Linux Kernel Userfaultfd Vulnerability Leading to Potential Fault Handling Issues

CVE-2026-64514

What is CVE-2026-64514?

A vulnerability in the Linux kernel's handling of userfaultfd could lead to unpredictable behavior when dealing with page table entries (PTEs). Specifically, the checks implemented in userfaultfd_must_wait() and userfaultfd_huge_must_wait() do not appropriately account for the state of PTEs without acquiring the necessary page table lock. This oversight can result in erroneously decoded bits when inspecting swap or migration entries, potentially leaving threads in a wait state indefinitely, thus impacting overall system stability. Properly gating the writability check on the presence of the PTE would enhance handling during fault scenarios and prevent threads from being held in limbo unnecessarily.

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