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 EEA5EC433EF for ; Sat, 26 Mar 2022 06:46:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 647BF6B0071; Sat, 26 Mar 2022 02:46:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5F6D56B0073; Sat, 26 Mar 2022 02:46:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4982F6B0074; Sat, 26 Mar 2022 02:46:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0070.hostedemail.com [216.40.44.70]) by kanga.kvack.org (Postfix) with ESMTP id 3635B6B0071 for ; Sat, 26 Mar 2022 02:46:34 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id DB8181828AE3E for ; Sat, 26 Mar 2022 06:46:33 +0000 (UTC) X-FDA: 79285603866.29.5CF1FF6 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by imf04.hostedemail.com (Postfix) with ESMTP id 16E834003C for ; Sat, 26 Mar 2022 06:46:32 +0000 (UTC) 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 X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=none; spf=pass (imf04.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.255 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 16E834003C X-Stat-Signature: orsmxuj1byepyns4hg94hcqxkb4prgrn X-HE-Tag: 1648277192-128497 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 2022/3/26 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. >