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 <cstdlib>
22 #include <cstring>
23 #include <initializer_list>
24 #include <limits>
25 #include <string>
26 #include <type_traits>
27 #include <utility>
28 #include <vector>
29 30 // In addition to the comments below, the API is also briefly documented at
31 // https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
32 class FuzzedDataProvider {
33 public:
34 // |data| is an array of length |size| that the FuzzedDataProvider wraps to
35 // provide more granular access. |data| must outlive the FuzzedDataProvider.
36 FuzzedDataProvider(const uint8_t *data, size_t size)
37 : data_ptr_(data), remaining_bytes_(size) {}
38 ~FuzzedDataProvider() = default;
39 40 // See the implementation below (after the class definition) for more verbose
41 // comments for each of the methods.
42 43 // Methods returning std::vector of bytes. These are the most popular choice
44 // when splitting fuzzing input into pieces, as every piece is put into a
45 // separate buffer (i.e. ASan would catch any under-/overflow) and the memory
46 // will be released automatically.
47 template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes);
48 template <typename T>
49 std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes, T terminator = 0);
50 template <typename T> std::vector<T> ConsumeRemainingBytes();
51 52 // Methods returning strings. Use only when you need a std::string or a null
53 // terminated C-string. Otherwise, prefer the methods returning std::vector.
54 std::string ConsumeBytesAsString(size_t num_bytes);
55 std::string ConsumeRandomLengthString(size_t max_length);
56 std::string ConsumeRandomLengthString();
57 std::string ConsumeRemainingBytesAsString();
58 59 // Methods returning integer values.
60 template <typename T> T ConsumeIntegral();
61 template <typename T> T ConsumeIntegralInRange(T min, T max);
62 63 // Methods returning floating point values.
64 template <typename T> T ConsumeFloatingPoint();
65 template <typename T> T ConsumeFloatingPointInRange(T min, T max);
66 67 // 0 <= return value <= 1.
68 template <typename T> T ConsumeProbability();
69 70 bool ConsumeBool();
71 72 // Returns a value chosen from the given enum.
73 template <typename T> T ConsumeEnum();
74 75 // Returns a value from the given array.
76 template <typename T, size_t size> T PickValueInArray(const T (&array)[size]);
77 template <typename T, size_t size>
78 T PickValueInArray(const std::array<T, size> &array);
79 template <typename T> T PickValueInArray(std::initializer_list<const T> list);
80 81 // Writes data to the given destination and returns number of bytes written.
82 size_t ConsumeData(void *destination, size_t num_bytes);
83 84 // Reports the remaining bytes available for fuzzed input.
85 size_t remaining_bytes() { return remaining_bytes_; }
86 87 private:
88 FuzzedDataProvider(const FuzzedDataProvider &) = delete;
89 FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
90 91 void CopyAndAdvance(void *destination, size_t num_bytes);
92 93 void Advance(size_t num_bytes);
94 95 template <typename T>
96 std::vector<T> ConsumeBytes(size_t size, size_t num_bytes);
97 98 template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value);
99 100 const uint8_t *data_ptr_;
101 size_t remaining_bytes_;
102 };
103 104 // Returns a std::vector containing |num_bytes| of input data. If fewer than
105 // |num_bytes| of data remain, returns a shorter std::vector containing all
106 // of the data that's left. Can be used with any byte sized type, such as
107 // char, unsigned char, uint8_t, etc.
108 template <typename T>
109 std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t num_bytes) {
110 num_bytes = std::min(num_bytes, remaining_bytes_);
111 return ConsumeBytes<T>(num_bytes, num_bytes);
112 }
113 114 // Similar to |ConsumeBytes|, but also appends the terminator value at the end
115 // of the resulting vector. Useful, when a mutable null-terminated C-string is
116 // needed, for example. But that is a rare case. Better avoid it, if possible,
117 // and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.
118 template <typename T>
119 std::vector<T> FuzzedDataProvider::ConsumeBytesWithTerminator(size_t num_bytes,
120 T terminator) {
121 num_bytes = std::min(num_bytes, remaining_bytes_);
122 std::vector<T> result = ConsumeBytes<T>(num_bytes + 1, num_bytes);
123 result.back() = terminator;
124 return result;
125 }
126 127 // Returns a std::vector containing all remaining bytes of the input data.
128 template <typename T>
129 std::vector<T> FuzzedDataProvider::ConsumeRemainingBytes() {
130 return ConsumeBytes<T>(remaining_bytes_);
131 }
132 133 // Returns a std::string containing |num_bytes| of input data. Using this and
134 // |.c_str()| on the resulting string is the best way to get an immutable
135 // null-terminated C string. If fewer than |num_bytes| of data remain, returns
136 // a shorter std::string containing all of the data that's left.
137 inline std::string FuzzedDataProvider::ConsumeBytesAsString(size_t num_bytes) {
138 static_assert(sizeof(std::string::value_type) == sizeof(uint8_t),
139 "ConsumeBytesAsString cannot convert the data to a string.");
140 141 num_bytes = std::min(num_bytes, remaining_bytes_);
142 std::string result(
143 reinterpret_cast<const std::string::value_type *>(data_ptr_), num_bytes);
144 Advance(num_bytes);
145 return result;
146 }
147 148 // Returns a std::string of length from 0 to |max_length|. When it runs out of
149 // input data, returns what remains of the input. Designed to be more stable
150 // with respect to a fuzzer inserting characters than just picking a random
151 // length and then consuming that many bytes with |ConsumeBytes|.
152 inline std::string
153 FuzzedDataProvider::ConsumeRandomLengthString(size_t max_length) {
154 // Reads bytes from the start of |data_ptr_|. Maps "\\" to "\", and maps "\"
155 // followed by anything else to the end of the string. As a result of this
156 // logic, a fuzzer can insert characters into the string, and the string
157 // will be lengthened to include those new characters, resulting in a more
158 // stable fuzzer than picking the length of a string independently from
159 // picking its contents.
160 std::string result;
161 162 // Reserve the anticipated capacity to prevent several reallocations.
163 result.reserve(std::min(max_length, remaining_bytes_));
164 for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
165 char next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
166 Advance(1);
167 if (next == '\\' && remaining_bytes_ != 0) {
168 next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
169 Advance(1);
170 if (next != '\\')
171 break;
172 }
173 result += next;
174 }
175 176 result.shrink_to_fit();
177 return result;
178 }
179 180 // Returns a std::string of length from 0 to |remaining_bytes_|.
181 inline std::string FuzzedDataProvider::ConsumeRandomLengthString() {
182 return ConsumeRandomLengthString(remaining_bytes_);
183 }
184 185 // Returns a std::string containing all remaining bytes of the input data.
186 // Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
187 // object.
188 inline std::string FuzzedDataProvider::ConsumeRemainingBytesAsString() {
189 return ConsumeBytesAsString(remaining_bytes_);
190 }
191 192 // Returns a number in the range [Type's min, Type's max]. The value might
193 // not be uniformly distributed in the given range. If there's no input data
194 // left, always returns |min|.
195 template <typename T> T FuzzedDataProvider::ConsumeIntegral() {
196 return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
197 std::numeric_limits<T>::max());
198 }
199 200 // Returns a number in the range [min, max] by consuming bytes from the
201 // input data. The value might not be uniformly distributed in the given
202 // range. If there's no input data left, always returns |min|. |min| must
203 // be less than or equal to |max|.
204 template <typename T>
205 T FuzzedDataProvider::ConsumeIntegralInRange(T min, T max) {
206 static_assert(std::is_integral_v<T>, "An integral type is required.");
207 static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
208 209 if (min > max)
210 abort();
211 212 // Use the biggest type possible to hold the range and the result.
213 uint64_t range = static_cast<uint64_t>(max) - static_cast<uint64_t>(min);
214 uint64_t result = 0;
215 size_t offset = 0;
216 217 while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
218 remaining_bytes_ != 0) {
219 // Pull bytes off the end of the seed data. Experimentally, this seems to
220 // allow the fuzzer to more easily explore the input space. This makes
221 // sense, since it works by modifying inputs that caused new code to run,
222 // and this data is often used to encode length of data read by
223 // |ConsumeBytes|. Separating out read lengths makes it easier modify the
224 // contents of the data that is actually read.
