linux-kernel - [PATCH v5 8/9] ovl: Check for casefold consistency when creating new dentries

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Message-Id: <20250814-tonyk-overlayfs-v5-8-c5b80a909cbd@igalia.com>
Date: Thu, 14 Aug 2025 14:22:19 -0300
From: André Almeida <andrealmeid@...lia.com>
To: Miklos Szeredi <miklos@...redi.hu>, Amir Goldstein <amir73il@...il.com>, 
 Theodore Tso <tytso@....edu>, Gabriel Krisman Bertazi <krisman@...nel.org>
Cc: linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-fsdevel@...r.kernel.org, Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
 kernel-dev@...lia.com, 
 André Almeida <andrealmeid@...lia.com>
Subject: [PATCH v5 8/9] ovl: Check for casefold consistency when creating
 new dentries

In a overlayfs with casefold enabled, all new dentries should have
casefold enabled as well. Check this at ovl_create_real().

Signed-off-by: André Almeida <andrealmeid@...lia.com>
---
Changes from v4:
- Add pr_warn()

Changes from v3:
- New patch
---
 fs/overlayfs/dir.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 70b8687dc45e8e33079c865ae302ac58464224a6..88e888ed8696363d6cde39817f6c21e795f0760a 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -187,6 +187,12 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent,
 			/* mkdir is special... */
 			newdentry =  ovl_do_mkdir(ofs, dir, newdentry, attr->mode);
 			err = PTR_ERR_OR_ZERO(newdentry);
+			/* expect to inherit casefolding from workdir/upperdir */
+			if (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) {
+				pr_warn_ratelimited("dentry wrong casefold inheritance");
+				dput(newdentry);
+				err = -EINVAL;
+			}
 			break;
 
 		case S_IFCHR:

-- 
2.50.1