CVE-2026-68103 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu: reject mapping a reserved doorbell to a new queue
When creating an user-queue, the user space provides a doorbell BO handle and an offset within the bo to obtain a doorbell.
However current implementation using xa_store_irq() to store a doorbell, which allows a later queue created with the same BO and offset parameters to overwrite an existing queue and doorbell mapping.
This can cause problems like misrouting fence IRQ processing to a wrong queue, and mislead the cleanup process of one queue erasing the mapping of another queue.
This commit fixes this issue by replacing xa_store_irq with xa_insert_irq, which rejects mapping a reserved doorbell to a newly created queue
(cherry picked from commit 6244eae22966350db52faf9c1369d3b2ffc5de4e)
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability in question affects the Linux kernel's AMDGPU Direct Rendering Manager subsystem, specifically within the doorbell mapping mechanism used for queue management. This issue resides in the graphics driver component responsible for handling user-space queue creation and doorbell allocation. Doorbells serve as critical synchronization mechanisms that allow the GPU to signal completion events back to the CPU through interrupt notifications. The flaw demonstrates a classic race condition and improper resource management pattern that can lead to significant system instability and potential security implications.
The technical root cause stems from the use of xa_store_irq() function during doorbell mapping operations. This implementation allows for overwriting existing doorbell-to-queue mappings when identical buffer object handles and offsets are provided by subsequent queue creation requests. The xa_store_irq() function operates without checking for existing mappings, creating a scenario where a newly created queue can inadvertently overwrite and invalidate the mapping of an already established queue. This behavior violates fundamental resource management principles and creates a path for malicious or accidental interference with active GPU operations.
The operational impact of this vulnerability extends beyond simple resource conflicts into potentially catastrophic system behavior. When doorbell mappings are overwritten, fence interrupt processing becomes misrouted to incorrect queues, causing the GPU driver to process completion events for the wrong queue contexts. This misrouting can lead to complete loss of synchronization between GPU operations and CPU processing, resulting in application crashes, data corruption, or even system hangs. The cleanup processes for one queue can accidentally erase mappings belonging to other active queues, creating cascading failures that may persist until system reboot.
The fix implemented addresses this vulnerability by replacing xa_store_irq() with xa_insert_irq() which enforces strict mapping uniqueness constraints. This change ensures that once a doorbell is reserved for a specific queue, subsequent attempts to map the same buffer object and offset combination will be rejected rather than allowing overwrites. The solution aligns with established security practices for resource management and prevents the type of mapping conflicts that could lead to privilege escalation or denial of service conditions. This remediation specifically addresses weakness categories related to improper handling of resource identifiers and race conditions, providing robust protection against unauthorized interference with GPU queue operations.
From a cybersecurity perspective, this vulnerability demonstrates the importance of proper resource lifecycle management in kernel space drivers. The fix represents a defensive programming approach that prevents the type of mapping conflicts that could enable attackers to manipulate GPU synchronization mechanisms. This aligns with security principles outlined in CWE categories related to improper handling of resources and race conditions, while also supporting ATT&CK techniques focused on privilege escalation through kernel-level resource manipulation. The patch ensures that GPU queue management maintains proper isolation between concurrent operations, preventing cross-contamination of interrupt processing and maintaining system stability under concurrent access patterns.