linux-kernel - Re: [dm-devel] [PATCH 1/2] Fail I/O to thin pool devices

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Date:   Tue, 7 Feb 2023 11:19:19 -0500
From:   Demi Marie Obenour <demi@...isiblethingslab.com>
To:     Joe Thornber <thornber@...hat.com>
Cc:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>, linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] [PATCH 1/2] Fail I/O to thin pool devices

On Tue, Feb 07, 2023 at 03:02:51PM +0000, Joe Thornber wrote:
> Nack.
> 
> I don't see the security issue; how is this any different from running the
> thin tools on any incorrect device?  Or even the data device that the pool
> is mirroring.

I special-cased the pool device for two reasons:

1. I have run the thin tools on the pool device myself before realising
   that they needed to be run on the metadata device.  It took me a
   while to realize that I was using the wrong device.  I have not made
   that mistake with other devices, which is why I special-cased the
   pool device in this patch.

2. Doing I/O to the pool device is pointless.  The pool device is
   strictly slower than the data device and exposes the exact same
   contents, so accessing the pool device directly is never what one
   wants.

If there are backwards compatibility concerns, I could make this be
controlled by a Kconfig option, module parameter, or both.

> In general the thin tools don't modify the metadata they're
> running on.  If you know of a security issue with the thin tools please let
> me know.

I am not aware of a concrete security problem, but in general I prefer
not to expose unnecessary attack surface.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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