netdev - Re: [PATCH net v4] ipv6/netfilter: Discard first fragment not including all headers

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Date:   Mon, 16 Nov 2020 10:16:28 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Georg Kohmann <geokohma@...co.com>, netdev@...r.kernel.org,
        kadlec@...filter.org, fw@...len.de, davem@...emloft.net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org
Subject: Re: [PATCH net v4] ipv6/netfilter: Discard first fragment not
 including all headers

On Sun, 15 Nov 2020 12:15:20 +0100 Pablo Neira Ayuso wrote:
> On Wed, Nov 11, 2020 at 12:50:25PM +0100, Georg Kohmann wrote:
> > Packets are processed even though the first fragment don't include all
> > headers through the upper layer header. This breaks TAHI IPv6 Core
> > Conformance Test v6LC.1.3.6.
> > 
> > Referring to RFC8200 SECTION 4.5: "If the first fragment does not include
> > all headers through an Upper-Layer header, then that fragment should be
> > discarded and an ICMP Parameter Problem, Code 3, message should be sent to
> > the source of the fragment, with the Pointer field set to zero."
> > 
> > The fragment needs to be validated the same way it is done in
> > commit 2efdaaaf883a ("IPv6: reply ICMP error if the first fragment don't
> > include all headers") for ipv6. Wrap the validation into a common function,
> > ipv6_frag_thdr_truncated() to check for truncation in the upper layer
> > header. This validation does not fullfill all aspects of RFC 8200,
> > section 4.5, but is at the moment sufficient to pass mentioned TAHI test.
> > 
> > In netfilter, utilize the fragment offset returned by find_prev_fhdr() to
> > let ipv6_frag_thdr_truncated() start it's traverse from the fragment
> > header.
> > 
> > Return 0 to drop the fragment in the netfilter. This is the same behaviour
> > as used on other protocol errors in this function, e.g. when
> > nf_ct_frag6_queue() returns -EPROTO. The Fragment will later be picked up
> > by ipv6_frag_rcv() in reassembly.c. ipv6_frag_rcv() will then send an
> > appropriate ICMP Parameter Problem message back to the source.
> > 
> > References commit 2efdaaaf883a ("IPv6: reply ICMP error if the first
> > fragment don't include all headers")
> > 
> > Signed-off-by: Georg Kohmann <geokohma@...co.com>  
> 
> Acked-by: Pablo Neira Ayuso <pablo@...filter.org>

Applied, thanks!