---
id: CVE-2026-89640
title: 'cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0

  With len == 0 (clone to EOF), the effective length is computed as:

      len = src_inode->i_size - o…
severity: high
cvss: 7.1
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-787
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 <
    f3d1ae1e6bc4a9f559185b6e7bd2b6375ec2fdd4
  - >-
    Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 <
    7f62817fe049b0f3652518c1ba72631ec1e0a322
  - >-
    Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 <
    b098f5e5858797827666e6cd73033f52fc39b5f6
  - >-
    Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 <
    c2a0dcb5a7a1516aa6eb6d5cedca6a8e76527028
  - >-
    Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 <
    b057ca17b656345d04669cb87f2aff9b31d873db
  - >-
    Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 <
    6c322f5cf7476ded7a9a20f7be72462065a03c68
  - Linux 4.5
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-10-16T19:24:54.678656Z'
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:50:12.163Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89640'
references:
  - url: 'https://git.kernel.org/stable/c/f3d1ae1e6bc4a9f559185b6e7bd2b6375ec2fdd4'
  - url: 'https://git.kernel.org/stable/c/7f62817fe049b0f3652518c1ba72631ec1e0a322'
  - url: 'https://git.kernel.org/stable/c/b098f5e5858797827666e6cd73033f52fc39b5f6'
  - url: 'https://git.kernel.org/stable/c/c2a0dcb5a7a1516aa6eb6d5cedca6a8e76527028'
  - url: 'https://git.kernel.org/stable/c/b057ca17b656345d04669cb87f2aff9b31d873db'
  - url: 'https://git.kernel.org/stable/c/6c322f5cf7476ded7a9a20f7be72462065a03c68'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89640.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89640'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532516'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89640'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89640'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89640.mbox
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.00126
epssPercentile: 0.02274
scores:
  cna: 7.1
  vendor: 5.5
ingestedAt: '2026-09-14T15:23:07.450Z'
---

## Overview

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

cifs: fix loff_t underflow in cifs_remap_file_range() when len == 0

With len == 0 (clone to EOF), the effective length is computed as:

    len = src_inode->i_size - off;

If off > i_size, this is a negative loff_t, corrupting the ByteCount
in the FSCTL_DUPLICATE_EXTENTS_TO_FILE request and inverting the range
in filemap_write_and_wait_range().  The existing off >= i_size check
fires only after the ioctl has already been sent.

Snapshot i_size_read() once for both the bounds check and the length
calculation, eliminating the TOCTOU and 32-bit torn-read risk.  Reject
off > src_size with -EINVAL.  Treat off == src_size as a no-op,
consistent with __generic_remap_file_range_prep().

## Affected

- `Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 < f3d1ae1e6bc4a9f559185b6e7bd2b6375ec2fdd4`
- `Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 < 7f62817fe049b0f3652518c1ba72631ec1e0a322`
- `Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 < b098f5e5858797827666e6cd73033f52fc39b5f6`
- `Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 < c2a0dcb5a7a1516aa6eb6d5cedca6a8e76527028`
- `Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 < b057ca17b656345d04669cb87f2aff9b31d873db`
- `Linux >= 04b38d601239b4d9be641b412cf4b7456a041c67 < 6c322f5cf7476ded7a9a20f7be72462065a03c68`
- `Linux 4.5`

## Remediation

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

## Vendor advisories

- **Red Hat VEX** · Low · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89640.json)