1 ======================================================== 2 LibFuzzer -- a library for coverage-guided fuzz testing. 3 ======================================================== 4 .. contents:: 5 :local: 6 :depth: 4 7 8 Introduction 9 ============ 10 11 This library is intended primarily for in-process coverage-guided fuzz testing 12 (fuzzing) of other libraries. The typical workflow looks like this: 13 14 * Build the Fuzzer library as a static archive (or just a set of .o files). 15 Note that the Fuzzer contains the main() function. 16 Preferably do *not* use sanitizers while building the Fuzzer. 17 * Build the library you are going to test with 18 `-fsanitize-coverage={bb,edge}[,indirect-calls,8bit-counters]` 19 and one of the sanitizers. We recommend to build the library in several 20 different modes (e.g. asan, msan, lsan, ubsan, etc) and even using different 21 optimizations options (e.g. -O0, -O1, -O2) to diversify testing. 22 * Build a test driver using the same options as the library. 23 The test driver is a C/C++ file containing interesting calls to the library 24 inside a single function ``extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);``. 25 Currently, the only expected return value is 0, others are reserved for future. 26 * Link the Fuzzer, the library and the driver together into an executable 27 using the same sanitizer options as for the library. 28 * Collect the initial corpus of inputs for the 29 fuzzer (a directory with test inputs, one file per input). 30 The better your inputs are the faster you will find something interesting. 31 Also try to keep your inputs small, otherwise the Fuzzer will run too slow. 32 By default, the Fuzzer limits the size of every input to 64 bytes 33 (use ``-max_len=N`` to override). 34 * Run the fuzzer with the test corpus. As new interesting test cases are 35 discovered they will be added to the corpus. If a bug is discovered by 36 the sanitizer (asan, etc) it will be reported as usual and the reproducer 37 will be written to disk. 38 Each Fuzzer process is single-threaded (unless the library starts its own 39 threads). You can run the Fuzzer on the same corpus in multiple processes 40 in parallel. 41 42 43 The Fuzzer is similar in concept to AFL_, 44 but uses in-process Fuzzing, which is more fragile, more restrictive, but 45 potentially much faster as it has no overhead for process start-up. 46 It uses LLVM's SanitizerCoverage_ instrumentation to get in-process 47 coverage-feedback 48 49 The code resides in the LLVM repository, requires the fresh Clang compiler to build 50 and is used to fuzz various parts of LLVM, 51 but the Fuzzer itself does not (and should not) depend on any 52 part of LLVM and can be used for other projects w/o requiring the rest of LLVM. 53 54 Flags 55 ===== 56 The most important flags are:: 57 58 seed 0 Random seed. If 0, seed is generated. 59 runs -1 Number of individual test runs (-1 for infinite runs). 60 max_len 64 Maximum length of the test input. 61 cross_over 1 If 1, cross over inputs. 62 mutate_depth 5 Apply this number of consecutive mutations to each input. 63 timeout 1200 Timeout in seconds (if positive). If one unit runs more than this number of seconds the process will abort. 64 max_total_time 0 If positive, indicates the maximal total time in seconds to run the fuzzer. 65 help 0 Print help. 66 merge 0 If 1, the 2-nd, 3-rd, etc corpora will be merged into the 1-st corpus. Only interesting units will be taken. 67 jobs 0 Number of jobs to run. If jobs >= 1 we spawn this number of jobs in separate worker processes with stdout/stderr redirected to fuzz-JOB.log. 68 workers 0 Number of simultaneous worker processes to run the jobs. If zero, "min(jobs,NumberOfCpuCores()/2)" is used. 69 sync_command 0 Execute an external command "<sync_command> <test_corpus>" to synchronize the test corpus. 