Use binary write mode in WriteToFile function to avoid appended \r characters on Windows

Summary:
When using libfuzzer on Windows, in the contents of a crash sample, bytes that can be mistaken for a \n are replaced by a \r\n sequence. As a consequence, crashes are not reproducible. This patch will open files in binary mode to fix this issue. The patch does not affect POSIX systems.

Patch by tuktuk

Reviewers: kcc, vitalybuka

Reviewed By: vitalybuka

Subscribers: dexonsmith, jdoerfert, llvm-commits, #sanitizers

Tags: #llvm, #sanitizers

Differential Revision: https://reviews.llvm.org/D60008

llvm-svn: 357807

compiler-rt/lib/fuzzer/FuzzerIO.cpp

@@ -62,7 +62,7 @@ void CopyFileToErr(const std::string &Path) {
 
 void WriteToFile(const Unit &U, const std::string &Path) {
   // Use raw C interface because this function may be called from a sig handler.
-  FILE *Out = fopen(Path.c_str(), "w");
+  FILE *Out = fopen(Path.c_str(), "wb");
   if (!Out) return;
   fwrite(U.data(), sizeof(U[0]), U.size(), Out);
   fclose(Out);

compiler-rt/test/fuzzer/ReloadTest.cpp

@@ -0,0 +1,24 @@
+// 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
+
+// Test that fuzzer we can reload artifacts with any bytes inside.
+#include <algorithm>
+#include <cstdint>
+#include <numeric>
+#include <set>
+#include <stdio.h>
+
+extern "C" size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size,
+                                          size_t MaxSize, unsigned int Seed) {
+  std::srand(Seed);
+  std::generate(Data, Data + MaxSize, std::rand);
+  return MaxSize;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  if (Size > 5000 && std::set<uint8_t>(Data, Data + Size).size() > 255 &&
+      (uint8_t)std::accumulate(Data, Data + Size, uint8_t(Size)) == 0)
+    __builtin_trap();
+  return 0;
+}

compiler-rt/test/fuzzer/reload.test

@@ -0,0 +1,13 @@
+RUN: %cpp_compiler %S/ReloadTest.cpp -o %t-ReloadTest
+RUN: not %run %t-ReloadTest -max_len=10000 -seed=1 -timeout=15 -len_control=0 -exact_artifact_path=%t.crash 2>&1 | FileCheck %s
+
+CHECK: Test unit written to {{.*}}reload.test.tmp.crash
+
+RUN: not %run %t-ReloadTest %t.crash 2>&1 | FileCheck %s --check-prefix=ARTIFACT
+
+ARTIFACT: Running: {{.*}}reload.test.tmp.crash
+ARTIFACT: ERROR: libFuzzer: deadly signal
+
+# Sanity check that altered artifact is not going to crash
+RUN: echo z >> %t.crash
+RUN: %run %t-ReloadTest %t.crash