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merge bitcoin#18342: Add fuzzing quickstart guides for libFuzzer and afl-fuzz

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Fuzz-testing Dash Core
==========================
# Fuzzing Dash Core using libFuzzer
A special test harness in `src/test/fuzz/` is provided for each fuzz target to
provide an easy entry point for fuzzers and the like. In this document we'll
describe how to use it with AFL and libFuzzer.
## Quickstart guide
## Preparing fuzzing
To quickly get started fuzzing Dash Core using [libFuzzer](https://llvm.org/docs/LibFuzzer.html):
The fuzzer needs some inputs to work on, but the inputs or seeds can be used
interchangeably between libFuzzer and AFL.
Extract the example seeds (or other starting inputs) into the inputs
directory before starting fuzzing.
```
git clone https://github.com/bitcoin-core/qa-assets
export DIR_FUZZ_IN=$PWD/qa-assets/fuzz_seed_corpus
```sh
$ git clone https://github.com/dashpay/dash
$ cd dash/
$ ./autogen.sh
$ CC=clang CXX=clang++ ./configure --enable-fuzz --with-sanitizers=address,fuzzer,undefined
# macOS users: If you have problem with this step then make sure to read "macOS hints for
# libFuzzer" on https://github.com/dashpay/dash/blob/develop/doc/fuzzing.md#macos-hints-for-libfuzzer
$ make
$ src/test/fuzz/process_message
# abort fuzzing using ctrl-c
```
AFL needs an input directory with examples, and an output directory where it
will place examples that it found. These can be anywhere in the file system,
we'll define environment variables to make it easy to reference them.
## Fuzzing harnesses, fuzzing output and fuzzing corpora
So, only for AFL you need to configure the outputs path:
[`process_message`](https://github.com/dashpay/dash/blob/develop/src/test/fuzz/process_message.cpp) is a fuzzing harness for the [`ProcessMessage(...)` function (`net_processing`)](https://github.com/dashpay/dash/blob/develop/src/net_processing.cpp). The available fuzzing harnesses are found in [`src/test/fuzz/`](https://github.com/dashpay/dash/tree/develop/src/test/fuzz).
```
mkdir outputs
export AFLOUT=$PWD/outputs
The fuzzer will output `NEW` every time it has created a test input that covers new areas of the code under test. For more information on how to interpret the fuzzer output, see the [libFuzzer documentation](https://llvm.org/docs/LibFuzzer.html).
If you specify a corpus directory then any new coverage increasing inputs will be saved there:
```sh
$ mkdir -p process_message-seeded-from-thin-air/
$ src/test/fuzz/process_message process_message-seeded-from-thin-air/
INFO: Seed: 840522292
INFO: Loaded 1 modules (424174 inline 8-bit counters): 424174 [0x55e121ef9ab8, 0x55e121f613a6),
INFO: Loaded 1 PC tables (424174 PCs): 424174 [0x55e121f613a8,0x55e1225da288),
INFO: 0 files found in process_message-seeded-from-thin-air/
INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes
INFO: A corpus is not provided, starting from an empty corpus
#2 INITED cov: 94 ft: 95 corp: 1/1b exec/s: 0 rss: 150Mb
#3 NEW cov: 95 ft: 96 corp: 2/3b lim: 4 exec/s: 0 rss: 150Mb L: 2/2 MS: 1 InsertByte-
#4 NEW cov: 96 ft: 98 corp: 3/7b lim: 4 exec/s: 0 rss: 150Mb L: 4/4 MS: 1 CrossOver-
#21 NEW cov: 96 ft: 100 corp: 4/11b lim: 4 exec/s: 0 rss: 150Mb L: 4/4 MS: 2 ChangeBit-CrossOver-
#324 NEW cov: 101 ft: 105 corp: 5/12b lim: 6 exec/s: 0 rss: 150Mb L: 6/6 MS: 5 CrossOver-ChangeBit-CopyPart-ChangeBit-ChangeBinInt-
