1// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
2// See https://llvm.org/LICENSE.txt for license information.
3// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
4
5// A fuzz target that consumes a Zlib-compressed input.
6// This test verifies that we can find this bug with a custom mutator.
7#include <cstddef>
8#include <cstdint>
9#include <cstdio>
10#include <cstdlib>
11#include <zlib.h>
12
13// The fuzz target.
14// Uncompress the data, crash on input starting with "FU".
15// Good luck finding this w/o a custom mutator. :)
16extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
17 uint8_t Uncompressed[100];
18 size_t UncompressedLen = sizeof(Uncompressed);
19 if (Z_OK != uncompress(Uncompressed, &UncompressedLen, Data, Size))
20 return 0;
21 if (UncompressedLen < 2) return 0;
22 if (Uncompressed[0] == 'F' && Uncompressed[1] == 'U')
23 abort(); // Boom
24 return 0;
25}
26
27#ifdef CUSTOM_MUTATOR
28
29// Forward-declare the libFuzzer's mutator callback.
30extern "C" size_t
31LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize);
32
33// The custom mutator:
34// * deserialize the data (in this case, uncompress).
35// * If the data doesn't deserialize, create a properly serialized dummy.
36// * Mutate the deserialized data (in this case, just call LLVMFuzzerMutate).
37// * Serialize the mutated data (in this case, compress).
38extern "C" size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size,
39 size_t MaxSize, unsigned int Seed) {
40 uint8_t Uncompressed[100];
41 size_t UncompressedLen = sizeof(Uncompressed);
42 size_t CompressedLen = MaxSize;
43 if (Z_OK != uncompress(Uncompressed, &UncompressedLen, Data, Size)) {
44 // The data didn't uncompress.
45 // So, it's either a broken input and we want to ignore it,
46 // or we've started fuzzing from an empty corpus and we need to supply
47 // out first properly compressed input.
48 uint8_t Dummy[] = {'H', 'i'};
49 if (Z_OK != compress(Data, &CompressedLen, Dummy, sizeof(Dummy)))
50 return 0;
51 // fprintf(stderr, "Dummy: max %zd res %zd\n", MaxSize, CompressedLen);
52 return CompressedLen;
53 }
54 UncompressedLen =
55 LLVMFuzzerMutate(Uncompressed, UncompressedLen, sizeof(Uncompressed));
56 if (Z_OK != compress(Data, &CompressedLen, Uncompressed, UncompressedLen))
57 return 0;
58 return CompressedLen;
59}
60
61#endif // CUSTOM_MUTATOR
62