CVE-2025-39745: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability in the Linux kernel's rcutorture testing functionality has been identified and assigned CVE-2025-39745. The issue specifically affects kernels built with CONFIGPREEMPTRT=y configuration and manifests during rcutorture tests. The vulnerability was disclosed on September 11, 2025 (NVD).

The vulnerability occurs in the rcutortureoneextendcheck() function where there is a discrepancy in how Bottom Half (BH) disabling affects the SOFTIRQ bits in preemptcount() for RT kernels. The issue results in a kernel warning (splat) during rcutorture tests, with specific behavior observed when Current is 0x1, To add is 0x1, and To remove is 0x0 with preempt_count() at 0x0 (NVD).

The vulnerability affects the kernel's RCU (Read-Copy-Update) torture testing functionality in RT (Real-Time) kernels. While primarily impacting testing scenarios, it could potentially affect system stability in production environments using RT kernels (NVD).

The issue has been resolved in newer kernel versions by modifying the code to use softirqcount() instead of preemptcount() to check if BH is disabled in RT kernels (NVD).