CVE-2025-21696: mm: clear uffd-wp PTE/PMD state on mremap()
First published: Wed Feb 12 2025(Updated: )
In the Linux kernel, the following vulnerability has been resolved: mm: clear uffd-wp PTE/PMD state on mremap() When mremap()ing a memory region previously registered with userfaultfd as write-protected but without UFFD_FEATURE_EVENT_REMAP, an inconsistency in flag clearing leads to a mismatch between the vma flags (which have uffd-wp cleared) and the pte/pmd flags (which do not have uffd-wp cleared). This mismatch causes a subsequent mprotect(PROT_WRITE) to trigger a warning in page_table_check_pte_flags() due to setting the pte to writable while uffd-wp is still set. Fix this by always explicitly clearing the uffd-wp pte/pmd flags on any such mremap() so that the values are consistent with the existing clearing of VM_UFFD_WP. Be careful to clear the logical flag regardless of its physical form; a PTE bit, a swap PTE bit, or a PTE marker. Cover PTE, huge PMD and hugetlb paths.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux kernel | ||
| Linux kernel | >=5.7<6.12.11 | |
| Linux kernel | =6.13-rc1 | |
| Linux kernel | =6.13-rc2 | |
| Linux kernel | =6.13-rc3 | |
| Linux kernel | =6.13-rc4 | |
| Linux kernel | =6.13-rc5 | |
| Linux kernel | =6.13-rc6 | |
| Linux kernel | =6.13-rc7 |
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Reference Links
Frequently Asked Questions
What is the severity of CVE-2025-21696?
CVE-2025-21696 is classified as a low-severity vulnerability in the Linux kernel.
How do I fix CVE-2025-21696?
To resolve CVE-2025-21696, update your Linux kernel to the latest version where this vulnerability has been patched.
What software is affected by CVE-2025-21696?
CVE-2025-21696 affects the Linux kernel across various distributions.
What type of vulnerability is CVE-2025-21696?
CVE-2025-21696 is a memory handling vulnerability related to inconsistent flag clearing during the mremap() operation.
Is CVE-2025-21696 exploitable?
The exploitability of CVE-2025-21696 is considered limited, primarily affecting scenarios involving userfaultfd.
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