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CVE-2025-40220

Estado: AplazadaSin puntuar—

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

fuse: fix livelock in synchronous file put from fuseblk workers

I observed a hang when running generic/323 against a fuseblk server. This test opens a file, initiates a lot of AIO writes to that file descriptor, and closes the file descriptor before the writes complete. Unsurprisingly, the AIO exerciser threads are mostly stuck waiting for responses from the fuseblk server:

But the /weird/ part is that the fuseblk server threads are waiting for responses from itself:

The fuseblk server is fuse2fs so there's nothing all that exciting in the server itself. So why is the fuse server calling fuse_file_put? The commit message for the fstest sheds some light on that:

Leer descripción completaMostrar menos

"By closing the file descriptor before calling io_destroy, you pretty much guarantee that the last put on the ioctx will be done in interrupt context (during I/O completion).

Aha. AIO fgets a new struct file from the fd when it queues the ioctx. The completion of the FUSE_WRITE command from userspace causes the fuse server to call the AIO completion function. The completion puts the struct file, queuing a delayed fput to the fuse server task. When the fuse server task returns to userspace, it has to run the delayed fput, which in the case of a fuseblk server, it does synchronously.

Sending the FUSE_RELEASE command sychronously from fuse server threads is a bad idea because a client program can initiate enough simultaneous AIOs such that all the fuse server threads end up in delayed_fput, and now there aren't any threads left to handle the queued fuse commands.

Fix this by only using asynchronous fputs when closing files, and leave a comment explaining why.

Detalles técnicos trazas, registros y código del informe original
# cat /proc/372265/task/372313/stack
[<0>] request_wait_answer+0x1fe/0x2a0 [fuse]
[<0>] __fuse_simple_request+0xd3/0x2b0 [fuse]
[<0>] fuse_do_getattr+0xfc/0x1f0 [fuse]
[<0>] fuse_file_read_iter+0xbe/0x1c0 [fuse]
[<0>] aio_read+0x130/0x1e0
[<0>] io_submit_one+0x542/0x860
[<0>] __x64_sys_io_submit+0x98/0x1a0
[<0>] do_syscall_64+0x37/0xf0
[<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53

# cat /proc/372210/task/372232/stack
[<0>] request_wait_answer+0x1fe/0x2a0 [fuse]
[<0>] __fuse_simple_request+0xd3/0x2b0 [fuse]
[<0>] fuse_file_put+0x9a/0xd0 [fuse]
[<0>] fuse_release+0x36/0x50 [fuse]
[<0>] __fput+0xec/0x2b0
[<0>] task_work_run+0x55/0x90
[<0>] syscall_exit_to_user_mode+0xe9/0x100
[<0>] do_syscall_64+0x43/0xf0
[<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53

CVSS

NVD no ha asignado puntuación CVSS a esta CVE (habitual desde el cambio de política de abril de 2026).

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)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux KernelAI

Referencias

JSON original (NVD)

