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