Rework query relation permission checking

Currently, information about the permissions to be checked on relations
mentioned in a query is stored in their range table entries.  So the
executor must scan the entire range table looking for relations that
need to have permissions checked.  This can make the permission checking
part of the executor initialization needlessly expensive when many
inheritance children are present in the range range.  While the
permissions need not be checked on the individual child relations, the
executor still must visit every range table entry to filter them out.

This commit moves the permission checking information out of the range
table entries into a new plan node called RTEPermissionInfo.  Every
top-level (inheritance "root") RTE_RELATION entry in the range table
gets one and a list of those is maintained alongside the range table.
This new list is initialized by the parser when initializing the range
table.  The rewriter can add more entries to it as rules/views are
expanded.  Finally, the planner combines the lists of the individual
subqueries into one flat list that is passed to the executor for
checking.

To make it quick to find the RTEPermissionInfo entry belonging to a
given relation, RangeTblEntry gets a new Index field 'perminfoindex'
that stores the corresponding RTEPermissionInfo's index in the query's
list of the latter.

ExecutorCheckPerms_hook has gained another List * argument; the
signature is now:
typedef bool (*ExecutorCheckPerms_hook_type) (List *rangeTable,
					      List *rtePermInfos,
					      bool ereport_on_violation);
The first argument is no longer used by any in-core uses of the hook,
but we leave it in place because there may be other implementations that
do.  Implementations should likely scan the rtePermInfos list to
determine which operations to allow or deny.

Author: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/CA+HiwqGjJDmUhDSfv-U2qhKJjt9ST7Xh9JXC_irsAQ1TAUsJYg@mail.gmail.com

1 files changed, 11 insertions, 7 deletions

diff --git a/src/backend/parser/parse_target.c b/src/backend/parser/parse_target.c
index 8e0d6fd01f1..56d64c88516 100644
--- a/src/backend/parser/parse_target.c
+++ b/src/backend/parser/parse_target.c
@@ -1132,7 +1132,7 @@ ExpandColumnRefStar(ParseState *pstate, ColumnRef *cref,
 		 *
 		 * Note: this code is a lot like transformColumnRef; it's tempting to
 		 * call that instead and then replace the resulting whole-row Var with
-		 * a list of Vars.  However, that would leave us with the RTE's
+		 * a list of Vars.  However, that would leave us with the relation's
 		 * selectedCols bitmap showing the whole row as needing select
 		 * permission, as well as the individual columns.  That would be
 		 * incorrect (since columns added later shouldn't need select
@@ -1367,6 +1367,7 @@ ExpandSingleTable(ParseState *pstate, ParseNamespaceItem *nsitem,
 	else
 	{
 		RangeTblEntry *rte = nsitem->p_rte;
+		RTEPermissionInfo *perminfo = nsitem->p_perminfo;
 		List	   *vars;
 		ListCell   *l;
 
@@ -1381,7 +1382,10 @@ ExpandSingleTable(ParseState *pstate, ParseNamespaceItem *nsitem,
 		 * target relation of UPDATE/DELETE, which cannot be under a join.)
 		 */
 		if (rte->rtekind == RTE_RELATION)
-			rte->requiredPerms |= ACL_SELECT;
+		{
+			Assert(perminfo != NULL);
+			perminfo->requiredPerms |= ACL_SELECT;
+		}
 
 		/* Require read access to each column */
 		foreach(l, vars)
@@ -1414,11 +1418,11 @@ ExpandRowReference(ParseState *pstate, Node *expr,
 	/*
 	 * If the rowtype expression is a whole-row Var, we can expand the fields
 	 * as simple Vars.  Note: if the RTE is a relation, this case leaves us
-	 * with the RTE's selectedCols bitmap showing the whole row as needing
-	 * select permission, as well as the individual columns.  However, we can
-	 * only get here for weird notations like (table.*).*, so it's not worth
-	 * trying to clean up --- arguably, the permissions marking is correct
-	 * anyway for such cases.
+	 * with its RTEPermissionInfo's selectedCols bitmap showing the whole row
+	 * as needing select permission, as well as the individual columns.
+	 * However, we can only get here for weird notations like (table.*).*, so
+	 * it's not worth trying to clean up --- arguably, the permissions marking
+	 * is correct anyway for such cases.
 	 */
 	if (IsA(expr, Var) &&
 		((Var *) expr)->varattno == InvalidAttrNumber)