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{
  "id": "CVE-2025-40220",
  "cveTags": [],
  "metrics": {},
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5a18ec176c934ca1bc9dc61580a5e0e90a9b5733",
              "lessThan": "548e1f2bac1d4df91a6138f26bb4ab00323fd948",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5a18ec176c934ca1bc9dc61580a5e0e90a9b5733",
              "lessThan": "cfd1aa3e2b71f3327cb373c45a897c9028c62b35",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5a18ec176c934ca1bc9dc61580a5e0e90a9b5733",
              "lessThan": "83b375c6efef69b1066ad2d79601221e7892745a",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5a18ec176c934ca1bc9dc61580a5e0e90a9b5733",
              "lessThan": "bfd17b6138df0122a95989457d8e18ce0b86165e",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5a18ec176c934ca1bc9dc61580a5e0e90a9b5733",
              "lessThan": "b26923512dbe57ae4917bafd31396d22a9d1691a",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5a18ec176c934ca1bc9dc61580a5e0e90a9b5733",
              "lessThan": "f19a1390af448d9e193c08e28ea5f727bf3c3049",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5a18ec176c934ca1bc9dc61580a5e0e90a9b5733",
              "lessThan": "26e5c67deb2e1f42a951f022fdf5b9f7eb747b01",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9efe56738fecd591b5bf366a325440f9b457ebd6",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5c46eb076e0a1b2c1769287cd6942e4594ade1b1",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "83e6726210d6c815ce044437106c738eda5ff6f6",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "23d154c71721fd0fa6199851078f32e6bd765664",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "ca3edc920f5fd7d8ac040caaf109f925c24620a0",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "2.6.32.32",
              "lessThan": "2.6.33",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "2.6.33.8",
              "lessThan": "2.6.34",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "2.6.34.10",
              "lessThan": "2.6.35",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "2.6.35.12",
              "lessThan": "2.6.36",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "2.6.37.3",
              "lessThan": "2.6.38",
              "versionType": "semver"
            }
          ],
          "programFiles": [
            "fs/fuse/file.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.38"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "2.6.38",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "5.10.246",
              "versionType": "semver",
              "lessThanOrEqual": "5.10.*"
            },
            {
              "status": "unaffected",
              "version": "5.15.196",
              "versionType": "semver",
              "lessThanOrEqual": "5.15.*"
            },
            {
              "status": "unaffected",
              "version": "6.1.158",
              "versionType": "semver",
              "lessThanOrEqual": "6.1.*"
            },
            {
              "status": "unaffected",
              "version": "6.6.115",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
              "status": "unaffected",
              "version": "6.12.54",
              "versionType": "semver",
              "lessThanOrEqual": "6.12.*"
            },
            {
              "status": "unaffected",
              "version": "6.17.4",
              "versionType": "semver",
              "lessThanOrEqual": "6.17.*"
            },
            {
              "status": "unaffected",
              "version": "6.18",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "fs/fuse/file.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2025-12-04T15:15:58.033",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/26e5c67deb2e1f42a951f022fdf5b9f7eb747b01",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/548e1f2bac1d4df91a6138f26bb4ab00323fd948",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/83b375c6efef69b1066ad2d79601221e7892745a",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/b26923512dbe57ae4917bafd31396d22a9d1691a",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/bfd17b6138df0122a95989457d8e18ce0b86165e",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/cfd1aa3e2b71f3327cb373c45a897c9028c62b35",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/f19a1390af448d9e193c08e28ea5f727bf3c3049",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Deferred",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfuse: fix livelock in synchronous file put from fuseblk workers\n\nI observed a hang when running generic/323 against a fuseblk server.\nThis test opens a file, initiates a lot of AIO writes to that file\ndescriptor, and closes the file descriptor before the writes complete.\nUnsurprisingly, the AIO exerciser threads are mostly stuck waiting for\nresponses from the fuseblk server:\n\n# cat /proc/372265/task/372313/stack\n[<0>] request_wait_answer+0x1fe/0x2a0 [fuse]\n[<0>] __fuse_simple_request+0xd3/0x2b0 [fuse]\n[<0>] fuse_do_getattr+0xfc/0x1f0 [fuse]\n[<0>] fuse_file_read_iter+0xbe/0x1c0 [fuse]\n[<0>] aio_read+0x130/0x1e0\n[<0>] io_submit_one+0x542/0x860\n[<0>] __x64_sys_io_submit+0x98/0x1a0\n[<0>] do_syscall_64+0x37/0xf0\n[<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\nBut the /weird/ part is that the fuseblk server threads are waiting for\nresponses from itself:\n\n# cat /proc/372210/task/372232/stack\n[<0>] request_wait_answer+0x1fe/0x2a0 [fuse]\n[<0>] __fuse_simple_request+0xd3/0x2b0 [fuse]\n[<0>] fuse_file_put+0x9a/0xd0 [fuse]\n[<0>] fuse_release+0x36/0x50 [fuse]\n[<0>] __fput+0xec/0x2b0\n[<0>] task_work_run+0x55/0x90\n[<0>] syscall_exit_to_user_mode+0xe9/0x100\n[<0>] do_syscall_64+0x43/0xf0\n[<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\nThe fuseblk server is fuse2fs so there's nothing all that exciting in\nthe server itself.  So why is the fuse server calling fuse_file_put?\nThe commit message for the fstest sheds some light on that:\n\n\"By closing the file descriptor before calling io_destroy, you pretty\nmuch guarantee that the last put on the ioctx will be done in interrupt\ncontext (during I/O completion).\n\nAha.  AIO fgets a new struct file from the fd when it queues the ioctx.\nThe completion of the FUSE_WRITE command from userspace causes the fuse\nserver to call the AIO completion function.  The completion puts the\nstruct file, queuing a delayed fput to the fuse server task.  When the\nfuse server task returns to userspace, it has to run the delayed fput,\nwhich in the case of a fuseblk server, it does synchronously.\n\nSending the FUSE_RELEASE command sychronously from fuse server threads\nis a bad idea because a client program can initiate enough simultaneous\nAIOs such that all the fuse server threads end up in delayed_fput, and\nnow there aren't any threads left to handle the queued fuse commands.\n\nFix this by only using asynchronous fputs when closing files, and leave\na comment explaining why."
    }
  ],
  "lastModified": "2026-06-17T09:21:28.777",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}