Fix possible future cache reference leak in ALTER EXTENSION ADD/DROP.

recordExtObjInitPriv and removeExtObjInitPriv were sloppy about
calling ReleaseSysCache.  The cases cannot occur given current usage
in ALTER EXTENSION ADD/DROP, since we wouldn't get here for these
relkinds; but it seems wise to clean up better.

In passing, extend test logic in test_pg_dump to exercise the
dropped-column code paths here.

Since the case is unreachable at present, there seems no great
need to back-patch; hence fix HEAD only.

Kyotaro Horiguchi, with test case and comment adjustments by me

Discussion: https://postgr.es/m/20200417.151831.1153577605111650154.horikyota.ntt@gmail.com

Author: tglsfdc

src/backend/catalog/aclchk.c

@@ -5580,19 +5580,22 @@ recordExtObjInitPriv(Oid objoid, Oid classoid)
 			elog(ERROR, "cache lookup failed for relation %u", objoid);
 		pg_class_tuple = (Form_pg_class) GETSTRUCT(tuple);
 
-		/* Indexes don't have permissions */
+		/*
+		 * Indexes don't have permissions, neither do the pg_class rows for
+		 * composite types.  (These cases are unreachable given the
+		 * restrictions in ALTER EXTENSION ADD, but let's check anyway.)
+		 */
 		if (pg_class_tuple->relkind == RELKIND_INDEX ||
-			pg_class_tuple->relkind == RELKIND_PARTITIONED_INDEX)
-			return;
-
-		/* Composite types don't have permissions either */
-		if (pg_class_tuple->relkind == RELKIND_COMPOSITE_TYPE)
+			pg_class_tuple->relkind == RELKIND_PARTITIONED_INDEX ||
+			pg_class_tuple->relkind == RELKIND_COMPOSITE_TYPE)
+		{
+			ReleaseSysCache(tuple);
 			return;
+		}
 
 		/*
-		 * If this isn't a sequence, index, or composite type then it's
-		 * possibly going to have columns associated with it that might have
-		 * ACLs.
+		 * If this isn't a sequence then it's possibly going to have
+		 * column-level ACLs associated with it.
 		 */
 		if (pg_class_tuple->relkind != RELKIND_SEQUENCE)
 		{
@@ -5724,6 +5727,11 @@ recordExtObjInitPriv(Oid objoid, Oid classoid)
 		SysScanDesc scan;
 		Relation	relation;
 
+		/*
+		 * Note: this is dead code, given that we don't allow large objects to
+		 * be made extension members.  But it seems worth carrying in case
+		 * some future caller of this function has need for it.
+		 */
 		relation = table_open(LargeObjectMetadataRelationId, RowExclusiveLock);
 
 		/* There's no syscache for pg_largeobject_metadata */
@@ -5866,19 +5874,22 @@ removeExtObjInitPriv(Oid objoid, Oid classoid)
 			elog(ERROR, "cache lookup failed for relation %u", objoid);
 		pg_class_tuple = (Form_pg_class) GETSTRUCT(tuple);
 
-		/* Indexes don't have permissions */
+		/*
+		 * Indexes don't have permissions, neither do the pg_class rows for
+		 * composite types.  (These cases are unreachable given the
+		 * restrictions in ALTER EXTENSION DROP, but let's check anyway.)
+		 */
 		if (pg_class_tuple->relkind == RELKIND_INDEX ||
-			pg_class_tuple->relkind == RELKIND_PARTITIONED_INDEX)
-			return;
-
-		/* Composite types don't have permissions either */
-		if (pg_class_tuple->relkind == RELKIND_COMPOSITE_TYPE)
+			pg_class_tuple->relkind == RELKIND_PARTITIONED_INDEX ||
+			pg_class_tuple->relkind == RELKIND_COMPOSITE_TYPE)
+		{
+			ReleaseSysCache(tuple);
 			return;
+		}
 
 		/*
-		 * If this isn't a sequence, index, or composite type then it's
-		 * possibly going to have columns associated with it that might have
-		 * ACLs.
+		 * If this isn't a sequence then it's possibly going to have
+		 * column-level ACLs associated with it.
 		 */
 		if (pg_class_tuple->relkind != RELKIND_SEQUENCE)
 		{

src/test/modules/test_pg_dump/README

@@ -1,2 +1,4 @@
 test_pg_dump is an extension explicitly to test pg_dump when
 extensions are present in the system.
+
+We also make use of this module to test ALTER EXTENSION ADD/DROP.

src/test/modules/test_pg_dump/expected/test_pg_dump.out

@@ -4,7 +4,8 @@ ALTER EXTENSION test_pg_dump ADD DATABASE postgres; -- error
 ERROR:  syntax error at or near "DATABASE"
 LINE 1: ALTER EXTENSION test_pg_dump ADD DATABASE postgres;
                                          ^
-CREATE TABLE test_pg_dump_t1 (c1 int);
+CREATE TABLE test_pg_dump_t1 (c1 int, junk text);
+ALTER TABLE test_pg_dump_t1 DROP COLUMN junk;  -- to exercise dropped-col cases
 CREATE VIEW test_pg_dump_v1 AS SELECT * FROM test_pg_dump_t1;
 CREATE MATERIALIZED VIEW test_pg_dump_mv1 AS SELECT * FROM test_pg_dump_t1;
 CREATE SCHEMA test_pg_dump_s1;

src/test/modules/test_pg_dump/sql/test_pg_dump.sql

@@ -3,7 +3,8 @@ CREATE EXTENSION test_pg_dump;
 
 ALTER EXTENSION test_pg_dump ADD DATABASE postgres; -- error
 
-CREATE TABLE test_pg_dump_t1 (c1 int);
+CREATE TABLE test_pg_dump_t1 (c1 int, junk text);
+ALTER TABLE test_pg_dump_t1 DROP COLUMN junk;  -- to exercise dropped-col cases
 CREATE VIEW test_pg_dump_v1 AS SELECT * FROM test_pg_dump_t1;
 CREATE MATERIALIZED VIEW test_pg_dump_mv1 AS SELECT * FROM test_pg_dump_t1;
 CREATE SCHEMA test_pg_dump_s1;