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 3248AC433F5 for ; Tue, 22 Mar 2022 01:50:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A23E36B0072; Mon, 21 Mar 2022 21:50:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9AB4A6B0073; Mon, 21 Mar 2022 21:50:41 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 825A56B0074; Mon, 21 Mar 2022 21:50:41 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0204.hostedemail.com [216.40.44.204]) by kanga.kvack.org (Postfix) with ESMTP id 6CDDE6B0072 for ; Mon, 21 Mar 2022 21:50:41 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 1D5068249980 for ; Tue, 22 Mar 2022 01:50:41 +0000 (UTC) X-FDA: 79270343082.21.6B34D1C Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf25.hostedemail.com (Postfix) with ESMTP id A109DA0005 for ; Tue, 22 Mar 2022 01:50:39 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4KMvXv1j8KzfZSf; Tue, 22 Mar 2022 09:49:03 +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, 22 Mar 2022 09:50:35 +0800 Subject: Re: [PATCH v2] mm/mempolicy: fix mpol_new leak in shared_policy_replace To: Michal Hocko CC: , , , , References: <20220322083456.16563-1-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <8c7d2ef2-08d7-ea50-a82b-9e9800c5f54c@huawei.com> Date: Tue, 22 Mar 2022 09:50:35 +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: 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-Rspam-User: Authentication-Results: imf25.hostedemail.com; dkim=none; spf=pass (imf25.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A109DA0005 X-Stat-Signature: t8xstr5d9pccd6j8csnmn1efjoa4grag X-HE-Tag: 1647913839-499331 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 2022/3/21 20:12, Michal Hocko wrote: > On Tue 22-03-22 16:34:56, 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. > > I would just add: > > This would happen if mempolicy was updated on the shared shmem file > while the sp->lock has been dropped during the memory allocation. > Do you mean the below commit log? """ 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're 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); } """ >> This issue could be triggered easily with the below >> code snippet if there're 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); >> } >> >> Fixes: 42288fe366c4 ("mm: mempolicy: Convert shared_policy mutex to spinlock") >> Signed-off-by: Miaohe Lin >> Cc: # 3.8 > > Acked-by: Michal Hocko > > Thanks a lot! Many thanks for comment and Acked-by tag! :) >> --- >> v1->v2: >> Add reproducer snippet and Cc stable. >> Thanks Michal Hocko for review and comment! >> --- >> mm/mempolicy.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index a2516d31db6c..4cdd425b2752 100644 >> --- 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; >> } >> >> -- >> 2.23.0 >