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

[Jason A. Donenfeld]

Hi Toke,

On Thu, Jan 13, 2022 at 2:30 PM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> 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.

Jason