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

2 files changed, 12 insertions, 1 deletions

diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
index 962ebf65de1..3fd56ceccdf 100644
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -111,6 +111,9 @@ typedef Node *(*CoerceParamHook) (ParseState *pstate, Param *param,
  * Note that neither relname nor refname of these entries are necessarily
  * unique; searching the rtable by name is a bad idea.
  *
+ * p_rteperminfos: list of RTEPermissionInfo containing an entry corresponding
+ * to each RTE_RELATION entry in p_rtable.
+ *
  * p_joinexprs: list of JoinExpr nodes associated with p_rtable entries.
  * This is one-for-one with p_rtable, but contains NULLs for non-join
  * RTEs, and may be shorter than p_rtable if the last RTE(s) aren't joins.
@@ -181,6 +184,8 @@ struct ParseState
 	ParseState *parentParseState;	/* stack link */
 	const char *p_sourcetext;	/* source text, or NULL if not available */
 	List	   *p_rtable;		/* range table so far */
+	List	   *p_rteperminfos; /* list of RTEPermissionInfo nodes for each
+								 * RTE_RELATION entry in rtable */
 	List	   *p_joinexprs;	/* JoinExprs for RTE_JOIN p_rtable entries */
 	List	   *p_joinlist;		/* join items so far (will become FromExpr
 								 * node's fromlist) */
@@ -234,7 +239,8 @@ struct ParseState
  * join's first N columns, the net effect is just that we expose only those
  * join columns via this nsitem.)
  *
- * p_rte and p_rtindex link to the underlying rangetable entry.
+ * p_rte and p_rtindex link to the underlying rangetable entry, and
+ * p_perminfo to the entry in rteperminfos.
  *
  * The p_nscolumns array contains info showing how to construct Vars
  * referencing the names appearing in the p_names->colnames list.
@@ -271,6 +277,7 @@ struct ParseNamespaceItem
 	Alias	   *p_names;		/* Table and column names */
 	RangeTblEntry *p_rte;		/* The relation's rangetable entry */
 	int			p_rtindex;		/* The relation's index in the rangetable */
+	RTEPermissionInfo *p_perminfo;	/* The relation's rteperminfos entry */
 	/* array of same length as p_names->colnames: */
 	ParseNamespaceColumn *p_nscolumns;	/* per-column data */
 	bool		p_rel_visible;	/* Relation name is visible? */
diff --git a/src/include/parser/parse_relation.h b/src/include/parser/parse_relation.h
index 484db165dbf..2f8d417709f 100644
--- a/src/include/parser/parse_relation.h
+++ b/src/include/parser/parse_relation.h
@@ -99,6 +99,10 @@ extern ParseNamespaceItem *addRangeTableEntryForCTE(ParseState *pstate,
 extern ParseNamespaceItem *addRangeTableEntryForENR(ParseState *pstate,
 													RangeVar *rv,
 													bool inFromCl);
+extern RTEPermissionInfo *addRTEPermissionInfo(List **rteperminfos,
+											   RangeTblEntry *rte);
+extern RTEPermissionInfo *getRTEPermissionInfo(List *rteperminfos,
+											   RangeTblEntry *rte);
 extern bool isLockedRefname(ParseState *pstate, const char *refname);
 extern void addNSItemToQuery(ParseState *pstate, ParseNamespaceItem *nsitem,
 							 bool addToJoinList,