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

[David Laight]

From: Skidmore, Donald C 
> > > 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.
> 
> Allowing a VM to give itself the privilege of seeing every multicast packet
> could be seen as a hole in VM isolation.
> Now if the host system allows this policy I don't see this as an issue as
> someone specifically allowed this to happen and then must not be concerned.
> We could even log that it has occurred, which I believe your patch did do.
> The issue is also further muddied, as you mentioned above, since some of
> these multicast packets are leaking anyway (the HW currently uses a 12 bit mask).
> It's just that this change would greatly enlarge that hole from a fraction to
> all multicast packets.

Why does it have anything to do with VM isolation?
Isn't is just the same as if the VM were connected directly to the
ethernet cable?

	David