70 sync_timeout 600 Minimum timeout between syncs. 71 use_traces 0 Experimental: use instruction traces 72 only_ascii 0 If 1, generate only ASCII (isprint+isspace) inputs. 73 test_single_input "" Use specified file content as test input. Test will be run only once. Useful for debugging a particular case. 74 artifact_prefix "" Write fuzzing artifacts (crash, timeout, or slow inputs) as $(artifact_prefix)file 75 exact_artifact_path "" Write the single artifact on failure (crash, timeout) as $(exact_artifact_path). This overrides -artifact_prefix and will not use checksum in the file name. Do not use the same path for several parallel processes. 76 77 For the full list of flags run the fuzzer binary with ``-help=1``. 78 79 Usage examples 80 ============== 81 82 Toy example 83 ----------- 84 85 A simple function that does something interesting if it receives the input "HI!":: 86 87 cat << EOF >> test_fuzzer.cc 88 #include <stdint.h> 89 #include <stddef.h> 90 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { 91 if (size > 0 && data[0] == 'H') 92 if (size > 1 && data[1] == 'I') 93 if (size > 2 && data[2] == '!') 94 __builtin_trap(); 95 return 0; 96 } 97 EOF 98 # Get lib/Fuzzer. Assuming that you already have fresh clang in PATH. 99 svn co http://llvm.org/svn/llvm-project/llvm/trunk/lib/Fuzzer 100 # Build lib/Fuzzer files. 101 clang -c -g -O2 -std=c++11 Fuzzer/*.cpp -IFuzzer 102 # Build test_fuzzer.cc with asan and link against lib/Fuzzer. 103 clang++ -fsanitize=address -fsanitize-coverage=edge test_fuzzer.cc Fuzzer*.o 104 # Run the fuzzer with no corpus. 105 ./a.out 106 107 You should get ``Illegal instruction (core dumped)`` pretty quickly. 108 109 PCRE2 110 ----- 111 112 Here we show how to use lib/Fuzzer on something real, yet simple: pcre2_:: 113 114 COV_FLAGS=" -fsanitize-coverage=edge,indirect-calls,8bit-counters" 115 # Get PCRE2 116 svn co svn://vcs.exim.org/pcre2/code/trunk pcre 117 # Get lib/Fuzzer. Assuming that you already have fresh clang in PATH. 118 svn co http://llvm.org/svn/llvm-project/llvm/trunk/lib/Fuzzer 119 # Build PCRE2 with AddressSanitizer and coverage. 120 (cd pcre; ./autogen.sh; CC="clang -fsanitize=address $COV_FLAGS" ./configure --prefix=`pwd`/../inst && make -j && make install) 121 # Build lib/Fuzzer files. 122 clang -c -g -O2 -std=c++11 Fuzzer/*.cpp -IFuzzer 123 # Build the actual function that does something interesting with PCRE2. 124 cat << EOF > pcre_fuzzer.cc 125 #include <string.h> 126 #include <stdint.h> 127 #include "pcre2posix.h" 128 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { 129 if (size < 1) return 0; 130 char *str = new char[size+1]; 131 memcpy(str, data, size); 132 str[size] = 0; 133 regex_t preg; 134 if (0 == regcomp(&preg, str, 0)) { 135 regexec(&preg, str, 0, 0, 0); 136 regfree(&preg); 137 } 138 delete [] str; 139 return 0; 140 } 141 EOF 142 clang++ -g -fsanitize=address $COV_FLAGS -c -std=c++11 -I inst/include/ pcre_fuzzer.cc 143 # Link. 144 clang++ -g -fsanitize=address -Wl,--whole-archive inst/lib/*.a -Wl,-no-whole-archive Fuzzer*.o pcre_fuzzer.o -o pcre_fuzzer 145 146 This will give you a binary of the fuzzer, called ``pcre_fuzzer``. 147 Now, create a directory that will hold the test corpus:: 148 149 mkdir -p CORPUS 150 151 For simple input languages like regular expressions this is all you need. 152 For more complicated inputs populate the directory with some input samples. 153 Now run the fuzzer with the corpus dir as the only parameter:: 154 155 ./pcre_fuzzer ./CORPUS 156 157 You will see output like this:: 158 159 Seed: 1876794929 160 #0 READ cov 0 bits 0 units 1 exec/s 0 161 #1 pulse cov 3 bits 0 units 1 exec/s 0 162 #1 INITED cov 3 bits 0 units 1 exec/s 0 163 #2 pulse cov 208 bits 0 units 1 exec/s 0 164 #2 NEW cov 208 bits 0 units 2 exec/s 0 L: 64 165 #3 NEW cov 217 bits 0 units 3 exec/s 0 L: 63 166 #4 pulse cov 217 bits 0 units 3 exec/s 0 167 168 * The ``Seed:`` line shows you the current random seed (you can change it with ``-seed=N`` flag). 