netdev - Re: [PATCH net] ipv6: no CHECKSUM_PARTIAL on skbs with extension headers and recalc checksum during fragmentation

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Date:	Mon, 26 Oct 2015 10:49:06 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Tom Herbert <tom@...bertland.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Vlad Yasevich <vyasevich@...il.com>,
	Benjamin Coddington <bcodding@...hat.com>
Subject: Re: [PATCH net] ipv6: no CHECKSUM_PARTIAL on skbs with extension headers
 and recalc checksum during fragmentation

On Sun, Oct 25, 2015, at 14:32, Tom Herbert wrote:
> > Anyway, currently it is easy to generate broken checksums on the wire
> > and would like to solve that for net, we certainly can improve that in
> > net-next.
> >
> Hannes,
> 
> The IPv4 fragment code is very similar to IPv6 in that both will
> perform skb_checksum_help only in the slow_path, so it seems like
> skb_checksum_help should be called earlier before the fragments are
> generated in both cases. If we're not correctly setting checksum for
> packets that are fragmented that is an issue with the stack.

We already concluded that drivers do have this problem and not the stack
above ip6_fragment. The places I am aware of I fixed in this patch. Also
IPv4 to me seems unaffected, albeit one can certainly clean up the logic
in net-next.

Do you want to move the skb_checksum_help() check to the front of
ip_fragment in ipv4 now too?

My patch fixed the part above ip6_fragment (in ip6_append_data) and made
sure we don't send out packets with wrong checksums if we get to
ip6_fragment directly.

Bye,
Hannes
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