#1239 REDUCE cov: 102 ft: 106 corp: 6/24b lim: 14 exec/s: 0 rss: 150Mb L: 13/13 MS: 5 ChangeBit-CrossOver-EraseBytes-ChangeBit-InsertRepeatedBytes-
#1272 REDUCE cov: 102 ft: 106 corp: 6/23b lim: 14 exec/s: 0 rss: 150Mb L: 12/12 MS: 3 ChangeBinInt-ChangeBit-EraseBytes-
NEW_FUNC[1/677]: 0x55e11f456690 in std::_Function_base::~_Function_base() /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/std_function.h:255
NEW_FUNC[2/677]: 0x55e11f465800 in CDataStream::CDataStream(std::vector<unsigned char, std::allocator<unsigned char> > const&, int, int) src/./streams.h:248
#2125 REDUCE cov: 4820 ft: 4867 corp: 7/29b lim: 21 exec/s: 0 rss: 155Mb L: 6/12 MS: 2 CopyPart-CMP- DE: "block"-
NEW_FUNC[1/9]: 0x55e11f64d790 in std::_Rb_tree<uint256, std::pair<uint256 const, std::chrono::duration<long, std::ratio<1l, 1000000l> > >, std::_Select1st<std::pair<uint256 const, std::chrono::duration<long, std::ratio<1l, 1000000l> > > >, std::less<uint256>, std::allocator<std::pair<uint256 const, std::chrono::duration<long, std::ratio<1l, 1000000l> > > > >::~_Rb_tree() /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/stl_tree.h:972
NEW_FUNC[2/9]: 0x55e11f64d870 in std::_Rb_tree<uint256, std::pair<uint256 const, std::chrono::duration<long, std::ratio<1l, 1000000l> > >, std::_Select1st<std::pair<uint256 const, std::chrono::duration<long, std::ratio<1l, 1000000l> > > >, std::less<uint256>, std::allocator<std::pair<uint256 const, std::chrono::duration<long, std::ratio<1l, 1000000l> > > > >::_M_erase(std::_Rb_tree_node<std::pair<uint256 const, std::chrono::duration<long, std::ratio<1l, 1000000l> > > >*) /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/stl_tree.h:1875
#2228 NEW cov: 4898 ft: 4971 corp: 8/35b lim: 21 exec/s: 0 rss: 156Mb L: 6/12 MS: 3 EraseBytes-CopyPart-PersAutoDict- DE: "block"-
NEW_FUNC[1/5]: 0x55e11f46df70 in std::enable_if<__and_<std::allocator_traits<zero_after_free_allocator<char> >::__construct_helper<char, unsigned char const&>::type>::value, void>::type std::allocator_traits<zero_after_free_allocator<char> >::_S_construct<char, unsigned char const&>(zero_after_free_allocator<char>&, char*, unsigned char const&) /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/alloc_traits.h:243
NEW_FUNC[2/5]: 0x55e11f477390 in std::vector<unsigned char, std::allocator<unsigned char> >::data() /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/stl_vector.h:1056
#2456 NEW cov: 4933 ft: 5042 corp: 9/55b lim: 21 exec/s: 0 rss: 160Mb L: 20/20 MS: 3 ChangeByte-InsertRepeatedBytes-PersAutoDict- DE: "block"-
#2467 NEW cov: 4933 ft: 5043 corp: 10/76b lim: 21 exec/s: 0 rss: 161Mb L: 21/21 MS: 1 InsertByte-
#4215 NEW cov: 4941 ft: 5129 corp: 17/205b lim: 29 exec/s: 4215 rss: 350Mb L: 29/29 MS: 5 InsertByte-ChangeBit-CopyPart-InsertRepeatedBytes-CrossOver-
#4567 REDUCE cov: 4941 ft: 5129 corp: 17/204b lim: 29 exec/s: 4567 rss: 404Mb L: 24/29 MS: 2 ChangeByte-EraseBytes-
#6642 NEW cov: 4941 ft: 5138 corp: 18/244b lim: 43 exec/s: 2214 rss: 450Mb L: 43/43 MS: 3 CopyPart-CMP-CrossOver- DE: "verack"-
# abort fuzzing using ctrl-c
$ ls process_message-seeded-from-thin-air/
349ac589fc66a09abc0b72bb4ae445a7a19e2cd8 4df479f1f421f2ea64b383cd4919a272604087a7
a640312c98dcc55d6744730c33e41c5168c55f09 b135de16e4709558c0797c15f86046d31c5d86d7
c000f7b41b05139de8b63f4cbf7d1ad4c6e2aa7f fc52cc00ec1eb1c08470e69f809ae4993fa70082
$ cat --show-nonprinting process_message-seeded-from-thin-air/349ac589fc66a09abc0b72bb4ae445a7a19e2cd8
block^@M-^?M-^?M-^?M-^?M-^?nM-^?M-^?
