CVE-2025-21664 (GCVE-0-2025-21664)
Vulnerability from cvelistv5
Published
2025-01-21 12:18
Modified
2025-05-04 07:18
Severity ?
Summary
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. 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.
References
Impacted products
Vendor Product Version
Linux Linux Version: b10ebd34cccae1b431caf1be54919aede2be7cbe
Version: b10ebd34cccae1b431caf1be54919aede2be7cbe
Version: b10ebd34cccae1b431caf1be54919aede2be7cbe
Version: b10ebd34cccae1b431caf1be54919aede2be7cbe
Version: b10ebd34cccae1b431caf1be54919aede2be7cbe
Version: b10ebd34cccae1b431caf1be54919aede2be7cbe
Version: b10ebd34cccae1b431caf1be54919aede2be7cbe
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/md/dm-thin.c"
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      "cpeApplicability": [
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      "descriptions": [
        {
          "lang": "en",
          "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() -\u003e\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\u0027s\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\u0027s thin-provisioning\nsuites for delete and suspend and no regressions were observed."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-05-04T07:18:30.814Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/ec037fe8c0d0f6140e3d8a49c7b29cb5582160b8"
        },
        {
          "url": "https://git.kernel.org/stable/c/cd30a3960433ec2db94b3689752fa3c5df44d649"
        },
        {
          "url": "https://git.kernel.org/stable/c/802666a40c71a23542c43a3f87e3a2d0f4e8fe45"
        },
        {
          "url": "https://git.kernel.org/stable/c/12771050b6d059eea096993bf2001da9da9fddff"
        },
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          "url": "https://git.kernel.org/stable/c/6b305e98de0d225ccebfb225730a9f560d28ecb0"
        },
        {
          "url": "https://git.kernel.org/stable/c/cbd0d5ecfa390ac29c5380200147d09c381b2ac6"
        },
        {
          "url": "https://git.kernel.org/stable/c/80f130bfad1dab93b95683fc39b87235682b8f72"
        }
      ],
      "title": "dm thin: make get_first_thin use rcu-safe list first function",
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        "engine": "bippy-1.2.0"
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    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21664",
    "datePublished": "2025-01-21T12:18:19.015Z",
    "dateReserved": "2024-12-29T08:45:45.732Z",
    "dateUpdated": "2025-05-04T07:18:30.814Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-21664\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-01-21T13:15:10.053\",\"lastModified\":\"2025-02-02T11:15:15.697\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"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() -\u003e\\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\u0027s\\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\u0027s thin-provisioning\\nsuites for delete and suspend and no regressions were observed.\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: dm thin: hacer que get_first_thin use la funci\u00f3n list first de rcu-safe La documentaci\u00f3n en rculist.h explica la ausencia de list_empty_rcu() y advierte a los programadores que no conf\u00eden en una secuencia list_empty() -\u0026gt; list_first() en el c\u00f3digo 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 situaci\u00f3n en la que list_empty() ve una entrada de lista v\u00e1lida, pero el list_first() posterior ve una vista diferente del estado del encabezado de lista despu\u00e9s de una modificaci\u00f3n. En el caso de dm-thin, este autor tuvo un bloqueo del cuadro de producci\u00f3n debido a una falla de GP en la ruta process_deferred_bios. Esta funci\u00f3n vio un encabezado de lista v\u00e1lido en get_first_thin() pero cuando posteriormente desreferenciaba eso y lo convert\u00eda en un thin_c, obtuvo el interior del grupo de estructuras, ya que la lista ahora estaba vac\u00eda y se refer\u00eda a s\u00ed misma. El n\u00facleo en el que esto ocurri\u00f3 imprimi\u00f3 una advertencia sobre la saturaci\u00f3n de un refcount_t y un error UBSAN por un acceso a cpuid fuera de los l\u00edmites en el spinlock en cola, antes del fallo en s\u00ed. Cuando se examin\u00f3 el kdump resultante, fue posible ver otro hilo esperando pacientemente en elsynchronous_rcu de thin_dtr. La llamada thin_dtr logr\u00f3 sacar el thin_c de la lista de thins activa (y hacer que sea la \u00faltima entrada en la lista de active_thins) justo en el momento equivocado, lo que provoc\u00f3 este bloqueo. Afortunadamente, la soluci\u00f3n aqu\u00ed es sencilla. Cambie la funci\u00f3n get_first_thin() para usar list_first_or_null_rcu() que realiza solo un \u00fanico READ_ONCE() y devuelve NULL si la lista ya est\u00e1 vac\u00eda. Esto se ejecut\u00f3 contra las suites de aprovisionamiento fino del conjunto de pruebas devicemapper para eliminar y suspender y no se observaron regresiones.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/12771050b6d059eea096993bf2001da9da9fddff\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/6b305e98de0d225ccebfb225730a9f560d28ecb0\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/802666a40c71a23542c43a3f87e3a2d0f4e8fe45\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/80f130bfad1dab93b95683fc39b87235682b8f72\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/cbd0d5ecfa390ac29c5380200147d09c381b2ac6\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/cd30a3960433ec2db94b3689752fa3c5df44d649\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ec037fe8c0d0f6140e3d8a49c7b29cb5582160b8\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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