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Continuous Rust Fuzzing Example

This is an example of how to integrate your cargo-fuzz targets with Fuzzit Continuous Fuzzing Platform (Rust support is currently in Alpha).

This example will show the following steps:

Result:

Fuzzing for Rust can both help find complex bugs as well as correctness bugs. Rust is a safe language so memory corruption bugs are very unlikely to happen but some bugs can still have security implications.

This tutorial is less about how to build cargo-fuzz targets but more about how to integrate the targets with Fuzzit. A lot of great information is available at the cargo-fuzz repository.

Understanding the bug

The bug is located at src/lib.rs with the following code


pub fn parse_complex(data: &[u8]) -> bool{
	if data.len() == 5 {
		if data[0] == b'F' && data[1] == b'U' && data[2] == b'Z' && data[3] == b'Z' && data[4] == b'I' && data[5] == b'T' {
			return true
		}
	}
    return true;
}

This is the simplest example to demonstrate a classic off-by-one/out-of-bound error which causes the program to crash. Instead of len(data) == 5 the correct code will be len(data) == 6.

Understanding the fuzzer

the fuzzer is located at fuzz/fuzz_targets/fuzz_target_1.rs with the following code:


fuzz_target!(|data: &[u8]| {
    let _ = example_rust::parse_complex(&data);
});

Building & Running the fuzzer

Cargo fuzz required the nightly compiled ar describe in the cargo fuzz book

cargo fuzz run fuzz_target_1

Will print the following output and stacktrace:

INFO: Seed: 3265732669
INFO: Loaded 1 modules   (480 guards): 480 [0x100da12d8, 0x100da1a58), 
INFO:        6 files found in /Users/yevgenyp/PycharmProjects/example-rust/fuzz/corpus/fuzz_target_1
INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes
INFO: seed corpus: files: 6 min: 1b max: 5b total: 26b rss: 27Mb
#7      INITED cov: 87 ft: 87 corp: 5/21b lim: 4 exec/s: 0 rss: 27Mb
#262144 pulse  cov: 87 ft: 87 corp: 5/21b lim: 261 exec/s: 131072 rss: 51Mb
thread '<unnamed>' panicked at 'index out of bounds: the len is 5 but the index is 5', /Users/yevgenyp/PycharmProjects/example-rust/src/lib.rs:17:101
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
==84593== ERROR: libFuzzer: deadly signal
    #0 0x1025ae445 in __sanitizer_print_stack_trace (lib__rustc__clang_rt.asan_osx_dynamic.dylib:x86_64+0x4c445)
    #1 0x100d23b12 in fuzzer::PrintStackTrace() FuzzerUtil.cpp:206
    #2 0x100d0756a in fuzzer::Fuzzer::CrashCallback() FuzzerLoop.cpp:237
    #3 0x100d0750d in fuzzer::Fuzzer::StaticCrashSignalCallback() FuzzerLoop.cpp:209
    #4 0x100d50a07 in fuzzer::CrashHandler(int, __siginfo*, void*) FuzzerUtilPosix.cpp:36
    #5 0x7fff69804b5c in _sigtramp (libsystem_platform.dylib:x86_64+0x4b5c)
    #6 0x106db5b75 in dyld::fastBindLazySymbol(ImageLoader**, unsigned long) (dyld:x86_64+0x4b75)
    #7 0x7fff696be6a5 in abort (libsystem_c.dylib:x86_64+0x5b6a5)
    #8 0x100d79288 in panic_abort::__rust_start_panic::abort::h15c0489ebcc623d0 lib.rs:48
    #9 0x100d79278 in __rust_start_panic lib.rs:44
    #10 0x100d78b98 in rust_panic panicking.rs:526
    #11 0x100d78b79 in std::panicking::rust_panic_with_hook::h111bdf4b9efb2f62 panicking.rs:497
    #12 0x100d7858c in std::panicking::continue_panic_fmt::ha408c1f6b7a89584 panicking.rs:384
    #13 0x100d78478 in rust_begin_unwind panicking.rs:311
    #14 0x100d8b3d1 in core::panicking::panic_fmt::h22e65e952cbe8c74 panicking.rs:85
    #15 0x100d8b388 in core::panicking::panic_bounds_check::h3ed7e9d8bf4f5005 panicking.rs:61
    #16 0x100cf963e in example_rust::parse_complex::h2ee809da6efcf96d lib.rs:17
    #17 0x100cf82aa in rust_fuzzer_test_input fuzz_target_1.rs:6
    #18 0x100d048c5 in libfuzzer_sys::test_input_wrap::_$u7b$$u7b$closure$u7d$$u7d$::h39216f33af358cfa lib.rs:11
    #19 0x100d0022c in std::panicking::try::do_call::h99bafe87b57c13d6 panicking.rs:296
    #20 0x100d7926b in __rust_maybe_catch_panic lib.rs:28
    #21 0x100cff9fc in std::panicking::try::he224cd8d43f275c5 panicking.rs:275
    #22 0x100cfe3a5 in std::panic::catch_unwind::hdccdbf00115971fe panic.rs:394
    #23 0x100d04419 in LLVMFuzzerTestOneInput lib.rs:9
    #24 0x100d09111 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) FuzzerLoop.cpp:576
    #25 0x100d087b9 in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned long, bool, fuzzer::InputInfo*, bool*) FuzzerLoop.cpp:485
    #26 0x100d0ac78 in fuzzer::Fuzzer::MutateAndTestOne() FuzzerLoop.cpp:713
    #27 0x100d0bfb1 in fuzzer::Fuzzer::Loop(std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, fuzzer::fuzzer_allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > > > const&) FuzzerLoop.cpp:844
    #28 0x100d3f4bb in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) FuzzerDriver.cpp:765
    #29 0x100d61629 in main FuzzerMain.cpp:20
    #30 0x7fff696193d4 in start (libdyld.dylib:x86_64+0x163d4)

