From patchwork Wed Apr 7 10:52:46 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Roberto Sassu X-Patchwork-Id: 12187829 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 0714DC433B4 for ; Wed, 7 Apr 2021 10:54:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C4EB6610FB for ; Wed, 7 Apr 2021 10:54:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235032AbhDGKyd (ORCPT ); Wed, 7 Apr 2021 06:54:33 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:2790 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234547AbhDGKyc (ORCPT ); Wed, 7 Apr 2021 06:54:32 -0400 Received: from fraeml714-chm.china.huawei.com (unknown [172.18.147.200]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4FFh3G5j66z6830t; Wed, 7 Apr 2021 18:49:14 +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 12:54:20 +0200 From: Roberto Sassu To: , CC: , , , , Roberto Sassu Subject: [PATCH v5 06/12] evm: Ignore INTEGRITY_NOLABEL/INTEGRITY_NOXATTRS if conditions are safe Date: Wed, 7 Apr 2021 12:52:46 +0200 Message-ID: <20210407105252.30721-7-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 When a file is being created, LSMs can set the initial label with the inode_init_security hook. If no HMAC key is loaded, the new file will have LSM xattrs but not the HMAC. It is also possible that the file remains without protected xattrs after creation if no active LSM provided it. Unfortunately, EVM will deny any further metadata operation on new files, as evm_protect_xattr() will always return the INTEGRITY_NOLABEL error, or INTEGRITY_NOXATTRS if no protected xattrs exist. This would limit the usability of EVM when only a public key is loaded, as commands such as cp or tar with the option to preserve xattrs won't work. This patch ignores these errors when they won't be an issue, if no HMAC key is loaded and cannot be loaded in the future (which can be enforced by setting the EVM_SETUP_COMPLETE initialization flag). Signed-off-by: Roberto Sassu --- security/integrity/evm/evm_main.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 998818283fda..6556e8c22da9 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -90,6 +90,24 @@ static bool evm_key_loaded(void) return (bool)(evm_initialized & EVM_KEY_MASK); } +/* + * Ignoring INTEGRITY_NOLABEL/INTEGRITY_NOXATTRS is safe if no HMAC key + * is loaded and the EVM_SETUP_COMPLETE initialization flag is set. + */ +static bool evm_ignore_error_safe(enum integrity_status evm_status) +{ + if (evm_initialized & EVM_INIT_HMAC) + return false; + + if (!(evm_initialized & EVM_SETUP_COMPLETE)) + return false; + + if (evm_status != INTEGRITY_NOLABEL && evm_status != INTEGRITY_NOXATTRS) + return false; + + return true; +} + static int evm_find_protected_xattrs(struct dentry *dentry) { struct inode *inode = d_backing_inode(dentry); @@ -354,6 +372,8 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, -EPERM, 0); } out: + if (evm_ignore_error_safe(evm_status)) + return 0; if (evm_status != INTEGRITY_PASS) integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata", @@ -515,7 +535,8 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr) return 0; evm_status = evm_verify_current_integrity(dentry); if ((evm_status == INTEGRITY_PASS) || - (evm_status == INTEGRITY_NOXATTRS)) + (evm_status == INTEGRITY_NOXATTRS) || + (evm_ignore_error_safe(evm_status))) return 0; integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata",