---
id: CVE-2026-43067
title: 'ext4: handle wraparound when searching for blocks for indirect mapped blocks'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: handle wraparound when searching for blocks for indirect mapped blocks

  Commit 4865c768b563 ("ext4: always allocate blocks only from groups
  inode can use") restri…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 9d89b9d55e25cb340c5b4b769876edc551b7a9ff <
    f89bba144938921a2249237ad04a0183ff3f8930
  - >-
    Linux >= 1b0edd6022a3f44ce87fea9959a9310f4628fbea <
    83170a05908b6cf2fb3235d3065bf613ff866f3c
  - >-
    Linux >= 9eea2f57d11b30049ff996ac3eff6e0dc8089e5f <
    4bec4a498ce86314d470ae6144120461f2138c29
  - >-
    Linux >= 34c803edc0b3365a42efcf9815acab63b4cf54e0 <
    12624c5b724a81e14e532972b40d863b0de3b7d1
  - >-
    Linux >= 321ed8d559c951e71ad2d2d69a4cf0445644e865 <
    2a368ccddfc492a0aa951e2caef2985f20e96503
  - >-
    Linux >= 4865c768b563deff1b6a6384e74a62f143427b42 <
    bb81702370fad22c06ca12b6e1648754dbc37e0f
  - Linux 16fce6b6c0b247258c6c217fce5a48abf50f6964
  - Linux >= 5.15.203 < 5.16
  - Linux >= 6.1.167 < 6.1.168
  - Linux >= 6.6.130 < 6.6.134
  - Linux >= 6.12.77 < 6.12.80
  - Linux >= 6.18.14 < 6.18.21
  - Linux >= 6.19.4 < 6.19.11
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-10-16T15:14:16.994971Z'
published: '2026-05-05'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:20:31.250Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-43067'
references:
  - url: 'https://git.kernel.org/stable/c/f89bba144938921a2249237ad04a0183ff3f8930'
  - url: 'https://git.kernel.org/stable/c/83170a05908b6cf2fb3235d3065bf613ff866f3c'
  - url: 'https://git.kernel.org/stable/c/4bec4a498ce86314d470ae6144120461f2138c29'
  - url: 'https://git.kernel.org/stable/c/12624c5b724a81e14e532972b40d863b0de3b7d1'
  - url: 'https://git.kernel.org/stable/c/2a368ccddfc492a0aa951e2caef2985f20e96503'
  - url: 'https://git.kernel.org/stable/c/bb81702370fad22c06ca12b6e1648754dbc37e0f'
tags:
  - cve.org
epss: 0.00721
epssPercentile: 0.5301
ingestedAt: '2026-10-16T17:24:46.680Z'
---

## Overview

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

ext4: handle wraparound when searching for blocks for indirect mapped blocks

Commit 4865c768b563 ("ext4: always allocate blocks only from groups
inode can use") restricts what blocks will be allocated for indirect
block based files to block numbers that fit within 32-bit block
numbers.

However, when using a review bot running on the latest Gemini LLM to
check this commit when backporting into an LTS based kernel, it raised
this concern:

   If ac->ac_g_ex.fe_group is >= ngroups (for instance, if the goal
   group was populated via stream allocation from s_mb_last_groups),
   then start will be >= ngroups.

   Does this allow allocating blocks beyond the 32-bit limit for
   indirect block mapped files? The commit message mentions that
   ext4_mb_scan_groups_linear() takes care to not select unsupported
   groups. However, its loop uses group = *start, and the very first
   iteration will call ext4_mb_scan_group() with this unsupported
   group because next_linear_group() is only called at the end of the
   iteration.

After reviewing the code paths involved and considering the LLM
review, I determined that this can happen when there is a file system
where some files/directories are extent-mapped and others are
indirect-block mapped.  To address this, add a safety clamp in
ext4_mb_scan_groups().

## Affected

- `Linux >= 9d89b9d55e25cb340c5b4b769876edc551b7a9ff < f89bba144938921a2249237ad04a0183ff3f8930`
- `Linux >= 1b0edd6022a3f44ce87fea9959a9310f4628fbea < 83170a05908b6cf2fb3235d3065bf613ff866f3c`
- `Linux >= 9eea2f57d11b30049ff996ac3eff6e0dc8089e5f < 4bec4a498ce86314d470ae6144120461f2138c29`
- `Linux >= 34c803edc0b3365a42efcf9815acab63b4cf54e0 < 12624c5b724a81e14e532972b40d863b0de3b7d1`
- `Linux >= 321ed8d559c951e71ad2d2d69a4cf0445644e865 < 2a368ccddfc492a0aa951e2caef2985f20e96503`
- `Linux >= 4865c768b563deff1b6a6384e74a62f143427b42 < bb81702370fad22c06ca12b6e1648754dbc37e0f`
- `Linux 16fce6b6c0b247258c6c217fce5a48abf50f6964`
- `Linux >= 5.15.203 < 5.16`
- `Linux >= 6.1.167 < 6.1.168`
- `Linux >= 6.6.130 < 6.6.134`
- `Linux >= 6.12.77 < 6.12.80`
- `Linux >= 6.18.14 < 6.18.21`
- `Linux >= 6.19.4 < 6.19.11`

## Remediation

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