netdev - Re: [PATCH] net: fix duplicate logs of iptables TRACE target

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Date:   Mon, 24 Jan 2022 08:21:11 +0100
From:   Florian Westphal <fw@...len.de>
To:     kai zhang <zhangkaiheb@....com>
Cc:     pablo@...filter.org, kadlec@...filter.org, fw@...len.de,
        davem@...emloft.net, yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        kuba@...nel.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: fix duplicate logs of iptables TRACE target

kai zhang <zhangkaiheb@....com> wrote:
> Below configuration, mangle,filter and security tables have no rule:
> 
> There are 5 logs for incoming ssh packet:
> 
> kernel: [ 7018.727278] TRACE: raw:PREROUTING:policy:2 IN=enp9s0 ...
> kernel: [ 7018.727304] TRACE: mangle:PREROUTING:policy:1 IN=enp9s0 ...
> kernel: [ 7018.727327] TRACE: mangle:INPUT:policy:1 IN=enp9s0 ...
> kernel: [ 7018.727343] TRACE: filter:INPUT:policy:1 IN=enp9s0 ...
> kernel: [ 7018.727359] TRACE: security:INPUT:policy:1 IN=enp9s0 ...

Thats correct and exactly whats supposed to happen.

>  #if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE)
>  		/* The packet is traced: log it */
> -		if (unlikely(skb->nf_trace))
> +		if (unlikely(skb->nf_trace)) {
>  			trace_packet(state->net, skb, hook, state->in,
>  				     state->out, table->name, private, e);
> +			nf_reset_trace(skb);
> +		}

This breaks the long established behavior of TRACE,
we don't want users to have to TRACE tables individually which may also
be hard when nat is involved.