FKIE_CVE-2026-31667

Vulnerability from fkie_nvd - Published: 2026-04-24 15:16 - Updated: 2026-04-24 17:51
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: Input: uinput - fix circular locking dependency with ff-core A lockdep circular locking dependency warning can be triggered reproducibly when using a force-feedback gamepad with uinput (for example, playing ELDEN RING under Wine with a Flydigi Vader 5 controller): ff->mutex -> udev->mutex -> input_mutex -> dev->mutex -> ff->mutex The cycle is caused by four lock acquisition paths: 1. ff upload: input_ff_upload() holds ff->mutex and calls uinput_dev_upload_effect() -> uinput_request_submit() -> uinput_request_send(), which acquires udev->mutex. 2. device create: uinput_ioctl_handler() holds udev->mutex and calls uinput_create_device() -> input_register_device(), which acquires input_mutex. 3. device register: input_register_device() holds input_mutex and calls kbd_connect() -> input_register_handle(), which acquires dev->mutex. 4. evdev release: evdev_release() calls input_flush_device() under dev->mutex, which calls input_ff_flush() acquiring ff->mutex. Fix this by introducing a new state_lock spinlock to protect udev->state and udev->dev access in uinput_request_send() instead of acquiring udev->mutex. The function only needs to atomically check device state and queue an input event into the ring buffer via uinput_dev_event() -- both operations are safe under a spinlock (ktime_get_ts64() and wake_up_interruptible() do not sleep). This breaks the ff->mutex -> udev->mutex link since a spinlock is a leaf in the lock ordering and cannot form cycles with mutexes. To keep state transitions visible to uinput_request_send(), protect writes to udev->state in uinput_create_device() and uinput_destroy_device() with the same state_lock spinlock. Additionally, move init_completion(&request->done) from uinput_request_send() to uinput_request_submit() before uinput_request_reserve_slot(). Once the slot is allocated, uinput_flush_requests() may call complete() on it at any time from the destroy path, so the completion must be initialised before the request becomes visible. Lock ordering after the fix: ff->mutex -> state_lock (spinlock, leaf) udev->mutex -> state_lock (spinlock, leaf) udev->mutex -> input_mutex -> dev->mutex -> ff->mutex (no back-edge)
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/1534661043c434b81cfde26b97a2fb2460329cf0
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/1e09dfbb4f5d20ee111f92325a00f85778a5f328
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/271ee71a1917b89f6d73ec82dd091c33d92ee617
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4cda78d6f8bf2b700529f2fbccb994c3e826d7c2
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/546c18a14924eb521fe168d916d7ce28f1e13c1d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/71a9729f412e2c692a35c542e14b706fb342927f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/974f7b138c3a96dd5cd53d1b33409cd7b2229dc6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a3d6c9c053c9c605651508569230ead633b13f76
Impacted products
Vendor Product Version
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nInput: uinput - fix circular locking dependency with ff-core\n\nA lockdep circular locking dependency warning can be triggered\nreproducibly when using a force-feedback gamepad with uinput (for\nexample, playing ELDEN RING under Wine with a Flydigi Vader 5\ncontroller):\n\n  ff-\u003emutex -\u003e udev-\u003emutex -\u003e input_mutex -\u003e dev-\u003emutex -\u003e ff-\u003emutex\n\nThe cycle is caused by four lock acquisition paths:\n\n1. ff upload: input_ff_upload() holds ff-\u003emutex and calls\n   uinput_dev_upload_effect() -\u003e uinput_request_submit() -\u003e\n   uinput_request_send(), which acquires udev-\u003emutex.\n\n2. device create: uinput_ioctl_handler() holds udev-\u003emutex and calls\n   uinput_create_device() -\u003e input_register_device(), which acquires\n   input_mutex.\n\n3. device register: input_register_device() holds input_mutex and\n   calls kbd_connect() -\u003e input_register_handle(), which acquires\n   dev-\u003emutex.\n\n4. evdev release: evdev_release() calls input_flush_device() under\n   dev-\u003emutex, which calls input_ff_flush() acquiring ff-\u003emutex.\n\nFix this by introducing a new state_lock spinlock to protect\nudev-\u003estate and udev-\u003edev access in uinput_request_send() instead of\nacquiring udev-\u003emutex.  The function only needs to atomically check\ndevice state and queue an input event into the ring buffer via\nuinput_dev_event() -- both operations are safe under a spinlock\n(ktime_get_ts64() and wake_up_interruptible() do not sleep).  This\nbreaks the ff-\u003emutex -\u003e udev-\u003emutex link since a spinlock is a leaf in\nthe lock ordering and cannot form cycles with mutexes.\n\nTo keep state transitions visible to uinput_request_send(), protect\nwrites to udev-\u003estate in uinput_create_device() and\nuinput_destroy_device() with the same state_lock spinlock.\n\nAdditionally, move init_completion(\u0026request-\u003edone) from\nuinput_request_send() to uinput_request_submit() before\nuinput_request_reserve_slot().  Once the slot is allocated,\nuinput_flush_requests() may call complete() on it at any time from\nthe destroy path, so the completion must be initialised before the\nrequest becomes visible.\n\nLock ordering after the fix:\n\n  ff-\u003emutex -\u003e state_lock (spinlock, leaf)\n  udev-\u003emutex -\u003e state_lock (spinlock, leaf)\n  udev-\u003emutex -\u003e input_mutex -\u003e dev-\u003emutex -\u003e ff-\u003emutex (no back-edge)"
    }
  ],
  "id": "CVE-2026-31667",
  "lastModified": "2026-04-24T17:51:40.810",
  "metrics": {},
  "published": "2026-04-24T15:16:46.390",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/1534661043c434b81cfde26b97a2fb2460329cf0"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/1e09dfbb4f5d20ee111f92325a00f85778a5f328"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/271ee71a1917b89f6d73ec82dd091c33d92ee617"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/4cda78d6f8bf2b700529f2fbccb994c3e826d7c2"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/546c18a14924eb521fe168d916d7ce28f1e13c1d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/71a9729f412e2c692a35c542e14b706fb342927f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/974f7b138c3a96dd5cd53d1b33409cd7b2229dc6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a3d6c9c053c9c605651508569230ead633b13f76"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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