netdev - ip6t_SYNPROXY crashes kernel

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Message-ID: <20150727222716.GG20951@orbit.nwl.cc>
Date:	Tue, 28 Jul 2015 00:27:16 +0200
From:	Phil Sutter <phil@....cc>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	pablo@...filter.org, netdev@...r.kernel.org
Subject: ip6t_SYNPROXY crashes kernel

Hi,

When synproxy_send_server_ack() calls synproxy_send_tcp(), it passes
NULL as third parameter (struct nf_conntrack *nfct). And the first thing
synproxy_send_tcp() does, is dereference it:

| struct net *net = nf_ct_net((struct nf_conn *)nfct);

I could not find a commit leading to this breakage in the commit log,
which makes me doubt ip6t_SYNPROXY has ever worked at all.

If you need one, I have a reproducer at hand. (Though I would want to
strip it down a bit first.) Just let me know.

Cheers, Phil
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