ladybird/Meta/Lagom

Lagom

The Serenity C++ library, for other Operating Systems.

About

If you want to bring the comfortable Serenity classes with you to another system, look no further. This is basically a "port" of the AK and LibCore libraries to generic *nix systems.

Lagom is a Swedish word that means "just the right amount." (Wikipedia)

Fuzzing

Lagom can be used to fuzz parts of SerenityOS's code base. Fuzzers can be run locally, and they also run continuously on OSS-Fuzz.

Fuzzing locally

Lagom can be used to fuzz parts of SerenityOS's code base. This requires buildling with clang, so it's convenient to use a different build directory for that. Fuzzers work best with Address Sanitizer enabled. Run CMake like this:

# From the root of the SerenityOS checkout:
mkdir BuildLagom && cd BuildLagom
cmake -GNinja -DBUILD_LAGOM=ON -DENABLE_FUZZER_SANITIZER=ON -DENABLE_ADDRESS_SANITIZER=ON -DCMAKE_CXX_COMPILER=clang++ ..
ninja Meta/Lagom/all
# Or as a handy rebuild-rerun line:
ninja FuzzJs && Meta/Lagom/Fuzzers/FuzzJs

Any fuzzing results (particularly slow inputs, crashes, etc.) will be dropped in the current directory.

clang emits different warnings than gcc, so you may have to remove -Werror in CMakeLists.txt and Meta/Lagom/CMakeLists.txt.

Fuzzers work better if you give them a fuzz corpus, e.g. Meta/Lagom/Fuzzers/FuzzBMP ../Base/res/html/misc/bmpsuite_files/rgba32-61754.bmp Pay attention that LLVM also likes creating new files, don't blindly commit them (yet)!

To run several fuzz jobs in parallel, pass -jobs=24 -workers=24.

To get less log output, pass -close_fd_mask=3 -- but that but hides assertion messages. Just 1 only closes stdout. It's good to move overzealous log output behind FOO_DEBUG macros.

Fuzzing on OSS-Fuzz

https://oss-fuzz.com/ automatically runs all fuzzers in the Fuzzers/ subdirectory whose name starts with "Fuzz" and which are added to the build in Fuzzers/CMakeLists.txt if ENABLE_OSS_FUZZ is set. Looking for "serenity" on oss-fuzz.com finds interesting links, in particular:

• known open bugs found by fuzzers
  • oss-fuzz bug tracker for these
• coverage report
• build logs

Here's Serenity's OSS-Fuzz Config.

To run the oss-fuzz build locally:

git clone https://github.com/google/oss-fuzz/
cd oss-fuzz
python3 infra/helper.py build_image serenity
python3 infra/helper.py build_fuzzers serenity

These commands will put the fuzzers in build/out/serenity in the oss-fuzz repo. You can run the binaries in there individually, or simply type:

python3 infra/helper.py run_fuzzer serenity FUZZER_NAME

Analyzing a crash

LLVM fuzzers have a weird interface. In particular, to see the help, you need to call it with -help=1, and it will ignore --help and -help.

To reproduce a crash, run it like this: MyFuzzer crash-27480a219572aa5a11b285968a3632a4cf25388e

To reproduce a crash in gdb, you want to disable various signal handlers, so that gdb sees the actual location of the crash:

$ gdb ./Meta/Lagom/Fuzzers/FuzzBMP
<... SNIP some output ...>
(gdb) run -handle_abrt=0 -handle_segv=0 crash-27480a219572aa5a11b285968a3632a4cf25388e
<... SNIP some output ...>
FuzzBMP: ../../Libraries/LibGfx/Bitmap.cpp:84: Gfx::Bitmap::Bitmap(Gfx::BitmapFormat, const Gfx::IntSize &, Gfx::Bitmap::Purgeable): Assertion `m_data && m_data != (void*)-1' failed.

Thread 1 "FuzzBMP" received signal SIGABRT, Aborted.
__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
50	../sysdeps/unix/sysv/linux/raise.c: File or directory not found.
(gdb)