python: avoid crashes with fields

When accessing a field that doesn't exist,
we may get None, and then pass that NULL
pointer to C -- catch that and make the
num_field() method return None then.

Acked-by: Darren Hart <dvhltc@us.ibm.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>

2 files changed, 3 insertions, 0 deletions

diff --git a/ctracecmd.i b/ctracecmd.i
index f3daad2..efd5629 100644
--- a/ctracecmd.i
+++ b/ctracecmd.i
@@ -5,6 +5,7 @@
 
 %apply Pointer NONNULL { struct tracecmd_input *handle };
 %apply Pointer NONNULL { struct pevent *pevent };
+%apply Pointer NONNULL { struct format_field * };
 %apply unsigned long long *OUTPUT {unsigned long long *}
 %apply int *OUTPUT {int *}
 
diff --git a/tracecmd.py b/tracecmd.py
index 26f3ac2..aa690f9 100644
--- a/tracecmd.py
+++ b/tracecmd.py
@@ -71,6 +71,8 @@ class Event(object):
 
     def num_field(self, name):
         f = pevent_find_any_field(self._format, name)
+        if f is None:
+            return None
         ret, val = pevent_read_number_field(f, record_data_get(self._record))
         if ret:
             return None