Re: OpenSSL randomness seeding

> On 21 Jul 2020, at 22:00, David Steele <david(at)pgmasters(dot)net> wrote:
>
> On 7/21/20 3:44 PM, Daniel Gustafsson wrote:
>>> On 21 Jul 2020, at 17:31, David Steele <david(at)pgmasters(dot)net> wrote:
>>> On 7/21/20 8:13 AM, Daniel Gustafsson wrote:
>>>> Another thing that stood out when reviewing this code is that we optimize for
>>>> RAND_poll failing in pg_strong_random, when we already have RAND_status
>>>> checking for a sufficiently seeded RNG for us. ISTM that we can simplify the
>>>> code by letting RAND_status do the work as per 0002, and also (while unlikely)
>>>> survive any transient failures in RAND_poll by allowing all the retries we've
>>>> defined for the loop.
>>>
>>> I wonder how effective the retries are going to be if they happen immediately. However, most of the code paths I followed ended in a hard error when pg_strong_random() failed so it may not hurt to try. I just worry that some caller is depending on a faster failure here.
>> There is that, but I'm not convinced that relying on specific timing for
>> anything RNG or similarly cryptographic-related is especially sane.
>
> I wasn't thinking specific timing -- just that the caller might be expecting it to give up quickly if it doesn't work. That's what the code is trying to do and I wonder if there is a reason for it.

I think the original intention was to handle older OpenSSL versions where
multiple successful RAND_poll calls were required for RAND_status to succeed,
the check working as an optimization since a failing RAND_poll would render all
efforts useless anyway. I'm not sure this is true for the OpenSSL versions we
support in HEAD, and/or for modern platforms, but without proof of it not being
useful I would opt for keeping it.

cheers ./daniel