mirror of https://github.com/google/oss-fuzz.git
86 lines
4.1 KiB
Markdown
86 lines
4.1 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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## Fuzz target bugs
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Every issue has a [reproducer](glossary.md#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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([why?](faq.md#why-do-you-require-a-google-account-for-authentication))
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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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```bash
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$ ./fuzz_target_binary <testcase_path>
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```
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If this is a timeout bug, add the <b><i>-timeout=25</i></b> argument.<br />
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If this is an OOM bug, add the <b><i>-rss_limit_mb=2048</i></b> argument.<br />
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Read more on how timeouts and OOMs are handed [here](faq.md#how-do-you-handle-timeouts-and-ooms).
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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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## Building using Docker
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### Pull the latest Docker images
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```bash
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$ python infra/helper.py pull_images
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```
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Docker images get regularly updated with a newer version of build tools, build
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configurations, scripts, and other changes. In some cases, a particular issue
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can be reproduced only with a fresh image being used.
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### Build the image and the fuzzers
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```bash
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$ python infra/helper.py build_image $PROJECT_NAME
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$ python infra/helper.py build_fuzzers --sanitizer <address/memory/undefined> $PROJECT_NAME
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```
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## Reproducing bugs
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```bash
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$ python infra/helper.py reproduce $PROJECT_NAME <fuzz_target_name> <testcase_path>
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```
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E.g. for building [libxml2](../projects/libxml2) project with UndefinedBehaviorSanitizer instrumentation
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and reproduce a crash testcase for a fuzzer named `libxml2_xml_read_memory_fuzzer`, it will be:
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```bash
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$ python infra/helper.py build_image libxml2
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$ python infra/helper.py build_fuzzers --sanitizer undefined libxml2
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$ python infra/helper.py reproduce libxml2 libxml2_xml_read_memory_fuzzer ~/Downloads/testcase
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```
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## Reproduce using local source checkout
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```bash
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$ python infra/helper.py build_fuzzers --sanitizer <address/memory/undefined> $PROJECT_NAME <source_path>
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$ python infra/helper.py reproduce $PROJECT_NAME <fuzz_target_name> <testcase_path>
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```
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This is essentially the previous command that additionally mounts local sources into the running container.
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- *Fix issue*. Write a patch to fix the issue in your local checkout and then use the previous command to verify the fix (i.e. no crash occurred).
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[Use gdb](debugging.md#debugging-fuzzers-with-gdb) if needed.
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- *Submit fix*. Submit the fix in the project's repository. ClusterFuzz will automatically pick up the changes, recheck the testcase and will close the issue (in < 1 day).
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- *Improve fuzzing support*. Consider [improving fuzzing support](ideal_integration.md) in your project's build and test system.
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## Reproducing build failures
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Our infrastructure runs some sanity tests to make sure that your build was correctly configured, even if it succeeded. To reproduce these locally, run:
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```bash
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$ python infra/helper.py build_image $PROJECT_NAME
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$ python infra/helper.py build_fuzzers --sanitizer <address/memory/undefined> --engine <libfuzzer/afl/hongfuzz> $PROJECT_NAME
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$ python infra/helper.py check_build --sanitizer <address/memory/undefined> --engine <libfuzzer/afl/hongfuzz> $PROJECT_NAME <fuzz_target_name>```
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