Re: Slow GRANT ROLE on PostgreSQL 16 with thousands of ROLEs

On Wed, Mar 27, 2024 at 01:47:38PM -0300, Ranier Vilela wrote:
> Em qua., 27 de mar. de 2024 às 13:41, Nathan Bossart <
> nathandbossart(at)gmail(dot)com> escreveu:
>> On Wed, Mar 27, 2024 at 01:21:23PM -0300, Ranier Vilela wrote:
>> > I think that left an oversight in a commit d365ae7
>> > <
>> https://github.com/postgres/postgres/commit/d365ae705409f5d9c81da4b668f59c3598feb512
>> >
>> > If the admin_role is a NULL pointer, so, can be dereferenced
>> > in the main loop of the function roles_is_member_of and
>> > worst, IMO, can be destroying aleatory memory?
>> >
>> > First, is a better shortcut test to check if admin_role is NOT NULL.
>> > Second, !OidIsValid(*admin_role), It doesn't seem necessary anymore.
>> >
>> > Or am I losing something?
>>
>> If admin_role is NULL, then admin_of is expected to be set to InvalidOid.
>> See the assertion at the top of the function. AFAICT the code that
>> dereferences admin_role short-circuits if admin_of is invalid.
>>
> These conditions seem a little fragile and confusing to me.
> When a simple test, it protects the pointer and avoids a series of tests,
> which are unnecessary if the pointer is invalid.

Maybe. But that doesn't seem like an oversight in commit d365ae7.

- if (otherid == admin_of && form->admin_option &&
- OidIsValid(admin_of) && !OidIsValid(*admin_role))
+ if (admin_role != NULL && otherid == admin_of && form->admin_option &&
+ OidIsValid(admin_of))
*admin_role = memberid;

I'm not following why it's safe to remove the !OidIsValid(*admin_role)
check here. We don't want to overwrite a previously-set value of
*admin_role, as per the comment above roles_is_member_of():

* If admin_of is not InvalidOid, this function sets *admin_role, either
* to the OID of the first role in the result list that directly possesses
* ADMIN OPTION on the role corresponding to admin_of, or to InvalidOid if
* there is no such role.

--
Nathan Bossart
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