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

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

@@ -249,6 +249,9 @@ 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;
@@ -265,9 +268,27 @@ 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
@@ -326,6 +347,12 @@ 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

@@ -1008,6 +1008,9 @@ 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())
@@ -1031,7 +1034,22 @@ 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;
 
@@ -1046,7 +1064,7 @@ 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));
 
@@ -1064,6 +1082,12 @@ 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);
 
@@ -1102,6 +1126,9 @@ 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

@@ -1445,6 +1445,9 @@ index_concurrently_build(Oid heapRelationId,
 						 Oid indexRelationId)
 {
 	Relation	heapRel;
+	Oid			save_userid;
+	int			save_sec_context;
+	int			save_nestlevel;
 	Relation	indexRelation;
 	IndexInfo  *indexInfo;
 
@@ -1454,7 +1457,16 @@ 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);
 
 	/*
@@ -1470,6 +1482,12 @@ 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);
@@ -3299,7 +3317,17 @@ 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);
 
 	/*
@@ -3312,16 +3340,6 @@ 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.
 	 */
@@ -3530,6 +3548,9 @@ 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;
@@ -3557,6 +3578,16 @@ reindex_index(Oid indexId, bool skip_constraint_checks, char persistence,
 	if (!heapRelation)
 		return;
 
+	/*
+	 * 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)
 	{
 		const int	progress_cols[] = {
@@ -3775,12 +3806,18 @@ 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();
 }
 
 /*

src/backend/commands/cluster.c

@@ -310,6 +310,9 @@ void
 cluster_rel(Oid tableOid, Oid indexOid, ClusterParams *params)
 {
 	Relation	OldHeap;
+	Oid			save_userid;
+	int			save_sec_context;
+	int			save_nestlevel;
 	bool		verbose = ((params->options & CLUOPT_VERBOSE) != 0);
 	bool		recheck = ((params->options & CLUOPT_RECHECK) != 0);
 
@@ -339,6 +342,16 @@ cluster_rel(Oid tableOid, Oid indexOid, ClusterParams *params)
 		return;
 	}
 
+	/*
+	 * 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(OldHeap->rd_rel->relowner,
+						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+	save_nestlevel = NewGUCNestLevel();
+
 	/*
 	 * Since we may open a new transaction for each relation, we have to check
 	 * that the relation still is what we think it is.
@@ -350,11 +363,10 @@ cluster_rel(Oid tableOid, Oid indexOid, ClusterParams *params)
 	if (recheck)
 	{
 		/* Check that the user still owns the relation */
-		if (!pg_class_ownercheck(tableOid, GetUserId()))
+		if (!pg_class_ownercheck(tableOid, save_userid))
 		{
 			relation_close(OldHeap, AccessExclusiveLock);
-			pgstat_progress_end_command();
-			return;
+			goto out;
 		}
 
 		/*
@@ -369,8 +381,7 @@ cluster_rel(Oid tableOid, Oid indexOid, ClusterParams *params)
 		if (RELATION_IS_OTHER_TEMP(OldHeap))
 		{
 			relation_close(OldHeap, AccessExclusiveLock);
-			pgstat_progress_end_command();
-			return;
+			goto out;
 		}
 
 		if (OidIsValid(indexOid))
@@ -381,8 +392,7 @@ cluster_rel(Oid tableOid, Oid indexOid, ClusterParams *params)
 			if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(indexOid)))
 			{
 				relation_close(OldHeap, AccessExclusiveLock);
-				pgstat_progress_end_command();
-				return;
+				goto out;
 			}
 
 			/*
@@ -393,8 +403,7 @@ cluster_rel(Oid tableOid, Oid indexOid, ClusterParams *params)
 				!get_index_isclustered(indexOid))
 			{
 				relation_close(OldHeap, AccessExclusiveLock);
-				pgstat_progress_end_command();
-				return;
+				goto out;
 			}
 		}
 	}
@@ -447,8 +456,7 @@ cluster_rel(Oid tableOid, Oid indexOid, ClusterParams *params)
 		!RelationIsPopulated(OldHeap))
 	{
 		relation_close(OldHeap, AccessExclusiveLock);
-		pgstat_progress_end_command();
-		return;
+		goto out;
 	}
 
 	Assert(OldHeap->rd_rel->relkind == RELKIND_RELATION ||
@@ -468,6 +476,13 @@ cluster_rel(Oid tableOid, Oid indexOid, ClusterParams *params)
 
