Disallow CREATE STATISTICS on system catalogs

Add a check that CREATE STATISTICS does not add extended statistics on
system catalogs, similarly to indexes etc.  It can be overriden using
the allow_system_table_mods GUC.

This bug exists since 7b504eb282c, adding the extended statistics, so
backpatch all the way back to PostgreSQL 10.

Author: Tomas Vondra
Reported-by: Dean Rasheed
Backpatch-through: 10
Discussion: https://postgr.es/m/CAEZATCXAPrrOKwEsyZKQ4uzzJQWBCt6QAvOcgqRGdWwT1zb%2BrQ%40mail.gmail.com

3 files changed, 22 insertions, 10 deletions

diff --git a/src/backend/commands/statscmds.c b/src/backend/commands/statscmds.c
index 1a989050984..d30d1faac60 100644
--- a/src/backend/commands/statscmds.c
+++ b/src/backend/commands/statscmds.c
@@ -15,6 +15,7 @@
 #include "postgres.h"
 
 #include "access/relscan.h"
+#include "catalog/catalog.h"
 #include "catalog/dependency.h"
 #include "catalog/indexing.h"
 #include "catalog/namespace.h"
@@ -123,6 +124,13 @@ CreateStatistics(CreateStatsStmt *stmt)
 		if (!pg_class_ownercheck(RelationGetRelid(rel), stxowner))
 			aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
 						   RelationGetRelationName(rel));
+
+		/* Creating statistics on system catalogs is not allowed */
+		if (!allowSystemTableMods && IsSystemRelation(rel))
+			ereport(ERROR,
+					(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+					 errmsg("permission denied: \"%s\" is a system catalog",
+							RelationGetRelationName(rel))));
 	}
 
 	Assert(rel);
diff --git a/src/test/regress/expected/stats_ext.out b/src/test/regress/expected/stats_ext.out
index 5b7e1d46608..914e3f14730 100644
--- a/src/test/regress/expected/stats_ext.out
+++ b/src/test/regress/expected/stats_ext.out
@@ -6,6 +6,7 @@ SET max_parallel_workers = 0;
 SET max_parallel_workers_per_gather = 0;
 SET work_mem = '128kB';
 -- Verify failures
+CREATE TABLE ext_stats_test (x int, y int, z int);
 CREATE STATISTICS tst;
 ERROR:  syntax error at or near ";"
 LINE 1: CREATE STATISTICS tst;
@@ -20,16 +21,17 @@ LINE 1: CREATE STATISTICS tst FROM sometab;
                               ^
 CREATE STATISTICS tst ON a, b FROM nonexistant;
 ERROR:  relation "nonexistant" does not exist
-CREATE STATISTICS tst ON a, b FROM pg_class;
+CREATE STATISTICS tst ON a, b FROM ext_stats_test;
 ERROR:  column "a" does not exist
-CREATE STATISTICS tst ON relname, relname, relnatts FROM pg_class;
+CREATE STATISTICS tst ON x, x, y FROM ext_stats_test;
 ERROR:  duplicate column name in statistics definition
-CREATE STATISTICS tst ON relnatts + relpages FROM pg_class;
+CREATE STATISTICS tst ON x + y FROM ext_stats_test;
 ERROR:  only simple column references are allowed in CREATE STATISTICS
-CREATE STATISTICS tst ON (relpages, reltuples) FROM pg_class;
+CREATE STATISTICS tst ON (x, y) FROM ext_stats_test;
 ERROR:  only simple column references are allowed in CREATE STATISTICS
-CREATE STATISTICS tst (unrecognized) ON relname, relnatts FROM pg_class;
+CREATE STATISTICS tst (unrecognized) ON x, y FROM ext_stats_test;
 ERROR:  unrecognized statistics kind "unrecognized"
+DROP TABLE ext_stats_test;
 -- Ensure stats are dropped sanely, and test IF NOT EXISTS while at it
 CREATE TABLE ab1 (a INTEGER, b INTEGER, c INTEGER);
 CREATE STATISTICS IF NOT EXISTS ab1_a_b_stats ON a, b FROM ab1;
diff --git a/src/test/regress/sql/stats_ext.sql b/src/test/regress/sql/stats_ext.sql
index 2543dbfffa7..c1dda8ca7de 100644
--- a/src/test/regress/sql/stats_ext.sql
+++ b/src/test/regress/sql/stats_ext.sql
@@ -8,15 +8,17 @@ SET max_parallel_workers_per_gather = 0;
 SET work_mem = '128kB';
 
 -- Verify failures
+CREATE TABLE ext_stats_test (x int, y int, z int);
 CREATE STATISTICS tst;
 CREATE STATISTICS tst ON a, b;
 CREATE STATISTICS tst FROM sometab;
 CREATE STATISTICS tst ON a, b FROM nonexistant;
-CREATE STATISTICS tst ON a, b FROM pg_class;
-CREATE STATISTICS tst ON relname, relname, relnatts FROM pg_class;
-CREATE STATISTICS tst ON relnatts + relpages FROM pg_class;
-CREATE STATISTICS tst ON (relpages, reltuples) FROM pg_class;
-CREATE STATISTICS tst (unrecognized) ON relname, relnatts FROM pg_class;
+CREATE STATISTICS tst ON a, b FROM ext_stats_test;
+CREATE STATISTICS tst ON x, x, y FROM ext_stats_test;
+CREATE STATISTICS tst ON x + y FROM ext_stats_test;
+CREATE STATISTICS tst ON (x, y) FROM ext_stats_test;
+CREATE STATISTICS tst (unrecognized) ON x, y FROM ext_stats_test;
+DROP TABLE ext_stats_test;
 
 -- Ensure stats are dropped sanely, and test IF NOT EXISTS while at it
 CREATE TABLE ab1 (a INTEGER, b INTEGER, c INTEGER);