225 --remaining_bytes_;
226 result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
227 offset += CHAR_BIT;
228 }
229 230 // Avoid division by 0, in case |range + 1| results in overflow.
231 if (range != std::numeric_limits<decltype(range)>::max())
232 result = result % (range + 1);
233 234 return static_cast<T>(static_cast<uint64_t>(min) + result);
235 }
236 237 // Returns a floating point value in the range [Type's lowest, Type's max] by
238 // consuming bytes from the input data. If there's no input data left, always
239 // returns approximately 0.
240 template <typename T> T FuzzedDataProvider::ConsumeFloatingPoint() {
241 return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
242 std::numeric_limits<T>::max());
243 }
244 245 // Returns a floating point value in the given range by consuming bytes from
246 // the input data. If there's no input data left, returns |min|. Note that
247 // |min| must be less than or equal to |max|.
248 template <typename T>
249 T FuzzedDataProvider::ConsumeFloatingPointInRange(T min, T max) {
250 if (min > max)
251 abort();
252 253 T range = .0;
254 T result = min;
255 constexpr T zero(.0);
256 if (max > zero && min < zero && max > min + std::numeric_limits<T>::max()) {
257 // The diff |max - min| would overflow the given floating point type. Use
258 // the half of the diff as the range and consume a bool to decide whether
259 // the result is in the first of the second part of the diff.
260 range = (max / 2.0) - (min / 2.0);
261 if (ConsumeBool()) {
262 result += range;
263 }
264 } else {
265 range = max - min;
266 }
267 268 return result + range * ConsumeProbability<T>();
269 }
270 271 // Returns a floating point number in the range [0.0, 1.0]. If there's no
272 // input data left, always returns 0.
273 template <typename T> T FuzzedDataProvider::ConsumeProbability() {
274 static_assert(std::is_floating_point_v<T>,
275 "A floating point type is required.");
276 277 // Use different integral types for different floating point types in order
278 // to provide better density of the resulting values.
279 using IntegralType =
280 typename std::conditional_t<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
281 uint64_t>;
282 283 T result = static_cast<T>(ConsumeIntegral<IntegralType>());
284 result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
285 return result;
286 }
287 288 // Reads one byte and returns a bool, or false when no data remains.
289 inline bool FuzzedDataProvider::ConsumeBool() {
290 return 1 & ConsumeIntegral<uint8_t>();
291 }
292 293 // Returns an enum value. The enum must start at 0 and be contiguous. It must
294 // also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
295 // enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
296 template <typename T> T FuzzedDataProvider::ConsumeEnum() {
297 static_assert(std::is_enum_v<T>, "|T| must be an enum type.");
298 return static_cast<T>(
299 ConsumeIntegralInRange<uint32_t>(0, static_cast<uint32_t>(T::kMaxValue)));
300 }
301 302 // Returns a copy of the value selected from the given fixed-size |array|.
303 template <typename T, size_t size>
304 T FuzzedDataProvider::PickValueInArray(const T (&array)[size]) {
305 static_assert(size > 0, "The array must be non empty.");
306 return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
307 }
308 309 template <typename T, size_t size>
310 T FuzzedDataProvider::PickValueInArray(const std::array<T, size> &array) {
311 static_assert(size > 0, "The array must be non empty.");
312 return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
313 }
314 315 template <typename T>
316 T FuzzedDataProvider::PickValueInArray(std::initializer_list<const T> list) {
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>
378 TS FuzzedDataProvider::ConvertUnsignedToSigned(TU value) {
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 if constexpr (std::numeric_limits<TS>::is_modulo)
384 return static_cast<TS>(value);
385 386 // Avoid using implementation-defined unsigned to signed conversions.
387 // To learn more, see https://stackoverflow.com/questions/13150449.
388 constexpr auto TS_max = static_cast<TU>(std::numeric_limits<TS>::max());
389 if (value <= 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<TS>(value - TS_min);
394 }
395 }
396 397 #endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
398