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Date:   Sat, 20 Aug 2022 21:21:59 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Balazs Scheidler <bazsi77@gmail.com>
Cc:     Florian Westphal <fw@strlen.de>,
        netfilter-devel <netfilter-devel@vger.kernel.org>,
        Shell Chen <xierch@gmail.com>
Subject: Re: [PATCH nf] nefilter: nft_tproxy: restrict to prerouting hook
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Balazs Scheidler <bazsi77@gmail.com> wrote:
> I think this is not correct. TPROXY can be used from output as well to
> divert locally generated traffic. I didn't look into the output null
> reference case posted earlier but that's also a use case to redirect local
> output to a proxy.

Are you sure?

The upstreamed TPROXY doesn't support this.
xt_TPROXY sets:
  .hooks          = 1 << NF_INET_PRE_ROUTING,

and the backend code assumes that the inout device in the hook state is
available, which is only guaranteed in prerouting and input hooks.