mirror of https://github.com/google/oss-fuzz.git
52 lines
2.6 KiB
Markdown
52 lines
2.6 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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```
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./fuzz_target_binary REPRODUCER_FILE
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```
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Depending on the nature of the bug, the fuzz target binary needs to be built with the appropriate sanitizer
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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 the 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 target.
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- *Reproduce using the latest OSS-Fuzz build:*
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<pre>
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docker run --rm -v <b><i>$testcase_file</i></b>:/testcase -t ossfuzz/<b><i>$target</i></b> reproduce <b><i>$fuzzer</i></b>
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</pre>
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It builds the fuzzer from the most recent successfull OSS-Fuzz build (roughly, last night's sources)
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and feeds the testcase file to the target function.
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E.g. for the [libxml2](../target/libxml2) fuzzer named `libxml2_xml_read_memory_fuzzer` it will be:
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<pre>
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docker run --rm -ti -v <b><i>~/Downloads/testcase</i></b>:/testcase ossfuzz/<b><i>libxml2</i></b> reproduce <b><i>libxml2_xml_read_memory_fuzzer</i></b>
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</pre>
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- *Reproduce using the local source code:*
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<pre>
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docker run --rm -v <b><i>$target_checkout_dir</i></b>:/src/<b><i>$target</i></b> \
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-v <b><i>$reproducer_file</i></b>:/testcase -t ossfuzz/<b><i>$target</i></b> reproduce <b><i>$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 the issue.* Use the previous command to verify you fixed the issue locally.
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[Use gdb](debugging.md#debugging-fuzzers-with-gdb) if needed.
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- Consider [improving fuzzing support](ideal_integration.md) in your project's build and test system.
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- *Submit the fix.* ClusterFuzz will automatically pick up the changes, recheck the testcase
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and will close the issue.
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