# CVE-2025-38338: fs/nfs/read: fix double-unlock bug in nfs_return_empty_folio()

Status: published. Published: 2025-07-10. Updated: 2026-11-05.

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

fs/nfs/read: fix double-unlock bug in nfs_return_empty_folio()

Sometimes, when a file was read while it was being truncated by
another NFS client, the kernel could deadlock because folio_unlock()
was called twice, and the second call would XOR back the `PG_locked`
flag.

Most of the time (depending on the timing of the truncation), nobody
notices the problem because folio_unlock() gets called three times,
which flips `PG_locked` back off:

 1. vfs_read, nfs_read_folio, ... nfs_read_add_folio,
    nfs_return_empty_folio
 2. vfs_read, nfs_read_folio, ... netfs_read_collection,
    netfs_unlock_abandoned_read_pages
 3. vfs_read, ... nfs_do_read_folio, nfs_read_add_folio,
    nfs_return_empty_folio

The problem is that nfs_read_add_folio() is not supposed to unlock the
folio if fscache is enabled, and a nfs_netfs_folio_unlock() check is
missing in nfs_return_empty_folio().

Rarely this leads to a warning in netfs_read_collection():

 ------------[ cut here ]------------
 R=0000031c: folio 10 is not locked
 WARNING: CPU: 0 PID: 29 at fs/netfs/read_collect.c:133 netfs_read_collection+0x7c0/0xf00
 [...]
 Workqueue: events_unbound netfs_read_collection_worker
 RIP: 0010:netfs_read_collection+0x7c0/0xf00
 [...]
 Call Trace:
  <TASK>
  netfs_read_collection_worker+0x67/0x80
  process_one_work+0x12e/0x2c0
  worker_thread+0x295/0x3a0

Most of the time, however, processes just get stuck forever in
folio_wait_bit_common(), waiting for `PG_locked` to disappear, which
never happens because nobody is really holding the folio lock.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9; < 14f5549ad163be2c018abc1bb38370fff617a243 (affected, git); ≥ 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9; < 5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5 (affected, git); ≥ 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9; < 1e93b61d3eaa14bfebcc2716ac09d43f3845d420 (affected, git); ≥ 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9; < 4c10fa44bc5f700e2ea21de2fbae520ba21f19d9 (affected, git). Source: CNA: Linux
- Linux / Linux: 6.4 (affected); ≥ 0; < 6.4 (unaffected, semver); ≥ 6.6.95; ≤ 6.6.* (unaffected, semver); ≥ 6.12.35; ≤ 6.12.* (unaffected, semver); ≥ 6.15.4; ≤ 6.15.* (unaffected, semver); ≥ 6.16; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.18% as of 2026-11-05; percentile 8.20%

- 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/14f5549ad163be2c018abc1bb38370fff617a243 (CNA: Linux)

- https://git.kernel.org/stable/c/5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5 (CNA: Linux)

- https://git.kernel.org/stable/c/1e93b61d3eaa14bfebcc2716ac09d43f3845d420 (CNA: Linux)

- https://git.kernel.org/stable/c/4c10fa44bc5f700e2ea21de2fbae520ba21f19d9 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2025-38338; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2025-38338; retrieved 2026-11-05; source updated Not reported

Revision: 11bd3541143562fff13c96deefd9186ef29106d19db4de30b2bb6a8bae108013

Canonical: https://y2.dev/cve/CVE-2025-38338

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