Make relation-enumerating operations be security-restricted operations.

When a feature enumerates relations and runs functions associated with
all found relations, the feature's user shall not need to trust every
user having permission to create objects.  BRIN-specific functionality
in autovacuum neglected to account for this, as did pg_amcheck and
CLUSTER.  An attacker having permission to create non-temp objects in at
least one schema could execute arbitrary SQL functions under the
identity of the bootstrap superuser.  CREATE INDEX (not a
relation-enumerating operation) and REINDEX protected themselves too
late.  This change extends to the non-enumerating amcheck interface.
Back-patch to v10 (all supported versions).

Sergey Shinderuk, reviewed (in earlier versions) by Alexander Lakhin.
Reported by Alexander Lakhin.

Security: CVE-2022-1552

Author: nmisch

contrib/amcheck/expected/check_btree.out

@@ -177,11 +177,34 @@ SELECT bt_index_check('toasty', true);
 
 (1 row)
 
+--
+-- Check that index expressions and predicates are run as the table's owner
+--
+TRUNCATE bttest_a;
+INSERT INTO bttest_a SELECT * FROM generate_series(1, 1000);
+ALTER TABLE bttest_a OWNER TO regress_bttest_role;
+-- A dummy index function checking current_user
+CREATE FUNCTION ifun(int8) RETURNS int8 AS $$
+BEGIN
+	ASSERT current_user = 'regress_bttest_role',
+		format('ifun(%s) called by %s', $1, current_user);
+	RETURN $1;
+END;
+$$ LANGUAGE plpgsql IMMUTABLE;
+CREATE INDEX bttest_a_expr_idx ON bttest_a ((ifun(id) + ifun(0)))
+	WHERE ifun(id + 10) > ifun(10);
+SELECT bt_index_check('bttest_a_expr_idx', true);
+ bt_index_check 
+----------------
+ 
+(1 row)
+
 -- cleanup
 DROP TABLE bttest_a;
 DROP TABLE bttest_b;
 DROP TABLE bttest_multi;
 DROP TABLE delete_test_table;
 DROP TABLE toast_bug;
+DROP FUNCTION ifun(int8);
 DROP OWNED BY regress_bttest_role; -- permissions
 DROP ROLE regress_bttest_role;

contrib/amcheck/sql/check_btree.sql

@@ -115,11 +115,32 @@ INSERT INTO toast_bug SELECT repeat('a', 2200);
 -- Should not get false positive report of corruption:
 SELECT bt_index_check('toasty', true);
 
+--
+-- Check that index expressions and predicates are run as the table's owner
+--
+TRUNCATE bttest_a;
+INSERT INTO bttest_a SELECT * FROM generate_series(1, 1000);
+ALTER TABLE bttest_a OWNER TO regress_bttest_role;
+-- A dummy index function checking current_user
+CREATE FUNCTION ifun(int8) RETURNS int8 AS $$
+BEGIN
+	ASSERT current_user = 'regress_bttest_role',
+		format('ifun(%s) called by %s', $1, current_user);
+	RETURN $1;
+END;
+$$ LANGUAGE plpgsql IMMUTABLE;
+
+CREATE INDEX bttest_a_expr_idx ON bttest_a ((ifun(id) + ifun(0)))
+	WHERE ifun(id + 10) > ifun(10);
+
+SELECT bt_index_check('bttest_a_expr_idx', true);
+
 -- cleanup
 DROP TABLE bttest_a;
 DROP TABLE bttest_b;
 DROP TABLE bttest_multi;
 DROP TABLE delete_test_table;
 DROP TABLE toast_bug;
+DROP FUNCTION ifun(int8);
 DROP OWNED BY regress_bttest_role; -- permissions
 DROP ROLE regress_bttest_role;

contrib/amcheck/verify_nbtree.c

@@ -245,6 +245,9 @@ bt_index_check_internal(Oid indrelid, bool parentcheck, bool heapallindexed,
 	Relation	indrel;
 	Relation	heaprel;
 	LOCKMODE	lockmode;
+	Oid			save_userid;
+	int			save_sec_context;
+	int			save_nestlevel;
 
 	if (parentcheck)
 		lockmode = ShareLock;
@@ -261,9 +264,27 @@ bt_index_check_internal(Oid indrelid, bool parentcheck, bool heapallindexed,
 	 */
 	heapid = IndexGetRelation(indrelid, true);
 	if (OidIsValid(heapid))
+	{
 		heaprel = table_open(heapid, lockmode);
+
+		/*
+		 * Switch to the table owner's userid, so that any index functions are
+		 * run as that user.  Also lock down security-restricted operations
+		 * and arrange to make GUC variable changes local to this command.
+		 */
+		GetUserIdAndSecContext(&save_userid, &save_sec_context);
+		SetUserIdAndSecContext(heaprel->rd_rel->relowner,
+							   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+		save_nestlevel = NewGUCNestLevel();
+	}
 	else
+	{
 		heaprel = NULL;
+		/* for "gcc -Og" https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78394 */
+		save_userid = InvalidOid;
+		save_sec_context = -1;
+		save_nestlevel = -1;
+	}
 
