[boost] Assert post conditions for match (#3018)

* boost: Assert post conditions for match

* boost: Fix broken build

* boost regex: Use fuzzeddataprovider to extract regex pattern and text

projects/boost/Dockerfile

@@ -19,8 +19,5 @@ RUN apt-get update && apt-get install -y g++
 
 RUN git clone --recursive https://github.com/boostorg/boost.git
 WORKDIR boost
-# This bootstrap boost with the g++ toolchain.
-# The actual build will need to use CXX/CXXFLAGS provided by OSS-Fuzz.
-RUN ./bootstrap.sh && ./b2 headers
 # Preferably, move boost_regex_fuzzer.cc to the boost repository.
 COPY build.sh *.cc $SRC/

projects/boost/boost_regex_fuzzer.cc

@@ -1,16 +1,47 @@
 // From https://svn.boost.org/trac10/ticket/12818
 // This fuzz target can likely be enhanced to exercise more code.
 // The ideal place for this fuzz target is the boost repository.
-#include <boost/regex.hpp>
-extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
-  try {
-    std::string str((char *)Data, Size);
-    boost::regex e(str);
-    boost::match_results<std::string::const_iterator> what;
-    boost::regex_match(str, what, e,
-                       boost::match_default | boost::match_partial);
+#ifdef DEBUG
+#include <iostream>
+#endif
 
-  } catch (const std::exception &) {
+#include <boost/regex.hpp>
+#include <fuzzer/FuzzedDataProvider.h>
+
+namespace {
+  void assertPostConditions(boost::match_results<std::string::const_iterator> const& match, boost::regex const& e)
+  {
+    // See https://www.boost.org/doc/libs/1_71_0/libs/regex/doc/html/boost_regex/ref/regex_match.html
+    assert(match.size() == e.mark_count() + 1);
+    assert(!match.empty());
+    assert(!match.prefix().matched);
+    assert(!match.suffix().matched);
+  }
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  FuzzedDataProvider fuzzed_data(Data, Size);
+  // First value is length of the regex string
+  size_t regex_length = fuzzed_data.ConsumeIntegral<uint8_t>();
+  // Second value is regexp string whose length is `regex_length`
+  std::string regex_string = fuzzed_data.ConsumeBytesAsString(regex_length);
+  boost::regex e(regex_string);
+  // Last value is the text to be matched
+  std::string text = fuzzed_data.ConsumeRemainingBytesAsString();
+
+#ifdef DEBUG
+    std::cout << "Regexp string: " << regex_string << "Size: " << regex_string.size() << std::endl;
+    std::cout << "Text: " << text << "Size: " << text.size() << std::endl;
+#endif
+
+  try {
+    boost::match_results<std::string::const_iterator> what;
+    bool match = boost::regex_match(text, what, e,
+                       boost::match_default | boost::match_partial);
+    if (match)
+      assertPostConditions(what, e);
+  }
+  catch (const std::runtime_error &) {
   }
   return 0;
 }

projects/boost/build.sh

@@ -15,9 +15,10 @@
 #
 ################################################################################
 
+# Build boost
+./bootstrap.sh && ./b2 headers
 
 # Very simple build rule, but sufficient here.
-
 #boost regexp
 $CXX $CXXFLAGS -I . ../boost_regex_fuzzer.cc libs/regex/src/*.cpp $LIB_FUZZING_ENGINE -o boost_regex_fuzzer
 

projects/boost/project.yaml

@@ -5,4 +5,5 @@ homepage: "http://www.boost.org/"
 auto_ccs:  
    - "jz.maddock@googlemail.com"
    - "mclow@boost.org"
+   - "bshas3@gmail.com"
 #   - "someone-else@boost.org"