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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 E7D89C43381 for ; Wed, 13 Mar 2019 16:06:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B48862146E for ; Wed, 13 Mar 2019 16:06:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727106AbfCMQGa (ORCPT ); Wed, 13 Mar 2019 12:06:30 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:60698 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727062AbfCMQG3 (ORCPT ); Wed, 13 Mar 2019 12:06:29 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92 #3 (Red Hat Linux)) id 1h46OW-0000OV-TI; Wed, 13 Mar 2019 16:06:17 +0000 Date: Wed, 13 Mar 2019 16:06:16 +0000 From: Al Viro To: Theodore Ts'o , Amir Goldstein , Richard Weinberger , Miklos Szeredi , linux-fsdevel , linux-fscrypt@vger.kernel.org, overlayfs , linux-kernel , Paul Lawrence Subject: Re: overlayfs vs. fscrypt Message-ID: <20190313160616.GR2217@ZenIV.linux.org.uk> References: <4603533.ZIfxmiEf7K@blindfold> <1854703.ve7plDhYWt@blindfold> <4066872.KGdO14EQMx@blindfold> <20190313151633.GA672@mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190313151633.GA672@mit.edu> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 13, 2019 at 11:16:33AM -0400, Theodore Ts'o wrote: > Actually, the original use was for ChromeOS, but the primary > assumption is that keying is per user (or profile), and that users are > mutually distrustful. So when Alice logs out of the system, her keys > will be invalidated and removed from the kernel. We can (and do) try > to flush cache entries via "echo 3 > /proc/sys/vm/drop_caches" on > logout. However, this does not guarantee that all dcache entries will > be removed --- a dcache entry can be pinned due to an open file, a > process's current working directory, a bind mount, etc. > > The other issue is negative dentries; if you try open a file in an > encrypted file, the file system won't even *know* whether or not a > file exists, since the directory entries are encrypted; hence, there > may be some negative dentries that need to be invalidated. > > So a fundamental assumption with fscrypt is that keys will be added > and removed, and that when this happens, dentries will need to be > invalidated. This is going to surprise overlayfs, so if overlayfs is > going to support fscrypt it *has* to be aware of the fact that this > can happen. It's not even clear what the proper security semantics > should be; *especially* if the upper and lower directories aren't > similarly protected using the same fscrypt encryption key. Suppose > the lower directory is encrypted, and the upper is not. Now on a copy > up operation, the previously encrypted file, which might contain > credit card numbers, medical records, or other things that would cause > a GDPR regulator to have a freak out attack, would *poof* become > decrypted. Just to make sure - you do realize that ban on multiple dentries refering to the same directory inode is *NOT* conditional upon those dentries being hashed, right?