netdev - Re: [PATCH net] ipv6: tcp: drop silly ICMPv6 packet too big messages

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Date:   Wed, 7 Jul 2021 17:59:30 +0200
From:   Willy Tarreau <w@....eu>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Maciej Zenczykowski <maze@...gle.com>
Subject: Re: [PATCH net] ipv6: tcp: drop silly ICMPv6 packet too big messages

Hi Eric,

On Wed, Jul 07, 2021 at 08:46:30AM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> While TCP stack scales reasonably well, there is still one part that
> can be used to DDOS it.
> 
> IPv6 Packet too big messages have to lookup/insert a new route,
> and if abused by attackers, can easily put hosts under high stress,
> with many cpus contending on a spinlock while one is stuck in fib6_run_gc()

Just thinking loud, wouldn't it make sense to support randomly dropping
such packets on input (or even better rate-limit them) ? After all, if
a host on the net feels like it will need to send one, it will surely
need to send a few more until one is taken into account so it's not
dramatic. And this could help significantly reduce their processing cost.

Willy