Google Summer of Code 2020: [Final Report] RumpKernel Syscall Fuzzing


September 25, 2020 posted by Kamil Rytarowski

This report was prepared by Aditya Vardhan Padala as a part of Google Summer of Code 2020

This post is the third update to the project RumpKernel Syscall Fuzzing.

Part1 - https://blog.netbsd.org/tnf/entry/gsoc_reports_fuzzing_rumpkernel_syscalls1

Part2 - https://blog.netbsd.org/tnf/entry/gsoc_reports_fuzzing_rumpkernel_syscalls

The first and second coding period was entirely dedicated to fuzzing rumpkernel syscalls using hongfuzz. Initially a dumb fuzzer was developed to start fuzzing but it soon reached its limits.

For the duration of second coding peroid we concentrated on crash reproduction and adding grammar to the fuzzer which yielded in better results as we tested on a bug in ioctl with grammar. Although this works for now crash reproduction needs to be improved to generate a working c reproducer.

For the last coding period I have looked into the internals of syzkaller to understand how it pregenerates input and how it mutates data. I have continued to work on integrating buildrump.sh with build.sh. buildrump eases the task fo building the rumpkernel on any host for any target.

buildrump.sh is like a wrapper around build.sh to build the tools and rumpkernel from the source relevant to rumpkernel. So I worked to get buildrump.sh working with netbsd-src. Building the toolchain was successfull from netbsd-src. So binaries like rumpmake work just fine to continue building the rumpkernel.

But the rumpkernel failed to build due to some warnings and errors similar to the following. It can be due to the fact that buildrump.sh has been dormant recently I faced a lot of build issues.

nbmake[2]: nbmake[2]: don't know how to make /root/buildrump.sh/obj/dest.stage/usr/lib/crti.o. Stop

nbmake[2]: stopped in /root/buildrump.sh/src/lib/librumpuser
>> ERROR:
>> make /root/buildrump.sh/obj/Makefile.first dependall

Few of the similar errors were easily fixed but I couldn't integrate it during the time span of the coding period.

To Do

  • Research more on grammar definition and look into the existing grammar fuzzers for a better understanding of generating grammar.
  • Integrate syz2sys with the existing fuzzer to include grammar generation for better results.

GSoC with NetBSD has been an amazing journey throughout, in which I had a chance to learn from awesome people and work on amazing projects. I will continue to work on the project to achieve the goal of integrating my fuzzer with OSS Fuzz. I thank my mentors Siddharth Muralee, Maciej Grochowski, Christos Zoulas for their support and Kamil for his continuous guidance.

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