From patchwork Wed May 5 11:29:27 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Roberto Sassu X-Patchwork-Id: 12239777 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 B0FADC43617 for ; Wed, 5 May 2021 11:30:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 85EF061176 for ; Wed, 5 May 2021 11:30:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233064AbhEELbD (ORCPT ); Wed, 5 May 2021 07:31:03 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:3006 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232967AbhEELbB (ORCPT ); Wed, 5 May 2021 07:31:01 -0400 Received: from fraeml714-chm.china.huawei.com (unknown [172.18.147.207]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4FZvVl3R3hz6yjBC; Wed, 5 May 2021 19:24:15 +0800 (CST) Received: from roberto-ThinkStation-P620.huawei.com (10.204.62.217) 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 15.1.2176.2; Wed, 5 May 2021 13:30:03 +0200 From: Roberto Sassu To: , CC: , , , Roberto Sassu , Subject: [PATCH v6 03/11] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded Date: Wed, 5 May 2021 13:29:27 +0200 Message-ID: <20210505112935.1410679-4-roberto.sassu@huawei.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210505112935.1410679-1-roberto.sassu@huawei.com> References: <20210505112935.1410679-1-roberto.sassu@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.204.62.217] X-ClientProxiedBy: lhreml752-chm.china.huawei.com (10.201.108.202) To fraeml714-chm.china.huawei.com (10.206.15.33) X-CFilter-Loop: Reflected Precedence: bulk List-ID: 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 Reviewed-by: Mimi Zohar --- Documentation/ABI/testing/evm | 5 +++-- security/integrity/evm/evm_secfs.c | 5 ++--- 2 files changed, 5 insertions(+), 5 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..860c48b9a0c3 100644 --- a/security/integrity/evm/evm_secfs.c +++ b/security/integrity/evm/evm_secfs.c @@ -81,11 +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_ALLOW_METADATA_WRITES)) + (evm_initialized & EVM_INIT_HMAC) != 0) return -EPERM; if (i & EVM_INIT_HMAC) {