Use checkAsUser for selectivity estimator checks, if it's set.

In examine_variable() and examine_simple_variable(), when checking the
user's table and column privileges to determine whether to grant
access to the pg_statistic data, use checkAsUser for the privilege
checks, if it's set. This will be the case if we're accessing the
table via a view, to indicate that we should perform privilege checks
as the view owner rather than the current user.

This change makes this planner check consistent with the check in the
executor, so the planner will be able to make use of statistics if the
table is accessible via the view. This fixes a performance regression
introduced by commit e2d4ef8de8, which affects queries against
non-security barrier views in the case where the user doesn't have
privileges on the underlying table, but the view owner does.

Note that it continues to provide the same safeguards controlling
access to pg_statistic for direct table access (in which case
checkAsUser won't be set) and for security barrier views, because of
the nearby checks on rte->security_barrier and rte->securityQuals.

Back-patch to all supported branches because e2d4ef8de8 was.

Dean Rasheed, reviewed by Jonathan Katz and Stephen Frost.

1 files changed, 16 insertions, 4 deletions

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 1b16ebc27b2..da299a884ff 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -4560,11 +4560,18 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid,
 							{
 								/* Get index's table for permission check */
 								RangeTblEntry *rte;
+								Oid			userid;
 
 								rte = planner_rt_fetch(index->rel->relid, root);
 								Assert(rte->rtekind == RTE_RELATION);
 
 								/*
+								 * Use checkAsUser if it's set, in case we're
+								 * accessing the table via a view.
+								 */
+								userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();
+
+								/*
 								 * For simplicity, we insist on the whole
 								 * table being selectable, rather than trying
 								 * to identify which column(s) the index
@@ -4575,7 +4582,7 @@ examine_variable(PlannerInfo *root, Node *node, int varRelid,
 								 */
 								vardata->acl_ok =
 									rte->securityQuals == NIL &&
-									(pg_class_aclcheck(rte->relid, GetUserId(),
+									(pg_class_aclcheck(rte->relid, userid,
 												 ACL_SELECT) == ACLCHECK_OK);
 							}
 							else
@@ -4638,16 +4645,21 @@ examine_simple_variable(PlannerInfo *root, Var *var,
 
 		if (HeapTupleIsValid(vardata->statsTuple))
 		{
+			Oid			userid;
+
 			/*
 			 * Check if user has permission to read this column.  We require
 			 * all rows to be accessible, so there must be no securityQuals
-			 * from security barrier views or RLS policies.
+			 * from security barrier views or RLS policies.  Use checkAsUser
+			 * if it's set, in case we're accessing the table via a view.
 			 */
+			userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();
+
 			vardata->acl_ok =
 				rte->securityQuals == NIL &&
-				((pg_class_aclcheck(rte->relid, GetUserId(),
+				((pg_class_aclcheck(rte->relid, userid,
 									ACL_SELECT) == ACLCHECK_OK) ||
-				 (pg_attribute_aclcheck(rte->relid, var->varattno, GetUserId(),
+				 (pg_attribute_aclcheck(rte->relid, var->varattno, userid,
 										ACL_SELECT) == ACLCHECK_OK));
 		}
 		else