ossfuzz: Move to C++ for curl_fuzzer.

Automake gets confused if you want to use C++ static libraries with C
code - basically we need to involve the clang++ linker. The easiest way
of achieving this is to rename the C code as C++ code. This gets us a
bit further along the path and ought to be compatible with Google's
version of clang.

.gitignore

@@ -55,3 +55,4 @@ test-driver
 scripts/_curl
 curl_fuzzer
 curl_fuzzer_seed_corpus.zip
+libstandaloneengine.a

.travis.yml

@@ -145,7 +145,12 @@ script:
     - |
         if [ "$T" = "fuzzer" ]; then
           export CC=clang
+          export CXX=clang++
           export CFLAGS="-fsanitize=address"
+
+          # Specifically use libstdc++ for travis as libc++ is not installed.
+          # This is ok because we're not compiling against libFuzzer.
+          export CXXFLAGS="-fsanitize=address -stdlib=libstdc++"
           ./configure --disable-shared --enable-debug --enable-maintainer-mode
           make
           cd tests/fuzz

configure.ac

@@ -52,6 +52,7 @@ CURL_CHECK_OPTION_RT
 
 XC_CHECK_PATH_SEPARATOR
 AX_CODE_COVERAGE
+AC_PROG_CXX
 
 #
 # save the configure arguments

tests/fuzz/Makefile.am

@@ -30,12 +30,12 @@ AUTOMAKE_OPTIONS = foreign nostdinc
 # $(top_builddir)/lib is for libcurl's generated lib/curl_config.h file
 # $(top_srcdir)/lib for libcurl's lib/curl_setup.h and other "borrowed" files
 
-AM_CFLAGS = -I$(top_srcdir)/include        \
-            -I$(top_builddir)/lib          \
-            -I$(top_srcdir)/lib            \
-            -I$(top_srcdir)/tests/fuzz
+AM_CXXFLAGS = -I$(top_srcdir)/include        \
+              -I$(top_builddir)/lib          \
+              -I$(top_srcdir)/lib            \
+              -I$(top_srcdir)/tests/fuzz
 
-LIBS = -lpthread -lstdc++ -lm
+LIBS = -lpthread -lm
 
 # Run e.g. "make all LIB_FUZZING_ENGINE=/path/to/libFuzzer.a"
 # to link the fuzzer(s) against a real fuzzing engine.
@@ -53,4 +53,4 @@ checksrc:
 	@PERL@ $(top_srcdir)/lib/checksrc.pl $(srcdir)/*.c
 
 noinst_PROGRAMS = $(FUZZPROGS)
-noinst_LIBRARIES = $(FUZZLIBS)
+noinst_LIBRARIES = $(FUZZLIBS)

tests/fuzz/Makefile.inc

@@ -1,15 +1,15 @@
 FUZZPROGS = curl_fuzzer
 FUZZLIBS = libstandaloneengine.a
 
-curl_fuzzer_SOURCES = curl_fuzzer.c
-curl_fuzzer_CFLAGS = $(AM_CFLAGS)
+curl_fuzzer_SOURCES = curl_fuzzer.cc
+curl_fuzzer_CXXFLAGS = $(AM_CXXFLAGS)
 
-libstandaloneengine_a_SOURCES = standalone_fuzz_target_runner.c
-libstandaloneengine_a_CFLAGS = $(AM_CFLAGS)
+libstandaloneengine_a_SOURCES = standalone_fuzz_target_runner.cc
+libstandaloneengine_a_CXXFLAGS = $(AM_CXXFLAGS)
 
 # Some more targets.
 zip:
 	zip -q -r curl_fuzzer_seed_corpus.zip curl_fuzz_data
 
 check: all
-	./curl_fuzzer curl_fuzz_data/*
+	./curl_fuzzer curl_fuzz_data/*

tests/fuzz/README

@@ -8,7 +8,9 @@ Building the fuzz target
 From the CURL root directory:
 
 export CC=clang-5.0
+export CXX=clang++-5.0
 export CFLAGS="-fsanitize=address -fsanitize-address-use-after-scope -fsanitize-coverage=trace-pc-guard,trace-cmp"
+export CXXFLAGS="-fsanitize=address -fsanitize-address-use-after-scope -fsanitize-coverage=trace-pc-guard,trace-cmp -stdlib=libc++"
 ./configure --disable-shared --enable-debug --enable-maintainer-mode
 make -sj
 

tests/fuzz/curl_fuzzer.cc

@@ -32,15 +32,18 @@
  * Fuzzing entry point. This function is passed a buffer containing a test
  * case.  This test case should drive the CURL API into making a request.
  */
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
   int rc = 0;
   int tlv_rc;
   FUZZ_DATA fuzz;
   TLV tlv;
 
+  /* Have to set all fields to zero before getting to the terminate function */
+  memset(&fuzz, 0, sizeof(FUZZ_DATA));
+
   if(size < sizeof(TLV_RAW)) {
-    /* Not enough data */
+    /* Not enough data for a single TLV - don't continue */
     goto EXIT_LABEL;
   }
 
@@ -329,7 +332,7 @@ char *fuzz_tlv_to_string(TLV *tlv)
   char *tlvstr;
 
   /* Allocate enough space, plus a null terminator */
-  tlvstr = malloc(tlv->length + 1);
+  tlvstr = (char *)malloc(tlv->length + 1);
 
   if(tlvstr != NULL) {
     memcpy(tlvstr, tlv->value, tlv->length);

tests/fuzz/curl_fuzzer.h

@@ -21,6 +21,7 @@
  ***************************************************************************/
 
 #include <curl/curl.h>
+#include <testinput.h>
 
 /**
  * TLV types.
@@ -107,7 +108,6 @@ typedef struct fuzz_data
 } FUZZ_DATA;
 
 /* Function prototypes */
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
 uint32_t to_u32(uint8_t b[4]);
 uint16_t to_u16(uint8_t b[2]);
 int fuzz_initialize_fuzz_data(FUZZ_DATA *fuzz,

tests/fuzz/standalone_fuzz_target_runner.cc

@@ -24,7 +24,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-#include "standalone_fuzz_target_runner.h"
+#include "testinput.h"
 
 /**
  * Main procedure for standalone fuzzing engine.

tests/fuzz/testinput.h

@@ -20,4 +20,4 @@
  *
  ***************************************************************************/
 
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);