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CVE-2025-21696

Full vulnerability record from the local CVENow database.

Description

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.

Severity
MEDIUM
CVSS score
5.5 (v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-02-12 14:15:32.677000
Last modified
2026-10-30 13:17:51.523000
View original CVE JSON 
{
  "id": "CVE-2025-21696",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2025-02-12T14:15:32.677",
  "lastModified": "2026-10-30T13:17:51.523",
  "vulnStatus": "Modified",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: clear uffd-wp PTE/PMD state on mremap()\n\nWhen mremap()ing a memory region previously registered with userfaultfd as\nwrite-protected but without UFFD_FEATURE_EVENT_REMAP, an inconsistency in\nflag clearing leads to a mismatch between the vma flags (which have\nuffd-wp cleared) and the pte/pmd flags (which do not have uffd-wp\ncleared).  This mismatch causes a subsequent mprotect(PROT_WRITE) to\ntrigger a warning in page_table_check_pte_flags() due to setting the pte\nto writable while uffd-wp is still set.\n\nFix this by always explicitly clearing the uffd-wp pte/pmd flags on any\nsuch mremap() so that the values are consistent with the existing clearing\nof VM_UFFD_WP.  Be careful to clear the logical flag regardless of its\nphysical form; a PTE bit, a swap PTE bit, or a PTE marker.  Cover PTE,\nhuge PMD and hugetlb paths."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: mm: borrar el estado PTE/PMD de uffd-wp en mremap() Al borrar con mremap() una región de memoria registrada previamente con userfaultfd como protegida contra escritura pero sin UFFD_FEATURE_EVENT_REMAP, una inconsistencia en la depuración de indicadores provoca una falta de coincidencia entre los indicadores vma (que tienen uffd-wp borrado) y los indicadores pte/pmd (que no tienen uffd-wp borrado). Esta falta de coincidencia hace que un mprotect(PROT_WRITE) posterior active una advertencia en page_table_check_pte_flags() debido a la configuración de pte como escribible mientras uffd-wp aún está configurado. Solucione esto borrando siempre explícitamente los indicadores pte/pmd de uffd-wp en cualquier mremap() de este tipo para que los valores sean coherentes con la depuración existente de VM_UFFD_WP. Tenga cuidado de borrar el indicador lógico independientemente de su forma física: un bit PTE, un bit PTE de intercambio o un marcador PTE. Cubra las rutas PTE, PMD enormes y TLB enormes."
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