driver/fuzz_target_runner.cpp

// Copyright 2021 Code Intelligence GmbH
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "fuzz_target_runner.h"

#include <jni.h>

#include <fstream>
#include <iomanip>
#include <iostream>
#include <string>
#include <vector>

#include "absl/strings/escaping.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"
#include "absl/strings/str_replace.h"
#include "absl/strings/str_split.h"
#include "absl/strings/substitute.h"
#include "coverage_tracker.h"
#include "fuzzed_data_provider.h"
#include "gflags/gflags.h"
#include "glog/logging.h"
#include "java_reproducer.h"
#include "java_reproducer_templates.h"
#include "utils.h"

DEFINE_string(
    target_class, "",
    "The Java class that contains the static fuzzerTestOneInput function");
DEFINE_string(target_args, "",
              "Arguments passed to fuzzerInitialize as a String array. "
              "Separated by space.");

DEFINE_uint32(keep_going, 0,
              "Continue fuzzing until N distinct exception stack traces have"
              "been encountered. Defaults to exit after the first finding "
              "unless --autofuzz is specified.");
DEFINE_bool(dedup, true,
            "Emit a dedup token for every finding. Defaults to true and is "
            "required for --keep_going and --ignore.");
DEFINE_string(
    ignore, "",
    "Comma-separated list of crash dedup tokens to ignore. This is useful to "
    "continue fuzzing before a crash is fixed.");

DEFINE_string(reproducer_path, ".",
              "Path at which fuzzing reproducers are stored. Defaults to the "
              "current directory.");
DEFINE_string(coverage_report, "",
              "Path at which a coverage report is stored when the fuzzer "
              "exits. If left empty, no report is generated (default)");

DEFINE_string(autofuzz, "",
              "Fully qualified reference to a method on the classpath that "
              "should be fuzzed automatically (example: System.out::println). "
              "Fuzzing will continue even after a finding; specify "
              "--keep_going=N to stop after N findings.");
DEFINE_string(autofuzz_ignore, "",
              "Fully qualified class names of exceptions to ignore during "
              "autofuzz. Separated by comma.");

DECLARE_bool(hooks);

constexpr auto kManifestUtilsClass =
    "com/code_intelligence/jazzer/runtime/ManifestUtils";
constexpr auto kJazzerClass =
    "com/code_intelligence/jazzer/runtime/JazzerInternal";
constexpr auto kAutofuzzFuzzTargetClass =
    "com/code_intelligence/jazzer/autofuzz/FuzzTarget";

namespace jazzer {
// split a string on unescaped spaces
std::vector<std::string> splitOnSpace(const std::string &s) {
  if (s.empty()) {
    return {};
  }

  std::vector<std::string> tokens;
  std::size_t token_begin = 0;
  for (std::size_t i = 1; i < s.size() - 1; i++) {
    // only split if the space is not escaped by a backslash "\"
    if (s[i] == ' ' && s[i - 1] != '\\') {
      // don't split on multiple spaces
      if (i > token_begin + 1)
        tokens.push_back(s.substr(token_begin, i - token_begin));
      token_begin = i + 1;
    }
  }
  tokens.push_back(s.substr(token_begin));
  return tokens;
}

