sched/mmcid: Handle vfork()/CLONE_VM correctly

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Summary

CVECVE-2026-43417
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-08 15:16:53 UTC
Updated2026-05-08 15:16:53 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: sched/mmcid: Handle vfork()/CLONE_VM correctly Matthieu and Jiri reported stalls where a task endlessly loops in mm_get_cid() when scheduling in. It turned out that the logic which handles vfork()'ed tasks is broken. It is invoked when the number of tasks associated to a process is smaller than the number of MMCID users. It then walks the task list to find the vfork()'ed task, but accounts all the already processed tasks as well. If that double processing brings the number of to be handled tasks to 0, the walk stops and the vfork()'ed task's CID is not fixed up. As a consequence a subsequent schedule in fails to acquire a (transitional) CID and the machine stalls. Cure this by removing the accounting condition and make the fixup always walk the full task list if it could not find the exact number of users in the process' thread list.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected fbd0e71dc370af73f6b316e4de9eed273dd90340 e6761cdce78a8919a537989afb6aaf6881469f83 git Not specified
CNA Linux Linux affected fbd0e71dc370af73f6b316e4de9eed273dd90340 28b5a1395036d6c7a6c8034d85ad3d7d365f192c git Not specified
CNA Linux Linux affected 6.19 Not specified
CNA Linux Linux unaffected 6.19 semver Not specified
CNA Linux Linux unaffected 6.19.9 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/28b5a1395036d6c7a6c8034d85ad3d7d365f192c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e6761cdce78a8919a537989afb6aaf6881469f83 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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