luzer

a coverage-guided, native Lua fuzzer.

Overview

Fuzzing is a type of automated testing which continuously manipulates inputs to a program to find bugs. luzer uses coverage guidance to intelligently walk through the code being fuzzed to find and report failures to the user. Since it can reach edge cases which humans often miss, fuzz testing can be particularly valuable for finding security exploits and vulnerabilities.

luzer is a coverage-guided Lua fuzzing engine. It supports fuzzing of Lua code, but also C extensions written for Lua. Luzer is based off of libFuzzer. When fuzzing native code, luzer can be used in combination with Address Sanitizer or Undefined Behavior Sanitizer to catch extra bugs.

Quickstart

To use luzer in your own project follow these few simple steps:

1. Setup luzer module:

$ luarocks --local install luzer
$ eval $(luarocks path)

2. Create a fuzz target invoking your code:

local luzer = require("luzer")

local function TestOneInput(buf)
    local b = {}
    buf:gsub(".", function(c) table.insert(b, c) end)
    if b[1] == 'c' then
        if b[2] == 'r' then
            if b[3] == 'a' then
                if b[4] == 's' then
                    if b[5] == 'h' then
                        assert(nil)
                    end
                end
            end
        end
    end
end

luzer.Fuzz(TestOneInput)

3. Start the fuzzer using the fuzz target

$ luajit examples/example_basic.lua
INFO: Running with entropic power schedule (0xFF, 100).
INFO: Seed: 1557779137
INFO: Loaded 1 modules   (151 inline 8-bit counters): 151 [0x7f0640e706e3, 0x7f0640e7077a),
INFO: Loaded 1 PC tables (151 PCs): 151 [0x7f0640e70780,0x7f0640e710f0),
INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes
INFO: A corpus is not provided, starting from an empty corpus
#2	INITED cov: 17 ft: 18 corp: 1/1b exec/s: 0 rss: 26Mb
#32	NEW    cov: 17 ft: 24 corp: 2/4b lim: 4 exec/s: 0 rss: 26Mb L: 3/3 MS: 5 ShuffleBytes-ShuffleBytes-CopyPart-ChangeByte-CMP- DE: "\x00\x00"-
...

While fuzzing is in progress, the fuzzing engine generates new inputs and runs them against the provided fuzz target. By default, it continues to run until a failing input is found, or the user cancels the process (e.g. with Ctrl^C).

The first lines indicate that the "baseline coverage" is gathered before fuzzing begins.

To gather baseline coverage, the fuzzing engine executes both the seed corpus and the generated corpus, to ensure that no errors occurred and to understand the code coverage the existing corpus already provides.

See tests that uses luzer library in:

• Tarantool Lua API tests, https://github.com/ligurio/tarantool-lua-api-tests
• Lua standard library tests, https://github.com/ligurio/lua-stdlib-tests
• https://github.com/ligurio/snippets/tree/master/luzer-tests

Documentation

See documentation.

License

Copyright © 2022-2023 Sergey Bronnikov.

Distributed under the ISC License.