netdev - Re: [PATCH 2/2] net: fastopen: use endianness agnostic representation of the cookie

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Message-ID: <CAKv+Gu-xBCe09B1=GvXBH3V-p7=fOZcdL5pvFi5v19LT0J4KHA@mail.gmail.com>
Date:   Tue, 18 Jun 2019 20:40:18 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jason Baron <jbaron@...mai.com>,
        Christoph Paasch <cpaasch@...le.com>,
        David Laight <David.Laight@...lab.com>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH 2/2] net: fastopen: use endianness agnostic representation
 of the cookie

On Tue, 18 Jun 2019 at 20:22, Eric Biggers <ebiggers@...nel.org> wrote:
>
> On Tue, Jun 18, 2019 at 11:32:07AM +0200, Ard Biesheuvel wrote:
> > Use an explicit little endian representation of the fastopen
> > cookie, so that the value no longer depends on the endianness
> > of the system. This fixes a theoretical issue only, since
> > fastopen keys are unlikely to be shared across load balancing
> > server farms that are mixed in endiannes, but it might pop up
> > in validation/selftests as well, so let's just settle on little
> > endian across the board.
> >
> > Note that this change only affects big endian systems.
> >
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> > ---
> >  include/linux/tcp.h     |  2 +-
> >  net/ipv4/tcp_fastopen.c | 16 ++++++++--------
> >  2 files changed, 9 insertions(+), 9 deletions(-)
> >
>
> What about the TCP_FASTOPEN_KEY option for setsockopt and getsockopt?  Those
> APIs treat the key as an array of bytes (let's say it's little endian), so
> doesn't it need to be converted to/from the CPU endianness of siphash_key_t?
>

Yeah, good point.

Can we first agree on whether we care about this or not? If so, i can spin a v2.