CVE-2026-93092 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
firmware: arm_scmi: Unregister device notifier before IDR teardown
The requested-devices notifier looks up protocol fwnodes from the active_protocols IDR. During remove, unregister the notifier before releasing and destroying active_protocols so no notifier callback can race with the IDR teardown.
Keep the bus notifier registered until after the protocol state is torn down, matching the existing remove ordering for SCMI bus users.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel vulnerability identified in the arm_scmi subsystem represents a critical concurrency flaw arising from improper resource cleanup sequencing during device removal operations. The System Control and Management Interface (SCMI) provides a standardized protocol for firmware to communicate with operating systems regarding power management, clock control, and other system configurations. Within this framework, the driver maintains an Identifier Resource (IDR) structure known as active_protocols to track currently registered protocols. A key component of this architecture is the requested-devices notifier, which relies on looking up protocol firmwares nodes from this IDR during runtime operations. The core technical flaw lies in the order of teardown procedures within the remove function. Specifically, the driver was previously unregistering the bus notifier only after releasing and destroying the active_protocols IDR. This ordering creates a race condition window where the IDR is destroyed while the notifier remains registered and potentially active.
This architectural oversight allows for a scenario where asynchronous events or callbacks triggered by the still-registered notifier can attempt to access data structures that have already been freed. When the requested-devices notifier callback executes, it attempts to look up protocol fwnodes from the now-invalid active_protocols IDR. Because the underlying memory has been released, this lookup operation results in a use-after-free condition or an invalid pointer dereference. Such race conditions are particularly dangerous because they depend on timing and can manifest under varying system loads or during hot-plug events where device removal occurs concurrently with other kernel activities. The lack of synchronization between notifier unregistration and IDR teardown means that the driver fails to maintain atomicity in its state transitions, leading to potential kernel panics, data corruption, or arbitrary code execution if an attacker can influence the timing of these operations through crafted inputs or specific system states.
The operational impact of this vulnerability is severe, primarily affecting system stability and security integrity on ARM-based systems utilizing SCMI interfaces. A successful exploitation could lead to a denial of service by crashing the kernel, which disrupts all running services and requires a reboot. In more sophisticated attack scenarios, if the memory reuse patterns allow for controlled allocation after the free operation, an attacker might achieve arbitrary code execution with kernel privileges. This effectively grants full control over the underlying hardware and operating system, bypassing user-space security boundaries. The vulnerability is particularly relevant in environments where dynamic device configuration or frequent power state changes are common, as these actions increase the likelihood of triggering the race condition during driver removal sequences.
To mitigate this risk, the resolution involves reordering the cleanup steps within the arm_scmi remove function to ensure that the notifier is unregistered before the active_protocols IDR is released and destroyed. This change ensures that no notifier callback can be invoked after the data structures it depends on have been torn down, thereby eliminating the race condition window. By keeping the bus notifier registered until after the protocol state is fully torn down, the driver aligns its behavior with existing remove ordering practices for SCMI bus users, promoting consistency across the subsystem. This fix adheres to fundamental software engineering principles regarding resource lifecycle management and concurrency control. From a vulnerability classification perspective, this issue maps to CWE-416 Use After Free, as it involves accessing memory after it has been made available for reuse without proper synchronization. Additionally, from an offensive security standpoint such as the MITRE ATT&CK framework, this type of race condition can be leveraged in privilege escalation techniques where timing attacks are used to manipulate kernel state during initialization or teardown phases. System administrators should apply the relevant kernel patch immediately to close this gap and ensure that driver removal processes handle resource deallocation with strict ordering guarantees.