Fix memory corruptions around pg_dist_node accessors after a Citus downgrade is followed by an upgrade (#8144)

Unlike what has been fixed in #7950, #8120, #8124, #8121 and #8114, this
was not an issue in older releases but is a potential issue to be
introduced by the current (13.2) release because in one of recent
commits (#8122) two columns has been added to pg_dist_node. In other
words, none of the older releases since we started supporting downgrades
added new columns to pg_dist_node.

The mentioned PR actually attempted avoiding these kind of issues in one
of the code-paths but not in some others.

So, this PR, avoids memory corruptions around pg_dist_node accessors in
a standardized way (as implemented in other example PRs) and in all
code-paths.

src/backend/distributed/metadata/node_metadata.c

@@ -115,6 +115,8 @@ static bool NodeIsLocal(WorkerNode *worker);
 static void SetLockTimeoutLocally(int32 lock_cooldown);
 static void UpdateNodeLocation(int32 nodeId, char *newNodeName, int32 newNodePort,
 							   bool localOnly);
+static int GetNodePrimaryNodeIdAttrIndexInPgDistNode(TupleDesc tupleDesc);
+static int GetNodeIsCloneAttrIndexInPgDistNode(TupleDesc tupleDesc);
 static bool UnsetMetadataSyncedForAllWorkers(void);
 static char * GetMetadataSyncCommandToSetNodeColumn(WorkerNode *workerNode,
 													int columnIndex,
@@ -1196,6 +1198,11 @@ ActivateNodeList(MetadataSyncContext *context)
 void
 ActivateCloneNodeAsPrimary(WorkerNode *workerNode)
 {
+	Relation pgDistNode = table_open(DistNodeRelationId(), AccessShareLock);
+	TupleDesc tupleDescriptor = RelationGetDescr(pgDistNode);
+	TupleDesc copiedTupleDescriptor = CreateTupleDescCopy(tupleDescriptor);
+	table_close(pgDistNode, AccessShareLock);
+
 	/*
 	 * Set the node as primary and active.
 	 */
@@ -1203,9 +1210,13 @@ ActivateCloneNodeAsPrimary(WorkerNode *workerNode)
 							 ObjectIdGetDatum(PrimaryNodeRoleId()));
 	SetWorkerColumnLocalOnly(workerNode, Anum_pg_dist_node_isactive,
 							 BoolGetDatum(true));
-	SetWorkerColumnLocalOnly(workerNode, Anum_pg_dist_node_nodeisclone,
+	SetWorkerColumnLocalOnly(workerNode,
+							 GetNodeIsCloneAttrIndexInPgDistNode(copiedTupleDescriptor) +
+							 1,
 							 BoolGetDatum(false));
-	SetWorkerColumnLocalOnly(workerNode, Anum_pg_dist_node_nodeprimarynodeid,
+	SetWorkerColumnLocalOnly(workerNode,
+							 GetNodePrimaryNodeIdAttrIndexInPgDistNode(
+								 copiedTupleDescriptor) + 1,
 							 Int32GetDatum(0));
 	SetWorkerColumnLocalOnly(workerNode, Anum_pg_dist_node_hasmetadata,
 							 BoolGetDatum(true));
@@ -1779,14 +1790,14 @@ UpdateNodeLocation(int32 nodeId, char *newNodeName, int32 newNodePort, bool loca
 {
 	const bool indexOK = true;
 
-	ScanKeyData scanKey[1];
-	Datum values[Natts_pg_dist_node];
-	bool isnull[Natts_pg_dist_node];
-	bool replace[Natts_pg_dist_node];
-
 	Relation pgDistNode = table_open(DistNodeRelationId(), RowExclusiveLock);
 	TupleDesc tupleDescriptor = RelationGetDescr(pgDistNode);
 
+	ScanKeyData scanKey[1];
+	Datum *values = palloc0(tupleDescriptor->natts * sizeof(Datum));
+	bool *isnull = palloc0(tupleDescriptor->natts * sizeof(bool));
+	bool *replace = palloc0(tupleDescriptor->natts * sizeof(bool));
+
 	ScanKeyInit(&scanKey[0], Anum_pg_dist_node_nodeid,
 				BTEqualStrategyNumber, F_INT4EQ, Int32GetDatum(nodeId));
 
@@ -1801,8 +1812,6 @@ UpdateNodeLocation(int32 nodeId, char *newNodeName, int32 newNodePort, bool loca
 							   newNodeName, newNodePort)));
 	}
 
