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Date:   Tue, 3 May 2022 14:33:39 +0200
From:   Lennart Poettering <mzxreary@0pointer.de>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Alexander Graf <graf@amazon.com>, linux-kernel@vger.kernel.org,
        linux-crypto@vger.kernel.org,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Colm MacCarthaigh <colmmacc@amazon.com>,
        Torben Hansen <htorben@amazon.co.uk>,
        Jann Horn <jannh@google.com>
Subject: Re: [PATCH 2/2] random: add fork_event sysctl for polling VM forks
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On Di, 03.05.22 13:55, Jason A. Donenfeld (Jason@zx2c4.com) wrote:

> I'm still not convinced there's value in having a counter or a UUID, but
> if you had to choose, would you prefer a counter or a UUID? It sounds
> like the former, because you see a use for distinguishing between zero
> and non-zero? Or did you finally agree with me that vmgenid isn't
> granular enough for that?

I would prefer a monotonic counter, since it allows answering
questions like the following:

1. Did this image get cloned at all? (i.e. counter != 0; usecase as per the MAC address
   discussion)

2. Did the image get cloned since the last time I looked? (i.e. counter
   != my_previously_saved_counter; usecase: detect clones in an "offline"
   fashion, i.e. from a component that doesn't continously run, but
   only from time to time)

3. How many clones did I miss? (i.e. missed_clones =
   my_previously_saved_counter - counter; usecase: catch up with
   generating proxy D-Bus signal messages for clones).

There might be more.

Using a UUID would not give us #1 or #3. It would deliver #2 however.

Lennart

--
Lennart Poettering, Berlin