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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DD4F8C433FE for ; Fri, 30 Sep 2022 08:44:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231165AbiI3Iou (ORCPT ); Fri, 30 Sep 2022 04:44:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38680 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229530AbiI3Ioq (ORCPT ); Fri, 30 Sep 2022 04:44:46 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3985F1408F; Fri, 30 Sep 2022 01:44:45 -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 dfw.source.kernel.org (Postfix) with ESMTPS id C2A9462272; Fri, 30 Sep 2022 08:44:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 20573C433D6; Fri, 30 Sep 2022 08:44:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664527484; bh=d1ZEgyLvbAWwEvt+KDAgrmBxhZSgx4ZgAWldRS0Ue3w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hwJz6cn2OyQ2cLyL/dqHFljtF6OGMIoTUu220yVVdrM7DJyH9X6YBEe/a8miaZpk5 8MyCvQ6KRB3oIDvjNmoSh6K/wnO+yX2v/b5FKyEH917liXShZObmk5ik8IcDzHB1ex aTjM4y18yhtAJ75Dxxfzp0ThCMnc68glyl9+KsdY0PqUrMRy3xFaIRLruEYraySr6s 7z2U55caDoCFJucpSJIq3fc8EB5vvNcGBDnuZ5FHmryYWIJjuIB9H2tGylttw+J5JO MGOnfRWjJrcOGG7XYU5Hxwq6fMtaXy4mTRXSAW5OviPk+jW/H6OIxVPXq7SpP/y3qn xiOYiEyzEUeVQ== Date: Fri, 30 Sep 2022 10:44:38 +0200 From: Christian Brauner To: Mimi Zohar Cc: linux-fsdevel@vger.kernel.org, Seth Forshee , Christoph Hellwig , Al Viro , linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, Paul Moore Subject: Re: [PATCH v4 13/30] evm: add post set acl hook Message-ID: <20220930084438.4wuyeyogdthiwmmn@wittgenstein> References: <20220929153041.500115-1-brauner@kernel.org> <20220929153041.500115-14-brauner@kernel.org> <9b71392a68d9441697fcca12b30e26578ed7423f.camel@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <9b71392a68d9441697fcca12b30e26578ed7423f.camel@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Thu, Sep 29, 2022 at 09:44:45PM -0400, Mimi Zohar wrote: > Hi Christian, > > On Thu, 2022-09-29 at 17:30 +0200, Christian Brauner wrote: > > The security_inode_post_setxattr() hook is used by security modules to > > update their own security.* xattrs. Consequently none of the security > > modules operate on posix acls. So we don't need an additional security > > hook when post setting posix acls. > > > > However, the integrity subsystem wants to be informed about posix acl > > changes and specifically evm to update their hashes when the xattrs > > change. > > ^... to be informed about posix acl changes in order to reset the EVM > status flag. Substituted. > > > The callchain for evm_inode_post_setxattr() is: > > > > -> evm_inode_post_setxattr() > > Resets the EVM status flag for both EVM signatures and HMAC. > > > -> evm_update_evmxattr() > > evm_update_evmxattr() is only called for "security.evm", not acls. I've added both comments but note that I'm explaining this in the paragraph below as well. > > > -> evm_calc_hmac() > > -> evm_calc_hmac_or_hash() > > > > and evm_cacl_hmac_or_hash() walks the global list of protected xattr > > names evm_config_xattrnames. This global list can be modified via > > /sys/security/integrity/evm/evm_xattrs. The write to "evm_xattrs" is > > restricted to security.* xattrs and the default xattrs in > > evm_config_xattrnames only contains security.* xattrs as well. > > > > So the actual value for posix acls is currently completely irrelevant > > for evm during evm_inode_post_setxattr() and frankly it should stay that > > way in the future to not cause the vfs any more headaches. But if the > > actual posix acl values matter then evm shouldn't operate on the binary > > void blob and try to hack around in the uapi struct anyway. Instead it > > should then in the future add a dedicated hook which takes a struct > > posix_acl argument passing the posix acls in the proper vfs format. > > > > For now it is sufficient to make evm_inode_post_set_acl() a wrapper > > around evm_inode_post_setxattr() not passing any actual values down. > > This will still cause the hashes to be updated as before. > > ^This will cause the EVM status flag to be reset. Substituted.