udf: store cookie in private data

Store the cookie to detect concurrent seeks on directories in
file->private_data.

Link: https://lore.kernel.org/r/20240830-vfs-file-f_version-v1-15-6d3e4816aa7b@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/udf/dir.c

@@ -60,7 +60,7 @@ static int udf_readdir(struct file *file, struct dir_context *ctx)
 	 * identifying beginning of dir entry (names are under user control),
 	 * we need to scan the directory from the beginning.
 	 */
-	if (!inode_eq_iversion(dir, file->f_version)) {
+	if (!inode_eq_iversion(dir, *(u64 *)file->private_data)) {
 		emit_pos = nf_pos;
 		nf_pos = 0;
 	} else {
@@ -122,15 +122,37 @@ static int udf_readdir(struct file *file, struct dir_context *ctx)
 	udf_fiiter_release(&iter);
 out:
 	if (pos_valid)
-		file->f_version = inode_query_iversion(dir);
+		*(u64 *)file->private_data = inode_query_iversion(dir);
 	kfree(fname);
 
 	return ret;
 }
 
+static int udf_dir_open(struct inode *inode, struct file *file)
+{
+	file->private_data = kzalloc(sizeof(u64), GFP_KERNEL);
+	if (!file->private_data)
+		return -ENOMEM;
+	return 0;
+}
+
+static int udf_dir_release(struct inode *inode, struct file *file)
+{
+	kfree(file->private_data);
+	return 0;
+}
+
+static loff_t udf_dir_llseek(struct file *file, loff_t offset, int whence)
+{
+	return generic_llseek_cookie(file, offset, whence,
+				     (u64 *)file->private_data);
+}
+
 /* readdir and lookup functions */
 const struct file_operations udf_dir_operations = {
-	.llseek			= generic_file_llseek,
+	.open			= udf_dir_open,
+	.release		= udf_dir_release,
+	.llseek			= udf_dir_llseek,
 	.read			= generic_read_dir,
 	.iterate_shared		= udf_readdir,
 	.unlocked_ioctl		= udf_ioctl,