netdev - Re: [PATCH net-next 1/2] tcp: remove per-destination timestamp cache

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Message-ID: <20170315225726.GA28498@breakpoint.cc>
Date:   Wed, 15 Mar 2017 23:57:26 +0100
From:   Florian Westphal <fw@...len.de>
To:     David Miller <davem@...emloft.net>
Cc:     soheil.kdev@...il.com, netdev@...r.kernel.org, soheil@...gle.com,
        edumazet@...gle.com, ncardwell@...gle.com, ycheng@...gle.com,
        lvml@....de, fw@...len.de
Subject: Re: [PATCH net-next 1/2] tcp: remove per-destination timestamp cache

David Miller <davem@...emloft.net> wrote:
> From: Soheil Hassas Yeganeh <soheil.kdev@...il.com>
> Date: Wed, 15 Mar 2017 16:30:45 -0400
> 
> > Note that this cache was already broken for caching timestamps of
> > multiple machines behind a NAT sharing the same address.
> 
> That's the documented, well established, limitation of time-wait
> recycling.

Sigh.

"don't enable this if you connect your machine to the internet".
We're not in the 1990s anymore.  Even I am behind ipv4 CG-NAT nowadays.

So I disagree and would remove this thing.

> This limitation of the feature does not give us a reason to break the
> feature even further as a matter of convenience, or to remove it
> altogether for the same reason.
> 
> Please, instead, fix the bug that was introduced.

AFAIU we only have two alternatives, removal of the randomization feature
or switch to a offset computed via hash(saddr, daddr, secret).

Unless there are more comments I'll look into doing the latter tomorrow.