[Security-sig] Take a decision for os.urandom() in Python 3.6

[Nick Coghlan]

On 8 August 2016 at 14:22, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 8 August 2016 at 13:32, Nick Coghlan <ncoghlan at gmail.com> wrote:
>
>> The Fedora Rawhide experiment I'm proposing in that email to the Fedora
>> Python list should give us the data we (Fedora) need to decide whether or
>> not this is one of those cases where it makes sense for us to carry a patch
>> - if we get zero hits from the exception in ABRT, then it means the default
>> blocking behaviour should be relatively safe (since people won't be
>> encountering it), so we can drop the patch before the F26 Beta release, and
>> Guido will have a solid data point backing up his design instincts. If we
>> *do* get hits on the exception, then exactly what we do will depend on the
>> nature of those hits, and in particular whether or not the change is
>> helping folks find misconfigured Fedora environments they hadn't previously
>> noticed, or if they're spurious notifications in situations where just
>> blocking for a few hundred milliseconds would have resolved the problem on
>> its own (as tested by inserting a "python -c 'import os; os.getrandom(1)"
>> before whatever application startup is triggering the new exception).
>>
>
> I started thinking a bit more about the outcomes we'd be looking for from
> such an experiment [1], and that reminded of the fact we could potentially
> do that with a much lower level of divergence if the upstream
> implementation issued a runtime warning when it needed to fall back to
> blocking behaviour. That is, rather that just calling "getrandom(size, 0)"
> unconditionally, the current logic for trying "getrandom(size,
> GRND_NONBLOCK)" first could be kept, and only the fallback to reading from
> "/dev/random/" changed to instead call "getrandom(size, 0)" with a
> preceding call to PyErr_Warn.
>

Sorry, unhelpful typo there: the fallback is to "/dev/urandom", I just
mistyped it and missed the error on proofreading.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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