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

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Message-ID: <20201114105735.4e3bde7e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sat, 14 Nov 2020 10:57:35 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Georg Kohmann <geokohma@...co.com>
Cc:     netdev@...r.kernel.org, pablo@...filter.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 Wed, 11 Nov 2020 12:50:25 +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>

LGTM, awaiting ack from Pablo.