Add support for security invoker views.

A security invoker view checks permissions for accessing its
underlying base relations using the privileges of the user of the
view, rather than the privileges of the view owner. Additionally, if
any of the base relations are tables with RLS enabled, the policies of
the user of the view are applied, rather than those of the view owner.

This allows views to be defined without giving away additional
privileges on the underlying base relations, and matches a similar
feature available in other database systems.

It also allows views to operate more naturally with RLS, without
affecting the assignments of policies to users.

Christoph Heiss, with some additional hacking by me. Reviewed by
Laurenz Albe and Wolfgang Walther.

Discussion: https://postgr.es/m/b66dd6d6-ad3e-c6f2-8b90-47be773da240%40cybertec.at

1 files changed, 46 insertions, 27 deletions

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index fccffce5729..fbd11883e17 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -722,6 +722,8 @@ RelationBuildTupleDesc(Relation relation)
  * entry, because that keeps the update logic in RelationClearRelation()
  * manageable.  The other subsidiary data structures are simple enough
  * to be easy to free explicitly, anyway.
+ *
+ * Note: The relation's reloptions must have been extracted first.
  */
 static void
 RelationBuildRuleLock(Relation relation)
@@ -787,6 +789,7 @@ RelationBuildRuleLock(Relation relation)
 		Datum		rule_datum;
 		char	   *rule_str;
 		RewriteRule *rule;
+		Oid			check_as_user;
 
 		rule = (RewriteRule *) MemoryContextAlloc(rulescxt,
 												  sizeof(RewriteRule));
@@ -826,10 +829,23 @@ RelationBuildRuleLock(Relation relation)
 		pfree(rule_str);
 
 		/*
-		 * We want the rule's table references to be checked as though by the
-		 * table owner, not the user referencing the rule.  Therefore, scan
-		 * through the rule's actions and set the checkAsUser field on all
-		 * rtable entries.  We have to look at the qual as well, in case it
+		 * If this is a SELECT rule defining a view, and the view has
+		 * "security_invoker" set, we must perform all permissions checks on
+		 * relations referred to by the rule as the invoking user.
+		 *
+		 * In all other cases (including non-SELECT rules on security invoker
+		 * views), perform the permissions checks as the relation owner.
+		 */
+		if (rule->event == CMD_SELECT &&
+			relation->rd_rel->relkind == RELKIND_VIEW &&
+			RelationHasSecurityInvoker(relation))
+			check_as_user = InvalidOid;
+		else
+			check_as_user = relation->rd_rel->relowner;
+
+		/*
+		 * Scan through the rule's actions and set the checkAsUser field on
+		 * all rtable entries. We have to look at the qual as well, in case it
 		 * contains sublinks.
 		 *
 		 * The reason for doing this when the rule is loaded, rather than when
@@ -838,8 +854,8 @@ RelationBuildRuleLock(Relation relation)
 		 * the rule tree during load is relatively cheap (compared to
 		 * constructing it in the first place), so we do it here.
 		 */
-		setRuleCheckAsUser((Node *) rule->actions, relation->rd_rel->relowner);
-		setRuleCheckAsUser(rule->qual, relation->rd_rel->relowner);
+		setRuleCheckAsUser((Node *) rule->actions, check_as_user);
+		setRuleCheckAsUser(rule->qual, check_as_user);
 
 		if (numlocks >= maxlocks)
 		{
@@ -1164,27 +1180,6 @@ retry:
 	 */
 	RelationBuildTupleDesc(relation);
 
-	/*
-	 * Fetch rules and triggers that affect this relation
-	 */
-	if (relation->rd_rel->relhasrules)
-		RelationBuildRuleLock(relation);
-	else
-	{
-		relation->rd_rules = NULL;
-		relation->rd_rulescxt = NULL;
-	}
-
-	if (relation->rd_rel->relhastriggers)
-		RelationBuildTriggers(relation);
-	else
-		relation->trigdesc = NULL;
-
-	if (relation->rd_rel->relrowsecurity)
-		RelationBuildRowSecurity(relation);
-	else
-		relation->rd_rsdesc = NULL;
-
 	/* foreign key data is not loaded till asked for */
 	relation->rd_fkeylist = NIL;
 	relation->rd_fkeyvalid = false;
@@ -1217,6 +1212,30 @@ retry:
 	RelationParseRelOptions(relation, pg_class_tuple);
 
 	/*
+	 * Fetch rules and triggers that affect this relation.
+	 *
+	 * Note that RelationBuildRuleLock() relies on this being done after
+	 * extracting the relation's reloptions.
+	 */
+	if (relation->rd_rel->relhasrules)
+		RelationBuildRuleLock(relation);
+	else
+	{
+		relation->rd_rules = NULL;
+		relation->rd_rulescxt = NULL;
+	}
+
+	if (relation->rd_rel->relhastriggers)
+		RelationBuildTriggers(relation);
+	else
+		relation->trigdesc = NULL;
+
+	if (relation->rd_rel->relrowsecurity)
+		RelationBuildRowSecurity(relation);
+	else
+		relation->rd_rsdesc = NULL;
+
+	/*
 	 * initialize the relation lock manager information
 	 */
 	RelationInitLockInfo(relation); /* see lmgr.c */