//===- FuzzedDataProvider.h - Utility header for fuzz targets ---*- C++ -* ===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// A single header library providing an utility class to break up an array of
// bytes. Whenever run on the same input, provides the same output, as long as
// its methods are called in the same order, with the same arguments.
//===----------------------------------------------------------------------===//
#ifndef LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
#define LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
#include <algorithm>
#include <climits>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <initializer_list>
#include <string>
#include <type_traits>
#include <utility>
#include <vector>
// In addition to the comments below, the API is also briefly documented at
// https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
class FuzzedDataProvider
{
public:
// |data| is an array of length |size| that the FuzzedDataProvider wraps
// to provide more granular access. |data| must outlive the
// FuzzedDataProvider.
FuzzedDataProvider(const uint8_t *data, size_t size)
: data_ptr_(data), remaining_bytes_(size)
{
}
~FuzzedDataProvider() = default;
// Returns a std::vector containing |num_bytes| of input data. If fewer
// than |num_bytes| of data remain, returns a shorter std::vector
// containing all of the data that's left. Can be used with any byte
// sized type, such as char, unsigned char, uint8_t, etc.
template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes)
{
num_bytes = std::min(num_bytes, remaining_bytes_);
return ConsumeBytes<T>(num_bytes, num_bytes);
}
// Similar to |ConsumeBytes|, but also appends the terminator value at
// the end of the resulting vector. Useful, when a mutable
// null-terminated C-string is needed, for example. But that is a rare
// case. Better avoid it, if possible, and prefer using |ConsumeBytes|
// or |ConsumeBytesAsString| methods.
template <typename T>
std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes,
T terminator = 0)
{
num_bytes = std::min(num_bytes, remaining_bytes_);
std::vector<T> result =
ConsumeBytes<T>(num_bytes + 1, num_bytes);
result.back() = terminator;
return result;
}
// Returns a std::string containing |num_bytes| of input data. Using
// this and
// |.c_str()| on the resulting string is the best way to get an
// immutable null-terminated C string. If fewer than |num_bytes| of data
// remain, returns a shorter std::string containing all of the data
// that's left.
std::string ConsumeBytesAsString(size_t num_bytes)
{
static_assert(sizeof(std::string::value_type) ==
sizeof(uint8_t),
"ConsumeBytesAsString cannot convert the data to "
"a string.");
num_bytes = std::min(num_bytes, remaining_bytes_);
std::string result(
reinterpret_cast<const std::string::value_type *>(
data_ptr_),
num_bytes);
Advance(num_bytes);
return result;
}
// Returns a number in the range [min, max] by consuming bytes from the
// input data. The value might not be uniformly distributed in the given
// range. If there's no input data left, always returns |min|. |min|
// must be less than or equal to |max|.
template <typename T> T ConsumeIntegralInRange(T min, T max)
{
static_assert(std::is_integral<T>::value,
"An integral type is required.");
static_assert(sizeof(T) <= sizeof(uint64_t),
"Unsupported integral type.");
if (min > max)
abort();
// Use the biggest type possible to hold the range and the
// result.
uint64_t range = static_cast<uint64_t>(max) - min;
uint64_t result = 0;
size_t offset = 0;
while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
remaining_bytes_ != 0) {
// Pull bytes off the end of the seed data.
// Experimentally, this seems to allow the fuzzer to
// more easily explore the input space. This makes
// sense, since it works by modifying inputs that caused
// new code to run, and this data is often used to
// encode length of data read by |ConsumeBytes|.
// Separating out read lengths makes it easier modify
// the contents of the data that is actually read.
--remaining_bytes_;
result =
(result << CHAR_BIT) | data_ptr_[remaining_bytes_];
offset += CHAR_BIT;
}
// Avoid division by 0, in case |range + 1| results in overflow.
if (range != std::numeric_limits<decltype(range)>::max())
result = result % (range + 1);
return static_cast<T>(min + result);
}
// Returns a std::string of length from 0 to |max_length|. When it runs
// out of input data, returns what remains of the input. Designed to be
// more stable with respect to a fuzzer inserting characters than just
// picking a random length and then consuming that many bytes with
// |ConsumeBytes|.
std::string ConsumeRandomLengthString(size_t max_length)
{
// Reads bytes from the start of |data_ptr_|. Maps "\\" to "\",
// and maps "\" followed by anything else to the end of the
// string. As a result of this logic, a fuzzer can insert
// characters into the string, and the string will be lengthened
// to include those new characters, resulting in a more stable
// fuzzer than picking the length of a string independently from
// picking its contents.
std::string result;
// Reserve the anticipated capaticity to prevent several
// reallocations.
result.reserve(std::min(max_length, remaining_bytes_));
for (size_t i = 0; i < max_length && remaining_bytes_ != 0;
++i) {
char next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
Advance(1);
if (next == '\\' && remaining_bytes_ != 0) {
next =
ConvertUnsignedToSigned<char>(data_ptr_[0]);
Advance(1);
if (next != '\\')
break;
}
result += next;
}
result.shrink_to_fit();
return result;
}
// Returns a std::vector containing all remaining bytes of the input
// data.
template <typename T> std::vector<T> ConsumeRemainingBytes()
{
return ConsumeBytes<T>(remaining_bytes_);
}
// Returns a std::string containing all remaining bytes of the input
// data. Prefer using |ConsumeRemainingBytes| unless you actually need a
// std::string object.