 	/*
 	 * Open the target index relations separately (like relation_openrv(), but
@@ -323,6 +344,12 @@ bt_index_check_internal(Oid indrelid, bool parentcheck, bool heapallindexed,
 							 heapallindexed, rootdescend);
 	}
 
+	/* Roll back any GUC changes executed by index functions */
+	AtEOXact_GUC(false, save_nestlevel);
+
+	/* Restore userid and security context */
+	SetUserIdAndSecContext(save_userid, save_sec_context);
+
 	/*
 	 * Release locks early. That's ok here because nothing in the called
 	 * routines will trigger shared cache invalidations to be sent, so we can

src/backend/access/brin/brin.c

@@ -865,6 +865,9 @@ brin_summarize_range(PG_FUNCTION_ARGS)
 	Oid			heapoid;
 	Relation	indexRel;
 	Relation	heapRel;
+	Oid			save_userid;
+	int			save_sec_context;
+	int			save_nestlevel;
 	double		numSummarized = 0;
 
 	if (RecoveryInProgress())
@@ -891,7 +894,22 @@ brin_summarize_range(PG_FUNCTION_ARGS)
 	 */
 	heapoid = IndexGetRelation(indexoid, true);
 	if (OidIsValid(heapoid))
+	{
 		heapRel = table_open(heapoid, ShareUpdateExclusiveLock);
+
+		/*
+		 * Autovacuum calls us.  For its benefit, switch to the table owner's
+		 * userid, so that any index functions are run as that user.  Also
+		 * lock down security-restricted operations and arrange to make GUC
+		 * variable changes local to this command.  This is harmless, albeit
+		 * unnecessary, when called from SQL, because we fail shortly if the
+		 * user does not own the index.
+		 */
+		GetUserIdAndSecContext(&save_userid, &save_sec_context);
+		SetUserIdAndSecContext(heapRel->rd_rel->relowner,
+							   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+		save_nestlevel = NewGUCNestLevel();
+	}
 	else
 		heapRel = NULL;
 
@@ -906,7 +924,7 @@ brin_summarize_range(PG_FUNCTION_ARGS)
 						RelationGetRelationName(indexRel))));
 
 	/* User must own the index (comparable to privileges needed for VACUUM) */
-	if (!pg_class_ownercheck(indexoid, GetUserId()))
+	if (heapRel != NULL && !pg_class_ownercheck(indexoid, save_userid))
 		aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_INDEX,
 					   RelationGetRelationName(indexRel));
 
@@ -924,6 +942,12 @@ brin_summarize_range(PG_FUNCTION_ARGS)
 	/* OK, do it */
 	brinsummarize(indexRel, heapRel, heapBlk, true, &numSummarized, NULL);
 
+	/* Roll back any GUC changes executed by index functions */
+	AtEOXact_GUC(false, save_nestlevel);
+
+	/* Restore userid and security context */
+	SetUserIdAndSecContext(save_userid, save_sec_context);
+
 	relation_close(indexRel, ShareUpdateExclusiveLock);
 	relation_close(heapRel, ShareUpdateExclusiveLock);
 
@@ -965,6 +989,9 @@ brin_desummarize_range(PG_FUNCTION_ARGS)
 	 * passed indexoid isn't an index then IndexGetRelation() will fail.
 	 * Rather than emitting a not-very-helpful error message, postpone
 	 * complaining, expecting that the is-it-an-index test below will fail.
+	 *
+	 * Unlike brin_summarize_range(), autovacuum never calls this.  Hence, we
+	 * don't switch userid.
 	 */
 	heapoid = IndexGetRelation(indexoid, true);
 	if (OidIsValid(heapoid))

src/backend/catalog/index.c

@@ -1421,6 +1421,9 @@ index_concurrently_build(Oid heapRelationId,
 						 Oid indexRelationId)
 {
 	Relation	heapRel;
+	Oid			save_userid;
+	int			save_sec_context;
+	int			save_nestlevel;
 	Relation	indexRelation;
 	IndexInfo  *indexInfo;
 
