11d3098f40
Previously, we have not been validating the values for CSS declarations
inside the Parser. This causes issues, since we should be discarding
invalid style declarations, so that previous ones are used instead. For
example, in this code:
```css
.foo {
width: 2em;
width: orange;
}
```
... the `width: orange` declaration overwrites the `width: 2em` one,
even though it is invalid. According to the spec, `width: orange` should
be rejected at parse time, and discarded, leaving `width: 2em` as the
resulting value.
Many properties (mostly shorthands) are parsed specially, and so they
are already rejected if they are invalid. But for simple properties, we
currently accept any value. With `property_accepts_value()`, we can
check if the value is valid in `parse_css_value()`, and reject it if it
is not.
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|---|---|---|
| .. | ||
| Fuzzers | ||
| Tools | ||
| .gitignore | ||
| CMakeLists.txt | ||
| ReadMe.md | ||
| TestApp.cpp | ||
| TestJson.cpp | ||
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:
cmake -GNinja -S Meta/Lagom -B Build/lagom-fuzzers \
-DBUILD_LAGOM=ON \
-DENABLE_FUZZER_SANITIZER=ON \
-DENABLE_ADDRESS_SANITIZER=ON \
-DENABLE_UNDEFINED_SANITIZER=ON \
-DCMAKE_CXX_COMPILER=clang++ \
-DCMAKE_C_COMPILER=clang
cd Build/lagom-fuzzers
ninja
# Or as a handy rebuild-rerun line:
ninja FuzzJs && ./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. ./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.
Keeping track of interesting testcases
There are many quirky files that exercise a lot of interesting edge cases. We should probably keep track of them, somewhere.
We have a bmp suite and a jpg suite and several others. They are GPL'ed, and therefore not quite as compatible with the rest of Serenity. That's probably not a problem, but keeping "our" testcases separate from those GPL'ed suits sounds like a good idea.
We could keep those testcases somewhere else in the repository, like a fuzz directory.
But fuzzing tends to generate more and more and more files, and they will blow up in size.
Especially if we keep all interesting testcases, which is exactly what I intend to do.
So we should keep the actual testcases out of the main serenity repo, that's why we created https://github.com/SerenityOS/serenity-fuzz-corpora
Feel free to upload lots and lots files there, or use them for great good!
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:
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
To build the fuzzers using the oss-fuzz build process, but against a local serenity checkout:
python3 infra/helper.py build_fuzzers serenity $HOME/src/serenity/
To run a shell in oss-fuzz's serenity docker image:
docker run -it gcr.io/oss-fuzz/serenity bash
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 ./Fuzzers/FuzzBMP
<... SNIP some output ...>
(gdb) run -handle_abrt=0 -handle_segv=0 crash-27480a219572aa5a11b285968a3632a4cf25388e
<... SNIP some output ...>
FuzzBMP: ../../Userland/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)
UBSan doesn't always give useful information. use something like export UBSAN_OPTIONS=print_stacktrace=1 to always print stacktraces.
You may run into annoying issues with the stacktrace:
==123456==WARNING: invalid path to external symbolizer!
==123456==WARNING: Failed to use and restart external symbolizer!
That means it couldn't find the executable llvm-symbolizer, which could be in your OS's package llvm.
llvm-symbolizer-11 will not be recognized.