linux-kernel - Re: [PATCH v4] add stealth mode

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Message-ID: <20150916110629.GP24810@breakpoint.cc>
Date:	Wed, 16 Sep 2015 13:06:29 +0200
From:	Florian Westphal <fw@...len.de>
To:	Matteo Croce <matteo@...nwrt.org>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] add stealth mode

Matteo Croce <matteo@...nwrt.org> wrote:
> Add option to disable any reply not related to a listening socket,
> like RST/ACK for TCP and ICMP Port-Unreachable for UDP.
> Also disables ICMP replies to echo request and timestamp.
> The stealth mode can be enabled selectively for a single interface.

I think it would make more sense to extend the socket match
in xtables if it can't be used to achive this already.

seems like
*filter
:INPUT ACCEPT [0:0]
-A INPUT -p tcp -m socket --nowildcard -j ACCEPT
-A INPUT -p tcp -j DROP
COMMIT

Already does what you want for tcp, udp should work too.
I'd much rather see xtables and/or nftables to be extended
with whatever feature(s) are needed to configure such a policy
rather than pushing this into the core network stack.
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