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Date:   Tue, 4 Jul 2023 15:40:35 +0200
From:   Christian Brauner <brauner@kernel.org>
To:     Jan Kara <jack@suse.cz>
Cc:     linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
        Christoph Hellwig <hch@infradead.org>,
        Jens Axboe <axboe@kernel.dk>, Kees Cook <keescook@google.com>,
        Ted Tso <tytso@mit.edu>,
        syzkaller <syzkaller@googlegroups.com>,
        Alexander Popov <alex.popov@linux.com>,
        Eric Biggers <ebiggers@google.com>, linux-xfs@vger.kernel.org,
        linux-btrfs@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH RFC 0/6 v2] block: Add config option to not allow writing
 to mounted devices
Message-ID: <20230704-holzrahmen-diebstahl-cd758ca7158e@brauner>
References: <20230704122727.17096-1-jack@suse.cz>
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On Tue, Jul 04, 2023 at 02:56:48PM +0200, Jan Kara wrote:
> Hello!
> 
> This is second version of the patches to add config option to not allow writing
> to mounted block devices. For motivation why this is interesting see patch 1/6.
> I've been testing the patches more extensively this time and I've found couple
> of things that get broken by disallowing writes to mounted block devices:
> 1) Bind mounts get broken because get_tree_bdev() / mount_bdev() first try to
>    claim the bdev before searching whether it is already mounted. Patch 6
>    reworks the mount code to avoid this problem.
> 2) btrfs mounting is likely having the same problem as 1). It should be fixable

It likely would. Note that I've got a series to port btrfs to the new
mount api that I sent out which changes btrfs mounting quite
significantly.