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From: Luis Henriques <lhenriques@suse.de>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: "Theodore Ts'o" <tytso@mit.edu>,  Andreas Dilger
 <adilger.kernel@dilger.ca>,  Alexander Viro <viro@zeniv.linux.org.uk>,
  Christian Brauner <brauner@kernel.org>,  Jan Kara <jack@suse.cz>,  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
In-Reply-To: <CAJfpegtQSi0GFzUEDqdeOAq7BN2KvDV8i3oBFvPOCKfJJOBd2g@mail.gmail.com>
	(Miklos Szeredi's message of "Mon, 11 Mar 2024 10:25:20 +0100")
References: <20240307160225.23841-1-lhenriques@suse.de>
	<20240307160225.23841-4-lhenriques@suse.de>
	<CAJfpegtQSi0GFzUEDqdeOAq7BN2KvDV8i3oBFvPOCKfJJOBd2g@mail.gmail.com>
Date: Mon, 11 Mar 2024 10:34:49 +0000
Message-ID: <87le6p6oqe.fsf@suse.de>
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Miklos Szeredi <miklos@szeredi.hu> writes:

> On Thu, 7 Mar 2024 at 19:17, Luis Henriques <lhenriques@suse.de> wrote:
>>
>> This patch fixes the usage of mount parameters that are defined as strin=
gs
>> but which can be empty.  Currently, only 'lowerdir' parameter is in this
>> situation for overlayfs.  But since userspace can pass it in as 'flag'
>> type (when it doesn't have a value), the parsing will fail because a
>> 'string' type is assumed.
>
> I don't really get why allowing a flag value instead of an empty
> string value is fixing anything.
>
> It just makes the API more liberal, but for what gain?

The point is that userspace may be passing this parameter as a flag and
not as a string.  I came across this issue with ext4, by doing something
as simple as:

    mount -t ext4 -o usrjquota=3D /dev/sda1 /mnt/

(actually, the trigger was fstest ext4/053)

The above mount should succeed.  But it fails because 'usrjquota' is set
to a 'flag' type, not 'string'.

Note that I couldn't find a way to reproduce the same issue in overlayfs
with this 'lowerdir' parameter.  But looking at the code the issue is
similar.

Cheers,
--=20
Lu=C3=ADs