Re: RLS makes COPY TO process child tables

Yugo NAGATA <nagata@sraoss.co.jp> wrote:

> On Wed, 01 Feb 2023 12:45:57 +0100
> Antonin Houska <ah@cybertec.at> wrote:
> 
> > While working on [1] I noticed that if RLS gets enabled, the COPY TO command
> > includes the contents of child table into the result, although the
> > documentation says it should not:
> > 
> > 	"COPY TO can be used only with plain tables, not views, and does not
> > 	copy rows from child tables or child partitions. For example, COPY
> > 	table TO copies the same rows as SELECT * FROM ONLY table. The syntax
> > 	COPY (SELECT * FROM table) TO ... can be used to dump all of the rows
> > 	in an inheritance hierarchy, partitioned table, or view."
> > 
> > A test case is attached (rls.sql) as well as fix proposal
> > (copy_rls_no_inh.diff).
> 
> I think this is a bug because the current behaviour is different from
> the documentation. 
> 
> When RLS is enabled on a table in `COPY ... TO ...`, the query is converted
> to `COPY (SELECT * FROM ...) TO ...` to allow the rewriter to add in RLS
> clauses. This causes to dump the rows of child tables.
> 
> The patch fixes this by setting "inh" of the table in the converted query
> to false. This seems reasonable and actually fixes the problem.
> 
> However, I think we would want a comment on the added line.

A short comment added, see the new patch version.

> Also, the attached test should be placed in the regression test.

Hm, I'm not sure it's necessary. It would effectively test whether the 'inh'
field works, but if it didn't, many other tests would fail. I discovered the
bug by reading the code, so I wanted to demonstrate (also to myself) that it
causes incorrect behavior from user perspective. That was the purpose of the
test.

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com