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

From: Pablo Neira Ayuso <[email-masked]>
Date: Mon, 24 Jan 2022 12:54:30 +0100

On Mon, Jan 24, 2022 at 05:37:32AM +0000, kai zhang wrote:
> Below configuration, mangle,filter and security tables have no rule:

Yes, but there are loaded in your iptables-legacy environment.
In iptables-nft this will not happen.

> # iptables -t raw -I PREROUTING 1 -p tcp --dport 22 -j TRACE
> # sysctl net.netfilter.nf_log.2=nf_log_ipv4
> 
> 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 ...

tracing was not designed to display every registered table/chain even
if it has not rules.

> Signed-off-by: kai zhang <[email-masked]>
> ---
>  net/ipv4/netfilter/ip_tables.c  | 4 +++-
>  net/ipv6/netfilter/ip6_tables.c | 4 +++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
> index 2ed7c58b4..5f0e6096e 100644
> --- a/net/ipv4/netfilter/ip_tables.c
> +++ b/net/ipv4/netfilter/ip_tables.c
> @@ -304,9 +304,11 @@ ipt_do_table(void *priv,
>  
>  #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);
> +		}
>  #endif
>  		/* Standard target? */
>  		if (!t->u.kernel.target->target) {
> diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
> index 2d816277f..ae842a835 100644
> --- a/net/ipv6/netfilter/ip6_tables.c
> +++ b/net/ipv6/netfilter/ip6_tables.c
> @@ -327,9 +327,11 @@ ip6t_do_table(void *priv, struct sk_buff *skb,
>  
>  #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);
> +		}
>  #endif
>  		/* Standard target? */
>  		if (!t->u.kernel.target->target) {
> -- 
> 2.30.2
>