Make executor's SELECT INTO code save and restore original tuple receiver.

As previously coded, the QueryDesc's dest pointer was left dangling
(pointing at an already-freed receiver object) after ExecutorEnd.  It's a
bit astonishing that it took us this long to notice, and I'm not sure that
the known problem case with SQL functions is the only one.  Fix it by
saving and restoring the original receiver pointer, which seems the most
bulletproof way of ensuring any related bugs are also covered.

Per bug #6379 from Paul Ramsey.  Back-patch to 8.4 where the current
handling of SELECT INTO was introduced.

1 files changed, 15 insertions, 5 deletions

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 54df18d3c79..569d0ba7ade 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -2445,6 +2445,7 @@ typedef struct
 {
 	DestReceiver pub;			/* publicly-known function pointers */
 	EState	   *estate;			/* EState we are working with */
+	DestReceiver *origdest;		/* QueryDesc's original receiver */
 	Relation	rel;			/* Relation to write to */
 	int			hi_options;		/* heap_insert performance options */
 	BulkInsertState bistate;	/* bulk insert state */
@@ -2651,12 +2652,14 @@ OpenIntoRel(QueryDesc *queryDesc)
 	/*
 	 * Now replace the query's DestReceiver with one for SELECT INTO
 	 */
-	queryDesc->dest = CreateDestReceiver(DestIntoRel);
-	myState = (DR_intorel *) queryDesc->dest;
+	myState = (DR_intorel *) CreateDestReceiver(DestIntoRel);
 	Assert(myState->pub.mydest == DestIntoRel);
 	myState->estate = estate;
+	myState->origdest = queryDesc->dest;
 	myState->rel = intoRelationDesc;
 
+	queryDesc->dest = (DestReceiver *) myState;
+
 	/*
 	 * We can skip WAL-logging the insertions, unless PITR or streaming
 	 * replication is in use. We can skip the FSM in any case.
@@ -2677,8 +2680,11 @@ CloseIntoRel(QueryDesc *queryDesc)
 {
 	DR_intorel *myState = (DR_intorel *) queryDesc->dest;
 
-	/* OpenIntoRel might never have gotten called */
-	if (myState && myState->pub.mydest == DestIntoRel && myState->rel)
+	/*
+	 * OpenIntoRel might never have gotten called, and we also want to guard
+	 * against double destruction.
+	 */
+	if (myState && myState->pub.mydest == DestIntoRel)
 	{
 		FreeBulkInsertState(myState->bistate);
 
@@ -2689,7 +2695,11 @@ CloseIntoRel(QueryDesc *queryDesc)
 		/* close rel, but keep lock until commit */
 		heap_close(myState->rel, NoLock);
 
-		myState->rel = NULL;
+		/* restore the receiver belonging to executor's caller */
+		queryDesc->dest = myState->origdest;
+
+		/* might as well invoke my destructor */
+		intorel_destroy((DestReceiver *) myState);
 	}
 }