CVE-2026-68237 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu/userq: fix indefinite fence wait during GPU reset
pre_reset only force-completes fences of MAPPED queues. A queue in any other state (e.g. mid-eviction) keeps its last_fence pending; after a GPU reset that fence never signals, so the eviction/suspend worker and process teardown (amdgpu_evf_mgr_flush_suspend) wait on it forever and wedge the machine:
INFO: task kworker/6:28 blocked for more than 120 seconds. Workqueue: events amdgpu_eviction_fence_suspend_worker [amdgpu]
Call Trace: dma_fence_wait_timeout+0x7e/0x130 amdgpu_userq_evict+0x67/0x140 [amdgpu]
amdgpu_eviction_fence_suspend_worker+0xd8/0x160 [amdgpu]
process_scheduled_works+0xa6/0x420
Force-complete every queue's fence regardless of state. The unmap and mark-hung step stays gated on MAPPED, since unmapping a queue that is not mapped is invalid.
(cherry picked from commit 9102b39fa924dcc3dc75a3137bfa9633c40b88c0)
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Analysis
by VulDB Data Team • 08/11/2026
This vulnerability exists within the amdgpu driver component of the Linux kernel and represents a critical race condition that can lead to system deadlock during GPU reset operations. The flaw specifically affects the drm/amdgpu/userq subsystem where the pre_reset function fails to properly handle fence completion for all queue states during GPU reset procedures. When a GPU reset occurs, the system attempts to complete fences associated with user queues, but only processes those in the MAPPED state while leaving fences from queues in other states such as mid-eviction pending. This incomplete fence handling creates a scenario where certain fences never signal, causing system threads to block indefinitely and ultimately leading to machine wedging.
The technical implementation issue stems from improper queue state management during GPU reset operations. During normal operation, user queues can exist in multiple states including MAPPED, UNMAPPED, EVICTED, or SUSPENDED. The current implementation only force-completes fences for queues that are explicitly in the MAPPED state, while queues transitioning through eviction or suspension processes maintain their last_fence values in a pending state. This design flaw was identified through kernel debugging output showing kworker threads blocked for over 120 seconds, with call traces indicating dma_fence_wait_timeout being invoked from amdgpu_userq_evict and amdgpu_eviction_fence_suspend_worker functions within the amdgpu driver module.
The operational impact of this vulnerability is severe as it can cause complete system hang conditions where the machine becomes unresponsive to user input and system operations. The affected system components include the amdgpu_evf_mgr_flush_suspend process and eviction/suspend worker threads that become trapped waiting for fences that will never signal due to the reset operation. This creates a denial-of-service condition that affects GPU-dependent applications and can potentially compromise system stability during critical operations such as system updates, driver reloads, or hardware maintenance procedures. The vulnerability specifically targets systems utilizing AMD GPU hardware through the amdgpu kernel driver and affects all versions prior to the applied fix.
The mitigation approach requires modifying the pre_reset function to force-complete fences for all queue states rather than limiting completion to only MAPPED queues. This ensures that regardless of a queue's current operational state during reset, its associated fence will be properly signaled and completed. The solution maintains the existing restriction that unmap operations should only occur on MAPPED queues since attempting to unmap non-mapped queues would result in invalid memory access patterns. The fix follows established kernel development practices by ensuring proper resource cleanup and fence management while maintaining backward compatibility with existing queue state handling mechanisms.
This vulnerability aligns with CWE-667 (Improper Synchronization) and represents a specific case of improper resource management during system reset operations. From an ATT&CK perspective, this issue relates to privilege escalation through system stability compromise and can be leveraged by malicious actors to create persistent denial-of-service conditions. The fix addresses the root cause by ensuring complete fence cleanup across all queue states, preventing the accumulation of pending fences that could lead to resource exhaustion and system hang conditions. The solution demonstrates proper kernel driver development practices for managing asynchronous operations and ensuring correct state transitions during critical system maintenance procedures such as GPU reset operations.