PT-2026-64735 · Linux · Linux
CVE-2026-64514
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Publicado
2026-07-25
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Atualizado
2026-07-25
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In the Linux kernel, the following vulnerability has been resolved:
userfaultfd: gate must wait writability check on pte present()
userfaultfd must wait() and userfaultfd huge must wait() read the PTE
without taking the page table lock and then apply pte write() /
huge pte write() to it. Those accessors decode bits from the present
encoding only; on a swap or migration entry they read the offset bits that
happen to share the same position and return an undefined result.
The intent of the check is "is this fault still WP-blocked?". A
non-marker swap entry means the page is in transit -- the userfault
context the original fault delivered against is no longer the same, and
the swap-in or migration completion path will re-deliver a fresh fault if
userspace still needs to handle it. Worst case under the current code the
garbage write bit says "wait", and the thread stays asleep until a
UFFDIO WAKE that may never arrive.
Gate the writability check on pte present() so the lockless re-check only
inspects present-PTE bits when the entry is actually present. The
non-present, non-marker case returns "don't wait" and lets the fault path
retry.
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