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 B5540C433F5 for ; Mon, 14 Mar 2022 03:49:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236128AbiCNDvD (ORCPT ); Sun, 13 Mar 2022 23:51:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53442 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236085AbiCNDux (ORCPT ); Sun, 13 Mar 2022 23:50:53 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E9F42201B0 for ; Sun, 13 Mar 2022 20:49:43 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.57]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4KH2V66tjbz1GCQ6; Mon, 14 Mar 2022 11:44:46 +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; Mon, 14 Mar 2022 11:49:41 +0800 Subject: Re: [PATCH] mm/mlock: fix potential imbalanced rlimit ucounts adjustment To: Hugh Dickins CC: , , Alexey Gladkov , "Eric W. Biederman" , , References: <20220310132417.41189-1-linmiaohe@huawei.com> <268b3146-2963-15b6-6d6-95a96853314@google.com> <1e758c8f-c87b-50ef-52db-942c8a86a32a@google.com> From: Miaohe Lin Message-ID: <291c20b2-0559-5226-0718-2d7bb1571079@huawei.com> Date: Mon, 14 Mar 2022 11:49:41 +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: <1e758c8f-c87b-50ef-52db-942c8a86a32a@google.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) 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 2022/3/14 11:11, Hugh Dickins wrote: > On Mon, 14 Mar 2022, Miaohe Lin wrote: >> On 2022/3/14 10:40, Hugh Dickins wrote: >>> On Thu, 10 Mar 2022, Miaohe Lin wrote: >>> >>>> user_shm_lock forgets to set allowed to 0 when get_ucounts fails. So >>>> the later user_shm_unlock might do the extra dec_rlimit_ucounts. Fix >>>> this by resetting allowed to 0. >>>> >>>> Fixes: 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY") >>>> Signed-off-by: Miaohe Lin >>> >>> NAK. user_shm_lock() remembers to declare "int allowed = 0" on entry. >>> >> >> If lock_limit is RLIM_INFINITY, "allowed" will be set to 1. And if get_ucounts fails >> in some corner cases, "allowed" will remain to be 1 while the user_shm_lock ops indeed >> fails. Or am I miss something? > > You are right, I am wrong: sorry. > Thanks for pointing now to that RLIM_INFINITY case. > > But then the Fixes tag is wrong: it should be > Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts") > which introduced the possibility of error down there. > You're right. commit 5ed44a401ddf ("do not limit locked memory when RLIMIT_MEMLOCK is RLIM_INFINITY") introduced RLIM_INFINITY and set "allowed" to 1 but there is no possibility of error down there. Will change this in V2. > With that, > Acked-by: Hugh Dickins Many thanks! > >> >> Many thanks for comment. >> >>>> --- >>>> mm/mlock.c | 1 + >>>> 1 file changed, 1 insertion(+) >>>> >>>> diff --git a/mm/mlock.c b/mm/mlock.c >>>> index 29372c0eebe5..efd2dd2943de 100644 >>>> --- a/mm/mlock.c >>>> +++ b/mm/mlock.c >>>> @@ -733,6 +733,7 @@ int user_shm_lock(size_t size, struct ucounts *ucounts) >>>> } >>>> if (!get_ucounts(ucounts)) { >>>> dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked); >>>> + allowed = 0; >>>> goto out; >>>> } >>>> allowed = 1; >>>> -- >>>> 2.23.0 > . >