fuzz: new target to fuzz jsonescapeu8fast

This code just feels complicated enough we should go ahead and give it
a dedicated fuzzer: we've found bugs in similar things before.

Differential Revision: https://phab.mercurial-scm.org/D7034

contrib/fuzz/jsonescapeu8fast.cc

@@ -0,0 +1,57 b''
+#include <Python.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "pyutil.h"
+
+#include <fuzzer/FuzzedDataProvider.h>
+#include <iostream>
+#include <string>
+
+extern "C" {
+
+static PyCodeObject *code;
+
+extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv)
+{
+	contrib::initpy(*argv[0]);
+	code = (PyCodeObject *)Py_CompileString(R"py(
+from parsers import jsonescapeu8fast
+
+try:
+    jsonescapeu8fast(data, paranoid)
+except Exception as e:
+    pass
+    # uncomment this print if you're editing this Python code
+    # to debug failures.
+    # print(e)
+)py",
+	                                        "fuzzer", Py_file_input);
+	if (!code) {
+		std::cerr << "failed to compile Python code!" << std::endl;
+	}
+	return 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
+{
+	FuzzedDataProvider provider(Data, Size);
+	bool paranoid = provider.ConsumeBool();
+	std::string remainder = provider.ConsumeRemainingBytesAsString();
+
+	PyObject *mtext = PyBytes_FromStringAndSize(
+	    (const char *)remainder.c_str(), remainder.size());
+	PyObject *locals = PyDict_New();
+	PyDict_SetItemString(locals, "data", mtext);
+	PyDict_SetItemString(locals, "paranoid", paranoid ? Py_True : Py_False);
+	PyObject *res = PyEval_EvalCode(code, contrib::pyglobals(), locals);
+	if (!res) {
+		PyErr_Print();
+	}
+	Py_XDECREF(res);
+	Py_DECREF(locals);
+	Py_DECREF(mtext);
+	return 0; // Non-zero return values are reserved for future use.
+}
+}

contrib/fuzz/Makefile

@@ -121,6 +121,14 b' fncache_fuzzer: fncache.cc manifest.o ch'
 	  -lFuzzingEngine `$$OUT/sanpy/bin/python-config --ldflags` \
 	  -o $$OUT/fncache_fuzzer
 
+jsonescapeu8fast_fuzzer: jsonescapeu8fast.cc manifest.o charencode.o parsers.o dirs.o pathencode.o revlog.o pyutil.o
+	$(CXX) $(CXXFLAGS) `$$OUT/sanpy/bin/python-config --cflags` \
+	  -Wno-register -Wno-macro-redefined \
+	  -I../../mercurial jsonescapeu8fast.cc \
+	  manifest.o charencode.o parsers.o dirs.o pathencode.o revlog.o pyutil.o \
+	  -lFuzzingEngine `$$OUT/sanpy/bin/python-config --ldflags` \
+	  -o $$OUT/jsonescapeu8fast_fuzzer
+
 manifest_corpus.zip:
 	python manifest_corpus.py $$OUT/manifest_fuzzer_seed_corpus.zip
 
@@ -171,6 +179,6 b' clean:'
 	  mpatch \
 	  xdiff
 
-oss-fuzz: bdiff_fuzzer mpatch_fuzzer mpatch_corpus.zip xdiff_fuzzer dirs_fuzzer fncache_fuzzer manifest_fuzzer manifest_corpus.zip revlog_fuzzer revlog_corpus.zip dirstate_fuzzer dirstate_corpus.zip fm1readmarkers_fuzzer fm1readmarkers_corpus.zip
+oss-fuzz: bdiff_fuzzer mpatch_fuzzer mpatch_corpus.zip xdiff_fuzzer dirs_fuzzer fncache_fuzzer jsonescapeu8fast_fuzzer manifest_fuzzer manifest_corpus.zip revlog_fuzzer revlog_corpus.zip dirstate_fuzzer dirstate_corpus.zip fm1readmarkers_fuzzer fm1readmarkers_corpus.zip
 
 .PHONY: all clean oss-fuzz