ovl: port ovl_lookup() to cred guard

Use the scoped ovl cred guard.

Link: https://patch.msgid.link/20251117-work-ovl-cred-guard-v4-38-b31603935724@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/overlayfs/namei.c

@@ -1376,7 +1376,6 @@ static int ovl_lookup_layers(struct ovl_lookup_ctx *ctx, struct ovl_lookup_data
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags)
 {
-	const struct cred *old_cred;
 	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
 	struct ovl_entry *poe = OVL_E(dentry->d_parent);
 	bool check_redirect = (ovl_redirect_follow(ofs) || ofs->numdatalayer);
@@ -1394,11 +1393,9 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	if (dentry->d_name.len > ofs->namelen)
 		return ERR_PTR(-ENAMETOOLONG);
 
-	old_cred = ovl_override_creds(dentry->d_sb);
-
-	err = ovl_lookup_layers(&ctx, &d);
+	with_ovl_creds(dentry->d_sb)
+		err = ovl_lookup_layers(&ctx, &d);
 
-	ovl_revert_creds(old_cred);
 	if (ctx.origin_path) {
 		dput(ctx.origin_path->dentry);
 		kfree(ctx.origin_path);