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CVE-2025-37999

Estado: AnalizadaMedia (5.5)—

In the Linux kernel, the following vulnerability has been resolved:

fs/erofs/fileio: call erofs_onlinefolio_split() after bio_add_folio()

If bio_add_folio() fails (because it is full), erofs_fileio_scan_folio() needs to submit the I/O request via erofs_fileio_rq_submit() and allocate a new I/O request with an empty `struct bio`. Then it retries the bio_add_folio() call.

However, at this point, erofs_onlinefolio_split() has already been called which increments `folio->private`; the retry will call erofs_onlinefolio_split() again, but there will never be a matching erofs_onlinefolio_end() call. This leaves the folio locked forever and all waiters will be stuck in folio_wait_bit_common().

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This bug has been added by commit ce63cb62d794 ("erofs: support unencoded inodes for fileio"), but was practically unreachable because there was room for 256 folios in the `struct bio` - until commit 9f74ae8c9ac9 ("erofs: shorten bvecs[] for file-backed mounts") which reduced the array capacity to 16 folios.

It was now trivial to trigger the bug by manually invoking readahead from userspace, e.g.:

This should be fixed by invoking erofs_onlinefolio_split() only after bio_add_folio() has succeeded. This is safe: asynchronous completions invoking erofs_onlinefolio_end() will not unlock the folio because erofs_fileio_scan_folio() is still holding a reference to be released by erofs_onlinefolio_end() at the end.

Detalles técnicos trazas, registros y código del informe original
 posix_fadvise(fd, 0, st.st_size, POSIX_FADV_WILLNEED);

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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  "id": "CVE-2025-37999",
  "cveTags": [],
  "metrics": {
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        "type": "Primary",
        "source": "nvd@nist.gov",
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          "version": "3.1",
          "baseScore": 5.5,
          "attackVector": "LOCAL",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 1.8
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          "programFiles": [
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          "defaultStatus": "affected"
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  "published": "2025-05-29T14:15:36.597",
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  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs/erofs/fileio: call erofs_onlinefolio_split() after bio_add_folio()\n\nIf bio_add_folio() fails (because it is full),\nerofs_fileio_scan_folio() needs to submit the I/O request via\nerofs_fileio_rq_submit() and allocate a new I/O request with an empty\n`struct bio`.  Then it retries the bio_add_folio() call.\n\nHowever, at this point, erofs_onlinefolio_split() has already been\ncalled which increments `folio->private`; the retry will call\nerofs_onlinefolio_split() again, but there will never be a matching\nerofs_onlinefolio_end() call.  This leaves the folio locked forever\nand all waiters will be stuck in folio_wait_bit_common().\n\nThis bug has been added by commit ce63cb62d794 (\"erofs: support\nunencoded inodes for fileio\"), but was practically unreachable because\nthere was room for 256 folios in the `struct bio` - until commit\n9f74ae8c9ac9 (\"erofs: shorten bvecs[] for file-backed mounts\") which\nreduced the array capacity to 16 folios.\n\nIt was now trivial to trigger the bug by manually invoking readahead\nfrom userspace, e.g.:\n\n posix_fadvise(fd, 0, st.st_size, POSIX_FADV_WILLNEED);\n\nThis should be fixed by invoking erofs_onlinefolio_split() only after\nbio_add_folio() has succeeded.  This is safe: asynchronous completions\ninvoking erofs_onlinefolio_end() will not unlock the folio because\nerofs_fileio_scan_folio() is still holding a reference to be released\nby erofs_onlinefolio_end() at the end."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: fs/erofs/fileio: llamar a erofs_onlinefolio_split() después de bio_add_folio(). Si bio_add_folio() falla (porque está lleno), erofs_fileio_scan_folio() debe enviar la solicitud de E/S mediante erofs_fileio_rq_submit() y asignar una nueva solicitud de E/S con un `struct bio` vacío. Luego, vuelve a intentar la llamada a bio_add_folio(). Sin embargo, en este punto, ya se ha llamado a erofs_onlinefolio_split(), lo que incrementa `folio->private`; el reintento llamará a erofs_onlinefolio_split() de nuevo, pero nunca habrá una llamada erofs_onlinefolio_end() coincidente. Esto deja el folio bloqueado para siempre y todos los que esperan quedarán atascados en folio_wait_bit_common(). Este error se añadió con el commit ce63cb62d794 (\"erofs: compatibilidad con inodos no codificados para fileio\"), pero era prácticamente imposible de solucionar porque había espacio para 256 folios en la estructura `struct bio`, hasta el commit 9f74ae8c9ac9 (\"erofs: acortar bvecs[] para montajes con respaldo de archivo\"), que redujo la capacidad del array a 16 folios. Ahora era fácil activar el error invocando manualmente la lectura anticipada desde el espacio de usuario, por ejemplo: posix_fadvise(fd, 0, st.st_size, POSIX_FADV_WILLNEED); Esto debería solucionarse invocando erofs_onlinefolio_split() solo después de que bio_add_folio() se haya ejecutado correctamente. Esto es seguro: las finalizaciones asincrónicas que invocan erofs_onlinefolio_end() no desbloquearán el folio porque erofs_fileio_scan_folio() todavía contiene una referencia que erofs_onlinefolio_end() liberará al final."
    }
  ],
  "lastModified": "2026-06-17T09:15:51.227",
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