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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-exception6//7//===----------------------------------------------------------------------===//8// A single header library providing an utility class to break up an array of9// bytes. Whenever run on the same input, provides the same output, as long as10// 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 at31// https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider32class FuzzedDataProvider {33 public:34 // |data| is an array of length |size| that the FuzzedDataProvider wraps to35 // 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 verbose41 // comments for each of the methods.42 43 // Methods returning std::vector of bytes. These are the most popular choice44 // when splitting fuzzing input into pieces, as every piece is put into a45 // separate buffer (i.e. ASan would catch any under-/overflow) and the memory46 // 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 null53 // 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 than105// |num_bytes| of data remain, returns a shorter std::vector containing all106// of the data that's left. Can be used with any byte sized type, such as107// char, unsigned char, uint8_t, etc.108template <typename T>109std::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 end115// of the resulting vector. Useful, when a mutable null-terminated C-string is116// needed, for example. But that is a rare case. Better avoid it, if possible,117// and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.118template <typename T>119std::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.128template <typename T>129std::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 and134// |.c_str()| on the resulting string is the best way to get an immutable135// null-terminated C string. If fewer than |num_bytes| of data remain, returns136// a shorter std::string containing all of the data that's left.137inline 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 of149// input data, returns what remains of the input. Designed to be more stable150// with respect to a fuzzer inserting characters than just picking a random151// length and then consuming that many bytes with |ConsumeBytes|.152inline std::string153FuzzedDataProvider::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 this156 // logic, a fuzzer can insert characters into the string, and the string157 // will be lengthened to include those new characters, resulting in a more158 // stable fuzzer than picking the length of a string independently from159 // 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_|.181inline 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::string187// object.188inline 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 might193// not be uniformly distributed in the given range. If there's no input data194// left, always returns |min|.195template <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 the201// input data. The value might not be uniformly distributed in the given202// range. If there's no input data left, always returns |min|. |min| must203// be less than or equal to |max|.204template <typename T>205T 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 to220 // allow the fuzzer to more easily explore the input space. This makes221 // 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 by223 // |ConsumeBytes|. Separating out read lengths makes it easier modify the224 // 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] by238// consuming bytes from the input data. If there's no input data left, always239// returns approximately 0.240template <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 from246// the input data. If there's no input data left, returns |min|. Note that247// |min| must be less than or equal to |max|.248template <typename T>249T 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. Use258 // the half of the diff as the range and consume a bool to decide whether259 // 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 no272// input data left, always returns 0.273template <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 order278 // 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.289inline 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 must294// also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:295// enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };296template <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|.303template <typename T, size_t size>304T 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 309template <typename T, size_t size>310T 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 315template <typename T>316T 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 there324// is not enough data left, writes all remaining bytes. Return value is the325// number of bytes written.326// In general, it's better to avoid using this function, but it may be useful327// in cases when it's necessary to fill a certain buffer or object with328// fuzzing data.329inline 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.337inline void FuzzedDataProvider::CopyAndAdvance(void *destination,338 size_t num_bytes) {339 std::memcpy(destination, data_ptr_, num_bytes);340 Advance(num_bytes);341}342 343inline 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 351template <typename T>352std::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 the356 // 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++ and358 // 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 it371 // to provide an additional assurance in case vector's constructor allocated372 // 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 377template <typename TS, typename TU>378TS 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 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<TS>(value - TS_min);394 }395}396 397#endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_398