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FuzzedDataProvider.h
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1 //===- FuzzedDataProvider.h - Utility header for fuzz targets ---*- C++ -* ===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 // A single header library providing an utility class to break up an array of
9 // bytes. Whenever run on the same input, provides the same output, as long as
10 // its methods are called in the same order, with the same arguments.
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
14 #define LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
15 
16 #include <algorithm>
17 #include <array>
18 #include <climits>
19 #include <cstddef>
20 #include <cstdint>
21 #include <cstring>
22 #include <initializer_list>
23 #include <limits>
24 #include <string>
25 #include <type_traits>
26 #include <utility>
27 #include <vector>
28 
29 // In addition to the comments below, the API is also briefly documented at
30 // https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
32  public:
33  // |data| is an array of length |size| that the FuzzedDataProvider wraps to
34  // provide more granular access. |data| must outlive the FuzzedDataProvider.
35  FuzzedDataProvider(const uint8_t *data, size_t size)
36  : data_ptr_(data), remaining_bytes_(size) {}
37  ~FuzzedDataProvider() = default;
38 
39  // See the implementation below (after the class definition) for more verbose
40  // comments for each of the methods.
41 
42  // Methods returning std::vector of bytes. These are the most popular choice
43  // when splitting fuzzing input into pieces, as every piece is put into a
44  // separate buffer (i.e. ASan would catch any under-/overflow) and the memory
45  // will be released automatically.
46  template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes);
47  template <typename T>
48  std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes, T terminator = 0);
49  template <typename T> std::vector<T> ConsumeRemainingBytes();
50 
51  // Methods returning strings. Use only when you need a std::string or a null
52  // terminated C-string. Otherwise, prefer the methods returning std::vector.
53  std::string ConsumeBytesAsString(size_t num_bytes);
54  std::string ConsumeRandomLengthString(size_t max_length);
55  std::string ConsumeRandomLengthString();
56  std::string ConsumeRemainingBytesAsString();
57 
58  // Methods returning integer values.
59  template <typename T> T ConsumeIntegral();
60  template <typename T> T ConsumeIntegralInRange(T min, T max);
61 
62  // Methods returning floating point values.
63  template <typename T> T ConsumeFloatingPoint();
64  template <typename T> T ConsumeFloatingPointInRange(T min, T max);
65 
66  // 0 <= return value <= 1.
67  template <typename T> T ConsumeProbability();
68 
69  bool ConsumeBool();
70 
71  // Returns a value chosen from the given enum.
72  template <typename T> T ConsumeEnum();
73 
74  // Returns a value from the given array.
75  template <typename T, size_t size> T PickValueInArray(const T (&array)[size]);
76  template <typename T, size_t size>
77  T PickValueInArray(const std::array<T, size> &array);
78  template <typename T> T PickValueInArray(std::initializer_list<const T> list);
79 
80  // Writes data to the given destination and returns number of bytes written.
81  size_t ConsumeData(void *destination, size_t num_bytes);
82 
83  // Reports the remaining bytes available for fuzzed input.
84  size_t remaining_bytes() { return remaining_bytes_; }
85 
86  private:
87  FuzzedDataProvider(const FuzzedDataProvider &) = delete;
89 
90  void CopyAndAdvance(void *destination, size_t num_bytes);
91 
92  void Advance(size_t num_bytes);
93 
94  template <typename T>
95  std::vector<T> ConsumeBytes(size_t size, size_t num_bytes);
96 
97  template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value);
98 
99  const uint8_t *data_ptr_;
101 };
102 
103 // Returns a std::vector containing |num_bytes| of input data. If fewer than
104 // |num_bytes| of data remain, returns a shorter std::vector containing all
105 // of the data that's left. Can be used with any byte sized type, such as
106 // char, unsigned char, uint8_t, etc.
107 template <typename T>
108 std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t num_bytes) {
109  num_bytes = std::min(num_bytes, remaining_bytes_);
110  return ConsumeBytes<T>(num_bytes, num_bytes);
111 }
112 
113 // Similar to |ConsumeBytes|, but also appends the terminator value at the end
114 // of the resulting vector. Useful, when a mutable null-terminated C-string is
115 // needed, for example. But that is a rare case. Better avoid it, if possible,
116 // and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.
117 template <typename T>
118 std::vector<T> FuzzedDataProvider::ConsumeBytesWithTerminator(size_t num_bytes,
119  T terminator) {
120  num_bytes = std::min(num_bytes, remaining_bytes_);
121  std::vector<T> result = ConsumeBytes<T>(num_bytes + 1, num_bytes);
122  result.back() = terminator;
123  return result;
124 }
125 
126 // Returns a std::vector containing all remaining bytes of the input data.
