linux-kernel - Re: [RFC][PATCH 0/6] /dev/random

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Date:	Tue, 3 May 2016 18:20:57 +0200
From:	Nikos Mavrogiannopoulos <nmav@...tls.org>
To:	"Theodore Ts'o" <tytso@....edu>,
	Nikos Mavrogiannopoulos <nmav@...tls.org>,
	Stephan Mueller <smueller@...onox.de>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Sandy Harris <sandyinchina@...il.com>
Subject: Re: [RFC][PATCH 0/6] /dev/random - a new approach

On Tue, May 3, 2016 at 4:48 PM,  <tytso@....edu> wrote:
> On Tue, May 03, 2016 at 03:57:15PM +0200, Nikos Mavrogiannopoulos wrote:
>> I believe their main concern is that they want to protect applications
>> which do not check error codes of system calls, when running on a
>> kernel which does not provide getrandom().  That way, they have an
>> almost impossible task to simulate getrandom() on kernel which do not
>> support it.
>
> The whole *point* of creating the getrandom(2) system call is that it
> can't be simulated/emulated in userspace.  If it can be, then there's
> no reason why the system call should exist.  This is one of the
> reasons why haven't implemented mysql or TLS inside the kernel.   :-)
> So if their standard is "we need to simulate getrandom(2) on a kernel
> which does not have it", we'll **never** see glibc support for it.  By
> definition, this is *impossible*.

I know, and I share this opinion. To their defense they will have to
provide a call which doesn't make applications fail in the following
scenario:
1. crypto/ssl libraries are compiled to use getrandom() because it is
available in libc and and in kernel
2. everything works fine
3. the administrator downgrades the kernel to a version without
getrandom() because his network card works better with that version
4. Mayhem as applications fail

However I don't see a way to avoid issues - though limited to corner
cases - with any imperfect emulation. It would be much clear for glibc
to just require a kernel with getrandom().

regards,
Nikos