From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DEABCC49EA3 for ; Sat, 19 Jun 2021 09:32:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA96C611CE for ; Sat, 19 Jun 2021 09:32:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234238AbhFSJfC (ORCPT ); Sat, 19 Jun 2021 05:35:02 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:7493 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233800AbhFSJe5 (ORCPT ); Sat, 19 Jun 2021 05:34:57 -0400 Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4G6Vqv3qKNzZcvB; Sat, 19 Jun 2021 17:29:47 +0800 (CST) Received: from huawei.com (10.175.104.170) by dggeme703-chm.china.huawei.com (10.1.199.99) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Sat, 19 Jun 2021 17:32:45 +0800 From: Miaohe Lin To: CC: , , , Subject: [PATCH 2/6] mm/z3fold: avoid possible underflow in z3fold_alloc() Date: Sat, 19 Jun 2021 17:31:47 +0800 Message-ID: <20210619093151.1492174-3-linmiaohe@huawei.com> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20210619093151.1492174-1-linmiaohe@huawei.com> References: <20210619093151.1492174-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.104.170] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It is not enough to just make sure the z3fold header is not larger than the page size. When z3fold header is equal to PAGE_SIZE, we would underflow when check alloc size against PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE in z3fold_alloc(). Make sure there has remaining spaces for its buddy to fix this theoretical issue. Signed-off-by: Miaohe Lin --- This causes the below checkpatch warning: WARNING: Comparisons should place the constant on the right side of the test #31: FILE: mm/z3fold.c:1812: + BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE); But I think the error is false positives as all members are constant. --- mm/z3fold.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/mm/z3fold.c b/mm/z3fold.c index 04d0e493bd2e..e261e14b7753 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -1805,8 +1805,11 @@ static int __init init_z3fold(void) { int ret; - /* Make sure the z3fold header is not larger than the page size */ - BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE); + /* + * Make sure the z3fold header is not larger than the page size and + * there has remaining spaces for its buddy. + */ + BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE); ret = z3fold_mount(); if (ret) return ret; -- 2.23.0