From 6ef5837e2d8c5d4d83eff51c0201eb2e08f719de Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Tue, 14 Feb 2023 18:42:40 +0000
Subject: [PATCH] python: Avoid crash if callback parameters cannot be built

In the case that building the parameters to the Python event callback
fails, args was returned as NULL.  We immediately tried to call
Py_INCREF on this which crashed.  Returning NULL means the Python
function threw an exception, so print the exception and return (there
is no way to return an error here - the event is lost).

Reported-by: Yonatan Shtarkman
See: https://listman.redhat.com/archives/libguestfs/2023-February/030653.html
---
 python/handle.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/python/handle.c b/python/handle.c
index c8752baf4..f37e939e0 100644
--- a/python/handle.c
+++ b/python/handle.c
@@ -134,18 +134,21 @@ guestfs_int_py_event_callback_wrapper (guestfs_h *g,
   args = Py_BuildValue ("(Kis#O)",
                         (unsigned PY_LONG_LONG) event, event_handle,
                         buf, buf_len, py_array);
+  if (args == NULL) {
+    PyErr_PrintEx (0);
+    goto out;
+  }
+
   Py_INCREF (args);
-
   py_r = PyObject_CallObject (py_callback, args);
-
   Py_DECREF (args);
-
   if (py_r != NULL)
     Py_DECREF (py_r);
   else
     /* Callback threw an exception: print it. */
     PyErr_PrintEx (0);
 
+ out:
   PyGILState_Release (py_save);
 }