CVE-2026-90270 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
arm_mpam: Disable driver unbind to avoid UAF
When a user unbinds an MSC and that MSC is the only MSC left for a component then the corresponding mpam_component will be freed. If the user then goes on to read the schemata file in the resctrl filesystem then the mpam_component will be accessed from resctrl_arch_get_config() leading to a use after free.
As the MPAM driver is not a module the unbind sysfs interface is the only way to trigger the remove. Instead of dealing with the complexity of allowing some unused MSC to unbind just remove the unbind sysfs interface.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel vulnerability identified in the arm_mpam subsystem represents a critical use-after-free condition that arises from improper handling of resource management during driver unbinding operations. The ARM Memory System Architecture Policy (MPAM) framework is responsible for managing hardware resources and policies related to memory system partitioning, ensuring isolation and quality-of-service guarantees across different components within an Arm-based processor architecture. Within this subsystem, the interaction between the MPAM driver and the resctrl filesystem creates a dangerous race condition when users attempt to unbind Memory System Components (MSCs). The vulnerability specifically manifests when a user initiates an unbind operation on an MSC that serves as the sole remaining component for its associated mpam_component structure. Under these circumstances, the kernel correctly frees the memory allocated for the mpam_component object to prevent resource leaks and maintain system integrity during removal processes.
However, the flaw lies in the subsequent access patterns triggered by user-space interactions with the resctrl filesystem. After the mpam_component has been deallocated due to the unbind operation, a user can read the schemata file within the resctrl interface. This action invokes the function resctrl_arch_get_config(), which attempts to retrieve configuration data for the affected component. Because the underlying mpam_component structure was already freed during the previous step, this access results in dereferencing a dangling pointer. The kernel subsequently reads from or writes to memory that is no longer validly owned by the driver, leading to undefined behavior. This use-after-free condition can potentially lead to system crashes, data corruption, or more severe security implications such as arbitrary code execution if an attacker can carefully craft inputs to exploit the freed memory region for control flow hijacking.
From a technical perspective, this vulnerability aligns with CWE-416, which describes Use After Free vulnerabilities where software continues to use pointers that point to freed memory. The operational impact is significant because it allows local users who have access to sysfs interfaces and resctrl filesystem mounts to trigger kernel-mode crashes or potentially escalate privileges depending on the state of the freed heap memory. Since MPAM drivers are built into the kernel rather than loaded as loadable modules, there is no alternative mechanism like module unloading that might offer different lifecycle management semantics. The only available interface for triggering the removal logic in this context is the sysfs unbind attribute, making it a direct and accessible attack vector for any user with appropriate permissions to interact with these device interfaces.
The mitigation strategy implemented by the Linux kernel maintainers addresses the root cause by removing the problematic functionality entirely rather than attempting complex synchronization fixes. Specifically, the developers have disabled or removed the driver unbind sysfs interface. This approach eliminates the possibility of triggering the remove path that leads to the premature freeing of mpam_component structures while they are still potentially accessible via resctrl operations. By restricting the ability to unbind MSCs in this specific manner, the kernel ensures that the lifecycle of these components remains stable and predictable during runtime operation. While this limits administrative flexibility regarding dynamic reconfiguration of MPAM resources, it prioritizes system stability and security over granular control features that were proven unsafe under concurrent access conditions.
In terms of industry standards mapping, this vulnerability can be correlated with MITRE ATT&CK techniques related to privilege escalation or denial of service through exploitation of software vulnerabilities. The specific mechanism falls under the category of exploiting improper resource management within operating system kernels. Security practitioners should ensure that systems running affected kernel versions are updated to apply these patches. Additionally, monitoring for unusual access patterns to resctrl filesystems and sysfs device interfaces may help in detecting potential exploitation attempts before they result in successful compromise or service disruption. The fix underscores the importance of rigorous lifecycle management in kernel drivers, particularly when multiple subsystems interact with shared hardware resources through different abstraction layers.