---
id: CVE-2026-68200
title: 'ALSA: timer: don''t re-enter an instance callback that is still running'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ALSA: timer: don't re-enter an instance callback that is still running

  The userspace-driven timer (utimer) TRIGGER ioctl calls
  snd_timer_interrupt() directly with no s…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 <
    996c24377eea4d4506b7c3ccbbf1e490440b5e0b
  - >-
    Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 <
    1395327a96614885552bae5fbb650e6dd182d49b
  - >-
    Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 <
    c1078130a4cd7e738f4b73afe99b3e68cbfbf884
  - >-
    Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 <
    70d28bfcd6224eed75986b3b987b997e59643fa4
  - Linux 6.12
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T15:45:45.952890Z'
published: '2026-08-10'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:53:03.285Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-68200'
references:
  - url: 'https://git.kernel.org/stable/c/996c24377eea4d4506b7c3ccbbf1e490440b5e0b'
  - url: 'https://git.kernel.org/stable/c/1395327a96614885552bae5fbb650e6dd182d49b'
  - url: 'https://git.kernel.org/stable/c/c1078130a4cd7e738f4b73afe99b3e68cbfbf884'
  - url: 'https://git.kernel.org/stable/c/70d28bfcd6224eed75986b3b987b997e59643fa4'
tags:
  - cve.org
epss: 0.0017
epssPercentile: 0.05976
ingestedAt: '2026-10-16T17:24:46.849Z'
---

## Overview

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

ALSA: timer: don't re-enter an instance callback that is still running

The userspace-driven timer (utimer) TRIGGER ioctl calls
snd_timer_interrupt() directly with no serialization, so two threads
triggering the same utimer can run snd_timer_interrupt() on one
snd_timer concurrently.

snd_timer_process_callbacks() drops timer->lock around each instance
callback and marks the in-flight callback with the single
SNDRV_TIMER_IFLG_CALLBACK bit; snd_timer_close_locked() waits on that
bit to drain an in-flight callback before freeing the instance. The bit
cannot represent two concurrent callbacks: when a second interrupt
re-queues an instance whose callback is still running, both run at once,
the first to finish clears the bit, and the close-path drain then frees
the instance (and its callback_data) while the other callback is still
live - a use-after-free reachable by any user able to open
/dev/snd/timer, both via a user timer instance and via a sequencer queue
timer bound to the utimer.

snd_timer_interrupt() sets IFLG_CALLBACK before dropping timer->lock, so
a concurrent interrupt already observes it under the lock. Skip
re-queuing an instance (and its slaves) to the ack/sack list while its
callback is in flight; the accumulated pticks are delivered on the next
tick, so no event is lost.

## Affected

- `Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 996c24377eea4d4506b7c3ccbbf1e490440b5e0b`
- `Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 1395327a96614885552bae5fbb650e6dd182d49b`
- `Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < c1078130a4cd7e738f4b73afe99b3e68cbfbf884`
- `Linux >= 37745918e0e7575bc40f38da93a99b9fa6406224 < 70d28bfcd6224eed75986b3b987b997e59643fa4`
- `Linux 6.12`

## Remediation

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