s390/hypfs: Avoid unnecessary ioctl registration in debugfs

[ Upstream commit fec7bdfe7f8694a0c39e6c3ec026ff61ca1058b9 ]

Currently, hypfs registers ioctl callbacks for all debugfs files,
despite only one file requiring them. This leads to unintended exposure
of unused interfaces to user space and can trigger side effects such as
restricted access when kernel lockdown is enabled.

Restrict ioctl registration to only those files that implement ioctl
functionality to avoid interface clutter and unnecessary access
restrictions.

Tested-by: Mete Durlu <meted@linux.ibm.com>
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Fixes: 5496197f9b08 ("debugfs: Restrict debugfs when the kernel is locked down")
Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 11 insertions, 7 deletions

diff --git a/arch/s390/hypfs/hypfs_dbfs.c b/arch/s390/hypfs/hypfs_dbfs.c
index 5d9effb0867c..e74eb8f9b23a 100644
--- a/arch/s390/hypfs/hypfs_dbfs.c
+++ b/arch/s390/hypfs/hypfs_dbfs.c
@@ -66,23 +66,27 @@ static long dbfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	long rc;
 
 	mutex_lock(&df->lock);
-	if (df->unlocked_ioctl)
-		rc = df->unlocked_ioctl(file, cmd, arg);
-	else
-		rc = -ENOTTY;
+	rc = df->unlocked_ioctl(file, cmd, arg);
 	mutex_unlock(&df->lock);
 	return rc;
 }
 
-static const struct file_operations dbfs_ops = {
+static const struct file_operations dbfs_ops_ioctl = {
 	.read		= dbfs_read,
 	.unlocked_ioctl = dbfs_ioctl,
 };
 
+static const struct file_operations dbfs_ops = {
+	.read		= dbfs_read,
+};
+
 void hypfs_dbfs_create_file(struct hypfs_dbfs_file *df)
 {
-	df->dentry = debugfs_create_file(df->name, 0400, dbfs_dir, df,
-					 &dbfs_ops);
+	const struct file_operations *fops = &dbfs_ops;
+
+	if (df->unlocked_ioctl)
+		fops = &dbfs_ops_ioctl;
+	df->dentry = debugfs_create_file(df->name, 0400, dbfs_dir, df, fops);
 	mutex_init(&df->lock);
 }