```
libFuzzer will use the input directory as output directory.
In this case the fuzzer managed to create a `block` message which when passed to `ProcessMessage(...)` increased coverage.
## AFL
The project's collection of seed corpora is found in the [`bitcoin-core/qa-assets`](https://github.com/bitcoin-core/qa-assets) repo.
### Building AFL
To fuzz `process_message` using the [`bitcoin-core/qa-assets`](https://github.com/bitcoin-core/qa-assets) seed corpus:
It is recommended to always use the latest version of afl:
```
wget http://lcamtuf.coredump.cx/afl/releases/afl-latest.tgz
tar -zxvf afl-latest.tgz
cd afl-<version>
make
export AFLPATH=$PWD
```sh
$ git clone https://github.com/bitcoin-core/qa-assets
$ src/test/fuzz/process_message qa-assets/fuzz_seed_corpus/process_message/
INFO: Seed: 1346407872
INFO: Loaded 1 modules (424174 inline 8-bit counters): 424174 [0x55d8a9004ab8, 0x55d8a906c3a6),
INFO: Loaded 1 PC tables (424174 PCs): 424174 [0x55d8a906c3a8,0x55d8a96e5288),
INFO: 991 files found in qa-assets/fuzz_seed_corpus/process_message/
INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes
INFO: seed corpus: files: 991 min: 1b max: 1858b total: 288291b rss: 150Mb
#993 INITED cov: 7063 ft: 8236 corp: 25/3821b exec/s: 0 rss: 181Mb
…
```
For macOS you may need to ignore x86 compilation checks when running `make`:
`AFL_NO_X86=1 make`.
If you find coverage increasing inputs when fuzzing you are highly encouraged to submit them for inclusion in the [`bitcoin-core/qa-assets`](https://github.com/bitcoin-core/qa-assets) repo.
### Instrumentation
Every single pull request submitted against the Dash Core repo is automatically tested against all inputs in the [`bitcoin-core/qa-assets`](https://github.com/bitcoin-core/qa-assets) repo. Contributing new coverage increasing inputs is an easy way to help make Dash Core more robust.
To build Dash Core using AFL instrumentation (this assumes that the
`AFLPATH` was set as above):
```
./configure --disable-shared --enable-tests --enable-fuzz CC=${AFLPATH}/afl-gcc CXX=${AFLPATH}/afl-g++
export AFL_HARDEN=1
make
```
## macOS hints for libFuzzer
If you are using clang you will need to substitute `afl-gcc` with `afl-clang`
and `afl-g++` with `afl-clang++`, so the first line above becomes:
```
./configure --disable-shared --enable-tests --enable-fuzz CC=${AFLPATH}/afl-clang CXX=${AFLPATH}/afl-clang++
```
We disable ccache because we don't want to pollute the ccache with instrumented
objects, and similarly don't want to use non-instrumented cached objects linked
in.
The fuzzing can be sped up significantly (~200x) by using `afl-clang-fast` and
`afl-clang-fast++` in place of `afl-gcc` and `afl-g++` when compiling. When
compiling using `afl-clang-fast`/`afl-clang-fast++` the resulting
binary will be instrumented in such a way that the AFL
features "persistent mode" and "deferred forkserver" can be used. See
https://github.com/google/AFL/tree/master/llvm_mode for details.
### Fuzzing
To start the actual fuzzing use:
```
export FUZZ_TARGET=bech32 # Pick a fuzz_target
mkdir ${AFLOUT}/${FUZZ_TARGET}
$AFLPATH/afl-fuzz -i ${DIR_FUZZ_IN}/${FUZZ_TARGET} -o ${AFLOUT}/${FUZZ_TARGET} -m52 -- src/test/fuzz/${FUZZ_TARGET}
```
You may have to change a few kernel parameters to test optimally - `afl-fuzz`
will print an error and suggestion if so.
