CVE-2026-43418
Race Condition in Linux Kernel Sched MMCID Fork
Publication date: 2026-05-08
Last updated on: 2026-05-08
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 occurs in the Linux kernel's scheduling subsystem related to MMCID (Memory Management Context ID) handling during task forking.
When a new task is forked, it is accounted as an MMCID user before it becomes visible in the process's thread list and the global task list. This timing issue can cause problems when multiple forks happen concurrently on different CPUs.
Specifically, if one task (tnew1) is not yet visible and another task (tnew2) forks and reaches a per-CPU threshold for MMCID users, the system tries to fix up allocated CIDs for other tasks. However, since tnew1 is not visible yet, the fix-up fails for tnew1's CID.
As a result, a subsequent scheduling operation might fail to acquire a transitional CID, causing the machine to stall.
The fix involves moving the invocation of sched_mm_cid_fork() to after the new task becomes visible in the thread and task lists, preventing this race condition and making the behavior symmetrical with task exit handling.
How can this vulnerability impact me? :
This vulnerability can cause the machine to stall during task scheduling due to failure in acquiring a transitional CID.
In practical terms, this means that under certain concurrent fork conditions, the system could become unresponsive or hang, impacting availability and stability.
What immediate steps should I take to mitigate this vulnerability?
The vulnerability is resolved by moving the invocation of sched_mm_cid_fork() after the new task becomes visible in the thread and task list. This prevents CID stalls caused by concurrent forks.
To mitigate this vulnerability immediately, you should update your Linux kernel to a version that includes this fix.