127 template <typename T>
129  return ConsumeBytes<T>(remaining_bytes_);
130 }
131 
132 // Returns a std::string containing |num_bytes| of input data. Using this and
133 // |.c_str()| on the resulting string is the best way to get an immutable
134 // null-terminated C string. If fewer than |num_bytes| of data remain, returns
135 // a shorter std::string containing all of the data that's left.
136 inline std::string FuzzedDataProvider::ConsumeBytesAsString(size_t num_bytes) {
137  static_assert(sizeof(std::string::value_type) == sizeof(uint8_t),
138  "ConsumeBytesAsString cannot convert the data to a string.");
139 
140  num_bytes = std::min(num_bytes, remaining_bytes_);
141  std::string result(
142  reinterpret_cast<const std::string::value_type *>(data_ptr_), num_bytes);
143  Advance(num_bytes);
144  return result;
145 }
146 
147 // Returns a std::string of length from 0 to |max_length|. When it runs out of
148 // input data, returns what remains of the input. Designed to be more stable
149 // with respect to a fuzzer inserting characters than just picking a random
150 // length and then consuming that many bytes with |ConsumeBytes|.
151 inline std::string
153  // Reads bytes from the start of |data_ptr_|. Maps "\\" to "\", and maps "\"
154  // followed by anything else to the end of the string. As a result of this
155  // logic, a fuzzer can insert characters into the string, and the string
156  // will be lengthened to include those new characters, resulting in a more
157  // stable fuzzer than picking the length of a string independently from
158  // picking its contents.
159  std::string result;
160 
161  // Reserve the anticipated capaticity to prevent several reallocations.
162  result.reserve(std::min(max_length, remaining_bytes_));
163  for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
164  char next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
165  Advance(1);
166  if (next == '\\' && remaining_bytes_ != 0) {
167  next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
168  Advance(1);
169  if (next != '\\')
170  break;
171  }
172  result += next;
173  }
174 
175  result.shrink_to_fit();
176  return result;
177 }
178 
179 // Returns a std::string of length from 0 to |remaining_bytes_|.
182 }
183 
184 // Returns a std::string containing all remaining bytes of the input data.
185 // Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
186 // object.
189 }
190 
191 // Returns a number in the range [Type's min, Type's max]. The value might
192 // not be uniformly distributed in the given range. If there's no input data
193 // left, always returns |min|.
194 template <typename T> T FuzzedDataProvider::ConsumeIntegral() {
195  return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
196  std::numeric_limits<T>::max());
197 }
198 
199 // Returns a number in the range [min, max] by consuming bytes from the
200 // input data. The value might not be uniformly distributed in the given
201 // range. If there's no input data left, always returns |min|. |min| must
202 // be less than or equal to |max|.
203 template <typename T>
205  static_assert(std::is_integral<T>::value, "An integral type is required.");
206  static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
207 
208  if (min > max)
209  abort();
210 
211  // Use the biggest type possible to hold the range and the result.
212  uint64_t range = static_cast<uint64_t>(max) - min;
213  uint64_t result = 0;
214  size_t offset = 0;
215 
216  while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
217  remaining_bytes_ != 0) {
218  // Pull bytes off the end of the seed data. Experimentally, this seems to
219  // allow the fuzzer to more easily explore the input space. This makes
220  // sense, since it works by modifying inputs that caused new code to run,
221  // and this data is often used to encode length of data read by
222  // |ConsumeBytes|. Separating out read lengths makes it easier modify the
223  // contents of the data that is actually read.
225  result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
226  offset += CHAR_BIT;
227  }
228 
229  // Avoid division by 0, in case |range + 1| results in overflow.
230  if (range != std::numeric_limits<decltype(range)>::max())
231  result = result % (range + 1);
232 
233  return static_cast<T>(min + result);
234 }
235 
236 // Returns a floating point value in the range [Type's lowest, Type's max] by
237 // consuming bytes from the input data. If there's no input data left, always
238 // returns approximately 0.
240  return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
241  std::numeric_limits<T>::max());
242 }
243 
244 // Returns a floating point value in the given range by consuming bytes from
245 // the input data. If there's no input data left, returns |min|. Note that
246 // |min| must be less than or equal to |max|.
