Re: [PATCH v2 3/3] ovl: fix the parsing of empty string mount parameters

From: Christian Brauner <brauner@kernel.org>
To: Luis Henriques <lhenriques@suse.de>,
	 Miklos Szeredi <miklos@szeredi.hu>, Jan Kara <jack@suse.cz>
Cc: Theodore Ts'o <tytso@mit.edu>,
	 Andreas Dilger <adilger.kernel@dilger.ca>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	 Amir Goldstein <amir73il@gmail.com>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	 linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/3] ovl: fix the parsing of empty string mount parameters
Date: Fri, 22 Mar 2024 15:22:41 +0100	[thread overview]
Message-ID: <20240322-ortseinfahrt-gespeichert-9fc21a98aa39@brauner> (raw)
In-Reply-To: <87h6hbhhcj.fsf@brahms.olymp>

On Tue, Mar 12, 2024 at 10:31:08AM +0000, Luis Henriques wrote:
> Christian Brauner <brauner@kernel.org> writes:
> 
> > On Mon, Mar 11, 2024 at 03:39:39PM +0100, Miklos Szeredi wrote:
> >> On Mon, 11 Mar 2024 at 14:25, Christian Brauner <brauner@kernel.org> wrote:
> >> 
> >> > Yeah, so with that I do agree. But have you read my reply to the other
> >> > thread? I'd like to hear your thoughs on that. The problem is that
> >> > mount(8) currently does:
> >> >
> >> > fsconfig(3, FSCONFIG_SET_FLAG, "usrjquota", NULL, 0) = -1 EINVAL (Invalid argument)
> >> >
> >> > for both -o usrjquota and -o usrjquota=
> >> 
> >> For "-o usrjquota" this seems right.
> >> 
> >> For "-o usrjquota=" it doesn't.  Flags should never have that "=", so
> >> this seems buggy in more than one ways.
> >> 
> >> > So we need a clear contract with userspace or the in-kernel solution
> >> > proposed here. I see the following options:
> >> >
> >> > (1) Userspace must know that mount options such as "usrjquota" that can
> >> >     have no value must be specified as "usrjquota=" when passed to
> >> >     mount(8). This in turn means we need to tell Karel to update
> >> >     mount(8) to recognize this and infer from "usrjquota=" that it must
> >> >     be passed as FSCONFIG_SET_STRING.
> >> 
> >> Yes, this is what I'm thinking.  Of course this only works if there
> >> are no backward compatibility issues, if "-o usrjquota" worked in the
> >> past and some systems out there relied on this, then this is not
> >> sufficient.
> >
> > Ok, I spoke to Karel and filed:
> >
> > https://github.com/util-linux/util-linux/issues/2837

This is now merged as of today and backported to at least util-linux
2.40 which is the current release.
https://github.com/util-linux/util-linux/pull/2849

If your distros ship 2.39 and won't upgrade to 2.40 for a while it might
be worth cherry-picking that fix.