---
id: CVE-2026-90186
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  null_blk: reject per-device queue resize for shared tag set

  When shared_tags is enabled, null_setup_tagset() makes the device use the
  global tag_set, whose driver_data…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  null_blk: reject per-device queue resize for shared tag set

  When shared_tags is enabled, null_setup_tagset() makes the device use the
  global tag_set, whose driver_data…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 45919fbfe1c487c17ea1d198534339a5e8abeae3 <
    9c7bae099ddc92676ad1b7e29dd6c089e5f6196c
  - >-
    Linux >= 45919fbfe1c487c17ea1d198534339a5e8abeae3 <
    fcd53f3e8b758c79c3f2420d28a2a1dce6fda61a
  - >-
    Linux >= 45919fbfe1c487c17ea1d198534339a5e8abeae3 <
    f609f7bf9ce8c2fc427705c4a9f623a281239d06
  - >-
    Linux >= 45919fbfe1c487c17ea1d198534339a5e8abeae3 <
    3e35ad503386a2e8a0e0460530dcbf421c79f6f2
  - >-
    Linux >= 45919fbfe1c487c17ea1d198534339a5e8abeae3 <
    baff300541a0012907cdde349728739fe16176d7
  - >-
    Linux >= 45919fbfe1c487c17ea1d198534339a5e8abeae3 <
    1cdfe2fa62b48728a9b436fbbd3dbe4c11593e24
  - Linux 5.5
published: '2026-09-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:17:13.127'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-90186'
references:
  - url: 'https://git.kernel.org/stable/c/1cdfe2fa62b48728a9b436fbbd3dbe4c11593e24'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/3e35ad503386a2e8a0e0460530dcbf421c79f6f2'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9c7bae099ddc92676ad1b7e29dd6c089e5f6196c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/baff300541a0012907cdde349728739fe16176d7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f609f7bf9ce8c2fc427705c4a9f623a281239d06'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/fcd53f3e8b758c79c3f2420d28a2a1dce6fda61a'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-17T16:21:47.865Z'
epss: 0.00215
epssPercentile: 0.10513
---

## Overview

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

null_blk: reject per-device queue resize for shared tag set

When shared_tags is enabled, null_setup_tagset() makes the device use the
global tag_set, whose driver_data stays NULL. null_map_queues() therefore
falls back to the module-wide g_submit_queues/g_poll_queues instead of any
per-device value.

Resizing submit_queues or poll_queues via configfs on such a device calls
blk_mq_update_nr_hw_queues() on the shared set, shrinking
set->nr_hw_queues.  __blk_mq_realloc_hw_ctxs() only grows the
q->queue_hw_ctx[] allocation, so on shrink it merely exits and NULLs the
now-excess hctx slots. null_map_queues(), however, keeps mapping CPUs with
the unchanged g_submit_queues/g_poll_queues, so mq_map[] ends up pointing
at those NULLed hctx slots. blk_mq_map_swqueue() then dereferences the NULL
hctx (hctx->cpumask), crashing the kernel:

[  460.218374] KASAN: null-ptr-deref in range [0x0000000000000098-0x000000000000009f]
[  460.219003] CPU: 24 UID: 0 PID: 1492 Comm: sh Not tainted 7.2.0-rc2+ #67 PREEMPT(full)
[  460.219792] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014
[  460.220452] RIP: 0010:blk_mq_map_swqueue+0x4db/0x1430
......
[  460.228977] Call Trace:
[  460.229175]  <TASK>
[  460.229354]  blk_mq_update_nr_hw_queues+0xd49/0x11c0
[  460.229779]  ? __pfx_blk_mq_update_nr_hw_queues+0x10/0x10
[  460.230200]  nullb_update_nr_hw_queues+0x1a9/0x370 [null_blk]
[  460.230694]  nullb_device_submit_queues_store+0xd9/0x170 [null_blk]
[  460.231190]  ? __pfx_nullb_device_submit_queues_store+0x10/0x10 [null_blk]
[  460.231776]  ? configfs_write_iter+0x35c/0x4e0
[  460.232122]  configfs_write_iter+0x286/0x4e0
[  460.232460]  vfs_write+0x52d/0xd00
[  460.232779]  ? __x64_sys_openat+0x108/0x1d0
[  460.233106]  ? __pfx_vfs_write+0x10/0x10
[  460.233413]  ? fdget_pos+0x1cf/0x4c0
[  460.233745]  ? fput_close+0x133/0x190
[  460.234038]  ? __pfx_expand_files+0x10/0x10
[  460.234368]  ksys_write+0xfc/0x1d0

Reproducer:
modprobe null_blk shared_tags=1 submit_queues=64 poll_queues=1
mkdir /sys/kernel/config/nullb/dev
echo 1 > /sys/kernel/config/nullb/dev/power
echo 1 > /sys/kernel/config/nullb/dev/submit_queues

A per-device resize of a shared tag set is meaningless anyway, so reject it
with -EINVAL in nullb_update_nr_hw_queues() when the device is bound to the
global tag_set.

## Remediation

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