linux-kernel - Re: [PATCH 2/2] lguest: virtio-rng support

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Date:	Sat, 17 May 2008 14:46:39 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	virtualization@...ts.linux-foundation.org,
	Jeff Garzik <jeff@...zik.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, "H. Anvin" <hpa@...or.com>,
	Theodore Tso <tytso@....edu>, Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH 2/2] lguest: virtio-rng support

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).

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?

Cheers,
Rusty.
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