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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
31 : : class FuzzedDataProvider {
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 : 144 : FuzzedDataProvider(const uint8_t *data, size_t size)
36 : 144 : : 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 : 5533 : size_t remaining_bytes() { return remaining_bytes_; }
85 : :
86 : : private:
87 : : FuzzedDataProvider(const FuzzedDataProvider &) = delete;
88 : : FuzzedDataProvider &operator=(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_;
100 : : size_t remaining_bytes_;
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 : 0 : std::vector<T> FuzzedDataProvider::ConsumeBytes(size_t num_bytes) {
109 : 0 : num_bytes = std::min(num_bytes, remaining_bytes_);
110 : 0 : 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>
128 : 0 : std::vector<T> FuzzedDataProvider::ConsumeRemainingBytes() {
129 : 0 : 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 : 144 : 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 : 144 : num_bytes = std::min(num_bytes, remaining_bytes_);
141 [ + - ][ + - ]: 288 : std::string result(
142 : 144 : reinterpret_cast<const std::string::value_type *>(data_ptr_), num_bytes);
143 [ + - ]: 144 : Advance(num_bytes);
144 : 144 : return result;
145 [ + - ]: 144 : }
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
152 : 5391 : FuzzedDataProvider::ConsumeRandomLengthString(size_t max_length) {
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 : 5391 : std::string result;
160 : :
161 : : // Reserve the anticipated capaticity to prevent several reallocations.
162 [ + - ][ + - ]: 5391 : result.reserve(std::min(max_length, remaining_bytes_));
163 [ + + ][ + + ]: 2356887 : for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
164 [ + - ]: 2356797 : char next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
165 [ + - ]: 2356797 : Advance(1);
166 [ + + ][ + + ]: 2356797 : if (next == '\\' && remaining_bytes_ != 0) {
167 [ + - ]: 140394 : next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
168 [ + - ]: 140394 : Advance(1);
169 [ + + ]: 140394 : if (next != '\\')
170 : 5301 : break;
171 : 135093 : }
172 [ + - ]: 2351496 : result += next;
173 : 2351496 : }
174 : :
175 : 5391 : result.shrink_to_fit();
176 : 5391 : return result;
177 [ + - ]: 5391 : }
178 : :
179 : : // Returns a std::string of length from 0 to |remaining_bytes_|.
180 : 5391 : inline std::string FuzzedDataProvider::ConsumeRandomLengthString() {
181 : 5391 : return ConsumeRandomLengthString(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.
187 : 0 : inline std::string FuzzedDataProvider::ConsumeRemainingBytesAsString() {
188 : 0 : return ConsumeBytesAsString(remaining_bytes_);
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 : 0 : template <typename T> T FuzzedDataProvider::ConsumeIntegral() {
195 : 0 : return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
196 : 0 : 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>
204 : 5389 : T FuzzedDataProvider::ConsumeIntegralInRange(T min, T max) {
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 [ # # ][ # # ]: 5389 : if (min > max)
[ - + ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
209 : 0 : abort();
210 : :
211 : : // Use the biggest type possible to hold the range and the result.
212 : 5389 : uint64_t range = static_cast<uint64_t>(max) - static_cast<uint64_t>(min);
213 : 5389 : uint64_t result = 0;
214 : 5389 : size_t offset = 0;
215 : :
216 [ # # ][ # # ]: 31922 : while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
[ # # ][ # # ]
[ # # ][ # # ]
[ + - ][ + + ]
[ + + ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
217 : 21257 : 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.
224 : 21144 : --remaining_bytes_;
225 : 21144 : result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
226 : 21144 : offset += CHAR_BIT;
227 : : }
228 : :
229 : : // Avoid division by 0, in case |range + 1| results in overflow.
230 [ # # ][ # # ]: 5389 : if (range != std::numeric_limits<decltype(range)>::max())
[ - + ][ # # ]
[ # # ][ # # ]
[ # # ][ # # ]
[ # # ]
231 : 5389 : result = result % (range + 1);
232 : :
233 : 5389 : return static_cast<T>(static_cast<uint64_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.
