linux-cve-announce - CVE-2025-71123: ext4: fix string copying in parse_apply_sb_mount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [day] [month] [year] [list]
Message-ID: <2026011416-CVE-2025-71123-221d@gregkh>
Date: Wed, 14 Jan 2026 16:06:28 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-71123: ext4: fix string copying in parse_apply_sb_mount_options()

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2025-71123 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.1.158 with commit e651294218d2684302ee5ed95ccf381646f3e5b4 and fixed in 6.1.160 with commit 6e37143560e37869d51b7d9e0ac61fc48895f8a0
	Issue introduced in 6.6.114 with commit 01829af7656b56d83682b3491265d583d502e502 and fixed in 6.6.120 with commit 902ca2356f1e3ec5355c5808ad5d3f9d0095b0cc
	Issue introduced in 6.12.54 with commit 2a0cf438320cdb783e0378570744c0ef0d83e934 and fixed in 6.12.64 with commit db9ee13fab0267eccf6544ee35b16c9522db9aac
	Issue introduced in 6.18 with commit 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 and fixed in 6.18.3 with commit 5bbacbbf1ca4419861dca3c6b82707c10e9c021c
	Issue introduced in 6.18 with commit 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 and fixed in 6.19-rc1 with commit ee5a977b4e771cc181f39d504426dbd31ed701cc
	Issue introduced in 5.4.301 with commit 7bf46ff83a0ef11836e38ebd72cdc5107209342d
	Issue introduced in 5.10.246 with commit b2bac84fde28fb6a88817b8b761abda17a1d300b
	Issue introduced in 6.17.4 with commit a6e94557cd05adc82fae0400f6e17745563e5412

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-71123
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ext4/super.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/6e37143560e37869d51b7d9e0ac61fc48895f8a0
	https://git.kernel.org/stable/c/902ca2356f1e3ec5355c5808ad5d3f9d0095b0cc
	https://git.kernel.org/stable/c/db9ee13fab0267eccf6544ee35b16c9522db9aac
	https://git.kernel.org/stable/c/5bbacbbf1ca4419861dca3c6b82707c10e9c021c
	https://git.kernel.org/stable/c/ee5a977b4e771cc181f39d504426dbd31ed701cc