 	/* NB: rebuild_relation does table_close() on OldHeap */
 
+out:
+	/* 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);
+
 	pgstat_progress_end_command();
 }
 

src/backend/commands/indexcmds.c

@@ -547,21 +547,22 @@ DefineIndex(Oid relationId,
 	LOCKTAG		heaplocktag;
 	LOCKMODE	lockmode;
 	Snapshot	snapshot;
-	int			save_nestlevel = -1;
+	Oid			root_save_userid;
+	int			root_save_sec_context;
+	int			root_save_nestlevel;
 	int			i;
 
+	root_save_nestlevel = NewGUCNestLevel();
+
 	/*
 	 * Some callers need us to run with an empty default_tablespace; this is a
 	 * necessary hack to be able to reproduce catalog state accurately when
 	 * recreating indexes after table-rewriting ALTER TABLE.
 	 */
 	if (stmt->reset_default_tblspc)
-	{
-		save_nestlevel = NewGUCNestLevel();
 		(void) set_config_option("default_tablespace", "",
 								 PGC_USERSET, PGC_S_SESSION,
 								 GUC_ACTION_SAVE, true, 0, false);
-	}
 
 	/*
 	 * Force non-concurrent build on temporary relations, even if CONCURRENTLY
@@ -640,6 +641,15 @@ DefineIndex(Oid relationId,
 	lockmode = concurrent ? ShareUpdateExclusiveLock : ShareLock;
 	rel = table_open(relationId, lockmode);
 
+	/*
+	 * Switch to the table owner's userid, so that any index functions are run
+	 * as that user.  Also lock down security-restricted operations.  We
+	 * already arranged to make GUC variable changes local to this command.
+	 */
+	GetUserIdAndSecContext(&root_save_userid, &root_save_sec_context);
+	SetUserIdAndSecContext(rel->rd_rel->relowner,
+						   root_save_sec_context | SECURITY_RESTRICTED_OPERATION);
+
 	namespaceId = RelationGetNamespace(rel);
 
 	/* Ensure that it makes sense to index this kind of relation */
@@ -715,7 +725,7 @@ DefineIndex(Oid relationId,
 	{
 		AclResult	aclresult;
 
-		aclresult = pg_namespace_aclcheck(namespaceId, GetUserId(),
+		aclresult = pg_namespace_aclcheck(namespaceId, root_save_userid,
 										  ACL_CREATE);
 		if (aclresult != ACLCHECK_OK)
 			aclcheck_error(aclresult, OBJECT_SCHEMA,
@@ -747,7 +757,7 @@ DefineIndex(Oid relationId,
 	{
 		AclResult	aclresult;
 
-		aclresult = pg_tablespace_aclcheck(tablespaceId, GetUserId(),
+		aclresult = pg_tablespace_aclcheck(tablespaceId, root_save_userid,
 										   ACL_CREATE);
 		if (aclresult != ACLCHECK_OK)
 			aclcheck_error(aclresult, OBJECT_TABLESPACE,
@@ -1138,15 +1148,17 @@ DefineIndex(Oid relationId,
 
 	ObjectAddressSet(address, RelationRelationId, indexRelationId);
 
-	/*
-	 * Revert to original default_tablespace.  Must do this before any return
-	 * from this function, but after index_create, so this is a good time.
-	 */
-	if (save_nestlevel >= 0)
-		AtEOXact_GUC(true, save_nestlevel);
-
 	if (!OidIsValid(indexRelationId))
 	{
+		/*
+		 * Roll back any GUC changes executed by index functions.  Also revert
+		 * to original default_tablespace if we changed it above.
+		 */
+		AtEOXact_GUC(false, root_save_nestlevel);
+
+		/* Restore userid and security context */
+		SetUserIdAndSecContext(root_save_userid, root_save_sec_context);
+
 		table_close(rel, NoLock);
 
 		/* If this is the top-level index, we're done */
@@ -1156,6 +1168,17 @@ DefineIndex(Oid relationId,
 		return address;
 	}
 