169 * The ``READ`` line shows you how many input files were read (since you passed an empty dir there were inputs, but one dummy input was synthesised). 170 * The ``INITED`` line shows you that how many inputs will be fuzzed. 171 * The ``NEW`` lines appear with the fuzzer finds a new interesting input, which is saved to the CORPUS dir. If multiple corpus dirs are given, the first one is used. 172 * The ``pulse`` lines appear periodically to show the current status. 173 174 Now, interrupt the fuzzer and run it again the same way. You will see:: 175 176 Seed: 1879995378 177 #0 READ cov 0 bits 0 units 564 exec/s 0 178 #1 pulse cov 502 bits 0 units 564 exec/s 0 179 ... 180 #512 pulse cov 2933 bits 0 units 564 exec/s 512 181 #564 INITED cov 2991 bits 0 units 344 exec/s 564 182 #1024 pulse cov 2991 bits 0 units 344 exec/s 1024 183 #1455 NEW cov 2995 bits 0 units 345 exec/s 1455 L: 49 184 185 This time you were running the fuzzer with a non-empty input corpus (564 items). 186 As the first step, the fuzzer minimized the set to produce 344 interesting items (the ``INITED`` line) 187 188 It is quite convenient to store test corpuses in git. 189 As an example, here is a git repository with test inputs for the above PCRE2 fuzzer:: 190 191 git clone https://github.com/kcc/fuzzing-with-sanitizers.git 192 ./pcre_fuzzer ./fuzzing-with-sanitizers/pcre2/C1/ 193 194 You may run ``N`` independent fuzzer jobs in parallel on ``M`` CPUs:: 195 196 N=100; M=4; ./pcre_fuzzer ./CORPUS -jobs=$N -workers=$M 197 198 By default (``-reload=1``) the fuzzer processes will periodically scan the CORPUS directory 199 and reload any new tests. This way the test inputs found by one process will be picked up 200 by all others. 201 202 If ``-workers=$M`` is not supplied, ``min($N,NumberOfCpuCore/2)`` will be used. 203 204 Heartbleed 205 ---------- 206 Remember Heartbleed_? 207 As it was recently `shown <https://blog.hboeck.de/archives/868-How-Heartbleed-couldve-been-found.html>`_, 208 fuzzing with AddressSanitizer can find Heartbleed. Indeed, here are the step-by-step instructions 209 to find Heartbleed with LibFuzzer:: 210 211 wget https://www.openssl.org/source/openssl-1.0.1f.tar.gz 212 tar xf openssl-1.0.1f.tar.gz 213 COV_FLAGS="-fsanitize-coverage=edge,indirect-calls" # -fsanitize-coverage=8bit-counters 214 (cd openssl-1.0.1f/ && ./config && 215 make -j 32 CC="clang -g -fsanitize=address $COV_FLAGS") 216 # Get and build LibFuzzer 217 svn co http://llvm.org/svn/llvm-project/llvm/trunk/lib/Fuzzer 218 clang -c -g -O2 -std=c++11 Fuzzer/*.cpp -IFuzzer 219 # Get examples of key/pem files. 220 git clone https://github.com/hannob/selftls 221 cp selftls/server* . -v 222 cat << EOF > handshake-fuzz.cc 223 #include <openssl/ssl.h> 224 #include <openssl/err.h> 225 #include <assert.h> 226 #include <stdint.h> 227 #include <stddef.h> 228 229 SSL_CTX *sctx; 230 int Init() { 231 SSL_library_init(); 232 SSL_load_error_strings(); 233 ERR_load_BIO_strings(); 234 OpenSSL_add_all_algorithms(); 235 assert (sctx = SSL_CTX_new(TLSv1_method())); 236 assert (SSL_CTX_use_certificate_file(sctx, "server.pem", SSL_FILETYPE_PEM)); 237 assert (SSL_CTX_use_PrivateKey_file(sctx, "server.key", SSL_FILETYPE_PEM)); 238 return 0; 239 } 240 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) { 241 static int unused = Init(); 242 SSL *server = SSL_new(sctx); 243 BIO *sinbio = BIO_new(BIO_s_mem()); 244 BIO *soutbio = BIO_new(BIO_s_mem()); 245 SSL_set_bio(server, sinbio, soutbio); 246 SSL_set_accept_state(server); 247 BIO_write(sinbio, Data, Size); 248 SSL_do_handshake(server); 249 SSL_free(server); 250 return 0; 251 } 252 EOF 253 # Build the fuzzer. 