On macOS you may need to set `AFL_NO_FORKSRV=1` to get the target to run.
```
export FUZZ_TARGET=bech32 # Pick a fuzz_target
mkdir ${AFLOUT}/${FUZZ_TARGET}
AFL_NO_FORKSRV=1 $AFLPATH/afl-fuzz -i ${DIR_FUZZ_IN}/${FUZZ_TARGET} -o ${AFLOUT}/${FUZZ_TARGET} -m52 -- src/test/fuzz/${FUZZ_TARGET}
```
## libFuzzer
A recent version of `clang`, the address/undefined sanitizers (ASan/UBSan) and
libFuzzer is needed (all found in the `compiler-rt` runtime libraries package).
To build all fuzz targets with libFuzzer, run
```
./configure --enable-fuzz --with-sanitizers=fuzzer,address,undefined CC=clang CXX=clang++
make
```
See https://llvm.org/docs/LibFuzzer.html#running on how to run the libFuzzer
instrumented executable.
Alternatively, you can run the script through the fuzzing test harness (only
libFuzzer supported so far). You need to pass it the inputs directory and
the specific test target you want to run.
```
./test/fuzz/test_runner.py ${DIR_FUZZ_IN} bech32
```
### macOS hints for libFuzzer
The default clang/llvm version supplied by Apple on macOS does not include
The default Clang/LLVM version supplied by Apple on macOS does not include
fuzzing libraries, so macOS users will need to install a full version, for
example using `brew install llvm`.
Should you run into problems with the address sanitizer, it is possible you
may need to run `./configure` with `--disable-asm` to avoid errors
with certain assembly code from Bitcoin Core's code. See [developer notes on sanitizers](https://github.com/bitcoin/bitcoin/blob/master/doc/developer-notes.md#sanitizers)
with certain assembly code from Dash Core's code. See [developer notes on sanitizers](https://github.com/dashpay/dash/blob/develop/doc/developer-notes.md#sanitizers)
for more information.
You may also need to take care of giving the correct path for clang and
clang++, like `CC=/path/to/clang CXX=/path/to/clang++` if the non-systems
clang does not come first in your path.
You may also need to take care of giving the correct path for `clang` and
`clang++`, like `CC=/path/to/clang CXX=/path/to/clang++` if the non-systems
`clang` does not come first in your path.
Full configure that was tested on macOS Catalina with `brew` installed `llvm`:
```
```sh
./configure --enable-fuzz --with-sanitizers=fuzzer,address,undefined CC=/usr/local/opt/llvm/bin/clang CXX=/usr/local/opt/llvm/bin/clang++ --disable-asm
```
Read the [libFuzzer documentation](https://llvm.org/docs/LibFuzzer.html) for more information. This [libFuzzer tutorial](https://github.com/google/fuzzing/blob/master/tutorial/libFuzzerTutorial.md) might also be of interest.
# Fuzzing Dash Core using american fuzzy lop (`afl-fuzz`)
## Quickstart guide
To quickly get started fuzzing Dash Core using [`afl-fuzz`](https://github.com/google/afl):
```sh
$ git clone https://github.com/dashpay/dash
$ cd dash/
$ git clone https://github.com/google/afl
$ make -C afl/
$ make -C afl/llvm_mode/
$ ./autogen.sh
$ CC=$(pwd)/afl/afl-clang-fast CXX=$(pwd)/afl/afl-clang-fast++ ./configure --enable-fuzz
$ make
# For macOS you may need to ignore x86 compilation checks when running "make". If so,
# try compiling using: AFL_NO_X86=1 make
$ mkdir -p inputs/ outputs/
$ echo A > inputs/thin-air-input
$ afl/afl-fuzz -i inputs/ -o outputs/ -- src/test/fuzz/bech32
# You may have to change a few kernel parameters to test optimally - afl-fuzz
# will print an error and suggestion if so.
```
Read the [`afl-fuzz` documentation](https://github.com/google/afl) for more information.