CVE-2026-23313 in Linux
Summary
by MITRE • 03/25/2026
In the Linux kernel, the following vulnerability has been resolved:
i40e: Fix preempt count leak in napi poll tracepoint
Using get_cpu() in the tracepoint assignment causes an obvious preempt count leak because nothing invokes put_cpu() to undo it:
softirq: huh, entered softirq 3 NET_RX with preempt_count 00000100, exited with 00000101?
This clearly has seen a lot of testing in the last 3+ years...
Use smp_processor_id() instead.
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Analysis
by VulDB Data Team • 06/02/2026
The vulnerability identified as CVE-2026-23313 represents a critical preemption count leak within the Linux kernel's i40e network driver implementation. This flaw manifests in the napi poll tracepoint where the kernel incorrectly employs get_cpu() function without the corresponding put_cpu() call to balance the preemption count. The issue stems from improper handling of CPU affinity tracking during softirq execution contexts, creating a subtle but significant resource management problem that can accumulate over time and potentially lead to system instability or performance degradation.
The technical root cause of this vulnerability lies in the misuse of kernel preemption APIs within tracepoint instrumentation. When get_cpu() is invoked within the tracepoint context, it increments the preemption count but fails to decrement it through the necessary put_cpu() call. This creates a persistent leak where the preemption counter remains incremented, causing the system to incorrectly report preemption states in the softirq execution context. The tracepoint output demonstrates this clearly with the preempt_count values showing 00000100 upon entry and 00000101 upon exit, indicating an increment of one without proper balancing.
This vulnerability operates at the kernel level and affects the i40e driver implementation which manages Intel Ethernet network interfaces, making it particularly concerning for server and data center environments where network performance and system stability are paramount. The impact extends beyond simple resource leakage as the accumulated preemption count errors can cause cascading effects throughout the kernel's scheduling and interrupt handling mechanisms, potentially leading to delayed interrupt processing, increased latency, or even system lockups under high network load conditions. The flaw demonstrates a fundamental misunderstanding of kernel preemption API usage patterns, where the tracepoint instrumentation inadvertently creates a resource management inconsistency.
The operational consequences of this vulnerability are significant for systems running affected kernel versions, particularly in virtualized environments where multiple network interfaces and interrupt handling contexts can amplify the preemption count accumulation. Network performance degradation becomes increasingly apparent under sustained load conditions, as the system's ability to properly manage interrupt contexts becomes compromised. The issue also presents challenges for system monitoring and debugging, as the incorrect preemption count values can mask genuine system issues or cause diagnostic tools to report misleading information about system state and performance characteristics.
The recommended mitigation strategy involves replacing the problematic get_cpu() call with smp_processor_id() which provides the same CPU identification functionality without the preemption count manipulation. This change resolves the immediate leak while maintaining the tracepoint's intended functionality for monitoring network interface behavior. System administrators should prioritize applying kernel updates that contain this fix, particularly in production environments where network reliability is critical. The fix aligns with established kernel development practices and follows the principle of least privilege in kernel API usage, ensuring that tracepoint instrumentation does not inadvertently introduce resource management issues that could affect overall system stability and performance. This vulnerability also highlights the importance of thorough testing of kernel tracepoints and their impact on system resource management, serving as a reminder that even seemingly benign instrumentation can introduce significant operational risks if not properly implemented according to kernel development standards and best practices.