FuzzTargetRunner::FuzzTargetRunner(
    JVM &jvm, const std::vector<std::string> &additional_target_args)
    : ExceptionPrinter(jvm), jvm_(jvm), ignore_tokens_() {
  auto &env = jvm.GetEnv();
  if (!FLAGS_target_class.empty() && !FLAGS_autofuzz.empty()) {
    std::cerr << "--target_class and --autofuzz cannot be specified together"
              << std::endl;
    exit(1);
  }
  if (!FLAGS_target_args.empty() && !FLAGS_autofuzz.empty()) {
    std::cerr << "--target_args and --autofuzz cannot be specified together"
              << std::endl;
    exit(1);
  }
  if (FLAGS_autofuzz.empty() && !FLAGS_autofuzz_ignore.empty()) {
    std::cerr << "--autofuzz_ignore requires --autofuzz" << std::endl;
    exit(1);
  }
  if (FLAGS_target_class.empty() && FLAGS_autofuzz.empty()) {
    FLAGS_target_class = DetectFuzzTargetClass();
  }
  // If automatically detecting the fuzz target class failed, we expect it as
  // the value of the --target_class argument.
  if (FLAGS_target_class.empty() && FLAGS_autofuzz.empty()) {
    std::cerr << "Missing argument --target_class=<fuzz_target_class>"
              << std::endl;
    exit(1);
  }
  if (!FLAGS_autofuzz.empty()) {
    FLAGS_target_class = kAutofuzzFuzzTargetClass;
    if (FLAGS_keep_going == 0) {
      FLAGS_keep_going = std::numeric_limits<gflags::uint32>::max();
    }
    // Pass the method reference string as the first argument to the generic
    // autofuzz fuzz target. Subseqeuent arguments are interpreted as exception
    // class names that should be ignored.
    FLAGS_target_args = FLAGS_autofuzz;
    if (!FLAGS_autofuzz_ignore.empty()) {
      FLAGS_target_args = absl::StrCat(
          FLAGS_target_args, " ",
          absl::StrReplaceAll(FLAGS_autofuzz_ignore, {{",", " "}}));
    }
  }
  // Set --keep_going to its real default.
  if (FLAGS_keep_going == 0) {
    FLAGS_keep_going = 1;
  }
  if ((!FLAGS_ignore.empty() || FLAGS_keep_going > 1) && !FLAGS_dedup) {
    std::cerr << "--nodedup is not supported with --ignore or --keep_going"
              << std::endl;
    exit(1);
  }
  jazzer_ = jvm.FindClass(kJazzerClass);
  last_finding_ =
      env.GetStaticFieldID(jazzer_, "lastFinding", "Ljava/lang/Throwable;");

  jclass_ = jvm.FindClass(FLAGS_target_class);
  // one of the following functions is required:
  //    public static void fuzzerTestOneInput(byte[] input)
  //    public static void fuzzerTestOneInput(FuzzedDataProvider data)
  fuzzer_test_one_input_bytes_ =
      jvm.GetStaticMethodID(jclass_, "fuzzerTestOneInput", "([B)V", false);
  fuzzer_test_one_input_data_ = jvm.GetStaticMethodID(
      jclass_, "fuzzerTestOneInput",
      "(Lcom/code_intelligence/jazzer/api/FuzzedDataProvider;)V", false);
  bool using_bytes = fuzzer_test_one_input_bytes_ != nullptr;
  bool using_data = fuzzer_test_one_input_data_ != nullptr;
  // Fail if none ore both of the two possible fuzzerTestOneInput versions is
  // defined in the class.
  if (using_bytes == using_data) {
    LOG(ERROR) << FLAGS_target_class
               << " must define exactly one of the following two functions:";
    LOG(ERROR) << "public static void fuzzerTestOneInput(byte[] ...)";
    LOG(ERROR)
        << "public static void fuzzerTestOneInput(FuzzedDataProvider ...)";
    LOG(ERROR) << "Note: Fuzz targets returning boolean are no longer "
                  "supported; exceptions should be thrown instead of "
                  "returning true.";
    exit(1);
  }

  // check existence of optional methods for initialization and destruction
  fuzzer_initialize_ =
      jvm.GetStaticMethodID(jclass_, "fuzzerInitialize", "()V", false);
  fuzzer_tear_down_ =
      jvm.GetStaticMethodID(jclass_, "fuzzerTearDown", "()V", false);
  fuzzer_initialize_with_args_ = jvm.GetStaticMethodID(
      jclass_, "fuzzerInitialize", "([Ljava/lang/String;)V", false);

  auto fuzz_target_args_tokens = splitOnSpace(FLAGS_target_args);
  fuzz_target_args_tokens.insert(fuzz_target_args_tokens.end(),
                                 additional_target_args.begin(),
                                 additional_target_args.end());

  if (fuzzer_initialize_with_args_) {
    // fuzzerInitialize with arguments gets priority
    jclass string_class = jvm.FindClass("java/lang/String");
    jobjectArray arg_array = jvm.GetEnv().NewObjectArray(
        fuzz_target_args_tokens.size(), string_class, nullptr);
    for (jint i = 0; i < fuzz_target_args_tokens.size(); i++) {
      jstring str = env.NewStringUTF(fuzz_target_args_tokens[i].c_str());
      env.SetObjectArrayElement(arg_array, i, str);
    }
    env.CallStaticObjectMethod(jclass_, fuzzer_initialize_with_args_,
                               arg_array);
  } else if (fuzzer_initialize_) {
    env.CallStaticVoidMethod(jclass_, fuzzer_initialize_);
  } else {
    LOG(INFO) << "did not call any fuzz target initialize functions";
  }

  if (jthrowable exception = env.ExceptionOccurred()) {
    LOG(ERROR) << "== Java Exception in fuzzerInitialize: ";
    LOG(ERROR) << getStackTrace(exception);
    std::exit(1);
  }

  if (FLAGS_hooks) {
    CoverageTracker::RecordInitialCoverage(env);
  }
  SetUpFuzzedDataProvider(jvm_.GetEnv());

