architecture (ALSA) PCM subsystem when running with the PREEMPT_RT configuration. The issue arises because the function 'snd_pcm_group_lock_irq()' acquires a spinlock and disables interrupts, which also turns off the handling of softirqs like TIMER_SOFTIRQ. However, in PREEMPT_RT, softirqs can be preempted, and 'spin_lock_irq()' does not disable them, potentially leading to a deadlock. This vulnerability affects several versions of the Linux kernel.

Impact

The vulnerability can cause a deadlock by improperly managing softirq handling during critical sections locked by spinlocks, particularly in the PREEMPT_RT configuration.

Reproduction

The vulnerability can be reproduced by enabling the PREEMPT_RT configuration in the Linux kernel and then using the ALSA PCM subsystem in a way that triggers the 'snd_pcm_group_lock_irq()' function. This will cause the softirq handling to be disrupted, leading to a possible deadlock scenario.

Remediation

Users can upgrade to the latest version of the Linux kernel where this vulnerability has been addressed. The specific commit that resolves this issue is available in the Linux kernel stable tree.