pgsql: contrib/earthdistance: Use SQL-standard function bodies.

contrib/earthdistance: Use SQL-standard function bodies.

The @extschema:name@ feature added by 72a5b1fc8 allows us to
make earthdistance's references to the cube extension fully
search-path-secure, so long as all those references are
resolved at extension installation time not runtime.
To do that, we must convert earthdistance's SQL functions to
the new SQL-standard style; but we wanted to do that anyway.

The functions can be updated in our customary style by running
CREATE OR REPLACE FUNCTION in an extension update script.
However, there's still problems in the "CREATE DOMAIN earth"
command: its references to cube functions could be captured
by hostile objects in earthdistance's installation schema,
if that's not where the cube extension is. Worse, the reference
to the cube type itself as the domain's base could be captured,
and that's not something we could fix after-the-fact in the
update script.

What I've done about that is to change the "CREATE DOMAIN earth"
command in the base script earthdistance--1.1.sql. Ordinarily,
changing a released extension script is forbidden; but I think
it's okay here since the results of successful (non-trojaned)
script execution will be identical to before.

A good deal of care is still needed to make the extension's scripts
proof against search-path-based attacks. We have to make sure that
all the function and operator invocations have exact argument-type
matches, to forestall attacks based on supplying a better match.
Fortunately earthdistance isn't very big, so I've just gone through
it and inspected each call to be sure of that. The only actual code
changes needed were to spell all floating-point constants in the style
'-1'::float8, rather than depending on runtime type conversions and/or
negations. (I'm not sure that the shortcuts previously used were
attackable, but removing run-time effort is a good thing anyway.)

I believe that this fixes earthdistance enough that we could
mark it trusted and remove the warnings about it that were
added by 7eeb1d986; but I've not done that here.

The primary reason for dealing with this now is that we've
received reports of pg_upgrade failing for databases that use
earthdistance functions in contexts like generated columns.
That's a consequence of 2af07e2f7 having restricted the search_path
used while evaluating such expressions. The only way to fix that
is to make the earthdistance functions independent of run-time
search_path. This patch is very much nicer than the alternative of
attaching "SET search_path" clauses to earthdistance's functions:
it is more secure and doesn't create a run-time penalty. Therefore,
I've chosen to back-patch this to v16 where @extschema:name@
was added. It won't help unless users update to 16.7 and issue
"ALTER EXTENSION earthdistance UPDATE" before upgrading to 17,
but at least there's now a way to deal with the problem without
manual intervention in the dump/restore process.

Tom Lane and Ronan Dunklau

Discussion: https://postgr.es/m/3316564.aeNJFYEL58@aivenlaptop
Discussion: https://postgr.es/m/6a6439f1-8039-44e2-8fb9-59028f7f2014@mailbox.org

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/969bbd0fafc0f4d9ef504ca98a127c8d945f71a0

Modified Files
--------------
contrib/earthdistance/Makefile | 3 +-
contrib/earthdistance/earthdistance--1.1--1.2.sql | 73 +++++++++++++++++++++++
contrib/earthdistance/earthdistance--1.1.sql | 8 +--
contrib/earthdistance/earthdistance.control | 2 +-
contrib/earthdistance/meson.build | 1 +
5 files changed, 81 insertions(+), 6 deletions(-)