netdev - Re: [PATCH RFC v1 2/3] ipv6: move from sha1 to blake2s in address calculation

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Date:   Thu, 13 Jan 2022 14:50:28 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" 
        <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Erik Kline <ek@...gle.com>,
        Fernando Gont <fgont@...networks.com>,
        Lorenzo Colitti <lorenzo@...gle.com>,
        YOSHIFUJI Hideaki <hideaki.yoshifuji@...aclelinux.com>
Subject: Re: [PATCH RFC v1 2/3] ipv6: move from sha1 to blake2s in address calculation

On Thu, 13 Jan 2022 at 14:46, Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> Hi Toke,
>
> On Thu, Jan 13, 2022 at 2:30 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
> > Right, but that implies we need to work on a transition mechanism. For
> > newly deployed systems changing the hash is obviously fine, it's the
> > "reboot and you have a new address" problem.
> >
> > We could introduce new values to the addr_gen_mode? I.e. values of 4 and
> > 5 would be equivalent to 2 and 3 (respectively), but with the new
> > hashing algorithm? And then document that 2 and 3 are considered
> > deprecated to be removed at some point in the future...
>
> Right, so this is exactly the flow of conversation I anticipated.
> "Let's change it!" "No, we can't." "Okay, let's add a knob."
>
> The knob I was thinking about, though, was actually a compile-time one
> CONFIG_NET_OBSOLETE_INSECURE_ADDRCONF_HASH, which itself is a `depends
> on CONFIG_OLD_N_CRUSTY` or something. This way we could gate the
> inclusion of sha1.c/sha1.o on that at compile time, and shave down
> vmlinux a bit, which would make Geert happy.
>
> Then, at some point down the road, we can talk about removing
> CONFIG_NET_OBSOLETE_INSECURE_ADDRCONF_HASH too.
>

What is the point of having CONFIG_OLD_N_CRUSTY if all distros are
going to enable it indefinitely?