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[libFuzzer] remove large examples from the libFuzzer docs and link to the libFuzzer tutorial instead; also fix a build error in another file
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285337 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Kostya Serebryany
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245c383b96
commit
f8e32dda35
@ -397,171 +397,13 @@ You should get an error pretty quickly::
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artifact_prefix='./'; Test unit written to ./crash-b13e8756b13a00cf168300179061fb4b91fefbed
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PCRE2
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-----
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More examples
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-------------
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Here we show how to use libFuzzer on something real, yet simple: pcre2_::
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Examples of real-life fuzz targets and the bugs they find can be found
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at http://tutorial.libfuzzer.info. Among other things you can learn how
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to detect Heartbleed_ in one second.
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COV_FLAGS=" -fsanitize-coverage=edge,indirect-calls,8bit-counters"
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# Get PCRE2
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wget ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre2-10.20.tar.gz
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tar xf pcre2-10.20.tar.gz
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# Build PCRE2 with AddressSanitizer and coverage; requires autotools.
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(cd pcre2-10.20; ./autogen.sh; CC="clang -fsanitize=address $COV_FLAGS" ./configure --prefix=`pwd`/../inst && make -j && make install)
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# Build the fuzzing target function that does something interesting with PCRE2.
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cat << EOF > pcre_fuzzer.cc
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#include <string.h>
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#include <stdint.h>
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#include "pcre2posix.h"
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extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
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if (size < 1) return 0;
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char *str = new char[size+1];
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memcpy(str, data, size);
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str[size] = 0;
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regex_t preg;
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if (0 == regcomp(&preg, str, 0)) {
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regexec(&preg, str, 0, 0, 0);
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regfree(&preg);
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}
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delete [] str;
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return 0;
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}
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EOF
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clang++ -g -fsanitize=address $COV_FLAGS -c -std=c++11 -I inst/include/ pcre_fuzzer.cc
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# Link.
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clang++ -g -fsanitize=address -Wl,--whole-archive inst/lib/*.a -Wl,-no-whole-archive libFuzzer.a pcre_fuzzer.o -o pcre_fuzzer
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This will give you a binary of the fuzzer, called ``pcre_fuzzer``.
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Now, create a directory that will hold the test corpus:
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.. code-block:: console
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mkdir -p CORPUS
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For simple input languages like regular expressions this is all you need.
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For more complicated/structured inputs, the fuzzer works much more efficiently
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if you can populate the corpus directory with a variety of valid and invalid
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inputs for the code under test.
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Now run the fuzzer with the corpus directory as the only parameter:
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.. code-block:: console
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./pcre_fuzzer ./CORPUS
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Initially, you will see Output_ like this::
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INFO: Seed: 2938818941
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INFO: -max_len is not provided, using 64
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INFO: A corpus is not provided, starting from an empty corpus
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#0 READ units: 1 exec/s: 0
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#1 INITED cov: 3 bits: 3 units: 1 exec/s: 0
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#2 NEW cov: 176 bits: 176 indir: 3 units: 2 exec/s: 0 L: 64 MS: 0
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#8 NEW cov: 176 bits: 179 indir: 3 units: 3 exec/s: 0 L: 63 MS: 2 ChangeByte-EraseByte-
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...
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#14004 NEW cov: 1500 bits: 4536 indir: 5 units: 406 exec/s: 0 L: 54 MS: 3 ChangeBit-ChangeBit-CrossOver-
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Now, interrupt the fuzzer and run it again the same way. You will see::
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INFO: Seed: 3398349082
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INFO: -max_len is not provided, using 64
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#0 READ units: 405 exec/s: 0
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#405 INITED cov: 1499 bits: 4535 indir: 5 units: 286 exec/s: 0
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#587 NEW cov: 1499 bits: 4540 indir: 5 units: 287 exec/s: 0 L: 52 MS: 2 InsertByte-EraseByte-
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#667 NEW cov: 1501 bits: 4542 indir: 5 units: 288 exec/s: 0 L: 39 MS: 2 ChangeBit-InsertByte-
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#672 NEW cov: 1501 bits: 4543 indir: 5 units: 289 exec/s: 0 L: 15 MS: 2 ChangeASCIIInt-ChangeBit-
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#739 NEW cov: 1501 bits: 4544 indir: 5 units: 290 exec/s: 0 L: 64 MS: 4 ShuffleBytes-ChangeASCIIInt-InsertByte-ChangeBit-
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...
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On the second execution the fuzzer has a non-empty input corpus (405 items). As
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the first step, the fuzzer minimized this corpus (the ``INITED`` line) to
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produce 286 interesting items, omitting inputs that do not hit any additional
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code.