-	memset(replace, 0, sizeof(replace));
-
 	values[Anum_pg_dist_node_nodeport - 1] = Int32GetDatum(newNodePort);
 	isnull[Anum_pg_dist_node_nodeport - 1] = false;
 	replace[Anum_pg_dist_node_nodeport - 1] = true;
@@ -1835,6 +1844,10 @@ UpdateNodeLocation(int32 nodeId, char *newNodeName, int32 newNodePort, bool loca
 
 	systable_endscan(scanDescriptor);
 	table_close(pgDistNode, NoLock);
+
+	pfree(values);
+	pfree(isnull);
+	pfree(replace);
 }
 
 
@@ -2105,11 +2118,10 @@ citus_internal_mark_node_not_synced(PG_FUNCTION_ARGS)
 	Relation pgDistNode = table_open(DistNodeRelationId(), AccessShareLock);
 	TupleDesc tupleDescriptor = RelationGetDescr(pgDistNode);
 
-	Datum values[Natts_pg_dist_node];
+	Datum *values = palloc0(tupleDescriptor->natts * sizeof(Datum));
-	bool isnull[Natts_pg_dist_node];
+	bool *isnull = palloc0(tupleDescriptor->natts * sizeof(bool));
-	bool replace[Natts_pg_dist_node];
+	bool *replace = palloc0(tupleDescriptor->natts * sizeof(bool));
 
-	memset(replace, 0, sizeof(replace));
 	values[Anum_pg_dist_node_metadatasynced - 1] = DatumGetBool(false);
 	isnull[Anum_pg_dist_node_metadatasynced - 1] = false;
 	replace[Anum_pg_dist_node_metadatasynced - 1] = true;
@@ -2123,6 +2135,10 @@ citus_internal_mark_node_not_synced(PG_FUNCTION_ARGS)
 
 	table_close(pgDistNode, NoLock);
 
+	pfree(values);
+	pfree(isnull);
+	pfree(replace);
+
 	PG_RETURN_VOID();
 }
 
@@ -2831,9 +2847,9 @@ SetWorkerColumnLocalOnly(WorkerNode *workerNode, int columnIndex, Datum value)
 	TupleDesc tupleDescriptor = RelationGetDescr(pgDistNode);
 	HeapTuple heapTuple = GetNodeTuple(workerNode->workerName, workerNode->workerPort);
 
-	Datum values[Natts_pg_dist_node];
+	Datum *values = palloc0(tupleDescriptor->natts * sizeof(Datum));
-	bool isnull[Natts_pg_dist_node];
+	bool *isnull = palloc0(tupleDescriptor->natts * sizeof(bool));
-	bool replace[Natts_pg_dist_node];
+	bool *replace = palloc0(tupleDescriptor->natts * sizeof(bool));
 
 	if (heapTuple == NULL)
 	{
@@ -2841,7 +2857,6 @@ SetWorkerColumnLocalOnly(WorkerNode *workerNode, int columnIndex, Datum value)
 							   workerNode->workerName, workerNode->workerPort)));
 	}
 
-	memset(replace, 0, sizeof(replace));
 	values[columnIndex - 1] = value;
 	isnull[columnIndex - 1] = false;
 	replace[columnIndex - 1] = true;
@@ -2857,6 +2872,10 @@ SetWorkerColumnLocalOnly(WorkerNode *workerNode, int columnIndex, Datum value)
 
 	table_close(pgDistNode, NoLock);
 
+	pfree(values);
+	pfree(isnull);
+	pfree(replace);
+
 	return newWorkerNode;
 }
 
@@ -3241,16 +3260,15 @@ InsertPlaceholderCoordinatorRecord(void)
 static void
 InsertNodeRow(int nodeid, char *nodeName, int32 nodePort, NodeMetadata *nodeMetadata)
 {
-	Datum values[Natts_pg_dist_node];
+	Relation pgDistNode = table_open(DistNodeRelationId(), RowExclusiveLock);
-	bool isNulls[Natts_pg_dist_node];
+	TupleDesc tupleDescriptor = RelationGetDescr(pgDistNode);
+
+	Datum *values = palloc0(tupleDescriptor->natts * sizeof(Datum));
+	bool *isNulls = palloc0(tupleDescriptor->natts * sizeof(bool));
 
 	Datum nodeClusterStringDatum = CStringGetDatum(nodeMetadata->nodeCluster);
 	Datum nodeClusterNameDatum = DirectFunctionCall1(namein, nodeClusterStringDatum);
 
