llvm/lib/Fuzzer/FuzzerMutate.cpp

//===- FuzzerMutate.cpp - Mutate a test input -----------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// Mutate a test input.
//===----------------------------------------------------------------------===//

#include <cstring>

#include "FuzzerInternal.h"

#include <algorithm>

namespace fuzzer {

typedef size_t (MutationDispatcher::*Mutator)(uint8_t *Data, size_t Size,
                                              size_t Max);

struct MutationDispatcher::Impl {
  std::vector<Unit> Dictionary;
  std::vector<Mutator> Mutators;
  Impl() {
    Mutators.push_back(&MutationDispatcher::Mutate_EraseByte);
    Mutators.push_back(&MutationDispatcher::Mutate_InsertByte);
    Mutators.push_back(&MutationDispatcher::Mutate_ChangeByte);
    Mutators.push_back(&MutationDispatcher::Mutate_ChangeBit);
    Mutators.push_back(&MutationDispatcher::Mutate_ShuffleBytes);
  }
  void AddWordToDictionary(const uint8_t *Word, size_t Size) {
    if (Dictionary.empty()) {
      Mutators.push_back(&MutationDispatcher::Mutate_AddWordFromDictionary);
    }
    Dictionary.push_back(Unit(Word, Word + Size));
  }
};


static char FlipRandomBit(char X, FuzzerRandomBase &Rand) {
  int Bit = Rand(8);
  char Mask = 1 << Bit;
  char R;
  if (X & (1 << Bit))
    R = X & ~Mask;
  else
    R = X | Mask;
  assert(R != X);
  return R;
}

static char RandCh(FuzzerRandomBase &Rand) {
  if (Rand.RandBool()) return Rand(256);
  const char *Special = "!*'();:@&=+$,/?%#[]123ABCxyz-`~.";
  return Special[Rand(sizeof(Special) - 1)];
}

size_t MutationDispatcher::Mutate_ShuffleBytes(uint8_t *Data, size_t Size,
                                               size_t MaxSize) {
  assert(Size);
  size_t ShuffleAmount = Rand(std::min(Size, 8UL)) + 1;  // [1,8] and <= Size.
  size_t ShuffleStart = Rand(Size - ShuffleAmount);
  assert(ShuffleStart + ShuffleAmount <= Size);
  std::random_shuffle(Data + ShuffleStart, Data + ShuffleStart + ShuffleAmount,
                      Rand);
  return Size;
}

size_t MutationDispatcher::Mutate_EraseByte(uint8_t *Data, size_t Size,
                                            size_t MaxSize) {
  assert(Size);
  if (Size == 1) return Size;
  size_t Idx = Rand(Size);
  // Erase Data[Idx].
  memmove(Data + Idx, Data + Idx + 1, Size - Idx - 1);
  return Size - 1;
}

size_t MutationDispatcher::Mutate_InsertByte(uint8_t *Data, size_t Size,
                                             size_t MaxSize) {
  if (Size == MaxSize) return Size;
  size_t Idx = Rand(Size + 1);
  // Insert new value at Data[Idx].
  memmove(Data + Idx + 1, Data + Idx, Size - Idx);
  Data[Idx] = RandCh(Rand);
  return Size + 1;
}

size_t MutationDispatcher::Mutate_ChangeByte(uint8_t *Data, size_t Size,
                                             size_t MaxSize) {
  size_t Idx = Rand(Size);
  Data[Idx] = RandCh(Rand);
  return Size;
}

size_t MutationDispatcher::Mutate_ChangeBit(uint8_t *Data, size_t Size,
                                            size_t MaxSize) {
  size_t Idx = Rand(Size);
  Data[Idx] = FlipRandomBit(Data[Idx], Rand);
  return Size;
}

size_t MutationDispatcher::Mutate_AddWordFromDictionary(uint8_t *Data,
                                                        size_t Size,
                                                        size_t MaxSize) {
  auto &D = MDImpl->Dictionary;
  if (D.empty()) return Size;  // FIXME: indicate failure.
  const Unit &Word = D[Rand(D.size())];
  if (Size + Word.size() > MaxSize) return Size;
  size_t Idx = Rand(Size + 1);
  memmove(Data + Idx + Word.size(), Data + Idx, Size - Idx);
  memcpy(Data + Idx, Word.data(), Word.size());
  return Size + Word.size();
}

// Mutates Data in place, returns new size.
size_t MutationDispatcher::Mutate(uint8_t *Data, size_t Size, size_t MaxSize) {
  assert(MaxSize > 0);
  assert(Size <= MaxSize);
  if (Size == 0) {
    for (size_t i = 0; i < MaxSize; i++)
      Data[i] = RandCh(Rand);
    return MaxSize;
  }
  assert(Size > 0);
  size_t MutatorIdx = Rand(MDImpl->Mutators.size());
  Size = (this->*(MDImpl->Mutators[MutatorIdx]))(Data, Size, MaxSize);
  assert(Size > 0);
  return Size;
}

void MutationDispatcher::AddWordToDictionary(const uint8_t *Word, size_t Size) {
  MDImpl->AddWordToDictionary(Word, Size);
}

MutationDispatcher::MutationDispatcher(FuzzerRandomBase &Rand) : Rand(Rand) {
  MDImpl = new Impl;
}

MutationDispatcher::~MutationDispatcher() { delete MDImpl; }

}  // namespace fuzzer