+	/*
+	 * Roll back any GUC changes executed by index functions, and keep
+	 * subsequent changes local to this command.  It's barely possible that
+	 * some index function changed a behavior-affecting GUC, e.g. xmloption,
+	 * that affects subsequent steps.  This improves bug-compatibility with
+	 * older PostgreSQL versions.  They did the AtEOXact_GUC() here for the
+	 * purpose of clearing the above default_tablespace change.
+	 */
+	AtEOXact_GUC(false, root_save_nestlevel);
+	root_save_nestlevel = NewGUCNestLevel();
+
 	/* Add any requested comment */
 	if (stmt->idxcomment != NULL)
 		CreateComments(indexRelationId, RelationRelationId, 0,
@@ -1202,6 +1225,9 @@ DefineIndex(Oid relationId,
 			{
 				Oid			childRelid = part_oids[i];
 				Relation	childrel;
+				Oid			child_save_userid;
+				int			child_save_sec_context;
+				int			child_save_nestlevel;
 				List	   *childidxs;
 				ListCell   *cell;
 				AttrMap    *attmap;
@@ -1209,6 +1235,12 @@ DefineIndex(Oid relationId,
 
 				childrel = table_open(childRelid, lockmode);
 
+				GetUserIdAndSecContext(&child_save_userid,
+									   &child_save_sec_context);
+				SetUserIdAndSecContext(childrel->rd_rel->relowner,
+									   child_save_sec_context | SECURITY_RESTRICTED_OPERATION);
+				child_save_nestlevel = NewGUCNestLevel();
+
 				/*
 				 * Don't try to create indexes on foreign tables, though. Skip
 				 * those if a regular index, or fail if trying to create a
@@ -1224,6 +1256,9 @@ DefineIndex(Oid relationId,
 								 errdetail("Table \"%s\" contains partitions that are foreign tables.",
 										   RelationGetRelationName(rel))));
 
+					AtEOXact_GUC(false, child_save_nestlevel);
+					SetUserIdAndSecContext(child_save_userid,
+										   child_save_sec_context);
 					table_close(childrel, lockmode);
 					continue;
 				}
@@ -1295,6 +1330,9 @@ DefineIndex(Oid relationId,
 				}
 
 				list_free(childidxs);
+				AtEOXact_GUC(false, child_save_nestlevel);
+				SetUserIdAndSecContext(child_save_userid,
+									   child_save_sec_context);
 				table_close(childrel, NoLock);
 
 				/*
@@ -1351,12 +1389,21 @@ DefineIndex(Oid relationId,
 					if (found_whole_row)
 						elog(ERROR, "cannot convert whole-row table reference");
 
+					/*
+					 * Recurse as the starting user ID.  Callee will use that
+					 * for permission checks, then switch again.
+					 */
+					Assert(GetUserId() == child_save_userid);
+					SetUserIdAndSecContext(root_save_userid,
+										   root_save_sec_context);
 					DefineIndex(childRelid, childStmt,
 								InvalidOid, /* no predefined OID */
 								indexRelationId,	/* this is our child */
 								createdConstraintId,
 								is_alter_table, check_rights, check_not_in_use,
 								skip_build, quiet);
+					SetUserIdAndSecContext(child_save_userid,
+										   child_save_sec_context);
 				}
 
 				pgstat_progress_update_param(PROGRESS_CREATEIDX_PARTITIONS_DONE,
@@ -1393,12 +1440,17 @@ DefineIndex(Oid relationId,
 		 * Indexes on partitioned tables are not themselves built, so we're
 		 * done here.
 		 */
+		AtEOXact_GUC(false, root_save_nestlevel);
+		SetUserIdAndSecContext(root_save_userid, root_save_sec_context);
 		table_close(rel, NoLock);
 		if (!OidIsValid(parentIndexId))
 			pgstat_progress_end_command();
 		return address;
 	}
 
+	AtEOXact_GUC(false, root_save_nestlevel);
+	SetUserIdAndSecContext(root_save_userid, root_save_sec_context);
+
 	if (!concurrent)
 	{
 		/* Close the heap and we're done, in the non-concurrent case */
@@ -3524,6 +3576,9 @@ ReindexRelationConcurrently(Oid relationOid, ReindexParams *params)
 		Oid			newIndexId;
 		Relation	indexRel;
 		Relation	heapRel;
+		Oid			save_userid;
+		int			save_sec_context;
+		int			save_nestlevel;
 		Relation	newIndexRel;
 		LockRelId  *lockrelid;
 		Oid			tablespaceid;
@@ -3532,6 +3587,16 @@ ReindexRelationConcurrently(Oid relationOid, ReindexParams *params)
 		heapRel = table_open(indexRel->rd_index->indrelid,
 							 ShareUpdateExclusiveLock);
 
