---
id: CVE-2025-38338
title: 'fs/nfs/read: fix double-unlock bug in nfs_return_empty_folio()'
summary: |-
  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 dea…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9 <
    14f5549ad163be2c018abc1bb38370fff617a243
  - >-
    Linux >= 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9 <
    5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5
  - >-
    Linux >= 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9 <
    1e93b61d3eaa14bfebcc2716ac09d43f3845d420
  - >-
    Linux >= 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9 <
    4c10fa44bc5f700e2ea21de2fbae520ba21f19d9
  - Linux 6.4
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T20:55:00.358504Z'
published: '2025-07-10'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T21:02:34.128Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-38338'
references:
  - url: 'https://git.kernel.org/stable/c/14f5549ad163be2c018abc1bb38370fff617a243'
  - url: 'https://git.kernel.org/stable/c/5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5'
  - url: 'https://git.kernel.org/stable/c/1e93b61d3eaa14bfebcc2716ac09d43f3845d420'
  - url: 'https://git.kernel.org/stable/c/4c10fa44bc5f700e2ea21de2fbae520ba21f19d9'
tags:
  - cve.org
epss: 0.00185
epssPercentile: 0.08162
ingestedAt: '2026-11-05T22:38:31.960Z'
---

## Overview

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.

## Affected

- `Linux >= 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9 < 14f5549ad163be2c018abc1bb38370fff617a243`
- `Linux >= 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9 < 5bf0b9eeb0174686f22c2e5b8fb9f47ad25da6f5`
- `Linux >= 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9 < 1e93b61d3eaa14bfebcc2716ac09d43f3845d420`
- `Linux >= 000dbe0bec058cbf2ca9e156e4a5584f5158b0f9 < 4c10fa44bc5f700e2ea21de2fbae520ba21f19d9`
- `Linux 6.4`

## Remediation

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