mirror of https://github.com/google/oss-fuzz.git
51 lines
2.8 KiB
Markdown
51 lines
2.8 KiB
Markdown
# Reproducing OSS-Fuzz issues
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You've been CC'ed on an OSS-Fuzz issue
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([examples](https://bugs.chromium.org/p/oss-fuzz/issues/list?can=1&q=Type%3ABug%2CBug-Security)), now what?
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Before attempting to fix the bug, you should be able to reliably reproduce it.
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Every issue has a reproducer (aka "testcase") file attached.
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Download it. If the issue is not public, you will need to login using your
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[Google account](https://support.google.com/accounts/answer/176347?hl=en)
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that the bug report CCs.
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This file contains the bytes that were fed to the [Fuzz Target](http://libfuzzer.info/#fuzz-target).
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If you have already [integrated](ideal_integration.md) the fuzz target with your build and test system,
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all you do is run:
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<pre>
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./fuzz_target_binary <b><i>$testcase_file</i></b>
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</pre>
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Depending on the nature of the bug, the fuzz target binary needs to be built with the appropriate [sanitizer](https://github.com/google/sanitizers)
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(e.g. if this is a buffer overflow, with [AddressSanitizer](http://clang.llvm.org/docs/AddressSanitizer.html)).
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If you are not sure how to build the fuzzer using the project's build system,
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you may also use Docker ([how?](installing_docker.md), [why?](faq.md#why-do-you-use-docker)) commands
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to replicate the exact build steps used by OSS-Fuzz and then feed the reproducer input to the fuzz target.
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- *Reproduce using latest OSS-Fuzz build:*
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<pre>
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docker run --rm -ti -v <b><i>$testcase_file</i></b>:/testcase ossfuzz/<b><i>$project</i></b> reproduce <b><i>$fuzzer</i></b>
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</pre>
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It builds the fuzzer from the most recent successful OSS-Fuzz build (usually last night's sources)
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and feeds the testcase file to the target function.
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E.g. for [libxml2](../target/libxml2) project with fuzzer named `libxml2_xml_read_memory_fuzzer`, it will be:
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<pre>
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docker run --rm -ti -v <b><i>~/Downloads/testcase</i></b>:/testcase ossfuzz/<b><i>libxml2</i></b> reproduce <b><i>libxml2_xml_read_memory_fuzzer</i></b>
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</pre>
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- *Reproduce using local source checkout:*
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<pre>
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docker run --rm -ti -v <b><i>$local_source_checkout_dir</i></b>:/src/<b><i>$project</i></b> \
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-v <b><i>$testcase_file</i></b>:/testcase ossfuzz/<b><i>$project</i></b> reproduce <b><i>$fuzzer</i></b>
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</pre>
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This is essentially the previous command that additionally mounts local sources into the running container.
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- *Fix issue*. Write a patch to fix the issue in your local checkout and then use the previous command to verify the fix (i.e. no crash occurred).
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[Use gdb](debugging.md#debugging-fuzzers-with-gdb) if needed.
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- *Submit fix*. Submit the fix in the project's repository. ClusterFuzz will automatically pick up the changes, recheck the testcase and will close the issue (in < 1 day).
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- *Improve fuzzing support*. Consider [improving fuzzing support](ideal_integration.md) in your project's build and test system.
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