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 C2DE5ECAAD4 for ; Tue, 30 Aug 2022 12:14:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230107AbiH3MOE (ORCPT ); Tue, 30 Aug 2022 08:14:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35670 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229686AbiH3MOD (ORCPT ); Tue, 30 Aug 2022 08:14:03 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 48C31155A51 for ; Tue, 30 Aug 2022 05:14:02 -0700 (PDT) Received: from dggpemm500024.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4MH5kt4WBTznTng; Tue, 30 Aug 2022 20:11:34 +0800 (CST) Received: from [10.67.110.173] (10.67.110.173) by dggpemm500024.china.huawei.com (7.185.36.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 30 Aug 2022 20:14:00 +0800 Message-ID: Date: Tue, 30 Aug 2022 20:13:59 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH] ima: Handle -ESTALE returned by ima_filter_rule_match() Content-Language: en-US To: Mimi Zohar , , , References: <20220818020551.18922-1-guozihua@huawei.com> <998ca87c-8eef-8d50-e1ee-da53ef8f0046@huawei.com> <6cd55a0f-366f-45b7-d0e5-4116de454c10@huawei.com> <117476d4f35be96ddba26675b849af44a5dbd6d1.camel@linux.ibm.com> <61bc81bc-1b4a-3c08-6232-afc0d04decee@huawei.com> <886d4588b9b6ab4e7dd903addf9809898defd6d9.camel@linux.ibm.com> <9da1b1ab4a0e75f717c78ff44d985318a955ccd7.camel@linux.ibm.com> <2ad8179d-9ed6-b0f4-7b8d-e47b3de70b26@huawei.com> <6e6fe95710fe50312633852dd96914141f8a7466.camel@linux.ibm.com> From: "Guozihua (Scott)" In-Reply-To: <6e6fe95710fe50312633852dd96914141f8a7466.camel@linux.ibm.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.110.173] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500024.china.huawei.com (7.185.36.203) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On 2022/8/30 20:03, Mimi Zohar wrote: > On Tue, 2022-08-30 at 16:41 +0800, Guozihua (Scott) wrote: >> On 2022/8/30 9:20, Mimi Zohar wrote: >>> On Sat, 2022-08-27 at 17:57 +0800, Guozihua (Scott) wrote: >>>> On 2022/8/25 21:02, Mimi Zohar wrote: >>>>> On Wed, 2022-08-24 at 09:56 +0800, Guozihua (Scott) wrote: >>>>>> On 2022/8/24 9:26, Mimi Zohar wrote: >>>>>>> On Tue, 2022-08-23 at 21:28 +0800, Guozihua (Scott) wrote: >>>>>>>> On 2022/8/23 21:21, Mimi Zohar wrote: >>>>>>>>> On Tue, 2022-08-23 at 16:12 +0800, Guozihua (Scott) wrote: >>>>>>>>>>> The question is whether we're waiting for the SELinux policy to change >>>>>>>>>>> from ESTALE or whether it is the number of SELinux based IMA policy >>>>>>>>>>> rules or some combination of the two. Retrying three times seems to be >>>>>>>>>>> random. If SELinux waited for ESTALE to change, then it would only be >>>>>>>>>>> dependent on the time it took to update the SELinux based IMA policy >>>>>>>>>>> rules. >>>>>>>>>> >>>>>>>>>> We are waiting for ima_lsm_update_rules() to finish re-initializing all >>>>>>>>>> the LSM based rules. >>>>>>>>> >>>>>>>>> Fine. Hopefully retrying a maximum of 3 times is sufficient. >>>>>>>>> >>>>>>>> Well, at least this should greatly reduce the chance of this issue from >>>>>>>> happening. >>>>>>> >>>>>>> Agreed >>>>>>> >>>>>>>> This would be the best we I can think of without locking and >>>>>>>> busy waiting. Maybe we can also add delays before we retry. Maybe you >>>>>>>> got any other thought in mind? >>>>>>> >>>>>>> Another option would be to re-introduce the equivalent of the "lazy" >>>>>>> LSM update on -ESTALE, but without updating the policy rule, as the >>>>>>> notifier callback will eventually get to it. >>>>>>> >>>>>> >>>>>> For this to happen we would need a way to tell when we are able to >>>>>> continue with the retry though. >>>>> >>>>> Previously with the lazy update, on failure security_filter_rule_init() >>>>> was called before the retry. To avoid locking or detecting when to >>>>> continue, another option would be to call to >>>>> security_filter_rule_init() with a local copy of the rule. The retry >>>>> would be based on a local copy of the rule. >>>>> >>>>> Eventually the registered callback will complete, so we don't need to >>>>> be concerned about updating the actual rules. >>>> >>>> Is it possible to cause race condition though? With this, the notifier >>>> path seems to be unnecessary. >>> >>> I don't see how there would be a race condition. The notifier callback >>> is the normal method of updating the policy rules. Hopefully -ESTALE >>> isn't something that happens frequently. >> >> The notifier callback uses RCU to update rules, I think we should mimic >> that behavior if we are to update individual rules in the matching logic. > > If the callback update hasn't completed causing an -ESTALE, the > fallback is to directly query the LSM for a single IMA policy rule. > Please keep it simple. > Got it, I'll send a new patch. -- Best GUO Zihua