---
id: CVE-2026-98809
title: 'Bluetooth: hci_sync: don''t drain cmd_sync backlog on unregister'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  Bluetooth: hci_sync: don't drain cmd_sync backlog on unregister

  hci_unregister_dev() disables cmd_work and cmd_timer, then calls
  hci_cmd_sync_clear(), whose cancel_wor…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 008ee9eb8a11bcabf12c91771dd4f470b082bd44 <
    143bde97c4101ae68eb656c87e620c45b07a3090
  - >-
    Linux >= 008ee9eb8a11bcabf12c91771dd4f470b082bd44 <
    7f16443a30f4e86d84ae4faf057d333b41ddb757
  - >-
    Linux >= 008ee9eb8a11bcabf12c91771dd4f470b082bd44 <
    e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c
  - >-
    Linux >= 008ee9eb8a11bcabf12c91771dd4f470b082bd44 <
    b1f24c1ab52345e810c42a1a81286cb5a7c92252
  - Linux 5.17
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:48:55.913Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98809'
references:
  - url: 'https://git.kernel.org/stable/c/143bde97c4101ae68eb656c87e620c45b07a3090'
  - url: 'https://git.kernel.org/stable/c/7f16443a30f4e86d84ae4faf057d333b41ddb757'
  - url: 'https://git.kernel.org/stable/c/e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c'
  - url: 'https://git.kernel.org/stable/c/b1f24c1ab52345e810c42a1a81286cb5a7c92252'
tags:
  - cve.org
ingestedAt: '2026-10-18T16:47:32.478Z'
---

## Overview

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

Bluetooth: hci_sync: don't drain cmd_sync backlog on unregister

hci_unregister_dev() disables cmd_work and cmd_timer, then calls
hci_cmd_sync_clear(), whose cancel_work_sync() waits for
hci_cmd_sync_work() to return. That worker dequeues and runs every
entry on cmd_sync_work_list. With cmd_work disabled nothing reaches
the controller, so each queued HCI command waits the full
HCI_CMD_TIMEOUT (2s).

The backlog has no bound. Userspace can keep queuing MGMT commands
such as MGMT_OP_GET_CLOCK_INFO against a controller that doesn't
answer. Closing /dev/vhci then blocks in vhci_release() for
backlog * 2s:

  INFO: task syz-executor:5749 blocked for more than 143 seconds.
   cancel_work_sync
   hci_cmd_sync_clear
   hci_unregister_dev
   vhci_release

In a local reproduction the backlog held more than 5000 entries,
which comes to hours of hang.

Stop the worker from taking new entries once HCI_UNREGISTER is set,
and wake any request still waiting with -ENODEV before cancelling
the work. The entries left over are destroyed with -ECANCELED by the
existing sweep in hci_cmd_sync_clear(). They stay on the list until
the work has stopped, so hci_cmd_sync_dequeue() and friends still see
them. A callback already running may still issue another command,
which delays unregister by at most one timeout per remaining command,
not by the whole backlog.

## Affected

- `Linux >= 008ee9eb8a11bcabf12c91771dd4f470b082bd44 < 143bde97c4101ae68eb656c87e620c45b07a3090`
- `Linux >= 008ee9eb8a11bcabf12c91771dd4f470b082bd44 < 7f16443a30f4e86d84ae4faf057d333b41ddb757`
- `Linux >= 008ee9eb8a11bcabf12c91771dd4f470b082bd44 < e8ba8c9c74d1035042cdf6cb5adf8f59b9b1271c`
- `Linux >= 008ee9eb8a11bcabf12c91771dd4f470b082bd44 < b1f24c1ab52345e810c42a1a81286cb5a7c92252`
- `Linux 5.17`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.