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From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Tom Herbert <tom@herbertland.com>
Cc: David Miller <davem@davemloft.net>,
	Network Development <netdev@vger.kernel.org>
Subject: Re: [PATCH net-next] flow_dissector: Add IPv6 flow label to symmetric keys
Date: Wed, 5 Aug 2020 10:26:37 +0200	[thread overview]
Message-ID: <CA+FuTSfw+XT9kQ4y-dY_M8zc2TksCSSEa-0WY+muyv_yr9_H=A@mail.gmail.com> (raw)
In-Reply-To: <20200804155642.52766-1-tom@herbertland.com>

On Tue, Aug 4, 2020 at 5:57 PM Tom Herbert <tom@herbertland.com> wrote:
>
> The definition for symmetric keys does not include the flow label so
> that when symmetric keys is used a non-zero IPv6 flow label is not
> extracted. Symmetric keys are used in functions to compute the flow
> hash for packets, and these functions also set "stop at flow label".
> The upshot is that for IPv6 packets with a non-zero flow label, hashes
> are only based on the address two tuple and there is no input entropy
> from transport layer information. This patch fixes this bug.

If this is a bug fix, it should probably target net and have a Fixes tag.

Should the actual fix be to remove the
FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL argument from
__skb_get_hash_symmetric?

The original commit mentions the symmetric key flow dissector to
compute a flat symmetric hash over only the protocol, addresses and
ports.

Autoflowlabel uses symmetric __get_hash_from_flowi6 to derive a flow
label, but this cannot be generally relied on. RFC 6437 suggests
even a PRNG as input, for instance.

  parent reply	other threads:[~2020-08-05  8:27 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-04 15:56 [PATCH net-next] flow_dissector: Add IPv6 flow label to symmetric keys Tom Herbert
2020-08-04 23:12 ` David Miller
2020-08-05  8:26 ` Willem de Bruijn [this message]
2020-08-17 14:44   ` Tom Herbert
2020-08-17 15:35     ` Willem de Bruijn

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