Speed and security of /dev/urandom

[Konstantin Belousov]

On Sat, Jul 19, 2014 at 09:47:12PM +0100, Steven Chamberlain wrote:
> On 19/07/14 20:26, Konstantin Belousov wrote:
> > I think that using sysctl for non-management functionality is wrong.
> > If this feature is for the libraries and applications, and not for
> > system management and introspection utilities, it should be normal
> > syscall.
> 
> If this is only to seed the arc4random in userland (with ~256 bytes or
> so), it would be just like OpenBSD getentropy(2)?
> 
> Just yesterday, something very similar is proposed for Linux, called
> getrandom(2):
> http://lists.openwall.net/linux-kernel/2014/07/18/329

We, in fact, do not use sysctl for seeding SSP canary.  Kernel puts
random bytes on stack, and libc fetches them.  But it is 64 bytes for
64-bit platforms, 32 bytes for 32-bit.

Yes, the interface of the getrandom(2) from the link above looks
reasonable.  The big question is, indeed, about its supposed use
models.  For one-time seeding of RNG with fixed amount of bytes,
the ELF aux vector mechanism is much less intrusive and faster.
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