netdev - Re: [PATCH net] net: ipv4: do not handle duplicate fragments as overlapping

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Date:   Wed, 12 Dec 2018 21:42:23 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     mkubecek@...e.cz
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        posk@...gle.com, eric.dumazet@...il.com, gfigueira@...e.com
Subject: Re: [PATCH net] net: ipv4: do not handle duplicate fragments as
 overlapping

From: Michal Kubecek <mkubecek@...e.cz>
Date: Thu, 13 Dec 2018 03:28:00 +0100 (CET)

> Since commit 7969e5c40dfd ("ip: discard IPv4 datagrams with overlapping
> segments.") IPv4 reassembly code drops the whole queue whenever an
> overlapping fragment is received. However, the test is written in a way
> which detects duplicate fragments as overlapping so that in environments
> with many duplicate packets, fragmented packets may be undeliverable.
> 
> Add an extra test and for (potentially) duplicate fragment, only drop the
> new fragment rather than the whole queue. Only starting offset and length
> are checked, not the contents of the fragments as that would be too
> expensive.  Check for duplicity with last (tail) fragment first as in real
> life scenarios this should be the most frequent case and we would have to
> iterate through the whole "run" otherwise.
> 
> Fixes: 7969e5c40dfd ("ip: discard IPv4 datagrams with overlapping segments.")
> Signed-off-by: Michal Kubecek <mkubecek@...e.cz>

I'll give Eric a chance to review this, thanks Michal.