Data Race Vulnerability in the Linux Kernel

CVE-2025-39749

What is CVE-2025-39749?

In certain configurations of the Linux kernel, a vulnerability arises due to a race condition involving the RCU (Read-Copy-Update) mechanism. Specifically, the function rcu_read_unlock_special() can operate within an interrupts-disabled context while simultaneously interacting with an irq-work handler, leading to potential data races. This situation can result in inconsistent states within the per-CPU rcu_data structure, particularly affecting the ->defer_qs_iw_pending field. The issue manifests in kernels using the rcutree.use_softirq=y setting and requires that interrupts be disabled during specific updates to ensure system stability. A recent commit has addressed this by disabling interrupts while the rcu_preempt_deferred_qs_handler function updates the relevant field.

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