---
id: CVE-2026-45920
title: 'ext4: fix dirtyclusters double decrement on fs shutdown'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: fix dirtyclusters double decrement on fs shutdown

  fstests test generic/388 occasionally reproduces a warning in
  ext4_put_super() associated with the dirty cluste…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c <
    523d5a4df3c649fa305c89efb552ec62a1ce9d3d
  - >-
    Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c <
    ca408af08544d96769c93a3d81a7f63f61129e95
  - >-
    Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c <
    55576fa14771d33994c29a9ae960e07bb3f56c20
  - >-
    Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c <
    dbc4e10619ed87a50e637b96f2e574df36a7a769
  - >-
    Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c <
    61e372122b6d95aec940fdaea0a16f988f359897
  - >-
    Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c <
    3924aea2c33df3864929c1acd178bfc29d8f005f
  - >-
    Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c <
    81982a11406c5da6c6e2b188028e7056e16b7128
  - >-
    Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c <
    94a8cea54cd935c54fa2fba70354757c0fc245e3
  - Linux 2.6.29
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-06T15:44:36.783306Z'
published: '2026-05-27'
updated: '2026-11-06'
sourceUpdated: '2026-11-06T15:53:13.103Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-45920'
references:
  - url: 'https://git.kernel.org/stable/c/523d5a4df3c649fa305c89efb552ec62a1ce9d3d'
  - url: 'https://git.kernel.org/stable/c/ca408af08544d96769c93a3d81a7f63f61129e95'
  - url: 'https://git.kernel.org/stable/c/55576fa14771d33994c29a9ae960e07bb3f56c20'
  - url: 'https://git.kernel.org/stable/c/dbc4e10619ed87a50e637b96f2e574df36a7a769'
  - url: 'https://git.kernel.org/stable/c/61e372122b6d95aec940fdaea0a16f988f359897'
  - url: 'https://git.kernel.org/stable/c/3924aea2c33df3864929c1acd178bfc29d8f005f'
  - url: 'https://git.kernel.org/stable/c/81982a11406c5da6c6e2b188028e7056e16b7128'
  - url: 'https://git.kernel.org/stable/c/94a8cea54cd935c54fa2fba70354757c0fc245e3'
tags:
  - cve.org
epss: 0.00146
epssPercentile: 0.03883
ingestedAt: '2026-11-06T16:57:43.385Z'
---

## Overview

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

ext4: fix dirtyclusters double decrement on fs shutdown

fstests test generic/388 occasionally reproduces a warning in
ext4_put_super() associated with the dirty clusters count:

  WARNING: CPU: 7 PID: 76064 at fs/ext4/super.c:1324 ext4_put_super+0x48c/0x590 [ext4]

Tracing the failure shows that the warning fires due to an
s_dirtyclusters_counter value of -1. IOW, this appears to be a
spurious decrement as opposed to some sort of leak. Further tracing
of the dirty cluster count deltas and an LLM scan of the resulting
output identified the cause as a double decrement in the error path
between ext4_mb_mark_diskspace_used() and the caller
ext4_mb_new_blocks().

First, note that generic/388 is a shutdown vs. fsstress test and so
produces a random set of operations and shutdown injections. In the
problematic case, the shutdown triggers an error return from the
ext4_handle_dirty_metadata() call(s) made from
ext4_mb_mark_context(). The changed value is non-zero at this point,
so ext4_mb_mark_diskspace_used() does not exit after the error
bubbles up from ext4_mb_mark_context(). Instead, the former
decrements both cluster counters and returns the error up to
ext4_mb_new_blocks(). The latter falls into the !ar->len out path
which decrements the dirty clusters counter a second time, creating
the inconsistency.

To avoid this problem and simplify ownership of the cluster
reservation in this codepath, lift the counter reduction to a single
place in the caller. This makes it more clear that
ext4_mb_new_blocks() is responsible for acquiring cluster
reservation (via ext4_claim_free_clusters()) in the !delalloc case
as well as releasing it, regardless of whether it ends up consumed
or returned due to failure.

## Affected

- `Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c < 523d5a4df3c649fa305c89efb552ec62a1ce9d3d`
- `Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c < ca408af08544d96769c93a3d81a7f63f61129e95`
- `Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c < 55576fa14771d33994c29a9ae960e07bb3f56c20`
- `Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c < dbc4e10619ed87a50e637b96f2e574df36a7a769`
- `Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c < 61e372122b6d95aec940fdaea0a16f988f359897`
- `Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c < 3924aea2c33df3864929c1acd178bfc29d8f005f`
- `Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c < 81982a11406c5da6c6e2b188028e7056e16b7128`
- `Linux >= 0087d9fb3f29f59e8d42c8b058376d80e5adde4c < 94a8cea54cd935c54fa2fba70354757c0fc245e3`
- `Linux 2.6.29`

## Remediation

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