fuzz: try *even harder* to prevent Python from looking up usernames

Differential Revision: https://phab.mercurial-scm.org/D5092

contrib/fuzz/manifest.cc

@@ -1,79 +1,81
 #include <Python.h>
 #include <assert.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 #include <string>
 
 extern "C" {
 
 /* TODO: use Python 3 for this fuzzing? */
 PyMODINIT_FUNC initparsers(void);
 
 static char cpypath[8192] = "\0";
 
 extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv)
 {
 	const std::string subdir = "/sanpy/lib/python2.7";
 	/* HACK ALERT: we need a full Python installation built without
 	   pymalloc and with ASAN, so we dump one in
 	   $OUT/sanpy/lib/python2.7. This helps us wire that up. */
 	std::string selfpath(*argv[0]);
 	std::string pypath;
 	auto pos = selfpath.rfind("/");
 	if (pos == std::string::npos) {
 		char wd[8192];
 		getcwd(wd, 8192);
 		pypath = std::string(wd) + subdir;
 	} else {
 		pypath = selfpath.substr(0, pos) + subdir;
 	}
 	strncpy(cpypath, pypath.c_str(), pypath.size());
 	setenv("PYTHONPATH", cpypath, 1);
 	setenv("PYTHONNOUSERSITE", "1", 1);
+	/* prevent Python from looking up users in the fuzz environment */
+	setenv("PYTHONUSERBASE", cpypath, 1);
 	Py_SetPythonHome(cpypath);
 	Py_InitializeEx(0);
 	return 0;
 }
 
 int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size)
 {
 	initparsers();
 	PyObject *mtext =
 	    PyBytes_FromStringAndSize((const char *)Data, (Py_ssize_t)Size);
 	PyObject *mainmod = PyImport_AddModule("__main__");
 	PyObject *globals = PyModule_GetDict(mainmod);
 	PyObject *locals = PyDict_New();
 	PyDict_SetItemString(locals, "mdata", mtext);
 	PyCodeObject *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);
 	PyObject *res = PyEval_EvalCode(code, globals, locals);
 	if (!res) {
 		PyErr_Print();
 	}
 	Py_XDECREF(res);
 	Py_DECREF(code);
 	Py_DECREF(locals);
 	Py_DECREF(mtext);
 	return 0; // Non-zero return values are reserved for future use.
 }
 }