netdev - Re: [PATCH net-next 0/5] tcp: Introduce a TFO key-pool for clean cookie-rotation

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Date:   Sun, 16 Dec 2018 12:19:52 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     cpaasch@...le.com
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, ycheng@...gle.com
Subject: Re: [PATCH net-next 0/5] tcp: Introduce a TFO key-pool for clean
 cookie-rotation

From: Christoph Paasch <cpaasch@...le.com>
Date: Fri, 14 Dec 2018 14:40:02 -0800

> Currently, TFO only allows a single TFO-secret. This means that whenever
> the secret gets changed for key-rotation purposes, all the previously
> issued TFO-cookies become invalid. This means that clients will fallback
> to "regular" TCP, incurring a cost of one additional round-trip.
> 
> This patchset introduces a TFO key-pool that allows to more gracefully
> change the key. The size of the pool is 2 (this could be changed in the
> future through a sysctl if needed). When a client connects with an "old"
> TFO cookie, the server will now accept the data in the SYN and at the
> same time announce a new TFO-cookie to the client.
> 
> We have seen a significant reduction of LINUX_MIB_TCPFASTOPENPASSIVEFAIL
> thanks to these patches. Invalid cookies are now solely observed when
> clients behind a NAT are getting a new public IP.

Yuchung and Eric, please review.