id: adjust/restrict smack support to newer versions of libsmack

There was slight change to libsmack such that positive values are
reserved for returning length of the label for smack_new_label_from_*
functions.

* m4/jm-macros.m4: Set HAVE_SMACK when both smack_new_label_from_self()
and recently added smack_new_label_from_path() are present.
The latter's presence indicates the newer API of the former.
* src/id.c (main): Check that smack_new_label_from_self() < 0,
and not just non-zero.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/id.c b/src/id.c
index 937b7234d..c91dbcdbc 100644
--- a/src/id.c
+++ b/src/id.c
@@ -210,7 +210,8 @@ main (int argc, char **argv)
       if (selinux_enabled && getcon (&context) && just_context)
         error (EXIT_FAILURE, 0, _("can't get process context"));
 #ifdef HAVE_SMACK
-      else if (smack_enabled && smack_new_label_from_self ((char **) &context))
+      else if (smack_enabled
+               && smack_new_label_from_self ((char **) &context) < 0)
         error (EXIT_FAILURE, 0, _("can't get process context"));
 #endif
     }