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59 lines
2.1 KiB
Markdown
59 lines
2.1 KiB
Markdown
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# About fuzzing
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Fuzzing is done by [OSS-Fuzz](https://google.github.io/oss-fuzz/).
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It works by creating a project-specific binary that combines fuzzer
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itself and a project provided entry point named
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`LLVMFuzzerTestOneInput()`. When invoked, this executable either
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searches for new test cases or runs an existing test case.
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File `fuzz/bpf-object-fuzzer.c` defines an entry point for the robot:
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- robot supplies bytes supposed to be an ELF file;
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- wrapper invokes `bpf_object__open_mem()` to process these bytes.
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File `scripts/build-fuzzers.sh` provides a recipe for fuzzer
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infrastructure on how to build the executable described above (see
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[here](https://github.com/google/oss-fuzz/tree/master/projects/libbpf)).
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# Reproducing fuzzing errors
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## Official way
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OSS-Fuzz project describes error reproduction steps in the official
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[documentation](https://google.github.io/oss-fuzz/advanced-topics/reproducing/).
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Suppose you received an email linking to the fuzzer generated test
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case, or got one as an artifact of the `CIFuzz` job (e.g. like
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[here](https://github.com/libbpf/libbpf/actions/runs/16375110681)).
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Actions to reproduce the error locally are:
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```sh
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git clone --depth=1 https://github.com/google/oss-fuzz.git
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cd oss-fuzz
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python infra/helper.py pull_images
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python infra/helper.py build_image libbpf
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python infra/helper.py build_fuzzers --sanitizer address libbpf <path-to-libbpf-checkout>
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python infra/helper.py reproduce libbpf bpf-object-fuzzer <path-to-test-case>
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```
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`<path-to-test-case>` is usually a `crash-<many-hex-digits>` file w/o
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extension, CI job wraps it into zip archive and attaches as an artifact.
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To recompile after some fixes, repeat the `build_fuzzers` and
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`reproduce` steps after modifying source code in
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`<path-to-libbpf-checkout>`.
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Note: the `build_fuzzers` step creates a binary
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`build/out/libbpf/bpf-object-fuzzer`, it can be executed directly if
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your environment is compatible.
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## Simple way
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From the project root:
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```sh
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SKIP_LIBELF_REBUILD=1 scripts/build-fuzzers.sh
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out/bpf-object-fuzzer <path-to-test-case>
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```
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`out/bpf-object-fuzzer` is the fuzzer executable described earlier,
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can be run with gdb etc.
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