---
id: CVE-2026-74387
title: 'ALSA: seq: midi: Serialize output teardown with event_input'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ALSA: seq: midi: Serialize output teardown with event_input

  event_process_midi() borrows msynth->output_rfile.output and then
  passes the substream to dump_midi() and 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 >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    f5d470b808bc01f70978e22e595c6f7768313406
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    936641af564c3d92721704b781e36aaf223efdd2
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    718f6a56b40875f19e6915799044a02df9abfd52
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    11165fe2c5ea0516debe486d91df67abbe36905e
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    d6fd2afb137f52bf00c5210cc44d08ed54dcffb4
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    ef7607ab1c8adc6258fb1b27d08e26aecdc18a58
  - Linux 2.6.12
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T18:55:07.666798Z'
published: '2026-08-15'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T18:55:36.992Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-74387'
references:
  - url: 'https://git.kernel.org/stable/c/f5d470b808bc01f70978e22e595c6f7768313406'
  - url: 'https://git.kernel.org/stable/c/936641af564c3d92721704b781e36aaf223efdd2'
  - url: 'https://git.kernel.org/stable/c/718f6a56b40875f19e6915799044a02df9abfd52'
  - url: 'https://git.kernel.org/stable/c/11165fe2c5ea0516debe486d91df67abbe36905e'
  - url: 'https://git.kernel.org/stable/c/d6fd2afb137f52bf00c5210cc44d08ed54dcffb4'
  - url: 'https://git.kernel.org/stable/c/ef7607ab1c8adc6258fb1b27d08e26aecdc18a58'
tags:
  - cve.org
epss: 0.00171
epssPercentile: 0.06041
ingestedAt: '2026-10-16T19:46:24.372Z'
---

## Overview

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

ALSA: seq: midi: Serialize output teardown with event_input

event_process_midi() borrows msynth->output_rfile.output and then
passes the substream to dump_midi() and snd_rawmidi_kernel_write()
without synchronizing with the output open/close transition.
midisynth_use() also publishes output_rfile before
snd_rawmidi_output_params() has finished.

The last midisynth_unuse() can therefore release the same rawmidi file
and free substream->runtime before snd_rawmidi_kernel_write1() takes
its runtime buffer reference. That leaves the event_input path using a
stale substream or runtime and can end in a NULL-deref or use-after-free.

Fix this with two pieces of synchronization. Keep a short IRQ-safe
spinlock only for publishing or clearing output_rfile and for pairing
the output snapshot with an snd_use_lock_t reference. Once
event_process_midi() has taken that in-flight reference, it drops the
spinlock before calling snd_seq_dump_var_event(), dump_midi(), or
snd_rawmidi_kernel_write(). midisynth_unuse() now detaches the visible
rawmidi file under the same spinlock, waits for the in-flight writers
to drain, and only then drains and releases the saved file.
midisynth_use() likewise opens into a local snd_rawmidi_file and
publishes it only after snd_rawmidi_output_params() succeeds.

The buggy scenario involves two paths, with each column showing the
order within that path:

event_input path:                     last unuse path:
1. event_process_midi() snapshots    1. midisynth_unuse() starts
   output_rfile.output.                 tearing down output_rfile.
2. dump_midi() reaches               2. snd_rawmidi_kernel_release()
   snd_rawmidi_kernel_write()           closes the output file.
   before runtime is pinned.         3. close_substream() frees
3. The callback keeps using             substream->runtime.
   the borrowed substream.

Validation reproduced this kernel report:
KASAN null-ptr-deref in snd_rawmidi_kernel_write1+0x56/0x360
RIP: 0033:0x7fde7dd0837f
RIP: 0010:snd_rawmidi_kernel_write1+0x56/0x360

## Affected

- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < f5d470b808bc01f70978e22e595c6f7768313406`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 936641af564c3d92721704b781e36aaf223efdd2`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 718f6a56b40875f19e6915799044a02df9abfd52`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 11165fe2c5ea0516debe486d91df67abbe36905e`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < d6fd2afb137f52bf00c5210cc44d08ed54dcffb4`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ef7607ab1c8adc6258fb1b27d08e26aecdc18a58`
- `Linux 2.6.12`

## Remediation

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