Off-by-One Vulnerability in Linux Kernel Impacting Root Migration

CVE-2025-21813

Summary

A vulnerability exists within the Linux kernel where the children's counter validation during root migration is mismanaged. This leads to the potential for multiple top-level roots being active, which undermines the intended single idle migrator design. Specifically, if an old root is pre-accounted but not connected properly to the new root during creation, it can result in incorrect children counting. This oversight may manifest in system warnings regarding the processor state, indicating a need for vigilance in future configurations. Proper adjustments to the connection process have been implemented to mitigate this issue.

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