linux-kernel - [PATCH v4 9/9] ovl: Allow case-insensitive lookup

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Message-Id: <20250813-tonyk-overlayfs-v4-9-357ccf2e12ad@igalia.com>
Date: Wed, 13 Aug 2025 19:36:45 -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 v4 9/9] ovl: Allow case-insensitive lookup

Drop the restriction for casefold dentries lookup to enable support for
case-insensitive filesystems in overlayfs.

Support case-insensitive filesystems with the condition that they should
be uniformly enabled across the stack and the layers (i.e. if the root
mount dir has casefold enabled, so should all the dirs bellow for every
layer).

Signed-off-by: André Almeida <andrealmeid@...lia.com>
---
Changes from v3:
- New patch, splited from the patch that creates ofs->casefold
---
 fs/overlayfs/namei.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 76d6248b625e7c58e09685e421aef616aadea40a..e93bcc5727bcafdc18a499b47a7609fd41ecaec8 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -239,13 +239,14 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
 	char val;
 
 	/*
-	 * We allow filesystems that are case-folding capable but deny composing
-	 * ovl stack from case-folded directories. If someone has enabled case
-	 * folding on a directory on underlying layer, the warranty of the ovl
-	 * stack is voided.
+	 * We allow filesystems that are case-folding capable as long as the
+	 * layers are consistently enabled in the stack, enabled for every dir
+	 * or disabled in all dirs. If someone has modified case folding on a
+	 * directory on underlying layer, the warranty of the ovl stack is
+	 * voided.
 	 */
-	if (ovl_dentry_casefolded(base)) {
-		warn = "case folded parent";
+	if (ofs->casefold != ovl_dentry_casefolded(base)) {
+		warn = "parent wrong casefold";
 		err = -ESTALE;
 		goto out_warn;
 	}
@@ -259,8 +260,8 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
 		goto out_err;
 	}
 
-	if (ovl_dentry_casefolded(this)) {
-		warn = "case folded child";
+	if (ofs->casefold != ovl_dentry_casefolded(this)) {
+		warn = "child wrong casefold";
 		err = -EREMOTE;
 		goto out_warn;
 	}

-- 
2.50.1