mirror of https://github.com/c-ares/c-ares.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
91 lines
2.9 KiB
91 lines
2.9 KiB
# Fuzzing Hints |
|
|
|
## LibFuzzer |
|
|
|
1. Set compiler that supports fuzzing, this is an example on MacOS using |
|
a homebrew-installed clang/llvm: |
|
``` |
|
export CC="/opt/homebrew/Cellar/llvm/18.1.8/bin/clang" |
|
export CXX="/opt/homebrew/Cellar/llvm/18.1.8/bin/clang++" |
|
``` |
|
|
|
2. Compile c-ares with both ASAN and fuzzing support. We want an optimized |
|
debug build so we will use `RelWithDebInfo`: |
|
``` |
|
export CFLAGS="-fsanitize=address,fuzzer-no-link -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION" |
|
export CXXFLAGS="-fsanitize=address,fuzzer-no-link -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION" |
|
export LDFLAGS="-fsanitize=address,fuzzer-no-link" |
|
mkdir buildfuzz |
|
cd buildfuzz |
|
cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo -G Ninja .. |
|
ninja |
|
``` |
|
|
|
3. Build the fuzz test itself linked against our fuzzing-enabled build: |
|
``` |
|
${CC} -W -Wall -Og -fsanitize=address,fuzzer -I../include -I../src/lib -I. -o ares-test-fuzz ../test/ares-test-fuzz.c -L./lib -Wl,-rpath ./lib -lcares |
|
${CC} -W -Wall -Og -fsanitize=address,fuzzer -I../include -I../src/lib -I. -o ares-test-fuzz-name ../test/ares-test-fuzz-name.c -L./lib -Wl,-rpath ./lib -lcares |
|
``` |
|
|
|
4. Run the fuzzer, its better if you can provide seed input but it does pretty |
|
well on its own since it uses coverage data to determine how to proceed. |
|
You can play with other flags etc, like `-jobs=XX` for parallelism. See |
|
https://llvm.org/docs/LibFuzzer.html |
|
``` |
|
mkdir corpus |
|
cp ../test/fuzzinput/* corpus |
|
./ares-test-fuzz -max_len=65535 corpus |
|
``` |
|
or |
|
``` |
|
mkdir corpus |
|
cp ../test/fuzznames/* corpus |
|
./ares-test-fuzz-name -max_len=65535 corpus |
|
``` |
|
|
|
|
|
## AFL |
|
|
|
To fuzz using AFL, follow the |
|
[AFL quick start guide](http://lcamtuf.coredump.cx/afl/QuickStartGuide.txt): |
|
|
|
- Download and build AFL. |
|
- Configure the c-ares library and test tool to use AFL's compiler wrappers: |
|
|
|
```console |
|
% export CC=$AFLDIR/afl-gcc |
|
% ./configure --disable-shared && make |
|
% cd test && ./configure && make aresfuzz aresfuzzname |
|
``` |
|
|
|
- Run the AFL fuzzer against the starting corpus: |
|
|
|
```console |
|
% mkdir fuzzoutput |
|
% $AFLDIR/afl-fuzz -i fuzzinput -o fuzzoutput -- ./aresfuzz # OR |
|
% $AFLDIR/afl-fuzz -i fuzznames -o fuzzoutput -- ./aresfuzzname |
|
``` |
|
|
|
## AFL Persistent Mode |
|
|
|
If a recent version of Clang is available, AFL can use its built-in compiler |
|
instrumentation; this configuration also allows the use of a (much) faster |
|
persistent mode, where multiple fuzz inputs are run for each process invocation. |
|
|
|
- Download and build a recent AFL, and run `make` in the `llvm_mode` |
|
subdirectory to ensure that `afl-clang-fast` gets built. |
|
- Configure the c-ares library and test tool to use AFL's clang wrappers that |
|
use compiler instrumentation: |
|
|
|
```console |
|
% export CC=$AFLDIR/afl-clang-fast |
|
% ./configure --disable-shared && make |
|
% cd test && ./configure && make aresfuzz |
|
``` |
|
|
|
- Run the AFL fuzzer (in persistent mode) against the starting corpus: |
|
|
|
```console |
|
% mkdir fuzzoutput |
|
% $AFLDIR/afl-fuzz -i fuzzinput -o fuzzoutput -- ./aresfuzz |
|
```
|
|
|