SERVER-38362 Prevent $out stage within $lookup

2 files changed, 13 insertions, 12 deletions

diff --git a/src/mongo/db/pipeline/document_source_lookup.cpp b/src/mongo/db/pipeline/document_source_lookup.cpp
index 84ff4c5496e..0d8ea164537 100644
--- a/src/mongo/db/pipeline/document_source_lookup.cpp
+++ b/src/mongo/db/pipeline/document_source_lookup.cpp
@@ -656,8 +656,14 @@ void DocumentSourceLookUp::initializeIntrospectionPipeline() {
     // Ensure that the pipeline does not contain a $changeStream stage. This check will be
     // performed recursively on all sub-pipelines.
     uassert(ErrorCodes::IllegalOperation,
-            "$changeStream is not allowed within a $lookup foreign pipeline",
+            "$changeStream is not allowed within a $lookup's pipeline",
             sources.empty() || !sources.front()->constraints().isChangeStreamStage());
+
+    // Ensure that the pipeline does not contain a $out stage. Since $out must be the last stage
+    // of a pipeline, we only need to check the last DocumentSource.
+    uassert(51047,
+            "$out is not allowed within a $lookup's pipeline",
+            sources.empty() || !sources.back()->constraints().writesPersistentData());
 }
 
 void DocumentSourceLookUp::serializeToArray(
diff --git a/src/mongo/db/pipeline/document_source_lookup_test.cpp b/src/mongo/db/pipeline/document_source_lookup_test.cpp
index 027a06c5e15..64e12231227 100644
--- a/src/mongo/db/pipeline/document_source_lookup_test.cpp
+++ b/src/mongo/db/pipeline/document_source_lookup_test.cpp
@@ -215,12 +215,12 @@ TEST_F(DocumentSourceLookUpTest, LookupEmptyPipelineDoesntUseDiskAndIsOKInATrans
            DocumentSource::TransactionRequirement::kAllowed);
 }
 
-TEST_F(DocumentSourceLookUpTest, LookupWithChildStagesInheritsDiskUseRequirement) {
+TEST_F(DocumentSourceLookUpTest, LookupWithOutInPipelineNotAllowed) {
+    auto ERROR_CODE_OUT_BANNED_IN_LOOKUP = 51047;
     auto expCtx = getExpCtx();
     NamespaceString fromNs("test", "coll");
     expCtx->setResolvedNamespace_forTest(fromNs, {fromNs, std::vector<BSONObj>{}});
-
-    auto docSource =
+    ASSERT_THROWS_CODE(
         DocumentSourceLookUp::createFromBson(BSON("$lookup" << BSON("from"
                                                                     << "coll"
                                                                     << "pipeline"
@@ -229,14 +229,9 @@ TEST_F(DocumentSourceLookUpTest, LookupWithChildStagesInheritsDiskUseRequirement
                                                                     << "as"
                                                                     << "as"))
                                                  .firstElement(),
-                                             expCtx);
-    auto lookup = static_cast<DocumentSourceLookUp*>(docSource.get());
-
-    ASSERT_TRUE(lookup->wasConstructedWithPipelineSyntax());
-    ASSERT(lookup->constraints(Pipeline::SplitState::kUnsplit).diskRequirement ==
-           DocumentSource::DiskUseRequirement::kWritesPersistentData);
-    ASSERT(lookup->constraints(Pipeline::SplitState::kUnsplit).transactionRequirement ==
-           DocumentSource::TransactionRequirement::kNotAllowed);
+                                             expCtx),
+        AssertionException,
+        ERROR_CODE_OUT_BANNED_IN_LOOKUP);
 }
 
 TEST_F(DocumentSourceLookUpTest, LiteParsedDocumentSourceLookupContainsExpectedNamespaces) {