94 lines
2.8 KiB
Markdown
94 lines
2.8 KiB
Markdown
# Fuzzing
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`bitcoin` and `bitcoin_hashes` have fuzzing harnesses setup for use with
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honggfuzz.
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To run the fuzz-tests as in CI -- briefly fuzzing every target -- simply
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run
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./fuzz.sh
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in this directory.
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To build honggfuzz, you must have libunwind on your system, as well as
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libopcodes and libbfd from binutils **2.38** on your system. The most
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recently-released binutils 2.39 has changed their API in a breaking way.
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On Nix, you can obtain these libraries by running
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nix-shell -p libopcodes_2_38 -p libunwind
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and then run fuzz.sh as above.
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# Long-term fuzzing
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To see the full list of targets, the most straightforward way is to run
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source ./fuzz-util.sh
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listTargetNames
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To run each of them for an hour, run
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./cycle.sh
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To run a single fuzztest indefinitely, run
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HFUZZ_BUILD_ARGS='--features honggfuzz_fuzz' cargo hfuzz run <target>
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This script uses the `chrt` utility to try to reduce the priority of the
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jobs. If you would like to run for longer, the most straightforward way
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is to edit `cycle.sh` before starting. To run the fuzz-tests in parallel,
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you will need to implement a custom harness.
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# Adding fuzz tests
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All fuzz tests can be found in the `fuzz_target/` directory. Adding a new
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one is as simple as copying an existing one and editing the `do_test`
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function to do what you want.
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If your test clearly belongs to a specific crate, please put it in that
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crate's directory. Otherwise you can put it directly in `fuzz_target/`.
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If you need to add dependencies, edit the file `generate-files.sh` to add
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it to the generated `Cargo.toml`.
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Once you've added a fuzztest, regenerate the `Cargo.toml` and CI job by
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running
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./generate-files.sh
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Then to test your fuzztest, run
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./fuzz.sh <target>
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If it is working, you will see a rapid stream of data for many seconds
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(you can hit Ctrl+C to stop it early). If not, you should quickly see
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an error.
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# Reproducing Failures
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If a fuzztest fails, it will exit with a summary which looks something like
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```
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...
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fuzzTarget : hfuzz_target/x86_64-unknown-linux-gnu/release/hashes_sha256
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CRASH:
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DESCRIPTION:
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ORIG_FNAME: 00000000000000000000000000000000.00000000.honggfuzz.cov
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FUZZ_FNAME: hfuzz_workspace/hashes_sha256/SIGABRT.PC.7ffff7c8abc7.STACK.18826d9b64.CODE.-6.ADDR.0.INSTR.mov____%eax,%ebp.fuzz
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...
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=====================================================================
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fff400610004
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```
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The final line is a hex-encoded version of the input that caused the crash. You
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can test this directly by editing the `duplicate_crash` test to copy/paste the
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hex output into the call to `extend_vec_from_hex`. Then run the test with
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RUSTFLAGS=--cfg=fuzzing cargo test
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It is important to add the `cfg=fuzzing` flag, which tells rustc to compile the
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library as though it were running a fuzztest. In particular, this will disable
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or weaken all the cryptography.
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