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 874ABC7EE23 for ; Wed, 7 Jun 2023 19:44:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231370AbjFGTon (ORCPT ); Wed, 7 Jun 2023 15:44:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54296 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229454AbjFGTol (ORCPT ); Wed, 7 Jun 2023 15:44:41 -0400 Received: from todd.t-8ch.de (todd.t-8ch.de [159.69.126.157]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AE36C1FE0; Wed, 7 Jun 2023 12:44:39 -0700 (PDT) Date: Wed, 7 Jun 2023 21:44:35 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=t-8ch.de; s=mail; t=1686167076; bh=DHQuMlD6tuImvscO3wkh4mwa16D27WZo2cWB+OFKZfk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=L1XqR3DytaNGIKKsOZQJRNxbUQYt9DIOlmIft3RqxBCPH5rwk4xKu39CNTZNM6G82 AludZr5yuij/sjLthOcA1tAnwMyRaeX8chijmaNKdVkhDy8cnyFuI5bS/ksdJqjaVv /+NqyPpaOatDI68pY+Hj/5dRvI4RveUEKmtUPDKU= From: Thomas =?utf-8?Q?Wei=C3=9Fschuh?= To: Christian Brauner Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, David Howells , Karel Zak , stable@vger.kernel.org Subject: Re: [PATCH] fs: avoid empty option when generating legacy mount string Message-ID: References: <20230607-fs-empty-option-v1-1-20c8dbf4671b@weissschuh.net> <20230607-rennpferd-stechen-2f645ac78fcc@brauner> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230607-rennpferd-stechen-2f645ac78fcc@brauner> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023-06-07 21:39:01+0200, Christian Brauner wrote: > On Wed, Jun 07, 2023 at 07:28:48PM +0200, Thomas Weißschuh wrote: > > As each option string fragment is always prepended with a comma it would > > happen that the whole string always starts with a comma. > > This could be interpreted by filesystem drivers as an empty option and > > may produce errors. > > > > For example the NTFS driver from ntfs.ko behaves like this and fails when > > mounted via the new API. > > > > Link: https://github.com/util-linux/util-linux/issues/2298 > > Yeah, the old ntfs driver implements its own option parser. It > overwrites/splits at ',' returning '\0' and then trips over this. > > Contrast with e.g., ovl_next_op() which does the same thing but skips > over '\0' in ovl_parse_opt(). > > So arguably also a bug in ntfs parsing. But there's no reason we should > prepend ',' for legacy mount option strings. > > And yeah, I can easily verify this... > > Using my custom move-mount tool I originally wrote for another patchset > but which is handy to pass mount options via the new mount api _system_ > calls and not via mount(): > https://github.com/brauner/move-mount-beneath > > I can do: > > sudo ./move-mount -f overlay -olowerdir=/mnt/a:/mnt/b,upperdir=/mnt/upper,workdir=/mnt/work /mnt/merged > > and clearly see: > > > sudo bpftrace -e 'kfunc:legacy_get_tree { @m = args->fc; printf("%s\n", str(((struct legacy_fs_context *)@m->fs_private)->legacy_data)); }' > Attaching 1 probe... > ,lowerdir=/mnt/a:/mnt/b,upperdir=/mnt/upper,workdir=/mnt/work > > > Fixes: 3e1aeb00e6d1 ("vfs: Implement a filesystem superblock creation/configuration context") > > Should be: > > Fixes: commit 3e1aeb00e6d1 ("vfs: Implement a filesystem superblock creation/configuration context") AFAIK the Fixes: tag does not use the "commit" keyword. Only inline commit references. This is how it's currently documented in Documentation/process/submitting-patches.rst. > and misses a: > > Cc: stable@vger.kernel.org This was fixed in v2. > I'll fix this up for you though. Thanks! Thomas