The Linux kernel vulnerability (CVE-2026-64430) involves the NTB (Non-Transparent Bridge) subsystem's epf driver calling pci_irq_vector() from a hardirq context within the interrupt service routine ntb_epf_vec_isr(). pci_irq_vector() internally calls msi_get_virq(), which takes a mutex. Taking a mutex in hardirq context is unsafe and triggers a 'scheduling while atomic' kernel bug, leading to kernel warnings and potential system instability. The fix involves caching the IRQ number when vectors are allocated to avoid calling pci_irq_vector() in hardirq context. The vulnerability affects multiple Linux kernel versions prior to 7.0.0-31.31 and related builds for Ubuntu 24.04 LTS. The vendor has released patched kernel versions to address this issue.

The vulnerability causes a kernel bug due to improper locking in interrupt context, leading to 'scheduling while atomic' errors. This can result in kernel warnings, instability, or crashes, impacting system availability. There is no indication of confidentiality or integrity compromise. No known exploits in the wild have been reported.

A patch is available and has been released by the vendor. Users should update their Linux kernel packages to the fixed versions as specified in the Ubuntu security notices (e.g., linux-image-7.0.0-31.31 and later). After updating, a system reboot is required to apply the fix. Due to ABI changes, third-party kernel modules must be recompiled and reinstalled. Follow the vendor's update instructions carefully.