SERVER-24380 Fix null deref. with coll/index having "simple" collation

2 files changed, 21 insertions, 3 deletions

diff --git a/src/mongo/db/catalog/database.cpp b/src/mongo/db/catalog/database.cpp
index 26eb99c0a9c..afc511accd8 100644
--- a/src/mongo/db/catalog/database.cpp
+++ b/src/mongo/db/catalog/database.cpp
@@ -630,8 +630,16 @@ Status userCreateNS(OperationContext* txn,
             return collator.getStatus();
         }
 
-        collectionOptions.collation =
-            CollationSerializer::specToBSON(collator.getValue()->getSpec());
+        // If the collator factory returned a non-null collator, set the collation option to the
+        // result of serializing the collator's spec back into BSON. We do this in order to fill in
+        // all options that the user omitted.
+        //
+        // If the collator factory returned a null collator (representing the "simple" collation),
+        // we can't use the collation serializer. In this case, we simply set the collation option
+        // to the original user BSON.
+        collectionOptions.collation = collator.getValue()
+            ? CollationSerializer::specToBSON(collator.getValue()->getSpec())
+            : collectionOptions.collation;
     }
 
     status =
diff --git a/src/mongo/db/catalog/index_catalog.cpp b/src/mongo/db/catalog/index_catalog.cpp
index b1ed77750ed..9ebbaea256a 100644
--- a/src/mongo/db/catalog/index_catalog.cpp
+++ b/src/mongo/db/catalog/index_catalog.cpp
@@ -1315,7 +1315,17 @@ StatusWith<BSONObj> IndexCatalog::_fixIndexSpec(OperationContext* txn,
             return collator.getStatus();
         }
 
-        b.append("collation", CollationSerializer::specToBSON(collator.getValue()->getSpec()));
+        // If the collator factory returned a non-null collator, set the collation option to the
+        // result of serializing the collator's spec back into BSON. We do this in order to fill in
+        // all options that the user omitted.
+        //
+        // If the collator factory returned a null collator (representing the "simple" collation),
+        // we can't use the collation serializer. In this case, we simply set the collation option
+        // to the original user BSON.
+        b.append("collation",
+                 collator.getValue()
+                     ? CollationSerializer::specToBSON(collator.getValue()->getSpec())
+                     : collationElt.Obj());
     } else if (collection->getDefaultCollator()) {
         // The user did not specify an explicit collation for this index and the collection has a
         // default collator. In this case, the index inherits the collection default.