Re: How to I select value of GUC that has - in its name?

On 2/9/21 9:00 AM, Tom Lane wrote:
> Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> writes:
>> On 2/9/21 7:45 AM, hubert depesz lubaczewski wrote:
>>> but I find it curious that I can set the guc using normal-ish SET, but
>>> can't get it using SHOW or even select current_setting()
>
>> Yeah, I think that part is a bug report.
>
> After digging around in the code, I find the reason is that the entries in
> pg_db_role_setting.setconfig are parsed with ParseLongOption, which quoth:
>
> /*
> * A little "long argument" simulation, although not quite GNU
> * compliant. Takes a string of the form "some-option=some value" and
> * returns name = "some_option" and value = "some value" in malloc'ed
> * storage. Note that '-' is converted to '_' in the option name. If
> * there is no '=' in the input string then value will be NULL.
> */
>
> Sure enough,
>
> regression=> show custom."bad-guc";
> ERROR: unrecognized configuration parameter "custom.bad-guc"
> regression=> show custom."bad_guc";
> custom.bad_guc
> ----------------
> 1a
> (1 row)
>
> So that's where the setting went.
>
> There's a second problem here with arbitrary GUC names, which is that
> a name containing '=' isn't exactly gonna do what you want either.
>
> There are probably other places that are not terribly careful about
> funny characters in GUC names. In a quick test, I see that pg_dumpall
> seems to dump the ALTER USER SET safely, but I wouldn't want to bet
> that everything else copes.
>
> I think we should probably sanitize custom GUC names at least to the
> extent of forbidding '=' and '-'. Maybe we should go further and
> insist they look like regular identifiers.
>
> (Fortunately, ALTER USER SET with a custom GUC is superuser-only,
> so there's no need to worry about security issues here. But we
> should eliminate surprises.)

Hmm, further food for thought:

test(5432)=# alter user aklaver reset custom."bad_guc" ;
ALTER ROLE

test(5432)=# select setconfig from pg_db_role_setting where setrole =
'aklaver'::regrole;
setconfig
---------------------
{custom.bad-guc=1a}
(1 row)

test(5432)=# alter user aklaver reset custom."bad-guc" ;
ALTER ROLE

test(5432)=# select setconfig from pg_db_role_setting where setrole =
'aklaver'::regrole;
setconfig
-----------
(0 rows)

>
> regards, tom lane
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com