-# I Can Haz Fuzz?
+Fuzzing OpenSSL
+===============
+
+OpenSSL can use either LibFuzzer or AFL to do fuzzing.
LibFuzzer
-=========
+---------
-Or, how to fuzz OpenSSL with [libfuzzer](http://llvm.org/docs/LibFuzzer.html).
+How to fuzz OpenSSL with [libfuzzer](http://llvm.org/docs/LibFuzzer.html),
+starting from a vanilla+OpenSSH server Ubuntu install.
-Starting from a vanilla+OpenSSH server Ubuntu install.
+With `clang` from a package manager
+-----------------------------------
-Use Chrome's handy recent build of clang. Older versions may also work.
+Install `clang`, which [ships with `libfuzzer`](http://llvm.org/docs/LibFuzzer.html#fuzzer-usage)
+since version 6.0:
- $ sudo apt-get install git
- $ mkdir git-work
- $ git clone https://chromium.googlesource.com/chromium/src/tools/clang
- $ clang/scripts/update.py
+ sudo apt-get install clang
-You may want to git pull and re-run the update from time to time.
+Configure `openssl` for fuzzing. For now, you'll still need to pass in the path
+to the `libFuzzer` library file while configuring; this is represented as
+`$PATH_TO_LIBFUZZER` below. A typical value would be
+`/usr/lib/llvm-7/lib/clang/7.0.1/lib/linux/libclang_rt.fuzzer-x86_64.a`.
-Update your path:
+ CC=clang ./config enable-fuzz-libfuzzer \
+ --with-fuzzer-lib=$PATH_TO_LIBFUZZER \
+ -DPEDANTIC enable-asan enable-ubsan no-shared \
+ -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION \
+ -fsanitize=fuzzer-no-link \
+ enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment \
+ enable-weak-ssl-ciphers enable-rc5 enable-md2 \
+ enable-ssl3 enable-ssl3-method enable-nextprotoneg \
+ --debug
- $ PATH=~/third_party/llvm-build/Release+Asserts/bin/:$PATH
+Clang uses the gcc libstdc++ library so this must also be installed. You can
+check which version of gcc clang is using like this:
-Get and build libFuzzer (there is a git mirror at
-https://github.com/llvm-mirror/llvm/tree/master/lib/Fuzzer if you prefer):
+ $ clang --verbose
+ Ubuntu clang version 14.0.0-1ubuntu1.1
+ Target: x86_64-pc-linux-gnu
+ Thread model: posix
+ InstalledDir: /usr/bin
+ Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/12
+ Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/10
+ Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
+ Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
+ Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
+ Candidate multilib: .;@m64
+ Selected multilib: .;@m64
- $ cd
- $ sudo apt-get install subversion
- $ mkdir svn-work
- $ cd svn-work
- $ svn co https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer Fuzzer
- $ cd Fuzzer
- $ clang++ -c -g -O2 -std=c++11 *.cpp
- $ ar r libFuzzer.a *.o
- $ ranlib libFuzzer.a
+So, in the above example clang is using gcc version 12. Ensure that the selected
+gcc version has the relevant libstdc++ files installed:
-Configure for fuzzing:
+ $ ls /usr/lib/gcc/x86_64-linux-gnu/12 | grep stdc++
+ libstdc++.a
+ libstdc++fs.a
+ libstdc++.so
+
+On Ubuntu for gcc-12 this requires the libstdc++-12-dev package installed.
+
+ $ sudo apt-get install libstdc++-12-dev
+
+Compile:
+
+ sudo apt-get install make
+ make clean
+ LDCMD=clang++ make -j4
+
+Finally, perform the actual fuzzing:
+
+ fuzz/helper.py $FUZZER
+
+where $FUZZER is one of the executables in `fuzz/`.
+It will run until you stop it.
+
+If you get a crash, you should find a corresponding input file in
+`fuzz/corpora/$FUZZER-crash/`.
+
+With `clang` from source/pre-built binaries
+-------------------------------------------
- $ CC=clang ./config enable-fuzz-libfuzzer \
- --with-fuzzer-include=../../svn-work/Fuzzer \
- --with-fuzzer-lib=../../svn-work/Fuzzer/libFuzzer.a \
+You may also wish to use a pre-built binary from the [LLVM Download
+site](http://releases.llvm.org/download.html), or to [build `clang` from
+source](https://clang.llvm.org/get_started.html). After adding `clang` to your
+path and locating the `libfuzzer` library file, the procedure for configuring
+fuzzing is the same, except that you also need to specify
+a `--with-fuzzer-include` option, which should be the parent directory of the
+prebuilt fuzzer library. This is represented as `$PATH_TO_LIBFUZZER_DIR` below.
