linux-kernel - Re: [PATCH 00/11] random: code cleanups

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Date:	Tue, 12 Nov 2013 20:02:09 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Theodore Ts'o" <tytso@....edu>, Greg Price <price@....EDU>,
	linux-kernel@...r.kernel.org, Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH 00/11] random: code cleanups

On 11/12/2013 07:32 PM, Theodore Ts'o wrote:
> On Tue, Nov 12, 2013 at 05:40:09PM -0500, Greg Price wrote:
>>
>> Beyond these easy cleanups, I have a couple of patches queued up (just
>> written yesterday, not quite finished) to make /dev/urandom block at
>> boot until it has enough entropy, as the "Mining your P's and Q's"
>> paper recommended and people have occasionally discussed since then.
>> Those patches were definitely for after 3.13 anyway, and I'll send
>> them when they're ready.  I see some notifications and warnings in
>> this direction in the random.git tree, which is great.
> 
> One of the things I've been thinking about with respect to making
> /dev/urandom block is being able to configure (via a module parameter
> which could be specified on the boot command line) which allows us to
> set a limit for how long /dev/urandom will block after which we log a
> high priority message that there was an attempt to read from
> /dev/urandom which couldn't be satisified, and then allowing the
> /dev/urandom read to succed.
> 
> The basic idea is that we don't want to break systems, but we do want
> to gently coerce people to do the right thing.  Otherwise, I'm worried
> that distros, or embedded/mobile/consume electronics engineers would
> just patch out the check.  If we make the default be something like
> "block for 5 minutes", and then log a message, we won't completely
> break a user who is trying to login to a VM, but it will be obvious,
> both from the delay and from the kern.crit log message, that there is
> a potential problem here that a system administrator needs to worry
> about.
> 

One thing, too, if we are talking about anything other than
boot-time-only blocking: going from a nonblocking to a blocking
condition means being able to accept a short read, and right now *many*
users of /dev/urandom are not ready to accept a short read.

	-hpa


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