CVE-2026-64430 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
NTB: epf: Avoid calling pci_irq_vector() from hardirq context
ntb_epf_vec_isr() calls pci_irq_vector() in hardirq context to derive the vector number. pci_irq_vector() calls msi_get_virq() that takes a mutex and can therefore trigger "scheduling while atomic" splats:
BUG: scheduling while atomic: kworker/u33:0/55/0x00010001 ... Call trace: ... schedule+0x38/0x110 schedule_preempt_disabled+0x28/0x50 __mutex_lock.constprop.0+0x848/0x908 __mutex_lock_slowpath+0x18/0x30 mutex_lock+0x4c/0x60 msi_domain_get_virq+0xe8/0x138 pci_irq_vector+0x2c/0x60 ntb_epf_vec_isr+0x28/0x120 [ntb_hw_epf]
__handle_irq_event_percpu+0x70/0x3a8 handle_irq_event+0x48/0x100 handle_edge_irq+0x100/0x1c8 ...
Cache the Linux IRQ number for vector 0 when vectors are allocated and use it as a base in the ISR. Running the ISR in a threaded IRQ handler would also avoid the problem, but that would be unnecessary here.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability exists within the Linux kernel's NTB (Non-Transparent Bridge) implementation, specifically in the endpoint function driver component. The issue manifests when the ntb_epf_vec_isr() interrupt service routine attempts to call pci_irq_vector() while already executing in hardirq context. This creates a dangerous scenario where atomic execution contexts attempt to perform scheduling operations, violating fundamental kernel safety principles.
The technical flaw stems from the pci_irq_vector() function calling msi_get_virq() which requires acquiring a mutex lock. When this occurs within an atomic context, it triggers the "scheduling while atomic" kernel panic condition. The call trace demonstrates this problematic execution path where schedule() gets called through the mutex locking mechanism, ultimately causing system instability and potential crashes.
The operational impact of this vulnerability is significant for systems relying on NTB functionality, particularly those using MSI (Message Signaled Interrupts) for device communication. When interrupt handlers execute in hardirq context, they must remain atomic and avoid any operations that could block or schedule. The vulnerability essentially creates a kernel oops condition that can lead to system crashes, data corruption, or denial of service scenarios in production environments.
This vulnerability maps directly to CWE-362, which addresses concurrent execution using locks and the improper handling of atomic contexts. The issue also relates to ATT&CK technique T1059.006 for kernel-level code execution and T1489 for system mediation denial of service. The root cause involves improper interrupt handling methodology where atomic context requirements are violated through mutex acquisition during critical interrupt processing.
The recommended mitigation strategy involves pre-caching the Linux IRQ number for vector 0 during initial vector allocation, then using this cached value as a base within the ISR handler. This approach eliminates the need to call pci_irq_vector() from atomic context while maintaining functional correctness. Alternative approaches such as converting to threaded IRQ handlers could also resolve the issue but would introduce unnecessary complexity and potential performance overhead in the current implementation.
The fix maintains backward compatibility while ensuring kernel stability by avoiding atomic context violations. It represents a defensive programming approach that prevents scheduling operations within interrupt handlers, which is a fundamental principle in kernel development. This solution aligns with Linux kernel best practices for interrupt handling and demonstrates proper consideration of atomic execution contexts in device driver development.
This vulnerability highlights the importance of understanding kernel context requirements when implementing interrupt handlers, particularly in complex subsystems like NTB where multiple layers of abstraction exist between hardware interrupts and software processing. The resolution demonstrates proper kernel development practices that prevent race conditions and maintain system integrity under all operational scenarios.