---
id: CVE-2026-89722
title: 'PCI/sysfs: Fix out-of-bounds read in pci_write_legacy_io()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  PCI/sysfs: Fix out-of-bounds read in pci_write_legacy_io()

  pci_write_legacy_io() loads 4 bytes from the kernfs write buffer
  regardless of how many bytes userspace wrot…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cvssSource: vendor
cwe:
  - CWE-125
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    e892f05f1f790d5721cd8e3c561ed76da7e08bae
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    7a99e9c7011905734cc2739038f2a224b6be0d1f
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    dc76258d0132df1d831a5a29758bd448ca9c566e
  - Linux 2.6.12
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:51:34.940Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89722'
references:
  - url: 'https://git.kernel.org/stable/c/e892f05f1f790d5721cd8e3c561ed76da7e08bae'
  - url: 'https://git.kernel.org/stable/c/7a99e9c7011905734cc2739038f2a224b6be0d1f'
  - url: 'https://git.kernel.org/stable/c/dc76258d0132df1d831a5a29758bd448ca9c566e'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89722.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89722'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532142'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89722'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89722'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89722.mbox
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.00206
epssPercentile: 0.10626
ingestedAt: '2026-09-14T15:23:07.476Z'
---

## Overview

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

PCI/sysfs: Fix out-of-bounds read in pci_write_legacy_io()

pci_write_legacy_io() loads 4 bytes from the kernfs write buffer
regardless of how many bytes userspace wrote:

  if (count != 1 && count != 2 && count != 4)
          return -EINVAL;

  return pci_legacy_write(bus, off, *(u32 *)buf, count);

kernfs_fop_write_iter() allocates the buffer with kmalloc(len + 1),
so a 1-byte write to the legacy_io sysfs file allocates 2 bytes and
the unconditional u32 load reads up to 2 bytes past the end of the
allocation, which KASAN reports as a slab-out-of-bounds read.
Similarly, a 2-byte write overreads by 1 byte.

Thus, read only the number of bytes requested using get_unaligned_le16()
and get_unaligned_le32() for the 2 and 4 byte cases, interpreting the
buffer as little-endian to match the byte ordering of PCI I/O port
space.

The PowerPC implementation previously compensated for the generic
code's native-endian 32-bit load by shifting the value into place
for the 1 and 2 byte cases.  The shifts were only correct on
big-endian kernels.

On little-endian PowerPC (POWER8 and later), they extracted the wrong
bytes, so a 1-byte write wrote an out-of-bounds byte instead of the
requested value.  On big-endian, the native load also caused out_le16()
and out_le32() to reverse the user's bytes on the wire for 2 and 4 byte
writes.  The little-endian helpers resolve both issues, so the shifts
are removed.

No changes are needed for the Alpha platform.

The legacy_io file is root-only and exists only on Alpha and PowerPC,
the two architectures that define HAVE_PCI_LEGACY.

## Affected

- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < e892f05f1f790d5721cd8e3c561ed76da7e08bae`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 7a99e9c7011905734cc2739038f2a224b6be0d1f`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < dc76258d0132df1d831a5a29758bd448ca9c566e`
- `Linux 2.6.12`

## Remediation

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

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, … · updated 2026-09-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89722.json)