CVE-2025-39992

Full vulnerability record from the local CVENow database.

Description

In the Linux kernel, the following vulnerability has been resolved: mm: swap: check for stable address space before operating on the VMA It is possible to hit a zero entry while traversing the vmas in unuse_mm() called from swapoff path and accessing it causes the OOPS: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000446--> Loading the memory from offset 0x40 on the XA_ZERO_ENTRY as address. Mem abort info: ESR = 0x0000000096000005 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x05: level 1 translation fault The issue is manifested from the below race between the fork() on a process and swapoff: fork(dup_mmap()) swapoff(unuse_mm) --------------- ----------------- 1) Identical mtree is built using __mt_dup(). 2) copy_pte_range()--> copy_nonpresent_pte(): The dst mm is added into the mmlist to be visible to the swapoff operation. 3) Fatal signal is sent to the parent process(which is the current during the fork) thus skip the duplication of the vmas and mark the vma range with XA_ZERO_ENTRY as a marker for this process that helps during exit_mmap(). 4) swapoff is tried on the 'mm' added to the 'mmlist' as part of the 2. 5) unuse_mm(), that iterates through the vma's of this 'mm' will hit the non-NULL zero entry and operating on this zero entry as a vma is resulting into the oops. The proper fix would be around not exposing this partially-valid tree to others when droping the mmap lock, which is being solved with [1]. A simpler solution would be checking for MMF_UNSTABLE, as it is set if mm_struct is not fully initialized in dup_mmap(). Thanks to Liam/Lorenzo/David for all the suggestions in fixing this issue.

