CVE-2026-31733
Race Condition in Linux Kernel sched_ext Scheduler
Publication date: 2026-05-01
Last updated on: 2026-05-01
Assigner: kernel.org
Description
Description
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| linux | linux_kernel | * |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-UNKNOWN |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
This vulnerability is in the Linux kernel's scheduler extension (sched_ext) and involves a stale direct dispatch state in the variable ddsp_dsq_id. The issue occurs because ddsp_dsq_id is not always cleared properly in all code paths that consume or cancel a direct dispatch verdict. This can lead to a spurious warning being triggered during task wakeup when certain functions like ops.select_cpu() call scx_bpf_dsq_insert().
The root cause is that ddsp_dsq_id was only cleared in dispatch_enqueue(), but some paths that handle direct dispatch do not reach this function, leaving ddsp_dsq_id set incorrectly. The fix involves clearing ddsp_dsq_id at multiple appropriate points in the scheduler code to ensure the direct dispatch state is properly reset in all scenarios.
How can this vulnerability impact me? :
This vulnerability can cause spurious warnings in the kernel logs related to direct dispatch state handling in the scheduler. While the description does not explicitly mention security impacts such as privilege escalation or denial of service, the presence of stale state and warnings could potentially affect system stability or debugging clarity.
Since the issue involves scheduler internals and task dispatching, it might lead to unexpected behavior in task scheduling or performance anomalies, but no direct impact on system security or data integrity is described.
How can this vulnerability be detected on my network or system? Can you suggest some commands?
This vulnerability can be detected by monitoring for a specific kernel warning message that appears when the stale direct dispatch state triggers a spurious warning.
The warning message to look for in system logs is:
- WARNING: kernel/sched/ext.c:1273 at scx_dsq_insert_commit+0xcd/0x140
To detect this on your system, you can use commands to search kernel logs for this warning, for example:
- dmesg | grep 'WARNING: kernel/sched/ext.c:1273'
- journalctl -k | grep 'WARNING: kernel/sched/ext.c:1273'
What immediate steps should I take to mitigate this vulnerability?
The vulnerability is fixed by clearing the direct dispatch state at the appropriate points in the Linux kernel scheduler code.
Immediate mitigation steps include:
- Update your Linux kernel to a version that includes the fix for this issue.
- Ensure that the kernel scheduler code clears the direct dispatch state in the following functions and paths as described:
- - direct_dispatch() clears the state before dispatch_enqueue() on synchronous paths.
- - process_ddsp_deferred_locals() clears the state before dispatch_to_local_dsq().
- - do_enqueue_task() clears the state on enqueue paths.
- - dequeue_task_scx() clears the state after dispatch_dequeue().
- - scx_disable_task() clears the state when transitioning a task out of the current scheduler.
If updating the kernel immediately is not possible, monitor for the warning messages and avoid workloads or configurations that trigger direct dispatch paths until patched.