From patchwork Thu Jun 18 16:01:27 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Roberto Sassu X-Patchwork-Id: 11612769 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0EE2592A for ; Thu, 18 Jun 2020 16:04:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F3F4D214D8 for ; Thu, 18 Jun 2020 16:04:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731753AbgFRQEb (ORCPT ); Thu, 18 Jun 2020 12:04:31 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:2334 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731811AbgFRQE1 (ORCPT ); Thu, 18 Jun 2020 12:04:27 -0400 Received: from lhreml735-chm.china.huawei.com (unknown [172.18.7.108]) by Forcepoint Email with ESMTP id 1342DB8A14AFCE0680A1; Thu, 18 Jun 2020 17:04:26 +0100 (IST) Received: from fraeml714-chm.china.huawei.com (10.206.15.33) by lhreml735-chm.china.huawei.com (10.201.108.86) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1913.5; Thu, 18 Jun 2020 17:04:25 +0100 Received: from roberto-HP-EliteDesk-800-G2-DM-65W.huawei.com (10.204.65.160) by fraeml714-chm.china.huawei.com (10.206.15.33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.1913.5; Thu, 18 Jun 2020 18:04:25 +0200 From: Roberto Sassu To: , CC: , , , Roberto Sassu Subject: [PATCH 05/11] evm: Allow xattr/attr operations for portable signatures if check fails Date: Thu, 18 Jun 2020 18:01:27 +0200 Message-ID: <20200618160133.937-5-roberto.sassu@huawei.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200618160133.937-1-roberto.sassu@huawei.com> References: <20200618160133.937-1-roberto.sassu@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.204.65.160] X-ClientProxiedBy: lhreml704-chm.china.huawei.com (10.201.108.53) To fraeml714-chm.china.huawei.com (10.206.15.33) X-CFilter-Loop: Reflected Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org If files with portable signatures are copied from one location to another or are extracted from an archive, verification can temporarily fail until all xattrs/attrs are set in the destination. Portable signatures are the only ones that can be moved to different files, as they don't depend on system-specific information such as the inode generation. Unlike other security.evm types, portable signatures can never be replaced even if an xattr/attr operation is granted, as once evm_update_evmxattr() detects this type, it returns without updating the HMAC. Thus, it wouldn't be a problem to allow those operations so that verification passes on the destination after all xattrs/attrs are copied. This patch first introduces a new integrity status called INTEGRITY_FAIL_IMMUTABLE, that allows callers of evm_verify_current_integrity() to detect that a portable signature didn't pass verification and then adds an exception in evm_protect_xattr() and evm_inode_setattr() for this status and returns 0 instead of -EPERM. Signed-off-by: Roberto Sassu --- include/linux/integrity.h | 1 + security/integrity/evm/evm_main.c | 25 ++++++++++++++++++++----- security/integrity/ima/ima_appraise.c | 1 + 3 files changed, 22 insertions(+), 5 deletions(-) diff --git a/include/linux/integrity.h b/include/linux/integrity.h index 2271939c5c31..2ea0f2f65ab6 100644 --- a/include/linux/integrity.h +++ b/include/linux/integrity.h @@ -13,6 +13,7 @@ enum integrity_status { INTEGRITY_PASS = 0, INTEGRITY_PASS_IMMUTABLE, INTEGRITY_FAIL, + INTEGRITY_FAIL_IMMUTABLE, INTEGRITY_NOLABEL, INTEGRITY_NOXATTRS, INTEGRITY_UNKNOWN, diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 4e9f5e8b21d5..30072030f05d 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -27,7 +27,8 @@ int evm_initialized; static const char * const integrity_status_msg[] = { - "pass", "pass_immutable", "fail", "no_label", "no_xattrs", "unknown" + "pass", "pass_immutable", "fail", "fail_immutable", "no_label", + "no_xattrs", "unknown" }; int evm_hmac_attrs; @@ -134,7 +135,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, enum integrity_status evm_status = INTEGRITY_PASS; struct evm_digest digest; struct inode *inode; - int rc, xattr_len; + int rc, xattr_len, evm_immutable = 0; if (iint && (iint->evm_status == INTEGRITY_PASS || iint->evm_status == INTEGRITY_PASS_IMMUTABLE)) @@ -179,8 +180,10 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, if (rc) rc = -EINVAL; break; - case EVM_IMA_XATTR_DIGSIG: case EVM_XATTR_PORTABLE_DIGSIG: + evm_immutable = 1; + fallthrough; + case EVM_IMA_XATTR_DIGSIG: /* accept xattr with non-empty signature field */ if (xattr_len <= sizeof(struct signature_v2_hdr)) { evm_status = INTEGRITY_FAIL; @@ -219,7 +222,8 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, if (rc) evm_status = (rc == -ENODATA) ? - INTEGRITY_NOXATTRS : INTEGRITY_FAIL; + INTEGRITY_NOXATTRS : evm_immutable ? + INTEGRITY_FAIL_IMMUTABLE : INTEGRITY_FAIL; out: if (iint) iint->evm_status = evm_status; @@ -351,6 +355,12 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, -EPERM, 0); } out: + /* It is safe to allow fail_immutable, portable signatures can never be + * updated + */ + if (evm_status == INTEGRITY_FAIL_IMMUTABLE) + return 0; + if (evm_status != INTEGRITY_PASS) integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata", @@ -488,9 +498,14 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr) if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))) return 0; evm_status = evm_verify_current_integrity(dentry); + /* It is safe to allow fail_immutable, portable signatures can never + * be updated + */ if ((evm_status == INTEGRITY_PASS) || - (evm_status == INTEGRITY_NOXATTRS)) + (evm_status == INTEGRITY_NOXATTRS) || + (evm_status == INTEGRITY_FAIL_IMMUTABLE)) return 0; + integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata", integrity_status_msg[evm_status], -EPERM, 0); diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index a9649b04b9f1..21bda264fc30 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -393,6 +393,7 @@ int ima_appraise_measurement(enum ima_hooks func, case INTEGRITY_NOLABEL: /* No security.evm xattr. */ cause = "missing-HMAC"; goto out; + case INTEGRITY_FAIL_IMMUTABLE: case INTEGRITY_FAIL: /* Invalid HMAC/signature. */ cause = "invalid-HMAC"; goto out;