-	/* form new shard tuple */
-	memset(values, 0, sizeof(values));
-	memset(isNulls, false, sizeof(isNulls));
-
 	values[Anum_pg_dist_node_nodeid - 1] = UInt32GetDatum(nodeid);
 	values[Anum_pg_dist_node_groupid - 1] = Int32GetDatum(nodeMetadata->groupId);
 	values[Anum_pg_dist_node_nodename - 1] = CStringGetTextDatum(nodeName);
@@ -3264,14 +3282,10 @@ InsertNodeRow(int nodeid, char *nodeName, int32 nodePort, NodeMetadata *nodeMeta
 	values[Anum_pg_dist_node_nodecluster - 1] = nodeClusterNameDatum;
 	values[Anum_pg_dist_node_shouldhaveshards - 1] = BoolGetDatum(
 		nodeMetadata->shouldHaveShards);
-	values[Anum_pg_dist_node_nodeisclone - 1] = BoolGetDatum(
+	values[GetNodeIsCloneAttrIndexInPgDistNode(tupleDescriptor)] =
-		nodeMetadata->nodeisclone);
+		BoolGetDatum(nodeMetadata->nodeisclone);
-	values[Anum_pg_dist_node_nodeprimarynodeid - 1] = Int32GetDatum(
+	values[GetNodePrimaryNodeIdAttrIndexInPgDistNode(tupleDescriptor)] =
-		nodeMetadata->nodeprimarynodeid);
+		Int32GetDatum(nodeMetadata->nodeprimarynodeid);
-
-	Relation pgDistNode = table_open(DistNodeRelationId(), RowExclusiveLock);
-
-	TupleDesc tupleDescriptor = RelationGetDescr(pgDistNode);
 	HeapTuple heapTuple = heap_form_tuple(tupleDescriptor, values, isNulls);
 
 	CATALOG_INSERT_WITH_SNAPSHOT(pgDistNode, heapTuple);
@@ -3283,6 +3297,9 @@ InsertNodeRow(int nodeid, char *nodeName, int32 nodePort, NodeMetadata *nodeMeta
 
 	/* close relation */
 	table_close(pgDistNode, NoLock);
+
+	pfree(values);
+	pfree(isNulls);
 }
 
 
@@ -3397,43 +3414,30 @@ TupleToWorkerNode(Relation pgDistNode, TupleDesc tupleDescriptor, HeapTuple heap
 				   1]);
 
 	/*
-	 * Attributes above this line are guaranteed to be present at the
+	 * nodecluster, nodeisclone and nodeprimarynodeid columns can be missing. In case
-	 * exact defined attribute number. Atleast till now. If you are droping or
+	 * of extension creation/upgrade, master_initialize_node_metadata function is
-	 * adding any of the above columns consider adjusting the code above
+	 * called before the nodecluster column is added to pg_dist_node table.
 	 */
-	Oid pgDistNodeRelId = RelationGetRelid(pgDistNode);
 
-	AttrNumber nodeClusterAttno = get_attnum(pgDistNodeRelId, "nodecluster");
+	if (!isNullArray[Anum_pg_dist_node_nodecluster - 1])
-
-	if (nodeClusterAttno > 0 &&
-		!TupleDescAttr(tupleDescriptor, nodeClusterAttno - 1)->attisdropped &&
-		!isNullArray[nodeClusterAttno - 1])
 	{
 		Name nodeClusterName =
-			DatumGetName(datumArray[nodeClusterAttno - 1]);
+			DatumGetName(datumArray[Anum_pg_dist_node_nodecluster - 1]);
 		char *nodeClusterString = NameStr(*nodeClusterName);
 		strlcpy(workerNode->nodeCluster, nodeClusterString, NAMEDATALEN);
 	}
 
-	if (nAtts > Anum_pg_dist_node_nodeisclone)
+	int nodeIsCloneIdx = GetNodeIsCloneAttrIndexInPgDistNode(tupleDescriptor);
+	int nodePrimaryNodeIdIdx = GetNodePrimaryNodeIdAttrIndexInPgDistNode(tupleDescriptor);
+
+	if (!isNullArray[nodeIsCloneIdx])
 	{
-		AttrNumber nodeIsCloneAttno = get_attnum(pgDistNodeRelId, "nodeisclone");
+		workerNode->nodeisclone = DatumGetBool(datumArray[nodeIsCloneIdx]);
-		if (nodeIsCloneAttno > 0 &&
+	}
-			!TupleDescAttr(tupleDescriptor, nodeIsCloneAttno - 1)->attisdropped &&
+
-			!isNullArray[nodeIsCloneAttno - 1])
+	if (!isNullArray[nodePrimaryNodeIdIdx])
-		{
+	{
-			workerNode->nodeisclone = DatumGetBool(datumArray[nodeIsCloneAttno - 1]);
+		workerNode->nodeprimarynodeid = DatumGetInt32(datumArray[nodePrimaryNodeIdIdx]);
-		}
-		AttrNumber nodePrimaryNodeIdAttno = get_attnum(pgDistNodeRelId,
-													   "nodeprimarynodeid");
-		if (nodePrimaryNodeIdAttno > 0 &&
-			!TupleDescAttr(tupleDescriptor, nodePrimaryNodeIdAttno - 1)->attisdropped &&
-			!isNullArray[nodePrimaryNodeIdAttno - 1])
-		{
-			workerNode->nodeprimarynodeid = DatumGetInt32(datumArray[
-															  nodePrimaryNodeIdAttno - 1])
-			;
-		}
 	}
 