std::string ConsumeRemainingBytesAsString()
{
return ConsumeBytesAsString(remaining_bytes_);
}
// Returns a number in the range [Type's min, Type's max]. The value
// might not be uniformly distributed in the given range. If there's no
// input data left, always returns |min|.
template <typename T> T ConsumeIntegral()
{
return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
std::numeric_limits<T>::max());
}
// Reads one byte and returns a bool, or false when no data remains.
bool ConsumeBool()
{
return 1 & ConsumeIntegral<uint8_t>();
}
// Returns a copy of the value selected from the given fixed-size
// |array|.
template <typename T, size_t size>
T PickValueInArray(const T (&array)[size])
{
static_assert(size > 0, "The array must be non empty.");
return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
}
template <typename T>
T PickValueInArray(std::initializer_list<const T> list)
{
// TODO(Dor1s): switch to static_assert once C++14 is allowed.
if (!list.size())
abort();
return *(list.begin() +
ConsumeIntegralInRange<size_t>(0, list.size() - 1));
}
// Returns an enum value. The enum must start at 0 and be contiguous. It
// must also contain |kMaxValue| aliased to its largest (inclusive)
// value. Such as: enum class Foo { SomeValue, OtherValue, kMaxValue =
// OtherValue };
template <typename T> T ConsumeEnum()
{
static_assert(std::is_enum<T>::value,
"|T| must be an enum type.");
return static_cast<T>(ConsumeIntegralInRange<uint32_t>(
0, static_cast<uint32_t>(T::kMaxValue)));
}
// Returns a floating point number in the range [0.0, 1.0]. If there's
// no input data left, always returns 0.
template <typename T> T ConsumeProbability()
{
static_assert(std::is_floating_point<T>::value,
"A floating point type is required.");
// Use different integral types for different floating point
// types in order to provide better density of the resulting
// values.
using IntegralType =
typename std::conditional<(sizeof(T) <= sizeof(uint32_t)),
uint32_t, uint64_t>::type;
T result = static_cast<T>(ConsumeIntegral<IntegralType>());
result /=
static_cast<T>(std::numeric_limits<IntegralType>::max());
return result;
}
// Returns a floating point value in the range [Type's lowest, Type's
// max] by consuming bytes from the input data. If there's no input data
// left, always returns approximately 0.
template <typename T> T ConsumeFloatingPoint()
{
return ConsumeFloatingPointInRange<T>(
std::numeric_limits<T>::lowest(),
std::numeric_limits<T>::max());
}
// Returns a floating point value in the given range by consuming bytes
// from the input data. If there's no input data left, returns |min|.
// Note that |min| must be less than or equal to |max|.
template <typename T> T ConsumeFloatingPointInRange(T min, T max)
{
if (min > max)
abort();
T range = .0;
T result = min;
constexpr T zero(.0);
if (max > zero && min < zero &&
max > min + std::numeric_limits<T>::max()) {
// The diff |max - min| would overflow the given
// floating point type. Use the half of the diff as the
// range and consume a bool to decide whether the result
// is in the first of the second part of the diff.
range = (max / 2.0) - (min / 2.0);
if (ConsumeBool()) {
result += range;
}
} else {
range = max - min;
}
return result + range * ConsumeProbability<T>();
}
// Reports the remaining bytes available for fuzzed input.
size_t remaining_bytes()
{
return remaining_bytes_;
}
private:
FuzzedDataProvider(const FuzzedDataProvider &) = delete;
FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
void Advance(size_t num_bytes)
{
if (num_bytes > remaining_bytes_)
abort();
data_ptr_ += num_bytes;
remaining_bytes_ -= num_bytes;
}
template <typename T>
std::vector<T> ConsumeBytes(size_t size, size_t num_bytes_to_consume)
{
static_assert(sizeof(T) == sizeof(uint8_t),
"Incompatible data type.");
// The point of using the size-based constructor below is to
// increase the odds of having a vector object with capacity
// being equal to the length. That part is always implementation
// specific, but at least both libc++ and libstdc++ allocate the
// requested number of bytes in that constructor, which seems to
// be a natural choice for other implementations as well. To
// increase the odds even more, we also call |shrink_to_fit|
// below.
std::vector<T> result(size);
if (size == 0) {
if (num_bytes_to_consume != 0)
abort();
return result;
}
std::memcpy(result.data(), data_ptr_, num_bytes_to_consume);
Advance(num_bytes_to_consume);
// Even though |shrink_to_fit| is also implementation specific,
// we expect it to provide an additional assurance in case
// vector's constructor allocated a buffer which is larger than
// the actual amount of data we put inside it.
result.shrink_to_fit();
return result;
}
template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value)
{
static_assert(sizeof(TS) == sizeof(TU),
"Incompatible data types.");
static_assert(!std::numeric_limits<TU>::is_signed,
"Source type must be unsigned.");
// TODO(Dor1s): change to `if constexpr` once C++17 becomes
// mainstream.
if (std::numeric_limits<TS>::is_modulo)
return static_cast<TS>(value);
// Avoid using implementation-defined unsigned to signer
// conversions. To learn more, see
// https://stackoverflow.com/questions/13150449.
if (value <= std::numeric_limits<TS>::max()) {
return static_cast<TS>(value);
} else {
constexpr auto TS_min = std::numeric_limits<TS>::min();
return TS_min + static_cast<char>(value - TS_min);
}
}
const uint8_t *data_ptr_;
size_t remaining_bytes_;
};
#endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
// no-check-code since this is from a third party