On Saturday 17 May 2008 14:50:31 H. Peter Anvin wrote: > Rusty Russell wrote: > > On Friday 16 May 2008 20:49:41 Johannes Berg wrote: > >>> + > >>> +/* Our random number generator device reads from /dev/urandom into the > >>> Guest's + * input buffers. The usual case is that the Guest doesn't > >>> want random numbers + * and so has no buffers although /dev/urandom is > >>> still readable, whereas + * console is the reverse. > >> > >> Is it really a good idea to use the hosts /dev/urandom to fill the > >> guests /dev/random? > > > > Technically it's up to rngd in the guest to decide whether to feed > > entropy or not (ie. /dev/urandom or /dev/random). > > 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. > > 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. > 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? Thanks, Rusty. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
