fuzz: restrict manifest input size

Again, let's keep the fuzzer from getting excited about huge inputs.

Differential Revision: https://phab.mercurial-scm.org/D5642

contrib/fuzz/manifest.cc

@@ -1,55 +1,60 b''
 #include <Python.h>
 #include <assert.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 #include "pyutil.h"
 
 #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 lazymanifest
 try:
   lm = lazymanifest(mdata)
   # iterate the whole thing, which causes the code to fully parse
   # every line in the manifest
   list(lm.iterentries())
   lm[b'xyzzy'] = (b'\0' * 20, 'x')
   # do an insert, text should change
   assert lm.text() != mdata, "insert should change text and didn't: %r %r" % (lm.text(), mdata)
   del lm[b'xyzzy']
   # should be back to the same
   assert lm.text() == mdata, "delete should have restored text but didn't: %r %r" % (lm.text(), mdata)
 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);
 	return 0;
 }
 
 int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
 {
+	// Don't allow fuzzer inputs larger than 100k, since we'll just bog
+	// down and not accomplish much.
+	if (Size > 100000) {
+		return 0;
+	}
 	PyObject *mtext =
 	    PyBytes_FromStringAndSize((const char *)Data, (Py_ssize_t)Size);
 	PyObject *locals = PyDict_New();
 	PyDict_SetItemString(locals, "mdata", mtext);
 	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.
 }
 }