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=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 8A3B0C433DF for ; Fri, 3 Jul 2020 19:23:48 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5BA76207FF for ; Fri, 3 Jul 2020 19:23:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="yoiqnMcc"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="cZz3+cYt" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5BA76207FF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=HTUTwGLVX9RB2Q0mjoJq22oq1mqHr7jQ087AKlkv4UE=; b=yoiqnMccnHqIYKj6HIuP/Lllh cy9qEmM2lKIYQocCtmJ68kflQcaFyC6XlQGzktM2oiDIrG6L4axdC9JCN71kZmFw71eQI/lVAAIAm OebiHtYJH304v386h0p8gMyJGOBvWENucF46YTVjhexCvTvykID4MLrqhMVtb6wtA97jNsIZJhys+ m6Moqk9wCzG6FFzegEm1tQ/W7r0i8mIPkKb84hd+LevAkOZPrI52ZBj0bBlRNuB4yJgiAeWq/Wngk 3wowoJG5zFXRkMYy8363QOO60dJkqj2MIRS4SzpTqzcEqEI0KYPcB2JnwxgVJvuiZ2seqbYNcv0bA tCr6nn+xA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jrRF8-0003RV-RY; Fri, 03 Jul 2020 19:21:02 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jrRF5-0003Qx-Lf for linux-mtd@lists.infradead.org; Fri, 03 Jul 2020 19:21:00 +0000 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 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-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200703_152059_794934_87F504BC X-CRM114-Status: GOOD ( 23.20 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kernel-team@android.com, Theodore Ts'o , Jonathan Corbet , Richard Weinberger , Andreas Dilger , Chao Yu , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fscrypt@vger.kernel.org, linux-mtd@lists.infradead.org, Alexander Viro , linux-fsdevel@vger.kernel.org, Jaegeuk Kim , linux-ext4@vger.kernel.org, Gabriel Krisman Bertazi Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.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 ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/