When fuzzing with AFL, if the LLVM-based instrumentation is
used (via the afl-clang-fast wrapper), then it is possible to
have a single execution of the fuzzer program iterate multiple
times over the fuzzing entrypoint (similar to libFuzzer's normal
mode of execution) with different data. This is much (e.g. 10x)
faster.
Add code to support this, by checking whether __AFL_LOOP is
defined at compile-time.
Also, shift the code to effectively be C rather than C++.
The tests are written in C++11, using the GoogleTest and GoogleMock
frameworks. They have their own independent autoconf setup, so that
users of the library need not have a C++ compiler just to get c-ares
working (however, the test/configure.ac file does assume the use of
a shared top-level m4/ directory). However, this autoconf setup has
only been tested on Linux and OSX so far.
Run with "./arestest", or "./arestest -v" to see extra debug info.
The GoogleTest options for running specific tests are also
available (e.g. "./arestest --gtest_filter=*Live*").
The tests are nowhere near complete yet (currently hitting around
60% coverage as reported by gcov), but they do include examples
of a few different styles of testing:
- There are live tests (ares-test-live.cc), which assume that the
current machine has a valid DNS setup and connection to the
internet; these tests issue queries for real domains but don't
particularly check what gets returned. The tests will fail on
an offline machine.
- There a few mock tests (ares-test-mock.cc) that set up a fake DNS
server and inject its port into the c-ares library configuration.
These tests allow specific response messages to be crafted and
injected, and so are likely to be used for many more tests in
future.
- To make this generation/injection easier, the dns-proto.h file
includes C++ helper classes for building DNS packets.
- Other library entrypoints that don't require network activity
(e.g. ares_parse_*_reply) are tested directly.
- There are few tests of library-internal functions that are not
normally visible to API users (in ares-test-internal.cc).
- A couple of the tests use a helper method of the test fixture to
inject memory allocation failures, using the earlier change to the
library to allow override of malloc/realloc/free.
- There is also an entrypoint to allow Clang's libfuzzer to drive
the packet parsing code in ares_parse_*_reply, together with a
standalone wrapper for it (./aresfuzz) to allow use of afl-fuzz
for further fuzz testing.
David Drysdale
Brad House