RE: [PATCH 1/2] wrapper: add a helper to generate numbers from a CSPRNG

[<rsbecker@nexbridge.com>]

On November 16, 2021 10:04 PM, Jeff King wrote:
> On Tue, Nov 16, 2021 at 05:50:44PM -0800, Carlo Arenas wrote:
> 
> > for the little amount of random data we need, it might be wiser to
> > fallback to something POSIX like lrand48 which is most likely to be
> > available, but of course your tests that consume lots of random data
> > will need to change.
> 
> Unfortunately that won't help. You have to seed lrand48 with something,
> which usually means pid and/or timestamp. Which are predictable to an
> attacker, which was the start of the whole conversation. You really need
> _some_ source of entropy, and only the OS can provide that.
> 
> > PS. Probably missing context as I don't know what was discussed
> > previously, but indeed making this the libc problem by using mkstemp
> > (plus some compatibility on top), like Peff mentioned seems like a
> > more straightforward "fix"
> 
> It might be nice if it works. I don't recall all of the reasons that led us to
> implement our own mkstemp in the first place. So the first step would
> probably be digging in the history and the archive to find that out, and
> whether it still applies.

mkstemp is more recent than mktemp and not implemented everywhere, sadly, and despite my whining about it. That may be why. It is actually available on recent NonStop platforms, so no real issue. mkstemp does allocate a file descriptor, which can be expensive and not always desired.
--Randall