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

On Thu, Jul 24, 2014 at 1:30 PM, Henrique de Moraes Holschuh
[off-list ref] wrote:

On Thu, 24 Jul 2014, Theodore Ts'o wrote:

quoted

On Thu, Jul 24, 2014 at 08:21:38AM -0700, Andy Lutomirski wrote:

quoted

quoted

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.

--Andy