+
+ CC=clang ./config enable-fuzz-libfuzzer \
+ --with-fuzzer-include=$PATH_TO_LIBFUZZER_DIR \
+ --with-fuzzer-lib=$PATH_TO_LIBFUZZER \
-DPEDANTIC enable-asan enable-ubsan no-shared \
-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION \
- -fsanitize-coverage=trace-pc-guard,indirect-calls,trace-cmp \
- enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment enable-tls1_3 \
+ -fsanitize=fuzzer-no-link \
+ enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment \
enable-weak-ssl-ciphers enable-rc5 enable-md2 \
enable-ssl3 enable-ssl3-method enable-nextprotoneg \
--debug
- $ sudo apt-get install make
- $ LDCMD=clang++ make -j
- $ fuzz/helper.py $FUZZER
-
-Where $FUZZER is one of the executables in `fuzz/`.
-
-If you get a crash, you should find a corresponding input file in
-`fuzz/corpora/$FUZZER-crash/`.
AFL
-===
+---
+
+This is an alternative to using LibFuzzer.
Configure for fuzzing:
- $ sudo apt-get install afl-clang
- $ CC=afl-clang-fast ./config enable-fuzz-afl no-shared no-module \
+ sudo apt-get install afl-clang
+ CC=afl-clang-fast ./config enable-fuzz-afl no-shared no-module \
-DPEDANTIC enable-tls1_3 enable-weak-ssl-ciphers enable-rc5 \
enable-md2 enable-ssl3 enable-ssl3-method enable-nextprotoneg \
enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment \
--debug
- $ make
+ make clean
+ make
The following options can also be enabled: enable-asan, enable-ubsan, enable-msan
Run one of the fuzzers:
- $ afl-fuzz -i fuzz/corpora/$FUZZER -o fuzz/corpora/$FUZZER/out fuzz/$FUZZER
+ afl-fuzz -i fuzz/corpora/$FUZZER -o fuzz/corpora/$FUZZER/out fuzz/$FUZZER
Where $FUZZER is one of the executables in `fuzz/`.
Reproducing issues
-==================
+------------------
If a fuzzer generates a reproducible error, you can reproduce the problem using
the fuzz/*-test binaries and the file generated by the fuzzer. They binaries
-don't need to be build for fuzzing, there is no need to set CC or the call
+don't need to be built for fuzzing, there is no need to set CC or the call
config with enable-fuzz-* or -fsanitize-coverage, but some of the other options
above might be needed. For instance the enable-asan or enable-ubsan option might
be useful to show you when the problem happens. For the client and server fuzzer
To reproduce the crash you can run:
- $ fuzz/$FUZZER-test $file
+ fuzz/$FUZZER-test $file
+
+To do all the tests of a specific fuzzer such as asn1 you can run
+
+ fuzz/asn1-test fuzz/corpora/asn1
+or
+ make test TESTS=fuzz_test_asn1
+
+To run several fuzz tests you can use for instance:
+
+ make test TESTS='test_fuzz_cmp test_fuzz_cms'
+
+To run all fuzz tests you can use:
+
+ make test TESTS='test_fuzz_*'
Random numbers
-==============
+--------------
The client and server fuzzer normally generate random numbers as part of the TLS
connection setup. This results in the coverage of the fuzzing corpus changing
emulated by the file, can be generated for that client hello.
Coverage changes
-================
+----------------
Since the corpus depends on the default behaviour of the client and the server,
changes in what they send by default will have an impact on the coverage. The
corpus will need to be updated in that case.
Updating the corpus
-===================
+-------------------
The client and server corpus is generated with multiple config options:
+
- The options as documented above
- Without enable-ec_nistp_64_gcc_128 and without --debug
- With no-asm
The libfuzzer merge option is used to add the additional coverage
from each config to the minimal set.
+
+Minimizing the corpus
+---------------------
+
+When you have gathered corpus data from more than one fuzzer run
+or for any other reason want to minimize the data
+in some corpus subdirectory `fuzz/corpora/DIR` this can be done as follows:
+
+ mkdir fuzz/corpora/NEWDIR
+ fuzz/$FUZZER -merge=1 fuzz/corpora/NEWDIR fuzz/corpora/DIR
projects / thirdparty / openssl.git / blobdiff