CVE-2023-52935

Summary

CVE-2023-52935 is a vulnerability affecting the Linux kernel's memory management subsystem (mm/khugepaged). The issue lies in the collision of three concurrent locks, which can result in page table traversals while assuming nothing else can access them. Specifically, if an anonymous memory area (->anon_vma) is attached to a Virtual Memory Area (VMA), the collapse_and_free_pmd function requires this lock to be held. However, the retract_page_tables function checks for the presence of an ->anon_vma before acquiring the mmap lock, allowing for a race condition. If an ->anon_vma is merged from a neighboring VMA while page tables are being concurrently removed, subsequent rmap traversals on the child process's pages can result in lockdep warnings, use-after-free access, or other unintended consequences. To mitigate this issue, the Linux kernel has been updated to ensure that the check for an ->anon_vma is performed after acquiring the mmap lock.

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