NOTE: libFuzzer has rudimentary signal handlers.
      Combine libFuzzer with AddressSanitizer or similar for better crash reports.
SUMMARY: libFuzzer: deadly signal
MS: 1 ChangeByte-; base unit: e4fd1292391a997176aa1c86db666f2d5d48fb90
0x46,0x55,0x5a,0x5a,0x49,
FUZZI
artifact_prefix='/Users/yevgenyp/PycharmProjects/example-rust/fuzz/artifacts/fuzz_target_1/'; Test unit written to /Users/yevgenyp/PycharmProjects/example-rust/fuzz/artifacts/fuzz_target_1/crash-df779ced6b712c5fca247e465de2de474d1d23b9
Base64: RlVaWkk=

Integrating with Fuzzit from CI

The best way to integrate with Fuzzit is by adding a two stages in your Contintous Build system (like Travis CI or Circle CI).

Fuzzing stage:

Regression stage

here is the relevant snippet from the ./ci/fuzzit.sh which is being run by .travis.yml

wget -q -O https://github.com/fuzzitdev/fuzzit/releases/latest/download/fuzzit_Linux_x86_64
chmod a+x fuzzit
if [ $1 == "fuzzing" ]; then
    ./fuzzit create job fuzzitdev/rust-parse-complex ./fuzz/target/x86_64-unknown-linux-gnu/debug/fuzz_parse_complex
else
    ./fuzzit create job --type local-regression fuzzitdev/rust-parse-complex ./fuzz/target/x86_64-unknown-linux-gnu/debug/fuzz_parse_complex
fi

NOTE: the url for Fuzzit works as follows (all the relase can be access through github releases) https://github.com/fuzzitdev/fuzzit/releases/latest/download/fuzzit_${OS}_${ARCH}. Valid values for ${OS} are: Linux, Darwin, Windows. Valid values for ${ARCH} are: x86_64 and i386.

The steps are: