[PATCH] D45693: [LibFuzzer] Tweak `MutationDispatcher::Mutate_CopyPart` mutation.

[Dan Liew via Phabricator via llvm-commits]

delcypher updated this revision to Diff 143238.
delcypher added a comment.

Add unit test.


https://reviews.llvm.org/D45693

Files:
  lib/fuzzer/FuzzerMutate.cpp
  lib/fuzzer/tests/FuzzerUnittest.cpp


Index: lib/fuzzer/tests/FuzzerUnittest.cpp
===================================================================
--- lib/fuzzer/tests/FuzzerUnittest.cpp
+++ lib/fuzzer/tests/FuzzerUnittest.cpp
@@ -381,6 +381,21 @@
 TEST(FuzzerMutate, CopyPart2) {
   TestCopyPart(&MutationDispatcher::Mutate, 1 << 13);
 }
+TEST(FuzzerMutate, CopyPartNoInsertAtMaxSize) {
+  // This (non exhaustively) tests if `Mutate_CopyPart` tries to perform an
+  // insert on an input of size `MaxSize`.  Performing an insert in this case
+  // will lead to the mutation failing.
+  std::unique_ptr<ExternalFunctions> t(new ExternalFunctions());
+  fuzzer::EF = t.get();
+  Random Rand(0);
+  std::unique_ptr<MutationDispatcher> MD(new MutationDispatcher(Rand, {}));
+  uint8_t Data[8] = {0x00, 0x11, 0x22, 0x33, 0x44, 0x00, 0x11, 0x22};
+  size_t MaxSize = sizeof(Data);
+  for (unsigned int count = 0; count < (1 << 18); ++count) {
+    size_t NewSize = MD->Mutate_CopyPart(Data, MaxSize, MaxSize);
+    ASSERT_EQ(NewSize, MaxSize);
+  }
+}
 
 void TestAddWordFromDictionary(Mutator M, int NumIter) {
   std::unique_ptr<ExternalFunctions> t(new ExternalFunctions());
Index: lib/fuzzer/FuzzerMutate.cpp
===================================================================
--- lib/fuzzer/FuzzerMutate.cpp
+++ lib/fuzzer/FuzzerMutate.cpp
@@ -339,7 +339,9 @@
 size_t MutationDispatcher::Mutate_CopyPart(uint8_t *Data, size_t Size,
                                            size_t MaxSize) {
   if (Size > MaxSize || Size == 0) return 0;
-  if (Rand.RandBool())
+  // If Size == MaxSize, `InsertPartOf(...)` will
+  // fail so there's no point using it in this case.
+  if (Size == MaxSize || Rand.RandBool())
     return CopyPartOf(Data, Size, Data, Size);
   else
     return InsertPartOf(Data, Size, Data, Size, MaxSize);


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D45693.143238.patch
Type: text/x-patch
Size: 1792 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180420/0f49f994/attachment.bin>