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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Message-Id: <20140107.191314.881648861654097224.davem@davemloft.net>
Date:	Tue, 07 Jan 2014 19:13:14 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
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

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 :-)

> +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.

Thanks.

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