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=-13.7 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 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 9460BC433B4 for ; Mon, 3 May 2021 07:55:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 64D7061221 for ; Mon, 3 May 2021 07:55:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230490AbhECH40 convert rfc822-to-8bit (ORCPT ); Mon, 3 May 2021 03:56:26 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:2984 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229817AbhECH4Z (ORCPT ); Mon, 3 May 2021 03:56:25 -0400 Received: from fraeml715-chm.china.huawei.com (unknown [172.18.147.201]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4FYZr86b8mz6wlK1; Mon, 3 May 2021 15:49:44 +0800 (CST) Received: from fraeml714-chm.china.huawei.com (10.206.15.33) by fraeml715-chm.china.huawei.com (10.206.15.34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Mon, 3 May 2021 09:55:30 +0200 Received: from fraeml714-chm.china.huawei.com ([10.206.15.33]) by fraeml714-chm.china.huawei.com ([10.206.15.33]) with mapi id 15.01.2176.012; Mon, 3 May 2021 09:55:30 +0200 From: Roberto Sassu To: Mimi Zohar , "mjg59@google.com" CC: "linux-integrity@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH v5 06/12] evm: Ignore INTEGRITY_NOLABEL/INTEGRITY_NOXATTRS if conditions are safe Thread-Topic: [PATCH v5 06/12] evm: Ignore INTEGRITY_NOLABEL/INTEGRITY_NOXATTRS if conditions are safe Thread-Index: AQHXK5xdbQY13c/E0Ea5lrgi3mZG3arQ6VCAgAChtnA= Date: Mon, 3 May 2021 07:55:29 +0000 Message-ID: References: <20210407105252.30721-1-roberto.sassu@huawei.com> <20210407105252.30721-7-roberto.sassu@huawei.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.221.98.153] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org > From: Mimi Zohar [mailto:zohar@linux.ibm.com] > Sent: Monday, May 3, 2021 2:13 AM > Hi Roberto, > > On Wed, 2021-04-07 at 12:52 +0200, Roberto Sassu wrote: > > 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; > > I agree with the concept, but the function name doesn't provide enough > context. Perhaps defining a function more along the lines of > "evm_hmac_disabled()" would be more appropriate and at the same time > self documenting. Since the function checks if the passed error can be ignored, would evm_ignore_error_hmac_disabled() also be ok? > > 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))) > > It would also remove the INTEGRITY_NOXATTRS test duplication here. Ok. Thanks Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > thanks, > > Mimi > > > return 0; > > integrity_audit_msg(AUDIT_INTEGRITY_METADATA, > d_backing_inode(dentry), > > dentry->d_name.name, "appraise_metadata",