From 393c9d79b9f8e0cd39c652ab7784f2c4977d5ecd Mon Sep 17 00:00:00 2001
From: Jack Mulrow <jack.mulrow@mongodb.com>
Date: Tue, 24 Sep 2019 18:59:52 +0000
Subject: [PATCH] SERVER-42367 Disallow refineCollectionShardKey in FCV < 4.4

---
 .../refine_collection_shard_key_fcv.js        | 36 +++++++++++++++++++
 ...vr_refine_collection_shard_key_command.cpp |  7 ++++
 2 files changed, 43 insertions(+)
 create mode 100644 jstests/multiVersion/refine_collection_shard_key_fcv.js

diff --git a/jstests/multiVersion/refine_collection_shard_key_fcv.js b/jstests/multiVersion/refine_collection_shard_key_fcv.js
new file mode 100644
index 0000000000000..1bdf5ca6461de
--- /dev/null
+++ b/jstests/multiVersion/refine_collection_shard_key_fcv.js
@@ -0,0 +1,36 @@
+// Verifies refineCollectionShardKey can only be run when a cluster's FCV is 4.4.
+
+(function() {
+"use strict";
+
+const dbName = "test";
+const collName = "foo";
+const ns = dbName + '.' + collName;
+
+const st = new ShardingTest({shards: 1});
+const configAdminDB = st.configRS.getPrimary().getDB("admin");
+
+assert.commandWorked(st.s.adminCommand({enableSharding: dbName}));
+assert.commandWorked(st.s.adminCommand({shardCollection: ns, key: {_id: 1}}));
+
+// Create an index that can be used for the following shard key refines.
+assert.commandWorked(st.s.getCollection(ns).createIndex({_id: 1, x: 1, y: 1}));
+
+// Refining a shard key succeeds in FCV 4.4.
+checkFCV(configAdminDB, latestFCV);
+assert.commandWorked(st.s.adminCommand({refineCollectionShardKey: ns, key: {_id: 1, x: 1}}));
+
+// Refining a shard key fails in FCV 4.2.
+assert.commandWorked(st.s.adminCommand({setFeatureCompatibilityVersion: lastStableFCV}));
+checkFCV(configAdminDB, lastStableFCV);
+assert.commandFailedWithCode(
+    st.s.adminCommand({refineCollectionShardKey: ns, key: {_id: 1, x: 1, y: 1}}),
+    ErrorCodes.CommandNotSupported);
+
+// Refining a shard key succeeds after upgrading back to FCV 4.4.
+assert.commandWorked(st.s.adminCommand({setFeatureCompatibilityVersion: latestFCV}));
+checkFCV(configAdminDB, latestFCV);
+assert.commandWorked(st.s.adminCommand({refineCollectionShardKey: ns, key: {_id: 1, x: 1, y: 1}}));
+
+st.stop();
+}());
diff --git a/src/mongo/db/s/config/configsvr_refine_collection_shard_key_command.cpp b/src/mongo/db/s/config/configsvr_refine_collection_shard_key_command.cpp
index 0020ae529b418..3b6a93370148d 100644
--- a/src/mongo/db/s/config/configsvr_refine_collection_shard_key_command.cpp
+++ b/src/mongo/db/s/config/configsvr_refine_collection_shard_key_command.cpp
@@ -37,6 +37,7 @@
 #include "mongo/db/repl/repl_client_info.h"
 #include "mongo/db/s/config/sharding_catalog_manager.h"
 #include "mongo/db/s/shard_key_util.h"
+#include "mongo/db/server_options.h"
 #include "mongo/s/catalog/dist_lock_manager.h"
 #include "mongo/s/grid.h"
 #include "mongo/s/request_types/refine_collection_shard_key_gen.h"
@@ -64,6 +65,12 @@ class ConfigsvrRefineCollectionShardKeyCommand final
                     "refineCollectionShardKey must be called with majority writeConcern",
                     opCtx->getWriteConcern().wMode == WriteConcernOptions::kMajority);
 
+            uassert(ErrorCodes::CommandNotSupported,
+                    "'refineCollectionShardKey' is only supported in feature compatibility version "
+                    "4.4",
+                    serverGlobalParams.featureCompatibility.getVersion() ==
+                        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44);
+
             // Set the operation context read concern level to local for reads into the config
             // database.
             repl::ReadConcernArgs::get(opCtx) =