---
id: CVE-2025-38066
title: 'dm cache: prevent BUG_ON by blocking retries on failed device resumes'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  dm cache: prevent BUG_ON by blocking retries on failed device resumes

  A cache device failing to resume due to mapping errors should not be
  retried, as the failure leav…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 66a636356647a9be8885c2ce2948de126577698a <
    c614584c2a66b538f469089ac089457a34590c14
  - >-
    Linux >= 66a636356647a9be8885c2ce2948de126577698a <
    c5356a5e80442131e2714d0d26bb110590e4e568
  - >-
    Linux >= 66a636356647a9be8885c2ce2948de126577698a <
    025c8f477625eb39006ded650e7d027bcfb20e79
  - >-
    Linux >= 66a636356647a9be8885c2ce2948de126577698a <
    00586b78eeb7c626a14ca13453a1631f88a7cf36
  - >-
    Linux >= 66a636356647a9be8885c2ce2948de126577698a <
    3986ef4a9b6a0d9c28bc325d8713beba5e67586f
  - >-
    Linux >= 66a636356647a9be8885c2ce2948de126577698a <
    cc80a5cc520939d0a7d071cc4ae4b3c55ef171d0
  - >-
    Linux >= 66a636356647a9be8885c2ce2948de126577698a <
    f3128e3074e8af565cc6a66fe3384a56df87f803
  - >-
    Linux >= 66a636356647a9be8885c2ce2948de126577698a <
    5da692e2262b8f81993baa9592f57d12c2703dea
  - Linux 4.2
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T20:48:55.834588Z'
published: '2025-06-18'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T20:52:14.383Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-38066'
references:
  - url: 'https://git.kernel.org/stable/c/c614584c2a66b538f469089ac089457a34590c14'
  - url: 'https://git.kernel.org/stable/c/c5356a5e80442131e2714d0d26bb110590e4e568'
  - url: 'https://git.kernel.org/stable/c/025c8f477625eb39006ded650e7d027bcfb20e79'
  - url: 'https://git.kernel.org/stable/c/00586b78eeb7c626a14ca13453a1631f88a7cf36'
  - url: 'https://git.kernel.org/stable/c/3986ef4a9b6a0d9c28bc325d8713beba5e67586f'
  - url: 'https://git.kernel.org/stable/c/cc80a5cc520939d0a7d071cc4ae4b3c55ef171d0'
  - url: 'https://git.kernel.org/stable/c/f3128e3074e8af565cc6a66fe3384a56df87f803'
  - url: 'https://git.kernel.org/stable/c/5da692e2262b8f81993baa9592f57d12c2703dea'
tags:
  - cve.org
epss: 0.00205
epssPercentile: 0.10514
ingestedAt: '2026-11-05T22:38:31.914Z'
---

## Overview

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

dm cache: prevent BUG_ON by blocking retries on failed device resumes

A cache device failing to resume due to mapping errors should not be
retried, as the failure leaves a partially initialized policy object.
Repeating the resume operation risks triggering BUG_ON when reloading
cache mappings into the incomplete policy object.

Reproduce steps:

1. create a cache metadata consisting of 512 or more cache blocks,
   with some mappings stored in the first array block of the mapping
   array. Here we use cache_restore v1.0 to build the metadata.

cat <<EOF >> cmeta.xml
<superblock uuid="" block_size="128" nr_cache_blocks="512" \
policy="smq" hint_width="4">
  <mappings>
    <mapping cache_block="0" origin_block="0" dirty="false"/>
  </mappings>
</superblock>
EOF
dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
cache_restore -i cmeta.xml -o /dev/mapper/cmeta --metadata-version=2
dmsetup remove cmeta

2. wipe the second array block of the mapping array to simulate
   data degradations.

mapping_root=$(dd if=/dev/sdc bs=1c count=8 skip=192 \
2>/dev/null | hexdump -e '1/8 "%u\n"')
ablock=$(dd if=/dev/sdc bs=1c count=8 skip=$((4096*mapping_root+2056)) \
2>/dev/null | hexdump -e '1/8 "%u\n"')
dd if=/dev/zero of=/dev/sdc bs=4k count=1 seek=$ablock

3. try bringing up the cache device. The resume is expected to fail
   due to the broken array block.

dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
dmsetup create cdata --table "0 65536 linear /dev/sdc 8192"
dmsetup create corig --table "0 524288 linear /dev/sdc 262144"
dmsetup create cache --notable
dmsetup load cache --table "0 524288 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"
dmsetup resume cache

4. try resuming the cache again. An unexpected BUG_ON is triggered
   while loading cache mappings.

dmsetup resume cache

Kernel logs:

(snip)
------------[ cut here ]------------
kernel BUG at drivers/md/dm-cache-policy-smq.c:752!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 332 Comm: dmsetup Not tainted 6.13.4 #3
RIP: 0010:smq_load_mapping+0x3e5/0x570

Fix by disallowing resume operations for devices that failed the
initial attempt.

## Affected

- `Linux >= 66a636356647a9be8885c2ce2948de126577698a < c614584c2a66b538f469089ac089457a34590c14`
- `Linux >= 66a636356647a9be8885c2ce2948de126577698a < c5356a5e80442131e2714d0d26bb110590e4e568`
- `Linux >= 66a636356647a9be8885c2ce2948de126577698a < 025c8f477625eb39006ded650e7d027bcfb20e79`
- `Linux >= 66a636356647a9be8885c2ce2948de126577698a < 00586b78eeb7c626a14ca13453a1631f88a7cf36`
- `Linux >= 66a636356647a9be8885c2ce2948de126577698a < 3986ef4a9b6a0d9c28bc325d8713beba5e67586f`
- `Linux >= 66a636356647a9be8885c2ce2948de126577698a < cc80a5cc520939d0a7d071cc4ae4b3c55ef171d0`
- `Linux >= 66a636356647a9be8885c2ce2948de126577698a < f3128e3074e8af565cc6a66fe3384a56df87f803`
- `Linux >= 66a636356647a9be8885c2ce2948de126577698a < 5da692e2262b8f81993baa9592f57d12c2703dea`
- `Linux 4.2`

## Remediation

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