254 clang++ -g handshake-fuzz.cc -fsanitize=address \ 255 openssl-1.0.1f/libssl.a openssl-1.0.1f/libcrypto.a Fuzzer*.o 256 # Run 20 independent fuzzer jobs. 257 ./a.out -jobs=20 -workers=20 258 259 Voila:: 260 261 #1048576 pulse cov 3424 bits 0 units 9 exec/s 24385 262 ================================================================= 263 ==17488==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x629000004748 at pc 0x00000048c979 bp 0x7fffe3e864f0 sp 0x7fffe3e85ca8 264 READ of size 60731 at 0x629000004748 thread T0 265 #0 0x48c978 in __asan_memcpy 266 #1 0x4db504 in tls1_process_heartbeat openssl-1.0.1f/ssl/t1_lib.c:2586:3 267 #2 0x580be3 in ssl3_read_bytes openssl-1.0.1f/ssl/s3_pkt.c:1092:4 268 269 Note: a `similar fuzzer <https://boringssl.googlesource.com/boringssl/+/HEAD/FUZZING.md>`_ 270 is now a part of the boringssl source tree. 271 272 Advanced features 273 ================= 274 275 Dictionaries 276 ------------ 277 *EXPERIMENTAL*. 278 LibFuzzer supports user-supplied dictionaries with input language keywords 279 or other interesting byte sequences (e.g. multi-byte magic values). 280 Use ``-dict=DICTIONARY_FILE``. For some input languages using a dictionary 281 may significantly improve the search speed. 282 The dictionary syntax is similar to that used by AFL_ for its ``-x`` option:: 283 284 # Lines starting with '#' and empty lines are ignored. 285 286 # Adds "blah" (w/o quotes) to the dictionary. 287 kw1="blah" 288 # Use \\ for backslash and \" for quotes. 289 kw2="\"ac\\dc\"" 290 # Use \xAB for hex values 291 kw3="\xF7\xF8" 292 # the name of the keyword followed by '=' may be omitted: 293 "foo\x0Abar" 294 295 Data-flow-guided fuzzing 296 ------------------------ 297 298 *EXPERIMENTAL*. 299 With an additional compiler flag ``-fsanitize-coverage=trace-cmp`` (see SanitizerCoverageTraceDataFlow_) 300 and extra run-time flag ``-use_traces=1`` the fuzzer will try to apply *data-flow-guided fuzzing*. 301 That is, the fuzzer will record the inputs to comparison instructions, switch statements, 302 and several libc functions (``memcmp``, ``strcmp``, ``strncmp``, etc). 303 It will later use those recorded inputs during mutations. 304 305 This mode can be combined with DataFlowSanitizer_ to achieve better sensitivity. 306 307 AFL compatibility 308 ----------------- 309 LibFuzzer can be used in parallel with AFL_ on the same test corpus. 310 Both fuzzers expect the test corpus to reside in a directory, one file per input. 311 You can run both fuzzers on the same corpus in parallel:: 312 313 ./afl-fuzz -i testcase_dir -o findings_dir /path/to/program -r @@ 314 ./llvm-fuzz testcase_dir findings_dir # Will write new tests to testcase_dir 315 316 Periodically restart both fuzzers so that they can use each other's findings. 317 318 How good is my fuzzer? 319 ---------------------- 320 321 Once you implement your target function ``LLVMFuzzerTestOneInput`` and fuzz it to death, 322 you will want to know whether the function or the corpus can be improved further. 323 One easy to use metric is, of course, code coverage. 324 You can get the coverage for your corpus like this:: 325 326 ASAN_OPTIONS=coverage_pcs=1 ./fuzzer CORPUS_DIR -runs=0 327 328 This will run all the tests in the CORPUS_DIR but will not generate any new tests 329 and dump covered PCs to disk before exiting. 330 Then you can subtract the set of covered PCs from the set of all instrumented PCs in the binary, 331 see SanitizerCoverage_ for details. 332 333 User-supplied mutators 334 ---------------------- 335 336 LibFuzzer allows to use custom (user-supplied) mutators, 337 see FuzzerInterface.h_ 338 339 Fuzzing components of LLVM 340 ========================== 341 342 clang-format-fuzzer 343 ------------------- 344 The inputs are random pieces of C++-like text. 345 346 Build (make sure to use fresh clang as the host compiler):: 347 348 cmake -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DLLVM_USE_SANITIZER=Address -DLLVM_USE_SANITIZE_COVERAGE=YES -DCMAKE_BUILD_TYPE=Release /path/to/llvm 349 ninja clang-format-fuzzer 350 mkdir CORPUS_DIR 351 ./bin/clang-format-fuzzer CORPUS_DIR 352 353 Optionally build other kinds of binaries (asan+Debug, msan, ubsan, etc). 