FuzzerMerge.cpp

//===- FuzzerMerge.cpp - merging corpora ----------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// Merging corpora.
//===----------------------------------------------------------------------===//

#include "FuzzerCommand.h"
#include "FuzzerMerge.h"
#include "FuzzerIO.h"
#include "FuzzerInternal.h"
#include "FuzzerTracePC.h"
#include "FuzzerUtil.h"

#include <fstream>
#include <iterator>
#include <set>
#include <sstream>

namespace fuzzer {

bool Merger::Parse(const std::string &Str, bool ParseCoverage) {
  std::istringstream SS(Str);
  return Parse(SS, ParseCoverage);
}

void Merger::ParseOrExit(std::istream &IS, bool ParseCoverage) {
  if (!Parse(IS, ParseCoverage)) {
    Printf("MERGE: failed to parse the control file (unexpected error)\n");
    exit(1);
  }
}

// The control file example:
//
// 3 # The number of inputs
// 1 # The number of inputs in the first corpus, <= the previous number
// file0
// file1
// file2  # One file name per line.
// STARTED 0 123  # FileID, file size
// DONE 0 1 4 6 8  # FileID COV1 COV2 ...
// STARTED 1 456  # If DONE is missing, the input crashed while processing.
// STARTED 2 567
// DONE 2 8 9
bool Merger::Parse(std::istream &IS, bool ParseCoverage) {
  LastFailure.clear();
  std::string Line;

  // Parse NumFiles.
  if (!std::getline(IS, Line, '\n')) return false;
  std::istringstream L1(Line);
  size_t NumFiles = 0;
  L1 >> NumFiles;
  if (NumFiles == 0 || NumFiles > 10000000) return false;

  // Parse NumFilesInFirstCorpus.
  if (!std::getline(IS, Line, '\n')) return false;
  std::istringstream L2(Line);
  NumFilesInFirstCorpus = NumFiles + 1;
  L2 >> NumFilesInFirstCorpus;
  if (NumFilesInFirstCorpus > NumFiles) return false;

  // Parse file names.
  Files.resize(NumFiles);
  for (size_t i = 0; i < NumFiles; i++)
    if (!std::getline(IS, Files[i].Name, '\n'))
      return false;

  // Parse STARTED and DONE lines.
  size_t ExpectedStartMarker = 0;
  const size_t kInvalidStartMarker = -1;
  size_t LastSeenStartMarker = kInvalidStartMarker;
  Vector<uint32_t> TmpFeatures;
  while (std::getline(IS, Line, '\n')) {
    std::istringstream ISS1(Line);
    std::string Marker;
    size_t N;
    ISS1 >> Marker;
    ISS1 >> N;
    if (Marker == "STARTED") {
      // STARTED FILE_ID FILE_SIZE
      if (ExpectedStartMarker != N)
        return false;
      ISS1 >> Files[ExpectedStartMarker].Size;
      LastSeenStartMarker = ExpectedStartMarker;
      assert(ExpectedStartMarker < Files.size());
      ExpectedStartMarker++;
    } else if (Marker == "DONE") {
      // DONE FILE_ID COV1 COV2 COV3 ...
      size_t CurrentFileIdx = N;
      if (CurrentFileIdx != LastSeenStartMarker)
        return false;
      LastSeenStartMarker = kInvalidStartMarker;
      if (ParseCoverage) {
        TmpFeatures.clear();  // use a vector from outer scope to avoid resizes.
        while (ISS1 >> std::hex >> N)
          TmpFeatures.push_back(N);
        std::sort(TmpFeatures.begin(), TmpFeatures.end());
        Files[CurrentFileIdx].Features = TmpFeatures;
      }
    } else {
      return false;
    }
  }
  if (LastSeenStartMarker != kInvalidStartMarker)
    LastFailure = Files[LastSeenStartMarker].Name;

  FirstNotProcessedFile = ExpectedStartMarker;
  return true;
}

size_t Merger::ApproximateMemoryConsumption() const  {
  size_t Res = 0;
  for (const auto &F: Files)
    Res += sizeof(F) + F.Features.size() * sizeof(F.Features[0]);
  return Res;
}

// Decides which files need to be merged (add those to NewFiles).
// Returns the number of new features added.
size_t Merger::Merge(const Set<uint32_t> &InitialFeatures,
                     Set<uint32_t> *NewFeatures,
                     Vector<std::string> *NewFiles) {
  NewFiles->clear();
  assert(NumFilesInFirstCorpus <= Files.size());
  Set<uint32_t> AllFeatures = InitialFeatures;

