CVE-2025-21696

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> mm: clear uffd-wp PTE/PMD state on mremap()<br /> <br /> When mremap()ing a memory region previously registered with userfaultfd as<br /> write-protected but without UFFD_FEATURE_EVENT_REMAP, an inconsistency in<br /> flag clearing leads to a mismatch between the vma flags (which have<br /> uffd-wp cleared) and the pte/pmd flags (which do not have uffd-wp<br /> cleared). This mismatch causes a subsequent mprotect(PROT_WRITE) to<br /> trigger a warning in page_table_check_pte_flags() due to setting the pte<br /> to writable while uffd-wp is still set.<br /> <br /> Fix this by always explicitly clearing the uffd-wp pte/pmd flags on any<br /> such mremap() so that the values are consistent with the existing clearing<br /> of VM_UFFD_WP. Be careful to clear the logical flag regardless of its<br /> physical form; a PTE bit, a swap PTE bit, or a PTE marker. Cover PTE,<br /> huge PMD and hugetlb paths.