netdev - Re: [PATCH next v2 2/3] ipvlan: Process fragmented multicast frames correctly

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Date:	Fri, 01 May 2015 21:12:25 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	maheshb@...gle.com
Cc:	netdev@...r.kernel.org, edumazet@...gle.com, dcbw@...hat.com
Subject: Re: [PATCH next v2 2/3] ipvlan: Process fragmented multicast
 frames correctly

From: Mahesh Bandewar <maheshb@...gle.com>
Date: Wed, 29 Apr 2015 11:19:18 -0700

> Multicast processing in IPvlan was faulty as is. Eric Dumazet
> pointed out that fragmented packets won't be processed correctly
> unless defrag step is introduced.
> 
> This patch adds the defrag step before driver attempts to process
> multicast frame(s).
> 
> Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>

And now you are potentially modifying the geometry of packets that
traverse ipvlan devices.

I am sorry but I am going to put my foot down and not allow another
instance of this to happen again.  We already have this being done by
netfilter, and I consider it unacceptable as well as inefficient.

If a fragmented frame is going to be forwarded by us, defragmenting
and refragmenting may create a different outgoing packet stream than
what arrived.  If the outgoing interface's MTU can accomodate the
incoming frames, this kind of modification is absolutely forbidden.
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