libdrgn/python: fix segfault on del prog.language and more

None of our setter functions handle deletions, which pass the value as
NULL. This results in a segfault when attempting to access the value.
Fix them all with a new convenience macro.

Fixes: 50e4ac8 ("libdrgn: allow overriding program default language")
Fixes: 4e83130 ("Introduce module and debug info finder APIs")
Signed-off-by: Omar Sandoval <[email protected]>

libdrgn/python/drgnpy.h

@@ -91,6 +91,18 @@ static inline PyObject *PyObject_CallOneArg(PyObject *callable, PyObject *arg)
 		Py_RETURN_FALSE;	\
 } while (0)
 
+/**
+ * Return from a PyGetSetDef setter with an error if attempting to delete the
+ * attribute.
+ */
+#define SETTER_NO_DELETE(name, value) do {				\
+	if (!(value)) {							\
+		PyErr_Format(PyExc_AttributeError,			\
+			     "can't delete '%s' attribute", (name));	\
+		return -1;						\
+	}								\
+} while (0)
+
 static inline void pydecrefp(void *p)
 {
 	Py_XDECREF(*(PyObject **)p);

libdrgn/python/module.c

@@ -214,6 +214,7 @@ static PyObject *Module_get_address_range(Module *self, void *arg)
 
 static int Module_set_address_range(Module *self, PyObject *value, void *arg)
 {
+	SETTER_NO_DELETE("address_range", value);
 	struct drgn_error *err;
 	if (value == Py_None) {
 		err = drgn_module_set_address_range(self->module, -1, -1);
@@ -258,6 +259,7 @@ static PyObject *Module_get_build_id(Module *self, void *arg)
 
 static int Module_set_build_id(Module *self, PyObject *value, void *arg)
 {
+	SETTER_NO_DELETE("build_id", value);
 	struct drgn_error *err;
 	if (value == Py_None) {
 		err = drgn_module_set_build_id(self->module, NULL, 0);
@@ -300,6 +302,7 @@ static PyObject *Module_get_##which##_file_status(Module *self, void *arg)	\
 static int Module_set_##which##_file_status(Module *self, PyObject *value,	\
 					    void *arg)				\
 {										\
+	SETTER_NO_DELETE(#which, value);					\
 	if (!PyObject_TypeCheck(value,						\
 				(PyTypeObject *)ModuleFileStatus_class)) {	\
 		PyErr_SetString(PyExc_TypeError,				\

libdrgn/python/program.c

@@ -1286,6 +1286,7 @@ static PyObject *Program_get_debug_info_path(Program *self, void *arg)
 
 static int Program_set_debug_info_path(Program *self, PyObject *value, void *arg)
 {
+	SETTER_NO_DELETE("debug_info_path", value);
 	const char *path;
 	if (value == Py_None) {
 		path = NULL;
@@ -1909,6 +1910,7 @@ static PyObject *Program_get_language(Program *self, void *arg)
 
 static int Program_set_language(Program *self, PyObject *value, void *arg)
 {
+	SETTER_NO_DELETE("language", value);
 	if (!PyObject_TypeCheck(value, &Language_type)) {
 		PyErr_SetString(PyExc_TypeError, "language must be Language");
 		return -1;

tests/test_module.py

@@ -351,6 +351,11 @@ def test_address_range_invalid(self):
         with self.assertRaisesRegex(ValueError, "invalid module address range"):
             module.address_range = (2**64 - 1, 2**64 - 1)
 
+    def test_address_range_del(self):
+        module = Program().extra_module("/foo/bar", create=True)[0]
+        with self.assertRaises(AttributeError):
+            del module.address_range
+
     def test_build_id(self):
         module = Program().extra_module("/foo/bar", create=True)[0]
 
@@ -376,6 +381,11 @@ def test_build_id_invalid_empty(self):
         with self.assertRaisesRegex(ValueError, "build ID cannot be empty"):
             module.build_id = b""
 
+    def test_build_id_del(self):
+        module = Program().extra_module("/foo/bar", create=True)[0]
+        with self.assertRaises(AttributeError):
+            del module.build_id
+
     def test_find_by_address(self):
         prog = Program()
         module1 = prog.extra_module("/foo/bar", create=True)[0]
@@ -456,6 +466,8 @@ def _test_file_status(self, which):
         setattr(module, status_attr, ModuleFileStatus.WANT)
         self.assertEqual(getattr(module, status_attr), ModuleFileStatus.WANT)
 
+        self.assertRaises(AttributeError, delattr, module, status_attr)
+
     def test_loaded_file_status(self):
         self._test_file_status("loaded")
 

tests/test_program.py

@@ -162,6 +162,10 @@ def test_language(self):
             TypeError, "language must be Language", setattr, prog, "language", "CPP"
         )
 
+    def test_language_del(self):
+        with self.assertRaises(AttributeError):
+            del Program().language
+
 
 class TestMemory(TestCase):
     def test_simple_read(self):