109 lines
3.5 KiB
Markdown
109 lines
3.5 KiB
Markdown
# Fuzzers
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These are fuzzers designed for use with `libFuzzer` or `afl`. They can
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be used to run on Google's OSS-Fuzz (https://github.com/google/oss-fuzz/).
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The convention used here is that the initial values for each parser fuzzer
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are taken from the $NAME.in directory.
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Crash reproducers from OSS-Fuzz are put into $NAME.repro directory for
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regression testing with top dir 'make check' or 'make check-valgrind'.
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The ./configure runs below are for libidn2.
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To test libicu replace 'libidn2' with 'libicu', to test with
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libidn replace 'libidn2' by 'libidn'.
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To test without IDNA libraries replace `--enable-runtime=...` with `--disable-runtime`
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and replace `--enable-builtin=...` with `--disable-builtin`.
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# Running a fuzzer using clang
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Use the following commands on top dir:
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```
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export CC=clang
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export LIB_FUZZING_ENGINE="-lFuzzer -lstdc++"
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export UBSAN_OPTIONS=print_stacktrace=1
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export ASAN_SYMBOLIZER_PATH=/usr/bin/llvm-symbolizer
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# set flags for clang asan
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CFLAGS="-O1 -fno-omit-frame-pointer -gline-tables-only -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address,leak,nonnull-attribute -fsanitize-address-use-after-scope -fsanitize-coverage=trace-pc-guard,trace-cmp"
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# set flags for clang ubsan
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CFLAGS="$CFLAGS -fsanitize=bool,array-bounds,float-divide-by-zero,function,integer-divide-by-zero,return,shift,signed-integer-overflow,vla-bound,vptr,undefined,alignment,null,enum,integer,builtin,float-divide-by-zero,function,object-size,returns-nonnull-attribute,unsigned-integer-overflow,unreachable -fsanitize=fuzzer-no-link"
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# unsigned-integer-overflow is not UB, so recover when we see it.
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CFLAGS="$CFLAGS -fno-sanitize-recover=all -fsanitize-recover=unsigned-integer-overflow"
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export CFLAGS
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./configure --enable-static --disable-gtk-doc --enable-fuzzing --enable-runtime=libidn2 --enable-builtin=libidn2
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make -j$(nproc)
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cd fuzz
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# run libpsl_fuzzer
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./run-clang.sh libpsl_fuzzer
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```
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If you see a crash, then a crash corpora is written that can be used for further
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investigation. E.g.
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```
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==2410==ERROR: AddressSanitizer: heap-use-after-free on address 0x602000004e90 at pc 0x00000049cf9c bp 0x7fffb5543f70 sp 0x7ff
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fb5543720
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...
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Test unit written to ./crash-adc83b19e793491b1c6ea0fd8b46cd9f32e592fc
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```
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To reproduce the crash:
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```
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./libpsl_fuzzer < ./crash-adc83b19e793491b1c6ea0fd8b46cd9f32e592fc
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```
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You can also copy/move that file into libpsl_fuzzer.repro/
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and re-build the project without fuzzing for a valgrind run, if you like that better.
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Just a `./configure` and a `make check-valgrind` should reproduce it.
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# Running a fuzzer using AFL
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Use the following commands on top dir:
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```
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$ CC=afl-clang-fast ./configure --disable-gtk-doc --enable-runtime=libidn2 --enable-builtin=libidn2
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$ make -j$(nproc) clean all
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$ cd fuzz
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$ ./run-afl.sh libpsl_fuzzer
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```
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# Fuzz code coverage using the corpus directories *.in/
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Code coverage reports currently work best with gcc+lcov+genhtml.
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In the top directory:
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```
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CC=gcc CFLAGS="-O0 -g" ./configure --disable-gtk-doc --enable-runtime=libidn2 --enable-builtin=libidn2
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make fuzz-coverage
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xdg-open lcov/index.html
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```
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Each fuzzer target has it's own functions to cover, e.g.
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`libpsl_fuzzer` covers psl_is_public_suffix.
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To work on corpora for better coverage, `cd fuzz` and use e.g.
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`./view-coverage.sh libpsl_fuzzer`.
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# Enhancing the testsuite for issues found
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Each reproducer file should be dropped into the appropriate *.repro/
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directory.
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# Clang CFI instrumentation
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```
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CC=clang CFLAGS="-B/usr/bin/gold -O0 -fsanitize=cfi -flto -fvisibility=default -fno-sanitize-trap=all" ./configure
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make clean
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make
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make check
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```
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