  // What features are in the initial corpus?
  for (size_t i = 0; i < NumFilesInFirstCorpus; i++) {
    auto &Cur = Files[i].Features;
    AllFeatures.insert(Cur.begin(), Cur.end());
  }
  size_t InitialNumFeatures = AllFeatures.size();

  // Remove all features that we already know from all other inputs.
  for (size_t i = NumFilesInFirstCorpus; i < Files.size(); i++) {
    auto &Cur = Files[i].Features;
    Vector<uint32_t> Tmp;
    std::set_difference(Cur.begin(), Cur.end(), AllFeatures.begin(),
                        AllFeatures.end(), std::inserter(Tmp, Tmp.begin()));
    Cur.swap(Tmp);
  }

  // Sort. Give preference to
  //   * smaller files
  //   * files with more features.
  std::sort(Files.begin() + NumFilesInFirstCorpus, Files.end(),
            [&](const MergeFileInfo &a, const MergeFileInfo &b) -> bool {
              if (a.Size != b.Size)
                return a.Size < b.Size;
              return a.Features.size() > b.Features.size();
            });

  // One greedy pass: add the file's features to AllFeatures.
  // If new features were added, add this file to NewFiles.
  for (size_t i = NumFilesInFirstCorpus; i < Files.size(); i++) {
    auto &Cur = Files[i].Features;
    // Printf("%s -> sz %zd ft %zd\n", Files[i].Name.c_str(),
    //       Files[i].Size, Cur.size());
    bool FoundNewFeatures = false;
    for (auto Fe: Cur) {
      if (AllFeatures.insert(Fe).second) {
        FoundNewFeatures = true;
        NewFeatures->insert(Fe);
      }
    }
    if (FoundNewFeatures)
      NewFiles->push_back(Files[i].Name);
  }
  return AllFeatures.size() - InitialNumFeatures;
}

Set<uint32_t> Merger::AllFeatures() const {
  Set<uint32_t> S;
  for (auto &File : Files)
    S.insert(File.Features.begin(), File.Features.end());
  return S;
}

// Inner process. May crash if the target crashes.
void Fuzzer::CrashResistantMergeInternalStep(const std::string &CFPath) {
  Printf("MERGE-INNER: using the control file '%s'\n", CFPath.c_str());
  Merger M;
  std::ifstream IF(CFPath);
  M.ParseOrExit(IF, false);
  IF.close();
  if (!M.LastFailure.empty())
    Printf("MERGE-INNER: '%s' caused a failure at the previous merge step\n",
           M.LastFailure.c_str());

  Printf("MERGE-INNER: %zd total files;"
         " %zd processed earlier; will process %zd files now\n",
         M.Files.size(), M.FirstNotProcessedFile,
         M.Files.size() - M.FirstNotProcessedFile);

  std::ofstream OF(CFPath, std::ofstream::out | std::ofstream::app);
  Set<size_t> AllFeatures;
  for (size_t i = M.FirstNotProcessedFile; i < M.Files.size(); i++) {
    Fuzzer::MaybeExitGracefully();
    auto U = FileToVector(M.Files[i].Name);
    if (U.size() > MaxInputLen) {
      U.resize(MaxInputLen);
      U.shrink_to_fit();
    }
    std::ostringstream StartedLine;
    // Write the pre-run marker.
    OF << "STARTED " << std::dec << i << " " << U.size() << "\n";
    OF.flush();  // Flush is important since Command::Execute may crash.
    // Run.
    TPC.ResetMaps();
    ExecuteCallback(U.data(), U.size());
    // Collect coverage. We are iterating over the files in this order:
    // * First, files in the initial corpus ordered by size, smallest first.
    // * Then, all other files, smallest first.
    // So it makes no sense to record all features for all files, instead we
    // only record features that were not seen before.
    Set<size_t> UniqFeatures;
    TPC.CollectFeatures([&](size_t Feature) {
      if (AllFeatures.insert(Feature).second)
        UniqFeatures.insert(Feature);
    });
    // Show stats.
    if (!(TotalNumberOfRuns & (TotalNumberOfRuns - 1)))
      PrintStats("pulse ");
    // Write the post-run marker and the coverage.
    OF << "DONE " << i;
    for (size_t F : UniqFeatures)
      OF << " " << std::hex << F;
    OF << "\n";
    OF.flush();
  }
}

