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, 16 insertions, 9 deletions

diff --git a/src/backend/rewrite/rowsecurity.c b/src/backend/rewrite/rowsecurity.c
index f49cfb6cc66..f03b36a6e4e 100644
--- a/src/backend/rewrite/rowsecurity.c
+++ b/src/backend/rewrite/rowsecurity.c
@@ -47,6 +47,7 @@
 #include "nodes/pg_list.h"
 #include "nodes/plannodes.h"
 #include "parser/parsetree.h"
+#include "parser/parse_relation.h"
 #include "rewrite/rewriteDefine.h"
 #include "rewrite/rewriteHandler.h"
 #include "rewrite/rewriteManip.h"
@@ -115,6 +116,7 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 	CmdType		commandType;
 	List	   *permissive_policies;
 	List	   *restrictive_policies;
+	RTEPermissionInfo *perminfo;
 
 	/* Defaults for the return values */
 	*securityQuals = NIL;
@@ -122,16 +124,21 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 	*hasRowSecurity = false;
 	*hasSubLinks = false;
 
+	Assert(rte->rtekind == RTE_RELATION);
+
 	/* If this is not a normal relation, just return immediately */
 	if (rte->relkind != RELKIND_RELATION &&
 		rte->relkind != RELKIND_PARTITIONED_TABLE)
 		return;
 
+	perminfo = getRTEPermissionInfo(root->rteperminfos, rte);
+
 	/* Switch to checkAsUser if it's set */
-	user_id = OidIsValid(rte->checkAsUser) ? rte->checkAsUser : GetUserId();
+	user_id = OidIsValid(perminfo->checkAsUser) ?
+		perminfo->checkAsUser : GetUserId();
 
 	/* Determine the state of RLS for this, pass checkAsUser explicitly */
-	rls_status = check_enable_rls(rte->relid, rte->checkAsUser, false);
+	rls_status = check_enable_rls(rte->relid, perminfo->checkAsUser, false);
 
 	/* If there is no RLS on this table at all, nothing to do */
 	if (rls_status == RLS_NONE)
@@ -196,7 +203,7 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 	 * which the user does not have access to via the UPDATE USING policies,
 	 * similar to how we require normal UPDATE rights for these queries.
 	 */
-	if (commandType == CMD_SELECT && rte->requiredPerms & ACL_UPDATE)
+	if (commandType == CMD_SELECT && perminfo->requiredPerms & ACL_UPDATE)
 	{
 		List	   *update_permissive_policies;
 		List	   *update_restrictive_policies;
@@ -243,7 +250,7 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 	 */
 	if ((commandType == CMD_UPDATE || commandType == CMD_DELETE ||
 		 commandType == CMD_MERGE) &&
-		rte->requiredPerms & ACL_SELECT)
+		perminfo->requiredPerms & ACL_SELECT)
 	{
 		List	   *select_permissive_policies;
 		List	   *select_restrictive_policies;
@@ -286,7 +293,7 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 		 * raised if a policy is violated; otherwise, we might end up silently
 		 * dropping rows to be added.
 		 */
-		if (rte->requiredPerms & ACL_SELECT)
+		if (perminfo->requiredPerms & ACL_SELECT)
 		{
 			List	   *select_permissive_policies = NIL;
 			List	   *select_restrictive_policies = NIL;
@@ -342,7 +349,7 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 			 * for this relation, also as WCO policies, again, to avoid
 			 * silently dropping data.  See above.
 			 */
-			if (rte->requiredPerms & ACL_SELECT)
+			if (perminfo->requiredPerms & ACL_SELECT)
 			{
 				get_policies_for_relation(rel, CMD_SELECT, user_id,
 										  &conflict_select_permissive_policies,
@@ -371,7 +378,7 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 			 * path of an INSERT .. ON CONFLICT DO UPDATE, if SELECT rights
 			 * are required for this relation.
 			 */
-			if (rte->requiredPerms & ACL_SELECT)
+			if (perminfo->requiredPerms & ACL_SELECT)
 				add_with_check_options(rel, rt_index,
 									   WCO_RLS_UPDATE_CHECK,
 									   conflict_select_permissive_policies,
@@ -474,8 +481,8 @@ get_row_security_policies(Query *root, RangeTblEntry *rte, int rt_index,
 	 * Copy checkAsUser to the row security quals and WithCheckOption checks,
 	 * in case they contain any subqueries referring to other relations.
 	 */
-	setRuleCheckAsUser((Node *) *securityQuals, rte->checkAsUser);
-	setRuleCheckAsUser((Node *) *withCheckOptions, rte->checkAsUser);
+	setRuleCheckAsUser((Node *) *securityQuals, perminfo->checkAsUser);
+	setRuleCheckAsUser((Node *) *withCheckOptions, perminfo->checkAsUser);
 
 	/*
 	 * Mark this query as having row security, so plancache can invalidate it