---
id: CVE-2025-71123
title: 'ext4: fix string copying in parse_apply_sb_mount_options()'
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: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= b2bac84fde28fb6a88817b8b761abda17a1d300b <
    52ac96c4a2dd7bc47666000440b0602d9742e820
  - >-
    Linux >= e651294218d2684302ee5ed95ccf381646f3e5b4 <
    6e37143560e37869d51b7d9e0ac61fc48895f8a0
  - >-
    Linux >= 01829af7656b56d83682b3491265d583d502e502 <
    902ca2356f1e3ec5355c5808ad5d3f9d0095b0cc
  - >-
    Linux >= 2a0cf438320cdb783e0378570744c0ef0d83e934 <
    db9ee13fab0267eccf6544ee35b16c9522db9aac
  - >-
    Linux >= 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 <
    5bbacbbf1ca4419861dca3c6b82707c10e9c021c
  - >-
    Linux >= 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 <
    ee5a977b4e771cc181f39d504426dbd31ed701cc
  - Linux 7bf46ff83a0ef11836e38ebd72cdc5107209342d
  - Linux a6e94557cd05adc82fae0400f6e17745563e5412
  - Linux >= 5.10.246 < 5.10.248
  - Linux >= 6.1.158 < 6.1.160
  - Linux >= 6.6.114 < 6.6.120
  - Linux >= 6.12.54 < 6.12.64
  - Linux >= 5.4.301 < 5.5
  - Linux >= 6.17.4 < 6.18
  - Linux 6.18
published: '2026-01-14'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:44:00.414Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-71123'
references:
  - url: 'https://git.kernel.org/stable/c/52ac96c4a2dd7bc47666000440b0602d9742e820'
  - url: 'https://git.kernel.org/stable/c/6e37143560e37869d51b7d9e0ac61fc48895f8a0'
  - url: 'https://git.kernel.org/stable/c/902ca2356f1e3ec5355c5808ad5d3f9d0095b0cc'
  - url: 'https://git.kernel.org/stable/c/db9ee13fab0267eccf6544ee35b16c9522db9aac'
  - url: 'https://git.kernel.org/stable/c/5bbacbbf1ca4419861dca3c6b82707c10e9c021c'
  - url: 'https://git.kernel.org/stable/c/ee5a977b4e771cc181f39d504426dbd31ed701cc'
tags:
  - cve.org
epss: 0.00167
epssPercentile: 0.05248
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 >= b2bac84fde28fb6a88817b8b761abda17a1d300b < 52ac96c4a2dd7bc47666000440b0602d9742e820`
- `Linux >= e651294218d2684302ee5ed95ccf381646f3e5b4 < 6e37143560e37869d51b7d9e0ac61fc48895f8a0`
- `Linux >= 01829af7656b56d83682b3491265d583d502e502 < 902ca2356f1e3ec5355c5808ad5d3f9d0095b0cc`
- `Linux >= 2a0cf438320cdb783e0378570744c0ef0d83e934 < db9ee13fab0267eccf6544ee35b16c9522db9aac`
- `Linux >= 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 < 5bbacbbf1ca4419861dca3c6b82707c10e9c021c`
- `Linux >= 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 < ee5a977b4e771cc181f39d504426dbd31ed701cc`
- `Linux 7bf46ff83a0ef11836e38ebd72cdc5107209342d`
- `Linux a6e94557cd05adc82fae0400f6e17745563e5412`
- `Linux >= 5.10.246 < 5.10.248`
- `Linux >= 6.1.158 < 6.1.160`
- `Linux >= 6.6.114 < 6.6.120`
- `Linux >= 6.12.54 < 6.12.64`
- `Linux >= 5.4.301 < 5.5`
- `Linux >= 6.17.4 < 6.18`
- `Linux 6.18`

## Remediation

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