+		/*
+		 * 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();
+
 		/* determine safety of this index for set_indexsafe_procflags */
 		idx->safe = (indexRel->rd_indexprs == NIL &&
 					 indexRel->rd_indpred == NIL);
@@ -3607,6 +3672,13 @@ ReindexRelationConcurrently(Oid relationOid, ReindexParams *params)
 
 		index_close(indexRel, NoLock);
 		index_close(newIndexRel, NoLock);
+
+		/* 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);
+
 		table_close(heapRel, NoLock);
 	}
 

src/backend/utils/init/miscinit.c

@@ -567,15 +567,21 @@ GetAuthenticatedUserId(void)
  * with guc.c's internal state, so SET ROLE has to be disallowed.
  *
  * SECURITY_RESTRICTED_OPERATION indicates that we are inside an operation
- * that does not wish to trust called user-defined functions at all.  This
- * bit prevents not only SET ROLE, but various other changes of session state
- * that normally is unprotected but might possibly be used to subvert the
- * calling session later.  An example is replacing an existing prepared
- * statement with new code, which will then be executed with the outer
- * session's permissions when the prepared statement is next used.  Since
- * these restrictions are fairly draconian, we apply them only in contexts
- * where the called functions are really supposed to be side-effect-free
- * anyway, such as VACUUM/ANALYZE/REINDEX.
+ * that does not wish to trust called user-defined functions at all.  The
+ * policy is to use this before operations, e.g. autovacuum and REINDEX, that
+ * enumerate relations of a database or schema and run functions associated
+ * with each found relation.  The relation owner is the new user ID.  Set this
+ * as soon as possible after locking the relation.  Restore the old user ID as
+ * late as possible before closing the relation; restoring it shortly after
+ * close is also tolerable.  If a command has both relation-enumerating and
+ * non-enumerating modes, e.g. ANALYZE, both modes set this bit.  This bit
+ * prevents not only SET ROLE, but various other changes of session state that
+ * normally is unprotected but might possibly be used to subvert the calling
+ * session later.  An example is replacing an existing prepared statement with
+ * new code, which will then be executed with the outer session's permissions
+ * when the prepared statement is next used.  These restrictions are fairly
+ * draconian, but the functions called in relation-enumerating operations are
+ * really supposed to be side-effect-free anyway.
  *
  * SECURITY_NOFORCE_RLS indicates that we are inside an operation which should
  * ignore the FORCE ROW LEVEL SECURITY per-table indication.  This is used to

src/test/regress/expected/privileges.out

@@ -1592,6 +1592,61 @@ SELECT has_table_privilege('regress_priv_user1', 'atest4', 'SELECT WITH GRANT OP
 -- security-restricted operations
 \c -
 CREATE ROLE regress_sro_user;
+-- Check that index expressions and predicates are run as the table's owner
+-- A dummy index function checking current_user
+CREATE FUNCTION sro_ifun(int) RETURNS int AS $$
+BEGIN
+	-- Below we set the table's owner to regress_sro_user
+	ASSERT current_user = 'regress_sro_user',
+		format('sro_ifun(%s) called by %s', $1, current_user);
+	RETURN $1;
+END;
+$$ LANGUAGE plpgsql IMMUTABLE;
+-- Create a table owned by regress_sro_user
+CREATE TABLE sro_tab (a int);
+ALTER TABLE sro_tab OWNER TO regress_sro_user;
+INSERT INTO sro_tab VALUES (1), (2), (3);
+-- Create an expression index with a predicate
+CREATE INDEX sro_idx ON sro_tab ((sro_ifun(a) + sro_ifun(0)))
+	WHERE sro_ifun(a + 10) > sro_ifun(10);
+DROP INDEX sro_idx;
+-- Do the same concurrently
+CREATE INDEX CONCURRENTLY sro_idx ON sro_tab ((sro_ifun(a) + sro_ifun(0)))
+	WHERE sro_ifun(a + 10) > sro_ifun(10);
+-- REINDEX
+REINDEX TABLE sro_tab;
+REINDEX INDEX sro_idx;
+REINDEX TABLE CONCURRENTLY sro_tab;
+DROP INDEX sro_idx;
+-- CLUSTER
+CREATE INDEX sro_cluster_idx ON sro_tab ((sro_ifun(a) + sro_ifun(0)));
+CLUSTER sro_tab USING sro_cluster_idx;
+DROP INDEX sro_cluster_idx;
+-- BRIN index
+CREATE INDEX sro_brin ON sro_tab USING brin ((sro_ifun(a) + sro_ifun(0)));
+SELECT brin_desummarize_range('sro_brin', 0);
+ brin_desummarize_range 
+------------------------
+ 
+(1 row)
+
+SELECT brin_summarize_range('sro_brin', 0);
+ brin_summarize_range 
+----------------------
+                    1
+(1 row)
+
+DROP TABLE sro_tab;
+-- Check with a partitioned table
+CREATE TABLE sro_ptab (a int) PARTITION BY RANGE (a);
+ALTER TABLE sro_ptab OWNER TO regress_sro_user;
+CREATE TABLE sro_part PARTITION OF sro_ptab FOR VALUES FROM (1) TO (10);
+ALTER TABLE sro_part OWNER TO regress_sro_user;
+INSERT INTO sro_ptab VALUES (1), (2), (3);
+CREATE INDEX sro_pidx ON sro_ptab ((sro_ifun(a) + sro_ifun(0)))
+	WHERE sro_ifun(a + 10) > sro_ifun(10);
+REINDEX TABLE sro_ptab;
+REINDEX INDEX CONCURRENTLY sro_pidx;
 SET SESSION AUTHORIZATION regress_sro_user;
 CREATE FUNCTION unwanted_grant() RETURNS void LANGUAGE sql AS
 	'GRANT regress_priv_group2 TO regress_sro_user';

