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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09656C04AB5 for ; Mon, 3 Jun 2019 14:44:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E0F4227B17 for ; Mon, 3 Jun 2019 14:44:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729389AbfFCOoU (ORCPT ); Mon, 3 Jun 2019 10:44:20 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:32980 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729238AbfFCOoS (ORCPT ); Mon, 3 Jun 2019 10:44:18 -0400 Received: from LHREML712-CAH.china.huawei.com (unknown [172.18.7.106]) by Forcepoint Email with ESMTP id 970C97DED53F5CEC1E01; Mon, 3 Jun 2019 15:44:14 +0100 (IST) Received: from [10.220.96.108] (10.220.96.108) by smtpsuk.huawei.com (10.201.108.35) with Microsoft SMTP Server (TLS) id 14.3.408.0; Mon, 3 Jun 2019 15:44:04 +0100 Subject: Re: [PATCH v2 2/3] ima: don't ignore INTEGRITY_UNKNOWN EVM status To: James Bottomley , Mimi Zohar , , CC: , , , , , References: <20190529133035.28724-1-roberto.sassu@huawei.com> <20190529133035.28724-3-roberto.sassu@huawei.com> <1559217621.4008.7.camel@linux.ibm.com> <1559569401.5052.17.camel@HansenPartnership.com> <3667fbd4-b6ed-6a76-9ff4-84ec3c2dda12@huawei.com> <1559572305.5052.19.camel@HansenPartnership.com> From: Roberto Sassu Message-ID: Date: Mon, 3 Jun 2019 16:44:12 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <1559572305.5052.19.camel@HansenPartnership.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.220.96.108] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/3/2019 4:31 PM, James Bottomley wrote: > On Mon, 2019-06-03 at 16:29 +0200, Roberto Sassu wrote: >> On 6/3/2019 3:43 PM, James Bottomley wrote: >>> On Mon, 2019-06-03 at 11:25 +0200, Roberto Sassu wrote: >>>> On 5/30/2019 2:00 PM, Mimi Zohar wrote: >>>>> On Wed, 2019-05-29 at 15:30 +0200, Roberto Sassu wrote: >>>>>> Currently, ima_appraise_measurement() ignores the EVM status >>>>>> when evm_verifyxattr() returns INTEGRITY_UNKNOWN. If a file >>>>>> has a valid security.ima xattr with type IMA_XATTR_DIGEST or >>>>>> IMA_XATTR_DIGEST_NG, ima_appraise_measurement() returns >>>>>> INTEGRITY_PASS regardless of the EVM status. The problem is >>>>>> that the EVM status is overwritten with the appraisal statu >>>>> >>>>> Roberto, your framing of this problem is harsh and >>>>> misleading. IMA and EVM are intentionally independent of each >>>>> other and can be configured independently of each other. The >>>>> intersection of the two is the call to >>>>> evm_verifyxattr(). INTEGRITY_UNKNOWN is >>>>> returned for a number of reasons - when EVM is not configured, >>>>> the EVM hmac key has not yet been loaded, the protected >>>>> security attribute is unknown, or the file is not in policy. >>>>> >>>>> This patch does not differentiate between any of the above >>>>> cases, requiring mutable files to always be protected by EVM, >>>>> when specified as an "ima_appraise=" option on the boot command >>>>> line. >>>>> >>>>> IMA could be extended to require EVM on a per IMA policy rule >>>>> basis. Instead of framing allowing IMA file hashes without EVM >>>>> as a bug that has existed from the very beginning, now that >>>>> IMA/EVM have matured and is being used, you could frame it as >>>>> extending IMA or hardening. >>>> >>>> I'm seeing it from the perspective of an administrator that >>>> manages an already hardened system, and expects that the system >>>> only grants access to files with a valid signature/HMAC. That >>>> system would not enforce this behavior if EVM keys are removed >>>> and the digest in security.ima is set to the actual file digest. >>>> >>>> Framing it as a bug rather than an extension would in my opinion >>>> help to convince people about the necessity to switch to the safe >>>> mode, if their system is already hardened. >>> >>> I have a use case for IMA where I use it to enforce immutability of >>> containers. In this use case, the cluster admin places hashes on >>> executables as the image is unpacked so that if an executable file >>> is changed, IMA will cause an execution failure. For this use >>> case, I don't care about the EVM, in fact we don't use it, because >>> the only object is to fail execution if a binary is mutated. >> >> How would you prevent root in the container from updating >> security.ima? > > We don't. We only guarantee immutability for unprivileged containers, > so root can't be inside. Ok. Regarding the new behavior, this must be explicitly enabled by adding ima_appraise=enforce-evm or log-evm to the kernel command line. Otherwise, the current behavior is preserved with this patch. Would this be ok? Roberto -- HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Bo PENG, Jian LI, Yanli SHI