From patchwork Wed Apr 7 10:52:43 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Roberto Sassu X-Patchwork-Id: 12187819 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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 01A98C433B4 for ; Wed, 7 Apr 2021 10:53:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C6DA6613A3 for ; Wed, 7 Apr 2021 10:53:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351616AbhDGKxY (ORCPT ); Wed, 7 Apr 2021 06:53:24 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:2787 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351596AbhDGKxR (ORCPT ); Wed, 7 Apr 2021 06:53:17 -0400 Received: from fraeml714-chm.china.huawei.com (unknown [172.18.147.226]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4FFgwm0cJkz681vb; Wed, 7 Apr 2021 18:43:36 +0800 (CST) Received: from fraphisprd00473.huawei.com (7.182.8.141) by fraeml714-chm.china.huawei.com (10.206.15.33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Wed, 7 Apr 2021 12:53:05 +0200 From: Roberto Sassu To: , CC: , , , , Roberto Sassu , Subject: [PATCH v5 03/12] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded Date: Wed, 7 Apr 2021 12:52:43 +0200 Message-ID: <20210407105252.30721-4-roberto.sassu@huawei.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210407105252.30721-1-roberto.sassu@huawei.com> References: <20210407105252.30721-1-roberto.sassu@huawei.com> MIME-Version: 1.0 X-Originating-IP: [7.182.8.141] X-ClientProxiedBy: lhreml753-chm.china.huawei.com (10.201.108.203) To fraeml714-chm.china.huawei.com (10.206.15.33) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org EVM_ALLOW_METADATA_WRITES is an EVM initialization flag that can be set to temporarily disable metadata verification until all xattrs/attrs necessary to verify an EVM portable signature are copied to the file. This flag is cleared when EVM is initialized with an HMAC key, to avoid that the HMAC is calculated on unverified xattrs/attrs. Currently EVM unnecessarily denies setting this flag if EVM is initialized with a public key, which is not a concern as it cannot be used to trust xattrs/attrs updates. This patch removes this limitation. Cc: stable@vger.kernel.org # 4.16.x Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-protected metadata") Signed-off-by: Roberto Sassu --- Documentation/ABI/testing/evm | 5 +++-- security/integrity/evm/evm_secfs.c | 4 ++-- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm index 3c477ba48a31..eb6d70fd6fa2 100644 --- a/Documentation/ABI/testing/evm +++ b/Documentation/ABI/testing/evm @@ -49,8 +49,9 @@ Description: modification of EVM-protected metadata and disable all further modification of policy - Note that once a key has been loaded, it will no longer be - possible to enable metadata modification. + Note that once an HMAC key has been loaded, it will no longer + be possible to enable metadata modification and, if it is + already enabled, it will be disabled. Until key loading has been signaled EVM can not create or validate the 'security.evm' xattr, but returns diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c index bbc85637e18b..197a4b83e534 100644 --- a/security/integrity/evm/evm_secfs.c +++ b/security/integrity/evm/evm_secfs.c @@ -81,10 +81,10 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf, return -EINVAL; /* Don't allow a request to freshly enable metadata writes if - * keys are loaded. + * an HMAC key is loaded. */ if ((i & EVM_ALLOW_METADATA_WRITES) && - ((evm_initialized & EVM_KEY_MASK) != 0) && + ((evm_initialized & EVM_INIT_HMAC) != 0) && !(evm_initialized & EVM_ALLOW_METADATA_WRITES)) return -EPERM;