linux-kernel - Re: [PATCH -v5] random: introduce getrandom(2) system call

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Message-ID: <20140724190206.GL6673@thunk.org>
Date:	Thu, 24 Jul 2014 15:02:06 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	linux-crypto@...r.kernel.org
Subject: Re: [PATCH -v5] random: introduce getrandom(2) system call

On Thu, Jul 24, 2014 at 08:21:38AM -0700, Andy Lutomirski wrote:
> >
> > Should we add E<SOMETHING> to be able to deny access to GRND_RANDOM or some
> > future extension ?
> 
> This might actually be needed sooner rather than later.  There are
> programs that use containers and intentionally don't pass /dev/random
> through into the container.  I know that Sandstorm does this, and I
> wouldn't be surprised if other things (Docker?) do the same thing.

I wouldn't add the error to the man page until we actually modify the
kernel to add such a restriction.

However, the thought crossed my mind a while back that perhaps the
right answer is a cgroup controller which controls the rate at which a
process is allowed to drain entropy from the /dev/random pool.  This
could be set to 0, or it could be set to N bits per unit time T, and
if the process exceeded the value, it would just block or return
EAGAIN.  So instead of making it be just a binary "you have access" or
"you don't", it would actually be a kernel resource that could be
controlled just like disk bandwidth, networking bandwidth, memory, and
CPU time.

Then I decided that it was overkill, but for people who are trying to
treat containers as a way to divide up OS resources between mutually
suspicious customers in a fashion which is more efficient thatn using
VM's, maybe it is something that someone will want to implement.

      	       	  	    	 	    	- Ted
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