Re: [PATCH] block: Add config option to not allow writing to mounted devices

From: Christian Brauner <brauner@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Dmitry Vyukov <dvyukov@google.com>, Jan Kara <jack@suse.cz>,
	Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Ted Tso <tytso@mit.edu>,
	yebin <yebin@huaweicloud.com>,
	linux-fsdevel@vger.kernel.org,
	syzkaller <syzkaller@googlegroups.com>
Subject: Re: [PATCH] block: Add config option to not allow writing to mounted devices
Date: Wed, 14 Jun 2023 10:18:16 +0200	[thread overview]
Message-ID: <20230614-anstalt-gepfercht-affd490e6544@brauner> (raw)
In-Reply-To: <ZIlphqM9cpruwU6m@infradead.org>

On Wed, Jun 14, 2023 at 12:17:26AM -0700, Christoph Hellwig wrote:
> On Tue, Jun 13, 2023 at 08:09:14AM +0200, Dmitry Vyukov wrote:
> > I don't question there are use cases for the flag, but there are use
> > cases for the config as well.
> > 
> > Some distros may want a guarantee that this does not happen as it
> > compromises lockdown and kernel integrity (on par with unsigned module
> > loading).
> > For fuzzing systems it also may be hard to ensure fine-grained
> > argument constraints, it's much easier and more reliable to prohibit
> > it on config level.
> 
> I'm fine with a config option enforcing write blocking for any
> BLK_OPEN_EXCL open.  Maybe the way to it is to:
> 
>  a) have an option to prevent any writes to exclusive openers, including
>     a run-time version to enable it

I really would wish we don't make this runtime configurable. Build time
and boot time yes but toggling it at runtime makes this already a lot
less interesting.