From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753478AbYEQEx3 (ORCPT ); Sat, 17 May 2008 00:53:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751250AbYEQExT (ORCPT ); Sat, 17 May 2008 00:53:19 -0400 Received: from terminus.zytor.com ([198.137.202.10]:48612 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751043AbYEQExS (ORCPT ); Sat, 17 May 2008 00:53:18 -0400 Message-ID: <482E6417.8040602@zytor.com> Date: Fri, 16 May 2008 21:50:31 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Rusty Russell CC: Johannes Berg , virtualization@lists.linux-foundation.org, Jeff Garzik , Herbert Xu , Christian Borntraeger , LKML , Theodore Tso , Matt Mackall Subject: Re: [PATCH 2/2] lguest: virtio-rng support References: <482C8595.5030509@garzik.org> <200805161539.59739.rusty@rustcorp.com.au> <1210934981.6381.1.camel@johannes.berg> <200805171446.39814.rusty@rustcorp.com.au> In-Reply-To: <200805171446.39814.rusty@rustcorp.com.au> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > 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? /dev/random = give me actual entropy, if you have some. /dev/urandom = give me what you have, regardless of quality. 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. The reason to provide anything at all from the host is to give it "golden" entropy bits. -hpa