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# Fuzzers
These are fuzzers designed for use with `libFuzzer`. Currently they are
primarily run on Google's OSS-Fuzz (https://github.com/google/oss-fuzz/).
OSS-Fuzz will automatically locate and compile any `*_fuzzer.cc` files and
assume they are fuzzers it should run.
The initial values for each parser fuzzer are taken from the $NAME.in
directory.
# Running a fuzzer using AFL
Use the following commands on top dir:
```
$ CC="afl-gcc" ./configure
$ make -j$(nproc)
$ cd devel/fuzz
$ make gnutls_pkcs7_parser_fuzzer
$ ./run-afl.sh gnutls_pkcs7_parser_fuzzer
```
This will execute AFL (which runs indefinitely until CTRL+C is pressed) and
provide its output in a "gnutls_pkcs7_parser_fuzzer.PID.out" directory.
# Reproducing a reported issue from oss-fuzz
Assuming an issue on the "gnutls_pkcs7_parser_fuzzer" was found, and the
reproducer is placed in $FILE, to reproduce locally use the following commands
on top dir:
```
$ CFLAGS="-fsanitize=address -g -O2" ./configure
$ make -j$(nproc)
$ cd devel/fuzz
$ make gnutls_pkcs7_parser_fuzzer
$ ./gnutls_pkcs7_parser_fuzzer <$FILE
```
Alternatively (if local reproduction is not possible), you can reproduce it
using the original docker instance used to find the issue as follows.
```
sudo docker run --rm -e ASAN_OPTIONS="detect_leaks=0" -ti -v $FILE:/testcase ossfuzz/gnutls reproduce gnutls_pkcs7_parser_fuzzer
```
# Enhancing the testsuite for issues found
For the following tests dropping a file to a subdirectory in tests is
sufficient:
| Fuzzer | Directory |
|:----------------------------:|:--------------------------:|
|gnutls_client_fuzzer | tests/client-interesting |
|gnutls_server_fuzzer | tests/server-interesting |
|gnutls_pkcs7_parser_fuzzer | tests/pkcs7-interesting |
|gnutls_x509_parser_fuzzer | tests/certs-interesting |
|gnutls_ocsp_resp_parser_fuzzer| tests/ocsp-resp-interesting|
The following require modifying a test case. Mappings are shown in the
table below.
| Fuzzer | Test case |
|:-------------------------------:|:--------------------------------------------------------:|
|gnutls_dn_parser_fuzzer |tests/x509-dn-decode.c |
|gnutls_pkcs8_key_parser_fuzzer |tests/key-tests/pkcs8-invalid,tests/key-tests/pkcs8-decode|
|gnutls_private_key_parser_fuzzer |tests/key-tests/key-invalid |
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