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

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Message-ID: <6a8e356c-cdb8-c535-b91f-4f5e2c793666@gmail.com>
Date:   Tue, 7 Feb 2023 18:50:41 +0100
From:   Zdenek Kabelac <zdenek.kabelac@...il.com>
To:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        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

Dne 07. 02. 23 v 17:19 Demi Marie Obenour napsal(a):
> 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.

lvm2 introduced 'protection' layer device - which keeps   -tpool opened and 
thus avoid possibility to use  i.e.  mkfs on thin-pool itself (as it requires 
exclusive open)

Zdenek