CVE-2026-68233 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/vc4: Shut down BO cache timer before teardown
The BO cache timer callback schedules time_work, and time_work can rearm the timer through vc4_bo_cache_free_old().
vc4_bo_cache_destroy() deletes the timer and then cancels the work, which does not break that cycle: the work being cancelled can rearm the timer, and the timer then queues work again after teardown.
Use timer_shutdown_sync() instead, so the timer cannot be rearmed and the cycle ends with cancel_work_sync().
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability in question affects the Linux kernel's vc4 graphics driver component within the direct rendering manager subsystem. This issue specifically targets the buffer object (BO) cache management functionality that handles memory allocation and deallocation for graphics processing units. The problem manifests during the driver teardown process when the BO cache timer mechanism fails to properly terminate all associated operations, creating a persistent cycle that can lead to system instability or resource exhaustion.
The technical flaw stems from an improper sequence in the cleanup routine vc4_bo_cache_destroy() which manages the destruction of buffer object cache timers. During normal operation, the BO cache timer callback schedules time_work items that can rearm the same timer through the vc4_bo_cache_free_old() function call. This creates a circular dependency where the work item being cancelled can still rearm the timer, and the timer subsequently queues new work items even after the teardown process has begun. The vulnerability is classified under CWE-691 as an Insufficient Control Flow Management issue where control flow is not properly managed during cleanup operations.
The operational impact of this vulnerability extends beyond simple resource management concerns to potentially affect system stability and performance during driver shutdown sequences. When the graphics driver attempts to terminate its operations, the persistent timer cycle can cause indefinite looping behavior that prevents proper cleanup. This could result in memory leaks, system hangs, or failure to properly release graphics resources that may impact subsequent driver initialization or system operation. The vulnerability is particularly concerning in embedded systems or devices where graphics processing is critical for proper operation.
The solution implemented addresses this by replacing the traditional timer deletion and work cancellation sequence with timer_shutdown_sync() which provides a more robust mechanism for terminating timer operations. This change ensures that once the timer shutdown process begins, it cannot be rearmed by any pending work items, allowing the subsequent cancel_work_sync() call to properly terminate all associated operations. The fix aligns with best practices for kernel development and follows established patterns for managing timer and work queue cleanup operations. This remediation prevents the circular dependency that could lead to resource exhaustion or system instability during driver termination sequences.
The vulnerability demonstrates a classic example of improper resource management in kernel space where asynchronous operations are not properly coordinated during cleanup phases. The ATT&CK framework would classify this under privilege escalation techniques through kernel exploitation, as improper cleanup can create opportunities for denial-of-service conditions that may be leveraged by malicious actors. This particular issue highlights the importance of proper synchronization and cleanup procedures in graphics driver development, particularly when dealing with memory management and timer-based operations that must function correctly even during system shutdown scenarios.