Re: Running the fdw test from the terminal crashes into the core-dump

On 2024-Feb-18, Alvaro Herrera wrote:

> On 2024-Feb-18, Tom Lane wrote:
> 
> > So I'd blame this on faulty handling of the zero-partitions case in
> > the RTEPermissionInfo refactoring.  (I didn't bisect to prove that
> > a61b1f748 is exactly where it broke, but I do see that the query
> > successfully does nothing in v15.)
> 
> You're right, this is the commit that broke it.  It's unclear to me if
> Amit is available to look at it, so I'll give this a look tomorrow if he
> isn't.

OK, so it turns out that the bug is older than that -- it was actually
introduced with MERGE itself (7103ebb7aae8) and has nothing to do with
partitioning or RTEPermissionInfo; commit a61b1f748 is only related
because it added the Assert() that barfs when there are no privileges to
check.

The real problem is that a MERGE ... DO NOTHING action reports that no
permissions need to be checked on the target relation, which is not a
problem when there are other actions in the MERGE command since they add
privs to check.  When DO NOTHING is the only action, the added assert in
a61b1f748 is triggered.

So, this means we can fix this by simply requiring ACL_SELECT privileges
on a DO NOTHING action.  We don't need to request specific privileges on
any particular column (perminfo->selectedCols continues to be the empty
set) -- which means that any role that has privileges on *any* column
would get a pass.  If you're doing MERGE with any other action besides
DO NOTHING, you already have privileges on at least some column, so
adding ACL_SELECT breaks nothing.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"Pido que me den el Nobel por razones humanitarias" (Nicanor Parra)