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GHSA-M3H2-47PX-55RM

Vulnerability from github – Published: 2026-08-06 09:30 – Updated: 2026-08-19 18:32
VLAI
Details

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

usb: gadget: f_midi: cancel pending IN work before freeing the midi object

The f_midi driver embeds a work item (midi->work) whose handler, f_midi_in_work(), dereferences the enclosing struct f_midi through container_of(). This work is armed from two sites: f_midi_complete(), on a normal IN-endpoint completion, and f_midi_in_trigger(), on an ALSA rawmidi output-stream start.

Neither f_midi_disable() nor f_midi_unbind() cancels midi->work. f_midi_disable() only disables the endpoints and drains the in_req_fifo; it does not synchronize the work item, and the sound card is released asynchronously to the final free of the midi object.

The midi object is reference-counted (midi->free_ref) and is freed in f_midi_free() only once both the usb_function reference and the rawmidi private_data reference have been dropped. In f_midi_unbind(), f_midi_disable() runs before the sound card is released, so while the USB endpoints are already disabled the rawmidi device is still usable by an open substream. A concurrent userspace write on such a substream can reach f_midi_in_trigger() and queue midi->work again after f_midi_disable() has returned. A work item armed this way may still be pending when the last reference drops and f_midi_free() proceeds to kfree(midi), letting f_midi_in_work() dereference the struct after it has been freed, a use-after-free.

For this reason cancelling midi->work in f_midi_disable() would not be sufficient: the ALSA trigger path can rearm the work after disable() returns. Cancelling at the refcount-zero free site is the boundary after which neither arming source can survive, because by then both references that keep the midi object alive have been dropped: the USB endpoints are already disabled and the rawmidi device has been released.

Fix this by calling cancel_work_sync(&midi->work) in the refcount-zero block of f_midi_free(), before the embedded work_struct is freed along with the rest of the structure. opts->lock is a sleeping mutex, so calling cancel_work_sync() under it is permitted, and the handler takes midi->transmit_lock rather than opts->lock, so no self-deadlock can occur while it waits for a running instance of the work to finish.

This issue was found by an in-house static analysis tool.

Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-64584"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-06T08:16:33Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_midi: cancel pending IN work before freeing the midi object\n\nThe f_midi driver embeds a work item (midi-\u003ework) whose handler,\nf_midi_in_work(), dereferences the enclosing struct f_midi through\ncontainer_of().  This work is armed from two sites: f_midi_complete(),\non a normal IN-endpoint completion, and f_midi_in_trigger(), on an ALSA\nrawmidi output-stream start.\n\nNeither f_midi_disable() nor f_midi_unbind() cancels midi-\u003ework.\nf_midi_disable() only disables the endpoints and drains the in_req_fifo;\nit does not synchronize the work item, and the sound card is released\nasynchronously to the final free of the midi object.\n\nThe midi object is reference-counted (midi-\u003efree_ref) and is freed in\nf_midi_free() only once both the usb_function reference and the rawmidi\nprivate_data reference have been dropped.  In f_midi_unbind(),\nf_midi_disable() runs before the sound card is released, so while the\nUSB endpoints are already disabled the rawmidi device is still usable by\nan open substream.  A concurrent userspace write on such a substream can\nreach f_midi_in_trigger() and queue midi-\u003ework again after\nf_midi_disable() has returned.  A work item armed this way may still be\npending when the last reference drops and f_midi_free() proceeds to\nkfree(midi), letting f_midi_in_work() dereference the struct after it\nhas been freed, a use-after-free.\n\nFor this reason cancelling midi-\u003ework in f_midi_disable() would not be\nsufficient: the ALSA trigger path can rearm the work after disable()\nreturns.  Cancelling at the refcount-zero free site is the boundary\nafter which neither arming source can survive, because by then both\nreferences that keep the midi object alive have been dropped: the USB\nendpoints are already disabled and the rawmidi device has been released.\n\nFix this by calling cancel_work_sync(\u0026midi-\u003ework) in the refcount-zero\nblock of f_midi_free(), before the embedded work_struct is freed along\nwith the rest of the structure.  opts-\u003elock is a sleeping mutex, so\ncalling cancel_work_sync() under it is permitted, and the handler takes\nmidi-\u003etransmit_lock rather than opts-\u003elock, so no self-deadlock can\noccur while it waits for a running instance of the work to finish.\n\nThis issue was found by an in-house static analysis tool.",
  "id": "GHSA-m3h2-47px-55rm",
  "modified": "2026-08-19T18:32:04Z",
  "published": "2026-08-06T09:30:32Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64584"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/380b4bef46c2eb260c7a9c6bb2c5be33ce5a38f9"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5650c18d93a1db7e27cb5a40b394747eb4686d5b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/620955b222c47332297d6bf38f78541aa699238a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/87bc316dd6fc90072297c635e10b9aa6075ecda1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ac9a51d910bb7465c554c45320cb6c09f3d0b49d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/df18150126f66817e4d3f79f309e9c92d6ff384e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f3c6f2c38062703d3dc7f86958bb0790c6959add"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f45089eaad0a083d71d84ff175741d7e157d9b69"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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