ovl: port ovl_rename() to cred guard

Use the scoped ovl cred guard.

Link: https://patch.msgid.link/20251117-work-ovl-cred-guard-v4-35-b31603935724@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/overlayfs/dir.c

@@ -1319,7 +1319,6 @@ static int ovl_rename(struct mnt_idmap *idmap, struct inode *olddir,
 		      struct dentry *old, struct inode *newdir,
 		      struct dentry *new, unsigned int flags)
 {
-	const struct cred *old_cred = NULL;
 	struct ovl_renamedata ovlrd = {
 		.old_parent		= old->d_parent,
 		.old_dentry		= old,
@@ -1332,17 +1331,13 @@ static int ovl_rename(struct mnt_idmap *idmap, struct inode *olddir,
 	int err;
 
 	err = ovl_rename_start(&ovlrd, &list);
-	if (err)
-		goto out;
-
-	old_cred = ovl_override_creds(old->d_sb);
-
-	err = ovl_rename_upper(&ovlrd, &list);
+	if (!err) {
+		with_ovl_creds(old->d_sb)
+			err = ovl_rename_upper(&ovlrd, &list);
+		ovl_rename_end(&ovlrd);
+	}
 
-	ovl_revert_creds(old_cred);
-	ovl_rename_end(&ovlrd);
-out:
-	dput(ovlrd->opaquedir);
+	dput(ovlrd.opaquedir);
 	ovl_cache_free(&list);
 	return err;
 }