From patchwork Mon Jul 12 06:02:22 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 475482 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=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT 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 80681C11F73 for ; Mon, 12 Jul 2021 07:42:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6B57C61456 for ; Mon, 12 Jul 2021 07:42:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349709AbhGLHoc (ORCPT ); Mon, 12 Jul 2021 03:44:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:46248 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345922AbhGLHjN (ORCPT ); Mon, 12 Jul 2021 03:39:13 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0487E611BF; Mon, 12 Jul 2021 07:34:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1626075242; bh=jOF2+mVU5Zoyesc5FztQrLVVkG6ddrANPmsqaU+DgXM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0+Ob6g0VnNNKhLcTZPiNUw5GnRAazrjtmCKfdPDmRJ/9KoGIh+NXJdsc9aeH4j1ps pt25Bv8kh9PN1fVIVhGC68m7V486qwyADlTYHh/y1UQKjmxFtuILzW7+NiklI2qXBQ 5Bds2BWyQhhVtfsZ0rtN6pdbsN618znqX3B7pfwY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Roberto Sassu , Mimi Zohar Subject: [PATCH 5.13 119/800] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded Date: Mon, 12 Jul 2021 08:02:22 +0200 Message-Id: <20210712060929.672173570@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210712060912.995381202@linuxfoundation.org> References: <20210712060912.995381202@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Roberto Sassu commit 9acc89d31f0c94c8e573ed61f3e4340bbd526d0c upstream. 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. Fixes: ae1ba1676b88e ("EVM: Allow userland to permit modification of EVM-protected metadata") Signed-off-by: Roberto Sassu Cc: stable@vger.kernel.org # 4.16.x Signed-off-by: Mimi Zohar Signed-off-by: Greg Kroah-Hartman --- Documentation/ABI/testing/evm | 26 ++++++++++++++++++++++++-- security/integrity/evm/evm_secfs.c | 8 ++++---- 2 files changed, 28 insertions(+), 6 deletions(-) --- a/Documentation/ABI/testing/evm +++ b/Documentation/ABI/testing/evm @@ -49,8 +49,30 @@ 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. + Echoing a value is additive, the new value is added to the + existing initialization flags. + + For example, after:: + + echo 2 >/evm + + another echo can be performed:: + + echo 1 >/evm + + and the resulting value will be 3. + + Note that once an HMAC key has been loaded, it will no longer + be possible to enable metadata modification. Signaling that an + HMAC key has been loaded will clear the corresponding flag. + For example, if the current value is 6 (2 and 4 set):: + + echo 1 >/evm + + will set the new value to 3 (4 cleared). + + Loading an HMAC key is the only way to disable metadata + modification. Until key loading has been signaled EVM can not create or validate the 'security.evm' xattr, but returns --- a/security/integrity/evm/evm_secfs.c +++ b/security/integrity/evm/evm_secfs.c @@ -80,12 +80,12 @@ static ssize_t evm_write_key(struct file if (!i || (i & ~EVM_INIT_MASK) != 0) return -EINVAL; - /* Don't allow a request to freshly enable metadata writes if - * keys are loaded. + /* + * Don't allow a request to enable metadata writes if + * 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) {