@@ -1430,7 +1433,16 @@ index_concurrently_build(Oid heapRelationId,
 	/* Open and lock the parent heap relation */
 	heapRel = table_open(heapRelationId, ShareUpdateExclusiveLock);
 
-	/* And the target index relation */
+	/*
+	 * Switch to the table owner's userid, so that any index functions are run
+	 * as that user.  Also lock down security-restricted operations and
+	 * arrange to make GUC variable changes local to this command.
+	 */
+	GetUserIdAndSecContext(&save_userid, &save_sec_context);
+	SetUserIdAndSecContext(heapRel->rd_rel->relowner,
+						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+	save_nestlevel = NewGUCNestLevel();
+
 	indexRelation = index_open(indexRelationId, RowExclusiveLock);
 
 	/*
@@ -1446,6 +1458,12 @@ index_concurrently_build(Oid heapRelationId,
 	/* Now build the index */
 	index_build(heapRel, indexRelation, indexInfo, false, true);
 
+	/* Roll back any GUC changes executed by index functions */
+	AtEOXact_GUC(false, save_nestlevel);
+
+	/* Restore userid and security context */
+	SetUserIdAndSecContext(save_userid, save_sec_context);
+
 	/* Close both the relations, but keep the locks */
 	table_close(heapRel, NoLock);
 	index_close(indexRelation, NoLock);
@@ -3283,7 +3301,17 @@ validate_index(Oid heapId, Oid indexId, Snapshot snapshot)
 
 	/* Open and lock the parent heap relation */
 	heapRelation = table_open(heapId, ShareUpdateExclusiveLock);
-	/* And the target index relation */
+
+	/*
+	 * Switch to the table owner's userid, so that any index functions are run
+	 * as that user.  Also lock down security-restricted operations and
+	 * arrange to make GUC variable changes local to this command.
+	 */
+	GetUserIdAndSecContext(&save_userid, &save_sec_context);
+	SetUserIdAndSecContext(heapRelation->rd_rel->relowner,
+						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+	save_nestlevel = NewGUCNestLevel();
+
 	indexRelation = index_open(indexId, RowExclusiveLock);
 
 	/*
@@ -3296,16 +3324,6 @@ validate_index(Oid heapId, Oid indexId, Snapshot snapshot)
 	/* mark build is concurrent just for consistency */
 	indexInfo->ii_Concurrent = true;
 
-	/*
-	 * Switch to the table owner's userid, so that any index functions are run
-	 * as that user.  Also lock down security-restricted operations and
-	 * arrange to make GUC variable changes local to this command.
-	 */
-	GetUserIdAndSecContext(&save_userid, &save_sec_context);
-	SetUserIdAndSecContext(heapRelation->rd_rel->relowner,
-						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
-	save_nestlevel = NewGUCNestLevel();
-
 	/*
 	 * Scan the index and gather up all the TIDs into a tuplesort object.
 	 */
@@ -3509,6 +3527,9 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
 	Relation	iRel,
 				heapRelation;
 	Oid			heapId;
+	Oid			save_userid;
+	int			save_sec_context;
+	int			save_nestlevel;
 	IndexInfo  *indexInfo;
 	volatile bool skipped_constraint = false;
 	PGRUsage	ru0;
@@ -3523,6 +3544,16 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
 	heapId = IndexGetRelation(indexId, false);
 	heapRelation = table_open(heapId, ShareLock);
 
+	/*
+	 * Switch to the table owner's userid, so that any index functions are run
+	 * as that user.  Also lock down security-restricted operations and
+	 * arrange to make GUC variable changes local to this command.
+	 */
+	GetUserIdAndSecContext(&save_userid, &save_sec_context);
+	SetUserIdAndSecContext(heapRelation->rd_rel->relowner,
+						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+	save_nestlevel = NewGUCNestLevel();
+
 	if (progress)
 	{
 		pgstat_progress_start_command(PROGRESS_COMMAND_CREATE_INDEX,
@@ -3696,12 +3727,18 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
 				 errdetail_internal("%s",
 									pg_rusage_show(&ru0))));
 
-	if (progress)
-		pgstat_progress_end_command();
+	/* Roll back any GUC changes executed by index functions */
+	AtEOXact_GUC(false, save_nestlevel);
+
+	/* Restore userid and security context */
+	SetUserIdAndSecContext(save_userid, save_sec_context);
 
 	/* Close rels, but keep locks */
 	index_close(iRel, NoLock);
 	table_close(heapRelation, NoLock);
+
+	if (progress)
+		pgstat_progress_end_command();
 }
 
 /*