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Date:   Wed, 14 Jun 2023 00:17:26 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     Christoph Hellwig <hch@infradead.org>, 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
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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
 b) allow to also block writes without that option.  And maybe an
    opt-in to allow writes might be the better way than doing it
    the other way around.