  // Parse a comma-separated list of hex dedup tokens.
  std::vector<std::string> str_ignore_tokens =
      absl::StrSplit(FLAGS_ignore, ',');
  for (const std::string &str_token : str_ignore_tokens) {
    if (str_token.empty()) continue;
    try {
      ignore_tokens_.push_back(std::stoull(str_token, nullptr, 16));
    } catch (...) {
      LOG(ERROR) << "Invalid dedup token (expected up to 16 hex digits): '"
                 << str_token << "'";
      // Don't let libFuzzer print a crash stack trace.
      _Exit(1);
    }
  }
}

FuzzTargetRunner::~FuzzTargetRunner() {
  if (FLAGS_hooks && !FLAGS_coverage_report.empty()) {
    std::string report = CoverageTracker::ComputeCoverage(jvm_.GetEnv());
    std::ofstream report_file(FLAGS_coverage_report);
    if (report_file) {
      report_file << report << std::flush;
    } else {
      LOG(ERROR) << "Failed to write coverage report to "
                 << FLAGS_coverage_report;
    }
  }
  if (fuzzer_tear_down_ != nullptr) {
    std::cerr << "calling fuzzer teardown function" << std::endl;
    jvm_.GetEnv().CallStaticVoidMethod(jclass_, fuzzer_tear_down_);
    if (jthrowable exception = jvm_.GetEnv().ExceptionOccurred())
      std::cerr << getStackTrace(exception) << std::endl;
  }
}

RunResult FuzzTargetRunner::Run(const uint8_t *data, const std::size_t size) {
  auto &env = jvm_.GetEnv();
  static std::size_t run_count = 0;
  if (run_count < 2) {
    run_count++;
    // For the first two runs only, replay the coverage recorded from static
    // initializers. libFuzzer cleared the coverage map after they ran and could
    // fail to see any coverage, triggering an early exit, if we don't replay it
    // here.
    // https://github.com/llvm/llvm-project/blob/957a5e987444d3193575d6ad8afe6c75da00d794/compiler-rt/lib/fuzzer/FuzzerLoop.cpp#L804-L809
    CoverageTracker::ReplayInitialCoverage(env);
  }
  if (fuzzer_test_one_input_data_ != nullptr) {
    FeedFuzzedDataProvider(data, size);
    env.CallStaticVoidMethod(jclass_, fuzzer_test_one_input_data_,
                             GetFuzzedDataProviderJavaObject(jvm_));
  } else {
    jbyteArray byte_array = env.NewByteArray(size);
    if (byte_array == nullptr) {
      env.ExceptionDescribe();
      throw std::runtime_error(std::string("Cannot create byte array"));
    }
    env.SetByteArrayRegion(byte_array, 0, size,
                           reinterpret_cast<const jbyte *>(data));
    env.CallStaticVoidMethod(jclass_, fuzzer_test_one_input_bytes_, byte_array);
    env.DeleteLocalRef(byte_array);
  }

  const auto finding = GetFinding();
  if (finding != nullptr) {
    jlong dedup_token = computeDedupToken(finding);
    // Check whether this stack trace has been encountered before if
    // `--keep_going` has been supplied.
    if (dedup_token != 0 && FLAGS_keep_going > 1 &&
        std::find(ignore_tokens_.cbegin(), ignore_tokens_.cend(),
                  dedup_token) != ignore_tokens_.end()) {
      env.DeleteLocalRef(finding);
      return RunResult::kOk;
    } else {
      ignore_tokens_.push_back(dedup_token);
      std::cout << std::endl;
      std::cerr << "== Java Exception: " << getStackTrace(finding);
      env.DeleteLocalRef(finding);
      if (FLAGS_dedup) {
        std::cout << "DEDUP_TOKEN: " << std::hex << std::setfill('0')
                  << std::setw(16) << dedup_token << std::endl;
      }
      if (ignore_tokens_.size() < static_cast<std::size_t>(FLAGS_keep_going)) {
        return RunResult::kDumpAndContinue;
      } else {
        return RunResult::kException;
      }
    }
  }
  return RunResult::kOk;
}

