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

1 files changed, 85 insertions, 13 deletions

diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index cd30f15eba6..eac13ac0b73 100644
--- a/src/backend/commands/indexcmds.c
+++ b/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);
 	}