Fuzzing Bind

Ondřej Surý ondrej at isc.org
Thu Aug 5 16:01:20 UTC 2021

Ondřej Surý (He/Him)
ondrej at isc.org

> On 5. 8. 2021, at 14:37, Siva Kakarla <sivakesava1 at gmail.com> wrote:
> Hello Everyone,
> I am trying to understand and set up a fuzzer for the Bind DNS implementation. My current goal is to fuzz the authoritative server with queries. 
> I have looked around and came across different fuzzing engines, but I have some trouble and some questions getting it to work. If anyone has anything to comment on, please reply, and that would be really helpful.
> 	• I configured with CC=/path/to/afl/afl-clang./configure --enable-fuzzing=afl or afl-clang-fast to enable fuzzing. Then, I did make and  make install.  I then tried fuzzing the named binary with afl-fuzz -i fuzz/dns_message_parse.in/ -o findings /usr/local/sbin/named -gbut then it stops immediately, sayingthe program crashed with one of the test cases provided. 
> 		• How to fuzz the named binary with queries?

Read bin/named/fuzz.c and associated code in bin/named/main.c — it’s more complicated to set it up (you need to pass -A extra option to `named`).

> 		• How to get the seed input in raw format? 
> 		• Honggfuzz seems to fuzz the named binary, but it produced too many files as crash reports within a minute. I have asked about it on their GitHub. Anyone that worked with Honggfuzz, please reply. 

I see, you got response from hongfuzz author directly.

> 	• A separate fuzz folder contains functions to fuzz small sections of the code. 
> 		• Was this created to improve coverage and modularity? (In the sense, can't named be fuzzed directly using the above setup?) 

Fuzzing a daemon that depends on various internal state (state of the cache, authoritative zones present or not, various configuration options enabled or not) is difficult and also sometimes it’s also useless to fuzz the big blob and you want to fuzz just specific parts (zone parser, DNS message parsers, etc…)

> 		• I could get them running with oss-fuzz but how to run them with afl-fuzz? The README mentions linking the files; can you please tell me how to do that?

with AFL++ do

CC=afl-clang-fast ./configure --enable-fuzzing=afl
make -j
cd fuzz

and then for each test:

make dns_message_parse
LD_LIBRARY_PATH=../lib/isc/.libs:../lib/dns/.libs afl-fuzz -i dns_message_parse.in/ -o xxx ./.libs/dns_message_parse

> 	• How to decode the packets given in https://gitlab.isc.org/isc-projects/bind9/-/tree/main/fuzz/dns_message_parse.in? How to add a new packet to the corpus? (How to convert into a raw packet?)

These are raw DNS messages.  There’s bigger corpus f.e. here: https://github.com/CZ-NIC/dns-fuzzing

> Thank you
> Siva
> --
> Siva Kakarla
> (sivak.dev)
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