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(Aside: although the fuzzer only saves new inputs that hit additional code, this
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does not mean that the corpus as a whole is kept minimized. For example, if
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an input hitting A-B-C then an input that hits A-B-C-D are generated,
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they will both be saved, even though the latter subsumes the former.)
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You may run ``N`` independent fuzzer jobs in parallel on ``M`` CPUs:
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.. code-block:: console
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N=100; M=4; ./pcre_fuzzer ./CORPUS -jobs=$N -workers=$M
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By default (``-reload=1``) the fuzzer processes will periodically scan the corpus directory
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and reload any new tests. This way the test inputs found by one process will be picked up
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by all others.
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If ``-workers=$M`` is not supplied, ``min($N,NumberOfCpuCore/2)`` will be used.
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Heartbleed
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----------
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Remember Heartbleed_?
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As it was recently `shown <https://blog.hboeck.de/archives/868-How-Heartbleed-couldve-been-found.html>`_,
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fuzzing with AddressSanitizer_ can find Heartbleed. Indeed, here are the step-by-step instructions
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to find Heartbleed with libFuzzer::
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wget https://www.openssl.org/source/openssl-1.0.1f.tar.gz
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tar xf openssl-1.0.1f.tar.gz
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COV_FLAGS="-fsanitize-coverage=edge,indirect-calls" # -fsanitize-coverage=8bit-counters
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(cd openssl-1.0.1f/ && ./config &&
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make -j 32 CC="clang -g -fsanitize=address $COV_FLAGS")
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# Get and build libFuzzer
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svn co http://llvm.org/svn/llvm-project/llvm/trunk/lib/Fuzzer
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clang -c -g -O2 -std=c++11 Fuzzer/*.cpp -IFuzzer
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# Get examples of key/pem files.
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git clone https://github.com/hannob/selftls
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cp selftls/server* . -v
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cat << EOF > handshake-fuzz.cc
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#include <openssl/ssl.h>
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#include <openssl/err.h>
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#include <assert.h>
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#include <stdint.h>
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#include <stddef.h>
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SSL_CTX *sctx;
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int Init() {
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SSL_library_init();
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SSL_load_error_strings();
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ERR_load_BIO_strings();
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OpenSSL_add_all_algorithms();
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assert (sctx = SSL_CTX_new(TLSv1_method()));
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assert (SSL_CTX_use_certificate_file(sctx, "server.pem", SSL_FILETYPE_PEM));
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assert (SSL_CTX_use_PrivateKey_file(sctx, "server.key", SSL_FILETYPE_PEM));
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return 0;
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}
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extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
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static int unused = Init();
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SSL *server = SSL_new(sctx);
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BIO *sinbio = BIO_new(BIO_s_mem());
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BIO *soutbio = BIO_new(BIO_s_mem());
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SSL_set_bio(server, sinbio, soutbio);
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SSL_set_accept_state(server);
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BIO_write(sinbio, Data, Size);
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SSL_do_handshake(server);
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SSL_free(server);
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return 0;
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}
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EOF
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# Build the fuzzer.
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clang++ -g handshake-fuzz.cc -fsanitize=address \
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openssl-1.0.1f/libssl.a openssl-1.0.1f/libcrypto.a Fuzzer*.o
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# Run 20 independent fuzzer jobs.
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./a.out -jobs=20 -workers=20
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Voila::
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#1048576 pulse cov 3424 bits 0 units 9 exec/s 24385
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=================================================================
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==17488==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x629000004748 at pc 0x00000048c979 bp 0x7fffe3e864f0 sp 0x7fffe3e85ca8
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READ of size 60731 at 0x629000004748 thread T0
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#0 0x48c978 in __asan_memcpy
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#1 0x4db504 in tls1_process_heartbeat openssl-1.0.1f/ssl/t1_lib.c:2586:3
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#2 0x580be3 in ssl3_read_bytes openssl-1.0.1f/ssl/s3_pkt.c:1092:4
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Note: a `similar fuzzer <https://boringssl.googlesource.com/boringssl/+/HEAD/FUZZING.md>`_
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is now a part of the BoringSSL_ source tree.
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Advanced features
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=================
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@ -337,6 +337,7 @@ Failure values are constructed using ``make_error<T>``, where ``T`` is any class
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that inherits from the ErrorInfo utility, E.g.:
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.. code-block:: c++
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class BadFileFormat : public ErrorInfo<BadFileFormat> {
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public:
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static char ID;
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