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268 lines
8.7 KiB
268 lines
8.7 KiB
//===- afl_driver.cpp - a glue between AFL and libFuzzer --------*- 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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/* This file allows to fuzz libFuzzer-style target functions
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(LLVMFuzzerTestOneInput) with AFL using AFL's persistent (in-process) mode.
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Usage:
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################################################################################
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cat << EOF > test_fuzzer.cc
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#include <stddef.h>
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#include <stdint.h>
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extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
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if (size > 0 && data[0] == 'H')
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if (size > 1 && data[1] == 'I')
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if (size > 2 && data[2] == '!')
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__builtin_trap();
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return 0;
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}
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EOF
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# Build your target with -fsanitize-coverage=trace-pc-guard using fresh clang.
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clang -g -fsanitize-coverage=trace-pc-guard test_fuzzer.cc -c
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# Build afl-llvm-rt.o.c from the AFL distribution.
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clang -c -w $AFL_HOME/llvm_mode/afl-llvm-rt.o.c
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# Build this file, link it with afl-llvm-rt.o.o and the target code.
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clang++ afl_driver.cpp test_fuzzer.o afl-llvm-rt.o.o
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# Run AFL:
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rm -rf IN OUT; mkdir IN OUT; echo z > IN/z;
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$AFL_HOME/afl-fuzz -i IN -o OUT ./a.out
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################################################################################
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AFL_DRIVER_STDERR_DUPLICATE_FILENAME: Setting this *appends* stderr to the file
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specified. If the file does not exist, it is created. This is useful for getting
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stack traces (when using ASAN for example) or original error messages on hard
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to reproduce bugs. Note that any content written to stderr will be written to
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this file instead of stderr's usual location.
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AFL_DRIVER_CLOSE_FD_MASK: Similar to libFuzzer's -close_fd_mask behavior option.
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If 1, close stdout at startup. If 2 close stderr; if 3 close both.
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*/
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#include <assert.h>
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#include <errno.h>
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#include <stdarg.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <fstream>
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#include <iostream>
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#include <vector>
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// Platform detection. Copied from FuzzerInternal.h
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#ifdef __linux__
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#define LIBFUZZER_LINUX 1
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#define LIBFUZZER_APPLE 0
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#define LIBFUZZER_NETBSD 0
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#define LIBFUZZER_FREEBSD 0
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#elif __APPLE__
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#define LIBFUZZER_LINUX 0
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#define LIBFUZZER_APPLE 1
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#define LIBFUZZER_NETBSD 0
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#define LIBFUZZER_FREEBSD 0
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#elif __NetBSD__
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#define LIBFUZZER_LINUX 0
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#define LIBFUZZER_APPLE 0
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#define LIBFUZZER_NETBSD 1
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#define LIBFUZZER_FREEBSD 0
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#elif __FreeBSD__
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#define LIBFUZZER_LINUX 0
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#define LIBFUZZER_APPLE 0
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#define LIBFUZZER_NETBSD 0
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#define LIBFUZZER_FREEBSD 1
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#else
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#error "Support for your platform has not been implemented"
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#endif
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// libFuzzer interface is thin, so we don't include any libFuzzer headers.
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extern "C" {
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int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);
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__attribute__((weak)) int LLVMFuzzerInitialize(int *argc, char ***argv);
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}
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// Notify AFL about persistent mode.
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static volatile char AFL_PERSISTENT[] = "##SIG_AFL_PERSISTENT##";
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extern "C" int __afl_persistent_loop(unsigned int);
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static volatile char suppress_warning2 = AFL_PERSISTENT[0];
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// Notify AFL about deferred forkserver.
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static volatile char AFL_DEFER_FORKSVR[] = "##SIG_AFL_DEFER_FORKSRV##";
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extern "C" void __afl_manual_init();
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static volatile char suppress_warning1 = AFL_DEFER_FORKSVR[0];
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// Input buffer.
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static const size_t kMaxAflInputSize = 1 << 20;
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static uint8_t AflInputBuf[kMaxAflInputSize];
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// Use this optionally defined function to output sanitizer messages even if
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// user asks to close stderr.
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extern "C" __attribute__((weak)) void __sanitizer_set_report_fd(void *);
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// Keep track of where stderr content is being written to, so that
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// dup_and_close_stderr can use the correct one.
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static FILE *output_file = stderr;
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// Experimental feature to use afl_driver without AFL's deferred mode.
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// Needs to run before __afl_auto_init.
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__attribute__((constructor(0))) static void __decide_deferred_forkserver(void) {
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if (getenv("AFL_DRIVER_DONT_DEFER")) {
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if (unsetenv("__AFL_DEFER_FORKSRV")) {
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perror("Failed to unset __AFL_DEFER_FORKSRV");
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abort();
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}
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}
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}
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// If the user asks us to duplicate stderr, then do it.
