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Date: Sun, 28 Apr 2024 14:00:00 +0300
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Subject: Re: Add SPLIT PARTITION/MERGE PARTITIONS commands
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To: Alexander Korotkov <aekorotkov@gmail.com>,
 Dmitry Koval <d.koval@postgrespro.ru>
Cc: Justin Pryzby <pryzby@telsasoft.com>, Robert Haas
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From: Alexander Lakhin <exclusion@gmail.com>
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Hello,

28.04.2024 03:59, Alexander Korotkov wrote:
> The revised patchset is attached.  I'm going to push it if there are
> no objections.

I have one additional question regarding security, if you don't mind:
What permissions should a user have to perform split/merge?

When we deal with mixed ownership, say, bob is an owner of a
partitioned table, but not an owner of a partition, should we
allow him to perform merge with that partition?
Consider the following script:
CREATE ROLE alice;
GRANT CREATE ON SCHEMA public TO alice;

SET SESSION AUTHORIZATION alice;
CREATE TABLE t (i int PRIMARY KEY, t text, u text) PARTITION BY RANGE (i);
CREATE TABLE tp_00 PARTITION OF t FOR VALUES FROM (0) TO (10);
CREATE TABLE tp_10 PARTITION OF t FOR VALUES FROM (10) TO (20);

CREATE POLICY p1 ON tp_00 USING (u = current_user);
ALTER TABLE tp_00 ENABLE ROW LEVEL SECURITY;

INSERT INTO t(i, t, u)  VALUES (0, 'info for bob', 'bob');
INSERT INTO t(i, t, u)  VALUES (1, 'info for alice', 'alice');
RESET SESSION AUTHORIZATION;

CREATE ROLE bob;
GRANT CREATE ON SCHEMA public TO bob;
ALTER TABLE t OWNER TO bob;
GRANT SELECT ON TABLE tp_00 TO bob;

SET SESSION AUTHORIZATION bob;
SELECT * FROM tp_00;
--- here bob can see his info only
\d
  Schema | Name  |       Type        | Owner
--------+-------+-------------------+-------
  public | t     | partitioned table | bob
  public | tp_00 | table             | alice
  public | tp_10 | table             | alice

-- but then bob can do:
ALTER TABLE t MERGE PARTITIONS (tp_00, tp_10) INTO tp_00;
-- (yes, he also can detach the partition tp_00, but then he couldn't
-- re-attach nor read it)

\d
  Schema | Name  |       Type        | Owner
--------+-------+-------------------+-------
  public | t     | partitioned table | bob
  public | tp_00 | table             | bob

Thus bob effectively have captured the partition with the data.

What do you think, does this create a new security risk?

Best regards,
Alexander