netdev - Re: [PATCH net-next v3 1/3] ipv4: introduce ip_dst_mtu_secure and protect forwarding path against pmtu spoofing

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Date:	Wed, 8 Jan 2014 06:02:25 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, eric.dumazet@...il.com,
	johnwheffner@...il.com, steffen.klassert@...unet.com,
	fweimer@...hat.com
Subject: Re: [PATCH net-next v3 1/3] ipv4: introduce ip_dst_mtu_secure and protect forwarding path against pmtu spoofing

Hi David!

On Tue, Jan 07, 2014 at 07:13:14PM -0500, David Miller wrote:
> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Date: Mon, 6 Jan 2014 09:48:27 +0100
> 
> > +ip_forward_use_pmtu - BOOLEAN
> > +	By default we don't trust protocol path MTUs while forwarding
> > +	because they could be easily forged and can lead to unwanted
> > +	fragmentation by the router.
> > +	You only need to enable this if you have user-space software
> > +	which tries to discover path mtus by itself and depends on the
> > +	kernel honoring this information. This is normally not the
> > +	case.
> > +	Default: 0 (disabled)
> > +	Possible values:
> > +	0 - disabled
> > +	1 - enabled
> 
> You made this default to off, great, but the description text still says
> that we don't trust PMTU information by default :-)

Hm, sorry, but I don't see the contradiction.

> > +static inline unsigned int ip_dst_mtu_secure(const struct dst_entry *dst,
> 
> Please do me a favor and remove the "_secure" bit from this helper function
> name.  This function doesn't implicitly do anything "secure", rather it
> simply calculates the dst's mtu based upon various conditions.

I'll follow the IPv6 one and will switch to _forward postfix.

Thanks,

  Hannes

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