 	pfree(datumArray);
@@ -3443,6 +3447,48 @@ TupleToWorkerNode(Relation pgDistNode, TupleDesc tupleDescriptor, HeapTuple heap
 }
 
 
+/*
+ * GetNodePrimaryNodeIdAttrIndexInPgDistNode returns attrnum for nodeprimarynodeid attr.
+ *
+ * nodeprimarynodeid attr was added to table pg_dist_node using alter operation
+ * after the version where Citus started supporting downgrades, and it's one of
+ * the two columns that we've introduced to pg_dist_node since then.
+ *
+ * And in case of a downgrade + upgrade, tupleDesc->natts becomes greater than
+ * Natts_pg_dist_node and when this happens, then we know that attrnum
+ * nodeprimarynodeid is not Anum_pg_dist_node_nodeprimarynodeid anymore but
+ * tupleDesc->natts - 1.
+ */
+static int
+GetNodePrimaryNodeIdAttrIndexInPgDistNode(TupleDesc tupleDesc)
+{
+	return tupleDesc->natts == Natts_pg_dist_node
+		   ? (Anum_pg_dist_node_nodeprimarynodeid - 1)
+		   : tupleDesc->natts - 1;
+}
+
+
+/*
+ * GetNodeIsCloneAttrIndexInPgDistNode returns attrnum for nodeisclone attr.
+ *
+ * Like, GetNodePrimaryNodeIdAttrIndexInPgDistNode(), performs a similar
+ * calculation for nodeisclone attribute because this is column added to
+ * pg_dist_node after we started supporting downgrades.
+ *
+ * Only difference with the mentioned function is that we know
+ * the attrnum for nodeisclone is not Anum_pg_dist_node_nodeisclone anymore
+ * but tupleDesc->natts - 2 because we added these columns consecutively
+ * and we first add nodeisclone attribute and then nodeprimarynodeid attribute.
+ */
+static int
+GetNodeIsCloneAttrIndexInPgDistNode(TupleDesc tupleDesc)
+{
+	return tupleDesc->natts == Natts_pg_dist_node
+		   ? (Anum_pg_dist_node_nodeisclone - 1)
+		   : tupleDesc->natts - 2;
+}
+
+
 /*
  * StringToDatum transforms a string representation into a Datum.
  */
@@ -3519,15 +3565,15 @@ UnsetMetadataSyncedForAllWorkers(void)
 		updatedAtLeastOne = true;
 	}
 
+	Datum *values = palloc(tupleDescriptor->natts * sizeof(Datum));
+	bool *isnull = palloc(tupleDescriptor->natts * sizeof(bool));
+	bool *replace = palloc(tupleDescriptor->natts * sizeof(bool));
+
 	while (HeapTupleIsValid(heapTuple))
 	{
-		Datum values[Natts_pg_dist_node];
+		memset(values, 0, tupleDescriptor->natts * sizeof(Datum));
-		bool isnull[Natts_pg_dist_node];
+		memset(isnull, 0, tupleDescriptor->natts * sizeof(bool));
-		bool replace[Natts_pg_dist_node];
+		memset(replace, 0, tupleDescriptor->natts * sizeof(bool));
-
-		memset(replace, false, sizeof(replace));
-		memset(isnull, false, sizeof(isnull));
-		memset(values, 0, sizeof(values));
 
 		values[Anum_pg_dist_node_metadatasynced - 1] = BoolGetDatum(false);
 		replace[Anum_pg_dist_node_metadatasynced - 1] = true;
@@ -3550,6 +3596,10 @@ UnsetMetadataSyncedForAllWorkers(void)
 	CatalogCloseIndexes(indstate);
 	table_close(relation, NoLock);
 
+	pfree(values);
+	pfree(isnull);
+	pfree(replace);
+
 	return updatedAtLeastOne;
 }