Tweak xd_append_arg to pacify -Wnull-dereference

* src/dbusbind.c (xd_append_arg): Redo to pacify gcc
-Wnull-dereference.  Also, check that the Lisp string won’t
overrun the C signature buffer.

1 files changed, 21 insertions, 16 deletions

diff --git a/src/dbusbind.c b/src/dbusbind.c
index 90ba461c6bc..7f4c8717f42 100644
--- a/src/dbusbind.c
+++ b/src/dbusbind.c
@@ -728,22 +728,27 @@ xd_append_arg (int dtype, Lisp_Object object, DBusMessageIter *iter)
             strcpy (signature, DBUS_TYPE_STRING_AS_STRING);
 
           else
-            /* If the element type is DBUS_TYPE_SIGNATURE, and this is
-               the only element, the value of this element is used as
-               the array's element signature.  */
-            if ((XD_OBJECT_TO_DBUS_TYPE (CAR_SAFE (object))
-                 == DBUS_TYPE_SIGNATURE)
-                && STRINGP (CAR_SAFE (XD_NEXT_VALUE (object)))
-                && NILP (CDR_SAFE (XD_NEXT_VALUE (object))))
-              {
-                lispstpcpy (signature, CAR_SAFE (XD_NEXT_VALUE (object)));
-                object = CDR_SAFE (XD_NEXT_VALUE (object));
-              }
-
-            else
-              xd_signature (signature,
-                            XD_OBJECT_TO_DBUS_TYPE (CAR_SAFE (object)),
-                            dtype, CAR_SAFE (XD_NEXT_VALUE (object)));
+            {
+              /* If the element type is DBUS_TYPE_SIGNATURE, and this is
+                 the only element, the value of this element is used as
+                 the array's element signature.  */
+              if (CONSP (object) && (XD_OBJECT_TO_DBUS_TYPE (XCAR (object))
+                                     == DBUS_TYPE_SIGNATURE))
+                {
+                  Lisp_Object val = XD_NEXT_VALUE (object);
+                  if (CONSP (val) && STRINGP (XCAR (val)) && NILP (XCDR (val))
+                      && SBYTES (XCAR (val)) < DBUS_MAXIMUM_SIGNATURE_LENGTH)
+                    {
+                      lispstpcpy (signature, XCAR (val));
+                      object = Qnil;
+                    }
+                }
+
+              if (!NILP (object))
+                xd_signature (signature,
+                              XD_OBJECT_TO_DBUS_TYPE (CAR_SAFE (object)),
+                              dtype, CAR_SAFE (XD_NEXT_VALUE (object)));
+            }
 
           XD_DEBUG_MESSAGE ("%c %s %s", dtype, signature,
                             XD_OBJECT_TO_STRING (object));