netdev - Re: [PATCH net-next v2 3/3] sctp: Convert cookie authentication to use HMAC-SHA256

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Message-ID: <CADvbK_fmCRARc8VznH8cQa-QKaCOQZ6yFbF=1-VDK=zRqv_cXw@mail.gmail.com>
Date: Sat, 16 Aug 2025 13:15:12 -0400
From: Xin Long <lucien.xin@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Eric Biggers <ebiggers@...nel.org>, Paolo Abeni <pabeni@...hat.com>, linux-sctp@...r.kernel.org, 
	netdev@...r.kernel.org, Marcelo Ricardo Leitner <marcelo.leitner@...il.com>, 
	linux-crypto@...r.kernel.org
Subject: Re: [PATCH net-next v2 3/3] sctp: Convert cookie authentication to
 use HMAC-SHA256

On Fri, Aug 15, 2025 at 9:06 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Fri, 15 Aug 2025 14:50:09 -0700 Eric Biggers wrote:
> > > > It'd be great to get an ack / review from SCTP maintainers, otherwise
> > > > we'll apply by Monday..
> > > Other than that, LGTM.
> > > Sorry for the late reply, I was running some SCTP-auth related tests
> > > against the patchset.
> >
> > Ideally we'd just fail the write and remove the last mentions of md5 and
> > sha1 from the code.  But I'm concerned there could be a case where
> > userspace is enabling cookie authentication by setting
> > cookie_hmac_alg=md5 or cookie_hmac_alg=sha1, and by just failing the
> > write the system would end up with cookie authentication not enabled.
> >
> > It would have been nice if this sysctl had just been a boolean toggle.
> >
> > A deprecation warning might be a good idea.  How about the following on
> > top of this patch:
>
> No strong opinion but I find the deprecation warnings futile.
> Chances are we'll be printing this until the end of time.
> Either someone hard-cares and we'll need to revert, or nobody
> does and we can deprecate today.
Reviewing past network sysctl changes, several commits have simply
removed or renamed parameters:

4a7f60094411 ("tcp: remove thin_dupack feature")
4396e46187ca ("tcp: remove tcp_tw_recycle")
d8b81175e412 ("tcp: remove sk_{tr}x_skb_cache")
3e0b8f529c10 ("net/ipv6: Expand and rename accept_unsolicited_na to
accept_untracked_na")
5027d54a9c30 ("net: change accept_ra_min_rtr_lft to affect all RA lifetimes")

It seems to me that if we deprecate something, it's okay to change the
sysctls, so I would prefer rejecting writes with md5 or sha1, or even
better following Eric’s suggestion and turn this into a simple boolean
toggle.

Thanks.