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CVE-2024-50250

Estado: ModificadaAlta (7.1)—

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

fsdax: dax_unshare_iter needs to copy entire blocks

The code that copies data from srcmap to iomap in dax_unshare_iter is very very broken, which bfoster's recent fsx changes have exposed.

If the pos and len passed to dax_file_unshare are not aligned to an fsblock boundary, the iter pos and length in the _iter function will reflect this unalignment.

dax_iomap_direct_access always returns a pointer to the start of the kmapped fsdax page, even if its pos argument is in the middle of that page. This is catastrophic for data integrity when iter->pos is not aligned to a page, because daddr/saddr do not point to the same byte in the file as iter->pos. Hence we corrupt user data by copying it to the wrong place.

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If iter->pos + iomap_length() in the _iter function not aligned to a page, then we fail to copy a full block, and only partially populate the destination block. This is catastrophic for data confidentiality because we expose stale pmem contents.

Fix both of these issues by aligning copy_pos/copy_len to a page boundary (remember, this is fsdax so 1 fsblock == 1 base page) so that we always copy full blocks.

We're not done yet -- there's no call to invalidate_inode_pages2_range, so programs that have the file range mmap'd will continue accessing the old memory mapping after the file metadata updates have completed.

Be careful with the return value -- if the unshare succeeds, we still need to return the number of bytes that the iomap iter thinks we're operating on.

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).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad local (AV:L, PR:L) que permite corrupción de datos (C:H, I:H) y exposición de contenido antiguo de memoria persistente; requiere ejecución de código de kernel para explotar la mala alineación en copias de bloques DAX.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Threat Intelligence ProgramRestrict File and Directory PermissionsRemote Data StorageExecution PreventionEncrypt Sensitive InformationApplication Isolation and Sandboxing

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfsdax: dax_unshare_iter needs to copy entire blocks\n\nThe code that copies data from srcmap to iomap in dax_unshare_iter is\nvery very broken, which bfoster's recent fsx changes have exposed.\n\nIf the pos and len passed to dax_file_unshare are not aligned to an\nfsblock boundary, the iter pos and length in the _iter function will\nreflect this unalignment.\n\ndax_iomap_direct_access always returns a pointer to the start of the\nkmapped fsdax page, even if its pos argument is in the middle of that\npage.  This is catastrophic for data integrity when iter->pos is not\naligned to a page, because daddr/saddr do not point to the same byte in\nthe file as iter->pos.  Hence we corrupt user data by copying it to the\nwrong place.\n\nIf iter->pos + iomap_length() in the _iter function not aligned to a\npage, then we fail to copy a full block, and only partially populate the\ndestination block.  This is catastrophic for data confidentiality\nbecause we expose stale pmem contents.\n\nFix both of these issues by aligning copy_pos/copy_len to a page\nboundary (remember, this is fsdax so 1 fsblock == 1 base page) so that\nwe always copy full blocks.\n\nWe're not done yet -- there's no call to invalidate_inode_pages2_range,\nso programs that have the file range mmap'd will continue accessing the\nold memory mapping after the file metadata updates have completed.\n\nBe careful with the return value -- if the unshare succeeds, we still\nneed to return the number of bytes that the iomap iter thinks we're\noperating on."
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      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: fsdax: dax_unshare_iter necesita copiar bloques enteros El código que copia datos de srcmap a iomap en dax_unshare_iter está muy, muy roto, lo que los cambios recientes de fsx de bfoster han expuesto. Si la posición y la longitud pasadas a dax_file_unshare no están alineadas con un límite de fsblock, la posición y la longitud de iter en la función _iter reflejarán esta desalineación. dax_iomap_direct_access siempre devuelve un puntero al inicio de la página fsdax kmapped, incluso si su argumento pos está en el medio de esa página. Esto es catastrófico para la integridad de los datos cuando iter->pos no está alineado con una página, porque daddr/saddr no apuntan al mismo byte en el archivo que iter->pos. Por lo tanto, corrompemos los datos del usuario copiándolos en el lugar equivocado. Si iter->pos + iomap_length() en la función _iter no está alineado con una página, entonces no copiamos un bloque completo y solo rellenamos parcialmente el bloque de destino. Esto es catastrófico para la confidencialidad de los datos porque exponemos contenidos pmem obsoletos. Solucione ambos problemas alineando copy_pos/copy_len con un límite de página (recuerde, esto es fsdax, por lo que 1 fsblock == 1 página base) de modo que siempre copiemos bloques completos. Aún no hemos terminado: no hay ninguna llamada a invalidate_inode_pages2_range, por lo que los programas que tienen el rango de archivos mmap seguirán accediendo al mapeo de memoria anterior después de que se hayan completado las actualizaciones de metadatos del archivo. Tenga cuidado con el valor de retorno: si la anulación del uso compartido tiene éxito, aún necesitamos devolver la cantidad de bytes en los que el iter iomap cree que estamos operando."
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