netdev - Re: [PATCHv4 net 2/2] IPv6: reply ICMP error if the first fragment don't include all headers

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Date:   Mon, 26 Oct 2020 20:55:19 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     "Georg Kohmann (geokohma)" <geokohma@...co.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCHv4 net 2/2] IPv6: reply ICMP error if the first fragment
 don't include all headers

On Mon, Oct 26, 2020 at 08:09:21AM +0000, Georg Kohmann (geokohma) wrote:
> > +	nexthdr = hdr->nexthdr;
> > +	offset = ipv6_skip_exthdr(skb, skb_transport_offset(skb), &nexthdr, &frag_off);
> > +	if (offset < 0)
> > +		goto fail_hdr;
> > +
> > +	/* Check some common protocols' header */
> > +	if (nexthdr == IPPROTO_TCP)
> > +		offset += sizeof(struct tcphdr);
> > +	else if (nexthdr == IPPROTO_UDP)
> > +		offset += sizeof(struct udphdr);
> > +	else if (nexthdr == IPPROTO_ICMPV6)
> > +		offset += sizeof(struct icmp6hdr);
> > +	else
> > +		offset += 1;
> 
> Maybe also check the special case IPPROTO_NONE?

IPPROTO_NONE defines the same with NEXTHDR_NONE. So ipv6_skip_exthdr() will
return -1, and we will goto fail_hdr and send ICMP parameter error message.

The question is if it's OK to reply a ICMP error for fragment + IPPROTO_NONE
packet? For pure IPPROTO_NONE message, we should drop silently, but what about
fragment message?

> > +
> > +	if (frag_off == htons(IP6_MF) && offset > skb->len) {
> > +		__IP6_INC_STATS(net, __in6_dev_get_safely(skb->dev), IPSTATS_MIB_INHDRERRORS);
> > +		icmpv6_param_prob(skb, ICMPV6_HDR_INCOMP, 0);
> > +		return -1;
> > +	}
> > +
> >  	iif = skb->dev ? skb->dev->ifindex : 0;
> >  	fq = fq_find(net, fhdr->identification, hdr, iif);
> >  	if (fq) {
> 
> Are you planning to also add this fix for the fragmentation handling in the netfilter?
> 
I have no plan to fix this on netfilter as netfilter is a module.
It may have different behavior during defragment.

Thanks
Hangbin