static void WriteNewControlFile(const std::string &CFPath,
                                const Vector<SizedFile> &OldCorpus,
                                const Vector<SizedFile> &NewCorpus) {
  RemoveFile(CFPath);
  std::ofstream ControlFile(CFPath);
  ControlFile << (OldCorpus.size() + NewCorpus.size()) << "\n";
  ControlFile << OldCorpus.size() << "\n";
  for (auto &SF: OldCorpus)
    ControlFile << SF.File << "\n";
  for (auto &SF: NewCorpus)
    ControlFile << SF.File << "\n";
  if (!ControlFile) {
    Printf("MERGE-OUTER: failed to write to the control file: %s\n",
           CFPath.c_str());
    exit(1);
  }
}

// Outer process. Does not call the target code and thus should not fail.
void CrashResistantMerge(const Vector<std::string> &Args,
                    const Vector<SizedFile> &OldCorpus,
                    const Vector<SizedFile> &NewCorpus,
                    Vector<std::string> *NewFiles,
                    const Set<uint32_t> &InitialFeatures,
                    Set<uint32_t> *NewFeatures,
                    const std::string &CFPath) {
  size_t NumAttempts = 0;
  if (FileSize(CFPath)) {
    Printf("MERGE-OUTER: non-empty control file provided: '%s'\n",
           CFPath.c_str());
    Merger M;
    std::ifstream IF(CFPath);
    if (M.Parse(IF, /*ParseCoverage=*/false)) {
      Printf("MERGE-OUTER: control file ok, %zd files total,"
             " first not processed file %zd\n",
             M.Files.size(), M.FirstNotProcessedFile);
      if (!M.LastFailure.empty())
        Printf("MERGE-OUTER: '%s' will be skipped as unlucky "
               "(merge has stumbled on it the last time)\n",
               M.LastFailure.c_str());
      if (M.FirstNotProcessedFile >= M.Files.size()) {
        Printf("MERGE-OUTER: nothing to do, merge has been completed before\n");
        exit(0);
      }

      NumAttempts = M.Files.size() - M.FirstNotProcessedFile;
    } else {
      Printf("MERGE-OUTER: bad control file, will overwrite it\n");
    }
  }

  if (!NumAttempts) {
    // The supplied control file is empty or bad, create a fresh one.
    NumAttempts = OldCorpus.size() + NewCorpus.size();
    Printf("MERGE-OUTER: %zd files, %zd in the initial corpus\n", NumAttempts,
           OldCorpus.size());
    WriteNewControlFile(CFPath, OldCorpus, NewCorpus);
  }

  // Execute the inner process until it passes.
  // Every inner process should execute at least one input.
  Command BaseCmd(Args);
  BaseCmd.removeFlag("merge");
  BaseCmd.removeFlag("fork");
  bool Success = false;
  for (size_t Attempt = 1; Attempt <= NumAttempts; Attempt++) {
    Fuzzer::MaybeExitGracefully();
    Printf("MERGE-OUTER: attempt %zd\n", Attempt);
    Command Cmd(BaseCmd);
    Cmd.addFlag("merge_control_file", CFPath);
    Cmd.addFlag("merge_inner", "1");
    auto ExitCode = ExecuteCommand(Cmd);
    if (!ExitCode) {
      Printf("MERGE-OUTER: succesfull in %zd attempt(s)\n", Attempt);
      Success = true;
      break;
    }
  }
  if (!Success) {
    Printf("MERGE-OUTER: zero succesfull attempts, exiting\n");
    exit(1);
  }
  // Read the control file and do the merge.
  Merger M;
  std::ifstream IF(CFPath);
  IF.seekg(0, IF.end);
  Printf("MERGE-OUTER: the control file has %zd bytes\n", (size_t)IF.tellg());
  IF.seekg(0, IF.beg);
  M.ParseOrExit(IF, true);
  IF.close();
  Printf("MERGE-OUTER: consumed %zdMb (%zdMb rss) to parse the control file\n",
         M.ApproximateMemoryConsumption() >> 20, GetPeakRSSMb());
  size_t NumNewFeatures = M.Merge(InitialFeatures, NewFeatures, NewFiles);
  Printf("MERGE-OUTER: %zd new files with %zd new features added\n",
         NewFiles->size(), NumNewFeatures);
}

} // namespace fuzzer