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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 E824AC83007 for ; Wed, 29 Apr 2020 07:42:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D00EE2083B for ; Wed, 29 Apr 2020 07:42:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726743AbgD2HmR (ORCPT ); Wed, 29 Apr 2020 03:42:17 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:2127 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726554AbgD2HmN (ORCPT ); Wed, 29 Apr 2020 03:42:13 -0400 Received: from lhreml707-chm.china.huawei.com (unknown [172.18.7.107]) by Forcepoint Email with ESMTP id 4A1DB5F8236ABC6C97AB; Wed, 29 Apr 2020 08:42:11 +0100 (IST) Received: from fraeml714-chm.china.huawei.com (10.206.15.33) by lhreml707-chm.china.huawei.com (10.201.108.56) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1913.5; Wed, 29 Apr 2020 08:42:10 +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; Wed, 29 Apr 2020 09:42:10 +0200 From: Roberto Sassu To: , , , CC: , , , , , Roberto Sassu Subject: [RFC][PATCH 3/3] evm: Return -EAGAIN to ignore verification failures Date: Wed, 29 Apr 2020 09:39:35 +0200 Message-ID: <20200429073935.11913-3-roberto.sassu@huawei.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200429073935.11913-1-roberto.sassu@huawei.com> References: <20200429073935.11913-1-roberto.sassu@huawei.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.204.65.160] X-ClientProxiedBy: lhreml701-chm.china.huawei.com (10.201.108.50) To fraeml714-chm.china.huawei.com (10.206.15.33) X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org By default, EVM maintains the same behavior as before hooks were moved outside the LSM infrastructure. When EVM returns -EPERM, callers stop their execution and return the error to user space. This patch introduces a new mode, called ignore, that changes the return value of the pre hooks from -EPERM to -EAGAIN. It also modifies the callers of pre and post hooks to continue the execution if -EAGAIN is returned. The error is then handled by the post hooks. The only error that is not ignored is when user space is trying to modify a portable signature. Once that signature has been validated with the current values of metadata, there is no valid reason to change them. >From user space perspective, operations on corrupted metadata are successfully performed but post hooks didn't update the HMAC. At the next IMA verification, when evm_verifyxattr() is called, corruption will be detected and access will be denied. Signed-off-by: Roberto Sassu --- fs/attr.c | 2 +- fs/xattr.c | 4 ++-- security/integrity/evm/evm_main.c | 23 +++++++++++++++++------ 3 files changed, 20 insertions(+), 9 deletions(-) diff --git a/fs/attr.c b/fs/attr.c index 6ce60e1eba34..6370e2f3704d 100644 --- a/fs/attr.c +++ b/fs/attr.c @@ -329,7 +329,7 @@ int notify_change(struct dentry * dentry, struct iattr * attr, struct inode **de if (error) return error; evm_error = evm_inode_setattr(dentry, attr); - if (evm_error) + if (evm_error && evm_error != -EAGAIN) return evm_error; error = try_break_deleg(inode, delegated_inode); if (error) diff --git a/fs/xattr.c b/fs/xattr.c index b1fd2aa481a8..73f0f3cd6c45 100644 --- a/fs/xattr.c +++ b/fs/xattr.c @@ -229,7 +229,7 @@ vfs_setxattr(struct dentry *dentry, const char *name, const void *value, goto out; evm_error = evm_inode_setxattr(dentry, name, value, size); - if (evm_error) { + if (evm_error && evm_error != -EAGAIN) { error = evm_error; goto out; } @@ -408,7 +408,7 @@ vfs_removexattr(struct dentry *dentry, const char *name) goto out; evm_error = evm_inode_removexattr(dentry, name); - if (evm_error) { + if (evm_error && evm_error != -EAGAIN) { error = evm_error; goto out; } diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index ca9eaef7058b..ef09caa3bbcf 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -54,11 +54,13 @@ static struct xattr_list evm_config_default_xattrnames[] = { LIST_HEAD(evm_config_xattrnames); -static int evm_fixmode; +static int evm_fixmode, evm_ignoremode __ro_after_init; static int __init evm_set_fixmode(char *str) { if (strncmp(str, "fix", 3) == 0) evm_fixmode = 1; + if (strncmp(str, "ignore", 6) == 0) + evm_ignoremode = 1; return 0; } __setup("evm=", evm_set_fixmode); @@ -311,6 +313,7 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, const void *xattr_value, size_t xattr_value_len) { enum integrity_status evm_status; + int rc = -EPERM; if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) { if (!capable(CAP_SYS_ADMIN)) @@ -345,12 +348,17 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, -EPERM, 0); } out: - if (evm_status != INTEGRITY_PASS) + if (evm_status != INTEGRITY_PASS) { + if (evm_ignoremode && evm_status != INTEGRITY_PASS_IMMUTABLE) + rc = -EAGAIN; + integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata", integrity_status_msg[evm_status], - -EPERM, 0); - return evm_status == INTEGRITY_PASS ? 0 : -EPERM; + rc, 0); + } + + return evm_status == INTEGRITY_PASS ? 0 : rc; } /** @@ -482,6 +490,7 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr) { unsigned int ia_valid = attr->ia_valid; enum integrity_status evm_status; + int rc = -EPERM; /* Policy permits modification of the protected attrs even though * there's no HMAC key loaded @@ -495,10 +504,12 @@ int evm_inode_setattr(struct dentry *dentry, struct iattr *attr) if ((evm_status == INTEGRITY_PASS) || (evm_status == INTEGRITY_NOXATTRS)) return 0; + if (evm_ignoremode && evm_status != INTEGRITY_PASS_IMMUTABLE) + rc = -EAGAIN; integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata", - integrity_status_msg[evm_status], -EPERM, 0); - return -EPERM; + integrity_status_msg[evm_status], rc, 0); + return rc; } /** -- 2.17.1