[libFuzzer] add CompressedTest.cpp, a real-life-ish test for a custom mutator

llvm-svn: 352265

compiler-rt/test/fuzzer/CompressedTest.cpp

@@ -0,0 +1,61 @@
+// 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 fuzz target that consumes a Zlib-compressed input.
+// This test verifies that we can find this bug with a custom mutator.
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <zlib.h>
+
+// The fuzz target.
+// Uncompress the data, crash on input starting with "FU".
+// Good luck finding this w/o a custom mutator. :)
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  uint8_t Uncompressed[100];
+  size_t UncompressedLen = sizeof(Uncompressed);
+  if (Z_OK != uncompress(Uncompressed, &UncompressedLen, Data, Size))
+    return 0;
+  if (UncompressedLen < 2) return 0;
+  if (Uncompressed[0] == 'F' && Uncompressed[1] == 'U')
+    abort();  // Boom
+  return 0;
+}
+
+#ifdef CUSTOM_MUTATOR
+
+// Forward-declare the libFuzzer's mutator callback.
+extern "C" size_t
+LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize);
+
+// The custom mutator:
+//   * deserialize the data (in this case, uncompress).
+//     * If the data doesn't deserialize, create a properly serialized dummy.
+//   * Mutate the deserialized data (in this case, just call LLVMFuzzerMutate).
+//   * Serialize the mutated data (in this case, compress).
+extern "C" size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size,
+                                          size_t MaxSize, unsigned int Seed) {
+  uint8_t Uncompressed[100];
+  size_t UncompressedLen = sizeof(Uncompressed);
+  size_t CompressedLen = MaxSize;
+  if (Z_OK != uncompress(Uncompressed, &UncompressedLen, Data, Size)) {
+    // The data didn't uncompress.
+    // So, it's either a broken input and we want to ignore it,
+    // or we've started fuzzing from an empty corpus and we need to supply
+    // out first properly compressed input.
+    uint8_t Dummy[] = {'H', 'i'};
+    if (Z_OK != compress(Data, &CompressedLen, Dummy, sizeof(Dummy)))
+      return 0;
+    // fprintf(stderr, "Dummy: max %zd res %zd\n", MaxSize, CompressedLen);
+    return CompressedLen;
+  }
+  UncompressedLen =
+      LLVMFuzzerMutate(Uncompressed, UncompressedLen, sizeof(Uncompressed));
+  if (Z_OK != compress(Data, &CompressedLen, Uncompressed, UncompressedLen))
+    return 0;
+  return CompressedLen;
+}
+
+#endif  // CUSTOM_MUTATOR

compiler-rt/test/fuzzer/compressed.test

@@ -0,0 +1,6 @@
+REQUIRES: linux
+# Custom mutator should find this bug, w/o custom -- no chance.
+RUN: %cpp_compiler %S/CompressedTest.cpp -o %t-CompressedTestCustom -DCUSTOM_MUTATOR -lz
+RUN: %cpp_compiler %S/CompressedTest.cpp -o %t-CompressedTestPlain -lz
+RUN: not %run %t-CompressedTestCustom -seed=1 -runs=1000000
+RUN:     %run %t-CompressedTestPlain  -seed=1 -runs=1000000