354 355 Tracking bug: https://llvm.org/bugs/show_bug.cgi?id=23052 356 357 clang-fuzzer 358 ------------ 359 360 The behavior is very similar to ``clang-format-fuzzer``. 361 362 Tracking bug: https://llvm.org/bugs/show_bug.cgi?id=23057 363 364 llvm-as-fuzzer 365 -------------- 366 367 Tracking bug: https://llvm.org/bugs/show_bug.cgi?id=24639 368 369 llvm-mc-fuzzer 370 -------------- 371 372 This tool fuzzes the MC layer. Currently it is only able to fuzz the 373 disassembler but it is hoped that assembly, and round-trip verification will be 374 added in future. 375 376 When run in dissassembly mode, the inputs are opcodes to be disassembled. The 377 fuzzer will consume as many instructions as possible and will stop when it 378 finds an invalid instruction or runs out of data. 379 380 Please note that the command line interface differs slightly from that of other 381 fuzzers. The fuzzer arguments should follow ``--fuzzer-args`` and should have 382 a single dash, while other arguments control the operation mode and target in a 383 similar manner to ``llvm-mc`` and should have two dashes. For example:: 384 385 llvm-mc-fuzzer --triple=aarch64-linux-gnu --disassemble --fuzzer-args -max_len=4 -jobs=10 386 387 Buildbot 388 -------- 389 390 We have a buildbot that runs the above fuzzers for LLVM components 391 24/7/365 at http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fuzzer . 392 393 Pre-fuzzed test inputs in git 394 ----------------------------- 395 396 The buildbot occumulates large test corpuses over time. 397 The corpuses are stored in git on github and can be used like this:: 398 399 git clone https://github.com/kcc/fuzzing-with-sanitizers.git 400 bin/clang-format-fuzzer fuzzing-with-sanitizers/llvm/clang-format/C1 401 bin/clang-fuzzer fuzzing-with-sanitizers/llvm/clang/C1/ 402 bin/llvm-as-fuzzer fuzzing-with-sanitizers/llvm/llvm-as/C1 -only_ascii=1 403 404 405 FAQ 406 ========================= 407 408 Q. Why Fuzzer does not use any of the LLVM support? 409 --------------------------------------------------- 410 411 There are two reasons. 412 413 First, we want this library to be used outside of the LLVM w/o users having to 414 build the rest of LLVM. This may sound unconvincing for many LLVM folks, 415 but in practice the need for building the whole LLVM frightens many potential 416 users -- and we want more users to use this code. 417 418 Second, there is a subtle technical reason not to rely on the rest of LLVM, or 419 any other large body of code (maybe not even STL). When coverage instrumentation 420 is enabled, it will also instrument the LLVM support code which will blow up the 421 coverage set of the process (since the fuzzer is in-process). In other words, by 422 using more external dependencies we will slow down the fuzzer while the main 423 reason for it to exist is extreme speed. 424 425 Q. What about Windows then? The Fuzzer contains code that does not build on Windows. 426 ------------------------------------------------------------------------------------ 427 428 The sanitizer coverage support does not work on Windows either as of 01/2015. 429 Once it's there, we'll need to re-implement OS-specific parts (I/O, signals). 430 431 Q. When this Fuzzer is not a good solution for a problem? 432 --------------------------------------------------------- 433 434 * If the test inputs are validated by the target library and the validator 435 asserts/crashes on invalid inputs, the in-process fuzzer is not applicable 436 (we could use fork() w/o exec, but it comes with extra overhead). 