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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 172BAC433E0 for ; Fri, 3 Jul 2020 19:21:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EC0E720884 for ; Fri, 3 Jul 2020 19:21:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593804062; bh=PEmsm7KiYhEynj7JM9OkcWwJJEMC5FTZ1MgB7GC3/kw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=S6SH/Gxf6Hxjn4HyCvGY74zqEHG6CFmoISqbyC2so5n9PAl3DAsipZq4S3Md6peFk isiphBbt5a1CNk387bFZ8CNUqE2ovSXuaf39kDn03RWNJSc18TfHUVkhfkltYPGrFi 83OiBRn91Wgk2QOJx8UbCp9V/r0FF4bH9dPTB5jY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726721AbgGCTU6 (ORCPT ); Fri, 3 Jul 2020 15:20:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:49142 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726147AbgGCTU5 (ORCPT ); Fri, 3 Jul 2020 15:20:57 -0400 Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EB37F207FF; Fri, 3 Jul 2020 19:20:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1593804057; bh=PEmsm7KiYhEynj7JM9OkcWwJJEMC5FTZ1MgB7GC3/kw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cZz3+cYtChLGxVGtGhI0iqF8NG4vRe7SyHyKP6rwlrniscYuLOgqOM9tC5bBvh6V9 rCNuVMRKKdD1/I05cjOph+0nERO2OeeH/Y1QSjn/3szq+YCjsBxWz49TxA/V8HiT6F N6pBBTbIdf7MhFFMTY1BRtmYQCvTyvOSvJ4M/pzg= Date: Fri, 3 Jul 2020 12:20:55 -0700 From: Eric Biggers To: Daniel Rosenberg Cc: Theodore Ts'o , linux-ext4@vger.kernel.org, Jaegeuk Kim , Chao Yu , linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, Alexander Viro , Richard Weinberger , linux-mtd@lists.infradead.org, Andreas Dilger , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Gabriel Krisman Bertazi , kernel-team@android.com Subject: Re: [PATCH v9 2/4] fs: Add standard casefolding support Message-ID: <20200703192055.GA2825@sol.localdomain> References: <20200624043341.33364-1-drosen@google.com> <20200624043341.33364-3-drosen@google.com> <20200624055707.GG844@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Jul 02, 2020 at 06:01:37PM -0700, Daniel Rosenberg wrote: > On Tue, Jun 23, 2020 at 10:57 PM Eric Biggers wrote: > > > > Note that the '!IS_ENCRYPTED(dir) || fscrypt_has_encryption_key(dir)' check can > > be racy, because a process can be looking up a no-key token in a directory while > > concurrently another process initializes the directory's ->i_crypt_info, causing > > fscrypt_has_encryption_key(dir) to suddenly start returning true. > > > > In my rework of filename handling in f2fs, I actually ended up removing all > > calls to needs_casefold(), thus avoiding this race. f2fs now decides whether > > the name is going to need casefolding early on, in __f2fs_setup_filename(), > > where it knows in a race-free way whether the filename is a no-key token or not. > > > > Perhaps ext4 should work the same way? It did look like there would be some > > extra complexity due to how the ext4 directory hashing works in comparison to > > f2fs's, but I haven't had a chance to properly investigate it. > > > > - Eric > > Hm. I think I should be able to just check for DCACHE_ENCRYPTED_NAME > in the dentry here, right? I'm just trying to avoid casefolding the > no-key token, and that flag should indicate that. Ideally yes, but currently the 'struct dentry' isn't always available. See how fscrypt_setup_filename(), f2fs_setup_filename(), f2fs_find_entry(), ext4_find_entry(), etc. take a 'struct qstr', not a 'struct dentry'. At some point we should fix that by passing down the dentry whenever it's available, so that we reliably know whether the name is a no-key name or not. So even my new f2fs code is still racy. But it at least handles each filename in a consistent way within each directory operation. In comparison, your proposed ext4 code can treat a filename as a no-key name while matching one dir_entry and then as a regular filename while matching the next. I think the f2fs way is more on the right track, both correctness-wise and efficiency-wise. - Eric