247 template <typename T>
249  if (min > max)
250  abort();
251 
252  T range = .0;
253  T result = min;
254  constexpr T zero(.0);
255  if (max > zero && min < zero && max > min + std::numeric_limits<T>::max()) {
256  // The diff |max - min| would overflow the given floating point type. Use
257  // the half of the diff as the range and consume a bool to decide whether
258  // the result is in the first of the second part of the diff.
259  range = (max / 2.0) - (min / 2.0);
260  if (ConsumeBool()) {
261  result += range;
262  }
263  } else {
264  range = max - min;
265  }
266 
267  return result + range * ConsumeProbability<T>();
268 }
269 
270 // Returns a floating point number in the range [0.0, 1.0]. If there's no
271 // input data left, always returns 0.
272 template <typename T> T FuzzedDataProvider::ConsumeProbability() {
273  static_assert(std::is_floating_point<T>::value,
274  "A floating point type is required.");
275 
276  // Use different integral types for different floating point types in order
277  // to provide better density of the resulting values.
278  using IntegralType =
279  typename std::conditional<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
280  uint64_t>::type;
281 
282  T result = static_cast<T>(ConsumeIntegral<IntegralType>());
283  result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
284  return result;
285 }
286 
287 // Reads one byte and returns a bool, or false when no data remains.
289  return 1 & ConsumeIntegral<uint8_t>();
290 }
291 
292 // Returns an enum value. The enum must start at 0 and be contiguous. It must
293 // also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
294 // enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
295 template <typename T> T FuzzedDataProvider::ConsumeEnum() {
296  static_assert(std::is_enum<T>::value, "|T| must be an enum type.");
297  return static_cast<T>(
298  ConsumeIntegralInRange<uint32_t>(0, static_cast<uint32_t>(T::kMaxValue)));
299 }
300 
301 // Returns a copy of the value selected from the given fixed-size |array|.
302 template <typename T, size_t size>
303 T FuzzedDataProvider::PickValueInArray(const T (&array)[size]) {
304  static_assert(size > 0, "The array must be non empty.");
305  return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
306 }
307 
308 template <typename T, size_t size>
309 T FuzzedDataProvider::PickValueInArray(const std::array<T, size> &array) {
310  static_assert(size > 0, "The array must be non empty.");
311  return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
312 }
313 
314 template <typename T>
315 T FuzzedDataProvider::PickValueInArray(std::initializer_list<const T> list) {
316  // TODO(Dor1s): switch to static_assert once C++14 is allowed.
317  if (!list.size())
318  abort();
319 
320  return *(list.begin() + ConsumeIntegralInRange<size_t>(0, list.size() - 1));
321 }
322 
323 // Writes |num_bytes| of input data to the given destination pointer. If there
324 // is not enough data left, writes all remaining bytes. Return value is the
325 // number of bytes written.
326 // In general, it's better to avoid using this function, but it may be useful
327 // in cases when it's necessary to fill a certain buffer or object with
328 // fuzzing data.
329 inline size_t FuzzedDataProvider::ConsumeData(void *destination,
330  size_t num_bytes) {
331  num_bytes = std::min(num_bytes, remaining_bytes_);
332  CopyAndAdvance(destination, num_bytes);
333  return num_bytes;
334 }
335 
336 // Private methods.
337 inline void FuzzedDataProvider::CopyAndAdvance(void *destination,
338  size_t num_bytes) {
339  std::memcpy(destination, data_ptr_, num_bytes);
340  Advance(num_bytes);
341 }
342 
343 inline void FuzzedDataProvider::Advance(size_t num_bytes) {
344  if (num_bytes > remaining_bytes_)
345  abort();
346 
347  data_ptr_ += num_bytes;
348  remaining_bytes_ -= num_bytes;
349 }
350 
351 template <typename T>
352 std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t size, size_t num_bytes) {
353  static_assert(sizeof(T) == sizeof(uint8_t), "Incompatible data type.");
354 
355  // The point of using the size-based constructor below is to increase the
356  // odds of having a vector object with capacity being equal to the length.
357  // That part is always implementation specific, but at least both libc++ and
358  // libstdc++ allocate the requested number of bytes in that constructor,
359  // which seems to be a natural choice for other implementations as well.
360  // To increase the odds even more, we also call |shrink_to_fit| below.
361  std::vector<T> result(size);
362  if (size == 0) {
363  if (num_bytes != 0)
364  abort();
365  return result;
366  }
367 
368  CopyAndAdvance(result.data(), num_bytes);
369 
370  // Even though |shrink_to_fit| is also implementation specific, we expect it
371  // to provide an additional assurance in case vector's constructor allocated
372  // a buffer which is larger than the actual amount of data we put inside it.
