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 2C1FDC49EA2 for ; Sat, 19 Jun 2021 09:32:53 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CCC4F60FDC for ; Sat, 19 Jun 2021 09:32:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CCC4F60FDC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 154426B0070; Sat, 19 Jun 2021 05:32:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D639C6B0075; Sat, 19 Jun 2021 05:32:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AF2CD6B0078; Sat, 19 Jun 2021 05:32:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0190.hostedemail.com [216.40.44.190]) by kanga.kvack.org (Postfix) with ESMTP id 5D0606B006E for ; Sat, 19 Jun 2021 05:32:49 -0400 (EDT) Received: from smtpin33.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id E180D19B32 for ; Sat, 19 Jun 2021 09:32:48 +0000 (UTC) X-FDA: 78269958816.33.FD7A21E Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf28.hostedemail.com (Postfix) with ESMTP id 3CA6C200110A for ; Sat, 19 Jun 2021 09:32:46 +0000 (UTC) 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-Type: text/plain 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 Authentication-Results: imf28.hostedemail.com; dkim=none; spf=pass (imf28.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=none) header.from=huawei.com X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 3CA6C200110A X-Stat-Signature: dii4i8kie8jjit8bjncc5xcjs7ichi76 X-HE-Tag: 1624095166-75526 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: It is not enough to just make sure the z3fold header is not larger than t= he 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; =20 - /* 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 =3D z3fold_mount(); if (ret) return ret; --=20 2.23.0