---
id: CVE-2025-71123
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: fix string copying in parse_apply_sb_mount_options()

  strscpy_pad() can't be used to copy a non-NUL-term string into a NUL-term
  string of possibly bigger size
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: fix string copying in parse_apply_sb_mount_options()

  strscpy_pad() can't be used to copy a non-NUL-term string into a NUL-term
  string of possibly bigger size.  C…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.4.301, < 5.5'
  - 'linux_kernel >= 5.10.246, < 5.10.248'
  - 'linux_kernel >= 6.1.158, < 6.1.160'
  - 'linux_kernel >= 6.6.114, < 6.6.120'
  - 'linux_kernel >= 6.12.54, < 6.12.64'
  - 'linux_kernel >= 6.17.4, < 6.18'
  - 'linux_kernel >= 6.18.1, < 6.18.3'
  - linux_kernel = 6.18
  - linux_kernel = 6.19
patched:
  - linux_kernel 6.18.3
published: '2026-01-14'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:18:23.170'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-71123'
references:
  - url: 'https://git.kernel.org/stable/c/52ac96c4a2dd7bc47666000440b0602d9742e820'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/5bbacbbf1ca4419861dca3c6b82707c10e9c021c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6e37143560e37869d51b7d9e0ac61fc48895f8a0'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/902ca2356f1e3ec5355c5808ad5d3f9d0095b0cc'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/db9ee13fab0267eccf6544ee35b16c9522db9aac'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/ee5a977b4e771cc181f39d504426dbd31ed701cc'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-457936.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00171
epssPercentile: 0.06438
ingestedAt: '2026-09-08T15:33:26.995Z'
---

## Overview

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

ext4: fix string copying in parse_apply_sb_mount_options()

strscpy_pad() can't be used to copy a non-NUL-term string into a NUL-term
string of possibly bigger size.  Commit 0efc5990bca5 ("string.h: Introduce
memtostr() and memtostr_pad()") provides additional information in that
regard.  So if this happens, the following warning is observed:

strnlen: detected buffer overflow: 65 byte read of buffer size 64
WARNING: CPU: 0 PID: 28655 at lib/string_helpers.c:1032 __fortify_report+0x96/0xc0 lib/string_helpers.c:1032
Modules linked in:
CPU: 0 UID: 0 PID: 28655 Comm: syz-executor.3 Not tainted 6.12.54-syzkaller-00144-g5f0270f1ba00 #0
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:__fortify_report+0x96/0xc0 lib/string_helpers.c:1032
Call Trace:
 <TASK>
 __fortify_panic+0x1f/0x30 lib/string_helpers.c:1039
 strnlen include/linux/fortify-string.h:235 [inline]
 sized_strscpy include/linux/fortify-string.h:309 [inline]
 parse_apply_sb_mount_options fs/ext4/super.c:2504 [inline]
 __ext4_fill_super fs/ext4/super.c:5261 [inline]
 ext4_fill_super+0x3c35/0xad00 fs/ext4/super.c:5706
 get_tree_bdev_flags+0x387/0x620 fs/super.c:1636
 vfs_get_tree+0x93/0x380 fs/super.c:1814
 do_new_mount fs/namespace.c:3553 [inline]
 path_mount+0x6ae/0x1f70 fs/namespace.c:3880
 do_mount fs/namespace.c:3893 [inline]
 __do_sys_mount fs/namespace.c:4103 [inline]
 __se_sys_mount fs/namespace.c:4080 [inline]
 __x64_sys_mount+0x280/0x300 fs/namespace.c:4080
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x64/0x140 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Since userspace is expected to provide s_mount_opts field to be at most 63
characters long with the ending byte being NUL-term, use a 64-byte buffer
which matches the size of s_mount_opts, so that strscpy_pad() does its job
properly.  Return with error if the user still managed to provide a
non-NUL-term string here.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

## Affected

- `linux_kernel >= 5.4.301, < 5.5`
- `linux_kernel >= 5.10.246, < 5.10.248`
- `linux_kernel >= 6.1.158, < 6.1.160`
- `linux_kernel >= 6.6.114, < 6.6.120`
- `linux_kernel >= 6.12.54, < 6.12.64`
- `linux_kernel >= 6.17.4, < 6.18`
- `linux_kernel >= 6.18.1, < 6.18.3`
- `linux_kernel = 6.18`
- `linux_kernel = 6.19`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.18.3`