src/test/regress/sql/privileges.sql

@@ -1043,6 +1043,53 @@ SELECT has_table_privilege('regress_priv_user1', 'atest4', 'SELECT WITH GRANT OP
 \c -
 CREATE ROLE regress_sro_user;
 
+-- Check that index expressions and predicates are run as the table's owner
+
+-- A dummy index function checking current_user
+CREATE FUNCTION sro_ifun(int) RETURNS int AS $$
+BEGIN
+	-- Below we set the table's owner to regress_sro_user
+	ASSERT current_user = 'regress_sro_user',
+		format('sro_ifun(%s) called by %s', $1, current_user);
+	RETURN $1;
+END;
+$$ LANGUAGE plpgsql IMMUTABLE;
+-- Create a table owned by regress_sro_user
+CREATE TABLE sro_tab (a int);
+ALTER TABLE sro_tab OWNER TO regress_sro_user;
+INSERT INTO sro_tab VALUES (1), (2), (3);
+-- Create an expression index with a predicate
+CREATE INDEX sro_idx ON sro_tab ((sro_ifun(a) + sro_ifun(0)))
+	WHERE sro_ifun(a + 10) > sro_ifun(10);
+DROP INDEX sro_idx;
+-- Do the same concurrently
+CREATE INDEX CONCURRENTLY sro_idx ON sro_tab ((sro_ifun(a) + sro_ifun(0)))
+	WHERE sro_ifun(a + 10) > sro_ifun(10);
+-- REINDEX
+REINDEX TABLE sro_tab;
+REINDEX INDEX sro_idx;
+REINDEX TABLE CONCURRENTLY sro_tab;
+DROP INDEX sro_idx;
+-- CLUSTER
+CREATE INDEX sro_cluster_idx ON sro_tab ((sro_ifun(a) + sro_ifun(0)));
+CLUSTER sro_tab USING sro_cluster_idx;
+DROP INDEX sro_cluster_idx;
+-- BRIN index
+CREATE INDEX sro_brin ON sro_tab USING brin ((sro_ifun(a) + sro_ifun(0)));
+SELECT brin_desummarize_range('sro_brin', 0);
+SELECT brin_summarize_range('sro_brin', 0);
+DROP TABLE sro_tab;
+-- Check with a partitioned table
+CREATE TABLE sro_ptab (a int) PARTITION BY RANGE (a);
+ALTER TABLE sro_ptab OWNER TO regress_sro_user;
+CREATE TABLE sro_part PARTITION OF sro_ptab FOR VALUES FROM (1) TO (10);
+ALTER TABLE sro_part OWNER TO regress_sro_user;
+INSERT INTO sro_ptab VALUES (1), (2), (3);
+CREATE INDEX sro_pidx ON sro_ptab ((sro_ifun(a) + sro_ifun(0)))
+	WHERE sro_ifun(a + 10) > sro_ifun(10);
+REINDEX TABLE sro_ptab;
+REINDEX INDEX CONCURRENTLY sro_pidx;
+
 SET SESSION AUTHORIZATION regress_sro_user;
 CREATE FUNCTION unwanted_grant() RETURNS void LANGUAGE sql AS
 	'GRANT regress_priv_group2 TO regress_sro_user';