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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EB5BAC433F5 for ; Sat, 26 Mar 2022 06:46:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231643AbiCZGsL (ORCPT ); Sat, 26 Mar 2022 02:48:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34214 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230061AbiCZGsH (ORCPT ); Sat, 26 Mar 2022 02:48:07 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 774062220C1 for ; Fri, 25 Mar 2022 23:46:31 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4KQTy147rbz1GCwq; Sat, 26 Mar 2022 14:46:17 +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; Sat, 26 Mar 2022 14:46:29 +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> From: Miaohe Lin Message-ID: Date: Sat, 26 Mar 2022 14:46:28 +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: <20220325172907.57dd381b746563be5dc77097@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: dggems702-chm.china.huawei.com (10.3.19.179) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Many thanks. >