linux-kernel - Re: [PATCH v2 1/2] ext4: fix string copying in parse_apply_sb_mount

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Message-ID: <176340680644.138575.9603909521172863181.b4-ty@mit.edu>
Date: Mon, 17 Nov 2025 14:13:34 -0500
From: "Theodore Ts'o" <tytso@....edu>
To: Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
        Fedor Pchelkin <pchelkin@...ras.ru>
Cc: "Theodore Ts'o" <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>,
        "Darrick J. Wong" <djwong@...nel.org>, linux-kernel@...r.kernel.org,
        lvc-project@...uxtesting.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] ext4: fix string copying in parse_apply_sb_mount_options()


On Sat, 01 Nov 2025 19:04:28 +0300, Fedor Pchelkin wrote:
> 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
> 
> [...]

Applied, thanks!

[1/2] ext4: fix string copying in parse_apply_sb_mount_options()
      commit: c517b381de9490b910ab451c2177aa32064678ad
[2/2] ext4: check if mount_opts is NUL-terminated in ext4_ioctl_set_tune_sb()
      commit: 687524bafd4e86cfa783857f8045460f4caee921

Best regards,
-- 
Theodore Ts'o <tytso@....edu>