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static void maybe_duplicate_stderr() {
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char *stderr_duplicate_filename =
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getenv("AFL_DRIVER_STDERR_DUPLICATE_FILENAME");
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if (!stderr_duplicate_filename)
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return;
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FILE *stderr_duplicate_stream =
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freopen(stderr_duplicate_filename, "a+", stderr);
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if (!stderr_duplicate_stream) {
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fprintf(
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stderr,
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"Failed to duplicate stderr to AFL_DRIVER_STDERR_DUPLICATE_FILENAME");
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abort();
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}
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output_file = stderr_duplicate_stream;
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}
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// Most of these I/O functions were inspired by/copied from libFuzzer's code.
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static void discard_output(int fd) {
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FILE *temp = fopen("/dev/null", "w");
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if (!temp)
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abort();
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dup2(fileno(temp), fd);
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fclose(temp);
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}
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static void close_stdout() { discard_output(STDOUT_FILENO); }
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// Prevent the targeted code from writing to "stderr" but allow sanitizers and
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// this driver to do so.
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static void dup_and_close_stderr() {
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int output_fileno = fileno(output_file);
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int output_fd = dup(output_fileno);
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if (output_fd <= 0)
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abort();
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FILE *new_output_file = fdopen(output_fd, "w");
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if (!new_output_file)
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abort();
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if (!__sanitizer_set_report_fd)
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return;
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__sanitizer_set_report_fd(reinterpret_cast<void *>(output_fd));
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discard_output(output_fileno);
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}
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static void Printf(const char *Fmt, ...) {
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va_list ap;
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va_start(ap, Fmt);
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vfprintf(output_file, Fmt, ap);
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va_end(ap);
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fflush(output_file);
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}
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// Close stdout and/or stderr if user asks for it.
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static void maybe_close_fd_mask() {
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char *fd_mask_str = getenv("AFL_DRIVER_CLOSE_FD_MASK");
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if (!fd_mask_str)
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return;
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int fd_mask = atoi(fd_mask_str);
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if (fd_mask & 2)
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dup_and_close_stderr();
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if (fd_mask & 1)
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close_stdout();
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}
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// Define LLVMFuzzerMutate to avoid link failures for targets that use it
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// with libFuzzer's LLVMFuzzerCustomMutator.
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extern "C" size_t LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize) {
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assert(false && "LLVMFuzzerMutate should not be called from afl_driver");
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return 0;
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}
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// Execute any files provided as parameters.
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static int ExecuteFilesOnyByOne(int argc, char **argv) {
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for (int i = 1; i < argc; i++) {
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std::ifstream in(argv[i], std::ios::binary);
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in.seekg(0, in.end);
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size_t length = in.tellg();
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in.seekg (0, in.beg);
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std::cout << "Reading " << length << " bytes from " << argv[i] << std::endl;
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// Allocate exactly length bytes so that we reliably catch buffer overflows.
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std::vector<char> bytes(length);
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in.read(bytes.data(), bytes.size());
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assert(in);
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LLVMFuzzerTestOneInput(reinterpret_cast<const uint8_t *>(bytes.data()),
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bytes.size());
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std::cout << "Execution successful" << std::endl;
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}
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return 0;
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}
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int main(int argc, char **argv) {
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Printf(
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"======================= INFO =========================\n"
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"This binary is built for AFL-fuzz.\n"
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"To run the target function on individual input(s) execute this:\n"
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" %s < INPUT_FILE\n"
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"or\n"
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" %s INPUT_FILE1 [INPUT_FILE2 ... ]\n"
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"To fuzz with afl-fuzz execute this:\n"
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" afl-fuzz [afl-flags] %s [-N]\n"
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"afl-fuzz will run N iterations before "
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"re-spawning the process (default: 1000)\n"
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"======================================================\n",
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argv[0], argv[0], argv[0]);
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maybe_duplicate_stderr();
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maybe_close_fd_mask();
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if (LLVMFuzzerInitialize)
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LLVMFuzzerInitialize(&argc, &argv);
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// Do any other expensive one-time initialization here.
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if (!getenv("AFL_DRIVER_DONT_DEFER"))
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__afl_manual_init();
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int N = 1000;
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if (argc == 2 && argv[1][0] == '-')
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N = atoi(argv[1] + 1);
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else if(argc == 2 && (N = atoi(argv[1])) > 0)
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Printf("WARNING: using the deprecated call style `%s %d`\n", argv[0], N);
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else if (argc > 1)
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return ExecuteFilesOnyByOne(argc, argv);
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assert(N > 0);
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// Call LLVMFuzzerTestOneInput here so that coverage caused by initialization
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// on the first execution of LLVMFuzzerTestOneInput is ignored.
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uint8_t dummy_input[1] = {0};
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LLVMFuzzerTestOneInput(dummy_input, 1);
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int num_runs = 0;
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while (__afl_persistent_loop(N)) {
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ssize_t n_read = read(0, AflInputBuf, kMaxAflInputSize);
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if (n_read > 0) {
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// Copy AflInputBuf into a separate buffer to let asan find buffer
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// overflows. Don't use unique_ptr/etc to avoid extra dependencies.
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uint8_t *copy = new uint8_t[n_read];
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memcpy(copy, AflInputBuf, n_read);
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num_runs++;
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LLVMFuzzerTestOneInput(copy, n_read);
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delete[] copy;
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}
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}
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Printf("%s: successfully executed %d input(s)\n", argv[0], num_runs);
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}
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