373  result.shrink_to_fit();
374  return result;
375 }
376 
377 template <typename TS, typename TU>
379  static_assert(sizeof(TS) == sizeof(TU), "Incompatible data types.");
380  static_assert(!std::numeric_limits<TU>::is_signed,
381  "Source type must be unsigned.");
382 
383  // TODO(Dor1s): change to `if constexpr` once C++17 becomes mainstream.
384  if (std::numeric_limits<TS>::is_modulo)
385  return static_cast<TS>(value);
386 
387  // Avoid using implementation-defined unsigned to signed conversions.
388  // To learn more, see https://stackoverflow.com/questions/13150449.
389  if (value <= std::numeric_limits<TS>::max()) {
390  return static_cast<TS>(value);
391  } else {
392  constexpr auto TS_min = std::numeric_limits<TS>::min();
393  return TS_min + static_cast<char>(value - TS_min);
394  }
395 }
396 
397 #endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
FuzzedDataProvider::ConsumeRemainingBytesAsString
std::string ConsumeRemainingBytesAsString()
Definition: FuzzedDataProvider.h:187
FuzzedDataProvider::ConsumeBytesWithTerminator
std::vector< T > ConsumeBytesWithTerminator(size_t num_bytes, T terminator=0)
Definition: FuzzedDataProvider.h:118
FuzzedDataProvider::ConsumeData
size_t ConsumeData(void *destination, size_t num_bytes)
Definition: FuzzedDataProvider.h:329
FuzzedDataProvider::ConsumeEnum
T ConsumeEnum()
Definition: FuzzedDataProvider.h:295
FuzzedDataProvider::ConsumeFloatingPoint
T ConsumeFloatingPoint()
Definition: FuzzedDataProvider.h:239
FuzzedDataProvider::PickValueInArray
T PickValueInArray(const T(&array)[size])
Definition: FuzzedDataProvider.h:303
FuzzedDataProvider::remaining_bytes_
size_t remaining_bytes_
Definition: FuzzedDataProvider.h:100
FuzzedDataProvider::ConsumeRemainingBytes
std::vector< T > ConsumeRemainingBytes()
Definition: FuzzedDataProvider.h:128
FuzzedDataProvider::data_ptr_
const uint8_t * data_ptr_
Definition: FuzzedDataProvider.h:99
FuzzedDataProvider::ConsumeRandomLengthString
std::string ConsumeRandomLengthString()
Definition: FuzzedDataProvider.h:180
FuzzedDataProvider::~FuzzedDataProvider
~FuzzedDataProvider()=default
FuzzedDataProvider::CopyAndAdvance
void CopyAndAdvance(void *destination, size_t num_bytes)
Definition: FuzzedDataProvider.h:337
FuzzedDataProvider::remaining_bytes
size_t remaining_bytes()
Definition: FuzzedDataProvider.h:84
FuzzedDataProvider::ConsumeProbability
T ConsumeProbability()
Definition: FuzzedDataProvider.h:272
FuzzedDataProvider
Definition: FuzzedDataProvider.h:31
FuzzedDataProvider::ConsumeIntegral
T ConsumeIntegral()
Definition: FuzzedDataProvider.h:194
FuzzedDataProvider::ConsumeBytesAsString
std::string ConsumeBytesAsString(size_t num_bytes)
Definition: FuzzedDataProvider.h:136
FuzzedDataProvider::operator=
FuzzedDataProvider & operator=(const FuzzedDataProvider &)=delete
FuzzedDataProvider::ConsumeBool
bool ConsumeBool()
Definition: FuzzedDataProvider.h:288
FuzzedDataProvider::ConsumeFloatingPointInRange
T ConsumeFloatingPointInRange(T min, T max)
Definition: FuzzedDataProvider.h:248
T
#define T(expected, seed, data)
FuzzedDataProvider::FuzzedDataProvider
FuzzedDataProvider(const uint8_t *data, size_t size)
Definition: FuzzedDataProvider.h:35
FuzzedDataProvider::ConvertUnsignedToSigned
TS ConvertUnsignedToSigned(TU value)
Definition: FuzzedDataProvider.h:378
FuzzedDataProvider::ConsumeIntegralInRange
T ConsumeIntegralInRange(T min, T max)
Definition: FuzzedDataProvider.h:204
FuzzedDataProvider::ConsumeBytes
std::vector< T > ConsumeBytes(size_t num_bytes)
Definition: FuzzedDataProvider.h:108
FuzzedDataProvider::Advance
void Advance(size_t num_bytes)
Definition: FuzzedDataProvider.h:343