239 : 0 : template <typename T> T FuzzedDataProvider::ConsumeFloatingPoint() {
240 : 0 : return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
241 : 0 : 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>
248 : 0 : T FuzzedDataProvider::ConsumeFloatingPointInRange(T min, T max) {
249 [ # # ][ # # ]: 0 : if (min > max)
250 : 0 : abort();
251 : :
252 : 0 : T range = .0;
253 : 0 : T result = min;
254 : 0 : constexpr T zero(.0);
255 [ # # ][ # # ]: 0 : 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 : 0 : range = (max / 2.0) - (min / 2.0);
260 [ # # ][ # # ]: 0 : if (ConsumeBool()) {
261 : 0 : result += range;
262 : 0 : }
263 : 0 : } else {
264 : 0 : range = max - min;
265 : : }
266 : :
267 : 0 : 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 : 0 : 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 : 0 : T result = static_cast<T>(ConsumeIntegral<IntegralType>());
283 : 0 : result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
284 : 0 : return result;
285 : : }
286 : :
287 : : // Reads one byte and returns a bool, or false when no data remains.
288 : 0 : inline bool FuzzedDataProvider::ConsumeBool() {
289 : 0 : 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 : 0 : T FuzzedDataProvider::PickValueInArray(const T (&array)[size]) {
304 : : static_assert(size > 0, "The array must be non empty.");
305 : 0 : return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
306 : : }
307 : :
308 : : template <typename T, size_t size>
309 : 0 : T FuzzedDataProvider::PickValueInArray(const std::array<T, size> &array) {
310 : : static_assert(size > 0, "The array must be non empty.");
311 : 0 : return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
312 : : }
313 : :
314 : : template <typename T>
315 : 0 : T FuzzedDataProvider::PickValueInArray(std::initializer_list<const T> list) {
316 : : // TODO(Dor1s): switch to static_assert once C++14 is allowed.
317 [ # # ][ # # ]: 0 : if (!list.size())
318 : 0 : abort();
319 : :
320 : 0 : 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 : 0 : inline size_t FuzzedDataProvider::ConsumeData(void *destination,
330 : : size_t num_bytes) {
331 : 0 : num_bytes = std::min(num_bytes, remaining_bytes_);
332 : 0 : CopyAndAdvance(destination, num_bytes);
333 : 0 : return num_bytes;
334 : : }
335 : :
336 : : // Private methods.
337 : 0 : inline void FuzzedDataProvider::CopyAndAdvance(void *destination,
338 : : size_t num_bytes) {
339 : 0 : std::memcpy(destination, data_ptr_, num_bytes);
340 : 0 : Advance(num_bytes);
341 : 0 : }
342 : :
343 : 2497335 : inline void FuzzedDataProvider::Advance(size_t num_bytes) {
344 [ - + ]: 2497335 : if (num_bytes > remaining_bytes_)
345 : 0 : abort();
346 : :
347 : 2497335 : data_ptr_ += num_bytes;
348 : 2497335 : remaining_bytes_ -= num_bytes;
349 : 2497335 : }
350 : :
351 : : template <typename T>
352 : 0 : 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 [ # # ][ # # ]: 0 : std::vector<T> result(size);
362 [ # # ][ # # ]: 0 : if (size == 0) {
363 [ # # ][ # # ]: 0 : if (num_bytes != 0)
364 : 0 : abort();
365 : 0 : return result;
366 : : }
367 : :
368 [ # # ][ # # ]: 0 : 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 [ # # ][ # # ]: 0 : result.shrink_to_fit();
374 : 0 : return result;
375 [ # # ][ # # ]: 0 : }
376 : :
377 : : template <typename TS, typename TU>
378 : 2497191 : 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 : : // 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 [ + + ]: 2497191 : if (value <= std::numeric_limits<TS>::max()) {
390 : 1975153 : return static_cast<TS>(value);
391 : : } else {
392 : 522038 : constexpr auto TS_min = std::numeric_limits<TS>::min();
393 : 522038 : return TS_min + static_cast<TS>(value - TS_min);
394 : : }
395 : 2497191 : }
396 : :
397 : : #endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
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