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 08D4FC433F5 for ; Tue, 15 Mar 2022 13:42:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 478558D0002; Tue, 15 Mar 2022 09:42:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 427538D0001; Tue, 15 Mar 2022 09:42:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2EE328D0002; Tue, 15 Mar 2022 09:42:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.25]) by kanga.kvack.org (Postfix) with ESMTP id 1DB888D0001 for ; Tue, 15 Mar 2022 09:42:36 -0400 (EDT) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id B1B7D21296 for ; Tue, 15 Mar 2022 13:42:35 +0000 (UTC) X-FDA: 79246735470.08.D87D2D0 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by imf02.hostedemail.com (Postfix) with ESMTP id 8961B80010 for ; Tue, 15 Mar 2022 13:42:34 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KHvgg1wSXzfYxQ; Tue, 15 Mar 2022 21:41:03 +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, 15 Mar 2022 21:42:30 +0800 Subject: Re: [PATCH] mm/mempolicy: fix potential mpol_new leak in shared_policy_replace To: Michal Hocko CC: , , , , References: <20220311093624.39546-1-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <26577566-ae1e-801c-8c64-89c2c89a487d@huawei.com> Date: Tue, 15 Mar 2022 21:42:29 +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: dggems704-chm.china.huawei.com (10.3.19.181) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 8961B80010 X-Stat-Signature: b6jqkui1epkk9jc1r5cwxcsdbtfw6gum X-Rspam-User: Authentication-Results: imf02.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf02.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-HE-Tag: 1647351754-957261 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 2022/3/15 0:44, Michal Hocko wrote: > On Fri 11-03-22 17:36:24, 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. > > The code is really hideous but is there really any bug there? AFAICS the > new policy is only allocated in if (n->end > end) branch and that one > will set the reference count on the retry. Or am I missing something? > Many thanks for your comment. IIUC, new policy is allocated via the below code: shared_policy_replace: alloc_new: write_unlock(&sp->lock); ret = -ENOMEM; n_new = kmem_cache_alloc(sn_cache, GFP_KERNEL); if (!n_new) goto err_out; mpol_new = kmem_cache_alloc(policy_cache, GFP_KERNEL); if (!mpol_new) goto err_out; goto restart; And mpol_new' reference count will be set before used in n->end > end case. But if that is "not" the case, i.e. mpol_new is not inserted into the rb_tree, mpol_new will be freed via mpol_put before return: shared_policy_replace: err_out: if (mpol_new) mpol_put(mpol_new); if (n_new) kmem_cache_free(sn_cache, n_new); But mpol_new' reference count is not set yet, we have trouble now. Does this makes sense for you? Or am I miss something? Thanks. >> Fixes: 42288fe366c4 ("mm: mempolicy: Convert shared_policy mutex to spinlock") >> Signed-off-by: Miaohe Lin >> --- >> mm/mempolicy.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index 34d2b29c96ad..f19f19d3558b 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 >