CVE-2026-98670 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
iio: adc: xilinx-xadc: free IRQ before cancelling the unmask worker on unbind
The ZYNQ XADC alarm IRQ handler queues zynq_unmask_work via schedule_delayed_work(); that work is cleared by a devm callback. Register the devm callback before devm_request_irq() so the devres LIFO teardown frees the IRQ first, ensuring the handler can no longer queue work by the time the workqueue is cleared. Otherwise the handler could re-arm the work and run it after the xadc structure has been freed.
This issue was found by an in-house static analysis tool.
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Analysis
by VulDB Data Team • 10/18/2026
The vulnerability identified within the Linux kernel's Industrial I/O (IIO) ADC driver for Xilinx Zynq devices represents a classic race condition arising from improper resource management during device unbinding operations. This specific flaw, located in the xilinx-xadc subsystem, stems from an incorrect ordering of teardown procedures when the driver is detached or removed from the system. The core issue involves the interaction between interrupt request (IRQ) handling and delayed workqueue execution mechanisms that are used to manage hardware alarms. Specifically, the alarm IRQ handler for the Zynq XADC queues a task named zynq_unmask_work using schedule_delayed_work(). This mechanism allows asynchronous processing of unmasking operations after a specified delay, which is critical for maintaining stable state transitions in hardware interaction scenarios.
The root cause lies in the sequence of resource deallocation during the driver's unbind phase. Originally, the devm (device managed) callback responsible for clearing or canceling this delayed work was registered after the IRQ request function call. This ordering created a window of vulnerability where the interrupt line remained active while the mechanism to stop pending asynchronous tasks had not yet been established. Consequently, if an alarm event triggered during the brief interval between releasing the device structure and ensuring no further interrupts could fire, the IRQ handler would successfully queue new work items even after the primary xadc data structures had already been freed from memory. This creates a use-after-free scenario where kernel code attempts to execute or reference memory that has been reclaimed by the system allocator.
From an operational impact perspective, this race condition can lead to severe stability issues including kernel panics, general protection faults, or unpredictable behavior depending on what data structures are accessed within the delayed work function after they have been freed. Since the IRQ handler runs in interrupt context and the workqueue executes in process context, synchronization becomes complex. If the work item accesses fields of the xadc structure that no longer exist due to premature freeing, it results in memory corruption or a crash. This type of vulnerability is particularly dangerous because it relies on timing conditions that may not trigger frequently under normal load but can be exploited through stress testing or specific hardware event patterns, potentially leading to denial of service against systems relying on this driver for critical monitoring functions such as temperature or voltage sensing.
The technical classification of this flaw aligns with CWE-416: Use After Free, specifically involving a race condition during resource teardown. In terms of the MITRE ATT&CK framework, while not an attack vector per se in the traditional sense of malicious exploitation by external actors, it falls under patterns related to improper cleanup and state management that could be leveraged for local privilege escalation or system instability if triggered intentionally through hardware manipulation or fuzzing techniques targeting interrupt handlers. The vulnerability highlights a common pitfall in kernel driver development where devm APIs are used but their LIFO (Last-In-First-Out) teardown semantics are not fully respected regarding the ordering of dependent resources like interrupts and workqueues.
To mitigate this issue, the fix involves reordering the registration of device-managed callbacks to ensure that the cancellation of delayed work occurs before or concurrently with the release of IRQs in a manner that guarantees no new work can be queued after the structure is freed. By registering the devm callback for clearing the unmask worker prior to requesting the IRQ, the teardown process ensures that when the driver is unloaded, the interrupt handler cannot queue any further delayed work items because the cancellation mechanism is already active and will prevent re-arming of timers once the free operation begins. This strict ordering guarantees that all pending asynchronous tasks are flushed or prevented before the underlying memory structures are deallocated, thereby eliminating the race condition entirely.
Developers maintaining similar drivers should adhere to best practices for resource management by ensuring that cleanup routines are registered in reverse order of acquisition when using devm APIs, but with specific attention to dependencies between interrupt handlers and workqueues. Static analysis tools play a crucial role here as they can detect these ordering violations before deployment. Regular auditing of driver unbind paths against known race condition patterns is essential for maintaining kernel stability. The resolution underscores the importance of understanding not just what resources are allocated, but precisely when their lifecycle ends relative to other dependent subsystems like interrupt controllers and workqueues within the Linux kernel architecture.