[PATCH] Add getrandom implementation [BZ #17252]

[Paul Eggert]

On 06/11/2016 04:13 AM, Florian Weimer wrote:
> programmers do not check for error returns from random number 
> generators.  Based on that, I concluded it was important to provide an 
> implementation which cannot fail.

Yes, as an app developer I prefer primitives like OpenBSD arc4random_buf 
that are always successful. In contrast, Linux getrandom (BUF, LEN, 0) 
is guaranteed to succeed only when called with LEN <= 256, which is good 
enough for hash nonces but not for general-purpose use.

> Implementing arc4random has both libc aspects (providing thread safety 
> and invalidating the internal state around clone/fork) and 
> cryptographic aspects (for performance reasons, it has to be a 
> deterministic random bit generator, and use the kernel for seeding 
> only).  I think the cryptographic aspect dominates, which is why it is 
> difficult to implement arc4random as part of glibc. 

Sorry, I don't understand. What's the difficulty? Why can't glibc 
implement the cryptographic aspect of arc4random_buf via an internal 
deterministic random bit generator? Can't glibc borrow a bit generator 
from Internet RFC 7539, or from GNU Coreutils, or whatever?