netdev - Re: [PATCH net v3] ipv4: allow local fragmentation in ip_finish_output

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Date:   Fri, 4 Nov 2016 11:40:14 +0200
From:   Shmulik Ladkani <shmulik.ladkani@...il.com>
To:     Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:     Lance Richardson <lrichard@...hat.com>, fw@...len.de,
        netdev@...r.kernel.org, jtluka@...hat.com
Subject: Re: [PATCH net v3] ipv4: allow local fragmentation in
 ip_finish_output_gso()

On Thu, 3 Nov 2016 22:34:34 +0100 Hannes Frederic Sowa <hannes@...essinduktion.org> wrote:
> Correct, but we should maybe redefine the code a bit. From my
> understanding we can now create an ICMP storm in case every fragment gets.

Yes, you are right.

Each segment gets into ip_fragment, and due to outer DF being set,
ICMP_FRAG_NEEDED is sent per segment.

BTW, suppose GRO is off, and sender actually did send a burst of
(non-gso) packets with outer DF set, and each was tunnel encapsulated,
resulting in oversized frames.

Would'nt the stack just send the ICMP_FRAG_NEEDED per encapsulated
frame?

If so, then the GRO behaviour is aligned, and there's nothing to fix.

Best,
Shmulik