netdev - Re: [PATCH net-next] ipv4: introduce hardened ip_no_pmtu

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Message-ID: <20131231054430.GD27636@order.stressinduktion.org>
Date:	Tue, 31 Dec 2013 06:44:30 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ipv4: introduce hardened ip_no_pmtu_disc mode

On Tue, Dec 31, 2013 at 12:37:11AM -0500, David Miller wrote:
> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Date: Sat, 21 Dec 2013 01:10:54 +0100
> 
> > This new ip_no_pmtu_disc mode only allowes fragmentation-needed errors
> > to be honored by protocols which do more stringent validation on the
> > ICMP's packet payload. This knob is useful for people who e.g. want to
> > run an unmodified DNS server in a namespace where they need to use pmtu
> > for TCP connections (as they are used for zone transfers or fallback
> > for requests) but don't want to use possibly spoofed UDP pmtu information.
> > 
> > Currently the whitelisted protocols are TCP, SCTP and DCCP as they check
> > if the returned packet is in the window or if the association is valid.
> > 
> > Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
> 
> I think this is going to have the same problem as the forwarding
> sysctl, someone is going to convince some distribution to turn this
> thing to the new "3" hardened mode by default.
> 
> I'm not applying this... for now, sorry.

Ok, I see your concerns. I really intended its use just for a namespace
sealing off a name server.

Should I make this mode unavailable in init_net? ;)
(maybe, seriously?)

Thanks!

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