Re: [COMMITTERS] pgsql: Replace PostmasterRandom() with a stronger way of generating ran

Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> On 10/17/2016 05:50 PM, Tom Lane wrote:
>> The real issue here is whether we are willing to say that
>> Postgres simply does not work anymore on machines without standard entropy
>> sources. Doesn't matter whether the user cares about the strength of
>> cancel keys, we're just blowing them off. That seems a bit extreme
>> from here. I think we should be willing to fall back to the old code
>> if we can't find a real entropy source.

> I'm scared of having pg_strong_random() that is willing to fall back to
> not-so-strong values. We can rename it, of course, but it seems
> dangerous to use a weak random-number generator for authentication
> purposes (query cancel, MD5 salts, SCRAM nonces).

I think that it's probably moot on all modern platforms, and even on
platforms as old as pademelon, the answer for people who care about
strong security is "--with-openssl". What I'm on about here is whether
we should make people who don't care about that jump through hoops.
Not caring is a perfectly reasonable stance for non-exposed postmasters;
otherwise we wouldn't have the "trust" auth method.

I would be satisfied with making it a non-default build option, eg
add this to pg_strong_random:

if (random_from_file("/dev/random", buf, len))
return true;

+#ifdef ALLOW_WEAK_SECURITY
+ ... old PostmasterRandom method here ...
+#endif
+
/* None of the sources were available. */
return false;

regards, tom lane