Re: [RFC][PATCH 0/6] /dev/random - a new approach

From: Nikos Mavrogiannopoulos
Date: Tue May 03 2016 - 12:21:42 EST

On Tue, May 3, 2016 at 4:48 PM, <tytso@xxxxxxx> 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
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().