Severity

Not scored

CVSS score

Not available

Vulnerability status

Deferred

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2025-10-15 08:15:37.317000

Last modified

2026-10-19 21:10:00.160000

View original CVE JSON

{
  "id": "CVE-2025-39992",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2025-10-15T08:15:37.317",
  "lastModified": "2026-10-19T21:10:00.160",
  "vulnStatus": "Deferred",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: swap: check for stable address space before operating on the VMA\n\nIt is possible to hit a zero entry while traversing the vmas in unuse_mm()\ncalled from swapoff path and accessing it causes the OOPS:\n\nUnable to handle kernel NULL pointer dereference at virtual address\n0000000000000446--> Loading the memory from offset 0x40 on the\nXA_ZERO_ENTRY as address.\nMem abort info:\n  ESR = 0x0000000096000005\n  EC = 0x25: DABT (current EL), IL = 32 bits\n  SET = 0, FnV = 0\n  EA = 0, S1PTW = 0\n  FSC = 0x05: level 1 translation fault\n\nThe issue is manifested from the below race between the fork() on a\nprocess and swapoff:\nfork(dup_mmap())\t\t\tswapoff(unuse_mm)\n---------------                         -----------------\n1) Identical mtree is built using\n   __mt_dup().\n\n2) copy_pte_range()-->\n\tcopy_nonpresent_pte():\n       The dst mm is added into the\n    mmlist to be visible to the\n    swapoff operation.\n\n3) Fatal signal is sent to the parent\nprocess(which is the current during the\nfork) thus skip the duplication of the\nvmas and mark the vma range with\nXA_ZERO_ENTRY as a marker for this process\nthat helps during exit_mmap().\n\n\t\t\t\t     4) swapoff is tried on the\n\t\t\t\t\t'mm' added to the 'mmlist' as\n\t\t\t\t\tpart of the 2.\n\n\t\t\t\t     5) unuse_mm(), that iterates\n\t\t\t\t\tthrough the vma's of this 'mm'\n\t\t\t\t\twill hit the non-NULL zero entry\n\t\t\t\t\tand operating on this zero entry\n\t\t\t\t\tas a vma is resulting into the\n\t\t\t\t\toops.\n\nThe proper fix would be around not exposing this partially-valid tree to\nothers when droping the mmap lock, which is being solved with [1].  A\nsimpler solution would be checking for MMF_UNSTABLE, as it is set if\nmm_struct is not fully initialized in dup_mmap().\n\nThanks to Liam/Lorenzo/David for all the suggestions in fixing this\nissue."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nmm: swap: verificar el espacio de direcciones estable antes de operar en el VMA\n\nEs posible encontrar una entrada cero mientras se recorren los vmas en unuse_mm() llamada desde la ruta de swapoff y acceder a ella causa el OOPS:\n\nNo se puede manejar la desreferencia de puntero NULL del kernel en la dirección virtual 0000000000000446--> Cargando la memoria desde el desplazamiento 0x40 en la XA_ZERO_ENTRY como dirección.\nInformación de aborto de memoria:\n  ESR = 0x0000000096000005\n  EC = 0x25: DABT (EL actual), IL = 32 bits\n  SET = 0, FnV = 0\n  EA = 0, S1PTW = 0\n  FSC = 0x05: fallo de traducción de nivel 1\n\nEl problema se manifiesta a partir de la siguiente condición de carrera entre el fork() en un proceso y swapoff:\nfork(dup_mmap())\t\t\tswapoff(unuse_mm)\n---------------                         -----------------\n1) Se construye un mtree idéntico\n   usando __mt_dup().\n\n2) copy_pte_range()-->\n\tcopy_nonpresent_pte():\n       El mm de destino se añade a la\n    mmlist para ser visible para la\n    operación de swapoff.\n\n3) Se envía una señal fatal al proceso\npadre (que es el actual durante el\nfork), lo que omite la duplicación de los\nvmas y marca el rango de vma con\nXA_ZERO_ENTRY como un marcador para este proceso\nque ayuda durante exit_mmap().\n\n\t\t\t\t     4) Se intenta swapoff en el\n\t\t\t\t\t'mm' añadido a la 'mmlist' como\n\t\t\t\t\tparte del punto 2.\n\n\t\t\t\t     5) unuse_mm(), que itera\n\t\t\t\t\ta través de los vma's de este 'mm'\n\t\t\t\t\tencontrará la entrada cero no-NULL\n\t\t\t\t\ty operar en esta entrada cero\n\t\t\t\t\tcomo un vma resulta en el\n\t\t\t\t\toops.\n\nLa solución adecuada sería no exponer este árbol parcialmente válido a otros al liberar el bloqueo de mmap, lo cual se está resolviendo con [1]. Una solución más simple sería verificar MMF_UNSTABLE, ya que se establece si mm_struct no está completamente inicializado en dup_mmap().\n\nGracias a Liam/Lorenzo/David por todas las sugerencias para solucionar este problema."
    }
  ],
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "programFiles": [
            "mm/swapfile.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "d2406291483775ecddaee929231a39c70c08fda2",
              "lessThan": "4e5f060d7347466f77aaff1c0d5a6c4f1fb217ac",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "d2406291483775ecddaee929231a39c70c08fda2",
              "lessThan": "9cddad3b26dac830407d2d3c0de5205ff6d6dda0",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "d2406291483775ecddaee929231a39c70c08fda2",
              "lessThan": "e4e99d69b8b8295c501b2eef89e13306b738b667",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "d2406291483775ecddaee929231a39c70c08fda2",
              "lessThan": "1367da7eb875d01102d2ed18654b24d261ff5393",
              "versionType": "git",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "affected",
          "programFiles": [
            "mm/swapfile.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "6.8",
              "status": "affected"
            },
            {
              "version": "0",
              "lessThan": "6.8",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.12.51",
              "lessThanOrEqual": "6.12.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.16.11",
              "lessThanOrEqual": "6.16.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.17.1",
              "lessThanOrEqual": "6.17.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.18",
              "lessThanOrEqual": "*",
              "versionType": "original_commit_for_fix",
              "status": "unaffected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {},
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/1367da7eb875d01102d2ed18654b24d261ff5393",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/4e5f060d7347466f77aaff1c0d5a6c4f1fb217ac",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/9cddad3b26dac830407d2d3c0de5205ff6d6dda0",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/e4e99d69b8b8295c501b2eef89e13306b738b667",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ]
}