Re: [uml-devel] /dev/random problems _not_ solved in 2.6.26

[Jeff Dike <jdike@addtoit.com>]

On Mon, Aug 04, 2008 at 02:40:01PM +0200, Stanislav Meduna wrote:
> this is just to let you know that the /dev/random problems
> are still not solved in the 2.6.26 version. A small dictionary
> attack on sshd (in my case 260 tries over 12 minutes)
> are able to produce
> 
> auth.log.0:Aug  3 05:30:35 dirk sshd[1825]: fatal: Couldn't obtain random bytes (error 
> 604389476)
> 
> and the sshd dies (followed by apache on the first subsequent
> SSL request and so on).

Off the top of my head, you need the following:
    2.6.26 UML, which you do
    rngtools installed in the UML
    sufficient entropy on the host

This last one shouldn't be taken for granted.  I had problems with
this when debugging the random driver changes - on my laptop with me
typing on it, mousing, disk going, and network traffic going in and
out.  It would be worse on a colocated, no-keyboard, no-mouse, server,
which are notorious for this problem.

> Unfortunately I can't help you in tracing the uml process
> or trying patches - this is a virtual server at my provider
> and I don't have any access there. I could try to get
> the .config file.

You could ask them about how their servers get their randomness.

If nothing else works, I suppose a nasty workaround might be to
replace /dev/random with dev/urandom, but that has security
implications.

    	      	   	 Jeff

-- 
Work email - jdike at linux dot intel dot com

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