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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 AFB2CC282DA for ; Wed, 17 Apr 2019 14:25:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8915520872 for ; Wed, 17 Apr 2019 14:25:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732299AbfDQOZF (ORCPT ); Wed, 17 Apr 2019 10:25:05 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:48590 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729356AbfDQOZF (ORCPT ); Wed, 17 Apr 2019 10:25:05 -0400 Received: from callcc.thunk.org (guestnat-104-133-0-109.corp.google.com [104.133.0.109] (may be forged)) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id x3HEOawa011053 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 17 Apr 2019 10:24:36 -0400 Received: by callcc.thunk.org (Postfix, from userid 15806) id E7C39420497; Wed, 17 Apr 2019 10:24:35 -0400 (EDT) Date: Wed, 17 Apr 2019 10:24:35 -0400 From: "Theodore Ts'o" To: Eric Biggers Cc: linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, linux-unionfs@vger.kernel.org, Sarthak Kukreti , Gao Xiang Subject: Re: [PATCH v2 5/5] fscrypt: fix race where ->lookup() marks plaintext dentry as ciphertext Message-ID: <20190417142435.GE4686@mit.edu> References: <20190320183913.12686-1-ebiggers@kernel.org> <20190320183913.12686-6-ebiggers@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190320183913.12686-6-ebiggers@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Wed, Mar 20, 2019 at 11:39:13AM -0700, Eric Biggers wrote: > From: Eric Biggers > > ->lookup() in an encrypted directory begins as follows: > > 1. fscrypt_prepare_lookup(): > a. Try to load the directory's encryption key. > b. If the key is unavailable, mark the dentry as a ciphertext name > via d_flags. > 2. fscrypt_setup_filename(): > a. Try to load the directory's encryption key. > b. If the key is available, encrypt the name (treated as a plaintext > name) to get the on-disk name. Otherwise decode the name > (treated as a ciphertext name) to get the on-disk name. > > But if the key is concurrently added, it may be found at (2a) but not at > (1a). In this case, the dentry will be wrongly marked as a ciphertext > name even though it was actually treated as plaintext. > > This will cause the dentry to be wrongly invalidated on the next lookup, > potentially causing problems. For example, if the racy ->lookup() was > part of sys_mount(), then the new mount will be detached when anything > tries to access it. This is despite the mountpoint having a plaintext > path, which should remain valid now that the key was added. > > Of course, this is only possible if there's a userspace race. Still, > the additional kernel-side race is confusing and unexpected. > > Close the kernel-side race by changing fscrypt_prepare_lookup() to also > set the on-disk filename (step 2b), consistent with the d_flags update. > > Fixes: 28b4c263961c ("ext4 crypto: revalidate dentry after adding or removing the key") > Signed-off-by: Eric Biggers Looks good, applied. - Ted