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 B995AC77B7A for ; Wed, 7 Jun 2023 19:39:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231214AbjFGTjM (ORCPT ); Wed, 7 Jun 2023 15:39:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51718 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231161AbjFGTjI (ORCPT ); Wed, 7 Jun 2023 15:39:08 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 284AD1FFA; Wed, 7 Jun 2023 12:39:07 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id AB12F61638; Wed, 7 Jun 2023 19:39:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 62FA4C433D2; Wed, 7 Jun 2023 19:39:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686166746; bh=lJeVIY8wRq/hgKma1+bBxZkFcZZ5cDlDkWbOyNaXnvc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Xz4QBOE+GgOXGoIFplwIU3a6LHqreR0Xv5BE+kO/1uA1Rf+jVP/UA6h33xPRokanN mbZnvfTuqd94S5u8WhzI7Er5R69VI+hhEry+yLmvtlpyvOiVvjYciPdXekoJfBsXsO xoUOxxam6HMvk3vLSJTxOjk7qZ8ce+35EcCcHnD5Yx8UMxNjFQTAImfqBbbWPA0Hfa uD8PM9rE6HhE1jyzsMi6ucAUZZ5oaJihxDVUk+/U0OmJMsJQzpXtl5NibPAbVF7mW5 UHNyEIJ69TiOrCWJTBPrLaMODZT8jzF5HVMPdRoyhr2dB5enllvlPMzkhlF8YP2yva WpDe4GTMX6jZA== Date: Wed, 7 Jun 2023 21:39:01 +0200 From: Christian Brauner To: Thomas =?utf-8?Q?Wei=C3=9Fschuh?= 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: <20230607-rennpferd-stechen-2f645ac78fcc@brauner> References: <20230607-fs-empty-option-v1-1-20c8dbf4671b@weissschuh.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230607-fs-empty-option-v1-1-20c8dbf4671b@weissschuh.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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") and misses a: Cc: stable@vger.kernel.org I'll fix this up for you though.