Linux Kernel ext4 Buffer Overflow in parse_apply_sb_mount_options
CVE-2025-71123 Published on January 14, 2026
ext4: fix string copying in parse_apply_sb_mount_options()
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.
Products Associated with CVE-2025-71123
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Affected Versions
Linux:- Version b2bac84fde28fb6a88817b8b761abda17a1d300b and below 52ac96c4a2dd7bc47666000440b0602d9742e820 is affected.
- Version e651294218d2684302ee5ed95ccf381646f3e5b4 and below 6e37143560e37869d51b7d9e0ac61fc48895f8a0 is affected.
- Version 01829af7656b56d83682b3491265d583d502e502 and below 902ca2356f1e3ec5355c5808ad5d3f9d0095b0cc is affected.
- Version 2a0cf438320cdb783e0378570744c0ef0d83e934 and below db9ee13fab0267eccf6544ee35b16c9522db9aac is affected.
- Version 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 and below 5bbacbbf1ca4419861dca3c6b82707c10e9c021c is affected.
- Version 8ecb790ea8c3fc69e77bace57f14cf0d7c177bd8 and below ee5a977b4e771cc181f39d504426dbd31ed701cc is affected.
- Version 7bf46ff83a0ef11836e38ebd72cdc5107209342d is affected.
- Version a6e94557cd05adc82fae0400f6e17745563e5412 is affected.
- Version 6.18 is affected.
- Before 6.18 is unaffected.
- Version 5.10.248, <= 5.10.* is unaffected.
- Version 6.1.160, <= 6.1.* is unaffected.
- Version 6.6.120, <= 6.6.* is unaffected.
- Version 6.12.64, <= 6.12.* is unaffected.
- Version 6.18.3, <= 6.18.* is unaffected.
- Version 6.19, <= * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.