linux-ext4 - [PATCH 2/2] ext4: in lookup call d_add

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Message-Id: <20240705062621.630604-3-eugen.hristev@collabora.com>
Date: Fri,  5 Jul 2024 09:26:21 +0300
From: Eugen Hristev <eugen.hristev@...labora.com>
To: viro@...iv.linux.org.uk,
	brauner@...nel.org,
	tytso@....edu,
	linux-ext4@...r.kernel.org
Cc: jack@...e.cz,
	adilger.kernel@...ger.ca,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	krisman@...e.de,
	kernel@...labora.com,
	shreeya.patel@...labora.com,
	Eugen Hristev <eugen.hristev@...labora.com>
Subject: [PATCH 2/2] ext4: in lookup call d_add_ci if there is a case mismatch

In lookup function, if we have a file match but not a case match in the
case-insensitive case, call d_add_ci to store the real filename into cache
instead of the case variant of the name that was looked up.
This avoids exposing into user space (e.g. /proc/self/cwd) internal cache
data.

Signed-off-by: Eugen Hristev <eugen.hristev@...labora.com>
---
 fs/ext4/namei.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index e6769b97a970..0676c21e1622 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1834,6 +1834,19 @@ static struct dentry *ext4_lookup(struct inode *dir, struct dentry *dentry, unsi
 		return NULL;
 	}
 
+	/* Create a case-insensitive cache entry with the real
+	 * name stored, in case our search pattern differs
+	 * in terms of case.
+	 */
+	if (inode && IS_CASEFOLDED(dir) &&
+	    memcmp(de->name, dentry->d_name.name, de->name_len)) {
+		struct qstr dname;
+
+		dname.len = de->name_len;
+		dname.name = de->name;
+		return d_add_ci(dentry, inode, &dname);
+	}
+
 	return d_splice_alias(inode, dentry);
 }
 
-- 
2.34.1