Switch user ID to the object owner when populating a materialized view.

This makes superuser-issued REFRESH MATERIALIZED VIEW safe regardless of
the object's provenance.  REINDEX is an earlier example of this pattern.
As a downside, functions called from materialized views must tolerate
running in a security-restricted operation.  CREATE MATERIALIZED VIEW
need not change user ID.  Nonetheless, avoid creation of materialized
views that will invariably fail REFRESH by making it, too, start a
security-restricted operation.

Back-patch to 9.3 so materialized views have this from the beginning.

Reviewed by Kevin Grittner.

doc/src/sgml/ref/create_materialized_view.sgml

@@ -105,7 +105,9 @@ CREATE MATERIALIZED VIEW <replaceable>table_name</replaceable>
     <listitem>
      <para>
       A <xref linkend="sql-select">, <link linkend="sql-table">TABLE</link>,
-      or <xref linkend="sql-values"> command.
+      or <xref linkend="sql-values"> command.  This query will run within a
+      security-restricted operation; in particular, calls to functions that
+      themselves create temporary tables will fail.
      </para>
     </listitem>
    </varlistentry>

src/backend/commands/createas.c

@@ -33,6 +33,7 @@
 #include "commands/prepare.h"
 #include "commands/tablecmds.h"
 #include "commands/view.h"
+#include "miscadmin.h"
 #include "parser/parse_clause.h"
 #include "rewrite/rewriteHandler.h"
 #include "storage/smgr.h"
@@ -69,7 +70,11 @@ ExecCreateTableAs(CreateTableAsStmt *stmt, const char *queryString,
 {
 	Query	   *query = (Query *) stmt->query;
 	IntoClause *into = stmt->into;
+	bool		is_matview = (into->viewQuery != NULL);
 	DestReceiver *dest;
+	Oid			save_userid = InvalidOid;
+	int			save_sec_context = 0;
+	int			save_nestlevel = 0;
 	List	   *rewritten;
 	PlannedStmt *plan;
 	QueryDesc  *queryDesc;
@@ -90,12 +95,28 @@ ExecCreateTableAs(CreateTableAsStmt *stmt, const char *queryString,
 	{
 		ExecuteStmt *estmt = (ExecuteStmt *) query->utilityStmt;
 
+		Assert(!is_matview);	/* excluded by syntax */
 		ExecuteQuery(estmt, into, queryString, params, dest, completionTag);
 
 		return;
 	}
 	Assert(query->commandType == CMD_SELECT);
 
+	/*
+	 * For materialized views, lock down security-restricted operations and
+	 * arrange to make GUC variable changes local to this command.	This is
+	 * not necessary for security, but this keeps the behavior similar to
+	 * REFRESH MATERIALIZED VIEW.  Otherwise, one could create a materialized
+	 * view not possible to refresh.
+	 */
+	if (is_matview)
+	{
+		GetUserIdAndSecContext(&save_userid, &save_sec_context);
+		SetUserIdAndSecContext(save_userid,
+						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+		save_nestlevel = NewGUCNestLevel();
+	}
+
 	/*
 	 * Parse analysis was done already, but we still have to run the rule
 	 * rewriter.  We do not do AcquireRewriteLocks: we assume the query either
@@ -160,6 +181,15 @@ ExecCreateTableAs(CreateTableAsStmt *stmt, const char *queryString,
 	FreeQueryDesc(queryDesc);
 
 	PopActiveSnapshot();
+
+	if (is_matview)
+	{
+		/* Roll back any GUC changes */
+		AtEOXact_GUC(false, save_nestlevel);
+
+		/* Restore userid and security context */
+		SetUserIdAndSecContext(save_userid, save_sec_context);
+	}
 }
 
 /*

src/backend/commands/matview.c

@@ -122,6 +122,9 @@ ExecRefreshMatView(RefreshMatViewStmt *stmt, const char *queryString,
 	RewriteRule *rule;
 	List	   *actions;
 	Query	   *dataQuery;
+	Oid			save_userid;
+	int			save_sec_context;
+	int			save_nestlevel;
 	Oid			tableSpace;
 	Oid			OIDNewHeap;
 	DestReceiver *dest;
@@ -191,6 +194,16 @@ ExecRefreshMatView(RefreshMatViewStmt *stmt, const char *queryString,
 	 */
 	CheckTableNotInUse(matviewRel, "REFRESH MATERIALIZED VIEW");
 
+	/*
+	 * Switch to the owner's userid, so that any functions are run as that
+	 * user.  Also lock down security-restricted operations and arrange to
+	 * make GUC variable changes local to this command.
+	 */
+	GetUserIdAndSecContext(&save_userid, &save_sec_context);
+	SetUserIdAndSecContext(matviewRel->rd_rel->relowner,
+						   save_sec_context | SECURITY_RESTRICTED_OPERATION);
+	save_nestlevel = NewGUCNestLevel();
+
 	/*
 	 * Tentatively mark the matview as populated or not (this will roll back
 	 * if we fail later).
@@ -217,6 +230,12 @@ ExecRefreshMatView(RefreshMatViewStmt *stmt, const char *queryString,
 					 RecentXmin, ReadNextMultiXactId());
 
 	RelationCacheInvalidateEntry(matviewOid);
+
+	/* Roll back any GUC changes */
+	AtEOXact_GUC(false, save_nestlevel);
+
+	/* Restore userid and security context */
+	SetUserIdAndSecContext(save_userid, save_sec_context);
 }
 
 /*