gpg: Assert that an opaque parameter is really what we expect.

* g10/gpg.h (SERVER_CONTROL_MAGIC): New const.
(server_control_s): Add field 'magic'.
* g10/gpg.c (gpg_init_default_ctrl): Init MAGIC.
* g10/import.c (impex_filter_getval): Assert MAGIC.

Signed-off-by: Werner Koch <wk@gnupg.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/g10/gpg.h b/g10/gpg.h
index 3bf023be6..c66358570 100644
--- a/g10/gpg.h
+++ b/g10/gpg.h
@@ -68,11 +68,20 @@ struct tofu_dbs_s;
 typedef struct tofu_dbs_s *tofu_dbs_t;
 
 
+#if SIZEOF_UNSIGNED_LONG == 8
+# define SERVER_CONTROL_MAGIC 0x53616c696e676572
+#else
+# define SERVER_CONTROL_MAGIC 0x53616c69
+#endif
+
 /* Session control object.  This object is passed to most functions to
    convey the status of a session.  Note that the defaults are set by
    gpg_init_default_ctrl(). */
 struct server_control_s
 {
+  /* Always has the value SERVER_CONTROL_MAGIC.  */
+  unsigned long magic;
+
   /* Local data for server.c  */
   struct server_local_s *server_local;