From patchwork Mon Sep 26 14:08:15 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 12988918 X-Patchwork-Delegate: paul@paul-moore.com Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 82153C32771 for ; Mon, 26 Sep 2022 15:24:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236514AbiIZPY2 (ORCPT ); Mon, 26 Sep 2022 11:24:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57374 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236642AbiIZPX4 (ORCPT ); Mon, 26 Sep 2022 11:23:56 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6977324B; Mon, 26 Sep 2022 07:09:32 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 8117DCE114D; Mon, 26 Sep 2022 14:09:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 742AAC433D7; Mon, 26 Sep 2022 14:09:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664201368; bh=mZiUJrvg8yaqgBdnDKc8+Ezywv02rJLKTDGCaJnn3OU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=IqZtyn/JKkfubM8GJuzxSffRB5aOiFKohVcQSGC2SR8LnaGO6xIxS/fKGvWgrzNW0 zuANfLYr0H8e3MwqJumW8OQRasTFzPt15cBkMda73e1S3rxByLNV55HcO6VordKJPB NBhFwDWdca1yfGK8SdEAzBLvOOXNMzNChOWexBWWel4aqZyPwY13NMzrh3MG6UbHBp Q3ii02eu3eayEqZpqoBGWVXGn68ZzKOabEPLBfTn0dYMXOjUpBFiYnRJnh0Cbo719m SQF8QHholkqKtn+60zFLWcqbOh3DdI0sPT9nq03ii7dXDB7w3PkbgBf8r82TvhsM0r Xh/oEQkkUxDLg== From: Christian Brauner To: linux-fsdevel@vger.kernel.org Cc: Christian Brauner , Seth Forshee , Christoph Hellwig , Al Viro , Mimi Zohar , linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH v2 18/30] evm: simplify evm_xattr_acl_change() Date: Mon, 26 Sep 2022 16:08:15 +0200 Message-Id: <20220926140827.142806-19-brauner@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220926140827.142806-1-brauner@kernel.org> References: <20220926140827.142806-1-brauner@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4006; i=brauner@kernel.org; h=from:subject; bh=mZiUJrvg8yaqgBdnDKc8+Ezywv02rJLKTDGCaJnn3OU=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMSQbbnI8nD+vU2XRUo206wdMFs3I1JiSnf/iscfV4J7aGWWB 2/x3dJSyMIhxMciKKbI4tJuEyy3nqdhslKkBM4eVCWQIAxenAEzkyEyGfzobjYXyCi9vYWG6+6OB/d WfyYf7LtydL75v3vTlrP2JnnMY/ofcW66kysX8nenC9vUsthMi0tvOiBc8KfE4s3/rOxWLs9wA X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Precedence: bulk List-ID: The posix acl api provides a dedicated security and integrity hook for setting posix acls. This means that evm_protect_xattr() -> evm_xattr_change() -> evm_xattr_acl_change() is now only hit during vfs_remove_acl() at which point we are guaranteed that xattr_value and xattr_value_len are NULL and 0. In this case evm always used to return 1. Simplify this function to do just that. Signed-off-by: Christian Brauner (Microsoft) --- Notes: /* v2 */ unchanged security/integrity/evm/evm_main.c | 62 +++++++------------------------ 1 file changed, 14 insertions(+), 48 deletions(-) diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 15aa5995fff4..1fbe1b8d0364 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -436,62 +436,29 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry) /* * evm_xattr_acl_change - check if passed ACL changes the inode mode - * @mnt_userns: user namespace of the idmapped mount - * @dentry: pointer to the affected dentry * @xattr_name: requested xattr * @xattr_value: requested xattr value * @xattr_value_len: requested xattr value length * - * Check if passed ACL changes the inode mode, which is protected by EVM. + * This is only hit during xattr removal at which point we always return 1. + * Splat a warning in case someone managed to pass data to this function. That + * should never happen. * * Returns 1 if passed ACL causes inode mode change, 0 otherwise. */ -static int evm_xattr_acl_change(struct user_namespace *mnt_userns, - struct dentry *dentry, const char *xattr_name, - const void *xattr_value, size_t xattr_value_len) +static int evm_xattr_acl_change(const void *xattr_value, size_t xattr_value_len) { -#ifdef CONFIG_FS_POSIX_ACL - umode_t mode; - struct posix_acl *acl = NULL, *acl_res; - struct inode *inode = d_backing_inode(dentry); - int rc; - - /* - * An earlier comment here mentioned that the idmappings for - * ACL_{GROUP,USER} don't matter since EVM is only interested in the - * mode stored as part of POSIX ACLs. Nonetheless, if it must translate - * from the uapi POSIX ACL representation to the VFS internal POSIX ACL - * representation it should do so correctly. There's no guarantee that - * we won't change POSIX ACLs in a way that ACL_{GROUP,USER} matters - * for the mode at some point and it's difficult to keep track of all - * the LSM and integrity modules and what they do to POSIX ACLs. - * - * Frankly, EVM shouldn't try to interpret the uapi struct for POSIX - * ACLs it received. It requires knowledge that only the VFS is - * guaranteed to have. - */ - acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode), - xattr_value, xattr_value_len); - if (IS_ERR_OR_NULL(acl)) - return 1; - - acl_res = acl; - /* - * Passing mnt_userns is necessary to correctly determine the GID in - * an idmapped mount, as the GID is used to clear the setgid bit in - * the inode mode. - */ - rc = posix_acl_update_mode(mnt_userns, inode, &mode, &acl_res); - - posix_acl_release(acl); - - if (rc) - return 1; + int rc = 0; - if (inode->i_mode != mode) - return 1; +#ifdef CONFIG_FS_POSIX_ACL + WARN_ONCE(xattr_value != NULL, + "Passing xattr value for POSIX ACLs not supported\n"); + WARN_ONCE(xattr_value_len != 0, + "Passing non-zero length for POSIX ACLs not supported\n"); + rc = 1; #endif - return 0; + + return rc; } /* @@ -514,8 +481,7 @@ static int evm_xattr_change(struct user_namespace *mnt_userns, int rc = 0; if (posix_xattr_acl(xattr_name)) - return evm_xattr_acl_change(mnt_userns, dentry, xattr_name, - xattr_value, xattr_value_len); + return evm_xattr_acl_change(xattr_value, xattr_value_len); rc = vfs_getxattr_alloc(&init_user_ns, dentry, xattr_name, &xattr_data, 0, GFP_NOFS);