Messages in this thread | | | Date | Sat, 17 May 2008 08:57:07 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 2/2] lguest: virtio-rng support |
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Rusty Russell wrote: >> Uhm, no. It's not. Unless the host provides actual entropy >> information, you have a security hole. > > Huh? We just can't assume it adds entropy. AFAICT rngd -H0 is what we want > here.
We can, if it comes from /dev/random.
>>> If we use /dev/random in the host, we risk a DoS. But since /dev/random >>> is 0666 on my system, perhaps noone actually cares? >> There is no point in feeding the host /dev/urandom to the guest (except >> for seeding, which can be handled through other means); it will do its >> own mixing anyway. > > Seeding is good, but unlikely to be done properly for first boot of some > standard virtualized container. In practice, feeding /dev/urandom from the > host will make /dev/urandom harder to predict in the guest.
Only up to a point.
>> The reason to provide anything at all from the host >> is to give it "golden" entropy bits. > > But you did not address the DoS question: can we ignore it? Or are we trading > off a DoS in the host against a potential security weakness in the guest? > > If so, how do we resolve it?
I don't think you have a DoS situation at all. The worst thing is that you don't have any entropy available at all, at which point /dev/urandom is as insecure as it ever is.
-hpa
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