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

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Date:	Wed, 21 Jan 2015 12:18:23 +0000
From:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
To:	David Laight <David.Laight@...LAB.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

> 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.

thanks for the comment. But I don't think that is the point.

I guess, introducing VF multicast promiscuous mode seems to add new privilege
to peek every multicast packet in VM and that doesn't look good.
On the other hand, I think that there has been the same privilege in the current
ixgbe/ixgbevf implementation already. Or I'm reading the code wrongly.
I'd like to clarify what is the issue of allowing to receive all multicast packets.

thanks,
Hiroshi