Subject: Re: [PATCH v2 net-next 2/2] sit: add support of x-netns

From: Nicolas Dichtel <[email-masked]>
Date: Wed, 26 Jun 2013 15:49:07 +0200

Le 26/06/2013 01:56, David Miller a écrit :
> From: Nicolas Dichtel <[email-masked]>
> Date: Tue, 25 Jun 2013 16:24:55 +0200
>
>> @@ -453,6 +454,8 @@ int ip_tunnel_rcv(struct ip_tunnel *tunnel, struct sk_buff *skb,
>>   	tstats->rx_bytes += skb->len;
>>   	u64_stats_update_end(&tstats->syncp);
>>
>> +	skb_scrub_packet(skb);
>> +
>>   	if (tunnel->dev->type == ARPHRD_ETHER) {
>>   		skb->protocol = eth_type_trans(skb, tunnel->dev);
>>   		skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
>
> I can't see how this can be ok.
>
> If something in netfilter depends upon the state you are clearing out
> here, someone's packet filtering setup is going to break.
Just for the record, note that nf_reset() is already called in 
iptunnel_pull_header() and iptunnel_xmit().
Hence 4in4 (ipip and sit) and gre tunnels are already reseting netfilter state.
6in4 (sit) do it only in xmit path and Xin6 (ip6_tunnel) never.

We can also notice that nf_reset() was added by the commit 3d7b46cd20e3 
"ip_tunnel: push generic protocol handling to ip_tunnel module." (net-next only) 
in rx path.

The nf_reset() of xmit path of 4in4 (ipip) is here for years (at least 2.6.12).
For gre, it has been added by c54419321455 "GRE: Refactor GRE tunneling code." 
(v3.10-rc1).

It seems that the code is different depending of the type of the tunnel. If we 
omit skb_orphan() (and maybe another one?, to be done only when changing 
namespace), it can be good to have a common function to have the same behavior 
for each tunnel.

Maybe something like:
void skb_scrub_packet(bool netnschange)
{
	if (netnschange)
	        skb_orphan(skb);
         skb->tstamp.tv64 = 0;
         skb->pkt_type = PACKET_HOST;
         skb->skb_iif = 0;
         skb_dst_drop(skb);
         skb->mark = 0;
         secpath_reset(skb);
         nf_reset(skb);
         nf_reset_trace(skb);
}

What's your opinion?