437 * Bugs in the target library may accumulate w/o being detected. E.g. a memory 438 corruption that goes undetected at first and then leads to a crash while 439 testing another input. This is why it is highly recommended to run this 440 in-process fuzzer with all sanitizers to detect most bugs on the spot. 441 * It is harder to protect the in-process fuzzer from excessive memory 442 consumption and infinite loops in the target library (still possible). 443 * The target library should not have significant global state that is not 444 reset between the runs. 445 * Many interesting target libs are not designed in a way that supports 446 the in-process fuzzer interface (e.g. require a file path instead of a 447 byte array). 448 * If a single test run takes a considerable fraction of a second (or 449 more) the speed benefit from the in-process fuzzer is negligible. 450 * If the target library runs persistent threads (that outlive 451 execution of one test) the fuzzing results will be unreliable. 452 453 Q. So, what exactly this Fuzzer is good for? 454 -------------------------------------------- 455 456 This Fuzzer might be a good choice for testing libraries that have relatively 457 small inputs, each input takes < 1ms to run, and the library code is not expected 458 to crash on invalid inputs. 459 Examples: regular expression matchers, text or binary format parsers. 460 461 Trophies 462 ======== 463 * GLIBC: https://sourceware.org/glibc/wiki/FuzzingLibc 464 465 * MUSL LIBC: 466 467 * http://git.musl-libc.org/cgit/musl/commit/?id=39dfd58417ef642307d90306e1c7e50aaec5a35c 468 * http://www.openwall.com/lists/oss-security/2015/03/30/3 469 470 * `pugixml <https://github.com/zeux/pugixml/issues/39>`_ 471 472 * PCRE: Search for "LLVM fuzzer" in http://vcs.pcre.org/pcre2/code/trunk/ChangeLog?view=markup; 473 also in `bugzilla <https://bugs.exim.org/buglist.cgi?bug_status=__all__&content=libfuzzer&no_redirect=1&order=Importance&product=PCRE&query_format=specific>`_ 474 475 * `ICU <http://bugs.icu-project.org/trac/ticket/11838>`_ 476 477 * `Freetype <https://savannah.nongnu.org/search/?words=LibFuzzer&type_of_search=bugs&Search=Search&exact=1#options>`_ 478 479 * `Harfbuzz <https://github.com/behdad/harfbuzz/issues/139>`_ 480 481 * `SQLite <http://www3.sqlite.org/cgi/src/info/088009efdd56160b>`_ 482 483 * `Python <http://bugs.python.org/issue25388>`_ 484 485 * OpenSSL/BoringSSL: `[1] <https://boringssl.googlesource.com/boringssl/+/cb852981cd61733a7a1ae4fd8755b7ff950e857d>`_ 486 487 * `Libxml2 488 <https://bugzilla.gnome.org/buglist.cgi?bug_status=__all__&content=libFuzzer&list_id=68957&order=Importance&product=libxml2&query_format=specific>`_ 489 490 * `Linux Kernel's BPF verifier <https://github.com/iovisor/bpf-fuzzer>`_ 491 492 * LLVM: `Clang <https://llvm.org/bugs/show_bug.cgi?id=23057>`_, `Clang-format <https://llvm.org/bugs/show_bug.cgi?id=23052>`_, `libc++ <https://llvm.org/bugs/show_bug.cgi?id=24411>`_, `llvm-as <https://llvm.org/bugs/show_bug.cgi?id=24639>`_, Disassembler: http://reviews.llvm.org/rL247405, http://reviews.llvm.org/rL247414, http://reviews.llvm.org/rL247416, http://reviews.llvm.org/rL247417, http://reviews.llvm.org/rL247420, http://reviews.llvm.org/rL247422. 493 494 .. _pcre2: http://www.pcre.org/ 495 496 .. _AFL: http://lcamtuf.coredump.cx/afl/ 497 498 .. _SanitizerCoverage: http://clang.llvm.org/docs/SanitizerCoverage.html 499 .. _SanitizerCoverageTraceDataFlow: http://clang.llvm.org/docs/SanitizerCoverage.html#tracing-data-flow 500 .. _DataFlowSanitizer: http://clang.llvm.org/docs/DataFlowSanitizer.html 501 502 .. _Heartbleed: http://en.wikipedia.org/wiki/Heartbleed 503 504 .. _FuzzerInterface.h: https://github.com/llvm-mirror/llvm/blob/master/lib/Fuzzer/FuzzerInterface.h 505
