---
id: CVE-2026-98975
title: 'xfs: stop exchanging reflink flags when exchanging mappings'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  xfs: stop exchanging reflink flags when exchanging mappings

  When an exchange covers both files from offset 0 to i_disk_size,
  xmi_can_exchange_reflink_flags() assumes e…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= f0bc4d134b46607967bda1205ce3226a1bd95f42 <
    1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be
  - >-
    Linux >= f0bc4d134b46607967bda1205ce3226a1bd95f42 <
    7d3b9b2c9dc57f93f36c716ab752548cb4db9900
  - >-
    Linux >= f0bc4d134b46607967bda1205ce3226a1bd95f42 <
    4756c94260e69ce42612b8220c3614f02f7a11d5
  - >-
    Linux >= f0bc4d134b46607967bda1205ce3226a1bd95f42 <
    d84d6c1a7f1e2de9e601703a326a4c1b7b421943
  - Linux 4.9
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T12:19:48.379Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98975'
references:
  - url: 'https://git.kernel.org/stable/c/1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be'
  - url: 'https://git.kernel.org/stable/c/7d3b9b2c9dc57f93f36c716ab752548cb4db9900'
  - url: 'https://git.kernel.org/stable/c/4756c94260e69ce42612b8220c3614f02f7a11d5'
  - url: 'https://git.kernel.org/stable/c/d84d6c1a7f1e2de9e601703a326a4c1b7b421943'
tags:
  - cve.org
ingestedAt: '2026-10-23T13:24:55.550Z'
---

## Overview

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

xfs: stop exchanging reflink flags when exchanging mappings

When an exchange covers both files from offset 0 to i_disk_size,
xmi_can_exchange_reflink_flags() assumes every mapping moved and hands
the reflink flag over to the other file.

That assumption is wrong.  A file can still own shared blocks past
i_disk_size, e.g. after EXCHANGE_RANGE_TO_EOF sets a smaller size
without unmapping anything.  The flag is cleared anyway, and the next
write to such a block happens in place instead of CoW, corrupting the
other file that shares it.

Commit a23eca88448e ("xfs: fix exchange-range reflink flag clearing
issue with INO1_WRITTEN") fixed one instance of this.  Rather than add
another special case, stop moving the flags.
xfs_exchmaps_ensure_reflink() already sets the flag on both inodes
before the exchange, so both just keep it.

Nothing sets CLEAR_INO{1,2}_REFLINK anymore.  Intents logged by older
kernels may still carry them; recovery already masks them off, so they
stay in the log format mask and are ignored.

XFS_IOC_SWAPEXT has the same problem: it moves the reflink flag from
one inode to the other along with the extents.  Just removing that is
not enough here: the exchange path flags both inodes up front in
xfs_exchmaps_ensure_reflink(), but swapext has no such step, so the
inode receiving the shared extents would be left without the flag.
Set it on both inodes instead, and make sure both have a CoW fork,
since an inode with the reflink flag is expected to have one.

The flag now stays until FALLOC_FL_UNSHARE_RANGE, xfs_scrub, or a
truncate to zero removes it.

## Affected

- `Linux >= f0bc4d134b46607967bda1205ce3226a1bd95f42 < 1fa2f3a7ef7ee0f2503a4b0afe24bc8c9d0820be`
- `Linux >= f0bc4d134b46607967bda1205ce3226a1bd95f42 < 7d3b9b2c9dc57f93f36c716ab752548cb4db9900`
- `Linux >= f0bc4d134b46607967bda1205ce3226a1bd95f42 < 4756c94260e69ce42612b8220c3614f02f7a11d5`
- `Linux >= f0bc4d134b46607967bda1205ce3226a1bd95f42 < d84d6c1a7f1e2de9e601703a326a4c1b7b421943`
- `Linux 4.9`

## Remediation

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