1 files changed, 26 insertions, 12 deletions

diff --git a/src/mongo/db/repl/initial_syncer.cpp b/src/mongo/db/repl/initial_syncer.cpp
index 8349428c3fd..53f020541b0 100644
--- a/src/mongo/db/repl/initial_syncer.cpp
+++ b/src/mongo/db/repl/initial_syncer.cpp
@@ -365,30 +365,44 @@ BSONObj InitialSyncer::getInitialSyncProgress() const {
     return _getInitialSyncProgress_inlock();
 }
 
+void InitialSyncer::_appendInitialSyncProgressMinimal_inlock(BSONObjBuilder* bob) const {
+    _stats.append(bob);
+    if (!_initialSyncState) {
+        return;
+    }
+    bob->appendNumber("fetchedMissingDocs", _initialSyncState->fetchedMissingDocs);
+    bob->appendNumber("appliedOps", _initialSyncState->appliedOps);
+    if (!_initialSyncState->beginTimestamp.isNull()) {
+        bob->append("initialSyncOplogStart", _initialSyncState->beginTimestamp);
+    }
+    if (!_initialSyncState->stopTimestamp.isNull()) {
+        bob->append("initialSyncOplogEnd", _initialSyncState->stopTimestamp);
+    }
+}
+
 BSONObj InitialSyncer::_getInitialSyncProgress_inlock() const {
-    BSONObjBuilder bob;
     try {
-        _stats.append(&bob);
+        BSONObjBuilder bob;
+        _appendInitialSyncProgressMinimal_inlock(&bob);
         if (_initialSyncState) {
-            bob.appendNumber("fetchedMissingDocs", _initialSyncState->fetchedMissingDocs);
-            bob.appendNumber("appliedOps", _initialSyncState->appliedOps);
-            if (!_initialSyncState->beginTimestamp.isNull()) {
-                bob.append("initialSyncOplogStart", _initialSyncState->beginTimestamp);
-            }
-            if (!_initialSyncState->stopTimestamp.isNull()) {
-                bob.append("initialSyncOplogEnd", _initialSyncState->stopTimestamp);
-            }
             if (_initialSyncState->dbsCloner) {
                 BSONObjBuilder dbsBuilder(bob.subobjStart("databases"));
                 _initialSyncState->dbsCloner->getStats().append(&dbsBuilder);
                 dbsBuilder.doneFast();
             }
         }
+        // In 3.4, BSONObjBuilder::obj() does not check the validity of the document it returns so
+        // we check it explicitly here.
+        auto obj = bob.obj();
+        uassert(ErrorCodes::InvalidBSON,
+                str::stream() << "Invalid BSONObj size: " << obj.objsize(),
+                obj.isValid());
+        return obj;
     } catch (const DBException& e) {
-        bob.resetToEmpty();
-        bob.append("error", e.toString());
         log() << "Error creating initial sync progress object: " << e.toString();
     }
+    BSONObjBuilder bob;
+    _appendInitialSyncProgressMinimal_inlock(&bob);
     return bob.obj();
 }