pgsql: Fix search_path to a safe value during maintenance operations.

Fix search_path to a safe value during maintenance operations.

While executing maintenance operations (ANALYZE, CLUSTER, REFRESH
MATERIALIZED VIEW, REINDEX, or VACUUM), set search_path to
'pg_catalog, pg_temp' to prevent inconsistent behavior.

Functions that are used for functional indexes, in index expressions,
or in materialized views and depend on a different search path must be
declared with CREATE FUNCTION ... SET search_path='...'.

This change addresses a security risk introduced in commit 60684dd834,
where a role with MAINTAIN privileges on a table may be able to
escalate privileges to the table owner. That commit is not yet part of
any release, so no need to backpatch.

Discussion: https://postgr.es/m/e44327179e5c9015c8dda67351c04da552066017.camel%40j-davis.com
Reviewed-by: Greg Stark
Reviewed-by: Nathan Bossart

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/05e17373517114167d002494e004fa0aa32d1fd1

Modified Files
--------------
contrib/amcheck/verify_nbtree.c | 2 ++
src/backend/access/brin/brin.c | 2 ++
src/backend/catalog/index.c | 8 ++++++++
src/backend/commands/analyze.c | 2 ++
src/backend/commands/cluster.c | 2 ++
src/backend/commands/indexcmds.c | 6 ++++++
src/backend/commands/matview.c | 2 ++
src/backend/commands/vacuum.c | 2 ++
src/bin/scripts/t/100_vacuumdb.pl | 4 ----
src/include/utils/guc.h | 6 ++++++
src/test/modules/test_oat_hooks/expected/test_oat_hooks.out | 4 ++++
src/test/regress/expected/privileges.out | 12 ++++++------
src/test/regress/expected/vacuum.out | 2 +-
src/test/regress/sql/privileges.sql | 8 ++++----
src/test/regress/sql/vacuum.sql | 2 +-
15 files changed, 48 insertions(+), 16 deletions(-)