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

From: Andy Lutomirski
Date: Thu Jul 24 2014 - 16:54:40 EST

On Thu, Jul 24, 2014 at 1:30 PM, Henrique de Moraes Holschuh
<hmh@xxxxxxxxxx> wrote:
> On Thu, 24 Jul 2014, Theodore Ts'o wrote:
>> 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.
> By then, it might be too late. It would be really sad to find ourselves
> forced to return ENOSYS to getrandom(GRND_RANDOM) when we actually wanted to
> return EPERM/EACCES.
> Actually, we might not be able to do even that much: all it takes is for
> someone to have the bright idea of deploying userspace code that checks for
> ENOSYS only on a first "probe" getrandom() syscall without GRND_RANDOM, and
> does something idiotic when it gets ENOSYS later on a
> getrandom(GRND_RANDOM). meh. We can't even abuse the system ourselves :-)

Or that someone writes userspace code that gets -EPERM/-EACCESS on
getrandom with GRND_RANDOM and falls back to something worse than
getrandom w/o GRND_RANDOM.

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