Re: [PATCH] tcp: sysctl to disable TCP simultaneous connect

[H. Peter Anvin]

On 02/07/2013 10:44 AM, Kees Cook wrote:
>>
>> This patch probably also breaks TCP STUNT that is used by some applications for NAT
>> traversal.
> 
> The patch would not break it -- it defaults the sysctl to staying enabled.
> 
> If you mean the documentation should be updated, sure, that's easy to do.
> 
> David: I know you aren't a fan of this patch, but I'd like to try to
> convince you. :) This leaves the feature enabled and add a toggle for
> systems (like Chrome OS) that don't want to risk this DoS at all.
> There are so very many other toggle, I don't see why this one would be
> a problem to add.
> 

It is not just STUNT, but in NAT-less configurations behind stateful
firewalls (which is expected to be the norm for IPv6), TCP rendezvous
via crossed SYN is a very effective way to establish peer-to-peer
connections.

	-hpa

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