Re: MD5 authentication needs help

On 3/5/15 2:17 PM, Stephen Frost wrote:
> * Jim Nasby (Jim(dot)Nasby(at)BlueTreble(dot)com) wrote:
>> On 3/4/15 2:56 PM, Stephen Frost wrote:
>>>> 2) The per-session salt sent to the client is only 32-bits, meaning
>>>>> that it is possible to reply an observed MD5 hash in ~16k connection
>>>>> attempts.
>>> Yes, and we have no (PG-based) mechanism to prevent those connection
>>> attempts, which is a pretty horrible situation to be in.
>>
>> Is there some reason we don't just fix that? I'm thinking that this
>> is a special case where we could just modify the pg_auth tuple
>> in-place without bloating the catalog (we already do that somewhere
>> else). Is there something else that makes this difficult? Are we
>> afraid of an extra GUC to control it?
>
> I'm all for it, though I would ask that we provide a way for superusers
> to delegate the ability to reset locked accounts to non-superusers.
>
> I'd want to think about it a bit more before settling on using pg_authid

I guess it's a question of how durable we want it to be. We could
conceivable keep it in shared memory and let it wipe on a crash.

But we already have code that ignores MVCC on a catalog table (IIRC for
updating pg_class stats after vacuum) so the pattern is there. I don't
see that we need more sophistication than that...

> to track the data. In any case, I do think we need a way to disable
> this ability for certain roles

In the interest of something for this release... do we really need that?
My thought is we just special-case the postgres user and be done with
it. Though, if there's some other way to reset an account from the
shell, no need to even special case postgres.

Though, I guess if we just follow the normal GUC behavior of allowing
per-database and -user overrides it wouldn't be that hard.

> and, furtherr, that we not track failed
> logins in cases where it's disabled (which might well be the default- I
> don't think we want to add this overhead for systems which have lots of
> recurring logins (think application users where they aren't doing
> pooling).

Yeah, presumably if allowed_authentication_failures < 0 then we don't
bother with the check at all.
--
Jim Nasby, Data Architect, Blue Treble Consulting
Data in Trouble? Get it in Treble! http://BlueTreble.com