linux-kernel - [PATCH v2 2/2] ext4: check if mount_opts is NUL-terminated in ext4_ioctl_set_tune

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Message-ID: <20251101160430.222297-2-pchelkin@ispras.ru>
Date: Sat,  1 Nov 2025 19:04:29 +0300
From: Fedor Pchelkin <pchelkin@...ras.ru>
To: "Theodore Ts'o" <tytso@....edu>,
	Jan Kara <jack@...e.cz>,
	linux-ext4@...r.kernel.org
Cc: Fedor Pchelkin <pchelkin@...ras.ru>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	"Darrick J. Wong" <djwong@...nel.org>,
	linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.org
Subject: [PATCH v2 2/2] ext4: check if mount_opts is NUL-terminated in ext4_ioctl_set_tune_sb()

params.mount_opts may come as potentially non-NUL-term string.  Userspace
is expected to pass a NUL-term string.  Add an extra check to ensure this
holds true.  Note that further code utilizes strscpy_pad() so this is just
for proper informing the user of incorrect data being provided.

Found by Linux Verification Center (linuxtesting.org).

Signed-off-by: Fedor Pchelkin <pchelkin@...ras.ru>
---

v2: check length of mount_opts in superblock tuning ioctl (Jan Kara)

    Can't plainly return error at strscpy_pad() call site in
    ext4_sb_setparams(), that's a void ext4_update_sb_callback.

v1: https://lore.kernel.org/lkml/20251028130949.599847-1-pchelkin@ispras.ru/T/#u

 fs/ext4/ioctl.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index a93a7baae990..3dec26c939fd 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -1394,6 +1394,10 @@ static int ext4_ioctl_set_tune_sb(struct file *filp,
 	if (copy_from_user(&params, in, sizeof(params)))
 		return -EFAULT;
 
+	if (strnlen(params.mount_opts, sizeof(params.mount_opts)) ==
+	    sizeof(params.mount_opts))
+		return -E2BIG;
+
 	if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
 		return -EOPNOTSUPP;
 
-- 
2.51.0