netdev - RE: [E1000-devel] [PATCH 1/2] if_link: Add VF multicast promiscuous mode control

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Date:	Wed, 21 Jan 2015 11:56:53 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Hiroshi Shimamoto' <h-shimamoto@...jp.nec.com>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>,
	Bjørn Mork <bjorn@...k.no>
CC:	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Choi, Sy Jong" <sy.jong.choi@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hayato Momma <h-momma@...jp.nec.com>
Subject: RE: [E1000-devel] [PATCH 1/2] if_link: Add VF multicast promiscuous
	mode control

From: Hiroshi Shimamoto
> My concern is what is the real issue that VF multicast promiscuous mode can cause.
> I think there is the 4k entries to filter multicast address, and the current ixgbe/ixgbevf
> can turn all bits on from VM. That is almost same as enabling multicast promiscuous mode.
> I mean that we can receive all multicast addresses by an onerous operation in untrusted VM.
> I think we should clarify what is real security issue in this context.

If you are worried about passing un-enabled multicasts to users then
what about doing a software hash of received multicasts and checking
against an actual list of multicasts enabled for that hash entry.
Under normal conditions there is likely to be only a single address to check.

It may (or may not) be best to use the same hash as any hashing hardware
filter uses.

	David