---
id: CVE-2026-90189
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  null_blk: register configfs subsystem after creating default devices

  In null_init(), configfs_register_subsystem() currently runs before
  register_blkdev(), so when nul…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  null_blk: register configfs subsystem after creating default devices

  In null_init(), configfs_register_subsystem() currently runs before
  register_blkdev(), so when nul…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa <
    2679b11e9256bd70a5ef41783bab6ad6c34a3db1
  - >-
    Linux >= 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa <
    dbcedbe4819ae21274ea77469e61e46a878b9943
  - >-
    Linux >= 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa <
    57debc907aef66319d244009d3370dcd97388d37
  - >-
    Linux >= 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa <
    d761be1b8f2bbabc41252deb79a426d3f0d4fa10
  - >-
    Linux >= 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa <
    cab9bf5f68f76cd44e0ec92bd4a60c9b83656a36
  - >-
    Linux >= 3bf2bd20734e3e6ffda53719a9c10fb3ee9c5ffa <
    c9d293d6bb0575fcb1f3408129453187e2a28a4e
  - Linux 4.14
published: '2026-09-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:17:13.533'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-90189'
references:
  - url: 'https://git.kernel.org/stable/c/2679b11e9256bd70a5ef41783bab6ad6c34a3db1'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/57debc907aef66319d244009d3370dcd97388d37'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c9d293d6bb0575fcb1f3408129453187e2a28a4e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cab9bf5f68f76cd44e0ec92bd4a60c9b83656a36'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d761be1b8f2bbabc41252deb79a426d3f0d4fa10'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/dbcedbe4819ae21274ea77469e61e46a878b9943'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-17T16:21:47.864Z'
epss: 0.00173
epssPercentile: 0.06997
---

## Overview

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

null_blk: register configfs subsystem after creating default devices

In null_init(), configfs_register_subsystem() currently runs before
register_blkdev(), so when null_blk is built as a module, a racing mkdir()
+ poweron from userspace can reach null_add_dev() while null_major is still
0. __add_disk() then hits WARN_ON(disk->minors) (major=0 with minors!=0)
and fails:

[root@fedora ~]# [ 2366.521436] WARNING: block/genhd.c:476 at __add_disk+0x8a7/0xde0,
[ 2366.523552] Modules linked in: null_blk(+) nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib
[ 2366.529081] CPU: 26 UID: 0 PID: 1600 Comm: sh Not tainted 7.2.0-rc1+ #66 PREEMPT(full)
......
[ 2366.547251] Call Trace:
[ 2366.547575]  <TASK>
[ 2366.547831]  ? _raw_spin_lock+0x84/0xe0
[ 2366.548260]  add_disk_fwnode+0x114/0x560
[ 2366.548739]  null_add_dev+0x102d/0x1b80 [null_blk]
[ 2366.549310]  ? __pfx_null_add_dev+0x10/0x10 [null_blk]
[ 2366.549906]  ? mutex_lock+0xde/0x1c0
[ 2366.550361]  ? __pfx_mutex_lock+0x10/0x10
[ 2366.550827]  nullb_device_power_store+0x1e7/0x280 [null_blk]
[ 2366.551499]  ? __pfx_nullb_device_power_store+0x10/0x10 [null_blk]
[ 2366.552177]  ? __kmalloc_cache_noprof+0x1f5/0x470
[ 2366.552748]  ? configfs_write_iter+0x35c/0x4e0
[ 2366.553242]  configfs_write_iter+0x286/0x4e0
[ 2366.553787]  vfs_write+0x52d/0xd00
[ 2366.554169]  ? __pfx_vfs_write+0x10/0x10
[ 2366.554679]  ? __pfx___css_rstat_updated+0x10/0x10
[ 2366.555196]  ? fdget_pos+0x1cf/0x4c0
[ 2366.555649]  ksys_write+0xfc/0x1d0
......

Additionally, the err_dev path destroys all devices on nullb_list while
configfs is still registered. If a racing mkdir() + poweron puts a user
device on the list, null_destroy_dev()->null_free_dev() kfrees the user
device's nullb_device but /sys/kernel/config/nullb/<name> is still
reachable. Any userspace access to the item will trigger a UAF.

For simplicity, move configfs_register_subsystem() to the end to solve
the problems above.

## Remediation

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