// Returns a fuzzer finding as a Throwable (or nullptr if there is none),
// clearing any JVM exceptions in the process.
jthrowable FuzzTargetRunner::GetFinding() const {
  auto &env = jvm_.GetEnv();
  jthrowable unprocessed_finding = nullptr;
  if (env.ExceptionCheck()) {
    unprocessed_finding = env.ExceptionOccurred();
    env.ExceptionClear();
  }
  // Explicitly reported findings take precedence over uncaught exceptions.
  if (auto reported_finding =
          (jthrowable)env.GetStaticObjectField(jazzer_, last_finding_);
      reported_finding != nullptr) {
    env.DeleteLocalRef(unprocessed_finding);
    unprocessed_finding = reported_finding;
  }
  jthrowable processed_finding = preprocessException(unprocessed_finding);
  env.DeleteLocalRef(unprocessed_finding);
  return processed_finding;
}

void FuzzTargetRunner::DumpReproducer(const uint8_t *data, std::size_t size) {
  auto &env = jvm_.GetEnv();
  std::string base64_data;
  if (fuzzer_test_one_input_data_) {
    // Record the data retrieved from the FuzzedDataProvider and supply it to a
    // Java-only CannedFuzzedDataProvider in the reproducer.
    FeedFuzzedDataProvider(data, size);
    jobject recorder = GetRecordingFuzzedDataProviderJavaObject(jvm_);
    env.CallStaticVoidMethod(jclass_, fuzzer_test_one_input_data_, recorder);
    const auto finding = GetFinding();
    if (finding == nullptr) {
      LOG(ERROR) << "Failed to reproduce crash when rerunning with recorder";
      return;
    }
    base64_data = SerializeRecordingFuzzedDataProvider(jvm_, recorder);
  } else {
    absl::string_view data_str(reinterpret_cast<const char *>(data), size);
    absl::Base64Escape(data_str, &base64_data);
  }
  const char *fuzz_target_call = fuzzer_test_one_input_data_
                                     ? kTestOneInputWithData
                                     : kTestOneInputWithBytes;
  std::string data_sha1 = jazzer::Sha1Hash(data, size);
  std::string reproducer =
      absl::Substitute(kBaseReproducer, data_sha1, base64_data,
                       FLAGS_target_class, fuzz_target_call);
  std::string reproducer_filename = absl::StrFormat("Crash_%s.java", data_sha1);
  std::string reproducer_full_path = absl::StrFormat(
      "%s%c%s", FLAGS_reproducer_path, kPathSeparator, reproducer_filename);
  std::ofstream reproducer_out(reproducer_full_path);
  reproducer_out << reproducer;
  std::cout << absl::StrFormat(
                   "reproducer_path='%s'; Java reproducer written to %s",
                   FLAGS_reproducer_path, reproducer_full_path)
            << std::endl;
}

std::string FuzzTargetRunner::DetectFuzzTargetClass() const {
  jclass manifest_utils = jvm_.FindClass(kManifestUtilsClass);
  jmethodID detect_fuzz_target_class = jvm_.GetStaticMethodID(
      manifest_utils, "detectFuzzTargetClass", "()Ljava/lang/String;", true);
  auto &env = jvm_.GetEnv();
  auto jni_fuzz_target_class = (jstring)(env.CallStaticObjectMethod(
      manifest_utils, detect_fuzz_target_class));
  if (env.ExceptionCheck()) {
    env.ExceptionDescribe();
    exit(1);
  }
  if (jni_fuzz_target_class == nullptr) return "";

  const char *fuzz_target_class_cstr =
      env.GetStringUTFChars(jni_fuzz_target_class, nullptr);
  std::string fuzz_target_class = std::string(fuzz_target_class_cstr);
  env.ReleaseStringUTFChars(jni_fuzz_target_class, fuzz_target_class_cstr);
  env.DeleteLocalRef(jni_fuzz_target_class);

  return fuzz_target_class;
}
}  // namespace jazzer