CVE-2025-21664
Estado: ModificadaMedia (5.5)—
In the Linux kernel, the following vulnerability has been resolved:
dm thin: make get_first_thin use rcu-safe list first function
The documentation in rculist.h explains the absence of list_empty_rcu() and cautions programmers against relying on a list_empty() -> list_first() sequence in RCU safe code. This is because each of these functions performs its own READ_ONCE() of the list head. This can lead to a situation where the list_empty() sees a valid list entry, but the subsequent list_first() sees a different view of list head state after a modification.
In the case of dm-thin, this author had a production box crash from a GP fault in the process_deferred_bios path.
Leer descripción completaMostrar menos
This function saw a valid list head in get_first_thin() but when it subsequently dereferenced that and turned it into a thin_c, it got the inside of the struct pool, since the list was now empty and referring to itself. The kernel on which this occurred printed both a warning about a refcount_t being saturated, and a UBSAN error for an out-of-bounds cpuid access in the queued spinlock, prior to the fault itself. When the resulting kdump was examined, it was possible to see another thread patiently waiting in thin_dtr's synchronize_rcu.
The thin_dtr call managed to pull the thin_c out of the active thins list (and have it be the last entry in the active_thins list) at just the wrong moment which lead to this crash.
Fortunately, the fix here is straight forward. Switch get_first_thin() function to use list_first_or_null_rcu() which performs just a single READ_ONCE() and returns NULL if the list is already empty.
This was run against the devicemapper test suite's thin-provisioning suites for delete and suspend and no regressions were observed.
CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- Puntuación base: 5.5
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.24%
- Percentil entre todas las CVEs puntuadas: 13
- Fecha de la puntuación: 5/10/2026
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)
CWE
- NVD-CWE-noinfo
Referencias
- https://git.kernel.org/stable/c/12771050b6d059eea096993bf2001da9da9fddff
- https://git.kernel.org/stable/c/6b305e98de0d225ccebfb225730a9f560d28ecb0
- https://git.kernel.org/stable/c/802666a40c71a23542c43a3f87e3a2d0f4e8fe45
- https://git.kernel.org/stable/c/80f130bfad1dab93b95683fc39b87235682b8f72
- https://git.kernel.org/stable/c/cbd0d5ecfa390ac29c5380200147d09c381b2ac6
- https://git.kernel.org/stable/c/cd30a3960433ec2db94b3689752fa3c5df44d649
- https://git.kernel.org/stable/c/ec037fe8c0d0f6140e3d8a49c7b29cb5582160b8
- https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html
- https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html
- https://cert-portal.siemens.com/productcert/html/ssa-265688.html
JSON original (NVD)
Mostrar
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\ndm thin: make get_first_thin use rcu-safe list first function\n\nThe documentation in rculist.h explains the absence of list_empty_rcu()\nand cautions programmers against relying on a list_empty() ->\nlist_first() sequence in RCU safe code. This is because each of these\nfunctions performs its own READ_ONCE() of the list head. This can lead\nto a situation where the list_empty() sees a valid list entry, but the\nsubsequent list_first() sees a different view of list head state after a\nmodification.\n\nIn the case of dm-thin, this author had a production box crash from a GP\nfault in the process_deferred_bios path. This function saw a valid list\nhead in get_first_thin() but when it subsequently dereferenced that and\nturned it into a thin_c, it got the inside of the struct pool, since the\nlist was now empty and referring to itself. The kernel on which this\noccurred printed both a warning about a refcount_t being saturated, and\na UBSAN error for an out-of-bounds cpuid access in the queued spinlock,\nprior to the fault itself. When the resulting kdump was examined, it\nwas possible to see another thread patiently waiting in thin_dtr's\nsynchronize_rcu.\n\nThe thin_dtr call managed to pull the thin_c out of the active thins\nlist (and have it be the last entry in the active_thins list) at just\nthe wrong moment which lead to this crash.\n\nFortunately, the fix here is straight forward. Switch get_first_thin()\nfunction to use list_first_or_null_rcu() which performs just a single\nREAD_ONCE() and returns NULL if the list is already empty.\n\nThis was run against the devicemapper test suite's thin-provisioning\nsuites for delete and suspend and no regressions were observed."
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"value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: dm thin: hacer que get_first_thin use la función list first de rcu-safe La documentación en rculist.h explica la ausencia de list_empty_rcu() y advierte a los programadores que no confíen en una secuencia list_empty() -> list_first() en el código seguro de RCU. Esto se debe a que cada una de estas funciones realiza su propio READ_ONCE() del encabezado de la lista. Esto puede llevar a una situación en la que list_empty() ve una entrada de lista válida, pero el list_first() posterior ve una vista diferente del estado del encabezado de lista después de una modificación. En el caso de dm-thin, este autor tuvo un bloqueo del cuadro de producción debido a una falla de GP en la ruta process_deferred_bios. Esta función vio un encabezado de lista válido en get_first_thin() pero cuando posteriormente desreferenciaba eso y lo convertía en un thin_c, obtuvo el interior del grupo de estructuras, ya que la lista ahora estaba vacía y se refería a sí misma. El núcleo en el que esto ocurrió imprimió una advertencia sobre la saturación de un refcount_t y un error UBSAN por un acceso a cpuid fuera de los límites en el spinlock en cola, antes del fallo en sí. Cuando se examinó el kdump resultante, fue posible ver otro hilo esperando pacientemente en elsynchronous_rcu de thin_dtr. La llamada thin_dtr logró sacar el thin_c de la lista de thins activa (y hacer que sea la última entrada en la lista de active_thins) justo en el momento equivocado, lo que provocó este bloqueo. Afortunadamente, la solución aquí es sencilla. Cambie la función get_first_thin() para usar list_first_or_null_rcu() que realiza solo un único READ_ONCE() y devuelve NULL si la lista ya está vacía. Esto se ejecutó contra las suites de aprovisionamiento fino del conjunto de pruebas devicemapper para eliminar y suspender y no se observaron regresiones."
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"lastModified": "2026-07-30T06:18:05.070",
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