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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6223FC433EF for ; Tue, 29 Mar 2022 02:13:41 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CBF888D0003; Mon, 28 Mar 2022 22:13:40 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C6F1E8D0001; Mon, 28 Mar 2022 22:13:40 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B10CE8D0003; Mon, 28 Mar 2022 22:13:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.a.hostedemail.com [64.99.140.24]) by kanga.kvack.org (Postfix) with ESMTP id A16208D0001 for ; Mon, 28 Mar 2022 22:13:40 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 758F4226FA for ; Tue, 29 Mar 2022 02:13:40 +0000 (UTC) X-FDA: 79295802600.05.7755C74 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by imf27.hostedemail.com (Postfix) with ESMTP id 95A2D40009 for ; Tue, 29 Mar 2022 02:13:39 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4KSCgM1bGYz9spN; Tue, 29 Mar 2022 10:09:35 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Tue, 29 Mar 2022 10:13:36 +0800 Subject: Re: [PATCH v3] mm/mempolicy: fix mpol_new leak in shared_policy_replace To: Andrew Morton CC: , , , , References: <20220322104345.36379-1-linmiaohe@huawei.com> <20220325172907.57dd381b746563be5dc77097@linux-foundation.org> <20220328142629.6ab7c5312d9ec154ccc502b2@linux-foundation.org> From: Miaohe Lin Message-ID: <8575a7af-eacf-db06-4e48-b825f37575db@huawei.com> Date: Tue, 29 Mar 2022 10:13:36 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20220328142629.6ab7c5312d9ec154ccc502b2@linux-foundation.org> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected X-Stat-Signature: cayzybymfznhjub1wbgioewkcxg466n6 Authentication-Results: imf27.hostedemail.com; dkim=none; spf=pass (imf27.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.189 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 95A2D40009 X-HE-Tag: 1648520019-608386 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: On 2022/3/29 5:26, Andrew Morton wrote: > On Sat, 26 Mar 2022 14:46:28 +0800 Miaohe Lin wrote: > >> On 2022/3/26 8:29, Andrew Morton wrote: >>> On Tue, 22 Mar 2022 18:43:45 +0800 Miaohe Lin wrote: >>> >>>> If mpol_new is allocated but not used in restart loop, mpol_new will be >>>> freed via mpol_put before returning to the caller. But refcnt is not >>>> initialized yet, so mpol_put could not do the right things and might leak >>>> the unused mpol_new. This would happen if mempolicy was updated on the >>>> shared shmem file while the sp->lock has been dropped during the memory >>>> allocation. >>>> >>>> This issue could be triggered easily with the below code snippet if there >>>> are many processes doing the below work at the same time: >>>> >>>> shmid = shmget((key_t)5566, 1024 * PAGE_SIZE, 0666|IPC_CREAT); >>>> shm = shmat(shmid, 0, 0); >>>> loop many times { >>>> mbind(shm, 1024 * PAGE_SIZE, MPOL_LOCAL, mask, maxnode, 0); >>>> mbind(shm + 128 * PAGE_SIZE, 128 * PAGE_SIZE, MPOL_DEFAULT, mask, >>>> maxnode, 0); >>>> } >>>> >>>> ... >>>> >>>> --- a/mm/mempolicy.c >>>> +++ b/mm/mempolicy.c >>>> @@ -2733,6 +2733,7 @@ static int shared_policy_replace(struct shared_policy *sp, unsigned long start, >>>> mpol_new = kmem_cache_alloc(policy_cache, GFP_KERNEL); >>>> if (!mpol_new) >>>> goto err_out; >>>> + refcount_set(&mpol_new->refcnt, 1); >>>> goto restart; >>>> } >>> >>> Two other sites in this file do >>> >>> atomic_set(&policy->refcnt, 1); >>> >>> >>> Could we please instead have a little helper function which does the >>> kmem_cache_alloc()+refcount_set()?> . >> >> There are usecases like below: >> >> struct mempolicy *new = kmem_cache_alloc(policy_cache, GFP_KERNEL); >> *new = *old; >> ^^^^^^^^^^^^ >> refcount_set(&new->refcnt, 1); >> >> If we use helper function to do kmem_cache_alloc()+refcount_set() above, separate >> refcount_set(&new->refcnt, 1) is still needed as old is copied to new and overwrites >> the refcnt field. So that little helper function might not work. Or am I miss something? >> > > Hm, spose so. I guess the helper doesn't add much in that case. > > Can we please redo this on mainline? I'm not happy with the bloat > which refcnt_t adds and I think I'll drop > mm-mempolicy-convert-from-atomic_t-to-refcount_t-on-mempolicy-refcnt.patch. Will do this soon. Many thanks. > . >