netdev - Re: Missing INET6_PROTO_FINAL in l2tp_ip6

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Date:	Mon, 23 May 2016 13:05:50 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Shmulik Ladkani <shmulik.ladkani@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Missing INET6_PROTO_FINAL in l2tp_ip6_protocol?

On 21.05.2016 22:02, Shmulik Ladkani wrote:
> On Sat, 21 May 2016 17:55:59 +0200 Hannes Frederic Sowa <hannes@...essinduktion.org> wrote:
>> On 21.05.2016 14:50, Shmulik Ladkani wrote:
>>> Hi,
>>>
>>> inet6_protocol's INET6_PROTO_FINAL flag denotes handler is expected not
>>> to request resubmission for local delivery.
>>>
>>> For an INET6_PROTO_FINAL handler, the following actions gets executed
>>> prior delivery, in ip6_input_finish:
>>>
>>> 			nf_reset(skb);
>>>
>>> 			skb_postpull_rcsum(skb, skb_network_header(skb),
>>> 					   skb_network_header_len(skb));
>>>
>>> For some reason, l2tp_ip6_protocol handler is NOT marked as
>>> INET6_PROTO_FINAL. Probably an oversight.
>>>
>>> Since 'l2tp_ip6_recv' never results in a resubmission, the above actions
>>> are not applied to skbs passed to l2tp_ip6.
>>>
>>> Any reason why l2tp_ip6_protocol should NOT be marked INET6_PROTO_FINAL?  
>>
>> I don't see any specific reason why it shouldn't be a INET6_PROTO_FINAL.
>> Anyway, receive path of L2TPv3 without UDP encapsulation doesn't deal
>> with checksums anyway, as far as I know.
>>
>>> What's the consequences not executing the above actions for l2tp_ip6
>>> packets?  
>>
>> Probably not a whole lot in this case.
> 
> OK, so the skb_postpull_rcsum is irrelevant for IPPROTO_L2TP over ipv6.
> 
> However, one more thing WRT to INET6_PROTO_FINAL not being set - we're
> also missing the multicast filtering of 'ip6_input_finish':
> 
> 			if (ipv6_addr_is_multicast(&hdr->daddr) &&
> 			    !ipv6_chk_mcast_addr(skb->dev, &hdr->daddr,
> 			    &hdr->saddr) &&
> 			    !ipv6_is_mld(skb, nexthdr, skb_network_header_len(skb)))
> 				goto discard;
> 
> I assume no reason to allow multicast daddr which aren't in the mc_list
> (or saddr excluded) to pass up into 'l2tp_ip6_recv'?
> 

Good point, seems we would benefit of the addition of the PROTO_FINAL
flag. Could you test and send a patch?

Thanks,
Hannes