[fuzzer] Don't crash if LLVMFuzzerMutate was called by CustomCrossOver

[vitalybuka]

Includes

[kcc]

LGTM with a nit

lib/Fuzzer/FuzzerMutate.h

146 ↗

(On Diff #90811)

CustomCrossOver needs its own buffer as a custom implementation may call
LLVMFuzzerMutate, which in turn may resize MutateInPlaceHere

[vitalybuka]

Comment

[vitalybuka]

Prev snapshot was invalid.

llvm/trunk/lib/Fuzzer/FuzzerMutate.h

private:
   std::vector<DictionaryEntry *> CurrentDictionaryEntrySequence;
 
   static const size_t kCmpDictionaryEntriesDequeSize = 16;
   DictionaryEntry CmpDictionaryEntriesDeque[kCmpDictionaryEntriesDequeSize];
   size_t CmpDictionaryEntriesDequeIdx = 0;
 
   const InputCorpus *Corpus = nullptr;
   std::vector<uint8_t> MutateInPlaceHere;
+  // CustomCrossOver needs its own buffer as a custom implementation may call
+  // LLVMFuzzerMutate, which in turn may resize MutateInPlaceHere.
+  std::vector<uint8_t> CustomCrossOverInPlaceHere;
 
   std::vector<Mutator> Mutators;
   std::vector<Mutator> DefaultMutators;
 };
 
 }  // namespace fuzzer
 
 #endif  // LLVM_FUZZER_MUTATE_H

llvm/trunk/lib/Fuzzer/FuzzerMutate.cpp

 size_t MutationDispatcher::Mutate_CustomCrossOver(uint8_t *Data, size_t Size,
                                                   size_t MaxSize) {
   if (!Corpus || Corpus->size() < 2 || Size == 0)
     return 0;
   size_t Idx = Rand(Corpus->size());
   const Unit &Other = (*Corpus)[Idx];
   if (Other.empty())
     return 0;
-  MutateInPlaceHere.resize(MaxSize);
-  auto &U = MutateInPlaceHere;
+  CustomCrossOverInPlaceHere.resize(MaxSize);
+  auto &U = CustomCrossOverInPlaceHere;
   size_t NewSize = EF->LLVMFuzzerCustomCrossOver(
       Data, Size, Other.data(), Other.size(), U.data(), U.size(), Rand.Rand());
   if (!NewSize)
     return 0;
   assert(NewSize <= MaxSize && "CustomCrossOver returned overisized unit");
   memcpy(Data, U.data(), NewSize);
   return NewSize;
 }

llvm/trunk/lib/Fuzzer/test/CMakeLists.txt

 set(Tests
   AbsNegAndConstantTest
   AbsNegAndConstant64Test
   AccumulateAllocationsTest
   BogusInitializeTest
   BufferOverflowOnInput
   CallerCalleeTest
   CounterTest
+  CustomCrossOverAndMutateTest
   CustomCrossOverTest
   CustomMutatorTest
   CxxStringEqTest
   DivTest
   EmptyTest
   EquivalenceATest
   EquivalenceBTest
   FourIndependentBranchesTest

llvm/trunk/lib/Fuzzer/test/CustomCrossOverAndMutateTest.cpp

+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+
+// Test that libFuzzer does not crash when LLVMFuzzerMutate called from
+// LLVMFuzzerCustomCrossOver.
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <string>
+#include <string.h>
+#include <vector>
+
+#include "FuzzerInterface.h"
+
+static volatile int sink;
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  std::string Str(reinterpret_cast<const char *>(Data), Size);
+  if (Size && Data[0] == '0')
+    sink++;
+  return 0;
+}
+
+extern "C" size_t LLVMFuzzerCustomCrossOver(const uint8_t *Data1, size_t Size1,
+                                            const uint8_t *Data2, size_t Size2,
+                                            uint8_t *Out, size_t MaxOutSize,
+                                            unsigned int Seed) {
+  std::vector<uint8_t> Buffer(MaxOutSize * 10);
+  LLVMFuzzerMutate(Buffer.data(), Buffer.size(), Buffer.size());
+  size_t Size = std::min<size_t>(Size1, MaxOutSize);
+  memcpy(Out, Data1, Size);
+  return Size;
+}

llvm/trunk/lib/Fuzzer/test/fuzzer-customcrossoverandmutate.test

+RUN: LLVMFuzzer-CustomCrossOverAndMutateTest -seed=1 -use_memcmp=0 -runs=100000