CVE-2026-98970 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/vc4: Free the BO cache size list on teardown
vc4_bo_cache_destroy() purges the cached BOs but never frees the size list, leaking it on every unbind.
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Analysis
by VulDB Data Team • 10/23/2026
The identified issue resides within the Linux kernel's Direct Rendering Manager subsystem, specifically affecting the Broadcom VC4 display driver which manages hardware for Raspberry Pi devices utilizing VideoCore IV GPUs. This vulnerability manifests as a memory leak during the lifecycle management of buffer objects, particularly when the device is unbound or the module is unloaded. The root cause lies in the implementation of the vc4_bo_cache_destroy function, which serves to clean up cached buffer object structures that are retained for performance optimization purposes. While this routine correctly purges and releases the individual buffer object entries stored within the cache, it fails to deallocate the underlying data structure responsible for tracking these objects by size class. This oversight results in a persistent allocation of kernel memory that is never returned to the system pool upon driver teardown or device unbinding operations.
From a technical perspective, this flaw represents a classic resource management error where cleanup routines are incomplete. The VC4 driver maintains a cache of buffer objects categorized by their allocated sizes to facilitate faster allocations for subsequent rendering requests. When the graphics context is destroyed or the hardware interface is detached, the system invokes teardown procedures intended to release all associated resources. However, because the size list itself remains allocated, each unbind event results in a small but cumulative loss of kernel memory. Over time, if such operations are performed repeatedly without full system reboots, this can contribute to gradual memory exhaustion within the kernel space, potentially degrading overall system stability and performance.
The operational impact of this vulnerability is primarily characterized by resource leakage rather than immediate security exploitation or privilege escalation. Since the leaked memory resides in kernel space and is tied to specific driver lifecycle events, it does not directly expose sensitive data to user-space applications nor allow for arbitrary code execution. However, sustained memory leaks can lead to increased pressure on the kernel's memory management subsystem. In environments where graphics contexts are frequently created and destroyed, such as during heavy application switching or automated testing scenarios, this leak could eventually trigger out-of-memory conditions within critical kernel pathways, leading to process termination or system instability. The severity is generally considered low due to the limited scope of impact, but it remains a significant quality assurance defect that violates best practices for resource lifecycle management in operating systems.
To mitigate this vulnerability and align with industry standards such as CWE-401 which addresses missing release of memory after effective lifetime, developers must ensure that all dynamically allocated structures are properly freed during cleanup sequences. The specific remediation involves modifying the vc4_bo_cache_destroy function to include a deallocation call for the size list data structure before returning control to the caller. This ensures complete resource reclamation and prevents accumulation over multiple unbind cycles. For system administrators, while this issue is resolved in updated kernel versions, maintaining up-to-date systems remains the primary defense against such defects. Additionally, monitoring kernel memory usage patterns can help detect similar issues in other drivers where cleanup routines may be similarly incomplete. Adherence to rigorous code review processes that verify symmetry between allocation and deallocation calls across all driver entry points will further prevent recurrence of this class of errors.