# CVE-2026-45920: ext4: fix dirtyclusters double decrement on fs shutdown

Status: published. Published: 2026-05-27. Updated: 2026-11-06.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 0087d9fb3f29f59e8d42c8b058376d80e5adde4c; < 523d5a4df3c649fa305c89efb552ec62a1ce9d3d (affected, git); ≥ 0087d9fb3f29f59e8d42c8b058376d80e5adde4c; < ca408af08544d96769c93a3d81a7f63f61129e95 (affected, git); ≥ 0087d9fb3f29f59e8d42c8b058376d80e5adde4c; < 55576fa14771d33994c29a9ae960e07bb3f56c20 (affected, git); ≥ 0087d9fb3f29f59e8d42c8b058376d80e5adde4c; < dbc4e10619ed87a50e637b96f2e574df36a7a769 (affected, git); ≥ 0087d9fb3f29f59e8d42c8b058376d80e5adde4c; < 61e372122b6d95aec940fdaea0a16f988f359897 (affected, git); ≥ 0087d9fb3f29f59e8d42c8b058376d80e5adde4c; < 3924aea2c33df3864929c1acd178bfc29d8f005f (affected, git); ≥ 0087d9fb3f29f59e8d42c8b058376d80e5adde4c; < 81982a11406c5da6c6e2b188028e7056e16b7128 (affected, git); ≥ 0087d9fb3f29f59e8d42c8b058376d80e5adde4c; < 94a8cea54cd935c54fa2fba70354757c0fc245e3 (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.29 (affected); ≥ 0; < 2.6.29 (unaffected, semver); ≥ 5.10.253; ≤ 5.10.* (unaffected, semver); ≥ 5.15.203; ≤ 5.15.* (unaffected, semver); ≥ 6.1.167; ≤ 6.1.* (unaffected, semver); ≥ 6.6.130; ≤ 6.6.* (unaffected, semver); ≥ 6.12.75; ≤ 6.12.* (unaffected, semver); ≥ 6.18.14; ≤ 6.18.* (unaffected, semver); ≥ 6.19.4; ≤ 6.19.* (unaffected, semver); ≥ 7.0; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.15% as of 2026-11-06; percentile 3.90%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/523d5a4df3c649fa305c89efb552ec62a1ce9d3d (CNA: Linux)

- https://git.kernel.org/stable/c/ca408af08544d96769c93a3d81a7f63f61129e95 (CNA: Linux)

- https://git.kernel.org/stable/c/55576fa14771d33994c29a9ae960e07bb3f56c20 (CNA: Linux)

- https://git.kernel.org/stable/c/dbc4e10619ed87a50e637b96f2e574df36a7a769 (CNA: Linux)

- https://git.kernel.org/stable/c/61e372122b6d95aec940fdaea0a16f988f359897 (CNA: Linux)

- https://git.kernel.org/stable/c/3924aea2c33df3864929c1acd178bfc29d8f005f (CNA: Linux)

- https://git.kernel.org/stable/c/81982a11406c5da6c6e2b188028e7056e16b7128 (CNA: Linux)

- https://git.kernel.org/stable/c/94a8cea54cd935c54fa2fba70354757c0fc245e3 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-45920; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-45920; retrieved 2026-11-06; source updated Not reported

Revision: 126707f259271b53b77c23d9368035d1d1f365f4d78d23f60ee1448f414ffd35

Canonical: https://y2.dev/cve/CVE-2026-45920

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